E-Mail Alert

Add your e-mail address to receive forthcoming issues of this journal:

Journal Browser

Journal Browser

Special Issue "Deformation, Fatigue and Fracture of Materials"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: 31 May 2019

Special Issue Editor

Guest Editor
Prof. Dr. Filippo Berto

Department of Industrial and Mechanical Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway
Website | E-Mail
Phone: +4748500574
Interests: fatigue of advanced and traditional materials; fracture mechanics; solid mechanics; structural integrity; additive materials

Special Issue Information

Dear Colleagues,

Deformation, fracture, and fatigue of structural components are very common problems to be managed during the design of complex products and structures. They can provoke unexpected failures or inappropriate behavior of structural components under in-service loading conditions with a shortening of the fatigue life. Aim of this Special Issue is to provide an update to the state-of-the-art on these problems, showing a clear link between material micro-nano behavior and the behavior of a real structure. Multiscale approaches are usually employed to capture these features in a unified way. Recent advanced criteria for fracture and fatigue predictions are fully considered in this Special Issue, keeping in mind the introduction and use of new advanced materials as additive materials, functionally graded materials, and multifunctional materials.

Prof. Dr. Filippo Berto
Guest Editor

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 papers will be 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 1800 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

  • local approaches
  • fatigue assessment
  • advanced design
  • multiscale approach
  • new materials

Published Papers (13 papers)

View options order results:
result details:
Displaying articles 1-13
Export citation of selected articles as:

Research

Open AccessArticle An Energy-Based Unified Approach to Predict the Low-Cycle Fatigue Life of Type 316L Stainless Steel under Various Temperatures and Strain-Rates
Materials 2019, 12(7), 1090; https://doi.org/10.3390/ma12071090
Received: 10 March 2019 / Revised: 29 March 2019 / Accepted: 29 March 2019 / Published: 2 April 2019
PDF Full-text (4505 KB) | HTML Full-text | XML Full-text
Abstract
An energy-based low-cycle fatigue model was proposed for applications at a range of temperatures. An existing model was extended to the integrated approach, incorporating the simultaneous effects of strain rate and temperature. A favored material at high temperature, type 316L stainless steel, was [...] Read more.
An energy-based low-cycle fatigue model was proposed for applications at a range of temperatures. An existing model was extended to the integrated approach, incorporating the simultaneous effects of strain rate and temperature. A favored material at high temperature, type 316L stainless steel, was selected in this study and its material characteristics were investigated. Tensile tests and low-cycle fatigue tests were performed using several strain rates at a temperature ranging from room temperature to 650 °C. Material properties were obtained in terms of temperature using the displacement-controlled tensile tests and further material response were investigated using strain-controlled tensile tests. Consequently, no pronounced reduction in strengths occurred at temperatures between 300 and 550 °C, and a negative strain rate response was observed in the temperature range. Based on the low-cycle fatigue tests by varying strain rates and temperature, it was found that a normalized plastic strain energy density and a strain-rate modified cycle were successfully correlated. The accuracy of the model was discussed by comparing between predicted and experimental lives. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Prediction of Corrosive Fatigue Life of Submarine Pipelines of API 5L X56 Steel Materials
Materials 2019, 12(7), 1031; https://doi.org/10.3390/ma12071031
Received: 28 January 2019 / Revised: 22 March 2019 / Accepted: 22 March 2019 / Published: 28 March 2019
PDF Full-text (6657 KB) | HTML Full-text | XML Full-text
Abstract
Corrosive fatigue failure of submarine pipelines is very common because the pipeline is immersed in a sea environment. In Bohai sea, many old pipelines are made of API 5L X56 steel materials, and it is necessary to provide an accurate method for predicting [...] Read more.
Corrosive fatigue failure of submarine pipelines is very common because the pipeline is immersed in a sea environment. In Bohai sea, many old pipelines are made of API 5L X56 steel materials, and it is necessary to provide an accurate method for predicting the residual life of these pipelines. As Paris law has been proven to be reliable in predicting the fatigue crack growth in metal materials, the two constants in Paris law for API 5L X56 steel materials are obtained by using a new proposed shape factor based on the analysis of experimental data measured from fatigue tests on compact tension specimens immersed in the water of Bohai sea. The results of the newly proposed shape factor show that, for a given stress intensity factor range (ΔK), the fatigue crack growth rate (da/dN) in seawater is 1.6 times of that that in air. With the increase of fatigue crack growth rate, the influence of seawater on corrosive fatigue decreases gradually. Thereafter, a finite element model for analyzing the stress intensity factor of fatigue crack in pipelines is built, and the corrosive fatigue life of a submarine pipeline is then predicted according to the Paris law. To verify the presented method, the fatigue crack growth (FCG) behavior of an API 5L X56 pipeline with an initial crack under cyclic load is tested. Comparison between the prediction and the tested result indicates that the presented method is effective in evaluating the corrosive fatigue life of API 5L X56 pipelines. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Numerical Simulation of Dynamic Mechanical Properties of Concrete under Uniaxial Compression
Materials 2019, 12(4), 643; https://doi.org/10.3390/ma12040643
Received: 29 January 2019 / Revised: 14 February 2019 / Accepted: 15 February 2019 / Published: 20 February 2019
Cited by 1 | PDF Full-text (9116 KB) | HTML Full-text | XML Full-text
Abstract
Based on the base force element method (BFEM), the dynamic mechanical behavior of concrete under uniaxial compression loading at different strain rates is investigated. The concrete can be considered as a three-phase composite material composed of aggregate, cement mortar, and interfacial transition zone [...] Read more.
