Abstract: In the present study a formula is proposed to predict the fatigue life of the composite which is made of the matrix of bismi-limide and unidirectionally reinforced by 66% T-300 carbon fibre by volume. All fatigue tests were carried out at stress ratio R=0.1 and f=5 Hz and the endurance limit was determined by up-down method. Test results show that the fatigue life of this composite approximately follows log-normal distribution and that the endurance limit is about 70% of the ultimate stress. The fatigue life test results can be well expressed by the follwing expression: Nt = A' (σmax -σc)-2, where A' may be referred as the fatigue resistance coefficient approximately equal to the square of ultimate stress of this composite? A' = 1.78×106 MPa, and σc may be defined as the theoretical endurance limit, σc=922MPa. Besides, the mechanism of fatigue damage of this composite was also observed and analysed.

Key words: composite fatigue life, endurance limit, mechanism of fatigue damage