Editorial

2 pages, 138 KiB

Open AccessEditorial

Fatigue and Fracture of Traditional and Advanced Structural Alloys

by Filippo Berto

Metals 2020, 10(12), 1645; https://doi.org/10.3390/met10121645 - 06 Dec 2020

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Prevention and prediction of unexpected fracture and fatigue failures constitute a key objective in any engineering application [...] Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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29 pages, 3904 KiB

Open AccessArticle

On the Influence of Control Type and Strain Rate on the Lifetime of 50CrMo4

by Max Benedikt Geilen, Josef Arthur Schönherr, Marcus Klein, Dominik Sebastian Leininger, Alexander Giertler, Ulrich Krupp and Matthias Oechsner

Metals 2020, 10(11), 1458; https://doi.org/10.3390/met10111458 - 30 Oct 2020

Cited by 8 | Viewed by 2843

Abstract

In this study, we investigate the influence of control type and strain rate on the lifetime of specimens manufactured from 50CrMo4. This influence is described by a strain rate dependent method that uses cyclic stress strain curves to correct displacement-controlled cyclic test results. [...] Read more.

In this study, we investigate the influence of control type and strain rate on the lifetime of specimens manufactured from 50CrMo4. This influence is described by a strain rate dependent method that uses cyclic stress strain curves to correct displacement-controlled cyclic test results. The objective of this correction is to eliminate the stress related differences between displacement-controlled cyclic test results and force-controlled cyclic test results. The method is applied to the results of ultrasonic fatigue tests of six different combinations of heat treatment, specimen geometry (notch factor) and atmosphere. In a statistical analysis, the corrected results show an improved agreement with test results obtained on conventional fatigue testing equipment with similar specimens: the standard deviation in combined data sets is significantly reduced (p = 4.1%). We discuss the literature on intrinsic and extrinsic strain rate effects in carbon steels. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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11 pages, 9398 KiB

Open AccessArticle

Fatigue Fracture Mechanism of a Nickel-Based Single Crystal Superalloy with Partially Recrystallized Grains at 550 °C by In Situ SEM Studies

by Hao Yang, Jishen Jiang, Zhuozheng Wang, Xianfeng Ma, Jiajun Tu, Hui-ji Shi, Hailin Zhai and Wenjie Zhang

Metals 2020, 10(8), 1007; https://doi.org/10.3390/met10081007 - 27 Jul 2020

Cited by 4 | Viewed by 3014

Abstract

The fatigue fracture mechanism of a nickel-based single crystal (NBSC) superalloy with recrystallized grains was studied at 550 °C by in situ observation with a scanning electron microscope (SEM) for the first time. Multiple crack initiations associated with recrystallized grain boundaries and carbides [...] Read more.

The fatigue fracture mechanism of a nickel-based single crystal (NBSC) superalloy with recrystallized grains was studied at 550 °C by in situ observation with a scanning electron microscope (SEM) for the first time. Multiple crack initiations associated with recrystallized grain boundaries and carbides were observed. By analysis of the slip traces and crack propagation planes, the operated slip systems were identified to be octahedral for both single crystal substrate and recrystallized grains. Distinct crystallographic fractures dominated, accompanied by recrystallized grain boundary associated crack initiations. This is different from the widely reported solely intergranular cracking at high temperature. Fatigue crack growth rate curves showed evident fluctuation, due to the interaction of fatigue cracks with local microstructures and the crack coalescence mechanism. Both the recrystallized grains and the competition between different slip systems were responsible for the deceleration and acceleration of fatigue microstructurally small crack behavior. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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22 pages, 10555 KiB

Open AccessArticle

Effect of In-Situ Synthesized Boride Phases on the Impact Behavior of Iron-Based Composites Reinforced by B₄C Particles

by Fehmi Nair and Mustafa Hamamcı

Metals 2020, 10(5), 554; https://doi.org/10.3390/met10050554 - 25 Apr 2020

Cited by 10 | Viewed by 2993

Abstract

The objective of this study is to investigate the impact behavior of iron-based composites reinforced with boron carbide (B₄C) particles and in-situ synthesized iron borides (Fe₂B/FeB). The composite specimens (Fe/B₄C) were fabricated by hot-pressing under a pressure [...] Read more.

