Analytical and experimental procedures in nonlinear viscoelastic parameter characterization using dynamic mechanical techniques

Abstract

Traditional methods of viscoelastic material characterization lack the ability to rapidly characterize nonlinear viscoelastic materials. A method of rapidly identifying linear viscoelastic material properties is Dynamic Mechanical Analysis (DMA). DMA, although proven as a method to quickly and accurately determine linear material properties, has not been extended for use of nonlinear characterizations. Creep and recovery tests have been the most widely used procedures for characterizing nonlinear material properties, however, these tests are time consuming and tedious. An approach is presented here which uses DMA to identify nonlinear material properties. The technique utilizes the speed in which properties are identified using DMA, but, like creep and recovery tests, the data provide more detail and information. The proposed method implements a dynamic or oscillatory input in Schapery's nonlinear viscoelastic model. This oscillatory input is accounted for by using a Taylor series expansion on the mean stress of the nonlinear viscoelastic model. These theoretical developments for nonlinear DMA are correlated to an experimental procedure which is introduced as a tool for nonlinear viscoelastic material characterization. Thin film polyethylene is characterized by the experimental procedure developed herein and is used as a validation of the nonlinear DMA theory.