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1.
This paper presents multiscale modeling substantiated with experimental aspects of state, filtration, and motion of the gas–liquid mixtures involving phase transition regions in concentrated volumes applicable to porous media and pipe flows. Based on physics, it is confirmed analytically that actual levels of underpressure in gas–liquids systems are considerably above traditional understanding of saturation pressure at which gas emission from the liquid and its dissolution in the liquid in a form of embryos can occur. It is demonstrated that these processes are not equilibrium processes, and they can also occur on nanoscales and microscales. Thermo-hydrodynamic analyses and experimental investigation of the gas–liquid systems in areas of phase transition presented here have resulted in useful equations governing such flows in filtration in the porous media and in straight pipes. 相似文献
2.
《Materials Science & Technology》2013,29(10):917-925
AbstractThe solidification structure and the initial deformability of continuously cast steel were investigated by assessment of cracks on billets and on rolled product. Some billets were rolled directly off the casting machine and some cooled to ambient temperature, then reheated to rolling temperature. On direct rolled steels, the number of defects increases with increasing aluminium content, while virtually no defects are found on steel rolled after reheating. By increasing the aluminium content, the solidification structure of steel is highly modified and a columnar structure obtained over the entire section of the billet. It was shown by chemical analysis and fracture examination that the increased hot shortness is not related to the effect of AIN. It is concluded that the hot shortness is related to the effect of aluminium on the solidification structure.MST/761 相似文献
3.
Tayfun E. Tezduyar Sunil Sathe Matthew Schwaab Jason Pausewang Jason Christopher Jason Crabtree 《Computational Mechanics》2008,43(1):133-142
In this paper, we focus on fluid–structure interaction (FSI) modeling of ringsail parachutes, where the geometric complexity
created by the “rings” and “sails” used in the construction of the parachute canopy poses a significant computational challenge.
It is expected that NASA will be using a cluster of three ringsail parachutes, referred to as the “mains”, during the terminal
descent of the Orion space vehicle. Our FSI modeling of ringsail parachutes is based on the stabilized space–time FSI (SSTFSI)
technique and the interface projection techniques that address the computational challenges posed by the geometric complexities
of the fluid–structure interface. Two of these interface projection techniques are the FSI Geometric Smoothing Technique and
the Homogenized Modeling of Geometric Porosity. We describe the details of how we use these two supplementary techniques in
FSI modeling of ringsail parachutes. In the simulations we report here, we consider a single main parachute, carrying one
third of the total weight of the space vehicle. We present results from FSI modeling of offloading, which includes as a special
case dropping the heat shield, and drifting under the influence of side winds. 相似文献
4.
More and more styrene–butadiene–styrene (SBS)-modified asphalt waste materials are being discarded with the increase in road service life. The recycling of these waste pavement materials can reduce environmental pollution and help save resources. However, the low-temperature performance and the fatigue resistance of recycled asphalt mixture are significantly affected by the addition of reclaimed asphalt pavement (RAP). In order to evaluate the low-temperature performance and the fatigue resistance of recycled SBS-modified asphalt mixture, three points bending test, Fénix test and Ensayo de BArrido de DEformaciones test were conducted. Additionally, the differences of recycling between SBS-modified RAP with different ageing conditions and ordinary unmodified RAP were compared. The results showed that fatigue resistance of modified recycling of asphalt mixture with different RAPs did not vary much under low temperature (?5 °C) while displaying an obvious difference under higher temperature. SBS-modified RAP under light ageing condition was suitable for modified recycling. However, the SBS-modified asphalt from RAP under serious ageing condition would lose modification effect resulting in a great reduction of the low-temperature crack resistance and the fatigue resistance. Therefore, it is necessary to evaluate the ageing degree of RAP before recycling SBS-modified asphalt mixture. The SBS-modified RAP under serious ageing condition (SM-RAP) is not recommended for directly modified recycling. But considering for further utilisation, the SM-RAP used for unmodified recycling as ordinary unmodified RAP can be regarded as a good choice and the RAP content should be restricted to less than 30%. 相似文献
5.
