Design of Multifunctional Body Panels for Conflicting Structural and Acoustic Requirements in Automotive Applications

Abstract

Over the past century, the automobile has become an integral part of society, with vast increases in safety, refinement, and complexity, but most unfortunately in mass. The trend of increasing mass cannot be maintained in the face of increasingly stringent regulations on fuel consumption and emissions. The body of work within this thesis exists to help the vehicle industry to take a step forward in producing vehicles for the future in a sustainable manner in terms of both economic and ecological costs. In particular, the fundamentally conflicting requirements of low weight and high stiffness in a structure which should have good acoustic performance is addressed. An iterative five step design method based on the concepts of multifunctionality and multidisciplinary engineering is proposed to address the problem, and explained with a case study. In the first step of the process, the necessary functional requirements of the system are evaluated. Focus is placed on the overall system behavior and diverted from sub-problems. For the case study presented, the functional requirements included: structural stiffness for various loading scenarios, mass efficiency, acoustic absorption, vibrational damping, protecting from the elements, durability of the external surfaces, and elements of styling. In the second step of the process, the performance requirements of the system were established. This involved a thorough literature survey to establish the state of the art, a rigorous testing program, and an assessment of numerical models and tools to evaluate the performance metrics. In the third step of the process, a concept to fulfil requirements is proposed. Here, a multi-layered, multi-functional panel using composite materials, and polymer foams with varying structural and acoustic properties was proposed. In the fourth step of the process, a method of refinement of the concept is proposed. Numerical tools and parameterized models were used to optimize the three dimensional topology of the panel,material properties, and dimensions of the layers in a stepwise manner to simultaneously address the structural and acoustic performance. In the fifth and final step of the process, the final result and effectiveness of the method used to achieve it is examined. Both the tools used and the final result in itself should be examined. In the case study the process is repeated several times with increasing degrees of complexity and success in achieving the overall design objectives. In addition to the design method, the concept of a multifunctional body panel is defined and developed and a considerable body of knowledge and understanding is presented. Variations in core topology, materials used, stacking sequence of layers, effects of perforations, and air gaps within the structure are examined and their effects on performance are explored and discussed. The concept shows promise in reducing vehicle weight while maintaining the structural and acoustic performance necessary in the context of sustainable vehicle development.