A. Chudnovsky, S. Preston*, and K. Sehanobish** Dept. of Civil & Materials Engineering University of Illinois at Chicago, 842 W. Taylor, Chicago IL 60607 *Department of Mathematical Sciences, Portland state University, Portland, OR, 97207-0751 **The Dow Chemical Company, Freeport, TX 77566
Keywords: Ageing, model, life assessment, creep, NDT
ABSTRACT
Material ageing is commonly understood as changes of material properties with time. The ageing in engineering materials is usually observed as an improvement of some properties, e. g. rigidity and strength while deterioration of others, e. g. toughness. In an attempt to model ageing phenomena on a continuum level one faces three major tasks. The first task is to identify the age parameter that represents, on a macroscopic scale, the micro and sub microscopic features, underlying processes such as nucleation and growth of micro defects, physico-chemical transformations etc. The second task consists of formulation of a constitutive equation of ageing. The third task obviously is the experimental examination of the condition that leads to catastrophes such as small perturbation in controlling parameters leading to large variations of age parameter. A material tensor "G" is introduced as an age parameter similar to stresses and temperature. A variational principle approach is proposed to formulate a constitutive equation for ageing. Interestingly, an evolution of "G" in four dimensional material space-time continuum leads to an inelastic behavior which manifests as time dependent material properties recorded by an external observer. For one of the simplest linearized case the approach leads to the well studied empirical creep behavior model.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.full paper not received Publisher:Ashgate Publishing Company
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