Chengzhi Qi

Abstract:

Deformation and fracture of materials exhibit temporal and spatial features. Based on the concept of structural hierarchy and relaxation model, the relationship between spatial and temporal properties of deformation and fracture of rock-like materials is investigated. It has been revealed that the relationship between spatial and temporal scales of deformation and fracture of quasi-brittle materials is in agreement with the available experimental data. This paper points out that the essence of the relationship between spatial and temporal scales of deformation and fracture of quasi-brittle materials lies in the finiteness of crack propagation velocity. From the viewpoint of structural hierarchy, size effect may be considered as the realization of the weakened structural surface strength of smaller scale structural elements with the decrease of the sample size. The essence of strain rate effect is that because of the finiteness of crack propagation velocity, the increase of loading rate, accordingly, the increase of strain rate activates the deformation and fracture process of smaller scale elements before the macro-fracture of the sample. The dynamic strength of material is the strength of weakened structural surface of the smallest activated elements before the macro-fracture of the sample as a whole. This investigation examines the size and strain rate effects on strength of quasi-brittle materials, which would give better understanding of dynamic phenomena of deformation and fracture of quasi-brittle materials.