2011 Vol.24(2)
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2011, 25(2).
Abstract:
Most of the important units of pressure equipment have been manufactured successfully in China related to the national key construction projects, such as 10 million tonsyear oil refinery, million tons/year ethylene, large coal chemical, etc. However, some of them failed to operate shortly after their putting into service. Some suffered severe damage even during the previous period of manufacture and installation. In this paper, cases of accident survey and failure analysis are given for some typical pressure vessels. It is found that many accidents are related to insufficient consideration of the design and manufacture of the equipment. These accidents occur fundamentally because of the Chinese design standards & codes for pressure equipment without risk or life concepts and the support from a database for potential risk existing in their dynamic service. Most designers and manufacturers are unable to make correct design, materials selection and manufacturing process all due to a lack of engineering experience. In order to avoid the repetition of the accidents and improve the safety, reliability and economy of pressure equipment, a platform is suggested for design, manufacture and maintenance of pressure equipment in China based on accidents survey. In other words, some effective precautionary measures are taken at the design and manufacture stage, and the design methodology has to be based on service life requirement and desirable risk level. At the service stage some reasonable inspection/monitoring approaches should be utilized to control risks and ensure the equipment operating safely until its desired lifespan. Finally, the basic scheme and some key technologies are briefly given for the platform construction. The concept of risk and life based design, manufacture and maintenance proposed herein has important significance for improving and perfecting the codes and standards for design, manufacture and maintenance of Chinese pressure-bearing equipment, enhancing the life and reliability of Chinese pressure-bearing equipment and promoting the development of in-service maintenance technology that combines safety and economy.
Most of the important units of pressure equipment have been manufactured successfully in China related to the national key construction projects, such as 10 million tonsyear oil refinery, million tons/year ethylene, large coal chemical, etc. However, some of them failed to operate shortly after their putting into service. Some suffered severe damage even during the previous period of manufacture and installation. In this paper, cases of accident survey and failure analysis are given for some typical pressure vessels. It is found that many accidents are related to insufficient consideration of the design and manufacture of the equipment. These accidents occur fundamentally because of the Chinese design standards & codes for pressure equipment without risk or life concepts and the support from a database for potential risk existing in their dynamic service. Most designers and manufacturers are unable to make correct design, materials selection and manufacturing process all due to a lack of engineering experience. In order to avoid the repetition of the accidents and improve the safety, reliability and economy of pressure equipment, a platform is suggested for design, manufacture and maintenance of pressure equipment in China based on accidents survey. In other words, some effective precautionary measures are taken at the design and manufacture stage, and the design methodology has to be based on service life requirement and desirable risk level. At the service stage some reasonable inspection/monitoring approaches should be utilized to control risks and ensure the equipment operating safely until its desired lifespan. Finally, the basic scheme and some key technologies are briefly given for the platform construction. The concept of risk and life based design, manufacture and maintenance proposed herein has important significance for improving and perfecting the codes and standards for design, manufacture and maintenance of Chinese pressure-bearing equipment, enhancing the life and reliability of Chinese pressure-bearing equipment and promoting the development of in-service maintenance technology that combines safety and economy.
2011, 25(2).
Abstract:
Currently most of control methods are of one degree of freedom (1-DOF) control structure for the robot systems which are affected by unmeasurable harmonic disturbances, at the same time in order to obtain perfect disturbance attenuation level, the controller gain must be increased. In practice, however, for robotic actuators, there are physical constraints that limit the amplitude of the available torques. This paper considers the problem of tracking control under input constraints for robot manipulators which are affected by unmeasurable harmonic disturbances. A new control scheme is proposed for the problem, which is composed of a parameter-dependent nonlinear observer and a tracking controller. The parameter-dependent nonlinear observer, designed based on the internal model principle, can achieve an estimation and compensation of a class of harmonic disturbances with unknown frequencies. The tracking controller, designed via adaptive control techniques, can make the systems asymptotically track the desired trajectories. In the control design, the continuous piecewise differentiable increasing function is used to limit control input amplitude, such that the control input saturation is avoided. The Lyapunov stability of closed loop systems is analyzed. To validate proposed control scheme, simulation results are provided for a two link horizontal robot manipulator. The simulation results show that the proposed control scheme ensures asymptotic tracking in presence of an uncertain external disturbance acting on the system. An important feature of the methodology consists of the fact that the designed controller is of 2-DOF control structure, namely, it has the ability to overcome the conflict between controller gain and robustness against external disturbances in the traditional 1-DOF control structure framework.
Currently most of control methods are of one degree of freedom (1-DOF) control structure for the robot systems which are affected by unmeasurable harmonic disturbances, at the same time in order to obtain perfect disturbance attenuation level, the controller gain must be increased. In practice, however, for robotic actuators, there are physical constraints that limit the amplitude of the available torques. This paper considers the problem of tracking control under input constraints for robot manipulators which are affected by unmeasurable harmonic disturbances. A new control scheme is proposed for the problem, which is composed of a parameter-dependent nonlinear observer and a tracking controller. The parameter-dependent nonlinear observer, designed based on the internal model principle, can achieve an estimation and compensation of a class of harmonic disturbances with unknown frequencies. The tracking controller, designed via adaptive control techniques, can make the systems asymptotically track the desired trajectories. In the control design, the continuous piecewise differentiable increasing function is used to limit control input amplitude, such that the control input saturation is avoided. The Lyapunov stability of closed loop systems is analyzed. To validate proposed control scheme, simulation results are provided for a two link horizontal robot manipulator. The simulation results show that the proposed control scheme ensures asymptotic tracking in presence of an uncertain external disturbance acting on the system. An important feature of the methodology consists of the fact that the designed controller is of 2-DOF control structure, namely, it has the ability to overcome the conflict between controller gain and robustness against external disturbances in the traditional 1-DOF control structure framework.
2011, 25(2).
Abstract:
Gecko-like robot (Geckobot), an important branch of bionic robotics, is a robot that simulates gecko’s capacity to climb walls and ceilings. The work environment of the traditional wall-climbing robot is greatly limited as the moving structure and adsorption principle of the robot have nothing to do with the real gecko. However, the adsorption principle and moving mode of the real gecko can provide a new way to break through the restrictions of the traditional wall-climbing robot. Inspired by the moving mechanism of geckos, this paper develops the Geckobot with motile body. Two types of Geckobots are addressed: one with compliant flat bar as the body, and the other with prismatic joint as the body. The compliant body not only resembles the moving mode of the real gecko body, but also simplifies the Geckobot’s structure. The prismatic joint body is used to adapt the change of body length in ground-to-wall transition. The gait planning on the plane and the transition between perpendicular intersectional planes is discussed, with an emphasis on the analysis of the kinematics degree of freedom (DOF) and body posture. Central pattern generator (CPG) neural network is realized in LabVIEW and utilized to control Geckobot’s movement. The CPG scheme in LabVIEW is given, and how CPG is used to control Geckobot to turn or move forward is explored. Simulations are conducted in ADAMS to verify the feasibility of the structure design and gait planning and to acquire some parameters for practical Geckobot development. The experiment with Geckobot-I and Geckobot-II on their crawling capacity on the plane and the ground-to-wall transition finds that the robot can complete the crawling movement and ground-to-wall transition, verifying the feasibility of the structure design, gait planning and the CPG motion control. The Geckobot structure design approach, gait planning and the CPG motion control presented would be useful for the research on wall-climbing robots.
