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8 pages, 607 KiB

Open AccessEditorial

Fatigue Crack Growth in Metallic Materials

by Fernando Ventura Antunes

Materials 2023, 16(1), 11; https://doi.org/10.3390/ma16010011 - 20 Dec 2022

Cited by 4 | Viewed by 1676

Abstract

Mechanical components and structures are submitted to cyclic loads in different applications; therefore, they must be designed to withstand fatigue [...] Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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9 pages, 957 KiB

Open AccessEditorial

Discussion and Comments on K_OP and ∆K_eff

by Daniel Kujawski

Materials 2020, 13(21), 4959; https://doi.org/10.3390/ma13214959 - 4 Nov 2020

Cited by 10 | Viewed by 1727

Abstract

This article addresses online discussions with comments related to K_op and ∆K_eff used in fatigue crack growth (FCG) analyses and modeling. The author of this article assembled an online discussion pertaining to the critical issues and challenges on Kop and ∆K [...] Read more.

This article addresses online discussions with comments related to K_op and ∆K_eff used in fatigue crack growth (FCG) analyses and modeling. The author of this article assembled an online discussion pertaining to the critical issues and challenges on Kop and ∆K_eff, which took place during the summer of 2020. The meetings were titled, Recent Advances on FCG Investigations and Modeling. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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Research

Jump to: Editorial, Review

14 pages, 5491 KiB

Open AccessArticle

Tribological Properties of Laser Cladded Alloys for Repair of Rail Components

by Panahsadat Fasihi, Olivia Kendall, Ralph Abrahams, Peter Mutton, Cong Qiu, Thomas Schläfer and Wenyi Yan

Materials 2022, 15(21), 7466; https://doi.org/10.3390/ma15217466 - 25 Oct 2022

Cited by 7 | Viewed by 1636

Abstract

Tram or light rail systems are heavily relied upon for passenger transit; however, low-carbon steel grades commonly used in special trackwork, such as in switches, are prone to wear, rolling contact fatigue (RCF), and deformation under cyclic wheel–rail contact. To address this, laser [...] Read more.

Tram or light rail systems are heavily relied upon for passenger transit; however, low-carbon steel grades commonly used in special trackwork, such as in switches, are prone to wear, rolling contact fatigue (RCF), and deformation under cyclic wheel–rail contact. To address this, laser cladding can be used to apply a metal coating to protect the underlying substrate and rebuild the worn rail profiles. Laser cladding may also be applied to remove cracking by rebuilding the rail head. The tribological characteristics of light rail components after laser cladding with Stellite 6 and a newly developed martensitic stainless steel were investigated, using roller-on-disc wear testing. Analysis of the microstructure, mechanical properties, and wear performance was undertaken to develop a comprehensive understanding of the influence of the laser cladding type on the wear and surface fatigue performance. Both cladding alloys significantly improved the tribological performance. These findings were compared to those for a laser cladded hypereutectoid rail type (reported in our previous study). It was found that laser cladding with a suitable alloy was an effective technique for improving the tribological properties, increasing the wear resistance, and increasing the retardation of cracking on both substrates. These findings suggest laser cladding may be used to repair light rail components, and this technique can be optimized to suit different rail grades. This makes laser cladding a flexible and versatile maintenance strategy, in both coating and repair applications, to prolong the operational lifetime of critical components for the railway industry. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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17 pages, 10208 KiB

Open AccessArticle

Early Spalling Analysis of Large Particles in High-Cr Steel during Thermal Fatigue: Relevant Mechanisms

by David Bombač, Goran Kugler, Jaka Burja and Milan Terčelj

Materials 2022, 15(19), 6705; https://doi.org/10.3390/ma15196705 - 27 Sep 2022

Cited by 3 | Viewed by 1548

Abstract

The aim of this study was to investigate the surface deterioration of high-Cr roll steel caused by the spalling of larger particles during thermal fatigue. The mechanisms of surface deterioration due to spalling of larger particles are discussed. Using a laboratory thermal fatigue [...] Read more.

