PSI - Issue 64

Quentin Sourisseau et al. / Procedia Structural Integrity 64 (2024) 893–900 Quentin SOURISSEAU/ Structural Integrity Procedia 00 (2019) 000 – 000

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The geometries and boundary conditions of each fracture mechanics test are presented in Figure 5. The inserted Teflon was simulated using contact (green lines in Figure 5). Contact surfaces were applied with default parameters from FEMAP SOL402 and no friction was used. In the case of MMB setting, the beams of the test bench were modelled using rigid elements. 3.2. Obtained cohesive zone model parameters It was then possible to determine the final parameters of the cohesive law in mode I, mode II and the coupling parameter that is used for the case of mixed mode in FEMAP SOL402, Siemens (2019). This was done minimizing the difference between the experimental and numerical curves of the force against the displacement, and adopting the experimental values of critical toughnesses in mode I and II. Those parameters are given in Table 2. It can be observed that, in mode I, the critical stress and the stiffness values seem to be dominated by the matrix/resin’s properties whereas, in mode II, the fiber reinforcement seems to have a large influence on both the critical stress value and the stiffness. It is important to note that those parameters are also closely linked to the way cohesive elements are implemented in FEMAP SOL402. Table 2: Cohesive zone models parameters obtained for the equivalent interface using the developed methodology. Mode Fracture toughness (kJ/M²) Critical stress (MPa) Stiffness (MPa/mm) Coupling parameter I 1.74 2 1000 0.6 II 1.46 23 158000

4. Comparison of the developed design approach and real scale experimental testing 4.1. Large size samples

In order to assess the validity of the developed approach, large size samples were realized. Their geometry is given in Figure 6. A scarf at the edges of the patch is done in order to decrease edge stress concentrations. In Figure 6, the green/grey/blue/dark grey colored layers correspond to the glass and carbon fibers plies at a given angle (from 0° to 90°). Finally, the orange layer corresponds to the steel substrate. It should be noted that the two upper fiber glass plies are only there to protect the carbon part of the patch from external aggressions.

Fig. 6: Stacking of the plies for the production of the FRP patch bonded to the large specimens.

The chosen manufacturing process for the realization of the patches is based on the method of impregnation by infusion. Consequently, a complete FRP patch (1m wide and 1.4 m long) was realized on a steel plate (1.5 m wide and 2m long. The surface preparation was the one defined in Sourisseau et al. (2023). The used resin is a post-cured epoxy resin in accordance with the provider ’s recommendations. The steel plate has a high elastic limit (900 MPa) to