INFLUENCE OF JOINT GAP WIDTH ON STRENGTH AND FRACTURE-TOUGHNESS OF COPPER BRAZED STEELS

The strength of brazed butt joints is commonly assessed in terms of the tensile performance of defect-free laboratory testpieces. In practice, brazed joints often contain crack-like defects which dominate the mechanical performance. The present work examines the strength and fracture toughness of copper brazed joints in steel. It is shown that the tensile strength of defect-free joints increases as the joint gap decreases and as the strength of the steel increases. Conversely, the fracture toughness is observed to decrease to a very low level as the joint gap decreases and as the strength of the steel increases. As a result, thin brazed joints are very susceptible to the presence of defects and, in practice, it is difficult to take advantage of the potential strength available. The reason for the relationship between toughness and joint gap is that toughness is determined by the extent of crack tip plasticity which, for a brazed joint, is controlled by the thickness of the braze metal. © 1990 The Institute of Metals.