Gecko-like robot (Geckobot), an important branch of bionic robotics, is a robot that simulates gecko’s capacity to climb walls and ceilings. The work environment of the traditional wall-climbing robot is greatly limited as the moving structure and adsorption principle of the robot have nothing to do with the real gecko. However, the adsorption principle and moving mode of the real gecko can provide a new way to break through the restrictions of the traditional wall-climbing robot. Inspired by the moving mechanism of geckos, this paper develops the Geckobot with motile body. Two types of Geckobots are addressed: one with compliant flat bar as the body, and the other with prismatic joint as the body. The compliant body not only resembles the moving mode of the real gecko body, but also simplifies the Geckobot’s structure. The prismatic joint body is used to adapt the change of body length in ground-to-wall transition. The gait planning on the plane and the transition between perpendicular intersectional planes is discussed, with an emphasis on the analysis of the kinematics degree of freedom (DOF) and body posture. Central pattern generator (CPG) neural network is realized in LabVIEW and utilized to control Geckobot’s movement. The CPG scheme in LabVIEW is given, and how CPG is used to control Geckobot to turn or move forward is explored. Simulations are conducted in ADAMS to verify the feasibility of the structure design and gait planning and to acquire some parameters for practical Geckobot development. The experiment with Geckobot-I and Geckobot-II on their crawling capacity on the plane and the ground-to-wall transition finds that the robot can complete the crawling movement and ground-to-wall transition, verifying the feasibility of the structure design, gait planning and the CPG motion control. The Geckobot structure design approach, gait planning and the CPG motion control presented would be useful for the research on wall-climbing robots.
2011, 25(2).
Abstract:
The existing investigations of vehicle ride comfort mainly include motion characteristics analysis based on creating a multi-body dynamic simulation model, and the parameters analysis to improve the suspension control for the target. In the study of creating multi-body dynamics simulation models, there is usually without considering calibration and test verification, which make it difficult to ensure the production of engineering. In the study of improving the suspension control parameters for the target, there is a lack of systematic match about comfortable and human characteristics, so it is difficult to implement in the field of driving and leading the vehicle design. In this paper, based on the different characteristic of suspension system that effects on the vehicle ride comfort, according to the suspension system dynamic mechanism, the research methods of vehicle road test, bench test and CAE simulation is used, at the same time, several sensitivity analysis of vehicle ride comfort related to suspension stiffness and damping and speed is made. As a result, the key suspension systematic parameters are given that have important impact on vehicle ride comfort. Through matching parameters, a calibration analysis of suspension system based on human comfort is obtained. The analysis results show that the analysis methods for the design target of making the vehicle with best comfort are effective. On the basis of the theory study, five suspension parameter matching principles are explored to promise the vehicle with perfect ride comfort, which also provide theoretical basis and design methods for the passenger car best match of suspension system stiffness and damping. The research results have the promotional value of practicability and a wide range of engineering application.
The existing investigations of vehicle ride comfort mainly include motion characteristics analysis based on creating a multi-body dynamic simulation model, and the parameters analysis to improve the suspension control for the target. In the study of creating multi-body dynamics simulation models, there is usually without considering calibration and test verification, which make it difficult to ensure the production of engineering. In the study of improving the suspension control parameters for the target, there is a lack of systematic match about comfortable and human characteristics, so it is difficult to implement in the field of driving and leading the vehicle design. In this paper, based on the different characteristic of suspension system that effects on the vehicle ride comfort, according to the suspension system dynamic mechanism, the research methods of vehicle road test, bench test and CAE simulation is used, at the same time, several sensitivity analysis of vehicle ride comfort related to suspension stiffness and damping and speed is made. As a result, the key suspension systematic parameters are given that have important impact on vehicle ride comfort. Through matching parameters, a calibration analysis of suspension system based on human comfort is obtained. The analysis results show that the analysis methods for the design target of making the vehicle with best comfort are effective. On the basis of the theory study, five suspension parameter matching principles are explored to promise the vehicle with perfect ride comfort, which also provide theoretical basis and design methods for the passenger car best match of suspension system stiffness and damping. The research results have the promotional value of practicability and a wide range of engineering application.
2011, 25(2).
Abstract:
During the process that implant materials are used for bone replacement, the cell responses to implant materials determine the long-term stability of bone replacement. The microstructure of implant materials is considered as a critical factor that influences the cell responses. Carbon/Carbon composites (C/C composites) are novel implant materials, but there are few reports on the effect of their microstructure, especially the carbon matrixes and holes, on cell behavior. In this paper, C/C composites with different carbon matrixes are prepared by chemical vapor infiltration and pressure impregnation carbonization technique, respectively. The structure of holes is analyzed. The cell responses to C/C composites with different carbon matrixes are evaluated with MG63 osteoblast-like cells. The morphologies of MG63 osteoblast-like cells on the surface of C/C composites, especially in the holes are assessed by scanning electron microscope, and cell proliferation behavior is evaluated by 3-[4, 5-dimethylthiozol-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) assay. The results show that MG63 osteoblast-like cells have a lamellar morphology with similar sizes and spreading areas as well as the same proliferation behaviors for CC composites with different carbon matrixes. Carbon matrix shows unapparent influence on the cell growth behavior. Besides, MG63 osteoblast-like cells have various interactions with the holes of C/C composites. The cells stride over the holes with 6-8 μm in size, and connect with each other or grow along the curvature wall of the holes with a size of 30-40 μm; the cells present three-dimensional morphologies inside the holes and display circular shapes along the ridge of the holes. Diverse cell-material interactions are found according to the size and position of the holes, which provides theoretical foundation for the microstructure design of clinical C/C composites.
During the process that implant materials are used for bone replacement, the cell responses to implant materials determine the long-term stability of bone replacement. The microstructure of implant materials is considered as a critical factor that influences the cell responses. Carbon/Carbon composites (C/C composites) are novel implant materials, but there are few reports on the effect of their microstructure, especially the carbon matrixes and holes, on cell behavior. In this paper, C/C composites with different carbon matrixes are prepared by chemical vapor infiltration and pressure impregnation carbonization technique, respectively. The structure of holes is analyzed. The cell responses to C/C composites with different carbon matrixes are evaluated with MG63 osteoblast-like cells. The morphologies of MG63 osteoblast-like cells on the surface of C/C composites, especially in the holes are assessed by scanning electron microscope, and cell proliferation behavior is evaluated by 3-[4, 5-dimethylthiozol-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) assay. The results show that MG63 osteoblast-like cells have a lamellar morphology with similar sizes and spreading areas as well as the same proliferation behaviors for CC composites with different carbon matrixes. Carbon matrix shows unapparent influence on the cell growth behavior. Besides, MG63 osteoblast-like cells have various interactions with the holes of C/C composites. The cells stride over the holes with 6-8 μm in size, and connect with each other or grow along the curvature wall of the holes with a size of 30-40 μm; the cells present three-dimensional morphologies inside the holes and display circular shapes along the ridge of the holes. Diverse cell-material interactions are found according to the size and position of the holes, which provides theoretical foundation for the microstructure design of clinical C/C composites.
2011, 25(2).
