Surface and through thickness crack growth in cruciform specimens subjected to biaxial loading

摘要

Fatigue surface crack growth are studied through experiments and computations for aluminum alloy D16T. Subjects for studies are cruciform specimens under different biaxial loading with external semi-elliptical surface crack. The variation of fatigue crack growth rate and surface crack paths behaviour was studied under cyclic uniaxial tension, equal biaxial tension and biaxial tension-compression loading. For the experimental surface crack paths in tested specimens the T-stress, the out-of-plane Tz factor, the local triaxiality parameter h and the governing parameter for the 3D-fields of the stresses and strains at the crack tip in the form of I_n-integral were calculated as a function of aspect ratio by finite element analysis to characterization of the constraint effects along semi-elliptical crack front. Both elastic and plastic stress intensity factor approach was applied to the fatigue crack growth on the free surface of the cruciform specimens as well as in the deepest point of the semi-elliptical surface crack front. As result principal particularities of the fatigue surface crack growth rate as a function of loading conditions were established. The experimental and numerical results of the present study provide an opportunity to explore the suggestion that crack growth rate may be represented by the plastic stress intensity factor, rather than the magnitude of the elastic SIF alone.