Optimal design of thermally actuated compliant mechanisms and its application to product -embedded disassembly.

Abstract

Compliant mechanisms are the type of mechanisms that use elastic deformation of flexible members to transfer force, motion or energy. This dissertation reviews the previous work on topology optimization design synthesis for compliant mechanisms, as well as suggests alternative problem formulations. Thermal transducers, which can be interpreted as thermally actuated compliant mechanisms, have found a wide range of applications, due to their accessible source, easy controllability and reliability. There has been research done to synthesize design of thermal actuation embedded electrical-thermal-compliant mechanisms, in which the non-uniform temperature change was generated by joule heating through non-uniform electric current. In this dissertation, time transient effect of heat transfer is proposed to produce the localized thermal actuation, while simple boundary heating is considered. Consequently non-uniform temperature distribution can be achieved by controlling the heating time. Homogenization design method is utilized for topology optimization where calculation of the effective material properties is conducted via homogenization theory. Numerical examples are presented to support the proposed design method with novel type of thermal actuators. Disassembly is a fundamental process needed for component reuse and material recycling in all assembled products. Integral attachments, also known as snap fits, are favored fastening means in design for assembly (DFA) methodologies, but not necessarily a favored choice for design for disassembly. In this dissertation, design methods of a new class of integral attachments are proposed, where the snapped joints can be disengaged by the application of localized heat. The design problem of reversible integral attachments is posed as the optimization of compliant mechanisms actuated by the localized thermal expansion of materials. Topology optimization techniques for compliant mechanisms are utilized to obtain conceptual layout of snap-fit mechanisms that realizes a desired deformation of snapped features for joint release. Two design approaches are attempted and design results of each approach are presented, where the obtained optimal topologies are simplified to enhance the manufacturability for the conventional injection molding technologies. Final designs have been verified with commercial FEA software ABAQUS. In topology optimization design problems, the design specifications, such as boundary conditions, loading conditions and definition of design domains are applied according to finite element discretization. The variables controlling these design specifications subsequently have discrete values. Discrete optimization methods deal with discrete variables. Genetic algorithm has been an effective discrete optimization algorithm. In this dissertation, the design specifications of topology optimization are proposed to be optimized using discrete optimization method. Two applications are presented using this improved design scheme. The first application involves the optimal shape and location of piezoelectric materials in flextensional actuators, while the second improves the performance of the heat-activated reversible snap-fit design.