Mechanical reliability characterization of low carbon steel brazed joints with copper filler metal

In this paper, mechanical reliability of low carbon steel brazed joints with copper as the filler metal is investigated. Tensile and shear strengths of the joint are evaluated by tension and torsion tests performed on butt-brazed joint specimens. Brazed joint failure under mixed mode loading is evaluated by biaxial tension-torsion tests as well. It is shown that a power law mixed mode failure criterion based on the single mode tensile and shear strengths well predicts the biaxial failure of the brazed joint. Furthermore, tensile, torsion, and biaxial tests are numerically simulated using ABAQUS software. Applying the experimentally measured deformations to the FE model the joint strengths are well estimated. Resistance of the brazed joint against crack propagation is evaluated by fracture toughness testing on SENB and SENT specimens. Crack extension is monitored using a video-microscope camera during the fracture test. The obtained fracture toughness values show dependency on the loading configurations applied to the specimens. SEM images of the joint fracture surfaces show two different failure mechanisms of dimple rupture and dendritic failure on the fracture specimens failed under tensile stresses. The EDS chemical analysis on the fracture surface of the tensile specimens reveals that MnS-rich dendrites are the source of dendritic failure, while the finer Fe-rich dendrites and microvoids cause the dimple rupture. Dimple rupture initiated from dendrites and microvoids is the only failure mechanism observed on the fracture surface of the torsion specimens failed under shear stresses. (C) 2011 Elsevier B.V. All rights reserved.