Based on the base force element method (BFEM), the dynamic mechanical behavior of concrete under uniaxial compression loading at different strain rates is investigated. The concrete can be considered as a three-phase composite material composed of aggregate, cement mortar, and interfacial transition zone (ITZ) on the meso-level. A two-dimensional random aggregate model is generated by the Monte Carlo method. A multi-linear two-dimensional damage model is applied to describe the damage properties of each phase in the concrete. The strain-softening behavior, strain-rate effect, and failure patterns of the concrete are studied. The numerical results find that the peaks of compressive stress and compressive strain of concrete show the rate-sensitivity in various degrees under different strain rates. The calculated results of the dynamic enhancement factors are in a good agreement with the formula given by the Comité Euro-International du Béton (CEB) and other experimental results. The failure diagram of the specimen clearly describes the compressive failure process of the concrete specimen. This failure’s characteristics are similar to the experimental results. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Grain-Size Distribution Effects on the Attenuation of Laser-Generated Ultrasound in α-Titanium Alloy
Materials 2019, 12(1), 102; https://doi.org/10.3390/ma12010102
Received: 27 November 2018 / Revised: 13 December 2018 / Accepted: 21 December 2018 / Published: 29 December 2018
PDF Full-text (5957 KB) | HTML Full-text | XML Full-text
Abstract
Average grain size is usually used to describe a polycrystalline medium; however, many investigations demonstrate the grain-size distribution has a measurable effect on most of mechanical properties. This paper addresses the experimental quantification for the effects of grain-size distribution on attenuation in α-titanium [...] Read more.
Average grain size is usually used to describe a polycrystalline medium; however, many investigations demonstrate the grain-size distribution has a measurable effect on most of mechanical properties. This paper addresses the experimental quantification for the effects of grain-size distribution on attenuation in α-titanium alloy by laser ultrasonics. Microstructures with different mean grain sizes of 26–49 μm are obtained via annealing at 800 °C for different holding times, having an approximately log-normal distribution of grain sizes. Experimental measurements were examined by using two different theoretical models: (i) the classical Rokhlin’s model considering a single mean grain size, and (ii) the improved Turner’s model incorporating a log-normal distribution of grain sizes in the attenuation evaluation. Quantitative agreement between the experiment and the latter model was found in the Rayleigh and the Rayleigh-to-stochastic transition regions. A larger attenuation level was exhibited than the classical theoretical prediction considering a single mean grain size, and the frequency dependence of attenuation reduced from a classical fourth power to an approximately second power due to a greater probability of large grains than the assumed Poisson statistics. The provided results would help support the use of laser ultrasound technology for the non-destructive evaluation of grain size distribution in polycrystalline materials. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Microstructure and Mechanical Properties of Hot- Rolled and Cold-Rolled Medium-Mn TRIP Steels
Materials 2018, 11(11), 2242; https://doi.org/10.3390/ma11112242
Received: 29 September 2018 / Revised: 8 November 2018 / Accepted: 9 November 2018 / Published: 11 November 2018
PDF Full-text (6300 KB) | HTML Full-text | XML Full-text
Abstract
This study investigated the microstructure and mechanical properties of hot-rolled and cold-rolled medium-Mn transformation-induced plasticity (TRIP) steel. The experimental steel, processed by quenching and tempering (Q & T) heat treatment, exhibited excellent mechanical properties for hot-rolled and Q & T steels (strength of [...] Read more.
This study investigated the microstructure and mechanical properties of hot-rolled and cold-rolled medium-Mn transformation-induced plasticity (TRIP) steel. The experimental steel, processed by quenching and tempering (Q & T) heat treatment, exhibited excellent mechanical properties for hot-rolled and Q & T steels (strength of 1050–1130 MPa and ductility of 16–34%), as well as for cold-rolled and Q & T steels (strength of 878–1373 MPa and ductility of 18–40%). The mechanical properties obtained after isothermal holding at 775 °C for one hour for cold-rolled/Q & T steel were superior to that of hot-rolled/Q & T steel. Excellent mechanical properties were attributed to the large amount of retained austenite, which produced a discontinuous TRIP effect. Additionally, the differences in mechanical properties correlated with the morphology, stability and content of retained austenite. The cold-rolled sample, quenched from 650 °C (CR 650°C) had extensive TRIP effects in the middle and late stages of the deformation, leading to better mechanical properties. The fracture modes of the hot-rolled sample, quenched from 650 °C, and the cold-rolled sample quenched from 650 °C, were ductile fractures, resulting in excellent ductility. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Low Cycle Fatigue Behavior of Steam Generator Tubes under Axial Loading
Materials 2018, 11(10), 1944; https://doi.org/10.3390/ma11101944
Received: 29 August 2018 / Revised: 29 September 2018 / Accepted: 7 October 2018 / Published: 11 October 2018
Cited by 1 | PDF Full-text (4653 KB) | HTML Full-text | XML Full-text
Abstract