Abstract:
The working frequency of the conventional electro-hydraulic vibration exciters, which consist of a servo valve and a hydraulic cylinder, is generally restricted within a narrow range due to limited frequency response capability of the servo valve itself. To counteract such restriction, a novel scheme for an electro-hydraulic vibrator, controlled by a two-dimensional valve(2D valve) and a bias valve in parallel, is therefore proposed. The frequency, amplitude and offset are independently controlled by rotary speed, axial sliding of the spool of the 2D valve and axial sliding of the spool of the bias valve. The principle of separate control was presented and the regulation approach of frequency, amplitude and offset was discussed. A mathematical model of the hydraulic power mechanism for the proposed vibration exciter was established to investigate the relationship between the amplitude and the axial sliding of the 2D valve’ spool, as well as that between the offset and the axial sliding of the bias valve’s spool at various frequencies. An experimental system was built to validate the theoretical analysis. It is verified that the 2D exciter is capable of working smoothly in a frequency range of 5– 200 Hz. And its frequency, amplitude and offset can be controlled respectively by either closed loop or open loop method. There is a linear relationship between the output amplitude and the spool axial opening of the 2D valve until a point when the flow rate becomes saturate and the amplitude remains constant. The offset displacement of the cylinder’s piston is linearly proportional to the axial displacement of the spool of the bias valve, when the valve opening is less than 25%. Thereafter, the slop of the offset curve decreases and tends to saturate. The proposed electro-hydraulic vibration controlled by the 2D valve not only facilitates the realization of high-frequency electro-hydraulic vibration, the high-accuracy of vibration can also be achieved by means of independent controls to the frequency, amplitude and offset
The working frequency of the conventional electro-hydraulic vibration exciters, which consist of a servo valve and a hydraulic cylinder, is generally restricted within a narrow range due to limited frequency response capability of the servo valve itself. To counteract such restriction, a novel scheme for an electro-hydraulic vibrator, controlled by a two-dimensional valve(2D valve) and a bias valve in parallel, is therefore proposed. The frequency, amplitude and offset are independently controlled by rotary speed, axial sliding of the spool of the 2D valve and axial sliding of the spool of the bias valve. The principle of separate control was presented and the regulation approach of frequency, amplitude and offset was discussed. A mathematical model of the hydraulic power mechanism for the proposed vibration exciter was established to investigate the relationship between the amplitude and the axial sliding of the 2D valve’ spool, as well as that between the offset and the axial sliding of the bias valve’s spool at various frequencies. An experimental system was built to validate the theoretical analysis. It is verified that the 2D exciter is capable of working smoothly in a frequency range of 5– 200 Hz. And its frequency, amplitude and offset can be controlled respectively by either closed loop or open loop method. There is a linear relationship between the output amplitude and the spool axial opening of the 2D valve until a point when the flow rate becomes saturate and the amplitude remains constant. The offset displacement of the cylinder’s piston is linearly proportional to the axial displacement of the spool of the bias valve, when the valve opening is less than 25%. Thereafter, the slop of the offset curve decreases and tends to saturate. The proposed electro-hydraulic vibration controlled by the 2D valve not only facilitates the realization of high-frequency electro-hydraulic vibration, the high-accuracy of vibration can also be achieved by means of independent controls to the frequency, amplitude and offset
2011, 25(2).
Abstract:
Pressure equipments in the process industries and the newly developing industries usually have extreme sizes and/or are subjected to extreme operating conditions such as high pressure, blast loading, cryogenic temperature, elevated temperature, complex corrosion, and so on. In order to understand, research and develop these equipments systematically, a concept of extreme pressure equipments(EPEs) is proposed. The applications and demands of EPEs in petrochemical industry, coal chemical industry, advanced energy, military, space technology, and environment protection are introduced. Basic scientific problems in material, design, inspection, and safety related to EPEs are discussed. Then, take chemical composition, manufacturing process, service duration, and operating conditions for example, main factors which affect material properties of EPEs are analyzed. New design concepts including design based on life cycle, dynamic design and light-weight design are introduced. EPEs with higher efficiency, lower cost and safer performance are in urgent demand in national major projects including ten million ton oil refinery, one million ton ethylene, liquefied natural gas transportation, and nuclear power plant. Thus, further research should be conducted on information acquisition, multi-mechanism damage coupling model, damage inspection, life prediction, online safety monitoring, maintenance strategy, safety pre-warning system, and emergency system.
Pressure equipments in the process industries and the newly developing industries usually have extreme sizes and/or are subjected to extreme operating conditions such as high pressure, blast loading, cryogenic temperature, elevated temperature, complex corrosion, and so on. In order to understand, research and develop these equipments systematically, a concept of extreme pressure equipments(EPEs) is proposed. The applications and demands of EPEs in petrochemical industry, coal chemical industry, advanced energy, military, space technology, and environment protection are introduced. Basic scientific problems in material, design, inspection, and safety related to EPEs are discussed. Then, take chemical composition, manufacturing process, service duration, and operating conditions for example, main factors which affect material properties of EPEs are analyzed. New design concepts including design based on life cycle, dynamic design and light-weight design are introduced. EPEs with higher efficiency, lower cost and safer performance are in urgent demand in national major projects including ten million ton oil refinery, one million ton ethylene, liquefied natural gas transportation, and nuclear power plant. Thus, further research should be conducted on information acquisition, multi-mechanism damage coupling model, damage inspection, life prediction, online safety monitoring, maintenance strategy, safety pre-warning system, and emergency system.
2011, 25(2).
Abstract:
All-position robots are widely applied in the welding of complicated parts. Welding of intersecting pipes is one of the most typical tasks. The welding seam is a complicated saddle-like space curve, which puts a great challenge to the pose planning of end-effector. The special robots designed specifically for this kind of tasks are rare in China and lack sufficient theoretical research. In this paper, a systematic research on the pose planning for the end-effectors of robot in the welding of intersecting pipes is conducted. First, the intersecting curve of pipes is mathematically analyzed. The mathematical model of the most general intersecting curve of pipes is derived, and several special forms of this model in degraded situations are also discussed. A new pose planning approach of bisecting angle in main normal plane (BAMNP) for the welding-gun is proposed by using differential geometry and the comparison with the traditional bisecting angle in axial rotation plane (BAARP) method is also analytically conducted. The optimal pose of the welding-gun is to make the orientation posed at the center of the small space formed by the two cylinders and the intersecting curve to help the welding-pool run smoothly. The BAMNP method can make sure the pose vertical to the curve and center between the two cylinders at the same time, therefore its performance in welding-technique is superior to the BAARP method. By using the traditional BAARP method, the robot structure can become simpler and easier to be controlled, because one degree of freedom (DOF) of the robot can be reduced. For the special case of perpendicular intersecting, an index is constructed to evaluate the quality of welding technique in the process of welding. The effect of different combination of pipe size on this index is also discussed. On the basis of practical consideration, selection principle for BAARP and BAMNP is described. The simulations of those two methods for a serial joint-type robot are made in MATLAB, and the simulation results are consistent to the analysis. The mathematical model and the proposed new pose-planning method will lay a solid foundation for future researches on the control and design of all-position welding robots.
All-position robots are widely applied in the welding of complicated parts. Welding of intersecting pipes is one of the most typical tasks. The welding seam is a complicated saddle-like space curve, which puts a great challenge to the pose planning of end-effector. The special robots designed specifically for this kind of tasks are rare in China and lack sufficient theoretical research. In this paper, a systematic research on the pose planning for the end-effectors of robot in the welding of intersecting pipes is conducted. First, the intersecting curve of pipes is mathematically analyzed. The mathematical model of the most general intersecting curve of pipes is derived, and several special forms of this model in degraded situations are also discussed. A new pose planning approach of bisecting angle in main normal plane (BAMNP) for the welding-gun is proposed by using differential geometry and the comparison with the traditional bisecting angle in axial rotation plane (BAARP) method is also analytically conducted. The optimal pose of the welding-gun is to make the orientation posed at the center of the small space formed by the two cylinders and the intersecting curve to help the welding-pool run smoothly. The BAMNP method can make sure the pose vertical to the curve and center between the two cylinders at the same time, therefore its performance in welding-technique is superior to the BAARP method. By using the traditional BAARP method, the robot structure can become simpler and easier to be controlled, because one degree of freedom (DOF) of the robot can be reduced. For the special case of perpendicular intersecting, an index is constructed to evaluate the quality of welding technique in the process of welding. The effect of different combination of pipe size on this index is also discussed. On the basis of practical consideration, selection principle for BAARP and BAMNP is described. The simulations of those two methods for a serial joint-type robot are made in MATLAB, and the simulation results are consistent to the analysis. The mathematical model and the proposed new pose-planning method will lay a solid foundation for future researches on the control and design of all-position welding robots.
2011, 25(2).
