Jet printing of colloidal solutions – Numerical modeling and experimental verification of the influence of ink and surface parameters on droplet spreading

Ink jet printing of functional materials promises an efficient route for the manufacturing of future low cost and large-area electronics applications. The effect of capillary flow of thin liquid films, the control of droplet spreading by suitably influencing the wetting properties of surfaces, the rheology of the ink and the process design play a relevant role in improvement of ink jet printed patterns. This work presents the experimentally based numerical study of the shape of single ink jetted droplets controlled by homogeneous contact angle distributions. The dynamics of the fluid on the substrate surface is treated in the frame of the lubrication theory using the concept of a precursor film and modeling the equilibrium contact angle by a disjoining pressure. The model describes the spreading of axisymmetric droplets considering different material and process parameter configurations. It is shown that the spreading process can be modeled separately from the drying process within a certain range of contact angles.     

Transient analysis of the DSIFs and dynamic T-stress for particulate composite materials—Numerical vs. experimental results

The fracture behavior of particulate composite materials when subjected to dynamic loading has been a great concern for many industrial applications as these materials are particularly susceptible to impact loading conditions. As a result, many numerical and experimental techniques have been developed to deal with this class of problems. In this work, the fracture behavior of particulate composites under impact loading conditions is numerically studied via the two most important fracture parameters: dynamic stress intensity factors (DSIFs) and dynamic T-stress (DTS), and the results are compared with the experimental data obtained in Refs. [1,2]. Here, micromechanics models (self-consistent, Mori–Tanaka, …) or experimental techniques need to be employed first to determine the effective material properties of particulate composites. Then, the symmetric-Galerkin boundary element method for elastodynamics in the Fourier-space frequency domain is used in conjunction with displacement correlation technique to evaluate the DSIFs and stress correlation technique to determine the DTS. To obtain transient responses of the fracture parameters, fast Fourier transform (FFT) and inverse FFT are subsequently used to convert the DSIFs and DTS from the frequency domain to the time domain. Test examples involving free–free beams made of particulate composites are considered in this study. The numerical results are found to agree very well with the experimental ones.     

Numerical and experimental studies on laminar forced convective heat transfer in a channel with surface‐mounted heated blocks

Abstract

The steady separated flow due to heated blocks mounted on one principal wall of a two‐dimensional channel has been numerically and experimentally studied. Numerical solutions of the Navier‐Stokes equations using the finite‐difference and the power‐law techniques have been obtained up to a Reynolds number of 2600. The effects of the Reynolds number and the block spacing on the fluid flow and heat transfer are investigated in detail. Results show that there exists two different types of flow between blocks, the D‐type and the K‐type flows. Furthermore, the Nusselt number monotonously increases or decreases along every face of the blocks. The calculated results of the reattachment length behind the second block and the local Nusselt number distribution compare well with the results obtained by the LDV and the naphthalene sublimation measurements, respectively. Heat transfer correlating equations are presented in terms of the Reynolds number and the block spacing.     

Application of a dynamic numerical solution to high speed fracture experiments—I. analysis of experimental geometries

The application of a dynamic, generation mode, finite element program to the analysis of experimental geometries is reported. Particular attention is given to the DCB specimen, which is widely used in high speed fracture studies despite strong inertia effects, which are described. Finite strip and infinite plate results are also considered. Here, idealised cases are discussed, while in Part II the application of the analysis to experimental measurements, to derive propagating crack fracture resistance data, is reported.     

Diagonal compressive strength of masonry samples—experimental and numerical approach

Masonry is a structural material that presents a quite complex behaviour that depends on the mechanical and geometrical characteristics of the units, the mortar and the link between these two elements. In particular, the characterization of the shear behaviour of masonry elements involves proper experimental campaigns that make these analyses particularly expensive. The main objective of this paper is to present a case study on the characterization of the shear behaviour of masonry through a methodology that merges a small number of laboratory tests with computer simulations. The methodology is applied to a new masonry system that has recently been developed in Portugal, and involves a FEM numerical approach based on micro3D modelling of masonry samples using nonlinear behaviour models that are calibrated through a small number of laboratory tests. As a result, the characterization of the masonry shear behaviour trough this methodology allowed simulating, with reasonably accuracy, a large set of expensive laboratory tests using numerical tools calibrated with small experimental resources.     

