LAUSR

Abstract This paper investigates monotonic and cyclic fracture behaviors of aluminum alloy 6061-T6511 and analyzes the cause of different fracture behaviors. This study adopts the η approach and a modified η approach to obtain monotonic and cyclic J-R curves respectively. The cyclic loaded SE(T) specimens with zero load ratio have similar J-R curves with monotonically load SE(T). In contrast, a tensile residual stress field at the crack front introduced by negative load ratios promotes a faster crack extension, which leads to a lower load resistance at the same CMOD level. The strain energy corresponding to the area under the P-CMOD envelope becomes lower, which induces the degradation of cyclic J-R curve with negative load ratios.