An experimental and numerical investigation of fracture resistance behaviour of a dissimilar metal welded joint

Abstract

Dissimilar welds impose a challenge to the engineers concerned with the structural integrity assessment of these joints. This is because of the highly inhomogeneous nature of these joints in terms of their microstructure, mechanical, thermal, and fracture properties. Fracture mechanics-based concepts cannot be directly used because of the problems associated with the definition of a suitable crack-tip loading parameter such as J -integral crack tip opening displacement (CTOD), etc. Again, depending upon the location of initial crack (i.e. base, weld, buttering, different interfaces, etc.), further crack propagation can occur in any material. The objective of the current work is to use micro-mechanical models of ductile fracture for initiation and propagation of cracks in the bimetallic welds. The authors have developed a finite element formulation that incorporates the porous plasticity yield function due to GursonTvergaard-Needleman and utilized it here for the analysis. Experiments have been conducted at MPA Stuttgart using single edge-notched bend (SEB) specimens with cracks at different locations of the joint. The micro-mechanical (Gurson) parameters of four different materials (i.e. ferrite, austenite, buttering, and weld) have been determined individually by simulation of fracture resistance behaviour of SEB specimens and comparing the simulated results with those of the experiment. In order to demonstrate the effectiveness of the damage model in predicting the crack growth in the actual bimetallic-welded specimen, simulation of two SEB specimens (with initial crack at ferrite-buttering and buttering-weld interface) has been carried out. The simulated fracture resistance behaviour compares well with those of the experiment.

Local fracture resistance behavior of interface regions in a dissimilar metal welded joint

“…(2)-(5) that higher stress triaxiality and plastic strain together promote the microvoid nucleation, growth and coalescence. In other words, both of them together promote the ductile crack initiation and growth, and further influence the crack growth resistance [10,12]. Fig.…”

“…1 is simplified as an idealized four-material 'sandwich' structure without heat-affected zone (HAZ) and residual stress. This simplified analysis is usually used for welded joints [10,12,21]. In the simplified four-material (A508, Alloy52Mb, Alloy52Mw and 316L) structure, there exist two interface regions of A508/Alloy52Mb and Alloy52Mw/316L.…”

“…The material with smaller f 0 value usually has higher ductile fracture resistance [32]. Although the GTN model parameters for simulating the ductile crack initiation and propagation of a material may not be unique [33], a set of parameters can be found by adjusting the different parameters in a calibration procedure of fitting the numerical J-resistance curve with experimental one [12,22,31,34]. And this set of parameters can be used to predict ductile fracture of specimens with different geometries [12,20,22,31,34].…”

“…However, due to the highly inhomogeneous microstructure, mechanical and fracture properties across the DMWJ, it is difficult to conduct analytical or experimental fracture investigations on the DMWJs. Only limited studies on the fracture behavior for the DMWJ can be found in the literature [5][6][7][8][9][10][11][12][13]. A series of fracture tests have been performed to evaluate the fracture resistance of DMWJ between SA508 ferritic steel and 304L stainless steel (SS) using E308L SS as a filler metal in the BiMET and ADIMEW programs within the European Commission [5][6][7].…”

“…Laukkanen et al [11] conducted an investigation using Charpy-size three point bend (3PB) specimens on the fracture behavior for various regions of SA508/ AISI304 DMWJ. Samal [12,13]. More recently, the authors conducted experimental investigations of local fracture resistance and fracture mechanism of an Alloy52 M dissimilar metal welded joint ( Fig.…”