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15 pages, 5072 KiB

Open AccessArticle

Understanding the Fatigue Notch Sensitivity of High-Strength Steels through Fracture Toughness

by Sergi Parareda, David Frómeta, Daniel Casellas, Henrik Sieurin and Antonio Mateo

Metals 2023, 13(6), 1117; https://doi.org/10.3390/met13061117 - 14 Jun 2023

Cited by 4 | Viewed by 1632

This study presents an innovative approach for selecting high-strength materials for fatigue dimensioning parts, considering both fracture toughness and fatigue performance. Warm and hot forming processes enable the construction of high-strength parts above 1000 MPa with complex geometries, making them suitable for lightweight [...] Read more.

This study presents an innovative approach for selecting high-strength materials for fatigue dimensioning parts, considering both fracture toughness and fatigue performance. Warm and hot forming processes enable the construction of high-strength parts above 1000 MPa with complex geometries, making them suitable for lightweight chassis in automotive and freight applications. This research reveals that high-strength steels can experience up to a 40% reduction in fatigue performance due to manufacturing defects introduced during punching and trimming. Fracture toughness has been proposed as a good indicator of notch sensitivity, with a strong correlation of 0.83 between fracture toughness and fatigue notch sensitivity. Therefore, by combining fracture toughness measurements and fatigue resistance obtained through the rapid fatigue test, it becomes possible to quickly identify the most fatigue-resistant materials to deal with defects. Among the nine materials analysed, warm-formed steels show promising characteristics for lightweight chassis construction, with high fatigue resistance and fracture toughness exceeding the proposed fracture threshold of 250 kJ/m². Full article

(This article belongs to the Special Issue New Trends in Fatigue of Metals)

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16 pages, 7453 KiB

Open AccessFeature PaperArticle

Effect of Residual Stresses on Fatigue Strength on the Smooth and Splined Parts of Spring Torsion Bars

by Vinko Močilnik, Jožef Predan and Nenad Gubeljak

Metals 2023, 13(6), 1004; https://doi.org/10.3390/met13061004 - 23 May 2023

Cited by 1 | Viewed by 1244

Abstract

The article discusses the effect of residual stresses on the fatigue strength of torsion bars by using the Dang Van fatigue criterion, at the stress concentration at the root of the tooth and at the smooth part of the torsion bar. Residual compressive [...] Read more.

The article discusses the effect of residual stresses on the fatigue strength of torsion bars by using the Dang Van fatigue criterion, at the stress concentration at the root of the tooth and at the smooth part of the torsion bar. Residual compressive stresses were induced on the surface during the technological processes by cold surface rolling and torsional pre-strain (pre-setting) to the plastic range, to increase the elastic linear range and to reduce the stress state during torsional loading. Normally, the stress reduction in the torsion bar at the mounting point is provided by the increased diameter of the splined part, compared to the smooth part of the torsion bar. In the case of a small difference between the diameter of the splined and the smooth parts of the torsion bar, a fatigue crack can be initiated in the notch, which causes the torsion bar to break during operation after a few hundred loading cycles. FEM stress analysis of a torsion bar was performed in the article. The actual residual stresses were measured by the non-destructive X-ray method at the place of stress concentration on the smooth and splined parts with a notch of the torsion bar, and Dang Van’s failure criterion was used to determine the fatigue behavior during torsional loading. Therefore, in the paper, the three methods were combined to determine the optimum lifetime of a torsion bar exposed to the required cyclic torque. The results of the analysis showed that the residual compressive stresses are useful up to a certain limit where the retarded fatigue crack initiation occurred, but a further increase of compressive stress caused an increase of the maximum shear stresses, which, in turn, caused the initiation of fatigue and failure at the splined part of the torsion bar before achieving the required number of cycles. Full article

(This article belongs to the Special Issue New Trends in Fatigue of Metals)

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18 pages, 3093 KiB

Open AccessFeature PaperArticle

Comparison between Fractal and Statistical Approaches to Model Size Effects in VHCF

by Stefano Invernizzi, Davide Paolino, Francesco Montagnoli, Andrea Tridello and Alberto Carpinteri

Metals 2022, 12(9), 1499; https://doi.org/10.3390/met12091499 - 10 Sep 2022

Cited by 6 | Viewed by 1337

Abstract

Size effects concern the anomalous scaling of relevant mechanical properties of materials and structures over a sufficiently wide dimensional range. In the last few years, thanks to technological advances, such effects have been experimentally detected also in the very high cycle fatigue (VHCF) [...] Read more.

