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9 pages, 1017 KiB

Open AccessArticle

Non-Isothermal Dynamic Mechanical Analysis of Ribbon Metallic Glasses and Its Thermodynamic Description

by Arseniy Berezner and Victor Fedorov

Materials 2022, 15(23), 8659; https://doi.org/10.3390/ma15238659 - 5 Dec 2022

Viewed by 1405

Abstract

In this work, derivation of the main thermodynamic relationships is realized together with the applied calculation of some parameters, providing the systematized description of non-linear thermo-mechanical deformation at dynamic mechanical analysis (DMA). Obtained equations and values agree well with experiments on different ribbon [...] Read more.

In this work, derivation of the main thermodynamic relationships is realized together with the applied calculation of some parameters, providing the systematized description of non-linear thermo-mechanical deformation at dynamic mechanical analysis (DMA). Obtained equations and values agree well with experiments on different ribbon metallic glasses. We generalize the main initial conditions (i.e., experimental and numerical parameters) by that the proposed model can be used for the investigation of DMA in different materials. The further opportunities of the found approach are also discussed in frames of phase transitions in metallic glass. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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10 pages, 3461 KiB

Open AccessArticle

Influence of Constant Magnetic Field upon Fatigue Life of Commercially Pure Titanium

by Krestina Aksenova, Dmitrii Zaguliaev, Sergey Konovalov, Vitalii Shlyarov and Yurii Ivanov

Materials 2022, 15(19), 6926; https://doi.org/10.3390/ma15196926 - 6 Oct 2022

Cited by 3 | Viewed by 1435

Abstract

Cyclic tests of the multicycle fatigue of commercially pure titanium were performed under normal conditions (without a magnetic field) and after exposure to a constant magnetic field of varying density (B = 0.3, 0.4, 0.5 T). It was shown that the application of [...] Read more.

Cyclic tests of the multicycle fatigue of commercially pure titanium were performed under normal conditions (without a magnetic field) and after exposure to a constant magnetic field of varying density (B = 0.3, 0.4, 0.5 T). It was shown that the application of the constant magnetic field of varying density led to a fold increase in the average number of cycles to destruction of the VT1-0 titanium samples by 64, 123, and 163%, respectively. Scanning electron microscopy revealed that the magnetic field led to a 1.45-fold increase in the critical length of the fracture (the width of the fatigue crack growth zone) and a 1.6-fold decrease in the distance between the fatigue striations in the accelerated crack growth zone of the destroyed titanium samples. It was established that a subgrain (fragmented) structure formed in the area of the fatigue growth of the fracture of the titanium samples. The size of the subgrains corresponded to the spaces between the fatigue striations, which had an inhibitory influence on the microcrack propagation. Collectively, the revealed facts are indicative of a higher material resistance to fatigue fracture propagation and increased operation resources under the fatigue tests in the magnetic field, which correlates with the data on the growth of the average number of cycles to fracture of the VT1-0 titanium samples. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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20 pages, 14545 KiB

Open AccessArticle

Active Crack Obstruction Mechanisms in Crofer^® 22H at 650 °C

by Torsten Fischer and Bernd Kuhn

Materials 2022, 15(18), 6280; https://doi.org/10.3390/ma15186280 - 9 Sep 2022

Cited by 4 | Viewed by 1273

Abstract

Increased cyclic loading of components and materials in future thermal energy conversion systems necessitates novel materials of increased fatigue resistance. The widely used 9–12% Cr steels were developed for high creep strength and thus base load application at temperatures below 620 °C. At [...] Read more.

Increased cyclic loading of components and materials in future thermal energy conversion systems necessitates novel materials of increased fatigue resistance. The widely used 9–12% Cr steels were developed for high creep strength and thus base load application at temperatures below 620 °C. At higher temperature, these materials present unstable grain structure, prone to polygonization under thermomechanical fatigue loading and limited resistance to steam oxidation. This seminal study compares thermomechanical fatigue resistance and long crack propagation of the advanced ferritic-martensitic steel grade 92 and Crofer^® 22H, a fully ferritic, high chromium (22 wt. %) stainless steel, strengthened by Laves phase precipitation. Crofer^® 22H features increased resistance to fatigue and steam oxidation resistance up to 650 °C. Both thermomechanical fatigue (crack initiation) and residual (crack propagation) lifetime of Crofer^® 22H exceeded that of grade 92. The main mechanisms for improved performance of Crofer^® 22H were increased stability of grain structure and “dynamic precipitation strengthening” (DPS). DPS, i.e., thermomechanically triggered precipitation of Laves phase particles and crack deflection at Laves phase-covered sub-grain boundaries, formed in front of crack tips, actively obstructed crack propagation in Crofer^® 22H. In addition, it is hypothesized that local strengthening may occur near the crack tip because of grain refinement, which in turn may be impacted by testing frequency. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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21 pages, 8378 KiB

Open AccessArticle

On the Corrosion Fatigue of Magnesium Alloys Aimed at Biomedical Applications: New Insights from the Influence of Testing Frequency and Surface Modification of the Alloy ZK60

by Mikhail Linderov, Alexander Brilevsky, Dmitry Merson, Alexei Danyuk and Alexei Vinogradov

Materials 2022, 15(2), 567; https://doi.org/10.3390/ma15020567 - 12 Jan 2022

Cited by 17 | Viewed by 2662

Abstract

Magnesium alloys are contemporary candidates for many structural applications of which medical applications, such as bioresorbable implants, are of significant interest to the community and a challenge to materials scientists. The generally poor resistance of magnesium alloys to environmentally assisted fracture, resulting, in [...] Read more.

