Impact of microstructural properties on the crack threshold of aluminium castings

Oberreiter, Matthias; Aigner, Roman; Pomberger, Sebastian; Leitner, Martin; Stoschka, Michael

doi:10.1016/j.engfracmech.2020.107431

Cited by 5 publications

(5 citation statements)

References 53 publications

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“…All crack growth data were evaluated at a probability of occurrence of

. Short and long crack growth behaviour of the aluminium series AlSi8Cu3-A and AlSi8Cu3-B, including detailed analysis of the microstructural relationship as well as a generalized dataset, is already reported in [ 93 ].…”

Section: Resultsmentioning

confidence: 99%

“…Maierhofer et al [ 92 ] recommends describing the crack extension from the intrinsic short crack threshold

up to the long crack threshold

by Equation ( 8 ) as functions of the predominant closure mechanisms i . Regarding the in-depth influence of microstructure on crack growth parameters and the effect of the highly stressed volume, the authors refer to previous investigations [ 93 , 94 ] for Al–Si cast alloys.

with

…”

Section: Introductionmentioning

confidence: 99%

“…This effective local load–stress ratio directly affects the local crack growth behaviour as the effective residual stress state opens or closes the crack flanks [ 100 , 101 , 102 ]. To consider the influence of the load–stress ratio on the long crack threshold values, Newman [ 103 ] introduced an engineering-feasible approach based on an initial crack threshold value

at tumescent load and a constant

, applied for steel in [ 92 ] and for aluminium alloys in [ 93 ]. In case of a defect free material, representing the upper border of the KTD, the effect of the load–stress ratio can be considered using the nominal stress approach of the common engineering guideline [ 58 ].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

et al. 2023

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The endurance limit of structural mechanical components is affected by the residual stress state, which depends strongly on the manufacturing process. In general, compressive residual stresses tend to result in an increased fatigue strength. Post-manufacturing processes such as shot peening or vibratory finishing may achieve such a compressive residual stress state. But within complex components, manufacturing-process-based imperfections severely limit the fatigue strength. Thus, the interactions of imperfections, residual stress state and material strength are key aspects in fatigue design. In this work, cast steel and aluminium alloys are investigated, each of them in vibratory finished and polished surface condition. A layer-based fatigue assessment concept is extended towards stable effective mean stress state considering the elastic–plastic material behaviour. Murakami’s concept was applied to incorporate the effect of hardness change and residual stress state. Residual stress relaxation is determined by elastic–plastic simulations invoking a combined hardening model. If the effective stress ratio within the local layer-based fatigue strength is evaluated as critical distance value, a sound calculation of fatigue strength can be achieved. Summing up, the layer-based fatigue strength design is extended and features an enhanced understanding of the effective stabilized mean stress state during cyclic loading.

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“…All crack growth data were evaluated at a probability of occurrence of

Section: Resultsmentioning

confidence: 99%

“…Maierhofer et al [ 92 ] recommends describing the crack extension from the intrinsic short crack threshold

up to the long crack threshold

with

…”

Section: Introductionmentioning

confidence: 99%

at tumescent load and a constant

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2023

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“…The base material strength σ LLF,0 was determined at specimens with HIP treatment; see the summary in Table 5. An extensive study about crack propagation in a varying microstructure is given in [82], enabling the determination of probabilistic crack growth parameters used to construct the Kitagawa diagram. The crack extension ∆a m,α,j (GEV) can be calculated using Equation (13), whereas the value a m,α,j (GEV) is determined based on the statistical distribution of the defects for a probability of occurrence of 50%.…”

Section: Layer-based Fatigue Assessment Methodologymentioning

confidence: 99%

A Probabilistic Fatigue Strength Assessment in AlSi-Cast Material by a Layer-Based Approach

Oberreiter

Fladischer

Stoschka

et al. 2022

Metals

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An advanced lightweight design in cast aluminium alloys features complexly shaped geometries with strongly varying local casting process conditions. This affects the local microstructure in terms of porosity grade and secondary dendrite arm spacing distribution. Moreover, complex service loads imply changing local load stress vectors within these components, evoking a wide range of highly stressed volumes within different microstructural properties per load sequence. To superimpose the effects of bulk and surface fatigue strength in relation to the operating load sequence for the aluminium alloy EN AC 46200, a layer-based fatigue assessment concept is applied in this paper considering a non-homogeneous distribution of defects within the investigated samples. The bulk fatigue property is now obtained by a probabilistic evaluation of computed tomography results per investigated layer. Moreover, the effect of clustering defects of computed tomography is studied according to recommendations from the literature, leading to a significant impact in sponge-like porosity layers. The highly stressed volume fatigue model is applied to computed tomography results. The validation procedure leads to a scattering of mean fatigue life from −2.6% to 12.9% for the investigated layers, inheriting strongly varying local casting process conditions.

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“…The crack length is measured by the direct current potential drop method, incorporating a compensation of crack length fluctuations due to ambient temperature changes. A detailed description of the testing procedure is given in [7].…”

Section: Experimental Workmentioning

confidence: 99%

Set-up of a Generalized Dataset for Crack-Closure-Mechanisms of Cast Steel

Horvath

Oberreiter

Stoschka

et al. 2021

JCME

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In components, crack propagation is subjected to crack-closure-mechanisms which affect the build-up of the relevant threshold stress intensity factor range during cyclic loading. As structural parts are exposed to service loads incorporating a variety of load ratios, a significant change of the long-crack threshold value occurs, leading to a severe stress ratio dependency of crack-closure-mechanisms. Thus, an extensive number of crack propagation experiments is required to gain statistically proven fracture mechanical parameters describing the build-up of closure effects as crack growth resistance curves.The article presents a generalized dataset to assess the formation of crack-closure-mechanisms of cast steel G21Mn5+N. Numerous crack propagation experiments utilizing single edge notched bending (SENB) sample geometries are conducted, incorporating alternate to tumescent stress ratios. The statistically derived, generalized crack growth resistance curve features the impact of closure effects on the crack propagation rate in a uniform manner. To extend the dataset to arbitrary load ratios, the long-crack threshold approach according to Newman is invoked. The generalized dataset for the cast steel G21Mn5+N is validated by analytical fracture mechanical calculations for the utilized SENB-sample geometries. Incorporating a modified NASGRO equation, a sound correlation of analytical and experimental crack propagation rates is observed. Moreover, the derived master crack propagation resistance curve is implemented as a user-defined script into a numerical crack growth calculation tool and supports a local, node--based numerical crack propagation study as demonstrated for a representative SENB-sample. Concluding, the derived dataset facilitates the calculation of fatigue life of crack-affected cast steel components subjected to arbitrary stress ratios.

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Impact of microstructural properties on the crack threshold of aluminium castings

Cited by 5 publications

References 53 publications

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

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

A Probabilistic Fatigue Strength Assessment in AlSi-Cast Material by a Layer-Based Approach

Set-up of a Generalized Dataset for Crack-Closure-Mechanisms of Cast Steel

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