Chapter 7 - Time Dependence, Repeated Loads and Energy Absorption Capacity

Abstract

In polymers, strong time dependence of fracture growth is caused primarily by visco-elasticity of the material. While, in rocks and ceramics, the time dependence of fracture is caused almost exclusively by the time dependence of the bond ruptures that cause fracture. The chapter discusses the rupture of an inter-atomic bond, which is a thermally activated process. The fact that the brittleness of response increases with a decreasing rate of loading or increasing load duration is also explained in the chapter. The chapter illustrates curves of nominal stress versus relative crack mouth opening displacement (CMOD) for different CMOD rates, calculated by the cohesive crack model, under the assumption that the material exhibits only visco-elasticity in bulk or only rate-dependent crack opening curve cracks. The concept of ductility is different from the maximum load or strength of the structure. Ductility characterizes the deformation capability under the most stable type of loading, which is the loading under displacement control.