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Title: Vibration isolation utilising the nonlinear deformation of anisotropic plates
Author: Shaw, Alexander
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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This thesis has two motivations; vibration isolation and the desire to yield additional functional benefits from composite materials. Vibration isolation is a vital requirement throughout much of engineering, particularly when there is a strong source of vibration such as a motor. It is frequently required to prevent the transmission of these vibrations to other elements of the system, for reasons such as passenger comfort, or the protection of delicate electronic equipment. Carbon fibre based composites are seeing widespread application wherever highly weight efficient strength or stiffness is required. However, their high cost and complex processing requirements motivates a desire to achieve additional benefits from their use, and many such 'benefits have been identified in the study of multifunctional composites. In particular, much work has shown that composite plates may be created to exhibit highly nonlinear behaviour, including bistability. In this work, we consider exploiting bistability and related nonlinear behaviours for the function of vibration isolation. Specifically, we wish to engineer the directional stiffness and residual stresses in composite laminates to achieve a lightweight and effective vibration isolation mount. Anti-vibration mounts typically exploit damping and low stiffness to reduce vibration. Damping is effective in limiting the peak response of the mount at resonance, but is detrimental to isolation at higher frequencies. Reducing the stiffness of the mount is beneficial to isolation, but can conflict with the usual requirement that the mount must support a static load. The approach adopted in this work is that of a High Static Low Dynamic Stiffness (HSLDS) mount, whereby the mount has a nonlinear force displacement response, that features a region of low stiffness near equilibrium for vibration isolation, whilst increasing stiffness elsewhere. This work presents new results for HSLDS mounts, providing insight into many features of their performance including high parameter sensitivity and possible unbounded response. The transverse force-displacement response of CFRP plates with asymmetric stacking sequences is investigated both numerically and experimentally. It is shown that a bistable plate may be connected in parallel with conventional springs to provide a HSLDS response, providing that bistable curvature is limited to exclude undesirable secondary buckling patterns. It is then shown that a mono-stable plate may be created that eliminates the requirement for additional springs, and therefore implements a HSLDS mount in a single lightweight shell.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available