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Abstract: Apparent
fatigue limits of surface hardened machine parts (gears, for examples)
are quantitatively studied according to comprehensive considerations to
overcome the limitations caused by science divisions. Small specimens
for three-point- bending fatigue test，as
well as gear specimens made of low-carbon steel 20CrMnTi are carburized
(and then quenched and low temperature tempered), and half of them were
then shot-peened. Another group of small specimens used for comparison
is pseudo-carburized. Compressive residual stress fields in the surface
region of small specimens are determined. Fatigue tests are carried out
on a high-frequency machine. The fatigue limit loads of the three-point
bending specimens and the teeth of gear specimens at 5×106
cycles and stress ratio=0.05 are determined. The fracture surfaces of
the specimens with longest fatigue lives in each groups are studied
under SEM. Stress fields near the tooth root of gear specimens are
calculated by using a finite-element method and the ANSYS software. The
relationships between the fatigue limits of small specimens and the
critical fatigue loads of gear specimens under both conditions are
analyzed according to a “micro-meso-processes theory for fatigue source
formation” and a concept of “surface / internal fatigue limits of
metals” developed. A method for calculation of critical fatigue load of
complex machine parts according to the fatigue limit determined with
small specimens, as well as a judgment for optimization of surface
hardening technology, is proposed.
Key words: Modeling
of mechanical behavior Fatigue limit Carburization
Shot peening Residual stress
CLC No: TG14
TB125
国家自然科学基金(59971040)和河北省自然科学基金(500193)资助项目.
Received 20030514, received in revised form 20040203
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