Numerical analyses for calculation of mixed-mode I/II stress intensity factors (SIFs) in edge cracked doughnut-shaped specimens subjected to diametral compression and diametral tension loads

In this research a doughnut-shaped specimen (DSS) is utilized for analysis of mixed mode I/II (tensile/compression and in-plane shear) fracture problem. The DSS sample is a ring specimen containing two same line cracks in the inner surface of the ring that can be loaded either by diametral compression forces applied to the outer surface of ring or diametral tension force applied to the inner surface of the DSS sample. By changing the geometrical and loading parameters including crack length ratio, type of applied loading and direction of loading relative to the cracks, the state of crack tip stresses and deformations is altered. It is shown that the DSS sample under both tensile and compressive point force loading can introduce pure mode I, pure mode II and different tensile-shear, and compression-shear deformations. The variations of three fracture parameters namely modes I and II stress intensity factors (KI and KII) are determined for the DSS sample under different geometrical and loading conditions via performing several finite element analyses. It is shown that the type of applied loading (tensile or compression) has a noticeable influence on the magnitudes of crack tip parameters. The crack inclination angle corresponding to pure mode II (pure shear deformation) are also determined for both compressed and tensile DSS specimens. This angle depends on the applied loading type, crack length ratio and inner to outer ring radius ratio.