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A unique design, engineering, and manufacturing approach has been used to create the first all-plastic door hardware module frame. The result of many years of intensive development efforts by a team of companies, the gas-assist injection molded frame features a high degree of parts consolidation and has been critically acclaimed as “the first major metal-replacement automotive part since the bumper, a quantum leap in injection molding complexity, and the biggest commercial breakthrough ever in gas assist molding [1].” The program also proved to be an excellent example of the types of technological breakthroughs that can come from concurrent engineering and strategic partnering. This paper will provide an overview of the component's development, describe the many challenges facing the team, and share solutions that contributed to the success of the program.

The C-section bumper design has developed through an evolutionary process and has come to be regarded as a reasonable geometry for frontal bumper impacts, especially for use with glass-filled sheet-stampable thermoplastic composite materials. C-section bumpers are now well proven and accepted in the automotive industry, performing satisfactorily in a variety of crash situations. A new and more complicated cross-section geometry (I-type with multiple ribbing) has recently been proposed for glass-filled thermoplastic composites. While, in some specialized cases, these highly engineered bumper cross-sections can be useful, they may not perform adequately in all reasonable crash scenarios. Further, it is important to consider manufacturing limitations and the realities of material performance in such complex geometries. Data will be presented to question the practical advantages of the use of ribbed bumper designs over the traditional C-section beam.

An interesting characteristic of virtually all materials is their strain-rate sensitivity. In the case of engineering thermoplastics, these materials exhibit ductility and very good impact resistance at low to average strain rates (<10 %/sec) but can become extremely brittle and unforgiving at high strain rates (100 - 5.000++%/sec). This becomes a concern in energy management applications, such as automotive instrument panels and knee bolsters, because, for example, the average head impact on an instrument panel induces a 1,000%/sec strain rate. Engineering analysis of the impact event typically under-predicts loads and over-predicts deflections. Making material substitutions within a design may be of little use since the newcandidate may be more strain-rate sensitive than the original polymer. Many of the most widely specified engineering thermoplastics behave very differently in standardized ASTM “static” tests than in high strain-rate situations.