Compared with the fatigue properties of the material (Inconel Alloy 690), the real fatigue lives of tubes are more meaningful in the fatigue design and assessment of steam generator (SG) tube bundles. However, it is almost impossible to get a satisfactory result by [...] Read more.
Compared with the fatigue properties of the material (Inconel Alloy 690), the real fatigue lives of tubes are more meaningful in the fatigue design and assessment of steam generator (SG) tube bundles. However, it is almost impossible to get a satisfactory result by conducting fatigue tests on the tube directly. A tube with a uniform and thin wall easily fails near the clamping ends under cyclic loading due to the stress concentration. In this research, a set-up for fatigue tests of real tubes is proposed to overcome the stress concentration. With the set-up, low cycle fatigue tests were conducted in accordance with an existing fatigue design curve for Alloy 690. Strain control mode was applied with fully reversed push–pull loading under different strain amplitudes (0.15%, 0.2%, 0.3%, and 0.4%). A favourable result was obtained, and the low cycle fatigue behavior was investigated. The results showed that the fatigue life tested by the real tube was below the strain–life curve of Alloy 690 which was fitted by conventional solid specimens. A cyclic hardening behavior was found by the cyclic stress–strain curve when compared with the monotonic stress–strain curve. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Effects of Loading Frequency and Loading Type on High-Cycle and Very-High-Cycle Fatigue of a High-Strength Steel
Materials 2018, 11(8), 1456; https://doi.org/10.3390/ma11081456
Received: 24 July 2018 / Revised: 14 August 2018 / Accepted: 14 August 2018 / Published: 16 August 2018
PDF Full-text (5222 KB) | HTML Full-text | XML Full-text
Abstract
High-cycle and very-high-cycle fatigue tests via rotary bending (52.5 Hz), electromagnetic resonance (120 Hz) axial cycling, and ultrasonic (20 kHz) axial cycling were performed for a high-strength steel with three heat treatment conditions, and the effects of loading frequency and loading type on [...] Read more.
High-cycle and very-high-cycle fatigue tests via rotary bending (52.5 Hz), electromagnetic resonance (120 Hz) axial cycling, and ultrasonic (20 kHz) axial cycling were performed for a high-strength steel with three heat treatment conditions, and the effects of loading frequency and loading type on fatigue strength and fatigue life were investigated. The results revealed that the loading frequency effect is caused by the combined response of strain rate increase and induced temperature rise. A parameter η was proposed to judge the occurrence of loading frequency effect, and the calculated results were in agreement with the experimental data. In addition, a statistical method based on the control volume was used to reconcile the effect of loading type, and the predicted data were consistent with the experimental results. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Low-Temperature Superplasticity and Deformation Mechanism of Ti-6Al-4V Alloy
Materials 2018, 11(7), 1212; https://doi.org/10.3390/ma11071212
Received: 24 May 2018 / Revised: 9 July 2018 / Accepted: 10 July 2018 / Published: 13 July 2018
Cited by 1 | PDF Full-text (6643 KB) | HTML Full-text | XML Full-text
Abstract
The low-temperature superplastic tensile behavior and the deformation mechanisms of Ti-6Al-4V alloy are investigated in this paper. Through the experiments carried out, elongation to failure (δ) is calculated and a set of values are derived that subsequently includes the strain rate sensitivity exponent [...] Read more.
The low-temperature superplastic tensile behavior and the deformation mechanisms of Ti-6Al-4V alloy are investigated in this paper. Through the experiments carried out, elongation to failure (δ) is calculated and a set of values are derived that subsequently includes the strain rate sensitivity exponent (m), deformation activation energy (Q) at low-temperature superplastic deformation, and the variation of δ, m and Q at different strain rates and temperatures. Microstructures are observed before and after superplastic deformation. The deformation mechanism maps incorporating the density of dislocations inside grains at temperatures of 973 and 1123 K are drawn respectively. By applying the elevated temperature deformation mechanism maps based on Burgers vector compensated grain size and modulus compensated stress, the dislocation quantities and low-temperature superplastic deformation mechanisms of Ti-6Al-4V alloy at different temperatures within appropriate processing regime are elucidated. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Health Degradation Monitoring and Early Fault Diagnosis of a Rolling Bearing Based on CEEMDAN and Improved MMSE
Materials 2018, 11(6), 1009; https://doi.org/10.3390/ma11061009
Received: 16 May 2018 / Revised: 6 June 2018 / Accepted: 11 June 2018 / Published: 14 June 2018
Cited by 10 | PDF Full-text (4302 KB) | HTML Full-text | XML Full-text
Abstract
Rolling bearings play a crucial role in rotary machinery systems, and their operating state affects the entire mechanical system. In most cases, the fault of a rolling bearing can only be identified when it has developed to a certain degree. At that moment, [...] Read more.
