Stress-transfer analysis for fibre/matrix interfaces in short-fibre-reinforced composites

In this paper, a simple theory and a special frictional contact element method are used to analyse the stress transfer from matrix to fibre in metal-matrix composites consisting of an aluminium alloy reinforced with short carbon fibres. In the simple theory from shear-lag theory, the influence of stress transfer from matrix to fibre through the end interface between fibre and matrix is taken into account. In the special frictional contact element method, the shear strength and the tensile strength of the fibre/matrix interface are used to judge the slipping or debonding of the interface. The interfacial normal and shear stresses are obtained on the axial interface and the end interface. The tensile stresses at some points on the axial interface and the end interface may cause debonding of the interface and prevent the interface from transfering stress from matrix to fibre. It is found that the end interface between short fibre and matrix is easy to debond in the loading process. After the debonding of the end interface. the stress transfer from matrix to fibre depends on the shear stress on the axial interface only. The influence of stress transfer from the matrix through the end interface is important only for fibres of very short length. The length of a short fibre below which the influence of stress transfer from the end interface is important is found to be 1/d approximate to 3 in the calculation for short-carbon-fibre-reinforced aluminium alloy. In the case where the tensile strength of the axial interface is not small, the contribution of a short fibre to the strength of the composite from the calculation in the paper may be approximately equal to that from shear-lag theory for short fibre with 1/d > 3. The tensile strength of fibre/matrix interface has the same importance as the shear strength of the interface in short-fibre-reinforced composites. (C) 2001 Elsevier Science Ltd. All rights reserved.