A MULTIPLICATIVE DAMAGE MODEL FOR STRENGTH OF FIBROUS COMPOSITE-MATERIALS

Knowledge of the tensile strength properties of a fibrous composite ma terial is essential in the design of reliable structures from that mat erial. Determination of statistical models for the tensile strength of a composite material which provide good fits to experimental data fro m tensile tests on material specimens is therefore important for engin eering design. Perhaps the most commonly used statistical model is the Weibull distribution, based on 'weakest link of a chain' arguments. H owever, in many cases the usual Weibull distribution does not adequate ly fit experimental data on tensile strength for composite materials m ade from brittle fibers such as carbon. Here, an alternative model is developed for tensile strength of carbon composites, which is based on a multiplicative cumulative-damage approach. This approach results in a S-parameter extension of the Birnbaum-Saunders fatigue model and in corporates the material specimen size (size effect) as a known variabl e. This new distribution can also be written as an inverse Gaussian-ty pe distribution, which can be interpreted as the first passage of the accumulated damage past a damage threshold, resulting in material fail ure. The new model fits experimental tensile-strength data for carbon micro-composites better than existing models, providing more accurate estimates of material strength.