Stress intensity factor, plastics mechanical behavior

Karger-Kocsis recorded the different fracture behaviors of non-nucleated and -modified PP (MFR 0.8 dg min 1) tested in a three-point bending configuration at 1 ms-1 at 23 °C, a-PP was semi-ductile and /3-PP ductile with a plastic hinge at - 40 °C a-PP was brittle, /i-PP ductile [72], The descriptors from the linear elastic fracture mechanics (LEFM), Kq, the stress intensity factor, and Gc, the energy release rate, used to quantify the toughness correlated well with the fracture picture. This conclusion is also valid for... 

Equations (9.14) to (9.18) do not constitute a fracture criterion since they do not specify whether and when material separation in the plastically deformed zone occurs. In order to use fracture mechanics to predict the stability of an elastic-plastic crack, limits of the plastic deformation have to exist and must be known explicitly or implicitly. Understandably the determination, interpretation, and application of critical stress intensity factors for viscoelastic solids is particularly complicated due to the pronounced time and temperature dependence of the mechanical properties of these materials. The fact that a material shows a ductile behavior does not preclude the use of fracture mechanics but it reduces — or even eliminates — the independence of the fracture mechanics functions (G, K, R) from the geometrical parameters [6]. The occurrence of plastic deformation in a material has a threefold effect ... 

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