Abstract
The interest in obtaining a standard method of measuring the fracture toughness of polymers is related. Descriptions are given of previous failed attempts. The crack layer model originated by Chudnovsky is outlined. It is noted that this model has been shown to accurately imitate slow crack growth in polymers. The equations of the crack layer model are used to perform a numerical simulation of a single edge notch specimen loaded under displacement control, for each of three values of the displacement rate. A load vs. displacement curve is generated from each simulation. Each curve is used to calculate the JR curve and Ji c, according to ASTM E8 13-81. Each JR curve is shown to be different from the other two curves, and each value of Jic is shown to be different from the other two values. The following proposals are then made. The JR curve and Jic are rate dependent, and so cannot be material properties. The JR curve and Jlc are not measures of material fracture toughness, and no universal measure of material fracture toughness exists. Along with material properties, fracture toughness depends on the specific conditions of usage, i.e., specimen geometry and type and magnitude of loading. The material properties, specimen geometry, and loading type and magnitude, are all specified for each numerical simulation of crack growth using the equations of the crack layer model. For an individual set of these toughness parameters, a numerical simulation can provide a measure of fracture toughness in the form of the time to failure, or lifetime.
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