Experimental investigation on statistics of extremes for three-dimensional distribution of non-metallic inclusions

Zhou, Shirong; Murakami, Yukitaka; Beretta, S.; Fukushima, Yoshihiro

doi:10.1179/026708302225007736

Cited by 25 publications

(14 citation statements)

References 13 publications

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“…As was recently shown in the problem of inclusions in steel, this method could be extended to the estimation of three-dimensional sizes of large pores in specified volumes of material. 36,40,43,44 Finally, different types of porosity could be taken into account by using new approaches, based on mixed model or competing risk model. [43][44][45] Conclusions In this paper, two statistical methods, based on the statistics of extremes theory, were studied to predict the maximum pore size in laser welded joints longer than the inspection domain.…”

Section: Suggestions For Further Studymentioning

confidence: 99%

Estimate of maximum pore size in keyhole laser welding of carbon steel

Beretta¹,

Previtali²

2009

Science and Technology of Welding and Joining

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Porosity is easily formed in welded joints during high power laser welding due to keyhole instability. Large pores have detrimental effects on the fatigue resistance of a component and cause many failures in welded parts. This paper is aimed at predicting the maximum pore dimension in long laser welded joints, starting from the sampling of large pores in shorter joints. Two sampling strategies and, consequently, two estimating techniques, both belonging to the statistics of extremes, were explored. The first approach, extreme value type, is used to estimate the size of the maximum pore in each of a series of steel samples. In each sample, the larger single pore or two large pores which are very close are the measured maximum pore. The second approach, threshold value type, is used to estimate the size of pores larger than a critical threshold in a single sample of steel. Both approaches lead to good estimates of the largest pore distribution in short laser welded joints. However, the first one is more adequate to describe the largest pore distribution, because it allows the synergetic effect of two adjacent pores to be considered. In particular, the Gumbel distribution adequately fits the experimental data even in the case of welded joints 10 times longer than the investigated bead length.List of symbols area 1=2 max square roots of the area of the largest pore in extreme value approach area 1=2 i square roots of the area of pores larger than the initial threshold in threshold value approach c a (12a) quantile of the x 2 1 distribution D deviance function k number of pores that exceed the threshold u l sample log likelihood function L return bead length L 0 standard testing length for extreme value approach L T total investigated length n total number of pores in the total investigated length N total number of block maxima examined T return period u threshold size u 0 initial threshold size for threshold value approach y T reduced variate for plotting GEV or SEV probability plot m GEV estimated location parameter of GEV distribution m SEV estimated location parameter of SEV distribution ĵ GEV estimated shape parameter of GEV distribution ĵ GP estimated shape parameter of GP distribution ŝ EXP estimated scale parameter of EXP distribution ŝ GEV estimated scale parameter of GEV distribution ŝ GP estimated scale parameter of GP distribution ŝ SEV estimated scale parameter of SEV distribution

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Section: Suggestions For Further Studymentioning

confidence: 99%

Estimate of maximum pore size in keyhole laser welding of carbon steel

Beretta¹,

Previtali²

2009

Science and Technology of Welding and Joining

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“…Furthermore, they concluded that the largest microstructural defect determines the fatigue limit. Based on the experimental works [9][10][11][12][13][14], it is possible to extract the following key points: (a) the investigated martensitic steels SAE 4150 and SAE 4140 show fatigue crack nucleation on free surfaces as well as at oxidic and sulfidic inclusions with varying sizes, shapes and orientations to loading axis, (b) the MnS inclusions reveal a complex delamination behavior in case of transversal loading and (c) the lower bound of fatigue properties is controlled by the maximum size of non-metallic inclusions within the high stressed volumes [15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Micromechanical Modeling of Fatigue Crack Nucleation around Non-Metallic Inclusions in Martensitic High-Strength Steels

