MULTIPLE CRACKING OF A COATING LAYER AND ITS INFLUENCE ON FIBER STRENGTH .1. CALCULATION OF THE ENERGY-RELEASE RATE OF THE FIBER AT CRACKS FOR NONUNIFORM CRACK SPACING

A calculation method to describe the influence of the non-uniform crac k-spacing in a strongly adhering coating layer, which shows multiple c racking, on the energy release rate of a coated fibre is presented and applied to some examples. Four main results were found. The energy re lease rate of the fibre at the crack in the region of narrow crack-spa cing was low. For any crack-spacing, the energy release rate was high when the Young's modulus of the fibre was low and that of the coating layer was high. From the calculation of energy release rates of the fi bre at all cracks, the strength-determining crack could be identified, and from this the fibre strength after multiple cracking of the coati ng layer could be estimated. Finally, the strength of the fibre for no n-uniform crack spacing was lower than that for a uniform one.