Experimental Research On Ⅰ-Ⅱ Mixed-Mode Fracture Of 45 Steel

45 steel is widely used in engineering,Its mechanical properties are subjected to many factors.Studies are not sufficient on its fracture mechanism under the condition of complex stress due to the conditions of experiment.Based on the 45 steelⅠ/Ⅱmixed-mode fracture experiments,this paper researched macroscopic fracture form and microscopic fracture mechanism of 45 steel underⅠ/Ⅱmixed-mode stress conditions,and observed micro-fracture process of the fracture surface under the conditions ofⅠ/Ⅱmixed mode loading by scanning electron microscopy(SEM).Finally,this paper analyzed and calculated the crack-tips stress field distribution under different loadings through the application of the finite element method and software of ANSYS,and drew the following conclusions:1.Under the condition of modeⅠand approximate modeⅠloadings of 45 steel-M,crack initiation mainly was due to void nucleation,propagation and polymerization of crack-tips leading edge.Start-split locations were along the central of the blunting crack-tips,and the directions of crack propagation were the same as the line directions of original cracks. Direction of crack propagation was of 58°under the condition of approximate modeⅡloadings,and changed between 0°to 58°under the condition ofⅠ/Ⅱmixed-mode loadings.2.Under the condition of modeⅠand approximate modeⅠloadings of 45 steel-CZ,crack initiation and propagation was normal failure.In this kind of fracture process,void nucleation, propagation was mainly on account of normal stress of crack-tips stress field.Under the condition of approximate modeⅡloadings,cracks fracture surface were mainly of cleavage surface.3.On the analysis of stress field of crack-tips showed that,with the loadings changing from modeⅠto modeⅡ,the value of stress tri-axiality ratio of crack tips decreased,and its distribution rotated along the clockwise direction.But with the increased loadings,the distribution characteristics of the maximum value was basically unchanged.