Abstract:
In asymmetric conditions, the movement and loads of left right wheels or frontback wheels of the aircraft with multi-wheel or four-wheel bogie landing gears are inconsistent. There are few open literatures related to anti-skid braking system for multi-wheels due to technology blockade. In China, the research on multi-channel control and non-equilibrium regulation has just started, and the design of multi-channel control system for anti-skid braking, the simulation of asymmetry taxiing under braking are not studied. In this paper, a dynamics model of ground movement for aircraft with four-wheel bogie landing gears is established for braking simulation, considering the six-degree-of-freedom aircraft body and the movement of bogies and wheels. A multi-channel anti-skid braking system is designed for the wheels of the main landing gears with four-wheel bogies. The eight wheels on left and right landing gears are divided into four groups, and each group is controlled via one channel. The cross protection and self-locked protection modules are added between different channels. A multi-channel anti-skid braking system with slip-ratio control or with slip-velocity control is established separately. Based on the aircraft dynamics model, aircraft braking to stop with anti-skid control on dry runway and on wet runway are simulated. The simulation results demonstrate that in asymmetric conditions, added with cross protection and self-locked protection modules, the slip-ratio-controlled braking system can automatically regulate brake torque to avoid deep slipping and correct aircraft course. The proposed research has reference value for improving brake control effect on wet runway.
In asymmetric conditions, the movement and loads of left right wheels or frontback wheels of the aircraft with multi-wheel or four-wheel bogie landing gears are inconsistent. There are few open literatures related to anti-skid braking system for multi-wheels due to technology blockade. In China, the research on multi-channel control and non-equilibrium regulation has just started, and the design of multi-channel control system for anti-skid braking, the simulation of asymmetry taxiing under braking are not studied. In this paper, a dynamics model of ground movement for aircraft with four-wheel bogie landing gears is established for braking simulation, considering the six-degree-of-freedom aircraft body and the movement of bogies and wheels. A multi-channel anti-skid braking system is designed for the wheels of the main landing gears with four-wheel bogies. The eight wheels on left and right landing gears are divided into four groups, and each group is controlled via one channel. The cross protection and self-locked protection modules are added between different channels. A multi-channel anti-skid braking system with slip-ratio control or with slip-velocity control is established separately. Based on the aircraft dynamics model, aircraft braking to stop with anti-skid control on dry runway and on wet runway are simulated. The simulation results demonstrate that in asymmetric conditions, added with cross protection and self-locked protection modules, the slip-ratio-controlled braking system can automatically regulate brake torque to avoid deep slipping and correct aircraft course. The proposed research has reference value for improving brake control effect on wet runway.
2011, 25(2).
Abstract:
Modern electronic circuit requires compact, multifunctional technology in communication systems. However, it is very difficult due to the limitations in passive component miniaturization and the complication of fabrication process. The bandpass filter is one of the most important passive components in millimeter(mm)-wave communication system, attracting significant interest in three-dimension (3D) miniaturized design, which is few reported. In this paper, a bandpass filter structure using low-temperature co-fired ceramic (LTCC) technology, which is fully integrated in a system-in package (SIP) communication module, is presented for miniaturized and high reliable mm-wave application. The bandpass filter with 3D end-coupled microstrip resonators is implemented in order to achieve a high performance bandwidth characteristic. Specifically, all of the resonators are embedded into different ceramic layers to decrease the insertion loss and enhance the out-of-band rejection performance by optimizing the coupling coefficient and the coupling strength. A fence structure, which is formed by metal-filled via array with the gap less than quarter wavelength, is placed around the embedded bandpass filter to avoid electromagnetic (EM) interference problem in multilayer structure. This structural model is validated through actual LTCC process. The bandpass filter is successfully manufactured by modifying the co-fireablity characteristics, adjusting the sintering profile, releasing the interfacial stress, and reducing the shrinkage mismatch with different materials. Measured results show good performance and agree well with the high frequency EM full wave simulation. The influence of layer thickness and dielectric constant on the frequency response in fabricated process is analyzed, where thicker ceramic sheets let the filter response shift to higher frequency. Moreover, measured S-parameters denote the center frequency is also strongly influenced by the variation of ceramic material’s dielectric constants. By analyzing the relationship between the characteristics of the ceramic tape and the center frequency of the filter, both theoretical and experimental data are accumulated for broadening application filed. With the coupling resonators embedded into the ceramic layers, the bandpass filter exhibits advantages of small size and high reliability compared to conventional planar filter structure, which makes the bandpass filter suitable for SIP communicational application.
Modern electronic circuit requires compact, multifunctional technology in communication systems. However, it is very difficult due to the limitations in passive component miniaturization and the complication of fabrication process. The bandpass filter is one of the most important passive components in millimeter(mm)-wave communication system, attracting significant interest in three-dimension (3D) miniaturized design, which is few reported. In this paper, a bandpass filter structure using low-temperature co-fired ceramic (LTCC) technology, which is fully integrated in a system-in package (SIP) communication module, is presented for miniaturized and high reliable mm-wave application. The bandpass filter with 3D end-coupled microstrip resonators is implemented in order to achieve a high performance bandwidth characteristic. Specifically, all of the resonators are embedded into different ceramic layers to decrease the insertion loss and enhance the out-of-band rejection performance by optimizing the coupling coefficient and the coupling strength. A fence structure, which is formed by metal-filled via array with the gap less than quarter wavelength, is placed around the embedded bandpass filter to avoid electromagnetic (EM) interference problem in multilayer structure. This structural model is validated through actual LTCC process. The bandpass filter is successfully manufactured by modifying the co-fireablity characteristics, adjusting the sintering profile, releasing the interfacial stress, and reducing the shrinkage mismatch with different materials. Measured results show good performance and agree well with the high frequency EM full wave simulation. The influence of layer thickness and dielectric constant on the frequency response in fabricated process is analyzed, where thicker ceramic sheets let the filter response shift to higher frequency. Moreover, measured S-parameters denote the center frequency is also strongly influenced by the variation of ceramic material’s dielectric constants. By analyzing the relationship between the characteristics of the ceramic tape and the center frequency of the filter, both theoretical and experimental data are accumulated for broadening application filed. With the coupling resonators embedded into the ceramic layers, the bandpass filter exhibits advantages of small size and high reliability compared to conventional planar filter structure, which makes the bandpass filter suitable for SIP communicational application.
2011, 25(2).
Abstract:
Because of the ill-posedness of the near-field acoustic holography (NAH), the regularization method is required to stabilize the computational process of NAH. The regularization effect is related to how to select the parameter correctly and effectively. However the L-curve method commonly used for the selection of regularization parameters has the disadvantages of wrong selection and incorrect selection, which influences the application of NAH. For the purpose of solving the problems existed in the L-curve method, the -curve method is introduced into the field of NAH, and the performance applied to NAH directly is analyzed on the basis of equivalent source method-based NAH. However, it is found out via investigations that the -curve method in NAH also has the problem of wrong selection and is unable to choose the regularization parameter correctly. In order to select the parameter correctly and effectively, a novel method for selecting regularization parameters is proposed based on the original -curve method, which can be called improved -curve method. In the proposed method the regularization parameters are discretized linearly between the largest singular value and the smallest singular value, and the solution norm and the residual norm corresponding to these regularization parameters are also described in a linear coordinate instead of in a lg-lg coordinate, which are the two main differences compared with the L-curve and with the original -curve method. In linear coordinate and using the linearly discretized regularization parameters, the solution norm is a monotonically decreasing function of the residual norm as the increase of the regularization parameter, moreover the curve is convex everywhere. So the regularization parameters can be selected correctly and effectively based on the improved -curve method. Then a numerical simulation is done with a simply supported plate to verify the validity of the proposed method. Experiments with two actual sources, a clamped plate and the double speakers, are carried out to do a further demonstration. The simulation result as well as the experimental result shows that the improved -curve method is efficacious and has some advantages over the L-curve method and the original -curve method. The proposed novel method is able to avoid the problem of wrong selection and to select the regularization parameter correctly even if the curve is smooth.
