Identification of a Thermoviscoelastic Crosslinked Polymer Model Taking into Account Large Deformations and its Application

The purpose of the work is to develop a model of viscoelastic thermomechanical behavior of cross-linked polyethylene (CLPE) products with a shape memory effect. The main area of application of this class of materials is heat-shrinkable tubes and their modifications. They are characterized by initial expansion values of 100 percent or more. Simo and Holzapfel proposed modified defining relations representing a synthesis of the viscoelastic Proni model and the hyperelastic model based on the elastic energy potential. The published work proposes a methodology for identification of both damping and nonlinear elastic material constants in case of large deformations. An experimental program is developed and implemented to determine the material constants of cross-linked polyethylene. It includes the procedure of reducing the dimension of the nonlinear optimization problem when finding exponential approximation coefficients of the relaxation function. A description is given of the developed algorithm for searching for the material constants of a hyperelastic model based on the results of an experiment on cyclic loading of a sample with large deformations in the range of highly elastic behavior. An adaptation of the hyperelastic model in ANSYS is made taking into account the presence of relaxation properties. As an illustration of the application of the updated physical model, an example of a finite element calculation of the pressure of heat-shrinkable tubes when deposited on a rigid cylindrical surface is given. An engineering technique is also proposed that allows similar calculations to be made in the Excel spreadsheet.