Small crack initiation and arrest behavior called pop-in is often observed in fracture toughness tests of welded joints. The material toughness is extremely sensitive to the local brittle zone (LBZ) in heterogeneous heat-affected zone (HAZ). The avoidance of pop-in initiation is very difficult in toughness tests of welded joints using high strength steels. These pop-ins may not always significant events in structural integrity due to the material heterogeneity in HAZ where the material surrounding LBZ has high crack arrest capability. The pop-in behavior in heterogeneous HAZ has been investigated using 3-dimensional dynamic finite element analyses (FEA) with calibrated cohesive elements. The models used are single edge notch bend and single edge notch tension specimens having material heterogeneities to assess loading mode and material heterogeneity effects on pop-in behaviors. It has been found that toughness heterogeneity in HAZ has a large effect on pop-in significance. And the effect of loading mode such as bending or tension on pop-in significance can be observed in FEA.
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