Magnesium alloys are contemporary candidates for many structural applications of which medical applications, such as bioresorbable implants, are of significant interest to the community and a challenge to materials scientists. The generally poor resistance of magnesium alloys to environmentally assisted fracture, resulting, in particular, in faster-than-desired bio-corrosion degradation in body fluids, strongly impedes their broad uptake in clinical practice. Since temporary structures implanted to support osteosynthesis or healing tissues may experience variable loading, the resistance to bio-corrosion fatigue is a critical issue that has yet to be understood in order to maintain the structural integrity and to prevent the premature failure of implants. In the present communication, we address several aspects of the corrosion fatigue behaviour of magnesium alloys, using the popular commercial ZK60 Mg-Zn-Zr alloy as a representative example. Specifically, the effects of the testing frequency, surface roughness and metallic coatings are discussed in conjunction with the fatigue fractography after the testing of miniature specimens in air and simulated body fluid. It is demonstrated that accelerated environmentally assisted degradation under cyclic loading occurs due to a complicated interplay between corrosion damage, stress corrosion cracking and cyclic loads. The occurrence of corrosion fatigue in Mg alloys is exaggerated by the significant sensitivity to the testing frequency. The fatigue life or strength reduced remarkably with a decrease in the test frequency. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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20 pages, 6242 KiB

Open AccessEditor’s ChoiceArticle

Structure Life Extension towards the Structural Integrity of Sukhoi Su-30MKM

by Arvinthan Venugopal, Roslina Mohammad, Md Fuad Shah Koslan, Ashaari Shafie, Alizarin Ali and Owi Eugene

Materials 2021, 14(19), 5562; https://doi.org/10.3390/ma14195562 - 25 Sep 2021

Cited by 3 | Viewed by 4536

Abstract

The airframe structures of most fighter aircraft in the Royal Malaysian Airforce have been in service for 10 to 20 years. The effect of fatigue loading, operating conditions, and environmental degradation has led to the structural integrity of the airframe being assessed for [...] Read more.

The airframe structures of most fighter aircraft in the Royal Malaysian Airforce have been in service for 10 to 20 years. The effect of fatigue loading, operating conditions, and environmental degradation has led to the structural integrity of the airframe being assessed for its airworthiness. Various NDT methods were used to determine the current condition of the aircraft structure after operation of beyond 10 years, and their outcomes are summarized. In addition, although there are six critical locations, the wing root was chosen since it has the highest possibility of fatigue failure. It was further analyzed using simulation analysis for fatigue life. This contributes to the development of the maintenance task card and ultimately assists in extending the service life of the fighter aircraft. Using the concept of either safe life or damage tolerance as its fatigue design philosophy, the RMAF has adopted the Aircraft Structural Integrity Program (ASIP) to monitor the structural integrity of its fighter aircraft. With the current budget constraints and structural life extension requirements, the RMAF has embarked on the non-destructive testing method and engineering analysis. The research outcome will enhance the ASIP for other aircraft platforms in the RMAF fleet for its structure life assessment or service life extension program. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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14 pages, 8659 KiB

Open AccessArticle

Low Cycle Fatigue Characteristics of Oxygen-Free Copper for Electric Power Equipment

by Takuma Tanaka, Togo Sugioka, Tatsuya Kobayashi, Ikuo Shohji, Yuya Shimada, Hiromitsu Watanabe and Yuichiro Kamakoshi

Materials 2021, 14(15), 4237; https://doi.org/10.3390/ma14154237 - 29 Jul 2021

Cited by 3 | Viewed by 2206

Abstract

The effect of heat treatment on tensile and low cycle fatigue properties of the oxygen-free copper for electric power equipment was investigated. The heat treatment at 850 °C for 20 min, which corresponds to the vacuum brazing process, caused the grain growth and [...] Read more.

The effect of heat treatment on tensile and low cycle fatigue properties of the oxygen-free copper for electric power equipment was investigated. The heat treatment at 850 °C for 20 min, which corresponds to the vacuum brazing process, caused the grain growth and relaxation of strain by recrystallization, and thus, the residual stress in the oxygen-free copper was reduced. The tensile strength and 0.2% proof stress were decreased, and elongation was increased by the heat treatment accompanying recrystallization. The plastic strain in the heat-treated specimen was increased compared with that in the untreated specimen under the same stress amplitude condition, and thus, the low cycle fatigue life of the oxygen-free copper was degraded by the heat treatment. Striation was observed in the crack initiation area of the fractured surface in the case of the stress amplitude less than 100 MPa regardless of the presence of the heat treatment. With an increase in the stress amplitude, the river pattern and the quasicleavage fracture were mainly observed in the fracture surfaces of the untreated specimens, and they were observed with striations in the fracture surfaces of the heat-treated ones. The result of the electron backscattered diffraction (EBSD) analysis showed that the grain reference orientation deviation (GROD) map was confirmed to be effective to investigate the fatigue damage degree in the grain by low cycle fatigue. In addition, the EBSD analysis revealed that the grains were deformed, and the GROD value reached approximately 28° in the fractured areas of heat-treated specimens after the low cycle fatigue test. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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14 pages, 45836 KiB

