Assessment of Short Arrested Brittle Fracture in Welded Joints

摘要

The behaviour of short arrested brittle fractures (pop - in) in welded joints were investigated experimentally on single edge notched three point bend specimens extracted from two different types of bead in groove (BIG) welds fabricated on S 355NL and S 550 ML steels. Fracture tests were conducted on wire electro discharge notched specimens where the notch was located at the fusion line and perpendicular to the plate surface with a relative depth of a/W=0.1 and a/W=0.5 respectively. In the fracture tests load -displacement traces were recorded and the transient recorder for dynamic measurements was triggered by a magnetic emmission signal. The dynamic measurements included also optical crack mouth opening. The results of the fracture tests show, that depending on the level of load - displacement at the initiation of brittle fracture the fracture can be arrested and leads to a typical pop - in behaviour (low load - displacement levels) or brittle fracture propagates throughout the whole ligament (high load - displacement levels). Dynamic CMOD signals revealed that brittle fracture propagation often consists of several brittle fracture initation/reinitiation and deceleration/arrest phases even it appears as a continuous fracture in the quasistaticly recorded load - displacement curve. A dominating parameter governing the brittle fracture events seems to be the elastic energy available at initiation of brittle crack propagation. Nevertheless different degrees of plastic deformation in the material of the ligament can cause different resistance against brittle fracture propagation and crack arrest.