13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- ϕ r Crack tip Ω [u]1 [u]2 x1 x2 (r,ϕ) (ξ,+π) (ξ,- π) Figure 2. Relative displacements of crack lips In Eqs. (1), (2), (3) and (4), ( ) r,j are the polar coordinates, k is the constant of Kolossov, Ac a are the weighting coefficients relative to opening mode (α=1) and shear mode (α=2) and ( ) 1 2 T ,T ,R are the rigid body motions. From Eqs. (4), the CRDF can be determined without an explicit knowledge of the material elastic properties. Moreover, this initial step aims to accurately characterize the kinematic state of the crack. 2.2. Stress Intensity Factor evaluation from numerical analysis In fracture mechanics, the stress state definition in the crack vicinity is expressed in terms of Stress Intensity Factor (SIF) ( ) Ks a . As previously mentioned, the experimental test is conducted under displacement control, while the numerical model is loaded by imposing an equivalent force. In this case, SIF amplitude depends solely on model geometry, crack length and the force loading value. The definition of these factors implies developing a classical finite element model (Figure 3). F Arcan fixtures Figure 3. Finite element model
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