Controlled fracture in brittle polymers

Knowing a value for the Young s modulus, E, the surface energy y can be found. 

Berry adopted a slightly different approach to evaluate y, and also confirmed the validity of Equation (12.2) for the fracture of PMMA and polystyrene by measuring the tensile strength of small samples containing deliberately introduced cracks of known magnitude. 

Berry s summary of his own results and those of other workers is shown in Table 13.1. The very important conclusion to be drawn from these values for fracture surface energy is that they are very much greater than values estimated from the assumption that the energy 

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