This research program focuses on a hybrid experimental and numerical approach to identifying the mechanical state in the vicinity of a crack. The digital image correlation, as corrected by interpolating a theoretical displacement field, enables determining the crack opening intensity factors representative of the kinematic state of crack lips. A finite element model is introduced for calculating stress intensity factors. The parallelism derived from the DIC method and FEM approach is presented by means of a specific identification algorithm that allows computing the energy release rate within a common finite element mesh. This algorithm is then illustrated by testing the opening-mode configuration for a PVC sample.
Abstract. Usually the element of real structures is subject of the mixed mode loadings. This fact can be explained by the elements geometry and the loading orientations. In this case the propagation of the eventual cracks is characterised by the mixed mode kinematics. In order to characterize the fracture process in mixed mode it's necessary to separate the fracture process in order to evaluate the influence of each mode. Our study is limited to plane configurations. The mixed mode is considered as an association of opening and shear modes. The mixed mode fracture is evaluated trough the experimental tests using the SEN specimen for different mixed mode ratios. The fracture process separation is operated by the invariant integral Mθ. Moreover, our study regroups an experimental and a numerical approaches.
Invariant integral. Mθ θ θ θ integralThe real structures are subject to complex loadings and the fracture process, which is characterised by mixed mode kinematics. In this case, in order to characterise the influence of the fracture mode on the crack propagation kinematics it is necessary to separate each fracture modes. In our study, the analyse is to plane configurations and the body is loaded in opening and in shear mode.According to a finite element approach, the mixed mode fracture separation is usually obtained by using an invariant integral Mθ [1,2]. Mθ integral involves the use of virtual displacement fields (ν i ) and virtual stress tensors (σ ij (ν) ) in accordance with the virtual work principle [3,4]. For plane configurations, the Mθ form is recalled in the next equation in which Ω designates the surface domain ( Figure 1):
In this paper a new formalism based on the complementarity between the optical full field techniques and integral invariant Mtheta is proposed in order to evaluate the fracture parameters in cracked specimen made of wood, under mixed mode loadings. The coupling between the experimental and numerical approaches allows identifying the fracture parameters in terms of energy release rate without any the material elastic properties such as the elastic modulus and the Poissons ratio. The proposed formalism allows also determining, in addition with the fracture parameters, the local elastic properties in terms of reduced elastic compliance. The fracture mixed mode tests are realized using a Single Edge Notch sample made in Douglas with the Arcan fixtures and dried to 11% moisture content and the crack is cutting in Radial-Longitudinal system.
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