Showing papers on "Volume fraction published in 2015"

Significantly Enhanced Breakdown Strength and Energy Density in Sandwich-Structured Barium Titanate/Poly(vinylidene fluoride) Nanocomposites.

Abstract: Sandwich-structured BaTiO3 /poly(vinylidene fluoride) (PVDF) nanocomposites are successfully prepared by the solution-casting method layer by layer. They possess both high breakdown strength and large dielectric polarization simultaneously. An ultra-high energy-storage density of 18.8 J cm(-3) can be achieved by adjusting the volume fraction of ceramic fillers: this is almost three times larger than that of pure PVDF.

Microstructure and mechanical properties of aluminium alloy cellular lattice structures manufactured by direct metal laser sintering

Abstract: This study thoroughly investigated the microstructure and mechanical properties of AlSi10Mg periodic cellular lattice structures with a wide range of volume fractions (5–20%) and unit cell sizes (3–7 mm) fabricated via direct metal laser sintering (DMLS). It was found that the arc-shaped melt pools are overlapping with each other and comprising near fully dense struts (relative densities≥99%) of the as-built lattice structures. The melt pools of the struts are characterized with very fine cellular-dendritic microstructure. Two distinctive zones in the melt pool can be distinguished: the boundary of melt pool possesses the coarse cellular/dendritic microstructure with the cell size or dendrite arm spacing ranging of 2–4 µm, while the interior of melt pool exhibits the much finer cellular microstructure consisting of the 400–700 nm cells mainly filled with the α-Al matrix and some embedded rod-type Si-phases, and the network boundaries predominantly generated by the aggregates of approximately 20 nm Si particles. Both compression strength and microhardness decrease with the increase in the unit cell size when the volume fraction is fixed. This is mainly because the thinner struts of the smaller unit cell size lattice structures were cooled faster by their surroundings and then exhibit a higher cooling rate, leading to finer microstructure. The compression strength increases with increasing the volume fraction, and an equation based on the Gibson–Ashby model is established to estimate the compression strength of DMLS-produced AlSi10Mg gyroid cellular lattice structures with the 3 mm unit cell size.

Uncertainty quantification for multiscale modeling of polymer nanocomposites with correlated parameters

Abstract: We propose a stochastic multiscale method to quantify the correlated key-input parameters influencing the mechanical properties of polymer nanocomposites (PNCs). The variations of parameters at nano-, micro-, meso- and macro-scales are connected by a hierarchical multiscale approach. The first-order and total-effect sensitivity indices are determined first. The input parameters include the single-walled carbon nanotube (SWNT) length, the SWNT waviness, the agglomeration and volume fraction of SWNTs. Stochastic methods consistently predict that the key parameters for the Young’s modulus of the composite are the volume fraction followed by the averaged longitudinal modulus of equivalent fiber (EF), the SWNT length, and the averaged transverse modulus of the EF, respectively. The averaged longitudinal modulus of the EF is estimated to be the most important parameter with respect to the Poisson’s ratio followed by the volume fraction, the SWNT length, and the averaged transverse modulus of the EF, respectively. On the other hand, the agglomeration parameters have insignificant effect on both Young’s modulus and Poisson’s ratio compared to other parameters. The sensitivity analysis (SA) also reveals the correlation between the input parameters and its effect on the mechanical properties.

Statistical optimization of microchannel heat sink (MCHS) geometry cooled by different nanofluids using RSM analysis

Abstract: In this work, an analytical investigation of the heat transfer for the microchannel heat sink (MCHS) cooled by different nanofluids (Cu, Al2O3, Ag, TiO2 in water and ethylene glycol as base fluids) is studied by the porous media approach and the Galerkin method and results are compared with numerical procedure. Response surface methodology (RSM) is applied to obtain the desirability of the optimum design of the channel geometry. The effective thermal conductivity and viscosity of the nanofluid are calculated by the Patel et al. and Khanafer et al. model, respectively, and MCHS is considered as a porous medium, as proposed by Kim and Kim. In addition, to deal with nanofluid heat transfer, a model based on the Brownian motion of nanoparticles is used. The effects of the nanoparticles volume fraction, nanoparticle type and size, base fluid type, etc., on the temperature distribution, velocity and Nusselt number are considered. Results show that, by increasing the nanoparticles volume fraction, the Brownian movement of the particles, which carries the heat and distributes it to the surroundings, increases and, consequently, the difference between coolant and wall temperature becomes less.

