Contact damage and crack patterns in whiteware layered structures

Abstract

Contact damage and crack patterns in two types of whiteware layered structure were investigated as a function of firing temperature, for single and multi-cyclic loading in Hertzian contact tests. In the layered structures fired at 1200°C, the damage mode and crack patterns were similar for different coating layer compositions, showing cone-like cracks at the coating layer and additional, upward extending transverse cracks at the internal interface, with cone-like cracks dominant. The damage was enhanced on increasing indentation load P and number of cycles n, with quasi-plastic deformation dominant. System failure occurred at higher indentation loads and number of cycles (n = 10⁴ at P = 500 N), following quasi-plastic deformation in the substrate and fracture in the coating layer. In the case of 1300°C firing, only cone-like cracks were initiated at the coating layer independent of the indentation load P in single cyclic loading. Two layered structures with different compositions in the coating layer showed no difference at a lower indentation load, P = 200 N, until n = 10⁵ and at a higher indentation load, P = 500 N, until n = 10⁴ in multi-cyclic loading. However, these structures showed a different damage mode at the higher indentation load and number of cycles, n = 10⁵ at P = 500 N. The dominant damage mode in the layered structure prepared at 1200°C was quasi-plasticity in the substrate, and at 1300°C was fracture in the coating layer, depending on the indentation load P and the number of cycles n.