2007 Vol.20(4)
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2007, 21(4).
Abstract:
A state-of-art review is given to the new advances on fatigue reliability design and analysis methods of Chinese railway vehicle’s structures. First, the structures are subject to a complicated random fatigue stressing history and this history should be determined by combining dynamic simulation and on-line inspection. Second, the random fatigue constitutions belong to an intrinsic fatigue phenomenon and a probabilistic model is developed to well describe them with two measurements of survival probability and confidence, similar model is also presented for the random stress-life rela-tions and extrapolated appropriately into long fatigue life regime. Third, concept of the fatigue limit should be understood as the fatigue strength at a given fatigue life and a so-called local Basquin model method is proposed for measuring the random strengths. In addition, drawing and application methods of the Goodman-Smith diagram for integrally characterizing the random fatigue strengths are established in terms of ten kilometers. Fourth, a reliability stress-based method is constructed with a consideration of the random constitutive relations. These new advances form a new frame work for railway fatigue reliability design and analysis.
A state-of-art review is given to the new advances on fatigue reliability design and analysis methods of Chinese railway vehicle’s structures. First, the structures are subject to a complicated random fatigue stressing history and this history should be determined by combining dynamic simulation and on-line inspection. Second, the random fatigue constitutions belong to an intrinsic fatigue phenomenon and a probabilistic model is developed to well describe them with two measurements of survival probability and confidence, similar model is also presented for the random stress-life rela-tions and extrapolated appropriately into long fatigue life regime. Third, concept of the fatigue limit should be understood as the fatigue strength at a given fatigue life and a so-called local Basquin model method is proposed for measuring the random strengths. In addition, drawing and application methods of the Goodman-Smith diagram for integrally characterizing the random fatigue strengths are established in terms of ten kilometers. Fourth, a reliability stress-based method is constructed with a consideration of the random constitutive relations. These new advances form a new frame work for railway fatigue reliability design and analysis.
2007, 21(4).
Abstract:
A method to reconstruct symmetric B-spline curves and surfaces is presented. The symmetry property is realized by using symmetric knot vector and symmetric control points. Firstly, data points are divided into two parts based on the symmetry axis or symmetry plane extracted from data points. Then the divided data points are parameterized and a symmetric knot vector is selected in order to get symmetric B-spline basis functions. Constraint equations regarding the control points are deduced to keep the control points of the B-spline curve or surface to be symmetric with respect to the extracted symmetry axis or symmetry plane. Lastly, the constrained least squares fitting problem is solved with the Lagrange multiplier method. Two examples from industry are given to show that the proposed method is efficient, robust and able to meet the general engineering requirements.
A method to reconstruct symmetric B-spline curves and surfaces is presented. The symmetry property is realized by using symmetric knot vector and symmetric control points. Firstly, data points are divided into two parts based on the symmetry axis or symmetry plane extracted from data points. Then the divided data points are parameterized and a symmetric knot vector is selected in order to get symmetric B-spline basis functions. Constraint equations regarding the control points are deduced to keep the control points of the B-spline curve or surface to be symmetric with respect to the extracted symmetry axis or symmetry plane. Lastly, the constrained least squares fitting problem is solved with the Lagrange multiplier method. Two examples from industry are given to show that the proposed method is efficient, robust and able to meet the general engineering requirements.
2007, 21(4).
Abstract:
In order to improve the computational accuracy and efficiency, it is necessary to establish a reasonable 3D FEM model for multi-pass spinning including not only spinning process but also springback and annealing processes. A numerical model for multi-pass spinning is established using the combination of explicit and implicit FEM, with the advantages of them in accuracy and efficiency. The procedures for model establishment are introduced in detail, and the model is validated. The application of the 3D FEM model to a two-pass spinning shows the following: The field variables such as the stress, strain and wall thickness during the whole spinning process can be obtained, not only during spinning process but also during springback and annealing processes, and the trends of their distributions and variations are in good agreement with a practical multi-spinning process. Thus the 3D FEM model for multi-pass spinning may be a helpful tool for determination and optimization of process parameters of multi-pass spinning process.
In order to improve the computational accuracy and efficiency, it is necessary to establish a reasonable 3D FEM model for multi-pass spinning including not only spinning process but also springback and annealing processes. A numerical model for multi-pass spinning is established using the combination of explicit and implicit FEM, with the advantages of them in accuracy and efficiency. The procedures for model establishment are introduced in detail, and the model is validated. The application of the 3D FEM model to a two-pass spinning shows the following: The field variables such as the stress, strain and wall thickness during the whole spinning process can be obtained, not only during spinning process but also during springback and annealing processes, and the trends of their distributions and variations are in good agreement with a practical multi-spinning process. Thus the 3D FEM model for multi-pass spinning may be a helpful tool for determination and optimization of process parameters of multi-pass spinning process.
2007, 21(4).