Because of the ill-posedness of the near-field acoustic holography (NAH), the regularization method is required to stabilize the computational process of NAH. The regularization effect is related to how to select the parameter correctly and effectively. However the L-curve method commonly used for the selection of regularization parameters has the disadvantages of wrong selection and incorrect selection, which influences the application of NAH. For the purpose of solving the problems existed in the L-curve method, the -curve method is introduced into the field of NAH, and the performance applied to NAH directly is analyzed on the basis of equivalent source method-based NAH. However, it is found out via investigations that the -curve method in NAH also has the problem of wrong selection and is unable to choose the regularization parameter correctly. In order to select the parameter correctly and effectively, a novel method for selecting regularization parameters is proposed based on the original -curve method, which can be called improved -curve method. In the proposed method the regularization parameters are discretized linearly between the largest singular value and the smallest singular value, and the solution norm and the residual norm corresponding to these regularization parameters are also described in a linear coordinate instead of in a lg-lg coordinate, which are the two main differences compared with the L-curve and with the original -curve method. In linear coordinate and using the linearly discretized regularization parameters, the solution norm is a monotonically decreasing function of the residual norm as the increase of the regularization parameter, moreover the curve is convex everywhere. So the regularization parameters can be selected correctly and effectively based on the improved -curve method. Then a numerical simulation is done with a simply supported plate to verify the validity of the proposed method. Experiments with two actual sources, a clamped plate and the double speakers, are carried out to do a further demonstration. The simulation result as well as the experimental result shows that the improved -curve method is efficacious and has some advantages over the L-curve method and the original -curve method. The proposed novel method is able to avoid the problem of wrong selection and to select the regularization parameter correctly even if the curve is smooth.
2011, 25(2).
Abstract:
The majority of topology optimization of compliant mechanisms uses linear finite element models to find the structure responses. Because the displacements of compliant mechanisms are intrinsically large, the topological design can not provide quantitatively accurate result. Thus, topological design of these mechanisms considering geometrical nonlinearities is essential. A new methodology for geometrical nonlinear topology optimization of compliant mechanisms under displacement loading is presented. Frame elements are chosen to represent the design domain because they are capable of capturing the bending modes. Geometrically nonlinear structural response is obtained by using the co-rotational total Lagrange finite element formulation, and the equilibrium is solved by using the incremental scheme combined with Newton-Raphson iteration. The multi-objective function is developed by the minimum strain energy and maximum geometric advantage to design the mechanism which meets both stiffness and flexibility requirements, respectively. The adjoint method and the direct differentiation method are applied to obtain the sensitivities of the objective functions. The method of moving asymptotes (MMA) is employed as optimizer. The numerical example is simulated to show that the optimal mechanism based on geometrically nonlinear formulation not only has more flexibility and stiffness than that based on linear formulation, but also has better stress distribution than the one. It is necessary to design compliant mechanisms using geometrically nonlinear topology optimization. Compared with linear formulation, the formulation for geometrically nonlinear topology optimization of compliant mechanisms can give the compliant mechanism that has better mechanical performance. A new method is provided for topological design of large displacement compliant mechanisms.
The majority of topology optimization of compliant mechanisms uses linear finite element models to find the structure responses. Because the displacements of compliant mechanisms are intrinsically large, the topological design can not provide quantitatively accurate result. Thus, topological design of these mechanisms considering geometrical nonlinearities is essential. A new methodology for geometrical nonlinear topology optimization of compliant mechanisms under displacement loading is presented. Frame elements are chosen to represent the design domain because they are capable of capturing the bending modes. Geometrically nonlinear structural response is obtained by using the co-rotational total Lagrange finite element formulation, and the equilibrium is solved by using the incremental scheme combined with Newton-Raphson iteration. The multi-objective function is developed by the minimum strain energy and maximum geometric advantage to design the mechanism which meets both stiffness and flexibility requirements, respectively. The adjoint method and the direct differentiation method are applied to obtain the sensitivities of the objective functions. The method of moving asymptotes (MMA) is employed as optimizer. The numerical example is simulated to show that the optimal mechanism based on geometrically nonlinear formulation not only has more flexibility and stiffness than that based on linear formulation, but also has better stress distribution than the one. It is necessary to design compliant mechanisms using geometrically nonlinear topology optimization. Compared with linear formulation, the formulation for geometrically nonlinear topology optimization of compliant mechanisms can give the compliant mechanism that has better mechanical performance. A new method is provided for topological design of large displacement compliant mechanisms.
2011, 25(2).
Abstract:
Flow accelerated corrosion (FAC) is the main failure cause of the secondary circuit carbon steel piping in nuclear power plants. The piping failures caused by FAC have resulted in numerous unplanned outages and tragic fatalities. The existing researches focus on the main factors contributing to FAC, which include metallurgical factors, environmental factors and hydrodynamic factors. Some effective FAC management methods and programs with long term monitoring and inspection data analysis are recommended. But a comprehensive FAC management system should be developed in order to mitigate and manage FAC systematically. In this paper, the FAC influencing factors are analyzed in combination with the operating conditions of the secondary circuit piping in the Third Qinshan Nuclear Power Plant(TQNPP), China (Third Qinshan Nuclear Power Company Limited, China). A comprehensive FAC mitigation and management system is developed for TQNPP secondary circuit piping. The system is composed of five processes, viz. materials substitution, water chemical optimization, long-term monitor strategy for the susceptible piping, integrity evaluation of the local thinning defects, and repair or replacement. With the implementation of the five processes, the material of FAC sensitive pipe fittings are modified from carbon steel to stainless steel, N2H4 and NH3 are finally selected as the water chemical regulator of secondary circuit, the secondary circuit pips are classified according to FAC susceptibility in order to conduct long term monitoring strategy, and an integrity evaluation flow for local thinning caused by FAC in carbon steel piping is developed. If the component with local thinning defects is not fit-for-service, corresponding repair or replacement should be conducted. The comprehensive FAC mitigation and management system with five interrelated processes would be a cost-effective method of increasing personnel safety, plant safety and availability.
Flow accelerated corrosion (FAC) is the main failure cause of the secondary circuit carbon steel piping in nuclear power plants. The piping failures caused by FAC have resulted in numerous unplanned outages and tragic fatalities. The existing researches focus on the main factors contributing to FAC, which include metallurgical factors, environmental factors and hydrodynamic factors. Some effective FAC management methods and programs with long term monitoring and inspection data analysis are recommended. But a comprehensive FAC management system should be developed in order to mitigate and manage FAC systematically. In this paper, the FAC influencing factors are analyzed in combination with the operating conditions of the secondary circuit piping in the Third Qinshan Nuclear Power Plant(TQNPP), China (Third Qinshan Nuclear Power Company Limited, China). A comprehensive FAC mitigation and management system is developed for TQNPP secondary circuit piping. The system is composed of five processes, viz. materials substitution, water chemical optimization, long-term monitor strategy for the susceptible piping, integrity evaluation of the local thinning defects, and repair or replacement. With the implementation of the five processes, the material of FAC sensitive pipe fittings are modified from carbon steel to stainless steel, N2H4 and NH3 are finally selected as the water chemical regulator of secondary circuit, the secondary circuit pips are classified according to FAC susceptibility in order to conduct long term monitoring strategy, and an integrity evaluation flow for local thinning caused by FAC in carbon steel piping is developed. If the component with local thinning defects is not fit-for-service, corresponding repair or replacement should be conducted. The comprehensive FAC mitigation and management system with five interrelated processes would be a cost-effective method of increasing personnel safety, plant safety and availability.
2011, 25(2).