The objective of this study is to investigate the impact behavior of iron-based composites reinforced with boron carbide (B₄C) particles and in-situ synthesized iron borides (Fe₂B/FeB). The composite specimens (Fe/B₄C) were fabricated by hot-pressing under a pressure of 250 MPa at 500 °C, and sintered at a temperature of 1000 °C. The effects of the reinforcement ratio on the formation of in-situ borides and impact behavior were investigated by means of different volume fractions of B₄C inside the iron matrix: 0% (un-reinforced), 5%, 10%, 20%, and 30%. Drop-weight impact tests were performed by an instrumented Charpy impactor on reinforced and un-reinforced test specimens. The results of the impact tests were supported with microstructural and fractographical analysis. As a result of in-situ reactions between the Fe matrix and B₄C particles, Fe₂B phases were formed in the iron matrix. The iron borides, formed in the iron matrix during sintering, heavily affected the hardness and the morphology of the fractured surface. Due to the high amount of B₄C (over 10%), porosity played a major role in decreasing the contact forces and fracture energy. The results showed that the in-situ synthesized iron boride phases affect the impact properties of the Fe/B₄C composites. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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10 pages, 2117 KiB

Open AccessFeature PaperArticle

A Numerical Study of the Effect of Isotropic Hardening Parameters on Mode I Fatigue Crack Growth

by M. F. Borges, F. V. Antunes, P. A. Prates and R. Branco

Metals 2020, 10(2), 177; https://doi.org/10.3390/met10020177 - 25 Jan 2020

Cited by 10 | Viewed by 2712

Abstract

The consideration of plastic crack tip opening displacement (CTOD, δ_p), as a crack driving force has given us the opportunity to predict fatigue crack growth (FCG) rate numerically, and, therefore, to develop parametric studies focused on the effect of loading, geometrical, [...] Read more.

The consideration of plastic crack tip opening displacement (CTOD, δ_p), as a crack driving force has given us the opportunity to predict fatigue crack growth (FCG) rate numerically, and, therefore, to develop parametric studies focused on the effect of loading, geometrical, and material parameters. The objective here is to study the effect of the isotropic hardening parameters of the Voce law on FCG, which are the isotropic saturation stress, Y_Sat, and the isotropic saturation rate, C_Y. The increase of these hardening parameters causes δ_p to decrease. However, this effect is much more pronounced for Y_Sat than C_Y. The variation is non-linear, and the rate of variation decreases with the increase of isotropic parameters. The increase of Y_Sat increases the crack closure phenomenon. Finally, the influence of the isotropic parameters is more relevant for pure isotropic hardening than for mixed hardening. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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16 pages, 8738 KiB

Open AccessArticle

Fatigue Property and Improvement of a Rounded Welding Region between the Diaphragm Plate and Closed Rib of an Orthotropic Steel Bridge Deck

by Datao Li, Chunguo Zhang and Pengmin Lu

Metals 2020, 10(2), 161; https://doi.org/10.3390/met10020161 - 21 Jan 2020

Cited by 11 | Viewed by 2609

Abstract

By means of finite element modeling (FEM) and fatigue experiments, we study the fatigue performance of the rounded welding region between the diaphragm plate and closed rib of orthotropic steel bridge deck in this work. A local sub-model of the rounded welding region [...] Read more.

By means of finite element modeling (FEM) and fatigue experiments, we study the fatigue performance of the rounded welding region between the diaphragm plate and closed rib of orthotropic steel bridge deck in this work. A local sub-model of the rounded welding region from the orthotropic steel bridge deck was developed to analyze the stress distributions. Based on the analysis results we designed the fatigue specimen for the fatigue test of this detailed structure. The fatigue experimental results revealed that the crack initiates from the weld toe of the rounded welding region and the stress concentration at the rounded welding region is the main mechanism of fatigue crack initiation. In addition, we propose three improvements to reduce the stress concentration of the rounded welding region, and the local structure optimization scheme of the diaphragm–rib weld can effectively improve the fatigue resistance of the detailed weld structure. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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14 pages, 8191 KiB

Open AccessArticle

Modelling of Fracture Toughness of X80 Pipeline Steels in DTB Transition Region Involving the Effect of Temperature and Crack Growth

by Jie Xu, Wei Song, Wenfeng Cheng, Lingyu Chu, Hanlin Gao, Pengpeng Li and Filippo Berto

Metals 2020, 10(1), 28; https://doi.org/10.3390/met10010028 - 23 Dec 2019

Cited by 4 | Viewed by 3066

Abstract

This work presents an investigation of the effects of temperature and crack growth on cleavage fracture toughness for weld thermal simulated X80 pipeline steels in the ductile-to-brittle transition (DBT) regime. A great bulk of fracture toughness (crack tip opening displacement—CTOD) tests and numerical [...] Read more.

