Study on Design of Fibrous Composite Materials Based on Stochastic Materials Design

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Studies of stochastic materials design of composite materials have been performed. For these purpose, design-oriented failure criteria of composite materials are applied to construct an evaluation model of probabilistiv safety based on the extended structural reliability theory. A new design diagra which shows the feasible region on in-plane strain space corresponding to the safety index or failure probability is also proposed. These stochastic failure envelop diagrams which are illustrated onto in-plane strain space enables one to evaluate the stochastic behavior of the composite laminate with any lamination orientation under multi-axial stress or strain condition. The sequential failure path of each layr of composite laminates in simulated by means of modulus degradation and safety Indies under the offaxis load conditions. From the simulation analysis, a typical failure path is evaluated corresponding to an in-plane strain vector. The mechanical behavior, such as decreasing modulus and increasing in-plane strain are also simulated in correspondence with each stage of sequential ply failure. It is necessary to select the important failure path whose occurrence probabilities are greater than others, since there are too many failure paths of multi-layr composite laminate evaluate. The proposed methods of selecting effective failure paths depends upon the heuristic procedure based on one branch and bound rule or selecting effective failure paths depends upon the heuristic procedure based on one branch and bound rule or genetic algorithm which enable one to estimate the effective failure path whose occurrence probabilities are greater. An extended study is performed in order to calculate the failure probability of multiple layr laminates resulting from the effective failure path, some examination for determination of lamination configuration under strength constraints was tried.