Axisymmetric natural damped frequencies of a viscous liquid in a circular cylindrical Container — An alternative semi-analytical solution

For axisymmetric liquid motion (m=0) in a circular cylindrical Container nlled with an incompressible and viscous liquid the natural damped frequencies are determined. The analysis satisfies the side wall conditions exactly while only the normal Container bottom condition could be satisfied. This restricts the Solution results to liquid height flllings h/a to larger values (h/a>1). It was found that with increase of the liquid height ratio h/a the oscillation frequency and decay magnitude are both increasing.     

Laser surface remelting of WC–12Co coating: finite element simulations and experimental analyses

A three-dimensional finite element model taking into account interfacial topography, porosity of plasma sprayed coatings, temperature dependent thermophysical parameters and phase change has been developed to simulate multipass laser remelting process. Temperature evolution, temperature gradient, melting pool shape and dimensions are simulated. The laser remelting experiments are carried out on the plasma sprayed WC–12Co coatings. The simulated results are in good agreement with the experimental measurements. After laser remelting, a denser and more homogenous coating is obtained. The microhardness of the coating is significantly enhanced owing to the dispersion strengthening, the fine grain strengthening and the solution strengthening, which is increased by three times compared with that of the plasma sprayed coatings.     

Simulation analysis and experimental verification of coal suction characteristics of the new railway tunnel fallen coal dust collection device北大核心CSCD

Due to air turbulence, large areas of coal will fall when the special coal-transportation trains pass the tunnel exits and entrances. Aiming at the problems of low efficiency and high cost of manual cleaning for long distance coal cleaning in the tunnel, a new railway tunnel fallen coal dust collection device which was composed of a main conveying coal feeding pipe and multiple branch pipes of coal suction was designed. It was used to clean the small particles and lightweight railway tunnel fallen coal. Firstly, the gas-solid two-phase flow model based on the Euler-Lagrange approach for the design of the main conveying coal feeding pipe was established in the coal conveying pipelines. Secondly, the effect of the coal particles' incident angle and multiple branch pipe spacing on the main coal conveying pipe flow field, which was based on Fluent finite element simulation software, was studied. What was more, the optimal angle of incidence and the optimal value of the number of branch coal suction pipe, which was installed on the main conveying pipe, were analyzed. Finally, the finite element simulation was verified by field test. Simulation and experimental results showed that it was more conducive to the railway tunnel fallen coal transportation when coal particles' incident angle was less than 45° and the branch pipe spacing was in the vicinity of 750 mm. For that when incident angle was less than 45°, the main conveying coal pipe pressure-drop became weaker and particle flow could obtain large horizontal transport velocity. And when the branch pipe spacing was in the vicinity of 750 mm, the horizontal transport velocity had a smaller fluctuation range and the transportation of coal was larger than that of the other groups. The research results are of great significance to improve the structure of the main conveying coal pipe, increase the efficiency of tunnel coal conveying and optimize the railway tunnel coal dust collection device.     

Numerical and experimental study on the flow history effects of axial flow on the Couette–Taylor flow

In this research, experimental and numerical techniques are used to study the flow history effects of axial flow on the Couette–Taylor flow. For the experimental investigation, the flow is visualized using the PIV technique with reflective particles with a density of 1.62 g/cm³. Dispersed in a solution, the particles have a strong refraction index equal to 1.85. In this study, two protocols are adopted to study the effect of an axial flow superimposed on a Couette–Taylor flow, and of the history of the flow. The first one, the direct protocol, consists of imposing an azimuthal flow to the inner cylinder. In this case, when the regime is established, the axial flow is superimposed. The second protocol, the inverse protocol, consists of imposing first the axial flow in the gap of the system, after which an azimuthal flow is conveyed. The Couette–Taylor flow with axial flow is strongly dependent on the flow history (the protocol). Thus, the flow structures and development for different protocols are studied and analyzed here experimentally and numerically. In addition, from the numerical results, mathematical models for the two protocols are presented. For the direct protocol, a new relation between the axial Reynolds number, which stabilizes the Couette–Taylor flow, and the Taylor number is presented; for the inverse protocol, a new mathematical model for the critical Taylor number is developed as a function of the axial Reynolds number and also the first critical Taylor number without axial flow.     

A perturbation solution of von-Kármán circular plates with different moduli in tension and compression under concentrated force

By modifying classical von-Kármán equations, we established bimodular von-Kármán equations of thin plates with different moduli in tension and compression. Adopting central deflection as a perturbation parameter, we used a perturbation method to solve the equations under various boundary conditions, including rigidly clamped, loosely clamped, simply hinged, and simply supported. The relation of load versus central deflection and stress formulas were derived via the perturbation solution obtained. The numerical simulation also shows that the perturbation solution based on central deflection is overall valid. The results indicate that when the compressive modulus of materials is greater than the tensile one, the bearing capacity of the plate will be further strengthened, which should be considered in the analysis and design of plate-like structures with obvious bimodular effect. Moreover, by comparing with the case under uniformly distributed load, the plate-membrane transition under centrally concentrated force presents discontinuity to some extent.     