This work presents an investigation of the effects of temperature and crack growth on cleavage fracture toughness for weld thermal simulated X80 pipeline steels in the ductile-to-brittle transition (DBT) regime. A great bulk of fracture toughness (crack tip opening displacement—CTOD) tests and numerical simulations are carried out by deep-cracked single-edge-notched bending (SENB) and shallow-cracked single-edge-notched tension (SENT) specimens at various temperatures (−90 °C, −60 °C, −30 °C, and 0 °C). Three-dimensional (3D) finite element (FE) models of tested specimens have been employed to obtain computational data. The results show that temperature exerts only a slight effect on the material hardening behavior, which indicates the crack tip constraint (as denoted by Q-parameter) is less dependent on the temperature. The measured CTOD-values give considerable scatter but confirm well-established trends of increasing toughness with increasing temperature and reducing constraint. Crack growth and 3D effect exhibited significant influences on CTOD-CMOD relations at higher temperatures, −30 °C and 0 °C for the SENT specimen. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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14 pages, 1764 KiB

Open AccessArticle

On the Behaviour of 316 and 304 Stainless Steel under Multiaxial Fatigue Loading: Application of the Critical Plane Approach

by Alejandro S. Cruces, Pablo Lopez-Crespo, Stefano Bressan, Takamoto Itoh and Belen Moreno

Metals 2019, 9(9), 978; https://doi.org/10.3390/met9090978 - 03 Sep 2019

Cited by 8 | Viewed by 3548

Abstract

In this work, the multiaxial fatigue behaviour of 316 and 304 stainless steel was studied. The study was based on the critical plane approach which is based on observations that cracks tend to nucleate and grow in specific planes. Three different critical plane [...] Read more.

In this work, the multiaxial fatigue behaviour of 316 and 304 stainless steel was studied. The study was based on the critical plane approach which is based on observations that cracks tend to nucleate and grow in specific planes. Three different critical plane models were employed to this end, namely Fatemi–Socie (FS), Smith–Watson–Topper (SWT) and the newly proposed Sandip–Kallmeyer–Smith (SKS) model. The study allowed equi-biaxial stress state, mean strain and non–proportional hardening effects to be taken into consideration. Experimental tests including different combinations of tension, torsion and inner pressure were performed and were useful to identify the predominant failure mode for the two materials. The results also showed that the SKS damage parameter returned more conservative results than FS with lower scatter level in both materials, with prediction values between FS and SWT. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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12 pages, 5300 KiB

Open AccessArticle

Study on the Corrosion Fatigue Properties of 12Cr1MoV Steel at High Temperature in Different Salt Environments

by Jianjun He, Jiangyong Bao, Kailiang Long, Cong Li and Gang Wang

Metals 2019, 9(7), 774; https://doi.org/10.3390/met9070774 - 10 Jul 2019

Cited by 3 | Viewed by 2367

Abstract

Biomass energy, as a reliable renewable energy source, has gained more and more attention. However, microstructure degradation and corrosion fatigue damage of heat pipes hinder its further application. In this paper, high temperature corrosion fatigue characteristics of 12Cr1MoV steel under a mixed alkali [...] Read more.

