This study experimentally investigates the influence of surface deformations on contact conductance when two dissimilar metals are brought into contact. Most relations between the contact conductance and the load use the surface hardness to characterize surface deformations. This inherently assumes that deformations are predominantly plastic. To check the validity of this assumption, five tests were conducted in the contact pressure range of 30 kPa to 4 MPa, with sample combinations of (I) smooth aluminum-rough stainless steel, (II) rough aluminum-smooth stainless steel, (III) rough copper-smooth stainless steel, (IV) smooth copper-rough stainless steel, and (V) smooth aluminum-smooth stainless steel. The experimental results of tests I, II, and IV indicate that the conductance of the first load-unload cycle showed hysteresis, suggesting that the plastic deformation was significant. However, for subsequent load cycles, no conductance hysteresis was observed, implying that elastic deformation was predominant. In contrast, no conductance hysteresis was observed for all load-unload cycles of tests III and V. Therefore, the surface deformation for this combination was always predominantly elastic. In practical applications where plastic deformation is significant for the first loading, mechanical vibrations can produce oscillating loads, which can finally lead to predominance of elastic deformation. Comparison of the results of tests II and V show that even though plastic deformation was significant for the first loading of a rough aluminum surface, elastic deformation was always predominant for the smoother aluminum surface

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