PSI - Issue 72

H.G.E. da Silva et al. / Procedia Structural Integrity 72 (2025) 26–33

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-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 σ y / τ avg x/L Upper Skin Lower Skin

0.5

0

-0.5

σ y / τ avg

-1

-1.5

-2

-2.5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x/L

Upper Skin

Lower Skin

a)

b)

Fig. 4.  y stress distribution for configuration 1 during 3PB test.

Evaluating sandwich core stresses, Fig. 5 (a) and (b) present Von Mises stresses distribution at P m in the upper skin subjected to the punch load, for configuration 1 and 2, respectively. Analyzing the figures extracted from the numerical analysis, it was observed that configuration 1 endures higher Von Mises stresses than configuration 2 (8.40%). This difference relates to the orientation of the reinforcement material applied in the different configurations.

a)

b)

Fig. 5. Von Mises stresses extracted in the skin during 3PB test: a) for configuration 1 and b) for configuration 2.

3.3. Failure mode comparison The numerical analysis indicates that sandwich failure occurs upon core failure. Therefore, to this end, the loading instant for which the numerical  xy stress of the core equals the experimentally obtained average compressive stress of the core, was analyzed. Fig. 6 (a) presents the Tsai-Wu criterion for the skins and Fig. 6 (b) the  xy stress in the core, at the P m loading instant. For configuration 1, during 3PB testing, it is visible through the Tsai-Wu criterion (Fig. 6 a) that in the punch zone, a small skin portion reaches 3.02 and since its higher than 1 the skin layer fails. In addition, the foam core (Fig. 6 b) fails since it reaches the determined experimental shear stress value of 1.26 MPa. Fig. 7 (a) and (b) present the Tsai-Wu criterion for the skins and  xy stresses in the core in the 3PB tests, respectively, for configuration 2. For the Tsai-Wu criterion, at the punch location, a small skin portion reaches 2.98 and, thus, the skin layer fails. In Fig. 7 (b), since  xy stresses reached 1.26 MPa it is observed that the core fails.

a)

b)

Fig. 6. 3PB tests results for Configuration 1: a) Tsai-Wu criterion results extracted in the skin and b)  xy stress retrieved on the sandwich core.