Deformation and fracture of Nb/α-Al2O3 composites in compression and bending studied by an optical method

Abstract The fracture behavior of Nb/a-Al2O3 composites was investigated both in compression tests and bending tests using an optical full-field method for the observation of strain fields on the metal surfaces. Joints of polycrystalline materials were prepared by high-vacuum diffusion bonding. The building up of the strain near the interface during the tests, finally leading to the fracture, was studied by examining the strain and displacement fields of the whole metal layer. In compression tests, two types of fracture, fracture of alumina and fracture of interfaces, were detected by cross-examination of the stress–strain curve and the strain maps. The fracture of alumina in compression tests was influenced by the Nb layer thickness and can be rationalized by an extension of Cottrell's model. For four-point bending tests, the results of the strain maps, determined experimentally by means of the optical method, confirmed the strain maps resulting from finite element simulations.