Tensile first cracking strain and strength of hybrid composites and laminates

Abstract

A hybrid like a multidirectional laminate contains at least two major load-bearing components whose failure strains are different. The failure strain of the higher elongation component is invariably reduced by the presence of the other, but the ultimate strain of the lower elongation component may remain the same or can be increased by decreasing its dimensions. The relevant dimension may be the diameter of a bundle or of separate fibres or the thickness of the transverse ply in a 0°/90° laminate. Our previous theory of multiple cracking and constrained failure is reviewed and applied to simple laminates and laminated hybrids. We also demonstrate that it can be applied to preventing cracking due to thermal strain. It is pointed out that, in 0°/90°/0° laminates, longitudinal splitting of the 0° plies may occur owing to the constraint imposed by the 90° plies, whether these have cracked or not. Simple rules are given to account for the longitudinal ultimate strength and ultimate fracture strain of intermingled glass and carbon hybrids in epoxy resin. In this system, stress concentrations due to failure of the low elongation component do not appear to be very important.