Experimental Investigation On Effection Of Torsional Prestrain On Stretch And Fatigue Behavior Of Steel35CrMo

The35CrMo steel was a kind of alloy structure steel which was usually used in industrial production and automobile industry because of its possesses good comprehensive mechanical properties. Because of its processed molding and used process would have different degrees of torsional prestrain and overload, for example, the automobile transmission shaft and engine crankshaft usually produced torsional prestrain and overload which could effect of the mechanics and fatigue behavior of material when its started and stopped moments. But there is not much study of mechanical behavior of the35CrMo steel after pretorsional and pretension intensify at present, it is not yet very know especially of the high cycle and low cycle fatigue behavior after torsional prestrain.The article studied of the mechanical and fatigue behavior of the35CrMo steel after torsional prestrain through the tensile and fatigue tests. Therefore, the article specifically designed the dual-used samples of tension and torsion、fatigue and torsion to study of mechanical behavior after pretorsional and pretension intensify and high cycle and low cycle fatigue behavior after torsional prestrain through the different of pretorsional angles and pretension strains, the changing regularity of tensile behavior、fatigue limit、S-N curve、 cycle hardening-softening properties、hysteresis loop、plastic strain energy、cycle elastic modulus of the35CrMo steel after torsional prestrain and the fracture of high cycle and low cycle fatigue texts were priority analyzed, getting the following main conclusion:(1)The specimens of35CrMo steel had no obviously physical yield process in tensile and torsion texts; the tensile yield limit and strength limit of the specimens of35CrMo steel were increased through the torsional prestrain, however, the tensile strain hardening exponent and strength coefficient of the specimens were reduced; the shear yield limit of the specimens of35CrMo steel were increased through the pretension intensify, however, which was a little effect of shear strength limit.(2)The high cycle fatigue limit of the specimens of35CrMo steel were measured through the up and down method after the specimens were reversed to0,37π/4、7π/4,respectively for321.6MPa、308.12MPa、294.90MPa; the fatigue life of the pretorsional specimens was obviously lower than the non-pretorsional specimens in the same cycle stress amplitude, and the fatigue life was more lower when the pretorsional angle was more larger.(3)The low cycle fatigue specimens of35CrMo steel of the pretorsional angle for0、 π/4、3π/4、5π/4showed cycle softening phenomenon and the basic same level of cycle softening regularity and attenuation; because of the specimens appeared work-hardening after pretorsional intensify, the breadth of the curve was reduced with the pretorsional angle increased in the hysteresis loop, that is to say, the scope of plastic strain was reduced in the fatigue cycle; the cycle elastic modulus of the specimens were gradually reduced with the fatigue life cycles increased, the attenuation of trend and reduction of cycle elastic modulus of the fatigue specimens get lower with the pretorsional angle increased; however, the plastic strain energy was increased with the fatigue cycle number increased, and the reduction of plastic strain energy was increased with the pretorsional angle increased.(4)The high cycle and low cycle fatigue crack of35CrMo steel engendered in surface of the specimens and the fracture of the crack source area was more lighter and flatter, there was a lot of second crack in the crack source area; the height of fatigue steps of the pretorsional specimens was more higher than the non-pretorsional specimens, and which was increased with the pretorsional angle increased; the transient breaking areas of the high cycle and low cycle fatigue fracture had obviously toughening nest morphology and the second crack and cracking phenomenon.