engleski

The effect of a material's heterogeneity on the stress and strain distribution in the vicinity of a crack front

In this investigation a high strength low allowed steel (HSLA) of 700 MPa strength class was used as a base material. A butt welded joint with X grooves was produced with an overmatched weld metal that had a yield strength 23% greater than that of the base material. Three-point bending Bx2B test specimens (thickness B=36 mm) were extracted from the welded joints. The straight crack front (a0=35, 571 mm) crosses different microstructures through the thickness of the specimen. Both fracture mechanics tests and 3D finite- element analysis were performed. The CTOD parameter of the fracture toughness was measured and calculated numerically. The loading level at which stable crack growth occurred was also determined. The comparison of the experimental and numerical values of CTOD (d5) displacements showed good agreement. The principal stress, Sy, the Mises equivalent stress, Seq, and the plastic equivalent strain Epl, eq at the moment of crack initiation were studied for six equidistant layers from the surface to the mid-thickness of the specimen. Crack opening stress (denoted as Sx in this paper) in dependence on the local fracture toughness value was considered as the parameter which determines the direction of crack front propagation. The results show that the lower strength of the base metal contributes to the crack path deviation in the mid-thickness of the specimen. Both the crack path deviation and the higher toughness of the base metal increase the critical fracture toughness value of the welded joint.

strength overmatched welded joint; crack; stress and strain distribution; finite element analysis

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