Cooperative Research and Development Agreement Final Report for Cooperative Research and Development Agreement Number ORNL93-0237 Adhesive Bonding Technologies for Automotive Structural Composites

Abstract

In 1993, the Oak Ridge National Laboratory (ORNL) entered into a Cooperative Research and Development Agreement (CRADA) with the Automotive Composites Consortium (ACC) to conduct research and development that would overcome technological hurdles to the adhesive bonding of current and future automotive materials. This effort is part of a larger Department of Energy (DOE) program to promote the use of lighter weight materials in automotive structures for the purpose of increasing fuel efficiency and reducing environmental pollutant emissions. In accomplishing this mission, the bonding of similar and dissimilar materials was identified as being of primary importance to the automotive industry since this enabling technology would give designers the freedom to choose from an expanded menu of low mass materials for component weight reduction. The research undertaken under this CRADA addresses the following areas of importance: bulk material characterization, structural fracture mechanics, modeling/characterization, process control and nondestructive evaluation (PC/NDE), manufacturing demonstration, and advanced processing. For the bulk material characterization task, the individual material properties of the adherends and adhesives were characterized. This included generating a database of mechanical and physical properties, after identifying and developing standard test methods to obtain properties. The structural fracture mechanics task concentrated on test development to characterize the fracture toughness of adhesively bonded joints subjected to Mode I, Mode II and mixed-mode conditions. Standard test procedures for quantifying an adhesive/adherend system's resistance to crack growth were developed for use by industry. In the modeling/characterization task, fracture mechanics-based design guidelines and predictive methodologies have been developed which will facilitate iteration on design concepts for bonded joints while alleviating the need for extensive testing. Methods for nondestructive evaluation of adhesive bonds that can be used for process optimization, in-line process control and product validation were evaluated in the PC/NDE task. Promising NDE techniques were identified for additional development. In the advanced processing task, rapid-cure and advanced surface preparation processes were investigated with the goal of increasing the manufacturability and performance as well as reducing the costs of bonded composites. Demonstration that a ''designed for composites'' structure is manufacturable was undertaken in the manufacturability demonstration task. In addition to the aforementioned efforts, ancillary topics that were coordinated by the CRADA partners will be discussed briefly. These include the performance of bonded composite structures in crashes and fatigue durability of bonded and hybrid joints. This report covers the activities undertaken during the CRADA through February 1997.