The Fracture Properties of High Strength Aluminium Casting Alloys

  • Philip E. Holden

    Student thesis: Doctoral ThesisDoctor of Philosophy

    Abstract

    The fracture properties of a range of high strength aluminium casting alloys, in various heat treated conditions, have been investigated
    in three point bending.

    Sharp cracks, necessary for fracture toughness testing, were produced by both fatigue cracking and spark machining and the compatibility
    of the two methods has been discussed. Stress intensity factors were determined for the curve crack fronts from experimental compliance data and a practical method of dealing with crack front
    curvature, has been proposed.

    The five available methods for determining the critical stress
    intensity factor (K1c) have been evaluated and their accuracies and
    limitations discussed. In order to measure the load-point displacements of the specimens, a rig, considered to be an improvement on existing rigs, has been developed. Initiation of the cracks was detected using an electrical potential techniaue, which could also be used to determine crack growth rates and predict crack lengths. Geometrical effects on the stress intensity factor, such as blunt
    notches and short cracks emanating from the roots of blunt notches,
    have been assessed and are compared with the theoretical solutions. Structural influences on the stress intensity factor, such as
    material condition and porosity, have also been investigated.

    The data collected from the majority of the specimens was tabulated, punched and fed into a computer programme designed to
    calculate the fracture toughness parameters. The results have been
    presented graphically and analysed statistically using standard analysis of variance packages. Optical and electron microscopy has been used to examine the fracture surfaces and an explanation of the mechanism of fracture has been suggested for each alloy.
    Date of Award1979
    Original languageEnglish
    Awarding Institution
    • Aston University

    Keywords

    • fracture properties
    • high strength aluminium casting alloys

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