The aim of this study was to investigate the surface deterioration of high-Cr roll steel caused by the spalling of larger particles during thermal fatigue. The mechanisms of surface deterioration due to spalling of larger particles are discussed. Using a laboratory thermal fatigue test that replicates hot rolling conditions, samples were tested cyclically (up to 4500 times) at maximum cycle temperatures of 500, 600 and 700 °C, followed by water cooling. Specimens with surface deterioration were selected for analysis, revealing important influencing parameters, i.e., the combination of test temperatures, chemical composition, thermal stress and microstructural properties, leading to oxidation-assisted crack growth in different directions and consequent surface deterioration due to early spalling of larger particles. Here, we describe the mechanisms of crack propagation, especially in the lateral direction, and their relation to the subsequent spalling of larger particles, which depend on the influence of the local chemical composition on the microstructural constituents, as well as their distribution and properties. The results obtained in this study can be used in the development of roll steel microstructures with improved resistance to the identified mechanisms of surface degradation. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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22 pages, 9330 KiB

Open AccessArticle

Experimental Research on Fatigue Crack Growth Behavior of Diffusion-Bonded Titanium Alloy Laminates with Preset Unbonded Areas

by Yang Liu and Shutian Liu

Materials 2022, 15(15), 5224; https://doi.org/10.3390/ma15155224 - 28 Jul 2022

Cited by 2 | Viewed by 1381

Abstract

This paper aimed to study the fatigue crack growth behavior of diffusion-bonded titanium alloy laminates (DB-TAL) with preset unbonded areas using an experimental method to understand the toughening mechanisms of presetting unbonded areas in DB-TAL. For two series of specimens of DB-TAL with [...] Read more.

This paper aimed to study the fatigue crack growth behavior of diffusion-bonded titanium alloy laminates (DB-TAL) with preset unbonded areas using an experimental method to understand the toughening mechanisms of presetting unbonded areas in DB-TAL. For two series of specimens of DB-TAL with preset unbonded areas with an open hole, which have a pre-notch at the open hole edge, fatigue experiments under tension–tension cyclic loading were conducted. The fatigue crack growth process, the crack growth rate, and the stress intensity factor on the crack front were analyzed. The results showed that the preset unbonded area leads the crack away from the stress concentration zone and slows down the crack growth rate. Therefore, the preset unbonded area significantly improved the fracture property of DB-TAL. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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13 pages, 5947 KiB

Open AccessArticle

A Novel Model of Ultrasonic Fatigue Test in Pure Bending

by Dongtong Yang, Sen Tang, Yongtao Hu, Alexander Nikitin, Qingyuan Wang, Yongjie Liu, Lang Li, Chao He, Yan Li, Bo Xu and Chong Wang

Materials 2022, 15(14), 4864; https://doi.org/10.3390/ma15144864 - 13 Jul 2022

Cited by 5 | Viewed by 1694

Abstract

The very high cycle fatigue (VHCF) failure of in-service components is mainly caused by the vibration of thin-wall elements at a high frequency. In this work, a novel model of ultrasonic fatigue test was developed to test thin-wall material in bending up to [...] Read more.

The very high cycle fatigue (VHCF) failure of in-service components is mainly caused by the vibration of thin-wall elements at a high frequency. In this work, a novel model of ultrasonic fatigue test was developed to test thin-wall material in bending up to VHCF with an accelerated frequency. The theoretical principle and finite element analysis were introduced for designing a sample that resonated at the frequency of 20 kHz in flexural vibration. In the advantage of the second-order flexural vibration, the gauge section of the sample was in the pure bending condition which prevented the intricate stress condition for thin-wall material as in the root of cantilever or the contact point of three points bending. Moreover, combining the constraint and the loading contact in one small section significantly reduced heating that originated from the friction at an ultrasonic frequency. Both strain gauge and deflection angle methods were applied to verify the controlling of stress amplitude. The fractography observation on Ti6Al4V samples indicated that the characterized fracture obtained from the novel model was the same as that from the conventional bending test. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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13 pages, 6157 KiB

Open AccessArticle

Fatigue Property and Small Crack Propagation Mechanism of MIG Welding Joint of 6005A-T6 Aluminum Alloy

by Zeng Peng, Shanglei Yang, Zhentao Wang and Zihao Gao

Materials 2022, 15(13), 4698; https://doi.org/10.3390/ma15134698 - 4 Jul 2022

Cited by 9 | Viewed by 2059

Abstract

In this study, metal inert gas welding (MIG) was applied to 4 mm thick 6005A-T6 aluminum alloy welding. Compared with other parts, the hardness of the weld zone (WZ) was the lowest, about 67 HV. There was the Softening in WZ, which might [...] Read more.

