Linear elastic fracture mechanics general concepts

Our discussion thus far has focused in a rather superficial way on the general evolution of the important area of fracture mechanics. The basic objective of fracture mechanics is to provide a useful parameter that is characteristic of the given material and independent of test specimen geometry. We wUl now consider how such a parameter, such as G (, is derived for polymers. In doing so we confine our discussion to the concepts of linear elastic fracture mechanics (LEFM). As the name suggests, LEFM apphes to materials that exhibit Hookean behavior. 

No crack instability developed in the tests of load vs. crack opening displacement (COD), and all specimens fractured in a ductile manner after general yielding. Neither the concept of linear elastic fracture mechanics (K) nor that of nonlinear fracture mechanics (COD, /-integral) for unstable fracture can be applied to the phenomenon such as a stable fracture of 5083-0. 

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