Ali Firat Cabalar Waleed Sulaiman Mustafa 《International Journal of Pavement Engineering》2017,18(8):714-726
Materials forming sand grains and colluvial soil deposits have a distinct structure, consisting of a composite matrix of coarse and fine soil grains. The influence of sand grains content on the behaviour of sand–clay mixtures was investigated by a series of intensive laboratory experiments. The California bearing ratio (CBR), unconfined compression strength (UCS) and compaction tests were carried out on various contents of sand and clay mixtures. The sand–clay mixtures were prepared with sand contents of 0, 10, 20, 30, 40, and 50% by weight. The laboratory tests on these mixtures have indicated that their behaviour will depend on the relative concentration of the sand and clay samples. The results of the tests showed a decrease in the UCS, and an increase the CBR values with an increase in the amount of sand. An increase in dry unit weight and a decrease in respective moisture content by an increase in the amount of sand were observed in the compaction tests. 相似文献
6.
An Al–Te mixture was mechanically alloyed with a planetary ball mill, and the structural evolution of the Al–Te mixture during ball milling was characterized by X-ray diffractiometry (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and thermodynamic computation. Although crystalline α-Al2Te3 was synthesized in the initial stage of milling, but the final product is a metastable Al2Te3 ? δ (Space group: Fm 3¯m) with lattice parameter a = 5.925 Å. The metastable Al2Te3 ? δ decomposes into Al and Te at about 140 °C. 相似文献
7.
AbstractA thermodynamic database for the Al–Co–Cr–Ni system is built via the Calphad method by extrapolating re-assessed ternary subsystems. A minimum number of quaternary parameters are included, which are optimized using experimental phase equilibrium data obtained by electron probe micro-analysis and x-ray diffraction analysis of NiCoCrAlY alloys spanning a wide compositional range, after annealing at 900 °C, 1100 °C and 1200 °C, and water quenching. These temperatures are relevant to oxidation and corrosion resistant MCrAlY coatings, where M corresponds to some combination of nickel and cobalt. Comparisons of calculated and measured phase compositions show excellent agreement for the β–γ equilibrium, and good agreement for three-phase β–γ–σ and β–γ–α equilibria. An extensive comparison with existing Ni-base databases (TCNI6, TTNI8, NIST) is presented in terms of phase compositions. 相似文献
8.
Thomas Gheno Xuan L Liu Greta Lindwall Zi-Kui Liu Brian Gleeson 《Science and Technology of Advanced Materials》2015,16(5)
A thermodynamic database for the Al–Co–Cr–Ni system is built via the Calphad method by extrapolating re-assessed ternary subsystems. A minimum number of quaternary parameters are included, which are optimized using experimental phase equilibrium data obtained by electron probe micro-analysis and x-ray diffraction analysis of NiCoCrAlY alloys spanning a wide compositional range, after annealing at 900 °C, 1100 °C and 1200 °C, and water quenching. These temperatures are relevant to oxidation and corrosion resistant MCrAlY coatings, where M corresponds to some combination of nickel and cobalt. Comparisons of calculated and measured phase compositions show excellent agreement for the β–γ equilibrium, and good agreement for three-phase β–γ–σ and β–γ–α equilibria. An extensive comparison with existing Ni-base databases (TCNI6, TTNI8, NIST) is presented in terms of phase compositions. 相似文献
9.
《Materials Letters》2003,57(26-27):4271-4275
Author's previous studies [J. Am. Ceram. Soc., in press] showed that the acidification of the precursor solution controls the strength and length of sol–gel PZT fibers. Two acids, acetic acid (CH3COOH) and methacrylic acid (C4H6O2), were studied. C4H6O2 produced longer fibers with small cracks, while CH3COOH produced shorter and denser fibers. In order to take advantage of the opposite effect of each of these acids, mixtures of acetic and methacrylic acid are used in this work to obtain longer and dense fibers. The effect of the ratio of CH3COOH/C4H6O2 mixture on the precursors' chemical structure, crystalline phase formation and microstructure of PZT fibers is investigated and discussed. Long and almost crack-free PZT fibers are obtained for a 1/2 ratio of CH3COOH/C4H6O2. 相似文献
10.
Silicon Substituted Hydroxyapatite (Si-HA) coatings were prepared on titanium substrates by electrophoretic deposition (EPD).