Size effects concern the anomalous scaling of relevant mechanical properties of materials and structures over a sufficiently wide dimensional range. In the last few years, thanks to technological advances, such effects have been experimentally detected also in the very high cycle fatigue (VHCF) tests. Research groups at Politecnico di Torino are very active in this field, observing size effects on fatigue strength, fatigue life and fatigue limit up to the VHCF regime for different metal alloys. In addition, different theoretical models have been put forward to explain these effects. In the present paper, two of them are introduced, respectively based on fractal geometry and statistical concepts. Furthermore, a comparison between the models and experimental results is provided. Both models are able to predict the decrement in the fatigue life and in the conventional fatigue limit. Full article

(This article belongs to the Special Issue New Trends in Fatigue of Metals)

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14 pages, 9419 KiB

Open AccessFeature PaperArticle

Fatigue Lifetime Analysis of a Bicycle Frame Made by Additive Manufacturing Technology from AlSi10Mg

by Matúš Margetin, Vladimir Chmelko, Miroslav Sulko, Róbert Ďurka and Tomáš Koščo

Metals 2022, 12(8), 1277; https://doi.org/10.3390/met12081277 - 29 Jul 2022

Cited by 2 | Viewed by 2034

Abstract

The development of additive manufactured metals is in the transition phase, from research into the technology of 3D printing and the resulting properties of the metals towards their use in industrial practice. The article analyses the possibilities of producing bicycle frames using 3D [...] Read more.

The development of additive manufactured metals is in the transition phase, from research into the technology of 3D printing and the resulting properties of the metals towards their use in industrial practice. The article analyses the possibilities of producing bicycle frames using 3D printing. The stresses in a bicycle frame are analysed for the measured load spectra and FEM simulation. The approach to the fatigue life assessment of the bicycle frame is based on directly measured load multipliers and detailed FEM simulation with the subsequent calculation of fatigue damage in the individual planes of the critical point of the frame respecting the multiaxial stress state. The scatter of the cyclic properties of the AM material is considered by a statistical approach. The operational fatigue lifetimes of a frame made by 3D printing and one of conventional technology are compared. Full article

(This article belongs to the Special Issue New Trends in Fatigue of Metals)

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30 pages, 1395 KiB

Open AccessArticle

Benchmarking Newer Multiaxial Fatigue Strength Criteria on Data Sets of Various Sizes

by Jan Papuga, Martin Nesládek, Alexander Hasse, Eva Cízová and Lukáš Suchý

Metals 2022, 12(2), 289; https://doi.org/10.3390/met12020289 - 07 Feb 2022

Cited by 5 | Viewed by 1926

Abstract

The paper presents a comparison of six recently introduced multiaxial fatigue strength estimation criteria to four methods, the large-scope validation of which has already been published. The results obtained for each newer method are analyzed and discussed. From the newer methods, only the [...] Read more.

The paper presents a comparison of six recently introduced multiaxial fatigue strength estimation criteria to four methods, the large-scope validation of which has already been published. The results obtained for each newer method are analyzed and discussed. From the newer methods, only the criterion by Böhme reaches an estimation quality similar to the best performing criteria. The validation was performed on the FatLim data sets, but the primary focus of the paper is set to analyzing the validation on a smaller AMSD25 data set derived from it. The comparison shows that the application of AMSD25 for validation practice allows users to reduce the number of evaluated test cases, while generally preserving the worst cases showing the weaknesses of various estimation methods. Full article

(This article belongs to the Special Issue New Trends in Fatigue of Metals)

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29 pages, 14202 KiB

Open AccessArticle

Analytical and Experimental Investigation into Pre-Stressed Carbon Fiber Reinforced Polymer (CFRP) Fatigue Retrofits for Steel Waterway Lock-Gate Structures

by Christine Lozano, Maggie Langston, Mohammad H. Kashefizadeh and Gary S. Prinz

Metals 2022, 12(1), 88; https://doi.org/10.3390/met12010088 - 04 Jan 2022

Cited by 2 | Viewed by 1757

Abstract

Lock gates are an important part of the transportation infrastructure within the United States (US). Unfortunately, many existing lock gates have reached or exceeded their initial design lives and require frequent repairs to remain in service. Unscheduled repairs often increase as gates age, [...] Read more.

