Relationship between stress distribution along slant crack and opening displacement on crack-surface

The load is not always vertical to the crack in an actual mechanical part, so it is necessary to study the crack deformation behavior under the mixed-mode stress condition. It is difficult to measure the stress distribution along a crack for complex mechanical structures. Using the cracks with slant angle of 45 introduced by the cycle stress of mode I at zero stress ratio, this work measured the opening and sliding discontinuous displacements along the crack, then calculated the mode I and mode II stress distributions. Furthermore, finite element method (FEM) was used to simulate the dimensions of the specimen used in the experiment. The factors influencing the opening and sliding discontinuous displacement on the crack surface were discussed by comparing experimental and FEM data. The results show that the sliding deformation of fatigue crack is restrained because of the contact of crack zigzag surfaces especially at the crack tip. This effect is outstanding while the contact surface increases, which causes by the decreased opening deformation. On the contrary, the crack opening deformation increases because of the crack surface contact. And the opening deformation behavior is affected by the compressive residual stress near the crack.