Abstract:
Aiming at the fatigue and comfort issues of human-machine contact interface in automobile driving and based on physiological and anatomical principle, the physiological and biochemical process of muscles and nerves in the formation and development of fatigue is analyzed systematically. The fatigue-causing physiological characteristic indexes are mapped to biomechanical indexes like muscle stress-strain, the compression deformation of blood vessels and nerves etc. from the perspective of formation mechanism. The geometrical model of skeleton and parenchyma is established by applying CT-scanned body data and MRI images. The general rule of comfort body pressure distribution is acquired through the analysis of anatomical structure of buttocks and femoral region. The comprehensive test platform for sitting comfort of 3D adjustable contact interface is constructed. The test of body pressure distribution of human-machine contact interface and its comparison with subjec-tive evaluation indicates that the biomechanical indexes of automobile driving human-machine con-tact interface and body pressure distribution rule studied can effectively evaluate the fatigue and comfort issues of human-machine contact interface and provide theoretical basis for the optimal de-sign of human-machine contact interface.
Aiming at the fatigue and comfort issues of human-machine contact interface in automobile driving and based on physiological and anatomical principle, the physiological and biochemical process of muscles and nerves in the formation and development of fatigue is analyzed systematically. The fatigue-causing physiological characteristic indexes are mapped to biomechanical indexes like muscle stress-strain, the compression deformation of blood vessels and nerves etc. from the perspective of formation mechanism. The geometrical model of skeleton and parenchyma is established by applying CT-scanned body data and MRI images. The general rule of comfort body pressure distribution is acquired through the analysis of anatomical structure of buttocks and femoral region. The comprehensive test platform for sitting comfort of 3D adjustable contact interface is constructed. The test of body pressure distribution of human-machine contact interface and its comparison with subjec-tive evaluation indicates that the biomechanical indexes of automobile driving human-machine con-tact interface and body pressure distribution rule studied can effectively evaluate the fatigue and comfort issues of human-machine contact interface and provide theoretical basis for the optimal de-sign of human-machine contact interface.
2007, 21(4).
Abstract:
Graphite becomes the prevailing electrode material in electrical discharging machining (EDM) currently. Orthogonal cutting experiments are carried out to study the characteristics of graphite chip formation process. High speed milling experiments are conducted to study tool wear and cutting forces. The results show that depth of cut has great influence on graphite chip formation. The removal process of graphite in high speed milling is the mutual result of cutting and grinding process. Graphite is prone to cause severe abrasion wear to coated carbide endmills due to its high abrasiveness nature. The major patterns of tool wear are flank wear, rake wear, micro-chipping and breakage. Cutting forces can be reduced by adoption of higher cutting speed, moderate feed per tooth, smaller radial and axial depths of cut, and up cutting.
Graphite becomes the prevailing electrode material in electrical discharging machining (EDM) currently. Orthogonal cutting experiments are carried out to study the characteristics of graphite chip formation process. High speed milling experiments are conducted to study tool wear and cutting forces. The results show that depth of cut has great influence on graphite chip formation. The removal process of graphite in high speed milling is the mutual result of cutting and grinding process. Graphite is prone to cause severe abrasion wear to coated carbide endmills due to its high abrasiveness nature. The major patterns of tool wear are flank wear, rake wear, micro-chipping and breakage. Cutting forces can be reduced by adoption of higher cutting speed, moderate feed per tooth, smaller radial and axial depths of cut, and up cutting.
2007, 21(4).
Abstract:
After 32CrMoV is selected to manufacture nitrided gears coated with TiN by multi-arc ion plating, all of these uncoated gears and coated gears run in the gearbox under the same initial conditions so as to compare their difference concerning properties and microstructure. Experiment results indicate that tooth surface of the coated-TiN gears does not suffer surface abnormalities in meshed zone. Instead, the gears with nitrided case exhibit an abrasion mark on the meshed zone of tooth surface, which results in more weight loss of nitrided gears. The morphology of the surface suggests TiN film with more than 2 000 HV is so dense and smooth that coated-TiN gears have higher wear resistance compared with the uncoated gears. The microstructure of coated-TiN gears is finer, hardness is higher and its distribution of coated-TiN gears is more reliable than uncoated ones, which makes nitride layer combined with TiN film tightly. Consequently, the wear-resistance of gears has been dramatically promoted.
After 32CrMoV is selected to manufacture nitrided gears coated with TiN by multi-arc ion plating, all of these uncoated gears and coated gears run in the gearbox under the same initial conditions so as to compare their difference concerning properties and microstructure. Experiment results indicate that tooth surface of the coated-TiN gears does not suffer surface abnormalities in meshed zone. Instead, the gears with nitrided case exhibit an abrasion mark on the meshed zone of tooth surface, which results in more weight loss of nitrided gears. The morphology of the surface suggests TiN film with more than 2 000 HV is so dense and smooth that coated-TiN gears have higher wear resistance compared with the uncoated gears. The microstructure of coated-TiN gears is finer, hardness is higher and its distribution of coated-TiN gears is more reliable than uncoated ones, which makes nitride layer combined with TiN film tightly. Consequently, the wear-resistance of gears has been dramatically promoted.
2007, 21(4).
