Static and vibration analysis of composite structures for robotic application

Abstract

During the past few decades, notable advances have been made in the area of polymer matrix composite materials and their use in structures and mechanisms has markedly increased. Composite fiber reinforced polymer (FRP) materials have been used to build carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) beams. In this thesis, the behaviour of CFRP and GFRP beams and the parameters that impact their static and free vibration response were investigated. Also, the use and effectiveness of these beams to replace aluminum alloys (AA) and steel beams in robot structures were examined. From a structural analysis viewpoint, the design and analysis of composite materials (and members and structures that are constructed using these materials) is more challenging than structures constructed using conventional isotropic materials such as steel and AA. In this research, design charts were developed and a simplified approach for selection of parameters that govern the behaviour of CFRP and GFRP beams is presented. Fiber angle orientation, laminate thickness, materials of construction, cross-sectional shape, and density were the main parameters that were considered. These parameters were studied as they have an impact on the structural response (i.e., deformation patterns, deflections, natural frequencies, strength, forced vibration response) and mass of the FRP beams. As the selection of the design parameters depends on the mode of loading, design charts were developed for axial, bending, torsional, and combined bending-torsional loading conditions. The CFRP and GFRP beams were analyzed using detailed three-dimensional (3D) finite element (FE) analyses and closed-form analytical solutions available in the literature. By comparing the numerical and analytical solutions, the FE models and results were validated. The results showed that the design charts and simplified approach can be used to determine the fiber angle orientation, laminate thickness, cross-sectional shape, and materials that could provide the desired static and free vibration responses. To examine the effectiveness of FRP beams to improve static and free vibration performance of a robot manipulator, a detailed simulation study using FE analysis was also carried out. For this purpose, a five degree of freedom robot manipulator previously developed in the Robotics Laboratory at the University of Saskatchewan was considered. This robot was constructed using AA and steel materials. The FE simulations performed in this study focused on determining stiffness and strength (while considering the mass) of the robot arm with CFRP beams and comparing the structural performance with the AA manipulator. Using the developed FE models, the CFRP arm deflections, natural frequencies, and safety factors for strength were determined. The FE analyses results were verified by comparing to closed-form analytical solutions and, where possible, validated by comparing to experimental results available in the literature. The obtained results showed that the CFRP arm has a higher specific strength (i.e., payload to weight ratio), higher stiffness and natural frequency, and lower deflections compared with the AA arm. Additionally, the CFRP robotic arm was lighter than the AA arm. Lighter robot structures are advantageous as they require smaller motors and actuators with lower power consumption and hence improve energy efficiency.