Effects of retained austenite volume fraction, morphology, and carbon content on strength and ductility of nanostructured TRIP-assisted steels

Abstract: With a suite of multi-modal and multi-scale characterization techniques, the present study unambiguously proves that a substantially-improved combination of ultrahigh strength and good ductility can be achieved by tailoring the volume fraction, morphology, and carbon content of the retained austenite (RA) in a transformation-induced-plasticity (TRIP) steel with the nominal chemical composition of 0.19C–0.30Si–1.76Mn–1.52Al (weight percent, wt%). After intercritical annealing and bainitic holding, a combination of ultimate tensile strength (UTS) of 1100 MPa and true strain of 50% has been obtained, as a result of the ultrafine RA lamellae, which are alternately arranged in the bainitic ferrite around junction regions of ferrite grains. For reference, specimens with a blocky RA, prepared without the bainitic holding, yield a low ductility (35%) and a low UTS (800 MPa). The volume fraction, morphology, and carbon content of RA have been characterized using various techniques, including the magnetic probing, scanning electron microscopy (SEM), electron-backscatter-diffraction (EBSD), and transmission electron microscopy (TEM). Interrupted tensile tests, mapped using EBSD in conjunction with the kernel average misorientation (KAM) analysis, reveal that the lamellar RA is the governing microstructure component responsible for the higher mechanical stability, compared to the blocky one. By coupling these various techniques, we quantitatively demonstrate that in addition to the RA volume fraction, its morphology and carbon content are equally important in optimizing the strength and ductility of TRIP-assisted steels.

Effect of martensite morphology and volume fraction on strain hardening and fracture behavior of martensite–ferrite dual phase steel

Abstract: Two different morphologies of martensite in dual phase (DP) steel were obtained using two different processing routes. In one case, intermediate quenching (IQ) was adapted, where DP steel was water-quenched to obtain martensite phase, followed by inter-critical annealing. In the second case, the steel was cold rolled, followed by inter-critical annealing (CR-IA). For IQ and CR-IA steels, the inter-critical temperatures varied from 750 °C to 850 °C to obtain different volume fractions of martensite. An understanding of structure–property was obtained using a combination of scanning electron microscope (SEM), transmission electron microscope (TEM), and tensile tests. It was observed that fibrous martensite presented in IQ samples, gradually transformed to blocky martensite with increase in inter-critical temperature, resembling the CR-IA steels. The fibrous martensite encouraged martensite cracking, however, the martensite cracking was dramatically decreased in the IQ samples with increase in martensite fraction. The strain hardening behavior studied using the differential C – J model indicated multistage depending on the fraction of martensite. The low volume fraction of martensite in the DP steel provided high ductility–toughness combination and improved strain hardening ability due to the presence of soft ferrite phase in DP steel. Fibrous martensite in DP steel resulted in less strain hardening than blocky martensite, prior to exceeding a threshold volume fraction. The threshold value was significantly smaller for DP steel with blocky martensite.

High-Temperature Tensile Strength of Al10Co25Cr8Fe15Ni36Ti6 Compositionally Complex Alloy (High-Entropy Alloy)

Abstract: Homogenizing at 1220°C for 20 h and subsequent aging at 900°C for 5 h and 50 h of a novel Al10Co25Cr8Fe15Ni36Ti6 compositionally complex alloy (high-entropy alloy) produces a microstructure consisting of an L12 ordered γ′ phase embedded in a face-centered cubic solid-solution γ matrix together with needle-like B2 precipitates (NiAl). The volume fraction of γ′ phase is ~46% and of needle-like B2 precipitates <5%, which is in accordance with the prediction of calculation of phase diagram method (CALPHAD using Thermo-Calc software with TTNi7 database; Thermo-Calc Software, Stockholm, Sweden). The high-temperature tensile tests were carried out at room temperature, 600°C, 700°C, 800°C, and 1000°C. The tensile strength as well as the elongation to failure of both heat-treated specimens is very high at all tested temperatures. The values of tensile strength has been compared with literature data of well-known Alloy 800H and Inconel 617, and is discussed in terms of the observed microstructure.

