13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- than the bulk material or non-nitrided specimen of 440 MPa. Hence, the plasma nitriding process has increased the fatigue limit stress by 61%. b) The plasma nitriding process has increased the material hardness from 454 to 885 mHV. c) Basquin’s empiric law for fatigue life of PH-42 Supra steel plasma nitrided specimens was (MPa) 2921 N 0.1024 f a − σ = and for non-nitrided specimens, (MPa) 2182.7 N 0.1159 f a − σ = . d) SEM analysis of fracture surface of fatigue test specimen of PH-42 Supra steel non-nitrided presented brittle fracture mechanism: the fatigue crack length near the surface was very small. e) SEM analysis of fracture surface of fatigue test specimen of PH-42 Supra steel plasma nitrided had shown rupture by brittle fracture and a very small fatigue region near specimen surface. The fatigue crack length near the specimen surface was evaluated approximately 20µm owing to plastic compressive deformations. f) The plasma nitrided specimens have increased the surface roughness Ra in relation to the non-nitrided specimens from Ra = 0.11µm to 0.35µm for non-nitrided and plasma nitrided respectively, but they both can be considered polished for their very low values. g) In tensile tests, surface cracks initiated in the nitrided layer and at 90 degree to the load line are seen. Hence, the fracture mechanism of the nitrided layer in tensile test was brittle fracture due to principal maximum tensile stress. Acknowledgements The authors would like to thank the company TOX Pressotechnik of Joinville/Brazil for providing the specimens, University of Santa Catarina State and CNPq of Brazil for financial support. References [1] C.E.S. Amorim, Análise dos recobrimentos anticorrosivos aplicados sobre um aço aeronáutico de alta resistência no comportamento em fadiga. Thesis (Doutoramento in Mechanical Engineering), Faculdade de Engenharia de Guaratinguetá, Guaratinguetá/Brazil, 2003. [2] Y. Murakami; S. Kodama; S. Konuma, Quantitative evaluation of effects of non-metallic inclusions on fatigue strength steels I: Basic fatigue mechanism and evaluation of correlation between fracture stress and the size and location of nonmetallic inclusions. Int. J. Fatigue, Sept. (1989) 291-298. [3] H.J.C. Voorvald; M.P. Silva; M.Y.P. Costa; M.O.H. Cioffi, Improvement in the fatigue strength of chromium electroplated AISI 4340 steel by shot peening. Fatigue &Structures, 32 (2009) 97-104. [4] Formadur PH-42 Superclean. Available in http://www.schmolz-bickenbach.com.br/ fileadmin/files/schmolz-bickenbach.com.br/documents/Fichas_Tecnicas_novo_formato_dez2011/M oldes/Formadur_Ph42superclean.pdf> acessed on 4 december 2011. [5] Rebrac Instrumentos de Medição, Rugosidade. Available in <http://www.rebrac.com.br/ downloads/RUGOSIDADE%20-par%C3%A2metros-.pdf>. acessed on april 2011. [6] Análise da rugosidade e Microestrutura de Camadas Nitretadas Obtidas pelos Processos Líquido, Gasoso e Iônico em Aço AISI H13. Available in <http://www.bodycote.com.br/artigos/ artigoNitretacao.pdf> acessed on 23 april 2011. [7] S.A. Meguid, Engineering Fracture Mechanics. Department of Mechanical Engineering, University of Toronto, Canada, Elsevier Applied Science, 1989, p. 75-79. [8] Norman E. Dowling, Mechanical Behavior of Materials. 3rd edition, Prentice-Hall, USA, 2006.
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