In this study, metal inert gas welding (MIG) was applied to 4 mm thick 6005A-T6 aluminum alloy welding. Compared with other parts, the hardness of the weld zone (WZ) was the lowest, about 67 HV. There was the Softening in WZ, which might make WZ the weakest zone. Then, fatigue tests were carried out on MIG welded joints. All the fatigue specimens fractured at the weld toe of the lap joint, and the fracture was characterized by a cleavage fracture. Crack closure induced by oxide was observed during the steady propagation of the fatigue crack. Impurities hindered crack propagation, changed the direction of crack propagation, and appeared in stepped fatigue strip distribution morphology; in the process of the main crack propagation, the initiation and propagation of small cracks were easily restricted and hindered by the main crack, which slowed down the propagation rate and even stopped the propagation directly. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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16 pages, 2909 KiB

Open AccessArticle

Effect of Residual Stresses on Fatigue Crack Growth: A Numerical Study Based on Cumulative Plastic Strain at the Crack Tip

by Diogo M. Neto, Micael F. Borges, Edmundo R. Sérgio and Fernando V. Antunes

Materials 2022, 15(6), 2156; https://doi.org/10.3390/ma15062156 - 15 Mar 2022

Cited by 14 | Viewed by 2476

Abstract

Residual stresses affect the fatigue behavior, given that compressive stresses delay the phenomenon, while tensile stresses accelerate it. However, the mechanisms behind the effect of residual stresses are not totally understood. A numerical study is developed here to understand the effect of thermal [...] Read more.

Residual stresses affect the fatigue behavior, given that compressive stresses delay the phenomenon, while tensile stresses accelerate it. However, the mechanisms behind the effect of residual stresses are not totally understood. A numerical study is developed here to understand the effect of thermal residual stresses (TRSs) on fatigue crack growth (FCG). The crack driving force was assumed to be the cumulative plastic strain at the crack tip. The heating of a region ahead of the crack tip produced elastic compressive TRS, which were 69% of material’s yield stress. Alternatively, plastic deformation was produced by severe cooling followed by heating to generate compressive residual stresses. The crack propagation in the compressive residual stress field produced a decrease in the FCG rate. On the other hand, without the contact of crack flanks, the TRS showed no effect on FCG. Therefore, the TRSs only affect FCG by changing the crack closure level. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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15 pages, 3333 KiB

Open AccessArticle

A Simplified Ductile Fracture Model for Predicting Ultra-Low Cycle Fatigue of Structural Steels

by Mingming Yu, Xu Xie and Shuailing Li

Materials 2022, 15(5), 1663; https://doi.org/10.3390/ma15051663 - 23 Feb 2022

Cited by 8 | Viewed by 1881

Abstract

Under strong earthquakes, steel structures are prone to undergoing ultra-low cycle fatigue (ULCF) fracture after sustaining cyclic large-strain loading, leading to severe earthquake-induced damage. Thus, establishing a prediction method for ULCF plays a significant role in the seismic design of steel structures. However, [...] Read more.

Under strong earthquakes, steel structures are prone to undergoing ultra-low cycle fatigue (ULCF) fracture after sustaining cyclic large-strain loading, leading to severe earthquake-induced damage. Thus, establishing a prediction method for ULCF plays a significant role in the seismic design of steel structures. However, a simple and feasible model for predicting the ULCF life of steel structures has not been recognized yet. Among existing models, the ductile fracture model based on ductility capacity consumption has the advantage of strong adaptability, while the loading history effect in the damage process can also be considered. Nevertheless, such models have too many parameters and are inconvenient for calibration and application. To this end, focusing on the prediction methods for ULCF damage in steel structures, with the fragile parts being in moderate and high stress triaxiality, this paper proposes a simplified uncoupled prediction model that considers the effect of stress triaxiality on damage and introduces a new historical-effect related variable function reducing the calibration work of model parameters. Finally, cyclic loading test results of circular notched specimens verify that the proposed model has the advantages of a small dispersion of parameters for calibration, being handy for application, and possessing reliable results, providing a prediction method for ULCF damage of structural steels. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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19 pages, 10612 KiB

Open AccessArticle

Combining H-Adaptivity with the Element Splitting Method for Crack Simulation in Large Structures

by Shi Song, Moritz Braun, Bjarne Wiegard, Hauke Herrnring and Sören Ehlers

Materials 2022, 15(1), 240; https://doi.org/10.3390/ma15010240 - 29 Dec 2021

Cited by 3 | Viewed by 2004

Abstract

H-adaptivity is an effective tool to introduce local mesh refinement in the FEM-based numerical simulation of crack propagation. The implementation of h-adaptivity could benefit the numerical simulation of fatigue or accidental load scenarios involving large structures, such as ship hulls. Meanwhile, in engineering [...] Read more.