Abstract:
The multisensor information fusion technology is adopted for real time measuring the four parameters which are connected closely with the weld nugget size(welding current, electrode displacement, dynamic resistance, welding time) , thus much more original information is obtained. In this way, the difficulty caused by measuring indirectly weld nugget size can be decreased in spot welding quality control, and the stability of spot welding quality can be improved. According to this method, two-dimensional fuzzy controllers are designed with the information fusion result as input and the thyristor control signal as output. The spot welding experimental results indicate that the spot welding quality intelligent control method based on multisensor information fusion technology can compensate the influence caused by variable factors in welding process and ensure the stability of welding quality.
The multisensor information fusion technology is adopted for real time measuring the four parameters which are connected closely with the weld nugget size(welding current, electrode displacement, dynamic resistance, welding time) , thus much more original information is obtained. In this way, the difficulty caused by measuring indirectly weld nugget size can be decreased in spot welding quality control, and the stability of spot welding quality can be improved. According to this method, two-dimensional fuzzy controllers are designed with the information fusion result as input and the thyristor control signal as output. The spot welding experimental results indicate that the spot welding quality intelligent control method based on multisensor information fusion technology can compensate the influence caused by variable factors in welding process and ensure the stability of welding quality.
2007, 21(4).
Abstract:
Proper meshing of Hy-Vo silent chain and sprocket is important for realizing the transmission of the silent chain with more efficiency and less noise. Based on the study of the meshing theory of the Hy-Vo silent chain with the sprocket and the roll cutting machining principle of the sprocket with the hob, the proper conditions of the meshing for the Hy-Vo silent chain and the sprocket are put forward with the variable pitch characteristic of the Hy-Vo silent chain taken into consideration, and the proper meshing design method on the condition that the value of the link tooth pressure angle is unequal to the value of the sprocket tooth pressure angle is studied. Experiments show that this new design method is feasible. In addition, the design of the pitch, the sprocket tooth pressure angle and the fillet radius of the sprocket addendum circle are studied. It is crucial for guiding the design of the hob which cuts the Hy-Vo silent chain sprocket.
Proper meshing of Hy-Vo silent chain and sprocket is important for realizing the transmission of the silent chain with more efficiency and less noise. Based on the study of the meshing theory of the Hy-Vo silent chain with the sprocket and the roll cutting machining principle of the sprocket with the hob, the proper conditions of the meshing for the Hy-Vo silent chain and the sprocket are put forward with the variable pitch characteristic of the Hy-Vo silent chain taken into consideration, and the proper meshing design method on the condition that the value of the link tooth pressure angle is unequal to the value of the sprocket tooth pressure angle is studied. Experiments show that this new design method is feasible. In addition, the design of the pitch, the sprocket tooth pressure angle and the fillet radius of the sprocket addendum circle are studied. It is crucial for guiding the design of the hob which cuts the Hy-Vo silent chain sprocket.
2007, 21(4).
Abstract:
Robot’s dynamic motion error and on-line compensation based on multi-axis force sensor are dealt with. It is revealed that the reasons of the error are formed and the relations of the error are delivered. A motion equation of robot’s termination with the error is established, and then, an error matrix and an error compensation matrix of the motion equation are also defined. An on-line error’s compensation method is put forward to decrease the displacement error, which is a degree of millimeter, shown by the result of simulation of PUMA562 robot.
Robot’s dynamic motion error and on-line compensation based on multi-axis force sensor are dealt with. It is revealed that the reasons of the error are formed and the relations of the error are delivered. A motion equation of robot’s termination with the error is established, and then, an error matrix and an error compensation matrix of the motion equation are also defined. An on-line error’s compensation method is put forward to decrease the displacement error, which is a degree of millimeter, shown by the result of simulation of PUMA562 robot.
2007, 21(4).
Abstract:
The product family design problem solved by evolutionary algorithms is discussed. A successful product family design method should achieve an optimal tradeoff among a set of competing objectives, which involves maximizing commonality across the family of products and optimizing the performances of each product in the family. A 2-level chromosome structured genetic algorithm (2LCGA) is proposed to solve this class of problems and its performance is analyzed in comparing its results with those obtained with other methods. By interpreting the chromosome as a 2-level linear structure, the variable commonality genetic algorithm (GA) is constructed to vary the amount of plat-form commonality and automatically searches across varying levels of commonality for the platform while trying to resolve the tradeoff between commonality and individual product performance within the product family during optimization process. By incorporating a commonality assessing index to the problem formulation, the 2LCGA optimize the product platform and its corresponding family of products in a single stage, which can yield improvements in the overall performance of the product family compared with two-stage approaches (the first stage involves determining the best settings for the platform variables and values of unique variables are found for each product in the second stage). The scope of the algorithm is also expanded by introducing a classification mechanism to allow mul-tiple platforms to be considered during product family optimization, offering opportunities for supe-rior overall design by more efficacious tradeoffs between commonality and performance. The effec-tiveness of 2LCGA is demonstrated through the design of a family of universal electric motors and comparison against previous results.
