Chapter 6 - Interface mechanics and fracture toughness theories

Abstract

This chapter deals with the theory of interface mechanics and fracture toughness. The term fracture toughness refers to the work dissipated in creating new fracture surfaces of a unit nominal cross-sectional area or the critical potential energy release rate of a composite specimen with a unit kJ/m2. Fracture toughness is also measured in terms of the critical stress intensity factor, based on linear elastic fracture mechanics (LEFM) principle. The various micro-failure mechanisms that make up the total specific work of fracture or fracture toughness are discussed. Theories for both elastic modulus and strength of composites are developed, and the factors governing these fundamental mechanical properties are described. Many theoretical and experimental studies carried out on the fracture behavior and toughening mechanisms in fiber reinforced composites are summarized. The chapter also discusses that composites made with brittle fibers and brittle matrices can exhibit high fracture toughness when failure occurs preferentially along the interface before the fibers fracture.