Abstract

Compliant shell mechanisms are thin shell structures that transmit loads and motion via large elastic deflections. These have advantages over classical mechanisms by reducing the need for traditional joints, thereby reducing part count, friction, and backlash. By replacing designs that utilise discrete joints and moving parts, compliant mechanisms have found application in areas including deployable structures, medical support braces and morphing aerostructures.

Designing compliant shell mechanisms is not without challenges. Typically, these mechanisms need to achieve specific force-displacement responses, and their nonlinear nature means that these responses can be sensitive to small changes in design parameters. Inclusion of anisotropic composite materials expands their design space through selection of the composite laminate layup and prestress, potentially offering alternative routes for stiffness tailoring for restricted design cases. Therefore, understanding the theoretical and practical limits of what is possible in this design space is very valuable.

The research presented investigates several compliant shell structures and 1) explores the potential of combining mechanical and thermal prestress with composite laminate layup to tailor the response of compliant shell mechanisms, 2) develops analytical and numerical models to characterise and visualise their response, and 3) validates these models against manufactured prototypes. Different combinations of thermal and mechanical prestress are investigated, as well as the effects of various design parameters (thickness, geometry, fibre angles etc.) on compliant mechanism behaviour. Detailed finite element models are presented and validated against prototypes of prestressed composite tape springs and helical lattice structures. Eigenscrew characterisation of compliant mechanisms has also been applied to composite shells for the first time, giving new insight into the interplay between material stiffness and shell geometry in mechanism behaviour, via visualisation of compliance axes. These findings pave the way for future studies of robust design, fatigue life enhancement and optimum material selection for compliant shell mechanisms.
Date of Award28 Sep 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorCarwyn Ward (Supervisor), Matt O'Donnell (Supervisor) & Mark Schenk (Supervisor)

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