MANUFACTURE AND EVALUATION OF HOOP-WOUND FIBER-REINFORCED ALUMINUM-ALLOY TUBE

A composite tube, consisting of aluminium-magnesium-silicon alloy (606 1) reinforced with hoop-wound lumina-based fibres, has been manufactur ed by using the method of liquid metal infiltration. The composite was well-consolidated with a good bond between the fibres and the matrix, as evinced by the close similarity between measured values of modulus and 'rule of mixtures' calculations. Although some matrix magnesium w as absorbed in the fibre surface regions during processing sufficient remained in the matrix to effect a significant precipitation-hardening response upon heat treatment. Mechanical measurements were carried ou t on the tube to determine properties in the principal directions. The tests involved internal pressurisation to produce a tensile stress pa rallel to the fibre direction, axial tension to create a stress perpen dicular to the fibres, and internal pressurisation to give a hi-axial tensile stress state. Stress-quarter diagrams were constructed by usin g experimental values of yield stress and failure strength to produce failure envelopes. Failure under the different stress conditions and t he microstructure of fracture surfaces correlated well with prediction s from the stress-quarter diagrams. Heat treatment affected the type o f failure mode for a given bi-axial stress ratio and this was reflecte d in the shape of the failure envelope. The results also indicated a s mall, but measurable, bi-axial strengthening effect in these materials . In conclusion, the correlation between the failure-envelope construc tions and the fracture path observations is considered justification f or using a maximum stress-failure approach when designing with this co mposite material in the bi-axial stress condition. (C) 1998 Elsevier S cience Limited. All rights reserved.