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Technical Paper

Comparative Life Cycle Assessment of Plastic and Steel Vehicle Fuel Tanks

Federal standards that mandate improved fuel economy have resulted in the increased use of lightweight materials in automotive applications. However, the environmental burdens associated with a product extend well beyond the use phase. Life cycle assessment is the science of determining the environmental burdens associated with the entire life cycle of a given product from cradle-to-grave. This report documents the environmental burdens associated with every phase of the life cycle of two fuel tanks utilized in full-sized 1996 GM vans. These vans are manufactured in two configurations, one which utilizes a steel fuel tank, and the other a multi-layered plastic fuel tank consisting primarily of high density polyethylene (HDPE). This study was a collaborative effort between GM and the University of Michigan's National Pollution Prevention Center, which received funding from EPA's National Risk Management Research Laboratory.
Technical Paper

Elevated Temperature Forming of Sheet Magnesium Alloys

The use of sheet magnesium for automobile body applications is limited, in part, due to its low room temperature formability. Elevated temperature forming of magnesium sheet could enable the manufacture of automobile body closure and structural panels to meet vehicle mass targets. The effect of temperature in improving the formability of sheet magnesium has been known since the 1940's; however, automobile applications for sheet magnesium still have been very limited. The present work characterizes the elevated temperature mechanical behavior of commercially available magnesium sheet alloys at temperatures between 300°C and 500°C. The materials are then evaluated using both warm forming and superplastic forming technologies.
Technical Paper

Formability Predictions of Hydroformed AKDQ Steel Tubes by Various Burst Criteria

The accurate prediction of burst of hydroformed tubes is a research area of considerable importance in order to evaluate a design before prototyping. This report applies the presently available criteria (forming limit diagram, stress-based forming limit diagram, extended stress based forming limit curve and the plastic strain criterion) to some of the benchmark examples carried out by the Auto/Steel partnership. It was found that the formability predictions are lowest if the plastic strain criterion is used and highest if either the stress-based criteria are used. Predicted and measured results were also compared.
Technical Paper

New Binder for Casting Cores: An Industrial Application to Safety Suspension Parts

A new core binder system (1) was used to produce foundry cores for casting hollow aluminum suspension parts by the low pressure, gravity flow, semi-permanent mold method. These and other prototype aluminum parts made using the system demonstrate that easy core removal from complex castings, core and sand recycling, and an improved environment in the core making facilities will increase productivity, improve product quality and reduce manufacturing costs.
Technical Paper

Recyclability and Characterization of Co-Extruded Multilayer Fuel Tanks

The recyclability of co-extruded multilayer fuel tanks, and characterization of the materials used in their manufacture, have been investigated. The ethylene-vinyl alcohol, EvOH, copolymer barrier layer, extruded as a sandwich between two adhesive layers of a maleated linear low density polyethylene, LLDPE, is surrounded by three high density polyethylene, HDPE, layers, one of which is composed of the regrind derived from the waste generated by manufacture. Particular attention has been focused on the mechanism of adhesion between the barrier layer and the adhesive layers. Surface analysis of the in situ surfaces has confirmed the formation of chemical bonds between the two polymers. Morphological information, concerning dispersion of the barrier layer in the HDPE matrix during recycling, has been obtained by scanning (SEM) and transmission (TEM) electron microscopy techniques.
Technical Paper

The Influence of the Material Model on the Stress-Based Forming Limit Criterion

The stress-based forming limit criterion has recently been shown to exhibit no significant dependence on strain path for a wide range of materials. This paper describes the effect of material models on the definition of the stress-based forming limit criterion. It is shown that although the shape of the forming limit curve in stress space is sensitive to the type of material model used, the degeneracy of the path dependent strain-based curves to a single curve in stress space shows little sensitivity to the material model. Consequently, the stress based forming limit criterion is shown to provide a more practical and robust measure of forming severity than is possible using the conventional forming limit diagram.