Augmentation of classical failure criteria for comprehensive applicability to interfacially deficient woven-roving composites

Abstract

The dominant mode of failure in the fiber-reinforced composite materials of poor fiber-matrix adhesion is the interfacial shear failure. The main objective of the current study is to modify the classical failure criteria to comprise this mode of failure as they ignore the actual failure mechanisms, which are emerging microscopic deficiencies. An interfacial shear correction factor is proposed to augment the local shear component (σ₆) in the investigated failure criteria. Thus, the shear stress concentration at fiber-matrix interface in the boundary of the deficient zone is considered. To conduct the experimental part, thin-walled cylindrical specimens are fabricated from two layers of woven-roving E-glass fabrics of [±45°] and [0°, 90°] fiber directions. The fabrics are reinforced with polyester. For each fiber orientation, the specimens are divided into four groups: the first group includes the pristine specimens and the other three groups having circular inclusions of 5, 7, or 9 mm radii, respectively. Each specimen is subjected to fully reversed bending loading using a strain-controlled testing machine. The S-N curves and the relative damage vs. number of cycles to failure (N) curves are plotted for each group. The relative damage values are used to examine the theories applicability to the studied material and to calculate the values of the proposed interfacial shear correction factor.