09.12: Assessment of old mild steel structures related to brittle fracture

Abstract

ABSTRACTIn the safety assessment of old mild 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 DIN EN 1993‐1‐10 [1] were developed. The determination of permissible element thickness for certain steel grades was derived and tabulated for welded structures made of steels according to DIN EN 10025 with predominantly high toughness's. This simplified method is not suitable for mild steel structures with holes for riveted or bolted joints. In this article, experimental and analytical 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 Institute of Steel and Timber Construction of the Technische Universität Dresden and its cooperation partners (see, e.g. [2]).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 grades of steel can be defined depending on the manufacturing process. Additionally, the newly obtained results will be compared to those from previous studies and existing correlations of impact and fracture toughness are checked for their suitability for old mild steels. Furthermore, the analysis of mechanical properties and metallography on components with punched holes to analyse the crack initiation of quasi‐static stressed components made of old mild steel are described.