Mixed-mode static and fatigue crack growth in central notched and compact tension shear specimens

Elastic-plastic crack growth under mixed Mode I and II in six types of aluminum alloys and three types of steel were investigated. The experimental study of fatigue crack growth in six types of the aluminum alloys and one type of the steel is performed on biaxially loaded eight-petal specimens (EPS). All specimens for biaxial loading contained inclined through thickness central cracks. Mixed Mode I/II static and fatigue crack growth experiments on the three types of steels and one type of the aluminum alloy used compact tension shear (CTS) specimens. Two approaches are developed for geometrical modeling of crack growth trajectories for the central notched and compact tension shear specimens respectively. The principal feature of such modeling is the determination of crack growth direction and the definition of crack length increment in this direction. On the basis of the analysis of the experimental data for the aluminum alloys and the steels an empirical crack reorientation criterion is suggested for both brittle and ductile materials. The damage process zone size concept is used for calculations of mixed-mode crack path. The influence of specimen geometry, biaxial loading and properties of the aluminum alloys and the steels on both crack growth direction and crack path at the macroscopic scale is discussed.