Experimental and numerical investigations on limit strains in ductile fracture

Abstract

Several incidents in the past showed the risk of a human and/or environmental caused accident which exceeds the design limit of a component. Therefore the quantification of safety margins becomes necessary. According to technical standards, the safety assessment is usually based on stress criteria. The deformation capability of the material is hardly taken into account with these criteria. Limit strain based safety assessment concepts can overcome this disadvantage.The main influence factors on limit strains are the stress triaxiality, the component size, the loading path and the strain rate. To quantify these factors, different experiments are performed with specimens made of the steel 20MnMoNi5-5, which is representative for German nuclear power-plants.In the range of high stress triaxiality values, different specimens are tested. All the specimens are simulated using Rousselier model to derive the crack initiation location and time. The experimental and numerical results can be used to derive a limit strain curve. The influence of loading paths on failure strains is shown at pre-loaded notched tensile specimens.Finally, an outlook on the planned experimental and numerical investigations in the range of small stress triaxiality values is given.