Biomass energy, as a reliable renewable energy source, has gained more and more attention. However, microstructure degradation and corrosion fatigue damage of heat pipes hinder its further application. In this paper, high temperature corrosion fatigue characteristics of 12Cr1MoV steel under a mixed alkali metal chloride salt environment and mixed sulfate salt environment were investigated. Fatigue tests with different total strain amplitudes were performed. Results show that the effect of total strain amplitude on the cyclic stress response of the alloy is approximately the same under three different deformation conditions. With the increase of the cyclic numbers, the alloyed steel mainly exhibited cyclic hardening during loading. The fatigue properties in air environment were the best, which is most obvious when the total strain amplitude is ±0.3%. The fatigue life of samples in mixed alkali metal salts is the shortest. Furthermore, the fatigue fracture morphology of the alloyed steel in different environments were also deeply analyzed. This experimental study attempts to provide a theoretical reference for solving the problem of rapid failure of heat pipes in biomass boilers, and to establish a scientific basis for the material selection and safety operation. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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13 pages, 5303 KiB

Open AccessArticle

Influence of Residual Stress on Fatigue Weak Areas and Simulation Analysis on Fatigue Properties Based on Continuous Performance of FSW Joints

by Guoqin Sun, Xinhai Wei, Jiangpei Niu, Deguang Shang and Shujun Chen

Metals 2019, 9(3), 284; https://doi.org/10.3390/met9030284 - 02 Mar 2019

Cited by 6 | Viewed by 2712

Abstract

The fatigue weak area of aluminum alloy for a friction stir-welded joint is investigated based on the hardness profile, the residual stress measurement and the simulation analysis of fatigue property. The maximum residual stresses appeared at the heat-affected zone of the joint in [...] Read more.

The fatigue weak area of aluminum alloy for a friction stir-welded joint is investigated based on the hardness profile, the residual stress measurement and the simulation analysis of fatigue property. The maximum residual stresses appeared at the heat-affected zone of the joint in the fatigue damage process, which was consistent with the fracture location of the fatigue specimen. The fatigue joint model of continuous performance is established ignoring the original negative residual stress; considering that it will be relaxed soon when the joint is under tension-tension cyclic loading. The fatigue parameters of joint model is based on the static mechanical properties of the joint that obtained from the micro-tensile tests and four-point correlation method. The predicted results for the fatigue weak locations and fatigue lives based on the continuous performance joint model are closer to the fatigue experimental results by comparison with the simulation results of the partitioned performance joint model. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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18 pages, 14179 KiB

Open AccessArticle

Analytical and Numerical Crack Growth Analysis of 1:3 Scaled Railway Axle Specimens

by David Simunek, Martin Leitner, Jürgen Maierhofer, Hans-Peter Gänser and Reinhard Pippan

Metals 2019, 9(2), 184; https://doi.org/10.3390/met9020184 - 03 Feb 2019

Cited by 10 | Viewed by 4240

Abstract

This paper deals with experimental fatigue crack propagation in rotating bending loaded round bar specimens as well as an analytical and numerical analysis of the residual lifetime. Constant amplitude (CA) load tests are performed with the surface crack length being evaluated using an [...] Read more.

This paper deals with experimental fatigue crack propagation in rotating bending loaded round bar specimens as well as an analytical and numerical analysis of the residual lifetime. Constant amplitude (CA) load tests are performed with the surface crack length being evaluated using an optical measurement system. Fracture surfaces are microscopically analyzed to determine crack growth in depth as well as the crack shape. In spite of identical testing conditions, the experimental results show some scatter in residual lifetime, which is mainly caused by different residual stress states. Although X-ray residual stress measurements reveal only minor values, a superposition of the residual stress state with the load-induced stress leads to a significant impact on the residual lifetime calculations, which explains the experimental scatter. Numerical analyses are conducted to consider the residual stress state and their effect on crack propagation by different options. Considering the residual stress distribution in depth within the residual lifetime assessment, the deviation to the most conservative experiment is reduced from +48% to +2%. In conclusion, the results in this paper highlight that it is of utmost importance to consider local residual stress conditions in the course of a crack propagation analysis in order to properly assess the residual lifetime. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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18 pages, 5623 KiB

Open AccessArticle

A Fatigue Life Prediction Model Based on Modified Resolved Shear Stress for Nickel-Based Single Crystal Superalloys

by Jialiang Wang, Dasheng Wei, Yanrong Wang and Xianghua Jiang

Metals 2019, 9(2), 180; https://doi.org/10.3390/met9020180 - 02 Feb 2019

Cited by 9 | Viewed by 3123

Abstract

In this paper, the viewpoint that maximum resolved shear stress corresponding to the two slip systems in a nickel-based single crystal high-temperature fatigue experiment works together was put forward. A nickel-based single crystal fatigue life prediction model based on modified resolved shear stress [...] Read more.

