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Recent Advances in Mechanisms of Fracture and Fatigue
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Recent Advances in Mechanisms of Fracture and Fatigue

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Mechanics of Materials".

Deadline for manuscript submissions: closed (20 April 2022) | Viewed by 42965

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Jaroslav Pokluda

E-Mail Website
Guest Editor
Brno University of Technology, Brno, Czech Republic
Interests: micro- and nanomechanics; fracture mechanics; multiscale modeling; fatigue properties; fractography
Prof. Reinhard Pippan

E-Mail Website
Guest Editor
Erich Schmid Institute of Materials Science, Leoben, Austria
Interests: micro- and nanomechanics; fracture mechanics; dislocation mechanics; nanomaterials by severe plastic deformation; complex materials

Special Issue Information

Dear Colleagues,

In recent years, we have witnessed a rapid development in our ability to understand fracture and fatigue processes from the point of view of underlying damage mechanisms. A massive application of advanced experimental methods such as tomography, holography, high resolution electron microscopy, in situ mechanical testing in TEM/SEM, and stereophotogrammetry in SEM has significantly contributed to this progress. Finite element models based on higher-order elasticity and plasticity started to be applied in fracture mechanics, and in addition, atomistic approaches based on density functional theory and/or molecular dynamics resulted in multiscale models unifying the nano–micro–macro description of damage mechanisms. At the same time, research focused on fracture and fatigue mechanisms in special materials and components such as biological materials, smart materials, ultrafine grained materials, nanomaterials, high-entropy alloys, concrete and metal/ceramics composites, materials with coatings, complex structures of microelectronic and micromechanical devices, epitaxial films or additive manufactured materials has become prominent compared to investigations of classical metallic materials.

The authors are invited to publish their research results on all these topics, and therefore, we believe that this Special Issue will sufficiently demonstrate the recent advances in understanding mechanisms of fracture and fatigue.

Prof. Jaroslav Pokluda
Prof. Reinhard Pippan
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • fracture and fatigue mechanisms
  • damage models
  • multiscale modeling
  • experimental methods
  • engineering materials
  • advanced materials

Published Papers (17 papers)

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Research

14 pages, 3901 KiB  
Article
Microstructure and Fatigue Damage of 316L Stainless Steel Manufactured by Selective Laser Melting (SLM)
by Zhentao Wang, Shanglei Yang, Yubao Huang, Cong Fan, Zeng Peng and Zihao Gao
Materials 2021, 14(24), 7544; https://doi.org/10.3390/ma14247544 - 8 Dec 2021
Cited by 19 | Viewed by 3251
Abstract
In this paper, 316L stainless steel powder was processed and formed by selective laser melting (SLM). The microstructure of the sample was studied using an optical microscope, and the fatigue failure of the sample and the characteristics of crack initiation and propagation were [...] Read more.
In this paper, 316L stainless steel powder was processed and formed by selective laser melting (SLM). The microstructure of the sample was studied using an optical microscope, and the fatigue failure of the sample and the characteristics of crack initiation and propagation were analyzed, providing a research basis for the application of SLM-316L. Due to the influence of microstructure and SLM process defects, the fatigue cracks of SLM-316L mainly emerged due to defects such as lack of fusion and pores, while the cracks of rolled 316L initiated at the inclusions near the surface of the specimen. After fatigue microcrack initiation of the SLM-316L specimen, due to the existence of shear stress and tear stress, the crack tip was passivated and Z-shaped propagation was formed. The existence of internal defects in SLM-316L made the microcrack initiation random and diverse. At the same time, the existence of defects affected the crack propagation in the form of bending, bifurcation and bridge, which made the main crack propagation deviate from the maximum load direction. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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15 pages, 6675 KiB  
Article
Determination of Mechanical and Fracture Properties of Silicon Single Crystal from Indentation Experiments and Finite Element Modelling
by Petr Skalka and Michal Kotoul
Materials 2021, 14(22), 6864; https://doi.org/10.3390/ma14226864 - 14 Nov 2021
Cited by 1 | Viewed by 1743
Abstract
It is well-known that cracks are observed around the impression during indentation of brittle materials. The cracks inception depends on load conditions, material and indenter geometry. The paper aims to use experimental micro-indentation data, FE simulations with cohesive zone modelling, and an optimisation [...] Read more.
