A wedge fracture toughness test for intermediate toughness materials: Application to brazed joints

A fracture toughness test for intermediate toughness materials is developed. The test configuration is a wedge-driven double cantilever beam, with design guided by analytical solutions for the energy release rate and compliance. Actual toughness measurements require finite element methods. To promote crack stability, a pre-cracking fixture is employed. The method is illustrated for a brazed joint. Measurements of the fracture resistance used both fractographic and compliance methods to ascertain crack length. The ensuing fracture resistance, ΓR ≈ 1 kJ m−2, is significantly greater than that for the intermetallic constituents. Approximately half of the toughening is attributed to plastic stretch of the ductile phase within the eutectic. The remainder is attributed to dissipation within a plastic zone that forms in the primary γ-Ni regions. A rationale for improving toughness is presented.