H-adaptivity is an effective tool to introduce local mesh refinement in the FEM-based numerical simulation of crack propagation. The implementation of h-adaptivity could benefit the numerical simulation of fatigue or accidental load scenarios involving large structures, such as ship hulls. Meanwhile, in engineering applications, the element deletion method is frequently used to represent cracks. However, the element deletion method has some drawbacks, such as strong mesh dependency and loss of mass or energy. In order to mitigate this problem, the element splitting method could be applied. In this study, a numerical method called ‘h-adaptive element splitting’ (h-AES) is introduced. The h-AES method is applied in FEM programs by combining h-adaptivity with the element splitting method. Two examples using the h-AES method to simulate cracks in large structures under linear-elastic fracture mechanics scenario are presented. The numerical results are verified against analytical solutions. Based on the examples, the h-AES method is proven to be able to introduce mesh refinement in large-scale numerical models that mostly consist of structured coarse meshes, which is also beneficial to the reduction of computational resources. By employing the h-AES method, very small cracks are well represented in large structures without any deletions of elements. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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13 pages, 5601 KiB

Open AccessArticle

Investigation of the Fatigue Stress of Orthotropic Steel Decks Based on an Arch Bridge with the Application of the Arlequin Method

by Cheng Cheng, Xu Xie and Wentao Yu

Materials 2021, 14(24), 7653; https://doi.org/10.3390/ma14247653 - 12 Dec 2021

Cited by 7 | Viewed by 2541

Abstract

Orthotropic steel decks are widely used in the construction of steel bridges. Although there are many fatigue-evaluation methods stipulated by codes, unexpected fatigue cracks are still detected in some bridges. To justify whether the local finite element model commonly used in fatigue investigations [...] Read more.

Orthotropic steel decks are widely used in the construction of steel bridges. Although there are many fatigue-evaluation methods stipulated by codes, unexpected fatigue cracks are still detected in some bridges. To justify whether the local finite element model commonly used in fatigue investigations on orthotropic decks can correctly instruct engineering practices, the Arlequin framework is applied in this paper to determine the full fatigue stress under traffic loads. The convergence on and validity of this application for orthotropic decks are checked. Results show that the Arlequin model for deck-fatigue analysis established in this paper tends to be an efficient method for complete fatigue stress acquisition, whereby the vulnerable sites of orthotropic steel decks under traffic loads are defined. Vehicles near the flexible components, such as hangers or cables, can have adverse effects on the fatigue durability of decks. Additionally, the total number of vehicles and their arrangement concentration also affect fatigue performance. Complex traffic conditions cannot be fully loaded in local models. Regardless of the gross bridge mechanics and deck deformation, the fatigue stress range is underestimated by about 30–40%. Such a difference in fatigue assessment seems to explain the premature cracks observed in orthotropic steel decks. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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11 pages, 2957 KiB

Open AccessArticle

Fatigue Crack Initiation Change of Cast AZ91 Magnesium Alloy from Low to Very High Cycle Fatigue Region

by Stanislava Fintová, Libor Trško, Zdeněk Chlup, Filip Pastorek, Daniel Kajánek and Ludvík Kunz

Materials 2021, 14(21), 6245; https://doi.org/10.3390/ma14216245 - 20 Oct 2021

Cited by 9 | Viewed by 2061

Abstract

Fatigue tests were performed on the AZ91 cast alloy to identify the mechanisms of the fatigue crack initiation. In different fatigue regions, different mechanisms were observed. In the low and high cycle fatigue regions, slip markings formation accompanied with Mg₁₇Al₁₂ [...] Read more.