It is well-known that cracks are observed around the impression during indentation of brittle materials. The cracks inception depends on load conditions, material and indenter geometry. The paper aims to use experimental micro-indentation data, FE simulations with cohesive zone modelling, and an optimisation procedure to determine the cohesive energy density of silicon single crystals. While previous studies available in the literature, which use cohesive zone finite element techniques for simulation of indentation cracks in brittle solids, tried to improve methods for the evaluation of material toughness from the indentation load, crack size, hardness, elastic constants, and indenter geometry, this study focuses on the evaluation of the cohesive energy density 2Γ from which the material toughness can be easily determined using the well-known Griffith-Irwin formula. There is no need to control the premise of the linear fracture mechanics that the cohesive zone is much shorter than the crack length. Hence, the developed approach is suitable also for short cracks for which the linear fracture mechanics premise is violated. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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15 pages, 8967 KiB  
Article
Study on Microstructure and Fatigue Properties of FGH96 Nickel-Based Superalloy
by Yishan Bai, Shanglei Yang, Minqi Zhu and Cong Fan
Materials 2021, 14(21), 6298; https://doi.org/10.3390/ma14216298 - 22 Oct 2021
Cited by 7 | Viewed by 1876
Abstract
In this study, using synchrotron radiation X-ray imaging, the microstructure, tensile properties, and fatigue properties of FGH96 nickel-based superalloy were tested, and the fatigue damage mechanism was analyzed. An analysis of the experimental results shows that the alloy structure is dense without voids [...] Read more.
In this study, using synchrotron radiation X-ray imaging, the microstructure, tensile properties, and fatigue properties of FGH96 nickel-based superalloy were tested, and the fatigue damage mechanism was analyzed. An analysis of the experimental results shows that the alloy structure is dense without voids or other defects. It was observed that the primary γ′ phase is distributed on the grain boundary in a chain shape, and the secondary γ′ phase is found inside the crystal grains. The X-ray diffraction (XRD) pattern indicates that no other phases were seen except for the γ and γ′ phases. The tensile strength of the alloy is 1570 MPa and the elongation is 12.1%. Using data fitting and calculation, it was found that the fatigue strength of the alloy under the condition of 5 × 106 cycles is 620.33 MPa. A fatigue fracture has the characteristics of secondary crack, cleavage step, fatigue stripe, tire indentation, and dimple. The fracture is a mix of cleavage fracture and ductile fracture. Through a three-dimensional reconstruction of the alloy synchrotron radiation imaging area, it was found that the internal defects are small and mostly distributed at the edge of the sample. The dimple morphology is formed by cavity aggregation and cavity germination resulting from defects in the material itself, fracture of the second-phase particles, and separation of the second-phase particles from the matrix interface. By analyzing the damage mechanism of fatigue fractures, it is concluded that the cleavage step is formed by the intersection of cleavage planes formed by branch cracks, with the main crack of the confluence extending forward to form a cleavage fracture. The crack propagation path was also analyzed, and under the action of cyclic load and tip passivation, the crack shows Z-shaped propagation. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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11 pages, 15355 KiB  
Article
Incorporation of Temperature and Plastic Strain Effects into Local Approach to Fracture
by Sergiy Kotrechko, Vladislav Kozák, Oleksandra Zatsarna, Galyna Zimina, Nataliya Stetsenko and Ivo Dlouhý
Materials 2021, 14(20), 6224; https://doi.org/10.3390/ma14206224 - 19 Oct 2021
Cited by 3 | Viewed by 2274
Abstract
An unjustified simplification of the local quantitative criterion regarding cleavage nucleation is a key problem in the utilisation of the Local Approach to Fracture (LA), particularly to predict the fracture toughness within the ductile-to-brittle transition (DBT) region. The theoretical concept of the effect [...] Read more.
