PSI - Issue 44

Ivan Marenda et al. / Procedia Structural Integrity 44 (2023) 2152–2157 Ivan Marenda et al./ Structural Integrity Procedia 00 (2022) 000–000

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The temperature rise of the sliding material is linked to the applied axial pressure and the test velocity. In addition, the surfaces of the contact joint shall have the same curvature to ensure a uniform vertical force distribution. Fig. 2 shows a pendulum device with different curvature between the sliding surfaces. Therefore, an external circular crown more compressed than the central part is noted. As result, the friction coefficient decreases.

Fig. 2. Sliding material with non-uniform pressure due to different curvatures of the joint surfaces

The temperature rise of the sliding material during repeated cycles changes its properties and as illustrates in Fig. 3, the effective stiffness and the energy dissipated per cycle (EDC) decrease.

Fig. 3. Change of the effective stiffness (bleu) and energy dissipated per cycle (red) during repeated cycles

Therefore, during the motion of pendulum devices, the roughness of the sliding material changes, thus leading to a change in the real contact area. Furthermore, the physical-mechanical properties of the thermoplastic material modify due to the increase in temperature. For these reasons, a thermo-mechanical process (Fig. 4) has been studied which is able to recreate the operating conditions already at the beginning of the motion.

Fig. 4. Disc of HI-M

4. Conclusions The behaviour of the pendulum device depends on the properties of the surfaces in contact. The roughness of the contact surfaces determines a real contact area lower than the net area of the sliding material which influences the friction coefficient of the system. In these spots the pressure due to external forces is concentrated and heat transfer occurs by contact. The thermal capacity of the joint is one of the most important characteristics to predict the behaviour of the system.