Fracture energy damag mechanisms

In short fiber composites, energy absorption mechanisms, such as interfacial debonding and matrix cracking, most often occur at the fiber ends (Curtis et al., 1978). The damage model proposed by Bader et al. (1979) assumes that short fiber composites fail over a critical cross-section which has been weakened by the accumulation of cracks, since the short fibers bridging this critical zone are unable to carry the load. In fatigue loading, sudden fracture takes place as a direct result from the far-field effect of the composite, rather than due to the near field of the crack tip... 

The actual contribution of this microfailure mechanisms to the interlaminar fracture energy of the composites tested under particular conditions are a function of the number of events taking place, the real area of fracture surface formed, and the size (length and width) of the damage zone (DZS) around the main crack. The larger the latter becomes the more side cracks have to be expected, and the more energy is consumed by plastic deformation of the polymer matrix material. 

Some of the more important methods of failure studies include stress-strain, impact loading, and fatigue. Creep and stress relaxation (Chapter 10) may cause serious damage to engineering materials, but they normally do not result in fracture per se except for creep rupture. Emphasis in this chapter will be on the study of fracture energy, kinetics of crack growth, and molecular mechanisms. The reader is directed to Chapter 13 for a fuller discussion of plastic toughening. 

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