PSI - Issue 27

Tuswan Tuswan et al. / Procedia Structural Integrity 27 (2020) 22–29 Tuswan et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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sandwich ( A total ). In this research, the debonding ratio is assumed by 5%. The analysis is conducted by using different debonding shapes with the same debonding ratio, as depicted in Fig. 2. In the present investigation, to model the debonding problem in finite element software, two different simplified modeling strategies can be adopted, namely, the spring contact model and assumed as a void without applying spring contact element (Burlayenko and Sadowski, 2009). In the term of debonding modeling, several assumptions are used: firstly, debonding is modeled as artificial damage embedded into interface region between the faceplate and the core material. Secondly, the spring contact element in the debonded region is applied between two nodes. Next, debonding is assumed to be determined before the vibration begins and to be constant during vibration. The shape of the debonded region is idealized with different regular shapes. Fig. 2 shows the variation of debonding shapes. The similar debonding modeling technique is also introduced previously to investigate debonding behavior in the car deck panel (Tuswan et al., 2020). The debonding is treated as an artificial imperfection at the interface layer between two consecutive layers and activated before the oscillation is carried out. During the preprocessor, the debonded region is modeled by creating a small gap between the faceplate and the upper surface of the core material in the bottom sandwich. The small gap is assumed by creating 10% of core thickness (0.015 mm). To prevent the probability of the two surfaces overlapping each other, a spring contact element is applied. In (ABAQUS, 2014), the spring elements (SPRING2) are used to connect the core and the outer faceplate nodes. Another modeling technique is assumed by removing the spring contact element in the debonded region and assuming as avoid. The detailed spring element modeling and its constitutive modeling is wholly illustrated in Fig. 3. To model spring element behavior, as illustrated in Fig. 3b, the spring stiffness is set to zero (k=0 N/m) when in tension and is set to a high value ( k = 210x10 9 N/m) when in compression and the displacement value between two nodes in the spring element is zero. In fact, there is no literature which states the spring stiffness value of the interface layer of the proposed sandwich material type. So, the spring element behavior is assumed to have similar spring stiffness, as stated in (Tuswan et al., 2020). In Tuswan et al. (2020) the contact behavior is assumed by the free debonding model with setting a zero stiffness (k=0 N/m) to the spring elements so the interfaces can move freely, while a nonzero stiffness value ( k =210x10 9 N/m) causes the constrained debonding model between them that restrains the faceplate and the core from moving together (Pardoen, 1989). In the model, both the geometry and material behavior are set to constant during oscillations. For modeling outside the debonded region, the tie constraint based on surface-surface contact is used.

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Fig. 2. Damaged ramp door with different debonding shapes (a) circular, (b) through-the-width, (c) through-the-length, and (d) square.

Spring element

Debonding region

Small gap between 2 nodes

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Fig. 3. (a) Debonding modeling with spring element, and (b) the constitutive law of spring element.