•NfNM from ASTM D7460 was used to evaluate fatigue performance instead of Nf50 from AASHTO T321-07.•Terminal Blend, which presents more storage stability than the traditional asphalt rubber, was used ...in it.•Healing was considered to analyze the fatigue performance.•Fatigue performance grading or analysis was conducted in 3 situations.
Modified asphalt concretes have been used in pavement widely now. Their fatigue life, which can be increased by healing effect, is one of the most important factors in mixture design, however, it is considered less in mixture design. The test in the study involves fatigue tests of 9 modified asphalt mixtures, together with two base asphalt mixtures. Fatigue performances were compared (or graded) through several four-point bending beam fatigue tests, under the same asphalt content (5%), volume design target, and high-temperature performance grading, which are the most common occurrence 3 situations in mixture design process, the results can be a guidance for selection of asphalt in engineering application. Results also demonstrates that crumb rubber and styrene–butadiene–styrene modified asphalt mixtures performed good healing effects. And a partition scatterplot based on the test results was plotted, which provides a modified asphalt mixture design guide.
In this paper, a powder feeding laser additive manufacturing technology has been used for fabricating the Inconel 718 super-alloy. Laves phases of different sizes and morphologies have been obtained ...by using three types of heat treatments. The influence of Laves phases on the room temperature tensile properties of laser additive manufactured Inconel 718 has been investigated. The results show that small and granular Laves phase can be gained after heat treatment at 1050 °C for 15 min (S-15 sample). When the holding time extends to 45 min, the morphologies of Laves phases basically remain unchanged while its volume fraction further decreases (S-45 sample). Nevertheless, irregular and long-striped Laves phases still exist in the samples only after direct aging heat treatment (DA sample). The room temperature tensile results reveal that the S-15 samples have better tensile strength and ductility than that of S-45 samples. Besides, the DA samples with irregular and long-striped Laves phases show the lowest tensile strength and ductility. Hence, a certain amount of small and granular Laves phases are presumably beneficial for the room temperature tensile properties of Inconel 718. Moreover, a model has been established to describe the fracture of the Laves phase. On the basis of the fracture model, the critical stress needed for the fracture of long-striped Laves phases is lower than that needed for the fracture of granular Laves phases. Therefore, the former generally suffered internal fracture while the latter often fail by interfacial decohesion. Through influencing the volume fraction, the size and the distribution of γ" phase, the effect of the Laves phases on the room temperature tensile property is achieved. Furthermore, a yield strength model has been developed to reveal this influence in terms of numbers. The yield strength increments caused by grains, solution elements and γ′ phase are almost the same for the three kinds of samples. The differences of the yield strength are mainly caused by γ" phase. In addition, in terms of ductility, granular Laves phases are more favorable than long-striped Laves phases.
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The mechanical anisotropy of laser directed energy deposition (L-DED) titanium alloys using laser solid forming (LSF) is significantly deteriorated owing to the coarse prior β columnar grains and ...continuous grain boundary α-laths (αGB). The influence mechanisms of trace boron (up to 0.25 wt%) on the microstructure, tensile properties and anisotropy of Ti6Al4V manufactured by LSF were investigated. The sizes of β grains and α phases both decreased with increasing boron content. Compared with the Ti6Al4V deposit, when the addition of boron was 0.08 wt%, the average width of β grains was reduced by about one order of magnitude owing to the growth restricting effect caused by boron and Zener pinning by TiB. Besides, the average length and aspect ratio of α-laths were reduced by 43% and 33%, respectively, owing to the refinement of β grains and the heterogeneous nucleation of α phases on TiB particles. With an increase in boron content, the strength anisotropy gradually decreased for the disappearance of αGB, the elongation anisotropy initially increased and then significantly decreased for the poor deformation compatibility between the TiB and the matrix. A better combination of strength and elongation could be obtained with the addition of 0.08 wt% boron to Ti6Al4V.
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•The prior β grains are significantly refined after the addition of boron.•The α phase aspect ratios are significantly reduced with the increase of boron content.•The highly orientated TiB phases play a significant role in the anisotropy.
In this paper, a comparative study of high-cycle fatigue tests (T=650°C, f=110Hz, R=0.1, Kt=1) were carried out with wrought Inconel 718 and LAMed Inconel 718. The results show that the influences of ...the Laves phases on high-cycle fatigue properties are based on the applied stress amplitudes. At a low stress amplitude, most of the Laves phases held their original morphologies. The fatigue cracks stopped in front or detoured around them, which means that the unbroken Laves phases play an important role in hindering crack propagation. In this way, the high-cycle fatigue life of LAMed Inconel 718 was superior to that of wrought Inconel 718. However, at a high stress amplitude almost all of the Laves phases in the crack propagation region splintered into smaller fragments, parts of which separated from the austenite matrix. Microscopic holes or cracks were formed at the interface, which provided passages for the fatigue cracks to propagate. In this case, the Laves phases were harmful, leading to the degradation of fatigue performance in LAMed Inconel 718 compared with wrought Inconel 718.
Wire and arc additive manufacturing (WAAM), using cold metal transfer (CMT) as heat source, exhibits a great potential for additive manufacturing of magnesium alloys due to low heat input. With the ...purpose of revealing the relationship between the microstructure and mechanical properties of WAAMed AZ31 material, the present study has been carried out. The manufactured AZ31 thin-walled deposit is mainly composed of columnar dendrite arrays, including dendritic α-Mg matrix, interdendritic eutectics (α-Mg and β-Mg17Al12) and some dispersive η-Al8Mn5 phases. The average primary dendrite arm spacing increases from 17 μm at the bottom to 39 μm at the top of the deposit, and the volume fraction of the interdendritic eutectic decreases from 52.1% to 39.3%. The microstructure of each layer except the top layer consists of vertical columnar dendrites and direction-changed columnar dendrites in sequence. The top layer appears equiaxed dendrites due to columnar to equiaxed transition (CET). The tensile properties present obvious anisotropic characteristics because of the epitaxial columnar dendritic growth along the building direction. The tensile properties also show obvious variation from the bottom to the top of the deposit because of the differing microstructures in different regions. The results are further analyzed in detail through the microstructure evolution resulted from the new manufacturing method.
