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Comportement thermomécanique de fontes à graphite sphéroïdal pour collecteurs d'échappement

Abstract : The increased output of automotive engines leads to higher temperature levels in exhaust manifolds. The ferritic cast irons (GS50 and SiMo) used by RENAULT experience microstructural evolutions at high temperature (800oC), that can be detrimental for their resistance. Rather than choosing more expensive higher grade materials, the better knowledge of the microstructural evolutions of GS cast irons and their behaviour would allow the optimisation of the component towards a compromise between light weight and reliability. Three main damage mechanisms were identified in a survey of bench-tested manifolds: oxidisation, decarburisation and phase transformation. They have been quantitatively investigated by isothermal and thermal cycling testing. The oxidisation and decarburisation kinetics were determined for various temperatures. Owing to the knowledge of these ageing mechanisms, specimens whose microstructures were similar to those observed were produced. As-cast and aged materials were compared in a testing program including dilatometry and low cycle fatigue tests. The parameters of constitutive equations for elastic-visco-plastic behaviour were identified for the as cast and aged materials. Results of thermal fatigue models, using the constitutive behaviour identified from isothermal tests, were in good agreement with experimental data. Thermo-mechanical analyses of partly decarburised specimens compared well with testing results, showing that the model can be applied to components of complex geometry, such as exhaust manifolds.
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Submitted on : Monday, May 19, 2008 - 8:00:00 AM
Last modification on : Wednesday, November 17, 2021 - 12:27:23 PM
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  • HAL Id : pastel-00003288, version 1


Philippe Bastid. Comportement thermomécanique de fontes à graphite sphéroïdal pour collecteurs d'échappement. Sciences de l'ingénieur [physics]. École Nationale Supérieure des Mines de Paris, 1995. Français. ⟨NNT : 1995ENMP1520⟩. ⟨pastel-00003288⟩



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