Effect of thermal ratcheting on the mechanical properties of Teflon and fiber based gasket materials

Abstract

This paper discusses the effect of thermal ratcheting on the material properties of expand polytetrafluoroethylene (ePTFE), virgin polytetrafluoroethylene (vPTFE), and compressed nonasbestos fiber (CNA) gasket materials. Comparison between the creep strain at constant temperature and when subjected to thermal ratcheting show a 7.7 and 28% increase in the creep strain of ePTFE and vPTFE, respectively. In addition, thermal ratcheting produces a substantial reduction of creep modulus of these materials. The CNA material does not exhibit significant change in creep strain or in creep modulus with thermal ratcheting. However, all three gasket materials show a momentous raise in the creep strain when the material temperature is reduced. On declining the gasket temperature from 212 to 100 °F at the end of 20th thermal cycle, the materials—ePTFE, vPTFE, and CNA exhibit 27, 48, and 15% increase in creep strain value, respectively. The percentage of thickness reduction raises with the increase of cyclic temperature and with increase of creep pre‐exposure time, except for CNA where only a small variation is observed. The coefficient of thermal expansion of both PTFE materials shows a significant change due to cyclic temperature and initial creep exposure. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47265.

Model Simulation of Creep and Thermal Ratcheting of Engineering Polymers

“…[23] To the author's best knowledge, there is little information on thermal ratcheting available in the literature. [24] The analysis is focused on the experimental results performed in refs. [22,24] for polymeric flange materials like HDPE and three types of gasket materials namely poly-tetrafluoroethylene PTFE (expanded e-and virgin v-) and CNA.…”

“…[24] The analysis is focused on the experimental results performed in refs. [22,24] for polymeric flange materials like HDPE and three types of gasket materials namely poly-tetrafluoroethylene PTFE (expanded e-and virgin v-) and CNA.…”

“…Regarding HDPE, creep strain results at various stress levels and temperatures are available in ref. [24], which are illustrated in Figure 1.…”

“…The expanded PTFE (ePTFE), the virgin one (vPTFE), and a compressed nano-asbestos fiber (CNA) gasket materials, were experimentally studied in ref. [24]. There are limited experimental creep results available for these materials, therefore, the set of parameters Σ, u min , u max, 𝛾 T has been evaluated at a single temperature and stress level.…”

“…Regarding virgin PTFE, as it is mentioned in ref. [24], it is the most susceptible under creep and thermal ratcheting. The creep behavior of vPTFE is shown in Figure 4, at 28 MPa, and the same with ePTFE heating-cooling conditions.…”