13th International Conference on Fracture June 16-21, 2013, Beijing, China Where the components can be represented as: S = 4EI l T = 2EI l F = AE l cos2 β+ 12EI l3 sin2 β G= AE l sinβcosβ− 12EI l3 sinβcosβ H=− 6EI l2 sinβ U= AE l sin2 β+ 12EI l3 cos2 β V = 6EI l2 cosβ 2.4. Energy Release Rate With the propagation of crack, it is found the surface energy decreases to form new crack surface. Using the stress intensity factor KI, the potential energy release rate Gcan be calculated as: G= 1−ν2 E K2 I . (10) When considering about double cantilever beam, with the Young’s modulus of E,and the moment of inertial of area as I, and the bending moment Macting on the free edge of the beam, the energy release rate can be calculated as: G= M2 2EI (11) 3. Analysis Model and Analysis method 3.1. Discrete Cohesive Zone Model Consider a linear elastic solid in Fig. 3 with Young’s modulus of E and Poisson’s ratio of ν and established with cohesive zone model in Fig. 4(a). Fig. 4(b) shows the general continuously cohesive zone model, while Fig. 4(c) is the discrete cohesive zone model on the basis of Fig. 4(b) with periodic characteristic length of l. In the periodic structure, set the cohesive zone model with the length of b,and make the last l −b of debonding area. Also in this study, we set b = 1/2l. The small scale yielding condition is assumed and the boundary condition is set with a displacement field of KI = ˙KIt with ˙KI =50GPa√m/s. Using the discrete cohesive model,crack propagation is studied. With the Griffith theory, fracture toughness KIC can be evaluated with surface energyΓas: KIC = √ EΓ 1−ν2 (12) -4-
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