The stability of Si-HA suspension in n-butanol and chloroform mixture has been studied by electricity conductivity and sedimentation
test. The microstructure, shear strength and bioactivity in vitro has been tested. The stability of Si-HA suspension containing
n-butanol and chloroform mixture as medium is better than that of pure n-butanol as medium. The good adhesion of the particles
with the substrate and good cohesion between the particles were obtained in n-butanol and chloroform mixture. Adding triethanolamine
(TEA) as additive into the suspension is in favor of the formation of uniform and compact Si-HA coatings on the titanium substrates
by EPD. The shear strength of the coatings can reach 20.43 MPa after sintering at 700 °C for 2 h, when the volume ratio of
n-butanol: chloroform is 2:1 and the concentration of TEA is 15 ml/L. Titanium substrates etched in H2O2/NH3 solution help to improve the shear strength of the coatings. After immersion in simulated body fluid for 7 days, Si-HA coatings
have the ability to induce the bone-like apatite formation. 相似文献
11.
Younes Bagheri Fauziah Ahmad Mohd Ashraf Mohamad Ismail 《Materials and Structures》2014,47(1-2):55-66
This study presents results of geotechnical investigations on treated silty sand soil with cement, lime and rice husk ash (CLR) and cement-lime (CL) admixture. Consolidated undrained triaxial test and unconfined compressive test were performed to estimate the potential of CLR and CL. The study investigates the influence of the amount of CLR%, main effective stress and curing days on soil strength, deformation, post peak behavior and brittleness. The percentages of the additives of CLR and CL varied from 2.5 to 12.5 % by dry weight of the soil with dry densities of 14.5 kN/m3 and the curing times of 3, 7, 28 and 60 days were examined. From the results, the stress–strain response is strongly influenced by the CLR contents and effective confining pressure. Strength and post peak strength of the CLR–soil are greatly improved by an increase in binder content. An increase of the effective cohesion c′ (kPa) and effective friction Φ′ (degree) is observed with increasing the CLR content, consistently. Brittle behavior observed at lower confining pressures and high CLR content. For both CLR and CL additives, linear trend was observed for variation of the q u (kPa) with respect to the additives percentages. RHA was also found to be effective in increasing the shear strength of CLR–soil mixture. 相似文献
12.
Mechanical alloying of iron–carbon (Fe–C) mixture powders was performed at various milling duration (2, 4, 6 and 8 h) and with different carbon content (1, 2, 3 and 4 wt.%). The milled powders were consolidated by cold pressing at 400 MPa and sintering at 1150 °C. The sintered samples were examined under an optical microscope and a scanning electron microscope for microstructure evolution, and measured for density, Rockwell F and Vickers hardness. This technique has produced Fe–C alloy with pearlite structure at lower temperature compared to conventional technique. With increasing milling time, more pearlite was formed which improved the hardness. Milling beyond 6 h, however, decreased the hardness due to the presence of higher porosity because hardened powder hindered densification. Similarly, the hardness value reached the maximum at 2% carbon before decreasing at 3% and 4% carbon levels due to the residual graphite. 相似文献
13.
In order to study the workability of Ti–6Al–4V alloy, the experimental stress–strain data from isothermal hot compression tests, in a wide range of temperatures (800–1050 °C) and strain rates (0.0005–1 s−1), were used to develop the constitutive equation of different phase regimes (α + β and β phase). The effects of temperature and strain rate on deformation behaviors a represented by Zener–Holloman parameter in an exponent-type equation. The influence of strain was incorporated in constitutive analysis by considering the effect of strain on material constants. Correlation coefficient (R) and average absolute relative error (AARE) were introduced to verify the validity of the constitutive equation. The values of R and AARE were 0.997% and 9.057% respectively, which indicated that the developed constitutive equation (considering the compensation of strain) could predict flow stress of Ti–6Al–4V alloy with good correlation and generalization. 相似文献
14.
