Failure Prediction of Woven Fabric Composites after Deformations Induced by Forming

Abstract

Polymer reinforced by woven fabrics is probably the most common type of composite used in structural applications such as aircraft, boats, reservoirs, pressure vessels, etc. Woven fabrics offer many advantages in terms of manipulative requirements, including dimensional stability, good conformability, and deep-draw shape ability. In many applications, when the part geometry has a double curvature, the forming process usually results in significant in-plane shear deformation of the interlaced yams and the fabric composite becomes a non-orthogonal structure. The existing models proposed for orthogonal fabrics are unable to predict the thermo-elastic properties and the strengths of the deformed fabric structure (non-orthogonal structure). Recently, a new model, called the sub-plies model, has been proposed for the characterization of thermo-elastic properties of any deformed woven fabric composites. In this model, a woven fabric is divided into four fictional unidirectional sub-plies. The model allows determination of the thermo-elastic properties of deformed fabric composites (non-orthogonal structure) and direct use of layered shell elements in finite element codes. This paper presents the results of a study on the application of the sub-plies model in the prediction of tensile and compressive strengths of orthogonal and deformed graphite/epoxy woven-fabric composites. A special procedure is also proposed to measure the effect of fiber undulation on the mechanical properties of the constituent fictional plies. The equivalent coefficients of the on-axis tensile and compressive strengths of the constituent plies, determined by the proposed method, are applied to the maximum strain and quadratic criteria to predict the failure envelop of the composite. Tensile and compressive tests on specimens made of 8-harness satin and plain weave fabric composites were carried out to verify the proposed approach. The fabric structure of the test specimens was deformed by shearing to various angles between the interlaced yams before molding. The results show that prediction of tensile and compressive strengths by the sub-plies model and the quadratic criterion is in good agreement with experimental data.