Mechanical behaviour of rigid-rod polymer fibres: 2. Improvement of compressive strength

Under axial compression, both poly( p-phenylene benzobisoxazole) and Kevlar® fibres fail by buckling of fibrils located just beneath the outer surface where lateral constraint is minimal. As the fibrils cascade buckle through the bulk of the fibre, a kink band is formed. A thin, well-adhered high-modulus ceramic coating on the surface increases the axial compressive strength by restraining the fibrils against buckling and kink band initiation. Compressive strength improvement is a function of coating thickness. The coating also reduces the radial thermal expansion coefficient in accord with finite-element predictions.