Failure criteria for weak-axis quasi-orthotropic woven fabric composites

Abstract

The failure behavior of woven fabric composites in the form of plain weave fiber unidirectional laminae is studied in this paper as defined by their failure stresses in simple tension and compression along the three principal stress directions. Since the transverse weave plane is the strong and isotropic plane of the composite, while the normal to it direction the weak one, the material is approximated as a weak-axis transversely isotropic composite. The elliptic paraboloid failure surface (EPFS) criterion, as introduced by the author [1], was shown to describe satisfactorily this type of interesting modern materials. It was shown that such weak-axis transversely isotropic composites correspond to tension strong composites and their failure surfaces consist of a single-sheet convex surface open to the tension-tension-tension octant of the principal stress space. The main characteristic of such surfaces is that they are oblate along the normal direction to the isotropic plane, in contrast with the typical (EPFS)-criterion for fiber composites, which, all of them, are prolate along the same direction. While the intersection of this (EPFS)-criterion by the (σ1,σ3) stress plane (σ3 is the weak axis) resembles closely the respective intersection for the unidirectional fiber composites the (σ1,σ2)-isotopic plane intersection, which coincides with the weaving strong plane approaches very closely a circle thus indicating that along this isotropic plane the failure stress is hydrostatic and independent of its orientation inside this plane. This property constitutes a significant and most promising property which makes this type of woven composites very attractive in applications. Experimental evidence of failure of such materials, which is very sparse, as derived from tests in a woven T-300 Carbon-epoxy composite corroborated excellently with the theory based on the (EPFS)-criterion.