Modern biomaterials: a review—bulk properties and implications of surface modifications

This review concerns the importance of length and time on physicochemical interactions between living tissue and biomaterials that occur on implantation. The review provides information on material host interactions, materials for medical applications and cell surface interactions, and then details the extent of knowledge concerning the role(s) that surface chemistry and topography play during the first stage of implant integration, namely protein adsorption. The key points are illustrated by data from model in vitro studies. Host implant interactions begin nanoseconds after first contact and from then on are in a state of flux due to protein adsorption, cell adhesion and physical and chemical alteration of the implanted material. The many questions concerning the conformational form and control of bound proteins and how this may impact on cell adhesion in the first instance and later on cell signalling and implant integration can be answered by systematic investigations using model materials. Only then we will be in a more informed position to design new materials for use in the body.     

Numerical simulation of hydrodynamics and heat transfer under conditions of turbulent transverse flow past a “trench” on a plane surface

Results are given of numerical simulation of hydrodynamics and heat transfer under conditions of transverse flow past a two-dimensional trench (a groove whose cross section has the form of a segment of circle) located on a plane isothermal surface. The calculations are performed for an incompressible liquid within two-dimensional Reynolds equations closed with the aid of the Menter and Spalart-Allmares turbulence models using multiblock overlapping grids. Detailed analysis is performed of the effect of the trench depth on the flow structure (configuration of separated-flow regions) and on the distribution of friction, pressure, and heat fluxes along the surface subjected to flow.Translated from Teplofizika Vysokikh Temperatur, Vol. 43, No. 1, 2005, pp. 086–099. Original Russian Text Copyright © 2005 by S. A. Isaev, A. I. Leontiev, and N. A. Kudryavtsev.     

Scattering of elastic P- and SV-waves by a circular coated nanofiber based on Gurtin–Murdoch model of surface elasticity: Scattering cross section results

In this article, an analytical study of elastic P- and SV-wave scattering by a circular nanofiber is presented. The nanofiber is assumed to be surrounded by an inhomogeneous interphase layer, and Gurtin–Murdoch's model of surface elasticity is utilized to study the surface/interface effects in the regions between the fiber and interphase and also interphase and matrix. The simultaneous effects of surface elasticity and interphase inhomogeneity are considered here; by taking the inhomogeneous interphase to be composed of several sublayers, a transfer matrix approach is used to find the unknown field variables and, consequently, the scattering cross sections. The results indicate that considering the effects of surface elasticity and interphase inhomogeneity has a considerable impact on the calculated scattering cross sections.     

Numerical and experimental investigations of the effects of the breakup of oil droplets on the performance of oil–gas cyclone separators in oil-injected compressor systems

A numerical simulation was conducted of the dynamic trajectories and the separation performance of oil droplets, with a focus on the breakup of oil droplets in an oil–gas cyclone separator. The separation efficiency was also studied experimentally, and the oil droplets' diameter distributions before and after the separator were measured with a Malvern particle size analyser to verify the simulation model. Both the experimental and simulation results showed that the breakup of oil droplets occurred in the separation process, clearly influencing the separation efficiency. In addition, the results indicated that inlet velocity played an important role in separation efficiency, as it not only significantly affected the tangential velocity inside the separator, but also determined the possibility and degree of the breakup of oil droplets.     

An experimental method for determining the total efficiency and the response function of a gamma-ray detector in the range 0.5–10 MeV

An experimental method is presented for the determination of the total efficiency and the response function of a γ-ray detector in the range 0.5–10 MeV. It consists of observing (p, γ) resonance reactions with two detectors: the one to be calibrated, in this case a cylindrical deuterated hexabenzene liquid scintillator, and a Ge detector used to select and resolve the main two-step cascades of the reaction. Efficiencies and response functions were obtained for thirteen γ-rays via the coincidence method, using targets of ²⁶Mg at proton energies of 1001 and 2220 keV, of ³⁰Si at 1398 keV and of ³⁴S at 1211 keV.The weighting function derived from these data was used to determine the capture area of the 1.15 keV neutron resonance in ⁵⁶Fe. By normalizing the data to the 5.2 eV resonance in ¹⁰⁹Ag, a value (gΓ_nΓ_γ/Γ) = 57.1 ± 2.1 meV was obtained, in excellent agreement with the result of recent transmission measurements.     

