PSI - Issue 8

Claudio Fichera et al. / Procedia Structural Integrity 8 (2018) 227–238 Author name / Structural Integrity Procedia 00 (2017) 000 – 000

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Also for the adhesive a power law was used to describe the plastic flow. For the substrate, the previously identified material model is used, whereas for the metal sheet a power law with the following parameters was used from Kalpakjian et al. (2003): plastic hardening constant k = 760 MPa, plastic hardening exponent n = 0.19. The total error obtained between the target and the numerical result is 2.8%. The set of identified parameters for the MS polymer adhesive is reported in Table 2.

Fig. 7. Experimental load-displacement curves (blue) and optimization target (red).

Table 2. Parameters of the power law of the MS polymer adhesive. Parameter (unit) Value Elastic modulus, E (MPa) 3.30 Plastic hardening constant, k (MPa) 5.25 Plastic hardening exponent, n (-) 0.46

4. Design of the prototype

4.1. Geometry

The final design phase consisted of the virtual analysis by FE simulation of the prototype. The virtual analysis is meant to check the validity of the proposed solution in terms of mechanical strength. Mechanical strength will be evaluated by the capacity to sustain the pressure loading due to the refrigerating (glycol) liquid in the under-bonnet heat exchanger. The virtual design procedure consists of the definition of the geometrical model, the implementation of the materials models and the numerical simulation of the whole system considering the loading conditions. The geometrical model of the lower part (polymeric) of the under-bonnet heat exchanger was obtained to be compatible with the space available. In the case of the analyzed application the whole central region of the bonnet is free and, thus, available as area for thermal exchange (about 1.42×10 5 mm 2 ). The lower part of the heat exchanger has been designed from the external geometry of the bonnet itself following the shape of the under-bonnet stiffeners as boundaries for the under-bonnet heat exchanger. The proposed prototype is shown in Fig. 8 as it appears mounted below the bonnet. In Fig. 9 a detailed top and bottom view is shown. It allows the passage of the liquid flow in a vertical space as large as 10 mm in the vertical direction and extending over almost all the internal area. The total volume of the refrigerating liquid containable in the heat exchanger is 7.3×10 5 mm 3 . The component is a thermoformed 3 mm thick ABS shell with the maximum longitudinal size of 825 mm and 205 mm in the transversal direction. The contour bonded area has an average width of 20 mm, whereas internal fixation areas (circular) have a diameter of 10 mm. They connect the lower surface of the bonnet to the rest of the ABS shell by means of frustum shaped supports. The fixation area for the frustum shaped supports is 8.9×10 3 mm 2 and 3.49×10 4 mm 2 for the contour, which means that 31% of the available free area for heat exchanging is exploited for bonding. Finally, at the sides, 12 mm diameter connections for the entrance and exit of the cooling liquid are provided.