Abstract
The mixed mode loading configuration occurs in many civil engineering and mechanical applications. In wood material, the study of this problem is very important due to the orthotropic character and the heterogeneity of the material. In order to study the mixed mode loading in wood material, Moutou Pitti et al [1] have proposed a new specimen called Mixed Mode Crack Growth (MMCG). The main goal of this geometry is to propose a decrease of the energy release rate during the crack growth process. In this case, the fracture parameters can be decoupled into Mode I and Mode II in order to determine the impact of time during creep crack test. The present work proposes to study the crack path stability in MMCG specimen for different sizes and thicknesses. The M? integral, combining real and virtual mechanical displacement fields is used in order to separate numerically mode I and mode II in the mixed mode ratio. The stability is shown for the opening mode (Mode I), the shear mode (Mode II), and the mixed mode of 15°, 30°, 45°, 60°, 75° by computing the energy release rate versus the crack length. Finally, it is shown that the MMCG specimen can be reduced in various shape and used for example in small climate chamber in order to perform creep test at different temperature and moisture content levels.
Highlights
Civil engineering and mechanical structures are usually submitted to mixed mode loading
Moutou Pitti & al [1] have proposed new specimen for mixed mode fracture of wood called Mixed Mode Crack Growth (MMCG), Fig. 1 (c). This specimen is a combination of a modified Double Cantilever Beam (DCB) developed by Dubois, but just usable in opening mode [2], Fig. 1 (a), and a Cantilever Tension Shear (CTS) specimen developed by Richard [3,4] and used by Ma and Zhang for metallic material [5] and adapted by Valentin and Caumes for timber material [3], Fig. 1 (b)
ADesign and geometry s described in introduction, the Mixed Mode Crack Growth (MMCG) specimen is a combination between modified DCB and CTS [1]
Summary
Civil engineering and mechanical structures are usually submitted to mixed mode loading. In order to know the real impact of time effects on the damage process during creep crack growth tests, it is necessary to separate fracture effects and time effect In this case, Moutou Pitti & al [1] have proposed new specimen for mixed mode fracture of wood called Mixed Mode Crack Growth (MMCG), Fig. 1 (c). I n this section we present the path integral which enabled us to obtain the energy release rate G under mixed mode solicitation. M and Mθ integral M-integral is an energetic approach that allows studying stress field around crack tip It is developed by Chen and Shield [8] in order to separate mixed mode fracture [8] and is a combination between real and virtual strain fields which enables computing fracture parameter. We can compute the energy release rate for each mode by combining expressions (4) and (5) according to real intensity factors:
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