13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- tests were performed by using a universal tension-compression test machine under displacement-control condition with a loading rate of 0.05 mm/min. The load-displacement curves recorded during the fracture tests were all linear and the specimens fractured suddenly. Therefore, the use of a brittle fracture criterion based on the linear elastic fracture mechanics (LEFM) is permissible. The mean values of fracture loads (F) recorded by the test machine are presented in Table 2, for each specimen. A review of Table 2 shows that the fracture load increases when the loading conditions change from pure mode I (β=0) towards mixed mode I+II. Furthermore the fracture load enhances for larger notch tip radii, regardless of the mode mixity. Figure 1. Geometry of the specimens (all dimensions in mm) 3. SED criterion In order to estimate the fracture load in notched graphite components, engineers need an appropriate fracture criterion developed based on the mechanical behaviour of material around the notch tip. In this section, a strain-energy-density based criterion is described by which the fracture loads obtained from the experiments can be estimated very well. ρ a=10 β W=50 H=200 Thickness t=10 mm θ0
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