PSI - Issue 42

T. Vandellos et al. / Procedia Structural Integrity 42 (2022) 50–57 C2 - Restricted Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 6. (a) Load vs displacement curves obtained by the elastic and the ODM models and comparison with the experimental curve. (b) Illustration of the matrix damage state ( dm1 ) and the yarn failure state ( df1t ) on the load displacement curve.

4.2. Influence of the cohesive zone model parameters on the damage mechanisms Two critical failure mechanisms were expected during the four-point bending test : the yarn failure of the CMC substrate and the delamination between the CMC and the bond. In this section, a damage cohesive zone model was added and several studies of influence were performed about the interface properties on the macroscopic behavior. The Fig. 7-a shows that the value of the critical energy release rate G C , defined between 0.1 N/mm and 0.5 N/mm, does not have any influence on the load/displacement curves. On the contrary, the Fig. 7-b shows a strong influence of the interfacial strength σ C : lower the strength is, higher the maximum load is. This observation can be explained by the compliance added in the structure. Indeed, when the interfacial strength σ C decreases, the number of damaged (but not already broken) cohesive elements increases, adding compliance on the structure behavior. As shown in Fig. 8, this compliance decreases the strain level into the element where the CMC breaks first. Therefore, when the interfacial strength is low, a higher loading is needed to reach the yarn failure in the substrate. Finally, we can observe in Fig. 7-b that the macroscopic response becomes similar when the strength values overcome 150MPa. For these values, the critical damage mechanism is the yarn failure of the CMC substrate.

Fig. 7. Influence of the critical energy release rate G C (a) and of the interfacial strength σ C (b) on the load vs displacement curves.