The product family design problem solved by evolutionary algorithms is discussed. A successful product family design method should achieve an optimal tradeoff among a set of competing objectives, which involves maximizing commonality across the family of products and optimizing the performances of each product in the family. A 2-level chromosome structured genetic algorithm (2LCGA) is proposed to solve this class of problems and its performance is analyzed in comparing its results with those obtained with other methods. By interpreting the chromosome as a 2-level linear structure, the variable commonality genetic algorithm (GA) is constructed to vary the amount of plat-form commonality and automatically searches across varying levels of commonality for the platform while trying to resolve the tradeoff between commonality and individual product performance within the product family during optimization process. By incorporating a commonality assessing index to the problem formulation, the 2LCGA optimize the product platform and its corresponding family of products in a single stage, which can yield improvements in the overall performance of the product family compared with two-stage approaches (the first stage involves determining the best settings for the platform variables and values of unique variables are found for each product in the second stage). The scope of the algorithm is also expanded by introducing a classification mechanism to allow mul-tiple platforms to be considered during product family optimization, offering opportunities for supe-rior overall design by more efficacious tradeoffs between commonality and performance. The effec-tiveness of 2LCGA is demonstrated through the design of a family of universal electric motors and comparison against previous results.
2007, 21(4).
Abstract:
Deposition of diamond thin films on tungsten wire substrate with the gas mixture of acetone and hydrogen by using bias-enhanced hot filament chemical vapor deposition (CVD) with the tantalum wires being optimized arranged is investigated. The self-supported diamond tubes are obtained by etching away the tungsten substrates. The quality of the diamond film before and after the removal of substrates is observed by scanning electron microscope (SEM) and Raman spectrum. The results show that the cylindrical diamond tubes with good quality and uniform thickness are obtained on tungsten wires by using bias enhanced hot filament CVD. The compressive stress in diamond film formed during the deposition is released after the substrate etches away by mixture of H2O2 and NH4OH. There is no residual stress in diamond tube after substrate removal.
Deposition of diamond thin films on tungsten wire substrate with the gas mixture of acetone and hydrogen by using bias-enhanced hot filament chemical vapor deposition (CVD) with the tantalum wires being optimized arranged is investigated. The self-supported diamond tubes are obtained by etching away the tungsten substrates. The quality of the diamond film before and after the removal of substrates is observed by scanning electron microscope (SEM) and Raman spectrum. The results show that the cylindrical diamond tubes with good quality and uniform thickness are obtained on tungsten wires by using bias enhanced hot filament CVD. The compressive stress in diamond film formed during the deposition is released after the substrate etches away by mixture of H2O2 and NH4OH. There is no residual stress in diamond tube after substrate removal.
2007, 21(4).
Abstract:
Welding arc spectral information is a rising welding information source. In some occasion, it can reflect many physical phenomena of welding process and solve many problems that cannot be done with arc electric information, acoustic information and other arc information. It is of important significance in developing automatic control technique of welding process and other similar process. Many years study work on welding arc spectral information of the anthor are discussed from three aspects of theory, method and application. Basic theory, view and testing methods of welding arc spectral information has been put forward. In application aspects, many applied examples, for example, monitoring of harmful gases in arc (such as hydrogen and nitrogen) with the method of welding arc spectral information; welding arc spectral imaging of the welding pool which is used in automatic seam tracking; controlling of welding droplet transfer with welding arc spectral informa-tion and so on, are introduced. Especially, the successful application in real time controlling of welding droplet transfer in pulsed GMAW is introduced too. These application examples show that the welding arc spectral information has great applied significance and development potentialities. These content will play an important role in applying and spreading welding arc spectral infor-mation technology.
Welding arc spectral information is a rising welding information source. In some occasion, it can reflect many physical phenomena of welding process and solve many problems that cannot be done with arc electric information, acoustic information and other arc information. It is of important significance in developing automatic control technique of welding process and other similar process. Many years study work on welding arc spectral information of the anthor are discussed from three aspects of theory, method and application. Basic theory, view and testing methods of welding arc spectral information has been put forward. In application aspects, many applied examples, for example, monitoring of harmful gases in arc (such as hydrogen and nitrogen) with the method of welding arc spectral information; welding arc spectral imaging of the welding pool which is used in automatic seam tracking; controlling of welding droplet transfer with welding arc spectral informa-tion and so on, are introduced. Especially, the successful application in real time controlling of welding droplet transfer in pulsed GMAW is introduced too. These application examples show that the welding arc spectral information has great applied significance and development potentialities. These content will play an important role in applying and spreading welding arc spectral infor-mation technology.
2007, 21(4).
Abstract:
In order to achieve precise, robust autonomous guidance and control of a tracked vehicle, a kinematic model with longitudinal and lateral slip is established. Four different nonlinear filters are used to estimate both state vector and time-varying parameter vector of the created model jointly. The first filter is the well-known extended Kalman filter. The second filter is an unscented version of the Kalman filter. The third one is a particle filter using the unscented Kalman filter to generate the importance proposal distribution. The last one is a novel and guaranteed filter that uses a linear set-membership estimator and can give an ellipsoid set in which the true state lies. The four different approaches have different complexities, behavior and advantages that are surveyed and compared.
