RECENT RESEARCH ON THERMAL FATIGUE OF COMPOSITE ELEMENTS OF TRANSPORT MEANS Andrzej Katunin 1, a, *, Wojciech Moczulski 1,b 1 Institute of Fundamentals of Machinery Design, Silesian University of Technology, Konarskiego 18A, 44-100 Gliwice, Poland a andrzej.katunin@polsl.pl, b wojciech.moczulski@polsl.pl, *corresponding author Keywords: thermal fatigue, self-heating effect, polymeric composites, structural diagnostics Abstract. Thermal fatigue occurred in many engineering constructions made of polymeric composites subjected to the intensive loading and vibrations. During this process the mechanical energy is dissipated in the form of heat due to the hysteretic behaviour of the material, which introduces the self-heating effect. In some cases the self-heating effect dominates the fatigue process and intensifies much structural degradation of composite elements. The paper presented a survey of engineering applications in which the self-heating effect and thermal fatigue occurred and recent advances in theoretical and experimental research in this area. Selected results of experimental studies were presented and discussed. Introduction Polymer composites are widely used in many scientific and industrial applications. New technologies of materials manufacturing and increasing expectations of reliability of machine elements caused appreciable increase of application of polymer composites in machine building in last decades. These materials used lately only for electromagnetic isolation and for the elements, which are not subjected to intensive loading and high stresses found now very responsible applications in civil engineering, military industry, aircraft and spacecraft industries, shipbuilding and machine building industries, etc. The application of polymer composites in such applications is resulted by great properties of these materials, first of all high strength-to-mass ratio achieved mainly by using novel reinforcement materials and techniques of manufacturing different reinforcement forms including three-dimensional ones. Moreover, these materials remain insensitive to some physical factors, which include corrosion resistance, thermal and electromagnetic isolation properties, neutrality to some chemical compounds and solutions. The application of polymeric composites allow for reducing a mass of machine elements with retaining specific mechanical properties of them, which is the most crucial factor in aircraft applications. However, designing, manufacturing and maintaining of elements made of polymeric composites is much more difficult then for traditional materials (e.g. steels and metallic alloys). Polymer composites characterized by high degree of material and geometric anisotropy. Their behaviour remains elastic in a very limited range of deformations and physical properties, in the most cases the viscoelastic behaviour of such materials could be observed for typical operation loadings. Therefore, functional characteristics of polymer composites are usually nonlinear. During loading of composite elements, due to their viscoelastic nature, the self-heating effect may occur. This effect is resulted during energy dissipation in loading conditions following a delay of stress response after applied strain and thus, changes in amplitudes phases of stress and strain. Such hysteretic behaviour causes that significant part of dissipated energy is converted into a heat. Considering a fact that the most of polymers used in machine building is characterized by low thermal conductivity and some other further-presented physical aspects a heat is stored into the structure and the self-heating temperature grows up in the region of the highest stress field until reaching the equilibrium state with the energy convected to the surrounding. The heating-up of the structure causes irreversible changes, which is resulted in drop of mechanical properties, increasing Key Engineering Materials Vol. 588 (2014) pp 243-248 Online available since 2013/Oct/11 at www.scientific.net © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/KEM.588.243 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 157.158.182.47-13/10/13,12:45:01)