An unjustified simplification of the local quantitative criterion regarding cleavage nucleation is a key problem in the utilisation of the Local Approach to Fracture (LA), particularly to predict the fracture toughness within the ductile-to-brittle transition (DBT) region. The theoretical concept of the effect of both temperature and the plastic strain value on the crack nuclei (CN) generation rate in iron and ferritic steels is presented. It is shown how the plastic strain and temperature affect CN formation rate and, as a consequence, govern the shape of the temperature dependence of fracture toughness KJc and its scatter limits. Within the framework of the microscopic model proposed, dependences of the CN bulk density on the plastic deformation value and temperature are predicted. Convenient approximation dependences for incorporating this effect into the LA are suggested. The experimental data of reactor pressure vessel steel and cast manganese steel demonstrate that the use of these dependences enables one to predict, with sufficient accuracy, the effect of temperature on the value of fracture toughness and its scatter limits over the DBT region. It is shown that accounting for both the temperature and strain dependence of CN bulk density gives rise to the invariance of parameters of the Weibull distribution to temperature. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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28 pages, 11471 KiB  
Article
Temperature Dependence of Fracture Characteristics of Variously Heat-Treated Grades of Ultra-High-Strength Steel: Experimental and Modelling
by Jaroslav Pokluda, Ivo Dlouhý, Marta Kianicová, Jan Čupera, Jana Horníková and Pavel Šandera
Materials 2021, 14(19), 5875; https://doi.org/10.3390/ma14195875 - 7 Oct 2021
Cited by 2 | Viewed by 1702
Abstract
The temperature dependence of tensile characteristics and fracture toughness of the standardly heat-treated low-alloyed steel OCHN3MFA along with three additionally heat-treated grades was experimentally studied. In the temperature range of ⟨−196; 22⟩ °C, all the additional heat treatments transferred the standard steel from [...] Read more.
The temperature dependence of tensile characteristics and fracture toughness of the standardly heat-treated low-alloyed steel OCHN3MFA along with three additionally heat-treated grades was experimentally studied. In the temperature range of ⟨−196; 22⟩ °C, all the additional heat treatments transferred the standard steel from a high- to ultra-high strength levels even with improved tensile ductility characteristics. This could be explained by a reduction of the inclusion content, refinement of the martensitic blocks, ductile retained austenite content, and homogenization of the shape ratio of martensitic laths as revealed by metallographic, X-ray, and EBSD techniques. On the other hand, the values of the fracture toughness of all grades were found to be comparable in the whole temperature range as the cause of a high stress triaxiality in the pre-cracked Charpy V-notch samples. The values of the fracture toughness of the standard steel grade could be predicted well using the fracture model proposed by Pokluda et al. based on the tensile characteristics. Such a prediction failed in the case of additionally heat-treated grades due to the different temperature dependence of the fracture mechanisms occurring in the tensile and fracture-toughness tests. While the tensile samples fractured in a ductile-dimple mode at all temperatures, the fracture-toughness specimens exhibited a transition from the ductile to quasi-brittle fracture mode with decreasing temperature. This transition could be interpreted in terms of a transfer from the model proposed by Rice and Johnson to the model of Tvergaard and Hutchinson. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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31 pages, 12942 KiB  
Article
About the Role of Interfaces on the Fatigue Crack Propagation in Laminated Metallic Composites
by Philip Manuel Pohl, Frank Kümmel, Christopher Schunk, Itziar Serrano-Munoz, Henning Markötter, Mathias Göken and Heinz Werner Höppel
Materials 2021, 14(10), 2564; https://doi.org/10.3390/ma14102564 - 14 May 2021
Cited by 8 | Viewed by 2530
Abstract
The influence of gradients in hardness and elastic properties at interfaces of dissimilar materials in laminated metallic composites (LMCs) on fatigue crack propagation is investigated experimentally for three different LMC systems: Al/Al-LMCs with dissimilar yield stress and Al/Steel-LMCs as well as Al/Ti/Steel-LMCs with [...] Read more.
