Constitutive Modeling of a Glass Fiber-Reinforced PTFE Gasketed-Joint Under a Re-torque James Williams and Ali P. Gordon Department of Mechanical & Aerospace Engineering, University of Central Florida, Orlando, FL 32816-2450 Keywords: Bolted-joint Relaxation, Gasket Creep, Viscoelastic Modeling. Abstract Joints gasketed with viscoelastic seals often receive an application of a secondary torque, i.e., re- torque, in order to ensure joint tightness and proper sealing. The motivation of this study is to characterize and analytically model the load and deflection re-torque response of a single 25% glass-fiber reinforced polytetrafluorethylene (PTFE) gasket-bolted joint with serrated flange detail. The Burger-type viscoelastic modeling constants of the material are obtained through isolating the gasket from the bolt by performing a gasket creep test via a MTS electromechanical test frame. The re-load creep response is also investigated by re-loading the gasket after a period of initial creep to observe the response. The modeling constants obtained from the creep tests are used with a Burger-type viscoelastic model to predict the re-torque response of a single bolt- gasket test fixture in order to validate the ability of the model to simulate the re-torque response under various loading conditions and flange detail. Introduction Bolted gasket joint systems are typically tightened and allowed to relax for a specific initial dwell period and then subsequently re-torqued to the desired torque levels. Re-torque is typically applied in order to re-tighten the joint, after the gasket has gone through some initial relaxation, to ensure optimal gasket sealing. The relationship between torque and the corresponding compressive load is given by: T F Kd  (1) where F is the compressive load and d is the nominal diameter of the bolt and K is the nut factor. The terms torque and load are used interchangeably for this study. Joint designers are interested in conditions that (1) minimize the joint relaxation or (2) reduce required dwell time prior to re-tightening the joint. Hence prior efforts have been made to qualitatively describe gasket behavior combined within bolted joints. For example, Waterland and Frew investigated the compressive creep resistance of various PTFE types of gaskets within bolted joints with the goal of identifying materials not requiring re-torque. Furthermore, the minimum acceptable initial dwell periods of PTFE types were also studied [1]. In a technical report, Gordon et al. optimized the parameters of gasket thickness, lubrication, flange detail, load level and initial and final dwell period on the initial and re-torqued clamping load relaxation response of a 25% glass-filled PTFE gasket bolted flange system [2]. 227 Characterization of Minerals, Metals, and Materials 2015 Edited by: John S. Carpenter, Chenguang Bai, Juan Pablo Escobedo, Jiann-Yang Hwang, Shadia Ikhmayies, Bowen Li, Jian Li, Sergio Neves Monteiro, Zhiwei Peng, and Mingming Zhang TMS (The Minerals, Metals & Materials Society), 2015