Kenji Takizawa Tayfun E. Tezduyar Joseph Boben Nikolay Kostov Cody Boswell Austin Buscher 《Computational Mechanics》2013,52(6):1351-1364
To increase aerodynamic performance, the geometric porosity of a ringsail spacecraft parachute canopy is sometimes increased, beyond the “rings” and “sails” with hundreds of “ring gaps” and “sail slits.” This creates extra computational challenges for fluid–structure interaction (FSI) modeling of clusters of such parachutes, beyond those created by the lightness of the canopy structure, geometric complexities of hundreds of gaps and slits, and the contact between the parachutes of the cluster. In FSI computation of parachutes with such “modified geometric porosity,” the flow through the “windows” created by the removal of the panels and the wider gaps created by the removal of the sails cannot be accurately modeled with the Homogenized Modeling of Geometric Porosity (HMGP), which was introduced to deal with the hundreds of gaps and slits. The flow needs to be actually resolved. All these computational challenges need to be addressed simultaneously in FSI modeling of clusters of spacecraft parachutes with modified geometric porosity. The core numerical technology is the Stabilized Space–Time FSI (SSTFSI) technique, and the contact between the parachutes is handled with the Surface-Edge-Node Contact Tracking (SENCT) technique. In the computations reported here, in addition to the SSTFSI and SENCT techniques and HMGP, we use the special techniques we have developed for removing the numerical spinning component of the parachute motion and for restoring the mesh integrity without a remesh. We present results for 2- and 3-parachute clusters with two different payload models. 相似文献
15.
In this work, a model for achieving stochastic analysis of vehicle–track interaction systems is proposed based on random field realization of track parameters and the finite element coupling of rigid-elastic bodies. Aiming at the clarification of the spatial variability and correlation of track parameters on the influence of vehicle–track dynamic performance, a general scheme based on Karhunen–Loève Expansion and cyclic calculation method is developed to realize a multi-dimensional random field that holds an arbitrary marginal distribution function and correlation structure, and to consider the inhomogeneity of system parameters along the longitudinal direction efficiently. Furthermore, the validation of the random field expansion against the vehicle–track system is implemented, and the dynamic effects of random track parameters are investigated through two special issues. Numerical results show that the spatial correlation of fastener stiffness affects the extreme response, especially the low-frequency component of rail displacement. The spatial dependence of the filling layer has little influence on the dynamic behavior of the vehicle subsystem, but it obviously changes the extreme stress and strain of the filling layer. Ignoring the spatial correlation of random variables might underestimate the performance of the track system. 相似文献
16.
A composite column consisting of steel, concrete and fiber reinforced polymer (FRP) is presented and assessed through experimental testing and analytical modeling. The composite column utilizes a glass FRP (GFRP) composite tube that surrounds a steel I-section, which is subsequently filled with concrete. The GFRP tube acts as a stay-in-place form in addition to providing confinement to the concrete. This study investigates the behavior of the proposed composite columns under axial loading. A total of seven specimens were tested. The influence of concrete shrinkage on the compressive behavior of the composite columns was also investigated. Significant confinement and composite action resulted in enhanced compressive behavior. The addition of a shrinkage reducing agent was found to further improve the compressive behavior of the composite columns. An analytical model was developed to predict the behavior of the composite columns under axial loading. 相似文献
17.
Application of carboxylated styrene–butadiene emulsion-Portland cement mixture as road base material
Mojtaba Shojaei Baghini Amiruddin Ismail 《International Journal of Pavement Engineering》2017,18(12):1070-1080
This study investigated the effects of the addition of a carboxylated styrene–butadiene emulsion (CSBE) and Portland cement on the long-term performance of road base. The specimens stabilised with Portland cement (0–6%) and CSBE (5–10%) were subjected to different stress sequences in order to study the unconfined compressive strength, flexural strength (FS), soaked and unsoaked California bearing ratio, dynamic creep and wheel-tracking characteristics of seven-day-cured specimens. The FS tests showed that the addition of a 4% Portland cement–7% CSBE mixture resulted in improvements of 48.9% of modulus of rupture as compared to the sample with 4% cement. The permanent strain behaviour of the samples was assessed by the Zhou three-stage creep model. The results of dynamic creep and wheel-tracking tests showed that the permanent deformation characteristics were considerably improved by the addition of a 4% Portland cement–7% CSBE mixture, which resulted in reduction of permanent strain of the mixture. Therefore, this research presents a new polymer additive with outstanding engineering properties for use in road bases. 相似文献
18.