The influence of gradients in hardness and elastic properties at interfaces of dissimilar materials in laminated metallic composites (LMCs) on fatigue crack propagation is investigated experimentally for three different LMC systems: Al/Al-LMCs with dissimilar yield stress and Al/Steel-LMCs as well as Al/Ti/Steel-LMCs with dissimilar yield stress and Young’s modulus, respectively. The damage tolerant fatigue behavior in Al/Al-LMCs with an alternating layer structure is enhanced significantly compared to constituent monolithic materials. The prevalent toughening mechanisms at the interfaces are identified by microscopical methods and synchrotron X-ray computed tomography. For the soft/hard transition, crack deflection mechanisms at the vicinity of the interface are observed, whereas crack bifurcation mechanisms can be seen for the hard/soft transition. The crack propagation in Al/Steel-LMCs was studied conducting in-situ scanning electron microscope (SEM) experiments in the respective low cycle fatigue (LCF) and high cycle fatigue (HCF) regimes of the laminate. The enhanced resistance against crack propagation in the LCF regime is attributed to the prevalent stress redistribution, crack deflection, and crack bridging mechanisms. The fatigue properties of different Al/Ti/Steel-LMC systems show the potential of LMCs in terms of an appropriate selection of constituents in combination with an optimized architecture. The results are also discussed under the aspect of tailored lightweight applications subjected to cyclic loading. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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10 pages, 2700 KiB  
Article
Critical Dynamics of Defects and Mechanisms of Damage-Failure Transitions in Fatigue
by Oleg Naimark, Vladimir Oborin, Mikhail Bannikov and Dmitry Ledon
Materials 2021, 14(10), 2554; https://doi.org/10.3390/ma14102554 - 14 May 2021
Cited by 8 | Viewed by 1776
Abstract
An experimental methodology was developed for estimating a very high cycle fatigue (VHCF) life of the aluminum alloy AMG-6 subjected to preliminary deformation. The analysis of fatigue damage staging is based on the measurement of elastic modulus decrement according to “in situ” data [...] Read more.
An experimental methodology was developed for estimating a very high cycle fatigue (VHCF) life of the aluminum alloy AMG-6 subjected to preliminary deformation. The analysis of fatigue damage staging is based on the measurement of elastic modulus decrement according to “in situ” data of nonlinear dynamics of free-end specimen vibrations at the VHCF test. The correlation of fatigue damage staging and fracture surface morphology was studied to establish the scaling properties and kinetic equations for damage localization, “fish-eye” nucleation, and transition to the Paris crack kinetics. These equations, based on empirical parameters related to the structure of the material, allows us to estimate the number of cycles for the nucleation and advance of fatigue crack. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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22 pages, 16583 KiB  
Article
Effect of Underload Cycles on Oxide-Induced Crack Closure Development in Cr-Mo Low-Alloy Steel
by Pavel Pokorný, Tomáš Vojtek, Michal Jambor, Luboš Náhlík and Pavel Hutař
Materials 2021, 14(10), 2530; https://doi.org/10.3390/ma14102530 - 13 May 2021
Cited by 7 | Viewed by 2089
Abstract
Underload cycles with small load amplitudes below the fatigue crack growth threshold are dominantly considered as insignificant cycles without any influence on fatigue lifespan of engineering structural components. However, this paper shows that in some cases these underload cycles can retard the consequent [...] Read more.
