13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- necessary to solve the two-parameter J-A2 equation (Eq. 4) are provided in tables developed by Chao et al. [13]. 3.3. Finite Element Analysis Models The FEA models developed using Abaqus [14] for the 3PB and 1T C(T) specimens are shown below in Fig. 3. Figure 3. FEA mesh for Fraunhofer 3PB specimen (left) and 1T C(T) specimen (right). Both meshes are composed mostly of eight node CPE8R quadratic plane strain elements, The extremely fine mesh around the crack tip includes elements with width of 0.001mm necessary to capture A2 within the range of 1 < r/(J/σ0) < 5. The innermost ring of elements at the crack tip is comprised of eight node wedge elements with collapsed nodes at the tip to allow for blunting of the crack and large scale deformation. The Fraunhofer cruciform is a small scale specimen. The overall dimensions are 90 mm x 90 mm. The specimen is machined with a shallow crack such that the crack depth ratio a/W = 0.08. The cruciform is tested in a five point bending configuration. In addition, two of the roller supports can be adjusted to allow for varying biaxiality ratios. However, only 1:1 biaxial loading was tested at the -85°C test temperature. Figure 4. FEA mesh for Fraunhofer cruciform specimen The cruciform specimen mesh shown in Fig. 4 contains 20,174 elements composed mostly of 20 node quadratic hexahedral C3D20R 3-D stress elements with a focused mesh around the crack tip. Elements in the focused mesh region are as small as 0.001 mm in order to capture the stress field in the region of cleavage fracture as defined by the RKR model. The average fracture toughness (Jc)
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