Estimating fatigue life under variable amplitude loading through quantitative fractography – A case study J.R. Tarpani a, *, C.O.F.T. Ruckert a , M.T. Milan a , R.V. Silva a ,A.RosatoJr. b , R.N. Pereira b ,W.W.Bose a , D. Spinelli a a Materials, Aeronautic and Automotive Engineering Department, Engineering School of Sa ˜o Carlos, University of Sa ˜o Paulo, Sa ˜o Carlos-SP, 13.566-590, Brazil b Embraer S/A, Sa ˜o Jose ´ dos Campos-SP, 12.227-901, Brazil Received 10 September 2003; accepted 27 September 2003 Abstract QuantitativefractographytechniqueshavebeenimplementedandfrequentlyusedintheFailureAnalysisLaboratory – LANAF, at the Engineering School of Sa˜o Carlos, for fatigue life estimations of structural components, whose fracturesurfacesaresubjectedtodetailedinspectionwiththeaidofscanningelectronmicroscopes.Thisworkdescribes oneoftherecentactivitiesinprogressattheLANAF,inwhichfatiguecrackinitiationandpropagationliveshavebeen estimated for an idealized aeronautical part tested in the laboratory, under variable amplitude loading condition – VAL, i.e., flight simulation testing. Fractographic reconstitution of sub-critical crack growth has been performed through the identification of marking load patterns left in the wake of the propagating crack, which have been corre- latedtothesignificantloadlevelsappliedduringthefatiguetest.Asemi-automatedproceduretoestimatefatiguelives under VAL has been developed and implemented by which a virtual marking load pattern is generated and compared to the real pattern determined fractographically. # 2004 Elsevier Ltd. All rights reserved. Keywords: Aluminium alloys; Fatigue markings; Fractography; Marker loads; Quantitative fractography 1. Introduction Fractographic techniques using scanning electron microscopes (SEM) are extensively used in failure analysis of aeronautical components and structures [1–5]. The more advanced procedure employed on the fatigue life estimation of in-service or in-test fractured components undergoing variable amplitude loading – VAL, is depicted in Fig. 1. The technique consists basically of generating a virtual pattern of fatigue load marks provided by the applied loading spectrum, using preferably computational techniques, and comparesitwiththepatternactuallyrecordedonthefracturesurfaceofthecomponent,obtainedthrough microscopic survey. In summary, to be successful this procedure depends basically on the correct 1350-6307/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2003.09.004 Engineering Failure Analysis 11 (2004) 547–559 www.elsevier.com/locate/engfailanal * Corresponding author. Tel.: +55-16-273-9590; fax: +55-16-273-9574. E-mail address: jrpan@sc.usp.br (J.R. Tarpani).