Abstract:
The eccentric-gear can be used for variable speed transmission. But, due to the vibrations caused by variation of backlash in working process, the eccentric-gear is seldom applied in engineering project. There is just a little study about the eccentric-gear. And it is necessary to take a further research on eccentric-gear transmission for the applications in the transplanting mechanism of high-speed rice transplanter. The key of this paper is to extend understanding of three following characteristics of this drive: (1) The rotation-center-distance and the geometrical-center-distance of the two meshing eccentric gears are respectively the hypotenuse and the straight edge of a right triangle in a cycle. (2) The geometrical center line of two meshing gears divides the linking-line of the two rotational centers equally. (3) When two times the eccentricity of gear, the rotation-center-distance and the geometrical-center-distance form a right triangle, the optimal value of rotation-center-distance can be determined. In addition, the kinematic analysis, such as the relationship between contact point and midpoint of the linking-line of two gears’ rotational centers, transmission ratio between the driving-gear and the driven-gear, contact angle and coordinate of contact point are be made, further the formula for calculation of contact force, flow chart for writing optimization program and curve for analysis of data are also be developed. The relationship between the rotation-center-distance and the geometrical-center-distance, which is determined by three characteristics mentioned above, is a key for the rational design and application of eccentric-gear transmission. Particularly, the presented right triangle property of eccentric gear drive is an important reference for effective analysis of dynamic characteristic of eccentric-gear mechanism and its reliable design.
The eccentric-gear can be used for variable speed transmission. But, due to the vibrations caused by variation of backlash in working process, the eccentric-gear is seldom applied in engineering project. There is just a little study about the eccentric-gear. And it is necessary to take a further research on eccentric-gear transmission for the applications in the transplanting mechanism of high-speed rice transplanter. The key of this paper is to extend understanding of three following characteristics of this drive: (1) The rotation-center-distance and the geometrical-center-distance of the two meshing eccentric gears are respectively the hypotenuse and the straight edge of a right triangle in a cycle. (2) The geometrical center line of two meshing gears divides the linking-line of the two rotational centers equally. (3) When two times the eccentricity of gear, the rotation-center-distance and the geometrical-center-distance form a right triangle, the optimal value of rotation-center-distance can be determined. In addition, the kinematic analysis, such as the relationship between contact point and midpoint of the linking-line of two gears’ rotational centers, transmission ratio between the driving-gear and the driven-gear, contact angle and coordinate of contact point are be made, further the formula for calculation of contact force, flow chart for writing optimization program and curve for analysis of data are also be developed. The relationship between the rotation-center-distance and the geometrical-center-distance, which is determined by three characteristics mentioned above, is a key for the rational design and application of eccentric-gear transmission. Particularly, the presented right triangle property of eccentric gear drive is an important reference for effective analysis of dynamic characteristic of eccentric-gear mechanism and its reliable design.
2011, 25(2).
Abstract:
Investigators are attracted by the complexity and significance of preventive maintenance problem, and there are hundreds of maintenance models and methods to solve the maintenance problems of companies and army, going with a lot of investigative harvests. However, one-component system or series system is focused by most of the literature. The problem of preventive maintenance (PM) on cold standby repairable system does not attach importance despite the fact that the cold standby repairable system is ubiquitous in engineering systems. In this paper, an optimal replacement model for gamma deteriorating system is studied. This methodology presented uses a gamma distribution to model the material degradation, and the impact of imperfect maintenance actions on system reliability is investigated. After an imperfect maintenance action, the state of a degrading system is assumed as a random variable and the maintenance time follows a geometric process. A maintenance policy ( ) is applied by which the system will be repaired whenever it experiences the Nth PM, and an optimal policy ( ) could be determined numerically or analytically for minimizing the long-run average cost per unit time. A numerical example about how to confirm the optimal maintenance time by the inspecting information of liquid coupling device is given to demonstrate the use of this policy. This paper presents a condition-based replacement policy for cold standby repairable system under continuous monitoring. Its contribution embody in two aspects, relaxing the restrictions of hypothesis and investigating the condition-based maintenance policy of the cold standby repairable system which is ignored by others.
Investigators are attracted by the complexity and significance of preventive maintenance problem, and there are hundreds of maintenance models and methods to solve the maintenance problems of companies and army, going with a lot of investigative harvests. However, one-component system or series system is focused by most of the literature. The problem of preventive maintenance (PM) on cold standby repairable system does not attach importance despite the fact that the cold standby repairable system is ubiquitous in engineering systems. In this paper, an optimal replacement model for gamma deteriorating system is studied. This methodology presented uses a gamma distribution to model the material degradation, and the impact of imperfect maintenance actions on system reliability is investigated. After an imperfect maintenance action, the state of a degrading system is assumed as a random variable and the maintenance time follows a geometric process. A maintenance policy ( ) is applied by which the system will be repaired whenever it experiences the Nth PM, and an optimal policy ( ) could be determined numerically or analytically for minimizing the long-run average cost per unit time. A numerical example about how to confirm the optimal maintenance time by the inspecting information of liquid coupling device is given to demonstrate the use of this policy. This paper presents a condition-based replacement policy for cold standby repairable system under continuous monitoring. Its contribution embody in two aspects, relaxing the restrictions of hypothesis and investigating the condition-based maintenance policy of the cold standby repairable system which is ignored by others.
2011, 25(2).
Abstract:
Only the fatigue initiation is considered by the safe-life design approach, while fatigue crack propagation is paid more attention by the damage tolerance approach. The reasonable fatigue design method and durability assessment standard should give these two phases equivalent concerns. To develop a unified model of fatigue initiation and crack propagation, a great deal of baseline fatigue properties of a material should be obtained by fatigue experiments. However, there is lack of thorough and comprehensive experiment study on the fatigue properties of 2024-T4 aluminum alloy, which is widely used as load-bearing components in aircraft industry. In this paper, strain-controlled uniaxial, torsion, and combined axial-torsion fatigue experiments are conducted on 2024-T4 aluminum alloy in ambient air. Fully reversed uniaxial and pure torsion experiments employ solid cylindrical specimens. Fatigue experiments under the fully reversed shear loading with a static axial stress, proportional axial-torsion loading, and 90 out-of-phase axial-torsion nonproportional loading are conducted by using thin-walled tubular specimens. The experimental results show that the mean stress has a significant influence on the fatigue strength of the material. A tensile mean stress decreases the fatigue life dramatically, while a compressive mean stress increases the fatigue life. The strain-life fatigue results obtained from the fully reversed uniaxial fatigue experiments can be represented by one smooth curve of a three-parameter equation. However, two fitting curves are needed for characterizing the results of the fully reversed pure torsion fatigue tests because of the existence of an obvious kink. The baseline fatigue properties of 2024-T4 aluminum alloy obtained from the fatigue experiments have applications for the fatigue design and safe assessment of engineering components.
Only the fatigue initiation is considered by the safe-life design approach, while fatigue crack propagation is paid more attention by the damage tolerance approach. The reasonable fatigue design method and durability assessment standard should give these two phases equivalent concerns. To develop a unified model of fatigue initiation and crack propagation, a great deal of baseline fatigue properties of a material should be obtained by fatigue experiments. However, there is lack of thorough and comprehensive experiment study on the fatigue properties of 2024-T4 aluminum alloy, which is widely used as load-bearing components in aircraft industry. In this paper, strain-controlled uniaxial, torsion, and combined axial-torsion fatigue experiments are conducted on 2024-T4 aluminum alloy in ambient air. Fully reversed uniaxial and pure torsion experiments employ solid cylindrical specimens. Fatigue experiments under the fully reversed shear loading with a static axial stress, proportional axial-torsion loading, and 90 out-of-phase axial-torsion nonproportional loading are conducted by using thin-walled tubular specimens. The experimental results show that the mean stress has a significant influence on the fatigue strength of the material. A tensile mean stress decreases the fatigue life dramatically, while a compressive mean stress increases the fatigue life. The strain-life fatigue results obtained from the fully reversed uniaxial fatigue experiments can be represented by one smooth curve of a three-parameter equation. However, two fitting curves are needed for characterizing the results of the fully reversed pure torsion fatigue tests because of the existence of an obvious kink. The baseline fatigue properties of 2024-T4 aluminum alloy obtained from the fatigue experiments have applications for the fatigue design and safe assessment of engineering components.
