PSI - Issue 5

Amal ben Ahmed et al. / Procedia Structural Integrity 5 (2017) 524–530 Amal ben Ahmed et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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1. Introduction A356-T6 aluminium alloy is extensively employed throughout the aerospace and automotive sectors owning to its high mechanical performances and low density comparing to other metals. Most Cast A356-T6 components are often subjected to cyclic mechanical loadings throughout their service lives. However, the A356-T6 HCF response shows a large dispersiondue especially to the random aspect of the aluminum matrix (SDAS)[IbenHouriya et al. (2015),M.J. Roy et al. (2011), M. Roy et al. (2012), Q.G Wang et al. (2001) and P.Li et al. (2009)].In fact, a simpledeterministic modelling seems to be unable to predictthe fatigue response of aluminum structures in more efficient and reliable way. Looking for a model /Engineering methodthat could evaluate HCF life of AL mechanical structures with an acceptable confidence level, still remains among a challenging point in several industrial sectors . The present paper aims to develop an engineering approach for HCF life prediction of A356-T6 Aluminum alloy that takes into account the effect of material dispersions. The FE method was implemented for modelingthe A356-T6 HCF under different fatigue conditions. The MCS is used to determine the iso-pobabilistic Kitagawa-Tkahashi Diagrams corresponding to 5%, 50% and 95% of reliability. A comparison between the suggested approach and available experimental data is performed. The DSG criterion was proposed by Nadot et al. [Nadot et al. (2006)] and improved by Vincent et al.[Vincent et al.(2014)] to evaluate the stress distribution around a defect and to evaluate its impact on the fatigue limit under different load conditions. It is may be expressed as follow: = , − , − ,∞ √ ≤ (1) Where: ∇ : The equivalent stress given by the DSG criterion. √ : The defect size , , ,∞ : two equivalent stresses given by a multiaxial fatigue criterion respectively in the most solicited defect point and far from the defect. an experimental campaign carried out on defective A356-T6 and made by IbenHouriya et al. [IbenHouriya et al.(2015)] proved that the Crossland criterion( ) is the most suitable to describe the stress distribution in the DSG approach. The authors have also proposed a new formulation of the DSG criterion that takes into accountthe microstructural heterogeneities effects (SDAS). i) For defect free alloy, fatigue limit is only influenced by microstructure (SDAS) and expressed as follow: ∇ = , = 0 exp(− 2 0 ) ሺʹሻ ii) For defective alloy, fatigue limit is influenced by both SDAS and defect size ( √ ) and expressed as follow: ∇M = , − ∇ , − ,∞ √ ሺ͵ሻ Where: 2 is the SDAS value 0 , 0 and ∇ are three parameters experimentally identified. 2. Theoretical Background: Defect Stress Gradient (DSG)criterion