Reduced-Volume Fracture Toughness Characterization for Transparent Polymers
Final rept. 1 Oct 2006-30 Nov 2012
DUKE UNIV DURHAM NC
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The research effort has made significant progress, both experimentally and computationally. A consistent approach was established to reliably measure the fracture toughness of very small volumes of transparent engineering polymers, utilizing photo elasticity to minimize the amount of retained stress in small samples and assure local stress concentrations were not affecting the measurements. A unique cohesive zone model was developed to simulate the ductile to brittle failure transition in polycarbonate. The model is formulated so that as rate or stress state changes within a simulation, the fracture energy and thus fracture mode may also change appropriately. The ductile to brittle transition occurs when the cohesive opening rate is greater than a threshold opening rate and when the stress state is close to plane strain in a fracture specimen. These effects are coupled in a phenomenological model, and the transition from slow to fast crack growth can be captured, even as test loading rate andor sample thickness are varied, by using a single set of bulk and cohesive zone material parameters.
- Polymer Chemistry