Use of deformation maps in predicting the time-dependent deformation of thermoplastics

Thermoplastic parts are being used in a variety of elevated temperature, load-bearing applications. Under these situations, they are observed to undergo time-dependent deformation termed viscoelasticity. Traditionally, the design engineer has used the mathematical theory of linear viscoelasticity in order to predict part performance. However, the mechanics of determining whether a particular application can be analyzed in this manner has not been clearly laid out. In this work, we present a simple graphical tool which will aid the designer in accurately treating time-dependent part performance. Such 'deformation maps' identify the limit of linear viscoelastic behavior as a function of time, stress and temperature. The approach has been demonstrated by considering an actual application. The results indicate the success and simplicity of this methodology and provide the basis for a better treatment of time-dependent part deformation.