Viscoelastic interphases in polymer-matrix composites: theoretical models and finite-element analysis

We investigate the mechanical property predictions for a three-phase viscoe lastic (VE) composite by the use of two micromechanical models: the origina l Mori-Tanaka (MT) method and an extension of the Mori-Tanaka solution deve loped by Benveniste to treat fibers with interphase regions. These micro-me chanical solutions were compared to a suitable finite-element analysis, whi ch provided the benchmark numerical results for a periodic array of inclusi ons. Several case studies compare the composite moduli predicted by each of these methods, highlighting the role of the interphase. We show that the M T method, in general, provides the better micromechanical approximation of the viscoelastic behavior of the composite; however, the micromechanical me thods only provide an order-of-magnitude approximation for the effective mo duli. Finally, these methods were used to study the physical aging of a vis coelastic composite. The results imply that the existence of an interphase region, with viscoelastic moduli different from those of the bulk matrix, i s not responsible for the difference in the shift rates, mu (22) and mu (66 ), describing the transverse Young's axial shear moduli, found experimental ly. (C) 2001 Published by Elsevier Science Ltd. All rights reserved.