Non-Darcy natural convection flow for non-Newtonian nanofluid over cone saturated in porous medium with uniform heat and volume fraction fluxes

Abstract: Purpose – The purpose of this paper is to investigate the effect of uniform lateral mass flux on non-Darcy natural convection of non-Newtonian fluid along a vertical cone embedded in a porous medium filled with a nanofluid. Design/methodology/approach – The resulting governing equations are non-dimensionalized and transformed into a non-similar form and then solved numerically by Keller box finite-difference method. Findings – A comparison with previously published works is performed and excellent agreement is obtained. Research limitations/implications – The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. It is assumed that the cone surface is preamble for possible nanofluid wall suction/injection, under the condition of uniform heat and nanoparticles volume fraction fluxes. Originality/value – The effects of nanofluid parameters, Ergun number, surface mass flux and viscosity index are investigated on the velocity, temperature, and volume fraction profiles as ...

Flexible BaTiO3/PVDF gradated multilayer nanocomposite film with enhanced dielectric strength and high energy density

Abstract: Organic–inorganic 0–3 nanocomposites, which combine the potentially high dielectric strength of the organic matrix and the high dielectric permittivity of the inorganic filler, are extensively studied as energy-storage dielectrics in high-performance capacitors. In this study, a gradated multilayer BaTiO3/poly(vinylidene fluoride) thin film structure is presented as a means to achieve both a higher breakdown strength and a superior energy-storage capability. The central layer of this film, designed to provide high electric displacement, is composed of a high volume fraction of 6–10 nm BTO nanocrystals produced by a TEG-sol method. The small particle size contributes to a high dispersibility of the nanocrystals in polymer media, as well as a high interfacial area to mitigate the local electric field concentration. The outer layers of the structure are predominantly PVDF, with a significantly low volume fraction of BTO, taking advantage of the high dielectric strength of pure PVDF at the electrode–nanocomposite interface. The film is mechanically flexible, and can be removed from the substrate, with total thicknesses in the range of 1.2–1.5 μm. Parallel plate capacitance devices exhibit highly improved dielectric performances with low-frequency permittivity values of 20–25, a maximal discharge energy density of 19.37 J cm−3 and dielectric (breakdown) strengths of up to 495 kV mm−1.

Turbulent forced convection heat transfer and thermophysical properties of Mgo–water nanofluid with consideration of different nanoparticles diameter, an empirical study

Abstract: In the present paper results of an experimental study on thermal conductivity, dynamic viscosity and Nusselt number of turbulent forced convection of Magnesium Oxide–water nanofluid in a circular straight pipe is presented. The considered pertinent parameters are Reynolds number, nanoparticles volume fraction and nanoparticles diameter. The pure water and nanofluid with the nanoparticle volume fraction of 0.005, 0.01, 0.015, 0.02 and the nanoparticles diameter of 60, 50, 40 and 20 nm are considered. The experimental values of the thermal conductivity and the dynamic viscosity shows that traditional formulas underestimates these thermophysical parameters. Also the experimental results indicates that the existence of the nanoparticles in the pure water with all considered values of the nanoparticles volume fraction and diameter motivates the rate of heat transfer to increase. The nanofluids with higher volume fraction and smaller nanoparticles diameter results in higher Nusselt number.

Influence of gradient structure volume fraction on the mechanical properties of pure copper

Abstract: This paper reports the influence of gradient structure volume fraction on the tensile mechanical behaviors of pure copper processed by surface mechanical attrition treatment at cryogenic temperature. Superior combinations of tensile strength and ductility are observed in a certain volume fraction, in which strain hardening uprising after yielding is also observed. The gradient structure produces a synergetic strengthening and extra work hardening. These findings suggest the existence of an optimum volume fraction of gradient structure for the best mechanical properties.