Post heat treatment is necessary to optimize the microstructure of additive manufactured Ti–6Al–4V to satisfy the aeronautical criterion. However, the relationship between the unique heat treated ...microstructure features and corresponding mechanical properties of wire and arc additive manufactured (WAAMed) Ti–6Al–4V has not been completely understood so far. In this study, five subtransus heat treatment regimes were used to the WAAMed Ti–6Al–4V alloy, and the different heat treated microstructure and the resultant mechanical properties were investigated. The microstructure was not substantially changed after heat treatment 600 °C/4 h/air cooling (AC). The α laths were coarsened after heat treatment 850 °C/2 h/AC, and the higher annealing temperature contributed to the appearance of αs. After solution and aging treatment, there were the discontinuous αGB, coarsened αp, and fine αs. There was the small Widmanstätten structural αs sharing the uniform crystallographic orientation after heat treatment 930 °C/1 h/AC + 550 °C/4 h/AC. The α′ martensite and extremely fine dispersed granular αs were obtained after heat treatment 930 °C/1 h/water quenching (WQ) + 550 °C/4 h/AC. The heat treatment 930 °C/1 h/WQ + 800 °C/2 h/AC was found to be the best heat treatment in this study. The discontinuous αGB, dispersed αs with various crystallographic orientations were obtained, which simultaneously increased the ultimate tensile strength (UTS) and elongation (EL) to 886 ± 8 MPa and 16.6 ± 1.6%, comparing to 847 ± 12 MPa and 12.2 ± 2.8% for the as-deposited specimen. Besides, the α/β interface phase distribution in the as-deposited and heat treated specimens was concerned. Two break-up mechanisms of αp, including boundary splitting and termination migration, were observed and discussed.
•The UTS and EL were simultaneously increased by heat treatment.•The strengthening mechanisms of unique heat treated microstructure were clarified.•Two mechanisms of αp break-up were identified and investigated in heat treated specimens.•The α/β interface phase in the as-deposited and heat treated specimens was observed and discussed.
Since the novel coronavirus (COVID-19) outbreak in China, and due to the open accessibility of COVID-19 data, several researchers and modellers revisited the classical epidemiological models to ...evaluate their practical applicability. While mathematical compartmental models can predict various contagious viruses' dynamics, their efficiency depends on the model parameters. Recently, several parameter estimation methods have been proposed for different models. In this study, we evaluated the Ensemble Kalman filter's performance (EnKF) in the estimation of time-varying model parameters with synthetic data and the real COVID-19 data of Hubei province, China. Contrary to the previous works, in the current study, the effect of damping factors on an augmented EnKF is studied. An augmented EnKF algorithm is provided, and we present how the filter performs in estimating models using uncertain observational (reported) data. Results obtained confirm that the augumented-EnKF approach can provide reliable model parameter estimates. Additionally, there was a good fit of profiles between model simulation and the reported COVID-19 data confirming the possibility of using the augmented-EnKF approach for reliable model parameter estimation.
In this work, the dense Ti-7.5Mo sample (over 99.5%) was prepared by using laser powder bed fusion (L-PBF) from powder mixture of pure Ti and pure Mo. Through the use of mechanical mixture process, ...Mo particles present an uniform distribution. As the laser scanning speed decreases from 1700 mm/s to 1000 mm/s, the sample's relative density increases from 85.5% to 99.5%. The microstructural analysis indicates that Mo particle was mostly fully melted during laser melting. But, some large sized Mo particles were partial melted, which possesses gradient interface structure. Then, the tensile properties of as-fabricated samples under several laser scanning speed were determined. The results shows that the as-fabricated dense sample presents Young's modulus, ultimate tensile strength and strain at failure about of 70 GPa, 740 MPa and 9.2% respectively. Given to this low Young's modulus, which is approximate to bone of 30 GPa, the L-PBF processed Ti-7.5Mo shows great application potential in implant component.
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•Dense Ti-7.5Mo (over 99.5%) was prepared by selective laser melting from powder mixture.•Special conchoidal structure, which consists by α and β Ti, appears at as fabricated sample.•The modulus and UTS of as-fabricated dense sample are about of 70 GPa and 700 MPa.
Brown adipose tissue (BAT) has long been recognized as an energy‐consuming organ and a possible target for combating metabolism disorder. Although numerous studies have demonstrated the ability of ...phytochemical phenolic acids to improve obesity by activating BAT, the underlying mechanism or mechanism therein remain obscure. In this study, diet‐induced obese mice, genetically obese mice, and C3H10T1/2 cells were used to examine the effects of p‐Coumaric acid (CA) on metabolism profiles. The results showed that CA prevented metabolic syndromes in the two mice models through the activation of BAT. This phenomenon was closely linked to the upregulation of uncoupling protein 1 (UCP1) and the accelerated burning of fatty acids and glucose, which consequently enhanced the energy expenditure and thermogenesis. Similar results were also obtained in vitro. Importantly, these effects were mediated by the mammalian target of rapamycin complex 1 (mTORC1)‐RPS6 pathway. These findings reveal, to the best of our knowledge for the first time, the close correlation between mTORC1‐RPS6 and BAT‐mediated thermogenesis, and, in addition, the key role played by mTORC1‐RPS6 in mediating phenolic acids‐induced activation of BAT, thus preventing obesity.
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