PSI - Issue 41

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A.R.F. Soares et al. / Procedia Structural Integrity 41 (2022) 48–59 Soares et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 1. The proposed testing device (a) and its exploded view (b).

3.1.1. Mechanisms The following brief description is referred to the exploded view in Fig. 1 (b). The device consists of a base to be fixed to the universal testing machine (UTM) (1) over which a support plate is mounted (2). Then, the lower perforated beam (3) is bolted on it. As all these parallel beams are perforated, such adjective will not be used in subsequent descriptions. The second beam (4) is connected to (3) through links (5), whilst the third beam (6) is also connected to (4) by another set of links (7). The adhesive joint would lie between these last two beams (4 and 6) and is connected to them via links (8 and 9, respectively). Contrarily to the previous links, the latter were machined from solid blocks of steel, aiming for improved stiffness. The displacement from the UTM is applied to the third beam through another linkage (10) to absorb the horizontal displacement of the pins throughout the testing. Once the specimen is pulled between the links (8) and (9) it is necessary to apply additional support, thus producing the desired loading mode. This is accomplished through support beams (11), which have rounded edges to reduce the marking of the specimen during testing. 3.1.2. Working principle The displacement from the UTM is imposed on the device through the linkage (10). The load is then transferred through the horizontal beam (6) to its supporting links (7 & 9). Link (9) is connected to the specimen’s upper adherend, and so the positions of (10) and (7) along (6) would determine the amount of load imposed on it. Furthermore, the pins holding the specimen to the links (7 & 9) are also connected to the LVDT system, one for the upper adherend and one for the lower. Thus, the adherend displacement can be recorded throughout the experiment. Similarly, the position of the supporting beams (11) influences the amount of load transfer to the specimen. Following Fig. 2 and performing free body diagrams (FBD) of the components, it is possible to determine the load imposed on the specimen. Starting with the assumption that mixed-mode load is the sum of mode I and mode II loads, by applying the superposition principle it is possible to calculate the load components on each mode, as shown in Fig. 3. From the upper beam (6 in Fig. 1), the load imposed by the UTM is held by the two vertical links (7 and 9 in Fig. 1), being their respective load a function of the distance between them, as shown in Fig. 2. Therefore, through free-body diagrams of each component on the device, including the specimen, it is possible to determine the forces acting on the specimen.