The brittle fracture behaviour of old mild steels

Abstract

In the assessment of old steel structures the verification of sufficient material toughness is important for the decision on necessary repair and reinforcement measures. Based on extensive fracture mechanics investigations the assessment methods in EN 1993-1-10 were developed. The determination of permissible element thickness for certain steel grades was determined for welded structures made of current steel grades (according to DIN EN 10025) with mostly high toughness's. This simplified method is not suitable for old mild steel structures with holes for riveted joints. In this article, experimental studies of the brittle fracture behaviour of structures with holes made of old mild steel are presented. The results were carried out through various research projects at the Technische Universität Dresden and its cooperation partners (see, e.g. Stroetmann et al. (2015)).The main topics are extensive material analyses to determine the fracture toughness in the brittle-ductile transition region according to the Master Curve concept. The evaluations confirm that different steel grades can be defined depending on the manufacturing process of the old steels. Additionally, the newly obtained results are compared to existing correlations of impact and fracture toughness and are checked for their suitability for old mild steels. Furthermore, the analysis of metallography and mechanical properties on components with punched holes are described to analyse the crack initiation of quasi-static stressed components made of old mild steel.