Tài liệu này nhằm phác thảo một khía cạnh quan trọng của các phản ứng cơ học của polyme và composite polymer-ma trận: các lĩnh vực của đàn nhớt tuyến tính. Các chủ đề bao gồm ở đây là nhằm mục đích cung cấp một giới thiệu hướng dẫn này chủ đề lớn và thanh lịch, và không nên được dùng như là một phương pháp điều trị triệt để, toàn diện. | ENGINEERING VISCOELASTICITY David Roylance Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA 02139 October 24 2001 1 Introduction This document is intended to outline an important aspect of the mechanical response of polymers and polymer-matrix composites the field of linear viscoelasticity. The topics included here are aimed at providing an instructional introduction to this large and elegant subject and should not be taken as a thorough or comprehensive treatment. The references appearing either as footnotes to the text or listed separately at the end of the notes should be consulted for more thorough coverage. Viscoelastic response is often used as a probe in polymer science since it is sensitive to the material s chemistry and microstructure. The concepts and techniques presented here are important for this purpose but the principal objective of this document is to demonstrate how linear viscoelasticity can be incorporated into the general theory of mechanics of materials so that structures containing viscoelastic components can be designed and analyzed. While not all polymers are viscoelastic to any important practical extent and even fewer are linearly viscoelastic1 this theory provides a usable engineering approximation for many applications in polymer and composites engineering. Even in instances requiring more elaborate treatments the linear viscoelastic theory is a useful starting point. 2 Molecular Mechanisms When subjected to an applied stress polymers may deform by either or both of two fundamentally different atomistic mechanisms. The lengths and angles of the chemical bonds connecting the atoms may distort moving the atoms to new positions of greater internal energy. This is a small motion and occurs very quickly requiring only w 10-12 seconds. If the polymer has sufficient molecular mobility larger-scale rearrangements of the atoms may also be possible. For instance the relatively facile rotation .