In this paper, the viewpoint that maximum resolved shear stress corresponding to the two slip systems in a nickel-based single crystal high-temperature fatigue experiment works together was put forward. A nickel-based single crystal fatigue life prediction model based on modified resolved shear stress amplitude was proposed. For the four groups of fatigue data, eight classical fatigue life prediction models were compared with the model proposed in this paper. Strain parameter is poor in fatigue life prediction as a damage parameter. The life prediction results of the fatigue life prediction model with stress amplitude as the damage parameter, the fatigue life prediction model with maximum resolved shear stress in 30 slip directions as the damage parameter, and the McDiarmid (McD) model, are better. The model proposed in this paper has higher life prediction accuracy. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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12 pages, 4369 KiB

Open AccessArticle

Precipitate Evolution and Fatigue Crack Growth in Creep and Artificially Aged Aluminum Alloy

by Chi Liu, Yilun Liu, Liyong Ma, Songbai Li, Xianqiong Zhao and Qing Wang

Metals 2018, 8(12), 1039; https://doi.org/10.3390/met8121039 - 07 Dec 2018

Cited by 5 | Viewed by 2765

Abstract

The fatigue performance of high-strength Al-Cu-Mg alloys is generally influenced by the process of creep age formation when applied to acquire higher strength. The results show that creep aging accelerates the precipitation process, leading to a more uniform precipitation of strengthening phases in [...] Read more.

The fatigue performance of high-strength Al-Cu-Mg alloys is generally influenced by the process of creep age formation when applied to acquire higher strength. The results show that creep aging accelerates the precipitation process, leading to a more uniform precipitation of strengthening phases in grains, as well as narrowed precipitation-free zones (PFZ). Compared with the artificially aged alloy, the yield strength and hardness of the creep aged alloy increased, but the fatigue resistance decreased. In the low stress intensity factor region (ΔK ≤ 7 MPa·m^1/2), the fatigue crack propagation (FCP) rate was mainly affected by the characteristics of precipitates, and the fatigue resistance noticeably decreased with the increased creep time. In a 4 h creep aged alloy, the microstructure was dominated by Cu-Mg clusters and Guinier-Preston (GP) zones, while S″ phases began to precipitate in the matrix, showing better fatigue resistance. After aging for 24 h, the needle-shaped S’ phases were largely precipitated and coarsened, which changed the mode of dislocation slip, reduced the reversibility of slip, and accelerated the accumulation of fatigue damage. In stable and rapid crack propagation regions, the influence of precipitates on the FCP rate was negligible. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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19 pages, 3281 KiB

Open AccessArticle

Fatigue Damage Accumulation Modeling of Metals Alloys under High Amplitude Loading at Elevated Temperatures

by Jarosław Szusta and Andrzej Seweryn

Metals 2018, 8(12), 1030; https://doi.org/10.3390/met8121030 - 06 Dec 2018

Cited by 1 | Viewed by 3014

Abstract

This article presents an approach related to the modeling of the fatigue life of constructional metal alloys working under elevated temperature conditions and in the high-amplitude load range. The article reviews the fatigue damage accumulation criteria that makes it possible to determine the [...] Read more.

This article presents an approach related to the modeling of the fatigue life of constructional metal alloys working under elevated temperature conditions and in the high-amplitude load range. The article reviews the fatigue damage accumulation criteria that makes it possible to determine the number of loading cycles until damage occurs. Results of experimental tests conducted on various technical metal alloys made it possible to develop a fatigue damage accumulation model for the LCF (Low Cycle Fatigue) range. In modeling, the material’s damage state variable was defined, and the damage accumulation law was formulated incrementally so as to enable the analysis of the influence of loading history on the material’s fatigue life. In the proposed model, the increment of the damage state variable was made dependent on the increment of plastic strain, on the tensile stress value in the sample, and also on the actual value of the damage state variable. The model was verified on the basis of data obtained from experiments in the field of uniaxial and multiaxial loads. Samples made of EN AW 2024T3 aluminum alloy were used for this purpose. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Traditional and Advanced Structural Alloys)

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