PSI - Issue 79

H.G.E. da Silva et al. / Procedia Structural Integrity 79 (2026) 97–104

103

1.8

1.8

1.5

1.5

1.2

1.2

P m

0.9

0.9

P [kN]

P [kN]

0.6

0.6

0.3

0.3

0

0

0

0

1

2

3

4

5

6

7

8

9 10

1

2

3

4

5

6

7

8

9 10

δ [mm]

δ [mm]

a)

b)

P2

P4

P3

Numerical curve

P5

Numerical curve

Fig. 9. Experimental and numerical P -  curves for configuration 1 (a) and configuration 2 (b).

Table 6. Numerical and experimental values of τ and σ for each configuration during 4PB

Configuration

τ (MPa) 1.36 1.37 1.38 1.73 0.32% 25.47%

σ (MPa)

Numerical value

64.94 63.93 1.56% 65.66 60.60 7.71%

1

Avg. experimental value Relative difference Avg. experimental value Relative difference Numerical value

2

By analysing the obtained results, it can be concluded that, apart from minor experimental variations, stresses are similar between tested configurations. The numerical results show that configuration 2, corresponding to skins with glass fibre layers at 0˚/90˚, achieved slightly higher τ and σ stresses than those of configuration 1. It can therefore be concluded that, as long as the 0˚ layer in contact with the punch does not rupture, the difference between the orientation of two intermediate layers of the laminate does not make a significant contribution to the overall behaviour of the laminate. When comparing the numerical and experimental τ and σ , it is clear that configuration 1 showed a smaller difference between the experimental and numerical values. For configuration 1, relative errors of 0.32% and 1.56% were obtained between the numerical and analytical values of τ and σ , respectively. In configuration 2, the relative errors were higher. Between the numerical and experimental values of τ and σ , the errors were 25.47% and 7.71%, in the same order. When comparing the values of the Tsai-Wu criterion between configurations (Fig. 7 (a) for configuration 1, and Fig. 7 (b) for configuration 2) it can be seen that in configuration 2 the laminate is closer to failure than in configuration 1. The stresses in the core are similar between the configurations. Fig. 10 shows a summary of experimental and numerical P m and δ rot . Most of the experimental values for P m and δ rot were higher than the numerical values. There was only one exception, namely specimen 3 of configuration 1 (P3_1), which suffered early failure.

1050 1200 1350

0 1.5 3 4.5 6 7.5

0 150 300 450 600 750 900

P m [N]

δ rot [mm]

a)

b)

Fig. 10. P m (a) and  rot (b) comparison graph.