Mixed mode surface crack growth in aluminium alloys under complex stress state
R.R. Yarullin, V. Shlyannikov, Daniele Amato, Roberto Citarella
Abstract
In this study fatigue crack growth tests were carried out on hollow cylindrical specimens, made of D16T and B95AT aluminum alloys (analogue of 2024 and 7075 aluminum), with initial external semi-elliptical surface cracks and undergoing complex stress state. The crack growth behavior of aforementioned materials was studied under cyclic axial tension, pure torsion and combined tension+torsion fatigue loading. Optical microscope measurements and the crack mouth opening displacement (CMOD) method were respectively used to monitor crack length and calculate crack depth. The experimental crack front positions were highlighted by using a beach mark procedure during the tests. The stress strain field along the crack front of semi-elliptical cracks in the cylindrical hollow specimens was assessed by Finite Element Method (FEM) analysis. The stress intensity factors (SIFs) were calculated by the 3D M-integral approach and the distributions of equivalent elastic SIFs along the crack front were used for crack growth rate assessment under mixed mode conditions. As a result, the fracture resistance parameters of aluminum alloys under complex stress state were presented. The simulation of cracks propagation turned out to be consistent with experimental results.