Damage Tolerance in Advanced Composite Materials

Investigations have been made into the residual strengths of a number of composite laminates that had machined. notches or had been damaged by foreign object impact. The laminates contained carbon, polysramid or glass fibres in epoxy resin matrices and had 0/90, 0/±45 or 0/90/±45 lay-ups. Fracture mechanics could be applied readily to the laminates with fracture toughnesses less than 25 MNm -3/2 but, for tougher laminates, corrections wepe needed to allow for the size of damage zones at the tips of notches. The size of the damage zone depended on the interfacial bond strength, the lay-up and the ply thickness as well as the fibre and matrix properties. The correlation between impact resistance and. fracture toughness is discussed.