Underload cycles with small load amplitudes below the fatigue crack growth threshold are dominantly considered as insignificant cycles without any influence on fatigue lifespan of engineering structural components. However, this paper shows that in some cases these underload cycles can retard the consequent crack propagation quite significantly. This phenomenon is a consequence of oxide-induced crack closure development during cyclic loading below the threshold. The experimentally described effect of fatigue crack growth retardation was supported by measurement of the width and the thickness of the oxide debris layer using the EDS technique and localized FIB cuts, respectively. Both the retardation effect and the amount of oxide debris were larger for higher number and larger amplitudes of the applied underload cycles. Crack closure measurement revealed a gradual increase of the closure level during underload cycling. Specimens tested in low air humidity, as well as specimens left with the crack open for the same time as that needed for application of the underload cycles, revealed no retardation effect. The results can improve our understanding of environmental effects on fatigue crack propagation and understanding the differences between the results of laboratory testing and the fatigue lives of components in service. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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24 pages, 10925 KiB  
Article
Usability of Ultrasonic Frequency Testing for Rapid Generation of High and Very High Cycle Fatigue Data
by Michael Fitzka, Bernd M. Schönbauer, Robert K. Rhein, Niloofar Sanaei, Shahab Zekriardehani, Srinivasan Arjun Tekalur, Jason W. Carroll and Herwig Mayer
Materials 2021, 14(9), 2245; https://doi.org/10.3390/ma14092245 - 27 Apr 2021
Cited by 23 | Viewed by 3128
Abstract
Ultrasonic fatigue testing is an increasingly used method to study the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of materials. Specimens are cycled at an ultrasonic frequency, which leads to a drastic reduction of testing times. This work focused [...] Read more.
Ultrasonic fatigue testing is an increasingly used method to study the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of materials. Specimens are cycled at an ultrasonic frequency, which leads to a drastic reduction of testing times. This work focused on summarising the current understanding, based on literature data and original work, whether and how fatigue properties measured with ultrasonic and conventional equipment are comparable. Aluminium alloys are not strain-rate sensitive. A weaker influence of air humidity at ultrasonic frequencies may lead to prolonged lifetimes in some alloys, and tests in high humidity or distilled water can better approximate environmental conditions at low frequencies. High-strength steels are insensitive to the cycling frequency. Strain rate sensitivity of ferrite causes prolonged lifetimes in those steels that show crack initiation in the ferritic phase. Austenitic stainless steels are less prone to frequency effects. Fatigue properties of titanium alloys and nickel alloys are insensitive to testing frequency. Limited data for magnesium alloys and graphite suggest no frequency influence. Ultrasonic fatigue tests of a glass fibre-reinforced polymer delivered comparable lifetimes to servo-hydraulic tests, suggesting that high-frequency testing is, in principle, applicable to fibre-reinforced polymer composites. The use of equipment with closed-loop control of vibration amplitude and resonance frequency is strongly advised since this guarantees high accuracy and reproducibility of ultrasonic tests. Pulsed loading and appropriate cooling serve to avoid specimen heating. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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20 pages, 9149 KiB  
Article
Effect of Wave Process of Plastic Deformation at Forging on the Fatigue Fracture Mechanism of Titanium Compressor Disks of Gas Turbine Engine
by Andrey A. Shanyavskiy, Alexey P. Soldatenkov and Alexandr D. Nikitin
Materials 2021, 14(8), 1851; https://doi.org/10.3390/ma14081851 - 8 Apr 2021
Cited by 5 | Viewed by 2666
Abstract
The low-cycle fatigue behavior of the VT3-1 titanium alloy (Ti–6Al–3Mo–2Cr alloy) under loading with a triangular and trapezoidal shape of cycle waveform was studied on round specimens prepared from forged compressor disks of a gas turbine engine. The filament type structure after forging [...] Read more.
The low-cycle fatigue behavior of the VT3-1 titanium alloy (Ti–6Al–3Mo–2Cr alloy) under loading with a triangular and trapezoidal shape of cycle waveform was studied on round specimens prepared from forged compressor disks of a gas turbine engine. The filament type structure after forging has alternating filaments with the ductile and quasi-brittle state of the metal as a result of the wave process of plastic deformation during the metal forging process. The crack propagation, regardless of the cyclic waveform shape, occurs by the crack meso-tunneling mechanism: initially, the cracks propagate along the filaments by a quasi-brittle mechanism with the formation of a facetted pattern relief on the fracture surface reflecting the two-phase structure of the titanium alloy, and then, the bridge between the meso-tunnels is fractured with the formation of fatigue striations. The part of the crack growth duration Np/Nf in the durability Nf is determined on the basis of measuring the fatigue striation spacing, and it depends on the crack path with respect to the material filaments. The growth of a fatigue crack in the case of in-service failure of a compressor disk of a gas turbine engine is considered, taking into account the crack meso-tunneling effect, and the fatigue crack growth duration in the disk is determined on the basis of quantitative fractography. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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21 pages, 7451 KiB  
Article
Machine-Learning-Based Atomistic Model Analysis on High-Temperature Compressive Creep Properties of Amorphous Silicon Carbide
by Atsushi Kubo and Yoshitaka Umeno
Materials 2021, 14(7), 1597; https://doi.org/10.3390/ma14071597 - 25 Mar 2021
Cited by 6 | Viewed by 2921
Abstract
Ceramic matrix composites (CMCs) based on silicon carbide (SiC) are used for high-temperature applications such as the hot section in turbines. For such applications, the mechanical properties at a high temperature are essential for lifetime prediction and reliability design of SiC-based CMC components. [...] Read more.
