Tuesday, 12 October 2004 - 2:15 PM

This presentation is part of : Damage and Composites I

Modeling of Cyclic Damage Evolution in Polymers

Aleksandra Vinogradov and Erik M. Rassi. Montana State University, 220 Roberts Hall, Bozeman, MT 59717

The paper concerns the time-dependent response of polymer systems subjected to superimposed static and cyclic loads. Under such conditions the behavior of polymers is characterized by highly nonlinear effects produced by the interaction between creep and damage evolution processes. As a result, polymers tend to undergo progressive deterioration of their qualities. Experiments indicate that the character of cyclic damage evolution in polymers is different than the damage processes produced by static creep. In particular, under static loading conditions, damage evolution is characterized by uniform microstructural changes until the onset of tertiary creep. In contrast, under cyclic loading conditions, localized damage in polymers is initiated immediately upon the load application. Further, the material follows several stages of progressive damage evolution involving craze formation, craze growth, crack nucleation and crack propagation. This paper represents an effort to characterize in phenomenological terms cyclic damage evolution in polymers using a nonlinear constitutive material model. The developed model is based on the basic principles of continuum damage mechanics combined with the theory of linear viscoelasticity. The concept of a fictitious undamaged viscoelastic continuum is utilized to represent the actual damaged viscoelastic media. Damage evolution is defined in terms of a damage function which depends on the number of loading cycles. It is shown that cyclic damage in viscoelastic media can be quantified. Experimental results providing validation of the developed constitutive model are presented.

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