Biaxial testing of continuous fibre reinforced aluminium tubes

Abstract

Composite tubes of aluminium and aluminium alloy containing hoop wound alumina (Altex) fibres were fabricated using a liquid metal infiltration method. The tubes were well consolidated, with low porosity, and good bonding between fibre and matrix, as confirmed using ‘rule of mixtures’ calculations of elastic modulus. Mechanical properties were evaluated in the principal directions of the tube under uniaxial and biaxial stress loading conditions, and damage modes were studied. Stress quarter diagrams were constructed on the basis of a maximum stress failure mechanism, and failure envelopes were produced using the measured values of yield stress and failure strength. The composition and condition of the matrix was shown to influence the shape of the failure envelope and, in turn, the mode of failure of the tube for a given biaxial stress ratio. Good correlation was obtained between predictions made from the stress quarter diagrams and the fracture paths observed in tested tubes.