Ceramic matrix composites (CMCs) based on silicon carbide (SiC) are used for high-temperature applications such as the hot section in turbines. For such applications, the mechanical properties at a high temperature are essential for lifetime prediction and reliability design of SiC-based CMC components. We developed an interatomic potential function based on the artificial neural network (ANN) model for silicon-carbon systems aiming at investigation of high-temperature mechanical properties of SiC materials. We confirmed that the developed ANN potential function reproduces typical material properties of the single crystals of SiC, Si, and C consistent with first-principles calculations. We also validated applicability of the developed ANN potential to a simulation of an amorphous SiC through the analysis of the radial distribution function. The developed ANN potential was applied to a series of creep test for an amorphous SiC model, focusing on the amorphous phase, which is expected to be formed in the SiC-based composites. As a result, we observed two types of creep behavior due to different atomistic mechanisms depending on the strain rate. The evaluated activation energies are lower than the experimental values in literature. This result indicates that an amorphous region can play an important role in the creep process in SiC composites. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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13 pages, 4532 KiB  
Article
Cyclic Deformation Induced Residual Stress Evolution and 3D Short Fatigue Crack Growth Investigated by Advanced Synchrotron Tomography Techniques
by Benjamin Dönges, Melanie Syha, Anne K. Hüsecken, Ullrich Pietsch, Wolfgang Ludwig, Ulrich Krupp and Hans-Jürgen Christ
Materials 2021, 14(6), 1562; https://doi.org/10.3390/ma14061562 - 22 Mar 2021
Cited by 2 | Viewed by 1966
Abstract
Diffraction and phase contrast tomography techniques were successfully applied to an austenitic–ferritic duplex stainless steel representing exemplarily a metallic material containing two phases with different crystal structures. The reconstructed volumes of both phases were discretized by finite elements. A crystal plasticity finite-element analysis [...] Read more.
Diffraction and phase contrast tomography techniques were successfully applied to an austenitic–ferritic duplex stainless steel representing exemplarily a metallic material containing two phases with different crystal structures. The reconstructed volumes of both phases were discretized by finite elements. A crystal plasticity finite-element analysis was executed in order to simulate the development of the experimentally determined first and second order residual stresses, which built up due to the manufacturing process of the material. Cyclic deformation simulations showed the single-grain-resolved evolution of initial residual stresses in both phases and were found to be in good agreement with the experimental results. Solely in ferritic grains, residual stresses built up due to cyclic deformation, which promoted crack nucleation in this phase. Furthermore, phase contrast tomography was applied in order to analyze the mechanisms of fatigue crack nucleation and short fatigue crack propagation three-dimensionally and nondestructively. The results clearly showed the significance of microstructural barriers for short fatigue crack growth at the surface, as well as into the material. The investigation presented aims for a better understanding of the three-dimensional mechanisms governing short fatigue crack propagation and, in particular, the effect of residual stresses on these mechanisms. The final goal was to generate tailored microstructures for improved fatigue resistance and enhanced fatigue life. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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12 pages, 2753 KiB  
Article
Incorporation of Obstacle Hardening into Local Approach to Cleavage Fracture to Predict Temperature Effects in the Ductile to Brittle Transition Regime
by Maria S. Yankova, Andrey P. Jivkov and Rajesh Patel
Materials 2021, 14(5), 1224; https://doi.org/10.3390/ma14051224 - 5 Mar 2021
Cited by 2 | Viewed by 1615
Abstract
Ductile-to-brittle-transition refers to observable change in fracture mode with decreasing temperature—from slow ductile crack growth to rapid cleavage. It is exhibited by body-centred cubic metals and presents a challenge for integrity assessment of structural components made of such metals. Local approaches to cleavage [...] Read more.
