Fracture mechanics of plastic-fiber composites

The concept of fracture mechanics is introduced to characterize the toughness of fiber-reinforced composites which should be distinguished from tensile strength. A material may have a high tensile strength but a low toughness meaning that it has a low resistance to crack extension. Depending on the analytical model used, the same experimental data may report different fracture toughness values. In general, the combination of crack propagation in directions parallel and perpendicular to the fibers makes the composite problem very difficult to analyze.Composites with well-aligned fibers are more susceptible to crack propagation parallel than perpendicular to the fibers and can be analyzed with a reasonable degree of accuracy by using the existing K_c or S_c-theory in fracture mechanics. The K_c-theory is used primarily in laboratory testing where the load is aligned normal to the crack plane whereas the S_c-theory is not subjected to such a restriction. The K_c or S_c values for several composites are reported and applied to solve various example problems illustrating the advantage of fiber reinforcement.