Open AccessArticle

Microstructure and Fatigue Behaviors of Dissimilar A6061/Galvannealed Steel Joints Fabricated by Friction Stir Spot Welding

by Koki Kumamoto, Tsuyoshi Kosaka, Tatsuya Kobayashi, Ikuo Shohji and Yuichiro Kamakoshi

Materials 2021, 14(14), 3877; https://doi.org/10.3390/ma14143877 - 12 Jul 2021

Cited by 12 | Viewed by 2473

Abstract

The microstructures, tensile shear properties, and tensile shear fatigue properties of dissimilar A6061/Galvannealed steel joints fabricated by friction stir spot welding (FSSW) were investigated. Fe₄Al₁₃ phases form as the intermetallic compound (IMC) layer at the joint interface between the A6061 [...] Read more.

The microstructures, tensile shear properties, and tensile shear fatigue properties of dissimilar A6061/Galvannealed steel joints fabricated by friction stir spot welding (FSSW) were investigated. Fe₄Al₁₃ phases form as the intermetallic compound (IMC) layer at the joint interface between the A6061 matrix and the galvannealed layer consisting of FeZn₇, Fe, and Zn. At the edge of the joint, the stirred layer in which the A6061 matrix and the galvannealed layer are stirred also forms. Moreover, the solidified part of the residual melt discharged from the joint area forms at the outer peripheries of the joint. In this study, FSSW was conducted for two total welding durations: 9 and 10 s. Although the thickness of the remaining A6061 sheet in the welded area decreased with an increase in the welding time, the effects of the total welding time on tensile shear and tensile shear fatigue properties were negligible. A fatigue fracture occurred in the A6061 matrix and at the joint interface at the high cycle fatigue region and the low cycle fatigue region, respectively. In the case of the interfacial fracture, the crack was generated in the solidified part of the residual melt or at the interface between the solidified part and the stirred layer. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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13 pages, 8564 KiB

Open AccessArticle

Effect of Small Amount of Ni Addition on Microstructure and Fatigue Properties of Sn-Sb-Ag Lead-Free Solder

by Mizuki Yamamoto, Ikuo Shohji, Tatsuya Kobayashi, Kohei Mitsui and Hirohiko Watanabe

Materials 2021, 14(14), 3799; https://doi.org/10.3390/ma14143799 - 7 Jul 2021

Cited by 17 | Viewed by 2100

Abstract

The effect of the addition volume of Ni on the microstructures and tensile and fatigue properties of Sn-6.4Sb-3.9Ag (mass%) was investigated using micro-size specimens. The addition of Ni into Sn-6.4Sb-3.9Ag tends to increase the number of grains formed in the solidification process and [...] Read more.

The effect of the addition volume of Ni on the microstructures and tensile and fatigue properties of Sn-6.4Sb-3.9Ag (mass%) was investigated using micro-size specimens. The addition of Ni into Sn-6.4Sb-3.9Ag tends to increase the number of grains formed in the solidification process and produce a high-angle grain boundary. An amount of 0.1% proof stress of Sn-6.4Sb-3.9Ag decreases with an increase in the Ni addition volume at a strain rate of 2.0 × 10⁻¹ s⁻¹. The effect of the addition of Ni into Sn-6.4Sb-3.9Ag on tensile strength is negligible at both 25 °C and 175 °C. The elongation of Sn-6.4Sb-3.9Ag decreases with an increase in the Ni addition volume at 25 °C according to the fracture mode change from ductile chisel point fracture to shear fracture. The effect of the addition of Ni into Sn-6.4Sb-3.9Ag on the elongation is negligible at 175 °C. The low cycle fatigue test result shows that the fatigue life does not degrade even at 175 °C in all alloys investigated. The fatigue life of Sn-6.4Sb-3.9Ag-0.4Ni (mass%) is superior to those of Sn-6.4Sb-3.9Ag and Sn-6.4Sb-3.9Ag-0.03Ni (mass%) in the high cycle fatigue area. The electron back scattering diffraction (EBSD) analysis result shows that fine recrystallized grains are generated at the cracked area in Sn-6.4Sb-3.9Ag-0.4Ni in the fatigue test at 175 °C, and the crack progresses in a complex manner at the grain boundaries. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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19 pages, 5163 KiB

Open AccessArticle

Effect of Thermomechanical Treatment on Structure and Functional Fatigue Characteristics of Biodegradable Fe-30Mn-5Si (wt %) Shape Memory Alloy

by Sergey Prokoshkin, Yury Pustov, Yulia Zhukova, Pulat Kadirov, Maria Karavaeva, Alexey Prosviryakov and Sergey Dubinskiy

Materials 2021, 14(12), 3327; https://doi.org/10.3390/ma14123327 - 16 Jun 2021

Cited by 10 | Viewed by 2274

Abstract

The Fe-Mn-Si shape memory alloys are considered promising materials for the biodegradable bone implant application since their functional properties can be optimized to combine bioresorbability with biomechanical and biochemical compatibility with bone tissue. The present study focuses on the fatigue and corrosion fatigue [...] Read more.

