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Determination of Dimensional Changes in Injection Molded Bosses Using Strain Gages: Effects on Joint Durability
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Abstract
Improvements in clamp load retention of fastened joints in instrument panels are desired by automotive OEMs to minimize warranty claims due to squeak and rattle problems. The decrease in torque retention of these plastic boss and metal fastener joints over time and temperature cycling was described in a previous SAE technical paper.1 This loss in clamp load retention (which is another measure of joint durability), as measured by torque, was shown to be affected by differences in the thermal expansion rates of the captured materials.
The purpose of this paper is to further quantify these differences by using strain gages to measure the thermal expansion rates and dimensional changes of the joint's various components: metal fastener, molded plastic boss, and captured material.
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Citation
Hoy, R., Bartos, C., Leung, R., Rozmus, R. et al., "Determination of Dimensional Changes in Injection Molded Bosses Using Strain Gages: Effects on Joint Durability," SAE Technical Paper 940653, 1994, https://doi.org/10.4271/940653.Also In
References
- Hoy, R.V. “Fastening Characteristics of Fiberglass Reinforced S/MA Copolymers in Instrument Panel Substrates.” Paper 1992 Society of Automotive Engineers International Congress Detroit, Ml February 1992 Paper number 920102
- Tech Note TN-513 “Thermal Expansion Measurement” 1986 Measurements Group, Inc. Raleigh, NC