In order to achieve precise, robust autonomous guidance and control of a tracked vehicle, a kinematic model with longitudinal and lateral slip is established. Four different nonlinear filters are used to estimate both state vector and time-varying parameter vector of the created model jointly. The first filter is the well-known extended Kalman filter. The second filter is an unscented version of the Kalman filter. The third one is a particle filter using the unscented Kalman filter to generate the importance proposal distribution. The last one is a novel and guaranteed filter that uses a linear set-membership estimator and can give an ellipsoid set in which the true state lies. The four different approaches have different complexities, behavior and advantages that are surveyed and compared.
2007, 21(4).
Abstract:
Electrochemical measurement and chemical immersion test are employed to investigate the inhibition mechanism of Na2MoO4 for carbon steel, which is studied in 55%LiBr+ 0.07mol/L LiOH solution at high temperature. Testing results indicate that the passive film on carbon steel surface is mainly composed of Fe3O4, and Mo is involved in the process of film forming, in a form of MoO3 and MoO2. The parametric analysis of the evolving potential and the blend potential of MoO2 shows that Mo mainly exists as MoO2 in passive film when the concentration of Na2MoO4 is lower than 150 mg/L. While its concentration is greater than 150 mg/L, it mainly exists as MoO3 inside the film and exists as MoO2 outside the film. MoO42− is deoxidized as MoO2 on the surface of carbon steel, which may impede the corrosion of active-site and raise the blend potential of carbon steel, and then MoO42− adsorbs onto the defects of the passive film and decompounds as MoO3 during the process of film forming. The electric field caused by different valence of Mo in passive film may retard the dissolution of carbon steel and lead to an increase in the polarization impedance and a decrease in hydrogen evolution. As a result, heavy concentrated Na2MoO4 solution (greater than 150 mg/L) has excellent inhibition effect on carbon steel in LiBr solution.
Electrochemical measurement and chemical immersion test are employed to investigate the inhibition mechanism of Na2MoO4 for carbon steel, which is studied in 55%LiBr+ 0.07mol/L LiOH solution at high temperature. Testing results indicate that the passive film on carbon steel surface is mainly composed of Fe3O4, and Mo is involved in the process of film forming, in a form of MoO3 and MoO2. The parametric analysis of the evolving potential and the blend potential of MoO2 shows that Mo mainly exists as MoO2 in passive film when the concentration of Na2MoO4 is lower than 150 mg/L. While its concentration is greater than 150 mg/L, it mainly exists as MoO3 inside the film and exists as MoO2 outside the film. MoO42− is deoxidized as MoO2 on the surface of carbon steel, which may impede the corrosion of active-site and raise the blend potential of carbon steel, and then MoO42− adsorbs onto the defects of the passive film and decompounds as MoO3 during the process of film forming. The electric field caused by different valence of Mo in passive film may retard the dissolution of carbon steel and lead to an increase in the polarization impedance and a decrease in hydrogen evolution. As a result, heavy concentrated Na2MoO4 solution (greater than 150 mg/L) has excellent inhibition effect on carbon steel in LiBr solution.
2007, 21(4).
Abstract:
During plastic process, the material flow is strongly influenced by the contact area between deformed workpiece and die. In rolling process, difference of roll diameter makes the contact area between roll and deformed tape different, which leads to different material flow and the distribution of powder density. A numerical modelling of the first rolling process for 61-filament high temperature superconducting tape is constructed and the influences of roll diameters on deformation behavior of the tape are discussed. It can be found that the BiSrCaCuO (BSCCO) powder in the center of the tape has higher relative density than those in the periphery of the tape during rolling process. With the increase of roll diameter, the length of the contact arc in the roll gap expands which lead to the in-creasing of transversal strain and the decreasing of the related longitudinal strain. It makes the value of longitudinal strain ratio decrease gradually, which decreases the possibility of occurrence of the transversal shear band, simultaneously it increases the risk of occurrence of longitudinal crack.
During plastic process, the material flow is strongly influenced by the contact area between deformed workpiece and die. In rolling process, difference of roll diameter makes the contact area between roll and deformed tape different, which leads to different material flow and the distribution of powder density. A numerical modelling of the first rolling process for 61-filament high temperature superconducting tape is constructed and the influences of roll diameters on deformation behavior of the tape are discussed. It can be found that the BiSrCaCuO (BSCCO) powder in the center of the tape has higher relative density than those in the periphery of the tape during rolling process. With the increase of roll diameter, the length of the contact arc in the roll gap expands which lead to the in-creasing of transversal strain and the decreasing of the related longitudinal strain. It makes the value of longitudinal strain ratio decrease gradually, which decreases the possibility of occurrence of the transversal shear band, simultaneously it increases the risk of occurrence of longitudinal crack.
2007, 21(4).