Lock gates are an important part of the transportation infrastructure within the United States (US). Unfortunately, many existing lock gates have reached or exceeded their initial design lives and require frequent repairs to remain in service. Unscheduled repairs often increase as gates age, having a local economic impact on freight transport, which can create economic ripples throughout the nation. Metal fatigue is a key cause of unscheduled service interruptions, degrading lock gate components over time. Additionally, because lock gates are submerged during operation, crack detection prior to component failure can be difficult, and repair costs can be high. This paper presents an analytical and experimental investigation into fatigue damage within common lock gate geometries, as well as fatigue mitigation strategies with a focus on extending gate service lives. Detailed finite element analyses are combined with fatigue and fracture mechanics theories to predict critical fatigue regions within common gate details and develop retrofit strategies for mitigating fatigue cracking. Full-scale experimental fatigue testing of a critical lock gate component is conducted to provide a baseline for the evaluation of retrofit strategies. Retrofit strategies and issues in using carbon fiber reinforced polymer (CFRP) plates having optimized pre-stress levels are discussed. Full article

(This article belongs to the Special Issue New Trends in Fatigue of Metals)

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18 pages, 6242 KiB

Open AccessFeature PaperArticle

A Novel Specimen Produced by Additive Manufacturing for Pure Plane Strain Fatigue Crack Growth Studies

by Joel de Jesus, Micael Borges, Fernando Antunes, José Ferreira, Luis Reis and Carlos Capela

Metals 2021, 11(3), 433; https://doi.org/10.3390/met11030433 - 05 Mar 2021

Cited by 5 | Viewed by 2206

Abstract

Fatigue crack growth is usually studied using C(T) or M(T) specimens with through-thickness cracks. The objective of the present study is to propose a cylindrical specimen with central crack, produced by additive manufacturing. This geometry allows to have pure plane strain state along [...] Read more.

Fatigue crack growth is usually studied using C(T) or M(T) specimens with through-thickness cracks. The objective of the present study is to propose a cylindrical specimen with central crack, produced by additive manufacturing. This geometry allows to have pure plane strain state along the whole crack front, avoiding the complexities associated with corner points, crack shape, and variation of crack closure along crack front. Additionally, this geometry may be used to develop studies in vacuum, avoiding expensive vacuum equipment, since the air is not in contact with the crack front. Cylindrical specimens of Ti6Al4V titanium alloy were produced by Selective Laser Melting and tested at a stress ratio R = 0. Marking with overloads was the solution adopted to measure the length of the internal cracks. The fracture surfaces presented circular crack fronts and the da/dN-ΔK curves showed a great influence of atmosphere on fatigue crack growth. An average difference of 50% was found between the results in air and vacuum. Therefore, this geometry with internal crack is an interesting alternative to through-thickness geometries. Full article

(This article belongs to the Special Issue New Trends in Fatigue of Metals)

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18 pages, 11514 KiB

Open AccessArticle

Monitoring the Damage Evolution in Rolling Contact Fatigue Tests Using Machine Learning and Vibrations

by Luca Provezza, Ileana Bodini, Candida Petrogalli, Matteo Lancini, Luigi Solazzi and Michela Faccoli

Metals 2021, 11(2), 283; https://doi.org/10.3390/met11020283 - 06 Feb 2021

Cited by 4 | Viewed by 1869

Abstract

This study shows the application of a system to monitor the state of damage of railway wheel steel specimens during rolling contact fatigue tests. This system can make continuous measurements with an evaluation of damage without stopping the tests and without destructive measurements. [...] Read more.

