Title: Size effect in transient thermal fatigue testing and thermo-mechanical screening of coatings

Authors: G. Dour, F. Medjedoub, G. Diaconu, D. Girardin, A. Michrafy, T.M. Loulou, F. Rezai-Aria

Addresses: CROMeP – Ecole Mines Albi, 81013 Albi Cedex 09, France. ' CROMeP – Ecole Mines Albi, 81013 Albi Cedex 09, France. ' CROMeP – Ecole Mines Albi, 81013 Albi Cedex 09, France. ' Centre de R&D, St. Gobain PAM, BP 109, 54 704, Pont a Mousson, France. ' LGPSD, UMR 2392, CROMeP – Ecole Mines Albi, 81013 Albi Cedex 09, France. ' Laboratoire d'Etudes Thermiques, Energetiques et Environnement, Universite de Bretagne-Sud, B.P. 92116, 56321 LORIENT Cedex, France. ' CROMeP – Ecole Mines Albi, 81013 Albi Cedex 09, France

Abstract: In an attempt to bring new ideas to thermal fatigue analysis of tools, we propose the principle of the two driving forces leading to damage by Thermal Fatigue (TF). After a definition of the two driving forces based on temperature and thermo-mechanical loadings, a procedure for evaluating them for in-service tools is proposed. In order to compare thermo-mechanical loadings in industrial tools to laboratory specimen, a normalisation of the thermo-mechanical equations is proposed. A size effect in those thermal mechanical problems is justified and used to set an original rule to design transient TF tests. In a second example related to coating tools or bi-materials tools, the concept of thermo-mechanical screening is explained: it corresponds to the optimum combination of materials properties leading to the vanishment of thermal stresses at the mating surface of a tool. An example is given that shows some conditions in which this can happen, depending on the combination of material properties. An example of application is then proposed.

Keywords: hot forming processes; shaping processes; hot work tool steels; thermal fatigue; thermo-mechanical loadings; thermal stresses; heat checking; coatings.

DOI: 10.1504/IJMMP.2008.018737

International Journal of Microstructure and Materials Properties, 2008 Vol.3 No.2/3, pp.311 - 325

Available online: 16 Jun 2008 *

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