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.