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3 pages, 177 KiB

Open AccessEditorial

Fatigue Design and Defects in Metals and Alloys

by Vigilio Fontanari and Matteo Benedetti

Metals 2020, 10(7), 865; https://doi.org/10.3390/met10070865 - 29 Jun 2020

Cited by 1 | Viewed by 1719

Abstract

The effort to correctly understand and account for the detrimental influence of defects in the design of components undergoing in service complex time-varying loads characterizes the major part of the history of metal fatigue [...] Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

Research

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19 pages, 10377 KiB

Open AccessArticle

Effect of Salt Bath Nitrocarburizing and Post-Oxidation on Static and Fatigue Behaviours of a Construction Steel

by Alberto Campagnolo, Manuele Dabalà and Giovanni Meneghetti

Metals 2019, 9(12), 1306; https://doi.org/10.3390/met9121306 - 04 Dec 2019

Cited by 11 | Viewed by 4579

Abstract

Several surface modification technologies are typically applied to improve the mechanical properties of the material surface of structural components subjected to severe conditions of load, wear and chemical erosion of the surface. The nitrocarburizing and post-oxidation heat treatment, also known as quench-polish-quench (QPQ), [...] Read more.

Several surface modification technologies are typically applied to improve the mechanical properties of the material surface of structural components subjected to severe conditions of load, wear and chemical erosion of the surface. The nitrocarburizing and post-oxidation heat treatment, also known as quench-polish-quench (QPQ), improves the fatigue, wear and corrosion resistance properties of the material, since it increases the surface hardness and generates surface compressive residual stresses. In the present contribution, the effects of the salt bath nitrocarburizing and post-oxidation heat treatment on the static and fatigue behaviours of 39NiCrMo3 construction steel have been investigated by experimentally testing plain as well as notched specimens. For comparison purposes, 39NiCrMo3 construction steel, both untreated and treated, and X5CrNiCuNb 16-4 stainless steel have been tested. First, the microstructure of the untreated and treated steel has been identified by metallographic analysis; micro-hardness measurements have been collected and residual stresses profiles have been obtained by using the X-ray diffraction technique. Then, experimental static and fatigue tests have been performed. Finally, the fracture surfaces have been analysed to locate fatigue crack nucleation sites. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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28 pages, 4445 KiB

Open AccessArticle

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

by Benjamin Josef Schäfer, Petra Sonnweber-Ribic, Hamad ul Hassan and Alexander Hartmaier

Metals 2019, 9(12), 1258; https://doi.org/10.3390/met9121258 - 25 Nov 2019

Cited by 18 | Viewed by 4458

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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18 pages, 9605 KiB

Open AccessArticle

Damage Evolution Due to Extremely Low-Cycle Fatigue for Inconel 718 Alloy

by Mohammed Algarni, Yuanli Bai, Mohammed Zwawi and Sami Ghazali

Metals 2019, 9(10), 1109; https://doi.org/10.3390/met9101109 - 17 Oct 2019

Cited by 12 | Viewed by 3525

Abstract

This paper evaluates the damage evolution process under extremely low-cycle fatigue (ELCF). The study explores the damage behavior under different stress states. The influence of the multiaxial state of stress on the metal’s life is determined. Two different stress states were examined: (a) [...] Read more.

This paper evaluates the damage evolution process under extremely low-cycle fatigue (ELCF). The study explores the damage behavior under different stress states. The influence of the multiaxial state of stress on the metal’s life is determined. Two different stress states were examined: (a) axisymmetric and (b) plane-strain. The study is based on the modified Mohr–Coulomb (MMC) ductile fracture criterion that was extended to cover the ELCF regime in a previous research study. Four distinctive geometries are designed to study the effect of different stress states on ELCF life and damage evolution. The damage model is calibrated for life prediction to agree with the ELCF experimental results. The investigation of the damage evolution behavior is dependent on equivalent plastic strain, stress triaxiality, Lode angle, and cyclic loading effect. The damage evolution is extracted from Abaqus finite element simulations and plotted versus the equivalent plastic strain. The damage accumulation shows nonlinear evolution behavior under cyclic loading conditions. SEM images were taken to further study the microscopic failure mechanisms of ELCF. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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14 pages, 4968 KiB

Open AccessArticle

The Auto-Correlation of Ultrasonic Lamb Wave Phased Array Data for Damage Detection

by Haiyan Zhang, Jiayan Zhang, Guopeng Fan, Hui Zhang, Wenfa Zhu, Qi Zhu and Rui Zheng

Metals 2019, 9(6), 666; https://doi.org/10.3390/met9060666 - 08 Jun 2019

Cited by 13 | Viewed by 3036

Abstract

Ultrasonic phased array is widely used for damage detection recently because of its high sensitivity and rapid scanning without sensor movements. However, the measured signal is always influenced by the remnants of the initial excitation and the nonlinear signals from the instrumentation, which [...] Read more.