Rolling bearings play a crucial role in rotary machinery systems, and their operating state affects the entire mechanical system. In most cases, the fault of a rolling bearing can only be identified when it has developed to a certain degree. At that moment, there is already not much time for maintenance, and could cause serious damage to the entire mechanical system. This paper proposes a novel approach to health degradation monitoring and early fault diagnosis of rolling bearings based on a complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and improved multivariate multiscale sample entropy (MMSE). The smoothed coarse graining process was proposed to improve the conventional MMSE. Numerical simulation results indicate that CEEMDAN can alleviate the mode mixing problem and enable accurate intrinsic mode functions (IMFs), and improved MMSE can reflect intrinsic dynamic characteristics of the rolling bearing more accurately. During application studies, rolling bearing signals are decomposed by CEEMDAN to obtain IMFs. Then improved MMSE values of effective IMFs are computed to accomplish health degradation monitoring of rolling bearings, aiming at identifying the early weak fault phase. Afterwards, CEEMDAN is performed to extract the fault characteristic frequency during the early weak fault phase. The experimental results indicate the proposed method can obtain a better performance than other techniques in objective analysis, which demonstrates the effectiveness of the proposed method in practical application. The theoretical derivations, numerical simulations, and application studies all confirmed that the proposed health degradation monitoring and early fault diagnosis approach is promising in the field of prognostic and fault diagnosis of rolling bearings. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Ballistic Performance of Nanostructured Metals Toughened by Elliptical Coarse-Grained Inclusions: A Finite Element Study with Failure Analysis
Materials 2018, 11(6), 977; https://doi.org/10.3390/ma11060977
Received: 4 May 2018 / Revised: 4 June 2018 / Accepted: 5 June 2018 / Published: 8 June 2018
PDF Full-text (7815 KB) | HTML Full-text | XML Full-text
Abstract
Bimodal nanostructured (NS) metals, in which the nano-grains or ultrafine grains serve as matrix phase while the coarse grains serve as toughening phase, can synergize the overall strength and ductility to achieve excellent bullet-proof performance. Because of the extrusion process in the fabrication, [...] Read more.
Bimodal nanostructured (NS) metals, in which the nano-grains or ultrafine grains serve as matrix phase while the coarse grains serve as toughening phase, can synergize the overall strength and ductility to achieve excellent bullet-proof performance. Because of the extrusion process in the fabrication, the coarse-grained (CG) inclusions are elongated in the extrusion direction and elliptical CG inclusions with different aspect ratios form. The shape, distribution, and volume fraction of these elliptical CG inclusions can all have significant influence on the overall ballistic performance. In this study, the strain gradient plasticity model together with the Johnson–Cook failure criterion is employed to investigate the ballistic performance of the bimodal NS Cu with elliptical CG inclusions. Our results show that the ballistic performance can be improved by increasing the aspect ratio of the elliptical CG inclusions. Furthermore, the staggered distribution of the elliptical CG inclusions will decrease the overall ability of the material to resist failure, but it will improve its overall ability to resist deformation. The larger stagger degree of elliptical CG inclusions can weaken their shape effects on the limit displacement. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Study on Flake Formation Behavior and Its Influence Factors in Cr5 Steel
Materials 2018, 11(5), 690; https://doi.org/10.3390/ma11050690
Received: 4 April 2018 / Revised: 23 April 2018 / Accepted: 23 April 2018 / Published: 27 April 2018
PDF Full-text (3555 KB) | HTML Full-text | XML Full-text
Abstract
A flake is a crack that is induced by trapped hydrogen within steel. To study its formation mechanism, previous studies mostly focused on the formation process and magnitude of hydrogen pressure in hydrogen traps such as cavities and cracks. However, according to recent [...] Read more.
