PSI - Issue 51

Hugo Vidinha et al. / Procedia Structural Integrity 51 (2023) 9–16 H. Vidinha et al./ Structural Integrity Procedia 00 (2019) 000–000

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4. Results and discussion The correlation between the numerical model and the experimental data in terms of stress-strain relationship is shown to be quite accurate. The tensile testing experiments revealed an average failure load of 9.2 kN. Regarding the numerical results, fibre failure is commonly referred to as the ultimate failure of fibre-reinforced polymers. Therefore, in the numerical model, the failure was assumed to occur when the fibre fracture crossed all the specimen width, in all plies with the fibre having the same direction as the force, accompanied by a sudden escalation of the displacement. Based on these assumptions, as can be seen in Table 1, the numerical model predicted the failure for a maximum force of 9.7 kN, which represents an error of 5.1% relative to the average experimental results. Regarding the displacement at failure, the simulations are also close to the experimental values. The average difference was lower than 15%.

Table 1. Maximum load and displacement at failure (experimental results versus numerical simulations). Type of analysis Maximum load (kN) Maximum displacement (mm) Experimental tests (average) 9.2 2.8 Numerical simulation 9.7 3.2 Difference (%) 5.1 13

15000

7500

 I [  m/m]

(a )

0

15000

7500

 I [  m/m]

(b )

0

Fig. 2. Comparison between the first principal strain (  I ) fields obtained (a) experimentally and (b) numerically for an applied load of 4.875 kN.

The strain field predicted by the simulation is compared side-by-side with DIC measurements in Fig. 2. In this analysis, the comparison is carried out by means of the first principal strain (  I ) field evaluated at the specimen surface. Overall, the predicted full-filed strains agree very well with the DIC measurements. Regarding the strain contours and the strain profiles, it can be observed that the results are considerably precise and similar. Additionally, it is interesting to note that, although during the tensile tests, the loads are uniformly applied on the external surfaces of the specimen, the experimental results (see Fig. 2(a)) show that the first principal strain field at the hole surface is not symmetrical. The combination of the Puck’s failure criterion along with the Element Weakening Method was able to predict this asymmetrical behaviour, as can be seen in Fig. 2(b), which is likely to be caused by the lamina arrangement. In terms of the damage development, the fatigue testing campaign carried out by Gonçalves (2019) for the same geometry and composite material shown that the hole’s borderline is where the cracks start to spread. Fig. 3 and Fig. 4 represent the IFF and FF progression at different plies for different loading levels, respectively. The loading