Ultrasonic phased array is widely used for damage detection recently because of its high sensitivity and rapid scanning without sensor movements. However, the measured signal is always influenced by the remnants of the initial excitation and the nonlinear signals from the instrumentation, which limits its application in thin-plate structures. To address this issue, an approach called auto-correlation subtraction is proposed to extract the scattering information of defects in this paper. In order to testify the feasibility of this method for damage detection, the experiments were carried out on three thin aluminum plates combined with the total focusing method (TFM) for imaging. By auto-correlating the full matrix data received by sensors and then subtracting the average auto-correlation of noise recorded by all receivers, the coherent scattered signal containing defect information is recovered. The experimental results indicate that the coherent travel time is in agreement with the theoretical value and the signal-to-noise ratio are improved. Additionally, compared with the cross-correlation technique, the time synchronization between different receivers is not necessary with the auto-correlation method. Results indicate that the presented method can improve the imaging resolution and has a great potential in the field of non-destructive testing. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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14 pages, 7325 KiB

Open AccessFeature PaperArticle

Tooth Root Bending Fatigue Strength of High-Density Sintered Small-Module Spur Gears: The Effect of Porosity and Microstructure

by Vigilio Fontanari, Alberto Molinari, Michelangelo Marini, Wolfgang Pahl and Matteo Benedetti

Metals 2019, 9(5), 599; https://doi.org/10.3390/met9050599 - 24 May 2019

Cited by 10 | Viewed by 3446

Abstract

The present paper is aimed at investigating the effect of porosity and microstructure on tooth root bending fatigue of small-module spur gears produced by powder metallurgy (P/M). Specifically, three steel variants differing in powder composition and alloying route were subjected either to case-hardening [...] Read more.

The present paper is aimed at investigating the effect of porosity and microstructure on tooth root bending fatigue of small-module spur gears produced by powder metallurgy (P/M). Specifically, three steel variants differing in powder composition and alloying route were subjected either to case-hardening or sinter-hardening. The obtained results were interpreted in light of microstructural and fractographic inspections. On the basis of the Murakami

\sqrt{a r e a}

method, it was found that fatigue strength is mainly dictated by the largest near-surface defect and by the hardness of the softest microstructural constituent. Owing to the very complicated shape of the critical pore, it was found that its maximum Feret diameter is the geometrical parameter that best captures the detrimental effect on fatigue. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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16 pages, 5218 KiB

Open AccessArticle

A New Empirical Life Prediction Model for 9–12%Cr Steels under Low Cycle Fatigue and Creep Fatigue Interaction Loadings

by Xiaowei Wang, Wei Zhang, Tianyu Zhang, Jianming Gong and Magd Abdel Wahab

Metals 2019, 9(2), 183; https://doi.org/10.3390/met9020183 - 03 Feb 2019

Cited by 23 | Viewed by 4062

Abstract

Low cycle fatigue (LCF) and creep fatigue interaction (CFI) loadings are the main factors resulting in the failure of many critical components in the infrastructure of power plants and aeronautics. Accurate prediction of life spans under specified loading conditions is significant for the [...] Read more.

Low cycle fatigue (LCF) and creep fatigue interaction (CFI) loadings are the main factors resulting in the failure of many critical components in the infrastructure of power plants and aeronautics. Accurate prediction of life spans under specified loading conditions is significant for the design and maintenance of components. In the present study, various LCF and CFI tests are conducted to investigate the effects of temperature, strain amplitude, hold time and hold direction on the fatigue life of P92 steel. To predict fatigue life under different experimental conditions, various conventional life prediction models are evaluated and discussed. Moreover, a new empirical life prediction model is proposed based on the conventional Manson-Coffin-Basquin (MCB) model. The newly proposed model is able to simultaneously consider the effects of temperature, strain amplitude, hold time and hold direction on predicted life. The main advantage is that only the known input experimental parameters are required to perform the prediction. In addition to the validation made through the experimental data of P92 steel conducted in the present paper, the model is also verified through numerous experimental data reported in the literature for various 9–12% Cr steels. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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11 pages, 2505 KiB

Open AccessFeature PaperArticle

VHCF Response of Two AISI H13 Steels: Effect of Manufacturing Process and Size-Effect

by Andrea Tridello

Metals 2019, 9(2), 133; https://doi.org/10.3390/met9020133 - 26 Jan 2019

Cited by 16 | Viewed by 3229

Abstract

In the last decades, the fatigue lifetime of structural components has increased significantly and in many industrial applications (aerospace, automotive, and energy production industry) is even larger than 10¹⁰ cycles. Therefore, the interest in the Very High Cycle Fatigue (VHCF) behavior of [...] Read more.

