13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- Figure 1. J vs. |A2| with Material Failure Curve and Crack Driving Force curve (left) and comparison of constraint levels (right) The J vs. |A2| plot can be used to predict failure of components when the Crack Driving Force curve is added. The Crack Driving Force curve is a plot of multiple (J, |A2|) pairs at any applied load, not just at the critical values. The intersection of the Material Failure Curve and the Crack Driving Force defines the critical J value (Jc) at which cleavage fracture will occur and can be used to predict the load at failure. The J vs. |A2| plot can also be used to determine the constraint effect of specimens with different geometries and loading configurations. An example is shown in right diagram of Fig. 1. Crack Driving Force curves for 3PB specimens are shown on the J vs. |A2| plot. Specimens with deep cracks are high constraint specimens and typically exhibit lower fracture toughness than shallow cracked specimens. It should be noted that constraint is a relative term. A2 provides a quantitative measure of constraint, although the magnitude of A2 is of little value. The A2 value of one specimen is simply compared to the A2 value of other specimens to determine if there exists “loss of constraint” or, rather, an increase in fracture toughness. 3. Fraunhofer Experimental Data 3.1. Background A set of published results to which the J-A2 method could be applied were found in journal articles [10, 11] published by a team of researchers from the Fraunhofer Institute for Mechanics of Materials. These specimens and results presented in the article will be hereinafter referred to as the “Fraunhofer” specimens and results. The goal of the Fraunhofer research was to determine the fracture toughness of a variety of cracked specimens. Specimens were tested over a wide range of lower shelf temperatures. Many trials with 3PB, C(T), and cruciform specimens were conducted at -85°C. The Fraunhofer cruciform specimen is shown below in Fig. 2. The cross sectional area of the small-scale cruciform arms
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