Schäfer

Sonnweber-Ribic

Hassan

et al. 2019

Metals

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Martensitic high-strength steels are prone to exhibit premature fatigue failure due to fatigue crack nucleation at non-metallic inclusions and other microstructural defects. This study investigates the fatigue crack nucleation behavior of the martensitic steel SAE 4150 at different microstructural defects by means of micromechanical simulations. Inclusion statistics based on experimental data serve as a reference for the identification of failure-relevant inclusions and defects for the material of interest. A comprehensive numerical design of experiment was performed to systematically assess the influencing parameters of the microstructural defects with respect to their fatigue crack nucleation potential. In particular, the effects of defect type, inclusion–matrix interface configuration, defect size, defect shape and defect alignment to loading axis on fatigue damage behavior were studied and discussed in detail. To account for the evolution of residual stresses around inclusions due to previous heat treatments of the material, an elasto-plastic extension of the micromechanical model is proposed. The non-local Fatemi–Socie parameter was used in this study to quantify the fatigue crack nucleation potential. The numerical results of the study exhibit a loading level-dependent damage potential of the different inclusion–matrix configurations and a fundamental influence of the alignment of specific defect types to the loading axis. These results illustrate that the micromechanical model can quantitatively evaluate the different defects, which can make a valuable contribution to the comparison of different material grades in the future.

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“…The size of frontal inclusions in a specimen was determined; they initiated a fatigue crack. It was demonstrated in [9,22] that the presence of large non-metallic inclusions which form during steel deoxidation results in a sudden drop in fatigue strength. Such inclusions often have a crucial effect on the mechanism of initiation of a fatigue crack, especially in the area close to infinite fatigue strength or with a high-frequency load [8,12,19].…”

Section: Introductionmentioning

confidence: 99%

“…Taking into consideration the results of fatigue tests on 16MnCr5 steel after LPC treatment and the main cause of the loss of cohesion under cycle loading, i.e. non-metallic inclusions based on calcium and aluminum presented in papers [8,9,19,22], the numerical model in ANSYS 18.0 environment was created. Original FEM model was complemented with a couple of possible positions of non-metallic inclusion in the technological surface layer.Based on observations of yield stress distribution around the inclusion, the possible crack initiation sited were sought after.…”

Section: Introductionmentioning

confidence: 99%

NUMERICAL ANALYSIS OF THE EFFECT OF NONMETALLIC INCLUSIONS LOCATION IN CARBURIZED LAYER OF 16MnCr5 STEEL ON INITIATION OF FATIGUE CRACKING

Lipa¹

2018

Adv. Sci. Technol. Res. J.

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This paper presents the results of a numerical analysis of the effect of the position of non-metallic inclusions in a hardened top layer in 16MnCr5 steel on the mechanism of fatigue destruction. An analysis of a hardened layer formed by thermo-chemical treatment using FineCarb® technology was conducted.Non-metallic inclusions formed by deoxidation of steel were studied; they are usually made of calcium and aluminum. Four positions of inclusions in the hardened layer were tested: under the layer, in the middle part of the layer, under the surface and on the border of two sublayers. The results of the FEM analysis were treated as a qualitative analysis. A map of plastic strains around the inclusion under study was observed. The appearance of plastic strains in the area under analysis signaledthe initiation of a fatigue crack. It was observed that the mechanism of destruction depends largely on the distribution of stress in the top layer and on the place where the inclusion is anchored in the layer. Inclusions under the layer were found to be the main cause of the loss of the structural continuity, which explains the most frequent cases of the initiation of fatigue cracks.

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Experimental investigation on statistics of extremes for three-dimensional distribution of non-metallic inclusions

Cited by 25 publications

References 13 publications

Estimate of maximum pore size in keyhole laser welding of carbon steel

Estimate of maximum pore size in keyhole laser welding of carbon steel

Micromechanical Modeling of Fatigue Crack Nucleation around Non-Metallic Inclusions in Martensitic High-Strength Steels

NUMERICAL ANALYSIS OF THE EFFECT OF NONMETALLIC INCLUSIONS LOCATION IN CARBURIZED LAYER OF 16MnCr5 STEEL ON INITIATION OF FATIGUE CRACKING

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