XFEM Analysis Of The Effects Of Material Defects On Fatigue Crack Propagation Behavior

Material defects will disturb the stress field at the crack tip to some extent.Under mode I loading,the perturbation causes the symmetry of the stress field at the crack tip to change.Therefore,the crack does not propagate in a direction perpendicular to mode I loading,but shows the characteristics of mixed mode crack propagation.In addition holes and inclusions will affect the crack propagation rate.The extended finite element method(XFEM)has the characteristics of high efficiency and accuracy in dealing with crack propagation problems with holes and inclusions.Based on the extended finite element theory,the effects of the position?radius of the holes and inclusions compact tensile(CT)specimens,as well as the material properties of the inclusions on the fatigue crack propagation behavior were studied.In order to quantitatively express the deflection degree of crack propagation path,the concept of deflection influence coefficient is proposed.The main conclusions are as follows:(1)The results show that crack deflection influence coefficient reaches the maximum value when ?=45°;The deflection influence coefficient increases with the increase of R and decreases with the increase of L;Under the combined influence of R and L,L is the dominant influence factor.(2)The effect of soft and rigid inclusions on crack propagation is obviously different.The effect of rigid inclusions on crack propagation path is "repulsive" and the effect of "repulsive" is more obvious with the increase of young's modulus E'.Under the action of soft inclusion,with the increase of young's modulus E',the"attraction" effect of inclusion on crack path decreases gradually.In addition to the material properties of inclusions,the effect of soft inclusions on crack propagation behavior is similar to that of holes.Specifically,when the Angle between the soft inclusion and the tip of the initial crack is 45°,the soft inclusion has the most obvious interference effect on the crack path,and the deflection influence coefficient reaches the maximum value.The deflection influence coefficient increases with the increase of radius R of the soft inclusion and decreases with the increase of distance L.Although the effect of soft inclusion on crack propagation behavior is similar to that of hole,the effect of hole on crack path is more obvious.(3)The rigid inclusion can reduce the crack growth rate to some extent.Compared with the homogeneous material,the crack growth rate increased obviously if the crack invade the holes or soft inclusion,but if cracks with large deflection degree and no invasion occurred,when the crack tip is about to get away from the hole or the soft inclusion,the growth rate will be temporarily reduced or the growth rate will slow down,and then the crack tip gradually gets away from the hole or the soft inclusion,and the crack growth rate gradually increases.