Ductile-to-brittle-transition refers to observable change in fracture mode with decreasing temperature—from slow ductile crack growth to rapid cleavage. It is exhibited by body-centred cubic metals and presents a challenge for integrity assessment of structural components made of such metals. Local approaches to cleavage fracture, based on Weibull stress as a cleavage crack-driving force, have been shown to predict fracture toughness at very low temperatures. However, they are ineffective in the transition regime without the recalibration of Weibull stress parameters, which requires further testing and thus diminishes their predictive capability. We propose new Weibull stress formulation with thinning function based on obstacle hardening model, which modifies the number of cleavage-initiating features with temperature. Our model is implemented as a post-processor of finite element analysis results. It is applied to analyses of standard compact tension specimens of typical reactor pressure vessel steel, for which deformation and fracture toughness properties in the transition regime are available. It is shown that the new Weibull stress is independent of temperature, and of Weibull shape parameter, within the experimental error. It accurately predicts the fracture toughness at any temperature in the transition regime without relying upon empirical fits for the first time. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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32 pages, 51752 KiB  
Article
Analysis of the Root Causes of Damage to the Edges of Tank Manholes on the Main Deck of Handy-Size Bulk Carriers
by Leszek Chybowski and Katarzyna Gawdzińska
Materials 2021, 14(3), 632; https://doi.org/10.3390/ma14030632 - 29 Jan 2021
Cited by 1 | Viewed by 2086
Abstract
This study analyzes the root causes of cracks in the deck plating around tank manholes. Four handy-size bulk carriers built in one shipyard were analyzed. In all cases, deck cracks were found near manholes, and the average time from the commencement of operation [...] Read more.
This study analyzes the root causes of cracks in the deck plating around tank manholes. Four handy-size bulk carriers built in one shipyard were analyzed. In all cases, deck cracks were found near manholes, and the average time from the commencement of operation until the occurrence of cracks was 1356 days. Due to this short wear-life of the vessel’s structural material, the authors believed that it was unlikely to be caused by corrosion fatigue. The authors hypothesized that main decks cracked around manholes because of very poor-quality welded joints and poor-quality steel (large amounts of non-metallic impurities) used to make the manholes. In order to verify this hypothesis, on each of the vessels, material samples were collected from near the cracks and then examined thoroughly. Each sample was subjected to the macroscopic examination of the natural surfaces of cracks and their vicinity, microscopic examination of the material, mechanical property tests, and scanning electron microscope fractography for samples obtained after impact tests. The examination and test results were used to draw detailed conclusions for each case study. The general conclusions based on examination of the whole damage population validated the authors’ hypothesis that main decks cracked around manholes because of very poor-quality welded joints and poor-quality steel used to make the manholes. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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18 pages, 5995 KiB  
Article
Strain Localizations in Notches for a Coarse-Grained Ni-Based Superalloy: Simulations and Experiments
by Francesco Sausto, Luca Patriarca, Stefano Foletti, Stefano Beretta and Erica Vacchieri
Materials 2021, 14(3), 564; https://doi.org/10.3390/ma14030564 - 25 Jan 2021
Cited by 2 | Viewed by 1900
Abstract
Alloys used for turbine blades have to safely sustain severe thermomechanical loadings during service such as, for example, centrifugal loadings, creep and high temperature gradients. For these applications, cast Ni-based superalloys characterized by a coarse-grained microstructure are widely adopted. This microstructure dictates a [...] Read more.