The Fe-Mn-Si shape memory alloys are considered promising materials for the biodegradable bone implant application since their functional properties can be optimized to combine bioresorbability with biomechanical and biochemical compatibility with bone tissue. The present study focuses on the fatigue and corrosion fatigue behavior of the thermomechanically treated Fe-30Mn-5Si (wt %) alloy compared to the conventionally quenched alloy because this important functionality aspect has not been previously studied. Hot-rolled and water-cooled, cold-rolled and annealed, and conventionally quenched alloy samples were characterized by X-ray diffraction, transmission electron microscopy, tensile fatigue testing in air atmosphere, and bending corrosion fatigue testing in Hanks’ solution. It is shown that hot rolling at 800 °C results in the longest fatigue life of the alloy both in air and in Hanks’ solution. This advantage results from the formation of a dynamically recrystallized γ-phase grain structure with a well-developed dislocation substructure. Another important finding is the experimental verification of Young’s modulus anomalous temperature dependence for the studied alloy system, its minimum at a human body temperature, and corresponding improvement of the biomechanical compatibility. The idea was realized by lowering M_s temperature down to the body temperature after hot rolling at 800 °C. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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20 pages, 12582 KiB

Open AccessArticle

The Effect of Tropical Environment on Fatigue Failure in Royal Malaysian Airforce (RMAF) Aircraft Structure and Operational Readiness

by Arvinthan Venugopal, Roslina Mohammad, Md Fuad Shah Koslan, Syed Roslee Sayd Bakar and Alizarin Ali

Materials 2021, 14(9), 2414; https://doi.org/10.3390/ma14092414 - 6 May 2021

Cited by 5 | Viewed by 2760

Abstract

The environmental condition in which the Royal Malaysian Airforce is currently operating its aircraft is prone to corrosion. This is due to the high relative humidity and temperature. With most of its aircraft being in the legacy aircraft era, the aircraft’s main construction [...] Read more.

The environmental condition in which the Royal Malaysian Airforce is currently operating its aircraft is prone to corrosion. This is due to the high relative humidity and temperature. With most of its aircraft being in the legacy aircraft era, the aircraft’s main construction consists of the aluminium 2024 material. However, this material is prone to corrosion, thus reducing fatigue life and leading to fatigue failure. Using the concept of either Safe Life or Damage Tolerance as its fatigue design philosophy, the RMAF adopts the Aircraft Structure Integrity Program (ASIP) to monitor its structural integrity. With the current problem of not having the structural limitation on corrosion-damaged structure, the RMAF has embarked on its fatigue testing method. Finite Element (FE) studies and flight tests were conducted, and the outcome is summarized. The conclusion is that the longeron tested on the aircraft can withstand the operational load, and its yield strength is below the ultimate yield strength of the material. These research outcomes will also enhance the ASIP for other aircraft platforms in the RMAF fleet for its structure life assessment or service life extension program. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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13 pages, 1580 KiB

Open AccessArticle

Low Cycle Fatigue Life Assessment Based on the Accumulated Plastic Strain Energy Density

by Yifeng Hu, Junping Shi, Xiaoshan Cao and Jinju Zhi

Materials 2021, 14(9), 2372; https://doi.org/10.3390/ma14092372 - 2 May 2021

Cited by 12 | Viewed by 3117

Abstract

The accumulated plastic strain energy density at a dangerous point is studied to estimate the low cycle fatigue life that is composed of fatigue initiation life and fatigue crack propagation life. The modified Ramberg–Osgood constitutive relation is applied to characterize the stress–strain relationship [...] Read more.

The accumulated plastic strain energy density at a dangerous point is studied to estimate the low cycle fatigue life that is composed of fatigue initiation life and fatigue crack propagation life. The modified Ramberg–Osgood constitutive relation is applied to characterize the stress–strain relationship of the strain-hardening material. The plastic strain energy density under uni-axial tension and cyclic load are derived, which are used as threshold and reference values, respectively. Then, a framework to assess the lives of fatigue initiation and fatigue crack propagation by accumulated plastic strain energy density is proposed. Finally, this method is applied to two types of aluminum alloy, LC9 and LY12 for low-cycle fatigue, and agreed well with the experiments. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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15 pages, 7393 KiB

Open AccessArticle

Dynamic Behaviour of Bridge Girders with Trapezoidal Profiled Webs Subjected to Moving Loads

by Zhiyu Wang, Yunzhong Shi, Xiang You, Ruijuan Jiang and Weiming Gai

Materials 2021, 14(1), 38; https://doi.org/10.3390/ma14010038 - 24 Dec 2020

Cited by 2 | Viewed by 2425

Abstract

The aim of this study is to find out the degradation of dynamic behaviour of bridge girders with trapezoidal profiled webs when subjected to different vehicle moving loads. Finite element modelling based parametric analysis is demonstrated to be desirable in capturing the dynamic [...] Read more.