2011, 25(2).
Abstract:
By increasing the yield strengths of austenitic stainless steels for pressure vessels with strain hardening techniques, the elastic load bearing capacity of austenitic stainless steel pressure vessels can be significantly improved. Two kinds of strain hardening methods are often used for austenitic stainless steel pressure vessels: Avesta model for ambient temperature applications and Ardeform model for cryogenic temperature applications. Both methods are obtained from conventional design rules based on the linear elastic theory, and only consider the hardening effect from materials. Consequently this limits the applications of strain hardening techniques for austenitic stainless steel pressure vessels because of safety concerns. This paper investigates the effect of strain hardening on the load bearing capacity of austenitic stainless steel pressure vessels under large deformation, based on the elastic-plastic theory. Firstly, to understand the effect of strain hardening on material behavior, the plastic instability loads of a round tensile bar specimen are derived under two different loading paths and validated by experiments. Secondly, to investigate the effect of strain hardening on pressure vessels strength, the plastic instability pressure under strain hardening is derived and further validated by finite element simulations. Further, the safety margin of pressure vessels after strain hardening is analyzed by comparing the safety factor values calculated from bursting tests, finite element analyses, and standards. The researching results show that the load bearing capacity of pressure vessels at ambient temperature is independent of the loading history when the effects of both material strain hardening and structural deformation are considered. Finite element simulations and bursting tests results show that the minimum safety factor of austenitic stainless steel pressure vessels with 5% strain hardening is close to the recommended value for common pressure vessels specified in the European pressure vessel standard. The proposed study also shows that in the strain hardening design of austenitic stainless steel pressure vessels, the calculation for plastic instability pressure could use theoretical formula or finite element analyses based on geometrical dimensions and material property parameters before strain hardening, but a 5% strain should be employed as a design limit. The proposed research can be used for the strain hardening design of austenitic stainless steel pressure vessels safely.
By increasing the yield strengths of austenitic stainless steels for pressure vessels with strain hardening techniques, the elastic load bearing capacity of austenitic stainless steel pressure vessels can be significantly improved. Two kinds of strain hardening methods are often used for austenitic stainless steel pressure vessels: Avesta model for ambient temperature applications and Ardeform model for cryogenic temperature applications. Both methods are obtained from conventional design rules based on the linear elastic theory, and only consider the hardening effect from materials. Consequently this limits the applications of strain hardening techniques for austenitic stainless steel pressure vessels because of safety concerns. This paper investigates the effect of strain hardening on the load bearing capacity of austenitic stainless steel pressure vessels under large deformation, based on the elastic-plastic theory. Firstly, to understand the effect of strain hardening on material behavior, the plastic instability loads of a round tensile bar specimen are derived under two different loading paths and validated by experiments. Secondly, to investigate the effect of strain hardening on pressure vessels strength, the plastic instability pressure under strain hardening is derived and further validated by finite element simulations. Further, the safety margin of pressure vessels after strain hardening is analyzed by comparing the safety factor values calculated from bursting tests, finite element analyses, and standards. The researching results show that the load bearing capacity of pressure vessels at ambient temperature is independent of the loading history when the effects of both material strain hardening and structural deformation are considered. Finite element simulations and bursting tests results show that the minimum safety factor of austenitic stainless steel pressure vessels with 5% strain hardening is close to the recommended value for common pressure vessels specified in the European pressure vessel standard. The proposed study also shows that in the strain hardening design of austenitic stainless steel pressure vessels, the calculation for plastic instability pressure could use theoretical formula or finite element analyses based on geometrical dimensions and material property parameters before strain hardening, but a 5% strain should be employed as a design limit. The proposed research can be used for the strain hardening design of austenitic stainless steel pressure vessels safely.
2011, 25(2).
Abstract:
The research of different kinds of permeable non-Newtonian fluid flow is increasing day by day owing to the development of science, technology and production modes. It is most common to use power rate equation to describe such flows. However, this equation is nonlinear and very difficult to derive explicit exact analytical solutions. Generally, people can only derive approximate solutions with numerical methods. Recently, an advanced separating variables method which can derive exact analytical solutions easier is developed by Academician CAI Ruixian (the method of separating variables with addition). It is assumed that the unknown variable may be indicated as the sum of one-dimensional functions rather than the product in the common method of separating variables. Such method is used to solve the radial permeable power rate flow unsteady nonlinear equations on account of making the process simple. Four concise (no special functions and infinite series) exact analytical solutions is derived with the new method about this flow to develop the theory of non-Newtonian permeable fluid, which are exponential solution, two-dimensional function with time and radius, logarithmic solution, and double logarithmic solution, respectively. In addition, the method of separating variables with addition is developed and applied instead of the conventional multiplication one. It is proven to be promising and encouraging by the deducing. The solutions yielded will be valuable to the theory of the permeable power rate flow and can be used as standard solutions to check numerical methods and their differencing schemes, grid generation ways, etc. They also can be used to verify the accuracy, convergency and stability of the numerical solutions and to develop the numerical computational approaches.
The research of different kinds of permeable non-Newtonian fluid flow is increasing day by day owing to the development of science, technology and production modes. It is most common to use power rate equation to describe such flows. However, this equation is nonlinear and very difficult to derive explicit exact analytical solutions. Generally, people can only derive approximate solutions with numerical methods. Recently, an advanced separating variables method which can derive exact analytical solutions easier is developed by Academician CAI Ruixian (the method of separating variables with addition). It is assumed that the unknown variable may be indicated as the sum of one-dimensional functions rather than the product in the common method of separating variables. Such method is used to solve the radial permeable power rate flow unsteady nonlinear equations on account of making the process simple. Four concise (no special functions and infinite series) exact analytical solutions is derived with the new method about this flow to develop the theory of non-Newtonian permeable fluid, which are exponential solution, two-dimensional function with time and radius, logarithmic solution, and double logarithmic solution, respectively. In addition, the method of separating variables with addition is developed and applied instead of the conventional multiplication one. It is proven to be promising and encouraging by the deducing. The solutions yielded will be valuable to the theory of the permeable power rate flow and can be used as standard solutions to check numerical methods and their differencing schemes, grid generation ways, etc. They also can be used to verify the accuracy, convergency and stability of the numerical solutions and to develop the numerical computational approaches.
2011, 25(2).
Abstract:
As a new type of low cracking suscepbility high strength steel, 07MnCrMoVR steel has excellent weldability, with low carbon equivalent and cold cracking susceptibility coefficient. However, there are still some problems when this steel is on the outdoor actual welding condition, such as having some extend cold cracking suscepbility and embrittlement of heat affected zone. Currently, researching works for the welding of this steel mostly focus on the evaluation the weldability of it, only few works are concentrated in how the heat input affecting the embrittlement of HAZ. The goal of this research is to study the effect of heat input on the embrittlement of the heat affected zone so as to get the optimal welding heat input range for it. In this paper, 38 mm 07MnCrMoVR steel made by Shougang is welded by manual arc welding technology, and the effect of heat input on the microstructure and mechanical properties of weld joints is also investigated by use of optical microscope(OM), scanning electron microscope(SEM), mechanical properties testing machines and Viker hardness tester. The microstructure and fractography observation results and the mechanical properties testing results indicate that the 07MnCrMoVR steel made by Shougang has a wide adaptable range for heat input, and when the heat input is in the range of 15–42 kJcm, the toughness of the weld joints is well. With the increase of heat input, the impact toughness of weld zone and heat affected zone decrease, whereas the tensile strength of the weld joints does not change at all. The microstructure of the weld is acicular ferrite with small amount of proeutectoid ferrite, and with the increase of heat input, the ratio of proeutectoid ferrite and the amount of M-A constituent increase, as well as the grain size and the width of the bainite lath in coarsened grain heat affected zone. Fractography results show that with the increase of heat input, the number of dimples in impact fracture specimens decreases, and the cleavage patterns increase, inducing the fracture from ductility to embrittlement. This research provides a theory support for guiding the penstock constructor how to use 07MnCrMoVR steel in actual welding.
