| Summary: | <p>Friction damping is commonly used in engineering structures for dissipating energy and reducing vibrations. However, friction can also introduce undesired effects such as the periodic or permanent sticking between the contacting parts or the magnification of the response amplitude. These behaviours need to be accounted for during the early design stages, where these structures are modelled as discrete single (SDOF) or multi-degree-of-freedom (MDOF) systems. However, even when Coulomb friction and simplified mechanical models are considered, the dynamic analysis of these systems is complicated by the nonlinearity of the friction forces.</p>
<p>In this thesis, the dynamic response of different lumped mechanical systems including a Coulomb friction contact and subjected to harmonic excitation is investigated analytically, numerically and experimentally, aiming at establishing how their response features and motion regimes are affected by the presence of multiple DOFs and by the motion of the contacting components.</p>
<p>Exact solutions are derived for the continuous steady-state response of these systems and validated numerically. These solutions enable the exploration of the Coulomb friction effects on response features such as resonant, low- and high-frequency behaviours, the presence of invariant points and inversions of the transmissibility curves. Moreover, the analytical boundaries among continuous, stickslip and permanent sticking regimes are represented in a two-dimensional parameter space, allowing for a quick prediction of the motion regimes during the design stage.</p>
<p>An experimental investigation of the response of SDOF and MDOF systems is carried out by using a base-excited shear frame setup with a brass-to-steel contact, leading to the validation of the theoretical results and the evaluation of different metrics for measuring friction from the dynamic response.</p>
<p>The main findings of this thesis are that: (1) MDOF systems exhibit significantly different behaviours depending on whether the friction and the harmonic forces are applied to the same or different masses; (2) the friction generated by a contact between oscillating components can magnify the response of the system at high frequencies; (3) Coulomb friction model is generally suitable for describing the dynamic behaviour of structures with a metal-to-metal contact.</p>
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