As automotive manufacturers continue to increase their use of thermoplastics for interior components (due to cost, weight, …), the potential for frictionally incompatible materials contacting each other, resulting in squeaks and rattles, will also increase. This will go counter to the increased customer demand for quieter interiors. To address this situation, Ford's Advanced Vehicle Technology Squeak and Rattle Prevention Engineering Department and Virginia Tech have developed a tester that can measure friction as a function of relative sliding velocity during frictional instabilities such as stick slip. The Ford/VT team is developing a polymeric material pairing database that will be used as a guide for current and future designs to eliminate potential squeak concerns. Based upon the database, along with a physical property analysis of the various plastic (viscoelastic) materials used in the interior, an analytical model will be developed as a tool to predict frictional behavior. The model will be integrated into the automotive component design process (CAD/CAM/CAE) so that potential concerns can be addressed prior to critical design milestone freeze dates.
This collaborative effort between Ford and VT, to investigate friction and noise in automotive components, was establish in 1990. Some summaries thus far are as follows:
- 1.
A negative slope in the coefficient of friction (COF) vs. sliding velocity curve is an indicator of frictional instabilities that can lead to noise.
- 2.
The static coefficient of friction of acrylonitrile-butadiene-styrene (ABS) and polycarbonate (PC) increases as the time of contact before sliding commences is increased.
- 3.
Unfilled polypropylene (PP) has a static friction which is equal to its kinetic friction and which is unaffected by the time of contact before sliding. Glass filled PP has a static friction higher than its kinetic friction.
- 4.
The decrease in friction that occurs when sliding commences is more a function of composition than surface roughness.
This paper will review our research results to date. The characterization of polymer surfaces will be provided to establish material structure/property relationships (surface roughness and bulk properties) which will predict and produce stable friction behavior. Also COF versus velocity curves will be presented for several different material pairs and surface types.