One of the tests for determining the bond strength of adhesives involves measuring the force or the work required to pull apart two surfaces separated by a thin film of adhesive. The pull-off force is measured via the bending of a cantilever that connects one of the surfaces to a motor controlled vertical traverse. Although such tests are routinely performed, little attention has been paid to the understanding of force measurements and their relation to the dynamics of the instrument. Specifically, the measured force versus gap profile for the pull-off process is different from that measured when the same adhesive is compressed between two approaching surfaces. Through experiments on Newtonian liquids and a simple analysis involving lubrication analysis of thin liquid films, we show that the hysteresis in measurements results from a combination of an instrument-related instability and the nucleation and collapse of cavitation bubbles in the flow field.
Summary
Sliding isolation system is one of the widely used base isolation systems. Traditional pure sliding base isolation systems, however, lack restoring force and possess low damping energy‐dissipation capacity. To overcome these disadvantages, a novel low‐friction sliding isolation system with adaptive behavior using sliding implant‐magnetic bearing (IMB) has been proposed in this paper. The isolation system consists of an upper block and a base block, both having polyurethane elastomer fillings and circumferentially implanted permanent magnets. This configuration allows an alterable damping force related to the eddy currents associated with bearing movement. Meanwhile, the interactions between magnets deployed in the upper and base blocks provide a capitalized repulsive force. A quasistatic test is performed to appraise the performance of the IMB system. Theoretical analysis and numerical simulation are carried out for quantification of the repulsive force, damping force, and Coulomb friction, which facilitates the modeling of the isolator. In order to verify the mitigation performance of the IMB deployed in seismic structures, a comparative study against the sliding hydromagnetic bearing (HMB) is carried out. It is revealed that the IMB exhibits reliable frictional performance and excellent damping energy‐dissipation capacity, which commits the adaptability of the IMB in protecting the structures from severe vibration induced by high‐frequency earthquake ground motions. Although exhibiting similar mitigation effectiveness to the HMB, the IMB has the capacity of fulfilling a more effective deformation constraint when subjected to pulse‐type ground motions.
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