13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- 3 3 3 IC 0 f d G δ τ δ = ∫ (12) where 3τ is normal traction. The final displacements 3 fδ can be obtained as: 3 IC 2 / f G N δ = . Figure 3. Pure Mode I bilinear constitutive law 3. Numerical simulation of DCB specimen The double cantilever beam (DCB) is a standard specimen for mode I fracture and has been widely investigated. In this section, we simulated the DCB test [8] using the proposed interface element and relevant FE model. The specimen is made up of T300/977-2 unidirectional laminates [0]24. The geometry and boundary conditions are shown in Fig. 4 and material properties are listed in Table 1. Figure 4. Geometry and boundary condition for DCB test Table 1. Properties for T300/977-2[8] 11 E 22 33 = E E 12 13 = G G 23 G 150.0 GPa 11.0 GPa 6.0 GPa 3.7 GPa 12 13 = ν ν 23ν ICG N 0.25 0.45 0.352 kJ/m2 60 MPa Figure 5. Irregular mesh for DCB model The FE model for DCB specimen was built with two layers of shell elements at the mid-planes of both beam arms. The interface elements were employed to connect the upper and lower shells except where of pre-crack. The interfacial stiffness was chosen as 6 3 =10 N/mm K . To demonstrate the applicability of the interface element, we established two models with regular and irregular Initial Crack Length：55 mm F F 150 mm 1.98 mm width=20 mm 0 3δ 3 fδ 3 δ N 3τ K 0 (1- )d K Compression Initial Crack Front Initial Crack Region Direction of Crack Growth
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