Fatigue tests were performed on the AZ91 cast alloy to identify the mechanisms of the fatigue crack initiation. In different fatigue regions, different mechanisms were observed. In the low and high cycle fatigue regions, slip markings formation accompanied with Mg₁₇Al₁₂ particles cracking were observed. Slip markings act as the fatigue crack initiation sites. The size and number of slip markings decreased with decreased stress amplitude applied. When slip markings formation was suppressed due to low stress amplitude, particle cracking became more important and the cracks continued to grow through the particle/solid solution interface. The change of the fatigue crack initiation mechanisms led the S-N curve to shift to the higher number of cycles to the fracture, demonstrated by its stepwise character. A lower fatigue limit of 60 MPa was determined at 20 kHz for 2 × 10⁹ cycles compared to the 80 MPa determined at 60 Hz for 1 × 10⁷ cycles. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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14 pages, 3991 KiB

Open AccessArticle

Estimation of the Plastic Zone in Fatigue via Micro-Indentation

by Cristina Lopez-Crespo, Alejandro S. Cruces, Stanislav Seitl, Belen Moreno and Pablo Lopez-Crespo

Materials 2021, 14(19), 5885; https://doi.org/10.3390/ma14195885 - 8 Oct 2021

Cited by 5 | Viewed by 2288

Abstract

Accurate knowledge of the plastic zone of fatigue cracks is a very direct and effective way to quantify the damage of components subjected to cyclic loads. In this work, we propose an ultra-fine experimental characterisation of the plastic zone based on Vickers micro-indentations. [...] Read more.

Accurate knowledge of the plastic zone of fatigue cracks is a very direct and effective way to quantify the damage of components subjected to cyclic loads. In this work, we propose an ultra-fine experimental characterisation of the plastic zone based on Vickers micro-indentations. The methodology is applied to different compact tension (CT) specimens made of aluminium alloy 2024-T351 subjected to increasing stress intensity factors. The experimental work and sensitivity analysis showed that polishing the surface to #3 μm surface finish and applying a 25 g-force load for 15 s produced the best results in terms of resolution and quality of the data. The methodology allowed the size and shape of both the cyclic and the monotonic plastic zones to be visualised through 2D contour maps. Comparison with Westergaard’s analytical model indicates that the methodology, in general, overestimates the plastic zone. Comparison with S355 low carbon steel suggests that the methodology works best for alloys exhibiting a high strain hardening ratio. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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17 pages, 5657 KiB

Open AccessArticle

FCG Modelling Considering the Combined Effects of Cyclic Plastic Deformation and Growth of Micro-Voids

by Edmundo R. Sérgio, Fernando V. Antunes, Micael F. Borges and Diogo M. Neto

Materials 2021, 14(15), 4303; https://doi.org/10.3390/ma14154303 - 31 Jul 2021

Cited by 8 | Viewed by 2049

Abstract

Fatigue is one of the most prevalent mechanisms of failure. Thus, the evaluation of the fatigue crack growth process is fundamental in engineering applications subjected to cyclic loads. The fatigue crack growth rate is usually accessed through the da/dN-ΔK curves, which [...] Read more.

Fatigue is one of the most prevalent mechanisms of failure. Thus, the evaluation of the fatigue crack growth process is fundamental in engineering applications subjected to cyclic loads. The fatigue crack growth rate is usually accessed through the da/dN-ΔK curves, which have some well-known limitations. In this study a numerical model that uses the cyclic plastic strain at the crack tip to predict da/dN was coupled with the Gurson–Tvergaard–Needleman (GTN) damage model. The crack propagation process occurs, by node release, when the cumulative plastic strain reaches a critical value. The GTN model is used to account for the material degradation due to the growth of micro-voids process, which affects fatigue crack growth. Predictions with GTN are compared with the ones obtained without this ductile fracture model. Crack closure was studied in order to justify the lower values of da/dN obtained in the model with GTN, when compared with the results without GTN, for lower ΔK values. Finally, the accuracy of both variants of the numerical model is accessed through the comparison with experimental results. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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14 pages, 3313 KiB

Open AccessArticle

Effect of the Crack Tip Bifurcation on the Plasticity-Induced Fatigue Propagation in Metallic Materials

by Jesús Toribio, Beatriz González and Juan-Carlos Matos

Materials 2021, 14(12), 3385; https://doi.org/10.3390/ma14123385 - 18 Jun 2021

Cited by 3 | Viewed by 1723

Abstract

This article deals with the influence of the crack path branching (at the micro level) on the plasticity-induced fatigue crack growth. With regard to this, a modeling by means of the finite element method was performed considering a cracked panel subjected to tension [...] Read more.