The aim of this study is to find out the degradation of dynamic behaviour of bridge girders with trapezoidal profiled webs when subjected to different vehicle moving loads. Finite element modelling based parametric analysis is demonstrated to be desirable in capturing the dynamic deflection and stress state of critical structural details of girders. The model is validated in the modal analysis through a comparison with theoretical eigenfrequencies. The vibration characteristics are shown to be significantly affected by the corrugation details. The structural service life results of analysed bridge girders are in close agreement with experimental data. It is shown that the dynamic nodal velocity and deflection of analysed bridge girders are greatly affected by the magnitude of the load corresponding to the overload of the vehicle in contrast to the vehicle travel speed. Similar observations can be made for the fatigue life prediction analysis related to the crack initiation when unfavourable effects of the overload vehicle are concerned. Presented analytical results using a fracture mechanics approach could be taken as a good basis for the service life assessment of related bridges with the desired level of performance or functionality. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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13 pages, 8093 KiB

Open AccessArticle

Fatigue-Induced Evolution of AISI 310S Steel Microstructure after Electron Beam Treatment

by Sergey Konovalov, Yurii Ivanov, Victor Gromov and Irina Panchenko

Materials 2020, 13(20), 4567; https://doi.org/10.3390/ma13204567 - 14 Oct 2020

Cited by 20 | Viewed by 2172

Abstract

Research was carried out to explore the effect of pulsed electron beam irradiation on the behavior of structure and phase state in AISI 310S steel exposed to high-cycle fatigue. A 2.2 times increase in the fatigue life of samples irradiated by electron beams [...] Read more.

Research was carried out to explore the effect of pulsed electron beam irradiation on the behavior of structure and phase state in AISI 310S steel exposed to high-cycle fatigue. A 2.2 times increase in the fatigue life of samples irradiated by electron beams was revealed. The outcomes of scanning and transmission electron microscopic studies suggest the most probable reason for the fracture of steel samples irradiated by a high-intensity electron beam to be microcraters originating on a treated surface and acting as stress risers initiating the propagation of microcracks. The irradiation with a pulsed electron beam causes extremely fast melting of the surface. As a result of the subsequent rapid crystallization, a polycrystalline structure nearly twice as small as an average grain in the untreated steel is formed. Since a surface layer crystallizes rapidly, crystallization cells ranging from 120 to 170 nm develop in the volume of grains. The fatigue testing is shown to be associated with a martensite transformation γ ⇒ ε in the surface layer. One option to intensify a fatigue life increase of the steel in focus is supposed to be the neutralization of crater-forming on a surface treated by electron beams. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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29 pages, 20288 KiB

Open AccessArticle

Increasing Fatigue Life of 09Mn2Si Steel by Helical Rolling: Theoretical–Experimental Study on Governing Role of Grain Boundaries

by Sergey Panin, Ilya Vlasov, Pavel Maksimov, Dmitry Moiseenko, Pavlo Maruschak, Alexander Yakovlev, Siegfried Schmauder and Filippo Berto

Materials 2020, 13(20), 4531; https://doi.org/10.3390/ma13204531 - 13 Oct 2020

Cited by 9 | Viewed by 1980

Abstract

The structure and mechanical properties of the 09Mn2Si high-strength low-alloyed steel after the five-stage helical rolling (HR) were studied. It was revealed that the fine-grained structure had been formed in the surface layer ≈ 1 mm deep as a result of severe plastic [...] Read more.

The structure and mechanical properties of the 09Mn2Si high-strength low-alloyed steel after the five-stage helical rolling (HR) were studied. It was revealed that the fine-grained structure had been formed in the surface layer ≈ 1 mm deep as a result of severe plastic strains. In the lower layers, the “lamellar” structure had been formed, which consisted of thin elongated ferrite grains oriented in the HR direction. It was shown that the five-stage HR resulted in the increase in the steel fatigue life by more than 3.5 times under cyclic tension. The highest values of the number of cycles before failure were obtained for the samples cut from the bar core. It was demonstrated that the degree of the elastic energy dissipation in the steel samples under loading directly depended on the area of the grain boundaries as well as on the grain shapes. The fine-grained structure possessed the maximum value of the average torsional energy among all the studied samples, which caused the local material structure transformation and the decrease in the elastic energy level. This improved the crack resistance under the cyclic mechanical loading. The effect of the accumulation of the rotational strain modes at the grain boundaries was discovered, which caused the local structure transformation at the boundary zones. In the fine-grained structure, the formation of grain conglomerates was observed, which increased the values of the specific modulus of the moment of force. This could be mutually compensated due to the small sizes of grains. At the same time, the coarse-grained structures were characterized by the presence of the small number of grains with a high level of the moments of forces at their boundaries. They could result in trans-crystalline cracking. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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13 pages, 3833 KiB

Open AccessArticle

On the Fatigue Performance of Friction-Stir Welded Aluminum Alloys

by Sergey Malopheyev, Igor Vysotskiy, Daria Zhemchuzhnikova, Sergey Mironov and Rustam Kaibyshev

Materials 2020, 13(19), 4246; https://doi.org/10.3390/ma13194246 - 23 Sep 2020

Cited by 6 | Viewed by 2170

Abstract

This work was undertaken in an attempt to ascertain the generic characteristics of fatigue behavior of friction-stir welded aluminum alloys. To this end, different alloy grades belonging to both the heat-treatable and non-heat-treatable types in both the cast and wrought conditions were studied. [...] Read more.