A flake is a crack that is induced by trapped hydrogen within steel. To study its formation mechanism, previous studies mostly focused on the formation process and magnitude of hydrogen pressure in hydrogen traps such as cavities and cracks. However, according to recent studies, the hydrogen leads to the decline of the mechanical properties of steel, which is known as hydrogen embrittlement, is another reason for flake formation. In addition, the phenomenon of stress induced hydrogen uphill diffusion should not be neglected. All of the three behaviors are at work simultaneously. In order to further explore the formation mechanism of flakes in steel, the process of flake initiation and growth were studied with the following three coupling factors: trap hydrogen pressure, hydrogen embrittlement, and stress induced hydrogen re-distribution. The analysis model was established using the finite element method, and a crack whose radius is 0.5 mm was set in its center. The cohesive method and Bilinear Traction Separate Law (BTSL) were used to address the coupling effect. The results show that trap hydrogen pressure is the main driving force for flake formation. After the high hydrogen pressure was generated around the trap, a stress field formed. In addition, the trap is the center of stress concentration. Then, hydrogen is concentrated in a distribution around this trap, and most of the steel mechanical properties are reduced. The trap size is a key factor for defining the critical hydrogen content for flake formation and propagation. However, when the trap size exceeds the specified value, the critical hydrogen content does not change any more. As for the crack whose radius is 0.5 mm, the critical hydrogen content of Cr5VMo steel is 2.2 ppm, which is much closer to the maximum safe hydrogen concentration of 2.0 ppm used in China. The work presented in this article increases our understanding of flake formation and propagation mechanisms in steel. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Low-Cycle Fatigue Behavior of 10CrNi3MoV High Strength Steel and Its Undermatched Welds
Materials 2018, 11(5), 661; https://doi.org/10.3390/ma11050661
Received: 30 March 2018 / Revised: 16 April 2018 / Accepted: 23 April 2018 / Published: 24 April 2018
Cited by 3 | PDF Full-text (11782 KB) | HTML Full-text | XML Full-text
Abstract
The use of high strength steel allows the design of lighter, more slender and simpler structures due to high strength and favorable ductility. Nevertheless, the increase of yield strength does not guarantee the corresponding improvement of fatigue resistance, which becomes a major concern [...] Read more.
The use of high strength steel allows the design of lighter, more slender and simpler structures due to high strength and favorable ductility. Nevertheless, the increase of yield strength does not guarantee the corresponding improvement of fatigue resistance, which becomes a major concern for engineering structure design, especially for the welded joints. The paper presents a comparison of the low cycle fatigue behaviors between 10CrNi3MoV high strength steel and its undermatched weldments. Uniaxial tension tests, Push-pull, strain-controlled fatigue tests were conducted on base metal and weldments in the strain range of 0.2–1.2%. The monotonic and cyclic stress-strain curves, stress-life, strain-life and energy-life in terms of these materials were analyzed for fatigue assessment of materials discrepancy. The stress-life results of base metal and undermatched weld metal exhibit cyclic softening behaviors. Furthermore, the shapes of 10CrNi3MoV steel hysteresis loops show a satisfactory Masing-type behavior, while the weld metal shows a non-Masing type behavior. Strain, plastic and total strain energy density amplitudes against the number of reversals to failure results demonstrate that the undermatched weld metal presents a higher resistance to fatigue crack initiation than 10CrNi3MoV high strength steel. Finally, fatigue fracture surfaces of specimens were compared by scanning electron microscopy to identify the differences of crack initiation and the propagation between them. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Open AccessArticle Fretting Wear Damage Mechanism of Uranium under Various Atmosphere and Vacuum Conditions
Materials 2018, 11(4), 607; https://doi.org/10.3390/ma11040607
Received: 1 March 2018 / Revised: 11 April 2018 / Accepted: 12 April 2018 / Published: 16 April 2018
Cited by 3 | PDF Full-text (38149 KB) | HTML Full-text | XML Full-text
Abstract
A fretting wear experiment with uranium has been performed on a linear reciprocating tribometer with ball-on-disk contact. This study focused on the fretting behavior of the uranium under different atmospheres (Ar, Air (21% O2 + 78% N2), and O2 [...] Read more.
A fretting wear experiment with uranium has been performed on a linear reciprocating tribometer with ball-on-disk contact. This study focused on the fretting behavior of the uranium under different atmospheres (Ar, Air (21% O2 + 78% N2), and O2) and vacuum conditions (1.05 and 1 × 10−4 Pa). Evolution of friction was assessed by coefficient of friction (COF) and friction-dissipated energy. The oxide of the wear surface was evaluated by Raman spectroscopy. The result shows that fretting wear behavior presents strong atmosphere and vacuum condition dependence. With increasing oxygen content, the COF decreases due to abrasive wear and formation of oxide film. The COF in the oxygen condition is at least 0.335, and it has a maximum wear volume of about 1.48 × 107 μm3. However, the COF in a high vacuum condition is maximum about 1.104, and the wear volume is 1.64 × 106 μm3. The COF in the low vacuum condition is very different: it firstly increased and then decreased rapidly to a steady value. It is caused by slight abrasive wear and the formation of tribofilm after thousands of cycles. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
Figures