As a new type of low cracking suscepbility high strength steel, 07MnCrMoVR steel has excellent weldability, with low carbon equivalent and cold cracking susceptibility coefficient. However, there are still some problems when this steel is on the outdoor actual welding condition, such as having some extend cold cracking suscepbility and embrittlement of heat affected zone. Currently, researching works for the welding of this steel mostly focus on the evaluation the weldability of it, only few works are concentrated in how the heat input affecting the embrittlement of HAZ. The goal of this research is to study the effect of heat input on the embrittlement of the heat affected zone so as to get the optimal welding heat input range for it. In this paper, 38 mm 07MnCrMoVR steel made by Shougang is welded by manual arc welding technology, and the effect of heat input on the microstructure and mechanical properties of weld joints is also investigated by use of optical microscope(OM), scanning electron microscope(SEM), mechanical properties testing machines and Viker hardness tester. The microstructure and fractography observation results and the mechanical properties testing results indicate that the 07MnCrMoVR steel made by Shougang has a wide adaptable range for heat input, and when the heat input is in the range of 15–42 kJcm, the toughness of the weld joints is well. With the increase of heat input, the impact toughness of weld zone and heat affected zone decrease, whereas the tensile strength of the weld joints does not change at all. The microstructure of the weld is acicular ferrite with small amount of proeutectoid ferrite, and with the increase of heat input, the ratio of proeutectoid ferrite and the amount of M-A constituent increase, as well as the grain size and the width of the bainite lath in coarsened grain heat affected zone. Fractography results show that with the increase of heat input, the number of dimples in impact fracture specimens decreases, and the cleavage patterns increase, inducing the fracture from ductility to embrittlement. This research provides a theory support for guiding the penstock constructor how to use 07MnCrMoVR steel in actual welding.
2011, 25(2).
Abstract:
The algorithms for feedrate profile generation, such as linear and S-curve profiles, have been widely used in machinery controllers, and these algorithms can greatly improve the smoothness of motion. However, most of the algorithms lead to the discontinuous acceleration/deceleration and jerk, or high jerk levels, which is very harmful to machine tool or robot in most occasions. This paper presents a smooth S-curve feedrate profiling generation algorithm that produces continuous feedrate, acceleration, and jerk profiles. Smooth jerk is obtained by imposing limits on the first and second time derivatives of acceleration, resulting in trapezoidal jerk profiles along the tool path. The discretization of smooth S-curve feedrate is realized with a novel approach that improves the efficiency without calculating the deceleration point in each sampled time. To ensure that the interpolation time is a multiple of the value of sampled time, the feedrate, acceleration, jerk, and jerk derivative are recalculated. Meantime, to improve the efficiency, the interpolation steps of all regions are computed before interpolation. According to the distance of trajectory, the smooth S-curve acceleration and decelerations are divided into three blocks: normal block, short block type-I, and short block type-II. Finally feedrate discretization of short block type-I and type-II is obtained with considering the efficiency. The proposed generation algorithm is tested in machining a part on a five axis milling machine, which is controlled with the CNC system for newly developed high-speed machine tools. The test result shows that the smooth S-curve approach has the smoother feedrate, acceleration, deceleration, and jerk profiles than S-curve. The proposed algorithm ensures the automated machinery motion smoothness, and improves the quality and efficiency of the automated machinery motion planning.
The algorithms for feedrate profile generation, such as linear and S-curve profiles, have been widely used in machinery controllers, and these algorithms can greatly improve the smoothness of motion. However, most of the algorithms lead to the discontinuous acceleration/deceleration and jerk, or high jerk levels, which is very harmful to machine tool or robot in most occasions. This paper presents a smooth S-curve feedrate profiling generation algorithm that produces continuous feedrate, acceleration, and jerk profiles. Smooth jerk is obtained by imposing limits on the first and second time derivatives of acceleration, resulting in trapezoidal jerk profiles along the tool path. The discretization of smooth S-curve feedrate is realized with a novel approach that improves the efficiency without calculating the deceleration point in each sampled time. To ensure that the interpolation time is a multiple of the value of sampled time, the feedrate, acceleration, jerk, and jerk derivative are recalculated. Meantime, to improve the efficiency, the interpolation steps of all regions are computed before interpolation. According to the distance of trajectory, the smooth S-curve acceleration and decelerations are divided into three blocks: normal block, short block type-I, and short block type-II. Finally feedrate discretization of short block type-I and type-II is obtained with considering the efficiency. The proposed generation algorithm is tested in machining a part on a five axis milling machine, which is controlled with the CNC system for newly developed high-speed machine tools. The test result shows that the smooth S-curve approach has the smoother feedrate, acceleration, deceleration, and jerk profiles than S-curve. The proposed algorithm ensures the automated machinery motion smoothness, and improves the quality and efficiency of the automated machinery motion planning.
2011, 25(2).
Abstract:
Micro-structure related behavior of diffusion bonding joints is a crucial issue in device and reactor fabrication of Micro Chemo Mechanical Systems. However, the previous studies have been focused on the macro mechanical performance of diffusion bonded joint, especially diffusion bonding conditions effects on tensile strength, shearing strength and fatigue strength. The research of interfacial micro-voids and microstructures evolution for failure mechanism has not been carried out for diffusion-bonded joints. An interfacial electrical resistance measuring method is proposed to evaluate the quality of bonded joints and verified by using two-dimensional finite-element simulation. The influences of micro void geometry on increments of resistance are analyzed and the relationship between bonded area fraction and resistance increment is established by theoretical analysis combined with simulated results. Metallographic inspections and micro-hardness testing are conducted near the interface of diffusion bonded joints. For the purpose of identifying the failure mechanisms of the joints, both microscopic tensile and fatigue tests are conducted on the self-developed in-situ microscopic fatigue testing system. Based on the microscopic observations, the mechanism of interfacial failure is addressed. The observation result shows that for 316LSS diffusion-bonded joints, microstructure evolution and effect of micro-voids play a key role in interfacial failure mechanism. Finally, a new life prediction model in terms of the increment of electrical resistance is developed and confirmed by the experimental results. The proposed study is initiated that constituted a primary interfacial failure mechanism on micron scale and provide the life prediction for reliability of components sealed by diffusion bonding.
Micro-structure related behavior of diffusion bonding joints is a crucial issue in device and reactor fabrication of Micro Chemo Mechanical Systems. However, the previous studies have been focused on the macro mechanical performance of diffusion bonded joint, especially diffusion bonding conditions effects on tensile strength, shearing strength and fatigue strength. The research of interfacial micro-voids and microstructures evolution for failure mechanism has not been carried out for diffusion-bonded joints. An interfacial electrical resistance measuring method is proposed to evaluate the quality of bonded joints and verified by using two-dimensional finite-element simulation. The influences of micro void geometry on increments of resistance are analyzed and the relationship between bonded area fraction and resistance increment is established by theoretical analysis combined with simulated results. Metallographic inspections and micro-hardness testing are conducted near the interface of diffusion bonded joints. For the purpose of identifying the failure mechanisms of the joints, both microscopic tensile and fatigue tests are conducted on the self-developed in-situ microscopic fatigue testing system. Based on the microscopic observations, the mechanism of interfacial failure is addressed. The observation result shows that for 316LSS diffusion-bonded joints, microstructure evolution and effect of micro-voids play a key role in interfacial failure mechanism. Finally, a new life prediction model in terms of the increment of electrical resistance is developed and confirmed by the experimental results. The proposed study is initiated that constituted a primary interfacial failure mechanism on micron scale and provide the life prediction for reliability of components sealed by diffusion bonding.
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