Abstract:
The finite element method(FEM) is used to analyze the effects of lead widths and pitches on reliability of soldered joints. The optimum simulation for QFP devices is also researched. The results indicate that when the lead pitches are the same, the maximum equivalent stress of the soldered joints increases with the increasing of lead widths, while the reliability of the soldered joints reduces. When the lead widths are the same, the maximum equivalent stress of the soldered joints doesn’t decrease completely with the increasing of lead pitches, a minimum value of the maximum equivalent stress values exists in all the curves. Under this condition the maximum equivalent stress of the soldered joints is relatively the least, the reliability of soldered joints is high and the assembly is excellent. The simulating results indicate the best parameter: The lead width is 0.2 mm and lead pitch is 0.3 mm (the distance between two leads is 0.1 mm), which are benefited for the micromation of QFP devices now. The minimum value of the maximum equivalent stress of soldered joints exists while lead width is 0.25 mm and lead pitch is 0.35 mm (the distance between two leads is 0.1 mm), the devices can serve for a long time and the reliability is the highest, the assembly is excellent. The simulating results also indicate the fact that the lead width is 0.15 mm and lead pitch is 0.2 mm maybe the limit of QFP, which is significant for the high lead count and micromation of assembly.
The finite element method(FEM) is used to analyze the effects of lead widths and pitches on reliability of soldered joints. The optimum simulation for QFP devices is also researched. The results indicate that when the lead pitches are the same, the maximum equivalent stress of the soldered joints increases with the increasing of lead widths, while the reliability of the soldered joints reduces. When the lead widths are the same, the maximum equivalent stress of the soldered joints doesn’t decrease completely with the increasing of lead pitches, a minimum value of the maximum equivalent stress values exists in all the curves. Under this condition the maximum equivalent stress of the soldered joints is relatively the least, the reliability of soldered joints is high and the assembly is excellent. The simulating results indicate the best parameter: The lead width is 0.2 mm and lead pitch is 0.3 mm (the distance between two leads is 0.1 mm), which are benefited for the micromation of QFP devices now. The minimum value of the maximum equivalent stress of soldered joints exists while lead width is 0.25 mm and lead pitch is 0.35 mm (the distance between two leads is 0.1 mm), the devices can serve for a long time and the reliability is the highest, the assembly is excellent. The simulating results also indicate the fact that the lead width is 0.15 mm and lead pitch is 0.2 mm maybe the limit of QFP, which is significant for the high lead count and micromation of assembly.
2007, 21(4).
Abstract:
A dynamic advanced planning and scheduling (DAPS) problem is addressed where new orders arrive on a continuous basis. A periodic policy with frozen interval is adopted to increase stability on the shop floor. A genetic algorithm is developed to find a schedule at each rescheduling point for both original orders and new orders that both production idle time and penalties on tardiness and earliness of orders are minimized. The proposed methodology is tested on a small example to illustrate the effect of the frozen interval. The results indicate that the suggested approach can improve the schedule stability while retaining efficiency.
A dynamic advanced planning and scheduling (DAPS) problem is addressed where new orders arrive on a continuous basis. A periodic policy with frozen interval is adopted to increase stability on the shop floor. A genetic algorithm is developed to find a schedule at each rescheduling point for both original orders and new orders that both production idle time and penalties on tardiness and earliness of orders are minimized. The proposed methodology is tested on a small example to illustrate the effect of the frozen interval. The results indicate that the suggested approach can improve the schedule stability while retaining efficiency.
2007, 21(4).
Abstract:
20 mm thick plates of 2519-T87 high strength aluminum alloy have been welded. The effects of the compositions of filler wires, the heat input and the compositions of shielding gas on the mechanical properties and microstructure of the welded joint have been investigated. The results indicate that finer microstructure, better mechanical properties and higher value of hardness of HAZ can be obtained by using lower heat input. The use of Ar/He mixed shielding gas has several advantages over pure Ar shielding gas. With the increase of the proportion of He in the mixed shielding gas, the grain size of the weld metal as well as porosity susceptibility decreases. When the volume ratio of He to Ar reaches 7 : 3, the porosity and the grain size of weld metal reach the minimum, and the porosity can be further reduced by filling some CO2.
20 mm thick plates of 2519-T87 high strength aluminum alloy have been welded. The effects of the compositions of filler wires, the heat input and the compositions of shielding gas on the mechanical properties and microstructure of the welded joint have been investigated. The results indicate that finer microstructure, better mechanical properties and higher value of hardness of HAZ can be obtained by using lower heat input. The use of Ar/He mixed shielding gas has several advantages over pure Ar shielding gas. With the increase of the proportion of He in the mixed shielding gas, the grain size of the weld metal as well as porosity susceptibility decreases. When the volume ratio of He to Ar reaches 7 : 3, the porosity and the grain size of weld metal reach the minimum, and the porosity can be further reduced by filling some CO2.
2007, 21(4).
Abstract:
Tip clearance between the blade tip and casing of a centrifugal compressor can be varied through two methods: by changing the blade height (M1) or by changing the casing diameter (M2). Numerical simulations are carried out to compare these two methods and their effect on the stage and impeller performance. The impeller and diffuser are connected through rotor stator boundary using frozen rotor approach. Overall stage performance and the flow configuration have been investigated for nine tip clearance levels from no gap to 1 mm. Impeller and diffuser performances are also presented separately. It has been found that the overall and impeller performance are comparatively better for M1 below tip clearance of 0.5 mm whereas M2 is found advantageous above 0.5 mm of tip clearance. Both M1 and M2 show performance degradation with the increase in tip clearance. Two models have been proposed for the stage total pressure ratio and efficiency, which are found to be in agreement with experimental results. The impeller efficiency and the pressure ratio are found to be maximum at tip clearance of 0.1 mm for both the cases however minimum diffuser effectiveness is also observed at the same clearance level. Diffuser effectiveness is found to be maximum at zero gap for both cases. As it is practically impossible to have zero gap for unshrouded impellers so it is concluded that the optimum thickness is 0.5 mm onwards for M1 and 0.5 mm for M2 in terms of diffuser effectiveness. Mass averaged flow parameters, entropy, blade loading diagram and relative pressure fields are presented, showing the loss production within the impeller passage with tip clearance.