This article deals with the influence of the crack path branching (at the micro level) on the plasticity-induced fatigue crack growth. With regard to this, a modeling by means of the finite element method was performed considering a cracked panel subjected to tension with different symmetric and asymmetric configurations of the bifurcated crack tip. The results show the appearance of a retardation effect in the growth rate of the bifurcated crack in relation to the growth rate of the fully straight crack in different cases studied, namely: (i) if the two branches of the bifurcation have different initial projected length, the propagation rate is greater at the crack tip corresponding to the long-branch than that of the short-branch, and the long-branch growth rate increases with the decrease of the initial branch angle and of the initial projected short-branch length and with the increase of the intensity of fatigue; (ii) if the two branches of the bifurcation have identical initial projected length, the retardation effect depends on the initial distance between the two bifurcated crack tips, the growth rate going up with the decrease of such a distance and with the increase of the fatigue intensity. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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14 pages, 8462 KiB

Open AccessEditor’s ChoiceArticle

The Numerical Analysis of the In-Plane Constraint Influence on the Behavior of the Crack Subjected to Cyclic Loading

by Jaroslaw Galkiewicz and Urszula Janus-Galkiewicz

Materials 2021, 14(7), 1764; https://doi.org/10.3390/ma14071764 - 2 Apr 2021

Cited by 3 | Viewed by 1595

Abstract

The paper presents the influence of in-plane constraints defined by T-stress on the behavior of a crack subjected to cyclic loading. In the analysis, a modified boundary layer model approach was used in which the cohesive model was introduced. In the simulations, the [...] Read more.

The paper presents the influence of in-plane constraints defined by T-stress on the behavior of a crack subjected to cyclic loading. In the analysis, a modified boundary layer model approach was used in which the cohesive model was introduced. In the simulations, the constant maximum value of the stress intensity factor and four levels of T-stress were defined. The model was subjected to ten repeated stress cycles. Based on the results obtained, an analysis of the effect of the in-plane constraint on selected aspects of crack behavior was made. The strong influence of in-plane constraint applied in the model on the crack closure and the fatigue crack growth rate was proven. Since the in-plane constraint described the influence of geometry on the stress field surrounding the fatigue crack tip in real geometry, the results suggested that it is possible to create precise formulae connecting the level of the in-plane constraint with the effective stress intensity factor range and to incorporate the T-stress or Q-stress level in the Paris law. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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13 pages, 4860 KiB

Open AccessArticle

Effect of Solution Annealing on Fatigue Crack Propagation in the AISI 304L TRIP Steel

by Michal Jambor, Tomáš Vojtek, Pavel Pokorný and Miroslav Šmíd

Materials 2021, 14(6), 1331; https://doi.org/10.3390/ma14061331 - 10 Mar 2021

Cited by 13 | Viewed by 2141

Abstract

Fatigue crack propagation in near-threshold regime was studied in the 304L austenitic stainless steel in two microstructural states: as-received (AR) with finer microstructure and low susceptibility to the transformation-induced plasticity (TRIP) effect, and solution-annealed (SA) with coarser microstructure and higher susceptibility to TRIP. [...] Read more.

Fatigue crack propagation in near-threshold regime was studied in the 304L austenitic stainless steel in two microstructural states: as-received (AR) with finer microstructure and low susceptibility to the transformation-induced plasticity (TRIP) effect, and solution-annealed (SA) with coarser microstructure and higher susceptibility to TRIP. At the load ratio R = 0.1 the threshold was higher in the SA state than in the AR state due to coarser grains and possibly the TRIP effect. In order to clarify the role of crack closure, experiments at R = 0.7 were done. The threshold in the SA state was still higher by 1 MPa·m^0.5. This effect was identified as crack tip shielding induced by phase transformation, an example of a non-closure shielding effect. Higher resistance to crack growth in the SA state was attributed to promoted martensitic transformation in non-favorable oriented grain families rather than thicker martensite layers in the crack path area. The conclusions were verified by experiments at R = 0.7 and temperature 150 °C > M_s which did not reveal any notable difference in thresholds. However, the threshold values were affected by the load-shedding gradient C = −dΔK/da, which had to be equalized in both experimental setups inside and outside the furnace. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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12 pages, 5295 KiB

Open AccessArticle

Fatigue Failure from Inner Surfaces of Additive Manufactured Ti-6Al-4V Components

by Joel de Jesus, José António Martins Ferreira, Luís Borrego, José D. Costa and Carlos Capela

Materials 2021, 14(4), 737; https://doi.org/10.3390/ma14040737 - 5 Feb 2021

Cited by 21 | Viewed by 3457

Abstract

Selective laser melting (SLM) is an additive manufacturing process for producing metallic components with complex geometries. A drawback of this process is the process-inherent poor surface finish, which is highly detrimental in materials submitted to fatigue loading situations. The goal of this work [...] Read more.

