The effect of toughness on the failure of high and very high strength structural steels in the elasto-plastic and fully plastic range

Within this research project 9 steels of varying strength and toughness have been investigated by different test procedures in order to examine differences in the failure behaviour of high strength steels. A major topic was the investigation concerning the influence of temperature on the deformation and failure behaviour of wide plates in the elastic plastic range and fully plastic range. It was shown that, with increasing strength, stable crack extension appears below the plastic collapse load. In addition, the influence of the amount of elastic energy which is available for the occurrence of fracture was investigated. It became clear that with decreasing stiffness the values of fracture strain declined visibly. Furthermore, safety concepts of fracture were examined with regard to their applicability to high strength steels. The statements about safety extend from gross estimations by the crack tip opening displacement (CTOD) design curve approach to exact predictions using finite element (FE) calculations.