PSI - Issue 33

R.F.P. Resende et al. / Procedia Structural Integrity 33 (2021) 126–137 Resende et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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2.2. SLJ geometry This work was based on the SLJ geometry and four overlap lengths ( L O ). These spanned from 12.5 mm to 50.0 mm, with increments of 12.5 mm. Fig. 1 details the main geometric parameters of the joint: total length ( L T ), adherend thickness ( t P ) and adhesive thickness ( t A ). The specimens’ width ( B ) was fixed at 25 mm. The structure is clamped at one edge and, at the other edge, a displacement is applied, and the edge is transversely fixed.

Fig. 1. SLJ joint geometry.

2.3. Fabrication and testing For the joint fabrication it was initially necessary to prepare the bonding surfaces. This process consisted of the adherends sandblasting with corundum sand followed by cleaning the surface with acetone until no traces of contaminants exist that can prevent a good bond. After the surface preparation, it is necessary to prepare the joints for bonding. With this purpose, the adherends should be aligned in a bonding jig and, to assure the designated t A for the joints, calibrated nylon wires with 0.2 mm diameter were attached to the adherends at the overlap ends, to stop the adherends’ from entering contact when pressed and acquire t A =0.2 mm. The adherends were then bonded together by applying adhesive to one of the elements and subsequent position the other correctly. Pressure was applied with grips to reach the required thickness and cast out the excess adhesive, which was later removed after its cure. The removal of the excess adhesive is done after its cure to achieve the theoretical layout of the joint without adhesive flaws at the joint boundaries. For testing, the joints were placed between the Universal Testing Machine (UTM) clamps using L T =170 mm for all L O . All the joints were experimentally tested using a UTM Shimadzu AG-X 100 with a 100 KN load cell. The tests were performed with a constant speed of 1 mm/min. The average failure load from each set was considered as the experimental P m . The experimental geometry corresponding to each L O was reproduced numerically by means of a custom-written MATLAB ® script following the procedure described by Ramalho et al. (2020). Such script creates the nodal distribution, imposes essential and natural boundary conditions, and defines the interface nodes, as previously described by Ramalho et al. (2020), an example of the geometry is depicted in Fig. 2. In addition, biases were applied to the nodal distribution because it allowed to concentrate nodes closer to the interface and to stress concentration areas. The bias can be defined as the ratio between the largest and smallest divisions. The nodal distribution was chosen aiming for a balance between resolution and computational cost and it is listed in Table 3. Moreover, it is important to note that the solutions from this meshless method are not sensitive to nodal density, as it was found in Belinha et al. (2013). As described in Section 2.1, the adherends were made of aluminum. For the numerical work, all the materials were considered as elastic-plastic using bilinear material models. The mechanical properties of the adhesive are listed in Table 2, while those corresponding to the substrate are in Table 1. The geometrical parameters t P =3 mm, t A =0.2 mm and L T =180 mm were kept constant in all cases while L O changed to 12.5, 25.0, 37.5, and 50.0 mm; consequently L S changed accordingly to maintain L T . 3. Numerical work 3.1. Pre-processing