This work was undertaken in an attempt to ascertain the generic characteristics of fatigue behavior of friction-stir welded aluminum alloys. To this end, different alloy grades belonging to both the heat-treatable and non-heat-treatable types in both the cast and wrought conditions were studied. The analysis was based on the premise that the fatigue endurance of sound welds (in which internal flaws and surface quality are not the major issues) is governed by residual stress and microstructure. Considering the relatively low magnitude of the residual stresses but drastic grain refinement attributable to friction-stir welding, the fatigue performance at relatively low cyclic stress was deduced to be dictated by the microstructural factor. Accordingly, the fatigue crack typically nucleated in relatively coarse-grained base material zone; thus, the fatigue strength of the welded joints was comparable to that of the parent metal. At relatively high fatigue stress, the summary (i.e., the cyclic-plus residual-) stress may exceed the material yield strength; thus, the fatigue cracking should result from the preceding macro-scale plastic deformation. Accordingly, the fatigue failure should occur in the softest microstructural region; thus; the fatigue strength of the welded joint may be inferior to that of the original material. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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13 pages, 3165 KiB

Open AccessArticle

Fatigue Life Appraisal and Its Corrected Stress Intensity Factor for Repaired Off-CentrallyCracked Aluminum Plates

by Xiang You, Zhiyu Wang, Xiafang Zhou, Zifeng Liu, Ruijuan Jiang and Weiming Gai

Materials 2020, 13(18), 4014; https://doi.org/10.3390/ma13184014 - 10 Sep 2020

Cited by 1 | Viewed by 1960

Abstract

This paper presents an experimental study on the fatigue life estimation of off-centrally cracked aluminum plates. Typical theoretical equations for off-central, central and edge cracks were reviewed and compared in terms of their sensitive parameters and applicability. A finite element model has been [...] Read more.

This paper presents an experimental study on the fatigue life estimation of off-centrally cracked aluminum plates. Typical theoretical equations for off-central, central and edge cracks were reviewed and compared in terms of their sensitive parameters and applicability. A finite element model has been validated in its capacity in modelling the influences of eccentricity and crack size on the boundary correction coefficients. The Forman equation has been employed along with numerical results for the prediction of fatigue lives. Based on the test data, the fatigue life results of aluminum plates with and without patched laminate repair have been compared with codified fatigue classes. It is demonstrated that the repair at the crack tip close to the plate edge is effective in the fatigue life improvement for off-centrally crackedaluminum plates. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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21 pages, 6281 KiB

Open AccessArticle

Fatigue Prediction of Aluminum Alloys Considering Critical Plane Orientation under Complex Stress States

by Marta Kurek

Materials 2020, 13(17), 3877; https://doi.org/10.3390/ma13173877 - 2 Sep 2020

Cited by 2 | Viewed by 2706

Abstract

This publication is intended to present a new way of estimating the fatigue life of various construction materials. Carpinteri’s proposal was modified by replacing the fatigue limits ratio with the value of the normal to shear stress ratio for a given number of [...] Read more.

This publication is intended to present a new way of estimating the fatigue life of various construction materials. Carpinteri’s proposal was modified by replacing the fatigue limits ratio with the value of the normal to shear stress ratio for a given number of cycles. In this study, the proposed criterion and calculation model was verified for the selected group of aluminium alloys. The purpose of the analysis of the experimental studies was to check the effectiveness of the proposed method of estimating fatigue life under the applied bending and torsional load conditions. The results of the fatigue calculations are presented in graphical form by means of diagrams showing the comparison of design and experimental strength. Before fatigue life was calculated, the critical plane orientation according to Carpinteri’s model and the proposed model were determined. After analyzing the results of the comparison of design and experimental durability, it can be stated that the proposed fatigue life estimation algorithm gives satisfactory results for multiaxial cyclic loads. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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16 pages, 5392 KiB

Open AccessArticle

Effect of Oxygen Variation on High Cycle Fatigue Behavior of Ti-6Al-4V Titanium Alloy

by Luyao Tang, Jiangkun Fan, Hongchao Kou, Bin Tang and Jinshan Li

Materials 2020, 13(17), 3858; https://doi.org/10.3390/ma13173858 - 1 Sep 2020

Cited by 11 | Viewed by 3222 | Correction

Abstract

The element oxygen is expected to be a low-cost, strengthening element of titanium alloys due to its strong solid solution strengthening effect. High cycle fatigue behaviors of Ti-6Al-4V alloys with different oxygen contents (0.17%, 0.20%, 0.23% wt.%) were investigated in this paper. The [...] Read more.

