Experiment Research On Subsequent Yield Surface And Fatigue Law Of A3Steel

The current plastic theory were not accurate to describe the relationship of stress and strain during plastic process,and the yield surface could be able to indicate the response of stress and strain under yield situation.Usually, macroscopic experiment approach were used to study yield surface,therefore,in order to perfect plasticity theory and find out evolution of subsequent yield surface as well as fatigue life law,the experiments of low cycle fatigue,initial yield surface and subsequent yield surface were studied with A3steel in the thesis.Low cycle fatigue experiment was launched with different strain amplitude, which included tension-compress cycle and torsion cycle respectively.The A3steel exhibited unique mechanical properties as Bauschinger effect and cyclic hardening under cycle loading.The plastic strain was very important for fatigue life, so the thesis obtained the relationship of plastic strain and fatigue life under different strain amplitude,and validate the applicability of existing single-axis fatigue life law.It was found that the test results was accorded with Manson-Coffin law.It made a foudation for multi-axis cycle research.The relationship between fatigue life and the plastic work as well as accumulated plastic strain, which was generated in cycle process,was studied preliminery.In order to comprehend the initial mechanical properties of metals,the initial yield surface was determined with offset strain approach. The test results showed that the shape of initial yield surface was similar to Mises circle when it was defined with larger plastic strain.The materials was isotropic approximately judging from initial yield surface.Subsequent yield surface was determined with multi-sample method under different proportional pre-loading path,which used offset strain approach to define yield.The results of experiment showed that evolution of subsequent yield surface was relevant to yield definition,as well as pre-loading path,and so on. The A3steel exhibited clearly orientational hardening and Bauschinger effect,therefore,the subsequent yield surface showed obvious concave and crossing phenomenon,which was not accordant with classical plasticity theory.It proved that the existing plasticity theory was essential to study furtherly to describe mechanical response rationally in subsequent yield.