Overstraining effects on the crack-opening displacement of microstructurally short cracks

The influence of different overstraining events on the crack-opening displacement of microstructurally short cracks in polycrystalline nickel was investigated. Both symmetric and asymmetric overstraining experiments were carried out and the influence of increasing overstraining ratio and number of overstraining cycles was analysed. Symmetric and asymmetric overstraining events lead to characteristic changes in the plastic part of the crack-opening displacement, which can be attributed to strain hardening and/or residual stresses. By applying asymmetric deformation modes in tension or compression, it is possible to separate the effects of strain hardening and residual stresses on crack-opening displacement. Additionally, some results for austenitic stainless steel are given.