PSI - Issue 72

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

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loads, which will cover the core with low specific weight and stiffness (Lacy and Hwang 2003, Magnucki et al. 2020, Upreti et al. 2020). This structure has advantages such as high specific stiffness and strength, corrosion resistance, and low thermal and acoustic conductivity (Upreti et al. 2020, Mohammadkhani et al. 2021). Nowadays, sandwich structures are found in aircraft (stabilizers, flaps, wing boxes, radome, and fairings), helicopters (skins, mechanical parts, and rotor blades), and ships (e.g., hull and deck). Since these structures have a high responsibility, it is necessary to have strength prediction methods that can reproduce their mechanical behavior in service. The finite element method (FEM) is currently integrated into simulation software, which makes it easier to carry out modelling and simulations. For damage modelling, CZM are a powerful technique, whose concept was proposed by Barenblatt (1959, 1962) and Dugdale (1960) to specify damage for static loading in the crack initiation zone. Damage criteria are used to simulate the behavior of different materials. In ceramics, Wang et al. (2019) used the brittle cracking criterion for foams, and Mostafa et al. (2014) applied the crushable foam criterion. To simulate the behavior of the adhesive, Thiagarajan and Munusamy (2020) used the CZM approach. The failure criteria for the laminates include the Hashin criterion to model fiber failure, the Puck criterion for matrix failure and the Tsai-Wu criterion for the layer (Gupta et al. 2017). Farrokhabadi et al. (2020) experimentally and numerically analyzed the behavior of a multilayer sandwich panel with glass fiber fabric laminates and a corrugated core. The Hashin- Puck’s and Puck and Schurmann criteria were used to predict the onset of damage to account for the non-linear response of materials. The separation between the skins and the core was modelled using a triangular CZM. It was possible to accurately replicate the experiments. Gao et al. (2020) investigated sandwich structures with continuous glass fiber reinforced polypropylene laminates and a polypropylene core. The Hashin failure criterion was used. The models were positively validated through experimental tests. Djama et al. (2020) studied a sandwich structure with a glass fiber reinforced truss core, focusing on its influence on the sandwich structure. First, the structure’s components were tested experimentally and then the Hashin criterion was used to numerically model the skins. When comparing the values obtained experimentally in the compression, shear and bending tests, stiffness errors of 13.02%, 6.06% and 12.35%, respectively, were estimated. This study addresses the behavior of sandwich structures under 3PB tests. Experimental tests were conducted to obtain the P - d curves. Two material configurations were evaluated for the composite skins, while PMI foam was considered for the core, and SikaForce ® -7710 L100 adhesive to bond the skins with the core. The numerical models involved CZM for the adhesive, the crushable foam model for the core, and the Tsai-Wu criterion for the skins. 2. Materials and methods 2.1. Sandwich test geometries and materials Two different configurations (skin layups) of sandwich structure were studied using the same materials. Initially, quadrangular sandwich panels were manufactured with edge size of 300 mm, which were cut to obtain specimens of 250 mm in length and 36 mm wide, meeting standard’s requirement ( b >2× h ; b is the width and h the height). Fig. 1 (a) represents the sandwich dimensions, and Fig. 1 (b) shows the 3PB configuration according to the ASTM C393 standard. In addition, the compressive test was carried out to the core material using the ASTM C365 standard.

b) ☺ Fig. 1. Sandwich structure geometry (a) and 3PB test configuration (b).

a)

The laminates were manufactured using unidirectional (UD) carbon fiber prepreg plies (HS 160 REM from SEAL ® ) and balanced bidirectional (0˚/90˚) glass fiber prepregs (EE300 ET445) from CIT - Composite Materials (Italy). The