### Monday, 11 October 2004 - 3:55 PM

### This presentation is part of : Graduate Student Competition

### Damage in composite plates under thermomechanical impact loading

**Noha M. Hassan**, Graduate Student, Virginia Polytechnic Institute and State University, Department of Engineering Science & Mechanics, Blacksburg, VA 24061 and Romesh C. Batra, Faculty Advisor, Virginia Polytechnic Institute and State University, Department of Engineering Science & Mechanics, 220 Norris Hall, Blacksburg, VA 24061.
Finite transient thermoelastoplastic deformations of a composite plate subjected to ballistic loads have been analyzed numerically by the finite element method. Damage due to fiber/matrix debonding, fiber breakage, and matrix cracking is represented by a set of three scalar variables. The failure surface due to delamination between adjoining layers is expressed in terms of transverse shear and transverse normal stresses. The free energy density is taken to equal the sum of three parts which express contributions to it due to elastic, plastic and damage deformations. The energy dissipated due to damage evolution and plastic deformations is accounted for in the heat equation. The Clausius-Duhem inequality is used to derive restrictions on the constitutive relations. Subsequently, constitutive relations for orthotropic materials are derived. Each lamina is assumed to be made of an orthotropic material. The Tsai-Wu yield criterion is employed to delineate plastic deformations of the composite.

Equations governing transient thermomechanical deformations of a composite plate are written in the Lagrangian description of motion. An approximate solution of the initial-boundary-value problem so formulated is found by the finite element method, and computed results are compared with those available in the literature.

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