Critical strains and necking phenomena for different steel sheet specimens under uniaxial loading

When defining ultimate loads or failure criteria for shells, vessels and containment liners, for instance, reference will be made to critical strains of the material under consideration. eral the critical strains are derived from uniaxial tensile test results obtained with rods. tual deformation behaviour of sheets (plate and shell type structures), however, differs considerably from the uniaxial rod behaviour. arious tests – along with theoretical investigations – it was found that for membrane or even bending stressed sheets higher ultimate strains are reached. pical strain behaviour caused by increasing load starts with uniform strain distribution over the specimen length and finally ends with localized necking. itical strains” the well known uniform elongation strain and the ultimate strain are defined. eets in addition the quasi uniform elongation strain has been introduced in this paper. s for rods under tension localized necking is directly following the uniform straining, tests with sheets show a so-called diffuse necking behaviour before localized necking starts. onsequence the deformation capacity of steel sheets turns out to be significantly higher than relying on the data from standard tension tests with rods.