Figure 1

Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

1. Tentative Title: Validation of the fracture load dependence on yield strength in the
ductile-to-brittle temperature region and a simplified method to predict fracture toughness
temperature dependence in a wide range


Authors: Toshiyuki Meshii (University of Fukui), Takashi Inoue and Go Yakushi


Tentative Abstract: The fracture toughness KJc of the material in the ductile to brittle transition
temperature (DBTT) region shows test specimen thickness (TST) effect and temperature dependence.
Master curve (MC) method, which provides an engineering approach to solve these two issues is
gathering attention. Though MC is intended to apply for arbitrary ferritic material whose yield stress
in the range of 275 to 825 MPa, one has to obtain KJc data to obtain the material dependent reference
temperature: T0. The applicable range of MC method is restricted to T0 +- 50 oC. Experiences from
many researchers show that additional pre-tests to obtain T0 are necessary and thus benefit of
“arbitrary” material applicability seems not to be enjoyed. In contrary, the authors have focused on
the mean KJc and have demonstrated that TST effect on KJc and temperature dependence of KJc are
due to “the loss in one-to-one correspondence between the J and the crack-tip stress distribution”
and that the “scaled” crack-tip stress distribution at fracture is independent of TST effect or
temperature dependence on KJc. T-scaling method was proposed and validated for this purpose. An
extension of the T-scaling method on KJc temperature dependence the was the SDS method (fracture
“load” is proportional to 1/(yield strength). In this paper, the SDS method was validated for Cr-Mo
steel JIS SCM440 and 0.55% carbon steel JIS S55C. Both tensile and fracture toughness tests were
performed for a wide range of for -166 to 100 °C for SCM440 and -166 to 20 °C for S55C. The SDS
method was validated for the DBTT region plus alpha. Finally, a simplified method was proposed
and validated to predict the KJc temperature dependence, by using the yield stress temperature
dependence and applying the SDS and using EPRI plastic J functional form.

2. Tentative Title: Application of the T-scaling method to account for the notch acuity
dependence on the apparent notch fracture toughness in the ductile-to-brittle temperature region


Authors: Toshiyuki Meshii (University of Fukui), Masayoshi Yamashita and Hiroki Nakano


