The effect of matrix shear strength on the out-of-plane compressive strength of CFRP cross-ply laminates

Abstract

The failure mechanism of 'indirect tension' is explored for cross-ply IM7/8552 carbon fibre/epoxy laminates subjected to quasi-static, out-of-plane compressive loading. The sensitivity of compressive response to strain rate and to the state of cure is measured, motivated by the hypothesis that the out-of-plane compressive strength is sensitive to the matrix shear strength. A pressure-sensitive film is placed between specimen and loading platen, and reveals that a shear lag zone of reduced compressive traction exists at the periphery of the specimen, giving rise to a size effect in compressive strength. The width of the shear lag zone reduces with increasing shear strength of the matrix. The laminates fail by the indirect tension mechanism: out-of-plane compressive loading generates tension in the fibre direction for each ply and ultimately induces fibre tensile failure. Finite element (FE) simulations and an analytical model are developed to account for the effect of matrix shear strength, specimen geometry, and strain rate on the out-of-plane compressive strength. Both the FE simulations and the analytical model suggest a recipe for increasing the through-thickness compressive strength.

Experimental study on temporary fastening damage of composite structures

“…Attwood et al 9 used a high-speed camera to study the impact damage mechanism of laminates with back support, and found that fiber indirect tensile fracture is the main damage mode. Yu et al 10,11 studied the sensitivity of strain rate and curing state to the out-of-plane compression response of laminates. With the increase in the shear strength of the matrix, the through-the-thickness compressive performance of the laminated plate increases, and the sensitivity to strain rate decreases.…”

Perforation of aluminium alloy-CFRP bilayer plates under quasi-static and impact loading

“…If a strategy can be developed whereby CFRP fails by indirect tension rather than by shear plugging, then a major advance could be made in terms of its penetration resistance. Recently, it has been shown that the indirect tension mechanism can be activated in CFRP cross-ply laminates under quasi-static out-of-plane compressive loading [9], indentation loading [10], and ballistic impact loading [10]. The ballistic limit (i.e.…”