Tip clearance between the blade tip and casing of a centrifugal compressor can be varied through two methods: by changing the blade height (M1) or by changing the casing diameter (M2). Numerical simulations are carried out to compare these two methods and their effect on the stage and impeller performance. The impeller and diffuser are connected through rotor stator boundary using frozen rotor approach. Overall stage performance and the flow configuration have been investigated for nine tip clearance levels from no gap to 1 mm. Impeller and diffuser performances are also presented separately. It has been found that the overall and impeller performance are comparatively better for M1 below tip clearance of 0.5 mm whereas M2 is found advantageous above 0.5 mm of tip clearance. Both M1 and M2 show performance degradation with the increase in tip clearance. Two models have been proposed for the stage total pressure ratio and efficiency, which are found to be in agreement with experimental results. The impeller efficiency and the pressure ratio are found to be maximum at tip clearance of 0.1 mm for both the cases however minimum diffuser effectiveness is also observed at the same clearance level. Diffuser effectiveness is found to be maximum at zero gap for both cases. As it is practically impossible to have zero gap for unshrouded impellers so it is concluded that the optimum thickness is 0.5 mm onwards for M1 and 0.5 mm for M2 in terms of diffuser effectiveness. Mass averaged flow parameters, entropy, blade loading diagram and relative pressure fields are presented, showing the loss production within the impeller passage with tip clearance.
2007, 21(4).
Abstract:
Blind source separation and estimation of the number of sources usually demand that the number of sensors should be greater than or equal to that of the sources, which, however, is very difficult to satisfy for the complex systems. A new estimating method based on power spectral density (PSD) is presented. When the relation between the number of sensors and that of sources is unknown, the PSD matrix is first obtained by the ratio of PSD of the observation signals, and then the bound of the number of correlated sources with common frequencies can be estimated by comparing every column vector of PSD matrix. The effectiveness of the proposed method is verified by theoretical analysis and experiments, and the influence of noise on the estimation of number of source is simulated.
Blind source separation and estimation of the number of sources usually demand that the number of sensors should be greater than or equal to that of the sources, which, however, is very difficult to satisfy for the complex systems. A new estimating method based on power spectral density (PSD) is presented. When the relation between the number of sensors and that of sources is unknown, the PSD matrix is first obtained by the ratio of PSD of the observation signals, and then the bound of the number of correlated sources with common frequencies can be estimated by comparing every column vector of PSD matrix. The effectiveness of the proposed method is verified by theoretical analysis and experiments, and the influence of noise on the estimation of number of source is simulated.
2007, 21(4).
Abstract:
As point cloud of one whole vehicle body has the traits of large geometric dimension, huge data and rigorous reverse precision, one pretreatment algorithm on automobile body point cloud is put forward. The basic idea of the registration algorithm based on the skeleton points is to construct the skeleton points of the whole vehicle model and the mark points of the separate point cloud, to search the mapped relationship between skeleton points and mark points using congruence triangle method and to match the whole vehicle point cloud using the improved iterative closed point (ICP) algorithm. The data reduction algorithm, based on average square root of distance, condenses data by three steps, computing datasets’ average square root of distance in sampling cube grid, sorting order according to the value computed from the first step, choosing sampling percentage. The accuracy of the two algo-rithms above is proved by a registration and reduction example of whole vehicle point cloud of a certain light truck.
As point cloud of one whole vehicle body has the traits of large geometric dimension, huge data and rigorous reverse precision, one pretreatment algorithm on automobile body point cloud is put forward. The basic idea of the registration algorithm based on the skeleton points is to construct the skeleton points of the whole vehicle model and the mark points of the separate point cloud, to search the mapped relationship between skeleton points and mark points using congruence triangle method and to match the whole vehicle point cloud using the improved iterative closed point (ICP) algorithm. The data reduction algorithm, based on average square root of distance, condenses data by three steps, computing datasets’ average square root of distance in sampling cube grid, sorting order according to the value computed from the first step, choosing sampling percentage. The accuracy of the two algo-rithms above is proved by a registration and reduction example of whole vehicle point cloud of a certain light truck.
MULTI-LAYER PIEZOELECTRIC ACTUATOR AND ITS APPLICATION IN CONTROLLABLE CONSTRAINED DAMPING TREATMENT
2007, 21(4).
