Ratcheting testing of polytetrafluoroethylene (PTFE) under multiple-step compression

Wei Wang; Xiaotao Zheng; Linwei Ma; Wei Lin; Jiuyang Yu

doi:10.3139/120.111183

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Ratcheting testing of polytetrafluoroethylene (PTFE) under multiple-step compression

Wei Wang , Xiaotao Zheng , Linwei Ma , Wei Lin und Jiuyang Yu

Veröffentlicht/Copyright: 15. November 2018

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Abstract

Uniaxial stress-controlled ratcheting experiments of PTFE (polytetrafluoroethylene) under cyclic compressive loads with multiple load steps were performed. The influence of stress rate, temperature, stress amplitude, loading sequence and peak holding on the compressive ratcheting behavior have been discussed systematically. Results indicate that ratcheting deformation increases significantly when enhancing temperature and stress amplitude and reducing stress rate. Only a slight, accumulated deformation occurs during the first 20 or so cycles at room temperature (RT), but it always turns to shakedown. Moreover, ratcheting strain is clearly influenced by the loading sequence. When greater compressive deformation was obtained during the prior load step due to a greater stress level (such as higher temperature or a lesser stress rate), increased compressive strain hardening and deformation resistance could be produced, which in turn restricts or even reduces ratcheting deformation in the pursuing load step. It is of great interest that no initial cyclic stress strain curve was observed under cyclic compression at peak holding time. This indicates that creep recovery due to anelastic relaxation decreases the ratcheting rate of PTFE material under compressive creep-fatigue conditions. This research provides an important testing approach and data for PTFE material subjected to repeated compressive loads influenced by temperature modulation.

Kurzfassung

Für den vorliegenden Beitrag wurden einachsige spannungskontrollierte Ratcheting-Versuche an PTFE unter zyklischen Drucklasten in mehreren Lastschritten durchgeführt. Die Einflüsse des Spannungszustandes, der Temperatur, der Spannungsamplitude, der Belastungssequenz und der Spitzenhaltezeit unter der Druckbeanspruchung werden systematisch diskutiert. Die Ergebnisse deuten darauf hin, dass die Deformation signifikant mit der Temperatur und der Spannungsamplitude sowie reduzierter Spannungsrate zunimmt. Insbesondere tritt eine leichte Deformation während der ersten 20 Zyklen bei Raumtemperatur auf, die aber immer zum Zusammenbruch führt. Darüber hinaus wird die Ratcheting-Dehnung offensichtlich durch die Bealstungsequenz beeinflusst. Je größer die Kompressionsdeformation im vorhergehenden Belastungsschritt aufgrund eines höheren Spannungsniveaus, einer höheren Temperatur oder eines geringeren Spannungszustandes ist, desto größer ist die Verfestigung unter Kompressionsdehnung, die im folgenden Lastschritt die Ratcheting-Deformation eingrenzt oder sogar reduziert. Von besonderem Interesse ist es, dass kein Öffnungsverhalten der zyklischen Spannungs-Dehnungs-Kurve unter zyklischer Kompression mit der Peakhaltezeit beobachtet wurde. Dies deutet darauf hin, dass die Erholung unter Kriechen aufgrund eines unelastischen Relaxationseffektes die Ratcheting-Rate des PTFE unter Kriech-Druck-Ermüdungsbedingungen verringert. Die vorliegenden Forschungsergebnisse zeigen wichtige Versuchsanordnungen und -daten für das Material PTFE unter wiederholten Kompressionsbeanspruchungen und unter Berücksichtigung des Temperatureinflusses.

*Correspondence Address, Associate Prof. Dr. Xiaotao Zheng, Hubei Provincial Key Laboratory, of Chemical Equipment, Intensification and Intrinsic Safety School of, Mechanical and Electrical Engineering, Wuhan Institute of Technology, Wuhan, 430205, P. R. China. E-mail: xiaotaozheng@163.com

Wei Wang, born in 1984, is a doctoral student at the Wuhan Institute of Technology, China. He obtained his master's degree in Mechanical Engineering. His primary research area is polymer engineering and characterization.

Assoc. Prof. Xiaotao Zheng, born in 1982, is Associate Professor at the Wuhan Institute of Technology, China. He obtained his doctor's degree in Mechanical Engineering from Huazhong University of Science and Technology, Wuhan, China. He was a visiting scholar at the University of Strathclyde, UK, in 2017. His study focuses on polymer testing and characterization.

Dr. Linwei Ma, born in 1978, is Lecturer at the Wuhan Institute of Technology, China. He obtained his doctor's degree in Mechanical Engineering from Huazhong University of Science and Technology, Wuhan, China. His study focuses on polymer processing and characterization.

Dr. Wei Lin, born in 1987, is a Lecturer at the Wuhan Institute of Technology, China. He obtained his doctor's degree in Mechanical Engineering from Wuhan University of Science and Technology in 2015. His primary research area is polymer testing and characterization.

Prof. Jiuyang Yu, born in 1962, is Professor at the Wuhan Institute of Technology, China. He obtained his master's degree in Mechanical Engineering at the Nanjing University of Technology, China. His studies focus on polymer engineering and application.

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Published Online: 2018-11-15

Published in Print: 2018-05-26

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https://doi.org/10.3139/120.111183