Modeling Of Fatigue Crack Growth Retardation With Artificial Wedges Using FE Method

Crack growth retardation with artificial wedges method(AW) is worked by injecting artificial polymers into crack,which can induce crack closure into fatigue crack and reduce the stress intensity factor region,so that the crack could be effectively retarded.By the support of National Natural Science Foundation of China and Science Technology Innovation Foundation of Sinopec,chemical mechanism department in Dalian University of Technology did a systematic research on AW.Shin' group conducted a comprehensive study as well. Researches show that:AW is a simple and effective way to retard the growth of through crack and surface crack.However,there are less research on mechanics and mechanism between wedge and crack surface.Based on the finite element method(FEM) and ANSYS software, this paper does studies on mechanism between wedge and crack surface.The main work and conclusions are as follows:(1) Through crack 2D FE model is established by PLANE 82 elements,and penalty function method is used to solve this contact model.While the outside force is more slowly to load,the model would be more likely to be convergent.Eventually,choose 3 as the final value.Under the case of convergence,it finds out that the greater stiffness is much more closed to the correct value.1/4 displacement singular elements can availably deal with mechanical properties of crack tip.It obtains the exact stress intensity factor(SIF),of which the relative error is less than 1%of theoretical value.Compared the SIF with Zhou Mingxu's model,the average relative error is round about 3.8%.As a result,it proves that Zhou's model can be applied in engineering practice.(2) Using ADPL,semi-elliptical surface crack-wedge 3D FE model is established by SOLID95 and SOLID45 elements.Compared the SIF of different crack length with Newman-Raju formula value,similar value is gained when the crack depth is less than 0.8 multiple of specimen thickness.Effective SIF range is computed by this model.Compared the SIF with Yin Jianzhong's model,the average relative error is round about 4.2%.As a result,it proves that Yin's model can be applied in engineering practice.(3) Injecting load(R_iw) and wedge material are the key factors of AW method.When the value of Riw is 0.8,the corresponding SIF ranges from 5.5 to 6.8MPa·m^1/2,which is very close to the threshold of crack growth.When the value of R_iw is 0.9,the corresponding SIF is about 3.8 MPa·m^1/2,which is lower than the threshold value.In the engineering practice,it recommends the value of R_iw to be 0.9.Meanwhile,the wedge elastic modulus is bigger,the effect of retarding crack is more obvious.(4) Contact pressure is unequally distributed between wedge and crack surface.Near to the crack mouth,the pressure is about 108MPa,which decreases to 30MPa next to the crack tip.For semi-elliptical surface crack,especially to the bending test piece,contact pressure in the depth direction(a direction) is bigger than the length direction(c direction).From the mouth to tip of crack,wedge and crack surface minishes too.Although the wedge effectiveness near tip is inconspicuous,it can not be ignored.The wedge should be injected near the crack tip.(5) Compared two kinds of crack growth finite element methods,it concludes that Jiang Yanyao injury model can be achieved.