Upper shelf toughness requirements as improved AUBI-Substitution

  Aufschweißbiegeversuch Copyright: IEHK

The design rules given by EC3 assume a certain ductile material behaviour. Thus, additionally to the general design check, in Ultimate Limit State (ULS) material choice according to DIN EN 1993-1-10 or DASt-Ri 009, respectively, is of utter importance to avoid brittle fracture.

For the upper-shelf toughness requirements in Germany the “Aufschweißbiegeversuch” (AUBI) according to SEP 1390 exists to assess the qualitative crack arrest capacity of the steel base material. This is in general required for welded steel constructions up to steel grade S355 and plate thickness up to 30 mm. In the process of harmonization of the European standards, the AUBI has not been accepted by the other Member States. A lower-shelf orientated substitution criterion has been introduced, whereby the improved properties of modern fine-grained structural steels have been taken advantage of.

However, the AUBI gives only an empirical approach for the determination of a certain delivery quality. Furthermore, the upper shelf criterion is not justifiable for safety demands and the AUBI was not designed for high strength steels and other geometries than plate material.

The aim of the project is to substitute the AUBI with an alternative toughness test (toughness impact energy) in the upper-shelf, to derive optimized upper-shelf demands (for mild steels, high-strength steels and other geometries than plates) on the base of nominal material properties. Innovative scientific methods under consideration of hybrid damage mechanic models will be used, which allow the numerical simulation of the AUBI and depicting the failure mechanisms cleavage fracture (lower-shelf) and ductile fracture (upper-shelf).

Within this project, a procedure will be developed to derive a substitution criterion of AUBI in terms of upper shelf requirements for impact toughness energy. This will lead to a safe and economic alternative of AUBI. More specifically, KMU will benefit of safe and efficient design rules. Furthermore, the introduction of precise upper shelf requirements will enhance the competitiveness of the quality-orientated national and European steel production sector.