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An analytical investigation was performed to study the damage in laminated composites containing an open hole and subjccted to compressive loading. A progressive damage model was developed during the inxstigation to predict the extent and the failure modes of the internal damage in the laminates as a function of the applied load and to simulate the in-plane response of the laminates from initial loading to final collapse. The model consists of a stress analysis and a failure analysis. Stresses and strains inside the laminates were calculated by a nonlinear finite element analysis which is based on finite deformation theory with consideration of material and geometric nonlinearities. The types and extent of damage in the material were predicted by a failure analysis which includes a set of proposed failure criteria and material degradation models.Numerical results from the model were compared with the data which were obtained during the investigation and are presented in a companion paper [l]. Good agreements were found between the predictions and the test results. A computer code was developed based on the model which can be used as a tool for sizing and designing composite plates containing holes and subjected to compression. Downloaded from 2. The in-plane response of the plate 3. The compressive strength of the plate 4. The residual stiffness and residual strength of the plates after a prescribed load ANALYTICAL AIODELSince the major interest of this research is in-plane compression failure in laminated composites due to material damage, rather than geometrically related

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There is an emerging interest in the aerospace industry to manufacture components with intricate geometries using discontinuous fibre carbon/polyether–ether–ketone moulding systems (obtained by cutting unidirectional tape into strands). This type of material system is termed randomly oriented strand composites and is appealing for structural applications as it bridges the gap between the lack of formability of continuous fibre composites and the lack of performance of short fibre composites. The objective of this study was to investigate mechanical properties (tensile, compressive, shear and fatigue) of randomly oriented strand composites and to quantify the effect of strand size on their properties. Overall, properties were found to be highly variable and dependent on the strand length. Interestingly, tensile, compressive and shear strength had similar magnitudes and exhibited the same failure mechanisms (strand fracture and debonding). This experimental work expands the knowledge base for randomly oriented strand composite materials.

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To validate the fatigue progressive damage model, developed in the first part of this paper, an experimental program was conducted using graphite/epoxy AS4/3501-6 material. As the input for the model, the material properties (residual stiffness, residual strength and fatigue life) of unidirectional AS4/3501-6 graphite/epoxy material are fully characterized under tension and compression, for fiber and matrix directions, and under in-plane and out-of-plane shear in static and fatigue loading conditions. An extensive experimental program, by using standard experimental techniques, is performed for this purpose. Some of the existing standard testing methods are necessarily modified and improved. To evaluate the progressive fatigue damage model, fatigue behaviour of pin/bolt-loaded composite laminates is simulated as a complicated example. The model is validated by conducting an experimental program on pin/bolt-loaded composite laminates and by comparison with experimental results from other authors. Different capabilities of the model are examined by conducting different types of experiments. The comparison between the analytical results and the experiments shows the successful simulation capability of the model.

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