This study shows the application of a system to monitor the state of damage of railway wheel steel specimens during rolling contact fatigue tests. This system can make continuous measurements with an evaluation of damage without stopping the tests and without destructive measurements. Four tests were carried out to train the system by recording torque and vibration data. Both statistical and spectral features were extracted from the sensors signals. A Principal Component Analysis (PCA) was performed to reduce the volume of the initial dataset; then, the data were classified with the k-means algorithm. The results were then converted into probabilities curves. Metallurgical investigations (optical micrographs, wear curves) and hardness tests were carried out to assess the trends of machine learning analysis. The training tests were used to train the proposed algorithm. Three validation tests were performed by using the real-time results of the k-means algorithm as a stop condition. Metallurgical analysis was performed also in this case. The validation tests follow the results of the training test and metallurgical analysis confirms the damage found with the machine learning analysis: when the membership probability of the cluster corresponding to the damage state reaches a value higher than 0.5, the metallurgical analysis clearly shows the cracks on the surface of the specimen due to the rolling contact fatigue (RCF) damage mechanism. These preliminary results are positive, even if reproduced on a limited set of specimens. This approach could be integrated in rolling contact fatigue tests to provide additional information on damage progression. Full article

(This article belongs to the Special Issue New Trends in Fatigue of Metals)

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11 pages, 3013 KiB

Open AccessArticle

On the Recovery and Fatigue Life Extension of Stainless Steel 316 Metals by Means of Recovery Heat Treatment

by Ali Haghshenas and M. M. Khonsari

Metals 2020, 10(10), 1290; https://doi.org/10.3390/met10101290 - 27 Sep 2020

Viewed by 2139

Abstract

In this paper, we propose a methodology for enhancing the fatigue life of SS316 by performing intermittent recovery heat-treatment (RHT) in the Argon environment at different temperatures. To this end, fully-reversed fatigue bending tests are conducted on the heat-treated SS316 specimens. Damping values [...] Read more.

In this paper, we propose a methodology for enhancing the fatigue life of SS316 by performing intermittent recovery heat-treatment (RHT) in the Argon environment at different temperatures. To this end, fully-reversed fatigue bending tests are conducted on the heat-treated SS316 specimens. Damping values are obtained using the impact excitation technique to assess the damage remaining in the material after each RHT and the corresponding fatigue life. Damping is also used to distinguish the three stages of the fatigue phenomenon and the onset of crack initiation. The results show that by performing intermittent RHTs, the density of dislocation is decreased substantially and fatigue life is improved. Examination of the damping results also reveals that the material becomes more brittle after the RHT due to the decrease in the density of dislocations. The fatigue life of the specimens is governed by these two phenomena. Full article

(This article belongs to the Special Issue New Trends in Fatigue of Metals)

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Review

Jump to: Research

38 pages, 894 KiB

Open AccessFeature PaperReview

A Review of Damage, Void Evolution, and Fatigue Life Prediction Models

by Hsiao Wei Lee and Cemal Basaran

Metals 2021, 11(4), 609; https://doi.org/10.3390/met11040609 - 09 Apr 2021

Cited by 28 | Viewed by 5758

Abstract

Degradation, damage evolution, and fatigue models in the literature for various engineering materials, mostly metals and composites, are reviewed. For empirical models established under the framework of Newtonian mechanics, Gurson–Tvergaard–Needleman (GTN) type model, Johnson-Cook (J-C) type damage model, microplasticity model, some other micro-mechanism [...] Read more.

Degradation, damage evolution, and fatigue models in the literature for various engineering materials, mostly metals and composites, are reviewed. For empirical models established under the framework of Newtonian mechanics, Gurson–Tvergaard–Needleman (GTN) type model, Johnson-Cook (J-C) type damage model, microplasticity model, some other micro-mechanism based damage models, and models using irreversible entropy as a metric with an empirical evolution function are thoroughly discussed. For Physics-based models, the development and applications of unified mechanics theory is reviewed. Full article

(This article belongs to the Special Issue New Trends in Fatigue of Metals)

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