XIAODONG HAN WENHUI ZOU RENHUI WANG SING JIN ZE ZHANG TONGCHUN LI DAZHI YANG 《Journal of Materials Science》1997,32(17):4723-4729
Cylinders of TiNi shape-memory alloy were synthesized from mixtures of equiatomic fine irregular titanium and nickel powders
by explosive-wave compression with a detonation velocity of about 6500 m s-1. B2 type parent phase, R phase, B19′ type martensite, Ti2Ni, Ti3Ni4 and Ti2Ni3 phases were observed in this as-synthesized material. In the B2 matrix high density dislocations existed. The Burgers vectors
of many dislocations were determined to be parallel to
directions. The R phase variants formed (0 0 1) B2 twinning structure. The substructure of the B19′ martensite was (0 0 1)
B19′ type I twin and stacking faults on the (0 0 1) B19′ plane. When increasing the temperature of the as-synthesized material
in a differential scanning calorimeter, no B19 ′ → R → B2 transitions were observed on the temperature range −50 to 100 °C.
However, B2 → B19′(R) transitions occurred during the cooling cycle. After heat treating the specimen at 800 °C for 1 h and
then ageing at 400 °C for 10 min, both B2 → R → B19′ and B19′(R) → B2 phase transitions were observed.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
19.
《材料与设计》2015
The stress–strain response of some materials, such as advanced high strength steels, during unloading is nonlinear after the material has been loaded into the plastic deformation region. Upon reloading, the response shows a nonlinear elastic response that is different from that in unloading. Therefore, unloading–reloading of these materials forms a hysteresis loop in the elastic region. The Quasi-plastic–elastic model (Sun and Wagoner, 2011) was modified and combined with both isotropic-nonlinear kinematic hardening and two-surface plasticity models to simultaneously describe the nonlinear unloading response and complex cyclic response of sheet metals in the plastic region. The model was implemented as user-defined material subroutines, i.e. UMAT and VUMAT, for ABAQUS/Standard and ABAQUS/Explicit finite element codes, respectively. Uniaxial loading-unloading tests were performed on three common grades of automotive sheet steel: DP600, DP980 and TRIP780 steel. The model was verified by comparing the predicted material response with the corresponding experimental response. Finally, the model was used to predict the springback of a U-shape channel section formed in a plane-strain channel draw process. The results showed that the model was able to considerably improve springback predictions compared to the usual assumption of linear elastic unloading. 相似文献
20.
The study of particle packing models for binary mixtures is important in the field of granular materials, from both theoretical and practical perspectives. A number of particle packing models have been developed for predicting packing density (or void ratio) of a binary mixture. However, the measured results and the predicted values do not always agree with each other, particularly in the range of fines content between 25 and 50%. It is postulated herein that the discrepancies between the measured results and the predicted values are primarily due to the incorrect assumptions used in the existing models. In the existing models, the packing density is determined from one of the following two assumed mechanisms of particle mixing: (1) the mixed packing has a dominant large-particle skeleton and the small particles fill the voids of the large-particle skeleton, or (2) the mixed packing has a dominant small-particle skeleton and the large particles are embedded in the small-particle skeleton. It is obvious that the first assumed mechanism is only applicable for mixtures with low fines content, whereas the second assumed mechanism is only applicable to mixtures with high fines content. Therefore, the predictions from existing models are unsuitable for mixtures with medium fines content, such as a mixture of fines content between 25 and 50%. In this study, a 3-D discrete element simulation is carried out to show that, for a mixture of medium fines content, the packing structure has a dual-skeleton, which is neither dominated by a large nor small-particle skeleton. Then, we postulate that, in the mixed packing, both mechanisms can take place: filling of small particles and embedment of large particles. The concepts of “dual-skeleton index” and “index size” are proposed to account for the interactive effects of filling and embedment. Based on this postulation, we develop an analytical method, which has the capability of predicting minimum void ratio for sand–silt mixtures with various fines contents. The developed model is then validated by the experimental results obtained from 16 types of sand–silt mixtures. 相似文献