Abstract:
A kind of novel multi-layer piezoelectric actuator is proposed and integrated with controllable constrained damping treatment to perform hybrid vibration control. The governing equation of the system is derived based on the constitutive equations of elastic, viscoelastic and piezoelectric materials, which shows that the magnitude of control force exerted by multi-layer piezoelectric actua-tor is the quadratic function of the number of piezoelectric laminates used but in direct proportion to control voltage. This means that the multi-layer actuator can produce greater actuating force than that by piezoelectric laminate actuator with the same area under the identical control voltage. The optimal location placement of the multi-layer piezoelectric actuator is also discussed. As an example, the hybrid vibration control of a cantilever rectangular thin-plate is numerically simulated and carried out experimentally. The simulated and experimental results validate the power of multi-layer piezoelectric actuator and indicate that the present hybrid damping technique can effectively suppress the low fre-quency modal vibration of the experimental thin-plate structure.
A kind of novel multi-layer piezoelectric actuator is proposed and integrated with controllable constrained damping treatment to perform hybrid vibration control. The governing equation of the system is derived based on the constitutive equations of elastic, viscoelastic and piezoelectric materials, which shows that the magnitude of control force exerted by multi-layer piezoelectric actua-tor is the quadratic function of the number of piezoelectric laminates used but in direct proportion to control voltage. This means that the multi-layer actuator can produce greater actuating force than that by piezoelectric laminate actuator with the same area under the identical control voltage. The optimal location placement of the multi-layer piezoelectric actuator is also discussed. As an example, the hybrid vibration control of a cantilever rectangular thin-plate is numerically simulated and carried out experimentally. The simulated and experimental results validate the power of multi-layer piezoelectric actuator and indicate that the present hybrid damping technique can effectively suppress the low fre-quency modal vibration of the experimental thin-plate structure.
2007, 21(4).
Abstract:
A novel active vibration control technique on the basis of linearized piezoelectric actuators is presented. An experimental apparatus consisting of a cantilever beam to which are attached strain patches and piezoceramic actuators to be used for active vibration suppression is described. A dy-namical model of the cantilever beam using Lagrange’s equation and two coordinate systems are presented. Based on the Lyapunov’s direct method, an active vibration controller with hysteresis compensation is designed. The controller is designed so that it guarantees the global stability of the overall system. The controller developed is assessed experimentally.
A novel active vibration control technique on the basis of linearized piezoelectric actuators is presented. An experimental apparatus consisting of a cantilever beam to which are attached strain patches and piezoceramic actuators to be used for active vibration suppression is described. A dy-namical model of the cantilever beam using Lagrange’s equation and two coordinate systems are presented. Based on the Lyapunov’s direct method, an active vibration controller with hysteresis compensation is designed. The controller is designed so that it guarantees the global stability of the overall system. The controller developed is assessed experimentally.
2007, 21(4).
Abstract:
The FRF estimator based on the errors-in-variables (EV) model of multi-input multi-output (MIMO) system is presented to reduce the bias error of FRF H1 estimator. The FRF H1 estimator is influenced by the noises in the inputs of the system and generates an under-estimation of the true FRF. The FRF estimator based on the EV model takes into account the errors in both the inputs and outputs of the system and would lead to more accurate FRF estimation. The FRF estimator based on the EV model is applied to the waveform replication on the 6-DOF (degree-of-freedom) hydraulic vibration table. The result shows that it is favorable to improve the control precision of the MIMO vibration control system.
The FRF estimator based on the errors-in-variables (EV) model of multi-input multi-output (MIMO) system is presented to reduce the bias error of FRF H1 estimator. The FRF H1 estimator is influenced by the noises in the inputs of the system and generates an under-estimation of the true FRF. The FRF estimator based on the EV model takes into account the errors in both the inputs and outputs of the system and would lead to more accurate FRF estimation. The FRF estimator based on the EV model is applied to the waveform replication on the 6-DOF (degree-of-freedom) hydraulic vibration table. The result shows that it is favorable to improve the control precision of the MIMO vibration control system.
2007, 21(4).
Abstract:
Plastic deformation is an important process to improve properties and obtain final products made of sintered powder materials. Sintered ferrous material is widely used in many engineering departments and its deformation characteristics are typical for most sintered powder materials. Factors such as deformation strengthening, instantaneous and initial relative densities, etc, on the subsequent yield strength are studied, and an approach to determine the plastic stress coefficient and hardening exponent is derived, which is based on the yield criterion and the strengthening laws of plastic deformation of sintered powder materials as well as on a uni-axial compression experiment of a sintered ferrous cylinder specimen. A unified form of the yield criterion function is obtained, in which the initial and the subsequent yields of sintered powder materials are expressed.
Plastic deformation is an important process to improve properties and obtain final products made of sintered powder materials. Sintered ferrous material is widely used in many engineering departments and its deformation characteristics are typical for most sintered powder materials. Factors such as deformation strengthening, instantaneous and initial relative densities, etc, on the subsequent yield strength are studied, and an approach to determine the plastic stress coefficient and hardening exponent is derived, which is based on the yield criterion and the strengthening laws of plastic deformation of sintered powder materials as well as on a uni-axial compression experiment of a sintered ferrous cylinder specimen. A unified form of the yield criterion function is obtained, in which the initial and the subsequent yields of sintered powder materials are expressed.
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