Description of the creep process and long-term strength by equations with one scalar damage parameter

Abstract

In the example of titanium and aluminum alloys the authors illustrate the possibility of describing the process of creep and fracture of materials whose strain in fracture depends on the magnitude and type of stressed state. The reduction of the experimental creep diagrams to a common curve in relative coordinates ({omega} = A/A*, {tau} = t/t*) (A and t are the instantaneous values of the scattered energy and time, and A* and t* are the corresponding values in fracture) permits the damage equation to be written in the form of an equation of state d{omega}/dt = {var_phi}({sigma}){psi}({omega}), and the damage parameter to be related to experimentally measurable quantities. This capability removes the leeway (uncertainty) from the determination of the coefficients of the creep and damage equations and provides a unified procedure for obtaining them. The consistency of an equation of state with one scalar parameter for describing the description of damage kinetics is substantiated experimentally in steady (smoothly varied with time) and stepped loading regimes. It is established that the cumulative damage in tension and compression differs for materials with different creep resistances, and the domain of validity of the governing equations is indicated.