Alloys used for turbine blades have to safely sustain severe thermomechanical loadings during service such as, for example, centrifugal loadings, creep and high temperature gradients. For these applications, cast Ni-based superalloys characterized by a coarse-grained microstructure are widely adopted. This microstructure dictates a strong anisotropic mechanical behaviour and, concurrently, a large scatter in the fatigue properties is observed. In this work, Crystal Plasticity Finite Element (CPFE) simulations and strain measurements performed by means of Digital Image Correlations (DIC) were adopted to study the variability introduced by the coarse-grained microstructure. In particular, the CPFE simulations were calibrated and used to simulate the effect of the grain cluster orientations in proximity to notches, which reproduce the cooling air ducts of the turbine blades. The numerical simulations were experimentally validated by the DIC measurements. This study aims to predict the statistical variability of the strain concentration factors and support component design. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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20 pages, 5592 KiB  
Article
Addressing H-Material Interaction in Fast Diffusion Materials—A Feasibility Study on a Complex Phase Steel
by Agustina Massone, Armin Manhard, Andreas Drexler, Christian Posch, Werner Ecker, Verena Maier-Kiener and Daniel Kiener
Materials 2020, 13(20), 4677; https://doi.org/10.3390/ma13204677 - 20 Oct 2020
Cited by 10 | Viewed by 3420
Abstract
Hydrogen embrittlement (HE) is one of the main limitations in the use of advanced high-strength steels in the automotive industry. To have a better understanding of the interaction between hydrogen (H) and a complex phase steel, an in-situ method with plasma charging was [...] Read more.
Hydrogen embrittlement (HE) is one of the main limitations in the use of advanced high-strength steels in the automotive industry. To have a better understanding of the interaction between hydrogen (H) and a complex phase steel, an in-situ method with plasma charging was applied in order to provide continuous H supply during mechanical testing in order to avoid H outgassing. For such fast-H diffusion materials, only direct observation during in-situ charging allows for addressing H effects on materials. Different plasma charging conditions were analysed, yet there was not a pronounced effect on the mechanical properties. The H concentration was calculated while using a simple analytical model as well as a simulation approach, resulting in consistent low H values, below the critical concentration to produce embrittlement. However, the dimple size decreased in the presence of H and, with increasing charging time, the crack propagation rate increased. The rate dependence of flow properties of the material was also investigated, proving that the material has no strain rate sensitivity, which confirmed that the crack propagation rate increased due to H effects. Even though the H concentration was low in the experiments that are presented here, different technological alternatives can be implemented in order to increase the maximum solute concentration. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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14 pages, 5237 KiB  
Article
Inverse Method to Determine Fatigue Properties of Materials by Combining Cyclic Indentation and Numerical Simulation
by Hafiz Muhammad Sajjad, Hamad ul Hassan, Matthias Kuntz, Benjamin J. Schäfer, Petra Sonnweber-Ribic and Alexander Hartmaier
Materials 2020, 13(14), 3126; https://doi.org/10.3390/ma13143126 - 13 Jul 2020
Cited by 10 | Viewed by 4110
Abstract
The application of instrumented indentation to assess material properties like Young’s modulus and microhardness has become a standard method. In recent developments, indentation experiments and simulations have been combined to inverse methods, from which further material parameters such as yield strength, work hardening [...] Read more.
The application of instrumented indentation to assess material properties like Young’s modulus and microhardness has become a standard method. In recent developments, indentation experiments and simulations have been combined to inverse methods, from which further material parameters such as yield strength, work hardening rate, and tensile strength can be determined. In this work, an inverse method is introduced by which material parameters for cyclic plasticity, i.e., kinematic hardening parameters, can be determined. To accomplish this, cyclic Vickers indentation experiments are combined with finite element simulations of the indentation with unknown material properties, which are then determined by inverse analysis. To validate the proposed method, these parameters are subsequently applied to predict the uniaxial stress–strain response of a material with success. The method has been validated successfully for a quenched and tempered martensitic steel and for technically pure copper, where an excellent agreement between measured and predicted cyclic stress–strain curves has been achieved. Hence, the proposed inverse method based on cyclic nanoindentation, as a quasi-nondestructive method, could complement or even substitute the resource-intensive conventional fatigue testing in the future for some applications. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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