A criterion for predicting the direction of crack extension in orthotropic composite materials is presented. The criterion is based upon the normal stress and the anisotropic tensile strength on arbitrary planes about the tip of a crack. Results are ob tained, via finite element solutions, for: (a.) isotropic mixed mode fracture, (b.) cracks in unidirectional off-axis slotted composite tensile coupons and (c.) cracks in cross plied laminates. Comparisons are made with other theories and experimental results.
Integrated Computational Materials Engineering OverviewThe accelerated insertion of materials (AIM) initiative provides the opportunity to reduce the materials development cycle time by up to 50% and thereby lessen the lead time required for new materials and processes. The program was founded to revolutionize the way designers and materials engineers interact, to achieve a leap forward in the application of computational materials science and integration with design engineering tools, and to create an environment where the design/materials team can learn from and build on previous developments. The centerpiece of the AIM system is the designer knowledge base, which provides a framework for managing experimental data, executing linked models describing processing, microstructure, properties, and producibility, and calculating confi dence bounds for system predictions.
The magnitude of tile maximum shear strain at the free edge of axially loaded [e2/-e2]s and [(±e)2]s composite laminates was investigated experimentally and numerically to ascertain the actual value of _ strain concentration in resin matrix laminates and to determine the ; accuracy of finite element results. Experimental results using moire : interferometry show large, but finite, shear strain concentrations at the free edge of graphite-epoxy and graphite-polyimide laminates.Comparison of the experimental results with those obtained using several different finite element representations showed that a four node isopari ametric finite element provided the best and most trouble free numerical J results. The results indicate that the ratio of maximum shear strain at the free edge to applied axial strain varies witn fiber orientation and 1 does not exceed nine for the most critical angle which is 15°.
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