The element oxygen is expected to be a low-cost, strengthening element of titanium alloys due to its strong solid solution strengthening effect. High cycle fatigue behaviors of Ti-6Al-4V alloys with different oxygen contents (0.17%, 0.20%, 0.23% wt.%) were investigated in this paper. The results illustrated that Ti-6Al-4V-0.20O alloy possesses the highest fatigue strength and the lowest fatigue crack propagation rate. The fatigue fracture morphology verified that the fatigue cracks propagated transgranularly in both Ti-6Al-4V-0.17O and Ti-6Al-4V-0.20O alloys, and the fatigue cracks tended to extend intergranularly in the Ti-6Al-4V-0.23O alloy. The maximum nano-hardness varied from the <0001> direction to the

< \bar{1} 2 \bar{1} 0 >

and

< 01 \bar{1} 0 >

directions with the increasing oxygen content, which suggested that the dominant slip system varied from prismatic slip to pyramidal slip. The number of the

< \vec{c} + \vec{a} >

type dislocations increased with the oxygen content, which indicated that the number of the first-order pyramidal and the second-order pyramidal

< \vec{c} + \vec{a} >

slip systems increased. The oxygen can significantly change the fatigue fracture mechanism of Ti-6Al-4V alloy: From transgranular fracture to intergranular fracture. These results are expected to provide valuable reference for the optimization of the composition and mechanical properties of titanium alloys. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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16 pages, 3975 KiB

Open AccessArticle

Application of the S-N Curve Mean Stress Correction Model in Terms of Fatigue Life Estimation for Random Torsional Loading for Selected Aluminum Alloys

by Michał Böhm, Krzysztof Kluger, Sławomir Pochwała and Mariusz Kupina

Materials 2020, 13(13), 2985; https://doi.org/10.3390/ma13132985 - 4 Jul 2020

Cited by 9 | Viewed by 3542

Abstract

The paper presents the experimental fatigue test results for cyclic constant amplitude loading conditions for the case of the torsion of the PA4 (AW-6082-T6), PA6 (AW-2017A-T4) and PA7 (AW-2024-T3) aluminum alloy for a drilled diabolo type test specimen. The tests have been performed [...] Read more.

The paper presents the experimental fatigue test results for cyclic constant amplitude loading conditions for the case of the torsion of the PA4 (AW-6082-T6), PA6 (AW-2017A-T4) and PA7 (AW-2024-T3) aluminum alloy for a drilled diabolo type test specimen. The tests have been performed for the stress asymmetry ratios R = −1, R = −0.7, R = −0.5 and R = −0.3. The experimental results have been used in the process of a fatigue life estimation performed for a random generated narrowband stress signal with a zero and a non-zero global mean stress value. The calculations have been performed within the time domain with the use of the rainflow cycle counting method and the Palmgren−Miner damage hypothesis. The mean stress compensation has been performed with the S-N curve mean stress model proposed by Niesłony and Böhm. The model has been modified in terms of torsional loading conditions. In order to obtain an appropriate R = 0 ratio S-N curve fatigue strength amplitude, the Smith−Watson−Topper model was used and compared with literature fatigue strength amplitudes. The presented solution extends the use of the correction model in terms of the torsional loading condition in order to obtain new S-N curves for other R values on the basis of the R = −1 results. The work includes the computational results for new fatigue curves with and without the mean stress effect correction. The results of the computations show that the mean stress effect plays a major role in the fatigue life assessment of the tested aluminum alloys and that the method can be used to assess the fatigue life under random conditions. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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20 pages, 2151 KiB

Open AccessArticle

Comparative Analysis of Fatigue Energy Characteristics of S355J2 Steel Subjected to Multi-Axis Loads

by Cyprian T. Lachowicz and Robert Owsiński

Materials 2020, 13(11), 2470; https://doi.org/10.3390/ma13112470 - 28 May 2020

Cited by 9 | Viewed by 2407

Abstract

In this study, a novel test system for estimating bending and torsion fatigue under selectable kinematic and dynamic loading modes was constructed. Using S355J2 steel specimens, a series of tests were conducted to determine material sensitivity to different load paths and loading modes. [...] Read more.

In this study, a novel test system for estimating bending and torsion fatigue under selectable kinematic and dynamic loading modes was constructed. Using S355J2 steel specimens, a series of tests were conducted to determine material sensitivity to different load paths and loading modes. The experimental results were supplemented with the results of numerical analyses, on the basis of which the components of strain and stress tensors for subsequent analyses were determined in the entire working part of the specimen. An original method for determining specific strain energy components was used. The experimental results showed the grouping of data according to the mode of loading chosen. This could signify that the selected fatigue models are sensitive to certain loading scenarios. We performed in-depth data analysis and complex numerical simulations, formulating likely explanations for the observed effect. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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17 pages, 4210 KiB

Open AccessArticle

Application of Life-Dependent Material Parameters to Fatigue Life Prediction under Multiaxial and Non-Zero Mean Loading

by Krzysztof Kluger, Aleksander Karolczuk and Szymon Derda

Materials 2020, 13(7), 1587; https://doi.org/10.3390/ma13071587 - 30 Mar 2020

Cited by 9 | Viewed by 2554

Abstract

This study presents the life-dependent material parameters concept as applied to several well-known fatigue models for the purpose of life prediction under multiaxial and non-zero mean loading. The necessity of replacing the fixed material parameters with life-dependent parameters is demonstrated. The aim of [...] Read more.

