DAMAGE-TOLERANT FATIGUE DESIGN IN METAL-MATRIX COMPOSITES

Damage tolerant fatigue design in MMCs relies on the assessment of ini tial and final damage states and on the determination of damage accumu lation rates. Fibre reinforced MMCs tend to have inherent manufacturin g defects in the form of micro-cracks or broken fibres due to the rela xation of matrix residual stresses and due to machining. For most mate rials the final outcome of damage accumulation is either crack arrest or failure. In MMCs however, another type of damage accumulation is th e unstable crack growth which can be considered as an alternative fail ure condition. The domains of these three damage zones and the bounds for arrest, failure and unstable crack growth are established within t he confines of a damage map. Within these bounds, fatigue damage accum ulates at a rate dictated by the degree of fibre bridging, fibre/matri x debonding and fibre failure. A micro-mechanical model for crack prop agation which incorporates explicitly these mechanisms is presented an d used to estimate a practical limit of failure-safe fatigue crack gro wth for a SCS6/Ti-15-3 composite. (C) 1997 Elsevier Science Limited.