Finite Element Analysis Of 3D Mixed-Mode Fracture Stress Intensity Factors

The stress intensity factor is a sign of strength of stress, strain field nearby crack tip, which can be taken as one criterion to assess that whether fracture has been in instability stage. So, acquirement of stress intensity factors (SIF) of crack is an important work in study of lineal elastic fracture mechanics.In this paper, four numerical analysis methods to calculate fracture crack stress intensity factors are introduced in detail, virtual closure crack integral method, modified virtual closure crack integral method, stress extrapolation method and displacement extrapolation method. Based on fracture computed and analyzed four methods, finite element software is used to model two dimension double edge notched specimen and stress intensity factors of crack tip are calculated. At the same time, the accuracies of different methods under different mesh are compared. Then, modified virtual crack closure integral method is chosen out to compute and analysis stress intensity factor of two dimension mixed-mode crack specimen with its good exactness and less processes. Based on the above study, this method is generalized to compute and analysis three dimension crack problem and validity of the method is verified.In order to examine accuracy of generalized modified virtual crack closure integral method in calculating three dimension crack problem, and to build foundation for computation of mixed crack problem, three dimensional finite element model of single notch compact tension specimen (CTS-specimen) is modeled. Plane strain boundary conditions are exerted in original model, and this calculated method is adopted to compute stress intensity factors and strain energy release rate (SERR) of model with plane tension and shear force respectively. Stress intensity factors under plane strain boundary conditions are compared with two dimension analyzed reference solution to verify the validity and accuracy of this method.According to above study, finite element analysis of three dimension compact tension specimen with inclined crack plane is carried out. At the same time, SIF and SERR of the crack tip with different angle loading are calculated. Through comparison with three dimension single notch compact tension specimen, effect of inclined crack plane and different angle loading to SIF and SERR of crack tip is analyzed and summarized. Combining with finite element charts and statistical data, and Irwin analyzed crack closed integral formula is used to analyze the results.