Fretting behavior of TPU under sub-ambient to elevated temperatures: Development of a novel high-resolution, high-frequency, low-amplitude test method for sealing materials

Fretting wear is a critical failure mechanism in elastomer seals used in dynamic systems, particularly under low-amplitude, high-frequency loading. In such conditions, localized surface damage progresses rapidly, with temperature exerting a significant influence on both mechanical behavior and wear processes. Low temperatures, especially during machine start-up, can dramatically affect the performance and longevity of sealing components. Despite this, experimental studies under sub-ambient conditions remain scarce, largely due to the technical complexity of cooling test setups.
To address this gap, we present a novel fretting test setup and method for elastomeric materials that enables controlled sub-ambient measurements. The novel measurement system for a modular compact rheometer (MCR) is based on a rotational Ball-on-Plate (BoP) configuration, where a steel ball serves as a counterpart against an elastomeric plate. The setup is especially designed for elastomeric materials, replicating realistic conditions in automotive, energy, or aerospace applications. Thermoplastic polyurethane (TPU) was investigated as a representative elastomer. A parameter study revealed that temperature is the dominant factor affecting fretting behavior. Between 10 °C and 80 °C, dissipated energy decreased by 75 %, and the hysteresis (Force-Displacement-diagram) angle was halved. These trends correlate well with DMA-derived viscoelastic properties and emphasize the high temperature sensitivity of TPU. At lower temperatures, stiffer material behavior promoted the formation of wear pits in shear-dominated zones of the contact area, particularly in the partial-slip regions. Higher normal forces increased energy dissipation and surface damage, while load duration had a negligible effect on hysteresis shape but contributed to progressive surface damage and wear.
The developed test setup enhances the investigation capabilities of fretting wear of elastomeric materials considering realistic conditions and offers a deeper understanding of temperature-dependent behavior and fretting wear mechanisms. These findings provide a basis for optimizing materials of sealing systems and improving durability, while also enhancing the understanding of the temperature-dependent fretting behavior of TPU.