In the last decades, the fatigue lifetime of structural components has increased significantly and in many industrial applications (aerospace, automotive, and energy production industry) is even larger than 10¹⁰ cycles. Therefore, the interest in the Very High Cycle Fatigue (VHCF) behavior of materials has grown rapidly, becoming a subject of primary interest among university and industries. In high-strength steels, VHCF failures generally originate from defects/inclusions; consequently, the steel cleanliness significantly affects the VHCF response. Furthermore, since the probability of finding critical defects in a loaded volume increases with the loaded volume, the loaded volume also significantly affects the VHCF response. This is generally referred to as the “size-effect” in VHCF. The present paper investigates the effects of the manufacturing process and the size-effect on the VHCF response of an AISI H13 steel. Experimental tests were performed on hourglass and Gaussian specimens made of two different types of AISI H13 steels: Unrefined H13 and refined Electroslag Remelting (ESR) H13. The analysis of variance (ANOVA), which was carried out on the test results, and the P–S–N curves showed that the two factors (i.e., the manufacturing process and the size-effect) significantly affect the VHCF response. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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16 pages, 4643 KiB

Open AccessArticle

Long-Life Fatigue of Carburized 12Cr2Ni Alloy Steel: Evaluation of Failure Characteristic and Prediction of Fatigue Strength

by Hailong Deng, Qichen Liu, Hang Liu and Huan Yu

Metals 2018, 8(12), 1006; https://doi.org/10.3390/met8121006 - 01 Dec 2018

Cited by 7 | Viewed by 3073

Abstract

In this study, the fatigue failure behaviors of carburized 12Cr2Ni alloy steel were examined in the long-life regime between 10⁴ and 10⁸ cycles with about 100 Hz under R = 0. Results showed that this alloy steel exhibited the double S [...] Read more.

In this study, the fatigue failure behaviors of carburized 12Cr2Ni alloy steel were examined in the long-life regime between 10⁴ and 10⁸ cycles with about 100 Hz under R = 0. Results showed that this alloy steel exhibited the double S-N characteristics with surface failure and interior failure. From a statistical point of view, the correlation coefficient further proved that the fine granular area (FGA) governed the fatigue performance of carburized 12Cr2Ni alloy steel. Based on the generalized extreme values (GEV) distribution and test data, the predicted maximum defect size was about 23.4 μm. Considering the effect of tensile limit, material hardness, and crack size characteristics, the fatigue strength prediction model under stress ratio of 0 could be established. The predicted fatigue limit for carburized 12Cr2Ni alloy steel at 10⁸ cycles under R = 0 was 507.86 MPa, and the prediction error of fatigue limit was within 0.04. Therefore, the results were extremely accurate. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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12 pages, 20536 KiB

Open AccessArticle

Microstructure and Fatigue Behavior of a Ni-Cu-Sn Alloy

by Leonardo Bertini, Francesco Bucchi, Francesco Frendo and Renzo Valentini

Metals 2018, 8(11), 888; https://doi.org/10.3390/met8110888 - 31 Oct 2018

Cited by 4 | Viewed by 2650

Abstract

In this paper, the static and fatigue properties of a Cu-Ni-Sn alloy are investigated. Tensile tests, hardness tests and microstructural analyses using optical and scanning electron microscopy (SEM) were performed and two sets of fatigue tests, with load ratio (R) [...] Read more.

