PSI - Issue 57

Nesrine Majed et al. / Procedia Structural Integrity 57 (2024) 502–509

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Nesrine Majed et al. / Structural Integrity Procedia 00 (2019) 000 – 000

Wang et al. (2001) proved that the fineness of the alloy is characterized by the secondary Dendritic Arm Spacing 'SDAS': inter-dendritic distance. In addition, the authors revealed that this parameter influences the number of cycles of both aluminium-cast alloys A356 and A357, under cyclic mechanical loadings. Iben Houria et al. (2015) proved that the microstructure (SDAS) impacts the torsional fatigue limit  D . Murakami (2002) defined the parameter √ which is equal to the square root of the defect surface on a plane perpendicular to the direction of maximum principal stress, to characterize the defect size. This parameter can be used to measure different defect morphologies. A Serrano-Munoz (2015) study demonstrated that the position of the defect is of importance. He found that the growth rate of the crack is higher when a crack propagates from a surface defect. Nadot and Billaudeau (2006) proposed the gradient model (DSG), which was then modified by Gadouini (2007), who uses the gradient on equivalent stress to describe the influence of defects on the fatigue limit. Nasr et al. (2018) developed an approach, based on the affected depth, to estimate the fatigue limit at a large number of cycles of a material with spherical or elliptical defects by applying the Crossland criterion. Nomenclature √ Equivalent defect size of defect perpendicular to the direction of the maximum principal stress (µm) HCF High cycle fatigue ASTM American Society of testing and fatigue AD Affected depth approach HLP Highest Loaded Plane Affected depth at fatigue limit (µm) E Young’s modulus (MPa) Ultimate tensile strength (MPa) 0.2 0.2% monotonous yield stress (MPa) Load ratio: = / The maximal hydrostatic stress during a loading cycle (MPa) 2, Amplitude over load cycle of the second invariant of deviatoric stress tensor ( 2 ) Coefficient in Crossland criterion Material parameter in Crossland Criteria (MPa) −1 Fatigue limit under fully reversed tension of defect-free material (MPa) Amplitude of torsion loading (MPa) Amplitude of tension loading (MPa) τ −1 Fatigue limit under fully reversed torsion loading of defect-free material (MPa) 3 −8 1 Fatigue limit under fully reversed tension of defect-free material with SDAS=38µm ±6 (MPa) 38−1 Fatigue limit under fully reversed torsion of defect-free material with SDAS=38µm ±6 (MPa) SDAS Secondary Dendrite Arms Spacing (μm) C The material parameter in the kinematic hardening model (MPa) γ The material parameter in the Kinematic hardening model

2. Material

Cast Al-Si-Mg alloys have a high strength-to-weight ratio, low production costs and good weldability and corrosion resistance as indicated by Polmear (2007) . The rapid cooling of the molten material produces a primary type α -Al dendritic microstructure containing approximately 1% Si in solid solution, silicon particles and intermetallic. The first figure shows the microstructure of the reference material as represented by Rotella et al (2015).