Selective laser melting (SLM) is an additive manufacturing process for producing metallic components with complex geometries. A drawback of this process is the process-inherent poor surface finish, which is highly detrimental in materials submitted to fatigue loading situations. The goal of this work is to analyze the fatigue behavior of Ti-6Al-4V specimens with internal axial channels under the following different conditions: hole drilled, hole as manufactured, and hole threaded M4 × 0.7. All the cases studied showed a lower fatigue performance as compared with solid samples due to the surface roughness and geometry effect that produced a surface stress concentration leading to a reduction in fatigue strength. The fractography revealed that crack initiation occurred from the internal surface in all specimens with internal channel mostly from defects as unfused particles and lack of fusion zones, while for the solid specimens crack initiation was observed from the external surface due to insufficient fusion defect. The application of the Smith-Watson-Topper energy-based parameter was revealed to be a good tool for fatigue life prediction of the different series studied. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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14 pages, 4309 KiB

Open AccessArticle

Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear Approach

by Micael F. Borges, Diogo M. Neto and Fernando V. Antunes

Materials 2020, 13(23), 5544; https://doi.org/10.3390/ma13235544 - 4 Dec 2020

Cited by 16 | Viewed by 1991

Abstract

Fatigue crack growth (FCG) has been studied for decades; however, several aspects are still objects of controversy. The objective here is to discuss different issues, using a numerical approach based on crack tip plastic strain, assuming that FCG is driven by crack tip [...] Read more.

Fatigue crack growth (FCG) has been studied for decades; however, several aspects are still objects of controversy. The objective here is to discuss different issues, using a numerical approach based on crack tip plastic strain, assuming that FCG is driven by crack tip deformation. ΔK was found to control cyclic plastic deformation at the crack tip, while K_max has no effect. Therefore, alternative mechanisms are required to justify models based on ΔK and K_max. The analysis of crack tip plastic deformation also showed that there is crack tip damage below crack closure. Therefore, the definition of an effective load range ΔK_eff = K_max − K_open is not correct, because the portion of load range below opening also contributes to FCG. Below crack closure, damage occurs during unloading while during loading the crack tip deformation is elastic. However, if the maximum load is decreased below the elastic limit, which corresponds to the transition between elastic and elasto–plastic regimes, there is no crack tip damage. Additionally, a significant effect of the crack ligament on crack closure was found in tests with different crack lengths and the same ΔK. Finally, the analysis of FCG after an overload with and without contact of crack flanks showed that the typical variation of da/dN observed is linked to crack closure variations, while the residual stresses ahead of crack tip are not affected by the contact of crack flanks. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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Review

Jump to: Editorial, Research

15 pages, 3835 KiB

Open AccessEditor’s ChoiceReview

Fatigue Crack Growth and Fracture of Internal Fixation Materials in In Vivo Environments—A Review

by Kailun Wu, Bin Li and Jiong Jiong Guo

Materials 2021, 14(1), 176; https://doi.org/10.3390/ma14010176 - 1 Jan 2021

Cited by 9 | Viewed by 4026

Abstract

The development of crack patterns is a serious problem affecting the durability of orthopedic implants and the prognosis of patients. This issue has gained considerable attention in the medical community in recent years. This literature focuses on the five primary aspects relevant to [...] Read more.

The development of crack patterns is a serious problem affecting the durability of orthopedic implants and the prognosis of patients. This issue has gained considerable attention in the medical community in recent years. This literature focuses on the five primary aspects relevant to the evaluation of the surface cracking patterns, i.e., inappropriate use, design flaws, inconsistent elastic modulus, allergic reaction, poor compatibility, and anti-corrosiveness. The hope is that increased understanding will open doors to optimize fabrication for biomedical applications. The latest technological issues and potential capabilities of implants that combine absorbable materials and shape memory alloys are also discussed. This article will act as a roadmap to be employed in the realm of orthopedic. Fatigue crack growth and the challenges associated with materials must be recognized to help make new implant technologies viable for wider clinical adoption. This review presents a summary of recent findings on the fatigue mechanisms and fracture of implant in the initial period after surgery. We propose solutions to common problems. The recognition of essential complications and technical problems related to various approaches and material choices while satisfying clinical requirements is crucial. Additional investigation will be needed to surmount these challenges and reduce the likelihood of fatigue crack growth after implantation. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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