In this paper, the static and fatigue properties of a Cu-Ni-Sn alloy are investigated. Tensile tests, hardness tests and microstructural analyses using optical and scanning electron microscopy (SEM) were performed and two sets of fatigue tests, with load ratio (R)

R = - 1

and

R = 0

, respectively, were carried out. The results showed the capability of the alloy to bear high static stress, thanks to its good strength properties. However, the fatigue tests showed a strong sensitivity of the alloy fatigue properties depending on the raw material batch. The comparison between microstructural analyses and fatigue test results showed a strong correlation; in particular, the specimens having a more inhomogeneous microstructure showed lower durability. In addition, the different microstructure also affected the fracture surface morphology as highlighted by SEM analyses. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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12 pages, 3958 KiB

Open AccessArticle

Assessing Corrosion Fatigue Characteristics of Dissimilar Material Weld between Alloy617 and 12Cr Steel Using Buttering Welding Technique

by Jeong Ho Hwang, Ju Hwa Lee, Hafiz Waqar Ahmad, Seung Woo Ha, Dong Ho Bae and Henok Yilma Kebede

Metals 2018, 8(10), 826; https://doi.org/10.3390/met8100826 - 15 Oct 2018

Cited by 7 | Viewed by 3159

Abstract

In this study, dissimilar material welding between Alloy617 and 12Cr steel was performed using the buttering welding technique on the 12Cr steel side in order to increase the weldability. After multi-pass welding, post weld heat treatment (PWHT) was performed in order to reduce [...] Read more.

In this study, dissimilar material welding between Alloy617 and 12Cr steel was performed using the buttering welding technique on the 12Cr steel side in order to increase the weldability. After multi-pass welding, post weld heat treatment (PWHT) was performed in order to reduce the welding residual stresses, and metallurgical microstructures were observed on dissimilar material weld. Additionally, the corrosion fatigue crack growth characteristics of dissimilar material weld was assessed according to Fracture Mechanics. Based on the results, the fatigue and corrosion fatigue strength of dissimilar material weld between Alloy617 and 12Cr steel did not show a big difference prior to and after post weld heat treatment. Fatigue and corrosion fatigue crack growth of dissimilar material weld were slightly faster than those of similar material weld of Alloy617. However, the characteristics of fatigue and corrosion fatigue crack growth did not show a big difference prior to and after PWHT. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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13 pages, 4440 KiB

Open AccessArticle

A Method for Predicting the Effects of Specimen Geometry and Loading Condition on Fatigue Strength

by Chengqi Sun and Qingyuan Song

Metals 2018, 8(10), 811; https://doi.org/10.3390/met8100811 - 10 Oct 2018

Cited by 41 | Viewed by 4497

Abstract

Specimen geometry and loading condition usually have a great influence on the fatigue strength of metallic materials, which is an important issue in evaluating the reliability of component parts. In this paper, a rotating bending fatigue test is performed at first on an [...] Read more.

Specimen geometry and loading condition usually have a great influence on the fatigue strength of metallic materials, which is an important issue in evaluating the reliability of component parts. In this paper, a rotating bending fatigue test is performed at first on an hourglass specimen and a notch specimen of a high strength titanium alloy. Experimental results indicate that, in terms of local stress, the notch specimen endures higher fatigue strength in comparison with the hourglass specimen due to its relatively smaller control volume. Then, a probabilistic control volume method is proposed for correlating the effects of specimen geometry and loading condition on the fatigue strength based on Weibull distribution and the concept of control volume. A simple formula is obtained for the fatigue strength in relation to control volumes, in which the parameter is the shape parameter of Weibull distribution of fatigue strength. The predicted results are in good agreement with the present experimental data for high strength titanium alloy and the data for the high strength steel and the full scale EA4T axle in the literature. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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14 pages, 6399 KiB

Open AccessArticle

Local Fatigue Strength Evaluation of Shot Peened 40Cr Notched Steel

by Xiaohui Zhao, Zhaoyi Sun, Desheng Xu and Yu Liu

Metals 2018, 8(9), 681; https://doi.org/10.3390/met8090681 - 29 Aug 2018

Cited by 4 | Viewed by 3177

Abstract

Fatigue life prediction for the notched components is an essential step within the design process of machines. Fatigue strength and life prediction of 40Cr notched steel before and after shot peening were studied. Fatigue fracture of specimens treated by three shot peening intensity [...] Read more.

Fatigue life prediction for the notched components is an essential step within the design process of machines. Fatigue strength and life prediction of 40Cr notched steel before and after shot peening were studied. Fatigue fracture of specimens treated by three shot peening intensity parameters was discussed. The life prediction considering residual stress, work hardening and surface roughness caused by shot peening was analyzed. The results indicated that fatigue strength was obviously improved after shot peening and the improvement effect was gradually enhanced with the increase of shot peening intensity. The predicted values based on R_z coefficient showed a good correspondence with the experimental data. Full article

(This article belongs to the Special Issue Fatigue Design and Defects in Metals and Alloys)

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