Boss-Fastener Strengths with SMC Materials

This paper will present the results of a boss testing program undertaken by International Harvester Company and Owens/Corning Fiberglas. The program represents an initial step to determine boss strengths possible with low profile sheet molding compound (SMC) and to assess the dependence of strength on boss configuration, material composition, and fastener type.

With the multitude of available fastener thread types and the wide variation of possible boss configurations, only a limited selection of variables could be evaluated. The study looks at Hi-Lo and BT thread fasteners in various lengths. The effects of gussets and fillets on boss strength are shown over a range of glass contents. Material properties of the different laminate compositions are compared with the boss strengths from each material.

This information should serve as a basic guideline of boss strengths and as a groundwork for improvement of current design philosophy to optimize boss performance. The direction for further appraisals of boss performance, including improved designs and fatigue studies, will also be discussed.