Tentative Abstract: Current defect assessment procedures based on fracture mechanics usually
assume flaws to be infinitely sharp. While this assumption may be appropriate for fatigue cracks, for
non-sharp flaws such as porosity, mechanical damage or weld undercut, it can be an
over-conservative assumption that can lead to pessimistic assessments of structural integrity and a
significant underestimation of the true safety margin against fracture. Irwin has studied notch and
pre-cracked fracture toughness in the lower shelf region and suggested that notch KIc is in proportion
to the square root of notch radius ρ, but is not continuous with the pre-cracked KIc (i.e., when zero is
substituted to ρ in the fitted KIc and ρ relationship, the obtained value differs from that of the
pre-cracked specimen KIc). In contrast, Begley et al. have made a similar study in the upper shelf
region and suggested that JIc ∝ ρ. In addition, they showed that notch JIc is continuous with the
pre-cracked JIc. Studies of this issue in the ductile-to-brittle transition temperature (DBTT) region
are few. In this paper, the effects of notch acuity on notch fracture toughness in the lower shelf and
DBTT region was studied for 0.55% C steel JIS S55C with 0.5TSE(B) specimen. The notch size ρ
was selected as 50, 150 and 375 μm. Fatigue pre-cracked specimens were also studied. The
experimental results showed that the notch KIc ∝ ρ 1/2, but is not continuous with the pre-cracked KIc
at lower shelf temperature of -166 °C. The DBTT notch fracture toughness KJc ∝ ρ1/2 and was
continuous with the pre-cracked KJc. By running elastic-plastic finite element analysis, the mid-plane
crack-opening stress distribution on the x1-axis, was shown that the scaled stress distribution at
fracture load could be T-scaled for pre-cracked and notch specimen. Thus, notch and pre-cracked KJc
has a reason to be continuous. The reason for notch size effect on Jc was explained as the difference
in load for notched specimens to reach the stress level of the pre-cracked specimen. The apparent
notch KJc dependence on notch acuity was also one of the “the loss in one-to-one correspondence
between the J and the crack-tip stress distribution.”

3. Tentative Title: Innovative elastoplastic J2-flow model with a unified simulation for failure effects of twisted metal tubes under monotonic and cyclic loadings

Authors: Lin Zhan, Si-Yu Wang, Hui-Feng Xi, Heng Xiao

Affiliation: School of Mechanics and Construction Engineering, MOE Key Lab of Disaster Forecast and Control in Engineering, Jinan University, 510632 Guangzhou, China

Tentative Abstract: New elastoplastic J2-flow equations with combined hardening are proposed without assuming the usual notion of yielding. Novel results are obtained based on these equations. First, fatigue failure effects under cyclic loading conditions are automatically incorporated as direct consequences of intrinsic constitutive features, without involving any assumed damage-like variables and any additional failure criteria of ad hoc nature. Second, both Swift effects and fatigue failure effects of twisted metal tubes under monotone and cyclic loadings may be simultaneously treated for the first time. As such, coupling effects of both finite strain and large rotation may be in a direct, unified manner simulated for both free-end and fixed-end torsion. Finally, numerical examples for model validation are presented and compared with experimental data and accurate agreement is achieved.

 

4. Tentative Title: Tensile strength, ductility, and fracture behavior of trimodal nanostructured metals

Authors: Guo, X. 1; Yang, G. 2; Wu, W. 1; Zhu, L.L. 3; Weng, G.J. 4,*

Affiliations: 1 School of Mechanical Engineering, Tianjin University, Tianjin 300072, China

2 Automotive Engineering Research Institute, China Automotive Technology and Research Center, Tianjin 300300, China

3 Department of Engineering Mechanics, School of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310027, Zhejiang, China

4 Department of Mechanical and Aerospace Engineering, Rutgers University, New Brunswick, NJ 08903, USA

Tentative Abstract: Trimodal nanostructured (NS) metals incorporate the advantages of a strong NS metallic matrix phase, a ductile coarse-grained (CG) inclusion phase, and a hard ceramic reinforcement phase. Its benefits are multifaceted, but its deformation and fracture behavior remain relatively unknown. In this work, we conduct a computational study based on the mechanism-based strain gradient plasticity, Johnson–Cook failure criterion, and Drucker–Prager plasticity model, on these two important issues. Our specific objectives are on the influence of distribution and shape of CG regions, and the influence of size and volume fraction of ceramic reinforcement on these mechanical properties. It is found that, among others, the trimodal NS metals with staggered arrangement of CG regions are stronger and more ductile than those with array arrangement of CG regions. The results further show that the size of ceramic reinforcement particles is also important. Several other interesting features of microstructural effects on the overall strength and ductility are also discussed.

Tentative Keywords: Trimodal nanostructured metals; Johnson–Cook failure criterion; Coarse-grained regions; Ceramic reinforcement; Volume fraction

 

Materials EISSN 1996-1944 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top