Date of Award

7-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Thompson, Lonny L

Committee Member

Grujicic , Mica

Committee Member

Biggers , Sherrill B

Abstract

Automotive seats provide comfort and safety to the occupant travelling in the vehicle. An optimized seat design should be aesthetically pleasing, lightweight and meet the safety requirements. An automotive seat with occupant is subjected to various kinds of forces in the event of crash and should be designed for strength and stiffness as measured by stress and strain, and deflection. In this work, finite element analysis, together with topology and free-size optimization is used to design a lightweight die cast automotive front seat backrest frame when subjected to loads prescribed by ECE R17 European government regulations and additional loads which are predicted in an event of crash. In particular, an effort is made here to study the characteristics of a die cast automotive front seat backrest frame and develop a method for predicting the optimized material and rib stiffener distribution which provides a lightweight seat which satisfies both strength and deflection requirements in a design space which includes the action of multiple load cases. The design and optimization procedure is to create a geometric computer-aided-design (CAD) model of an existing commercially available die cast backrest frame as the reference design space. Both 3D surface and solid models are created for representation as shell and solid finite element models for analysis. The CAD models were created using CATIA and then imported into Altair HyperMesh and OptiStruct software for finite element model creation and linear analysis with optimization. The objective function for topology optimization of the 3D solid model is to minimize mass of the component subject to stress and deflection constraints and is used as a guide in determining optimal geometric distribution of stiffening ribs. When the shell model of the reference seat is subjected to free-size optimization with this same constraint and objective given, an optimized material distribution measured by shell element thicknesses is obtained. For the topology optimization, manufacturing constraints of preferred draw direction are applied in order to obtain an optimized material distribution which can be manufactured in the die-cast process. Results from OptiStruct provide a guide for design, but are not optimal for manufacturing due to large changes and scattering of material distribution. Results from the topology optimized 3D solid model and free-size optimized 3D shell model are compared and combined manually to create a final lightweight design with optimal stiffening rib placement and material distribution which can be manufactured relative easily in a die-cast manufacturing process. Finite element analysis of both the reference and final optimized seat designs with geometric nonlinear and inelastic material behavior is also performed using ABAQUS to confirm deflection requirements and determine factor of safety at failure due to excessive strains. The procedure followed in this work generated an optimal material distribution and stiffening ribs in a lightweight die cast automotive seat backrest frame when subjected to multiple load cases. An overall reduction in weight of 12.95% is achieved for the backrest frame component.

Share

COinS