This paper reports an application of the strain invariant failure theory (SIFT) proposed by Gosse to through-thickness failure of composite structures [Gosse, J.H. and Christensen, S. (2001). Strain Invariant Failure Criteria for Polymers in Composite Materials, AIAA-2001-1184]. It includes global 3D finite element analysis on a ply-by-ply basis and the determination of amplification factors for strains in the intrafiber resin and the calculation of thermal residual strain due to manufacturing for intrafiber resin using micromechanical models. The new procedure has been applied to matrix failures for one type of curved beam, two types of I-beam and two types of T-cleat structures. The resulting predictions of the failure loads for both the I-beams and the T-cleats follow experimental trends. The limiting value of the first invariant strain for failure of the resin in the unidirectional tape is 17,000–20,000 ", and in the bidirectional fabric is 26,000–27,000 ".
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SYNOPSISOne of the key requirements for developing tough multiphase blend systems, for example, selecting the type of discrete phases (hard or soft) in a polymer matrix, is the ability to predict the fracture path. Most of these selections rely heavily on prior experience or on intuitive rationale. There are few mathematical guidelines for the materials scientists who are designing new multiphase systems. This article is designed mainly to provide such insight through the development of a theoretical model and through experimental observation. A finite element model has been used to predict the crack velocity and the crack path for a crack that approaches and penetrates a hard or a soft inclusion. A novel experimental approach is then utilized to verify these predictions by introducing hard and soft circular domains in poly (ethylene-co-carbon monoxide ) specimens by selective photodegradation. 0
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