This study presents the life-dependent material parameters concept as applied to several well-known fatigue models for the purpose of life prediction under multiaxial and non-zero mean loading. The necessity of replacing the fixed material parameters with life-dependent parameters is demonstrated. The aim of the research here is verification of the life-dependent material parameters concept when applied to multiaxial fatigue loading with non-zero mean stress. The verification is performed with new experimental fatigue test results on a 7075-T651 aluminium alloy and S355 steel subjected to multiaxial cyclic bending and torsion loading under stress ratios equal to R = −0.5 and 0.0, respectively. The received results exhibit the significant effect of the non-zero mean value of shear stress on the fatigue life of S355 steel. The prediction of fatigue life was improved when using the life-dependent material parameters compared to the fixed material parameters. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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8 pages, 3674 KiB

Open AccessArticle

Corrosion-Fatigue Failure of Gas-Turbine Blades in an Oil and Gas Production Plant

by Mojtaba Rajabinezhad, Abbas Bahrami, Mohammad Mousavinia, Seyed Jalil Seyedi and Peyman Taheri

Materials 2020, 13(4), 900; https://doi.org/10.3390/ma13040900 - 18 Feb 2020

Cited by 33 | Viewed by 9931

Abstract

This paper investigates the root cause of a failure in gas-turbine blades, made of Nimonic-105 nickel-based superalloy. The failure was reported in two blades in the second stage of a turbine-compressor of a gas turbine in the hot section. Two failed blades were [...] Read more.

This paper investigates the root cause of a failure in gas-turbine blades, made of Nimonic-105 nickel-based superalloy. The failure was reported in two blades in the second stage of a turbine-compressor of a gas turbine in the hot section. Two failed blades were broken from the root and from the airfoil. The failure took place after 20 k h of service exposure in the temperature range 700–850 °C, with the rotating speed being in the range 15,000–16,000 rpm. The microstructures of the failed blades were studied using optical/electron microscopes. Energy dispersive X-ray spectroscopy (EDS) was employed for phase identification. Results showed that failure first initiated from the root. The dominant failure mechanism in the root was concluded to be corrosion-fatigue. The failure scenario was suggested based on the results obtained. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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15 pages, 3309 KiB

Open AccessArticle

The Influence of the Strain and Stress Gradient in Determining Strain Fatigue Characteristics for Oscillatory Bending

by Andrzej Kurek, Justyna Koziarska and Tadeusz Łagoda

Materials 2020, 13(1), 173; https://doi.org/10.3390/ma13010173 - 1 Jan 2020

Cited by 11 | Viewed by 2723

Abstract

In this study, we created a new model to determine strain fatigue characteristics obtained from a bending test. The developed model consists of comparing the stress and strain gradient surface ratio for bending and tensile elements. For model verification, seven different materials were [...] Read more.

In this study, we created a new model to determine strain fatigue characteristics obtained from a bending test. The developed model consists of comparing the stress and strain gradient surface ratio for bending and tensile elements. For model verification, seven different materials were examined based on fatigue tests we conducted, or data available in the literature: 30CrNiMo8, 10HNAP, SM45C, 16Mo3 steel, MO58 brass, and 2017A-T4 and 6082-T6 aluminum alloys. As a result, we confirmed that the proposed method can be used to determine strain fatigue characteristics that agree with the values determined on the basis of a tensile compression test. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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16 pages, 19099 KiB

Open AccessArticle

The Effect of Microstructure and Axial Tension on Three-Point Bending Fatigue Behavior of TC4 in High Cycle and Very High Cycle Regimes

by Xuechun Bao, Li Cheng, Junliang Ding, Xuan Chen, Kaiju Lu and Wenbin Cui

Materials 2020, 13(1), 68; https://doi.org/10.3390/ma13010068 - 21 Dec 2019

Cited by 24 | Viewed by 3176

Abstract

The effects of microstructure and axial tension on the fatigue behavior of TC4 titanium alloy in high cycle (HCF) and very high cycle (VHCF) regimes are discussed in this paper. Ultrasonic three-point bending fatigue tests at 20 kHz were done on a fatigue [...] Read more.

The effects of microstructure and axial tension on the fatigue behavior of TC4 titanium alloy in high cycle (HCF) and very high cycle (VHCF) regimes are discussed in this paper. Ultrasonic three-point bending fatigue tests at 20 kHz were done on a fatigue life range among 10⁵–10⁹ cycles of the alloys with equiaxed, bimodal and Widmanstatten microstructures. Experimental results without axial tension show that three typical shapes of S-N curves clearly present themselves for the three different microstructures. Moreover, the crack initiation sites abruptly shifted from surface to subsurface of the specimen in the very high cycle fatigue regime for equiaxed and bimodal microstructures. But for the Widmanstatten microstructure, both surface and subsurface crack initiation appeared in the high cycle fatigue regime, and the multi-points crack initiation was found in the bimodal microstructure. The subsurface fatigue crack originated from the α_p grains in equiaxed and bimodal microstructures. However, it originated from the coarse grain boundary α in the Widmanstatten microstructure. Additionally, the S-N curve shape, fatigue life and fatigue crack initiation mechanism with axial tension are similar to that without axial tension. However, the crack origin point shifts inward with axial tension. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Metals and Alloys)

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