The purpose of this paper is to study the problem of the effect of material defects(round hole)on the mechanical behavior of the surface macro-crack tip of U71Mn steel in the elastic-plastic state based on the finite element method.In this paper,the effect of crack tip opening displacement(CTOD),free surface opening displacement(FSOD)and some other related variables such as round hole orientation an-gle β and hole radius r on the crack tip J-integral are analyzed mainly.The results show that the regions near the macro-crack surface have a shielding effect on the stress,which will lead to stress relaxation of the stress near the crack surface.However,the regions near the crack tip will amplify the stress,in other words,the stress is concentrated near the crack tip,and the macro-crack tip will further propagate as the increase in applied load.When the round hole is located in the range of about-75°＜β＜75°at the tip of the macro-crack,the round hole will promote the deformation of the crack tip and lead to the increase in CTOD and J-integral value,which promotes the propagation of the macro-crack.However,when the round hole is located in the range of 75°＜β＜90° or-90°＜β＜-75°,the round hole will hinder the deforma-tion of the crack tip,resulting in the fact that the integral values of CTOD and J-integral value are smaller than those without the hole,thus inhibiting the propagation of the macro-crack.
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