Fracture–Mechanical Assessment of the Effect of Defects on the Fatigue Lifetime and Limit in Cast and Additively Manufactured Aluminum–Silicon Alloys from HCF to VHCF Regime

Abstract

Aluminum–silicon alloys are commonly used in die-cast and additively manufactured (AM) light-weight components due to their good processability and high strength-to-weight ratio. As both processing routes lead to the formation of defects such as gas and shrinkage porosity, a defect-sensitive design of components is necessary for safe application. This study deals with the fatigue and crack propagation behavior of die-cast alloy AlSi7Mg0.3 and additively manufactured alloy AlSi12 and its relation to process-induced defects. The different porosities result in significant changes in the fatigue stress-lifetime (S–N) curves. Therefore, the local stress intensity factors of crack-initiating defects were determined in the high and very high cycle fatigue regime according to the fracture mechanics approach of Murakami. Through correlation with fatigue lifetime, the relationship of stress intensity factor (SIF) and fatigue lifetime (N) could be described by one power law (SIF–N curve) for all porosities. The relationship between fatigue limit and defect size was further investigated by Kitagawa–Takahashi (KT) diagrams. By using El Haddad’s intrinsic crack length, reliable differentiation between fracture and run out of the cast and AM aluminum alloys could be realized. SIF–N curves and KT diagrams enable a reliable fatigue design of cast and AM aluminum alloys for a finite and infinite lifetime.

Very high cycle fatigue (VHCF) response of additively manufactured materials: A review

“…In previous studies, [32][33][34][35][36] the VHCF response of AlSi12 alloy processed by AM technologies is investigated. The specimens subjected to VHCF tests are manufactured by using an SLM 250 HL machine, by SLM Solution company, with a laser power of 400 W. A chessboard scanning strategy with 90 between the chess fields is used.…”

“…In Tenkamp et al 32 a comparison between the VHCF strength of die‐cast alloy AlSi7Mg0.3 and additively manufactured AlSi12 is carried out. Die‐cast (DC) samples are manufactured by gravity die‐casting, including alloying procedure with AlTi5B1 and Sr.…”

“…S‐N plot of (A) batch DC (die‐cast process) and (B) AM (1‐no SR, 2‐with SR) from Tenkamp et al 32 [Colour figure can be viewed at wileyonlinelibrary.com]…”

Review on Fatigue of Additive Manufactured Metallic Alloys: Microstructure, Performance, Enhancement, and Assessment Methods

“…[ 14 ] Hence, the S‐N curve was described by the stress intensity factor amplitude in terms of Murakami's parameter rather than stress or strain, which markedly reduced the scatter in fatigue data. [ 92,120,318,321 ] In addition, Shimatani et al. [ 324 ] evaluated the fatigue life by the stress amplitude at the crack initiation site multiplied with $$\sqrt[{12}]{{{\mathrm{area}}}}$$.…”

Effect of Surface Finishing State on Fatigue Strength of Cast Aluminium and Steel Alloys

“…Lightweight engineering is often driven by topology optimization, yielding to complexly shaped components [ 1 ]. Due to benefits in castability and comparable low density, AlSi-cast alloys are broadly used in mobility industry and transport applications [ 2 , 3 , 4 ]. Besides Al-alloys, cast steel alloys play an important role as well due to improved structural load-bearing capability [ 5 , 6 , 7 ].…”