Transverse cracking of fibre bundle composites studied by acoustic emission and Weibull statistics—effects of postcuring and surface treatment

Transverse failure in composite materials is a mechanism in the ultimate failure of the engineering composite. It is controlled by the strength of the fibre/matrix interface and improvement in the strength of this interface will improve the overall transverse strength. Transverse fibre bundle composites (TFBC) have been tested to failure, where the condition of the composite and the fibre/matrix interface have been modified. Progression to failure has been monitored using acoustic emission with the AE data analysed in a novel way using Weibull statistics. Although Weibull statistics have previously been used to characterise fibre bundle failure, where the concept of weakest link applies, this work extends this approach in an empirical way using an acoustic emission form of Weibull equations. The AE profile, when compared to stress/strain data, showed a quiet-then-noisy profile for room cured resin, which changed to noisy-then-quiet when the resin was post cured. Kevlar reinforced TFBC showed regular AE from low strains. The pattern of AE changed when specimens had been post cured and when the Kevlar fibres had been subjected to ultrasound treatment. Although individual AE events were highly variable, Weibull analysis of the AE parameters derived from a glass reinforced composite proved highly robust, with the AE ringdown count distributions moving to higher values for the more brittle, stronger post-cured resin. Measuring interfacial failure stress via the onset of AE, suggested the interface was weakened, but in a selective way, which did not necessarily show in the final failure stress of the composite.     

CFD modeling and experimental verification of oscillating flow and heat transfer processes in the micro coaxial Stirling-type pulse tube cryocooler operating at 90–170 Hz

This paper presents the CFD modeling and experimental verifications of oscillating flow and heat transfer processes in the micro coaxial Stirling-type pulse tube cryocooler (MCSPTC) operating at 90–170 Hz. It uses neither double-inlet nor multi-bypass while the inertance tube with a gas reservoir becomes the only phase-shifter. The effects of the frequency on flow and heat transfer processes in the pulse tube are investigated, which indicates that a low enough frequency would lead to a strong mixing between warm and cold fluids, thereby significantly deteriorating the cooling performance, whereas a high enough frequency would produce the downward sloping streams flowing from the warm end to the axis and almost puncturing the gas displacer from the warm end, thereby creating larger temperature gradients in radial directions and thus undermining the cooling performance. The influence of the pulse tube length on the temperature and velocity when the frequencies are much higher than the optimal one are also discussed. A MCSPTC with an overall mass of 1.1 kg is worked out and tested. With an input electric power of 59 W and operating at 144 Hz, it achieves a no-load temperature of 61.4 K and a cooling capacity of 1.0 W at 77 K. The changing tendencies of tested results are in good agreement with the simulations. The above studies will help to thoroughly understand the underlying mechanism of the inertance MCSPTC operating at very high frequencies.     

Influence of Heat Input on Microstructure and Mechanical Properties of Laser Welding GH4169 Bolt Assembly—Numerical and Experimental Analysis

By conducting the numerical and experimental analysis, the influence of heat input on the microstructures and mechanical properties of laser welding GH4169 bolt assembly is systematically investigated. The weld formation, temperature field, and residual stress distribution during laser welding by using the finite element modeling are consistent with experimental results. The numerical simulation results show that the increase of heat input imparts lower residual stresses and higher temperature gradient. During the process of laser welding, the steepest temperature gradient and the peak residual stress arise in the fusion zone (FZ). In addition, the dissolution of γ″ and γ′ toward the fusion line increases in heat affected zone (HAZ), but only Laves phase is observed in FZ. With increasing heat input from 24 to 48 J mm⁻¹, the ultimate tensile strength of welded joints decreases. Both the lowest microhardness values and tensile failure of GH4169 alloy laser welded joint are in FZ. Herein, it is that the relationship among the heat input, microstructures, and mechanical properties of GH4196 bolt assembly in laser welding is systematically established, which will be of guiding significance for the selection of welding parameters in aerospace.     

Effect of the length and the aggregate size of MWNTs on the improvement efficiency of the mechanical and electrical properties of nanocomposites—experimental investigation

An experimental investigation of the effect of nanotube length and aggregate size on the mechanical and electrical properties of the composites was reported. Three treatments, that affect mainly the length and aggregate size, were applied on the CVD MWNTs before they were added into a resin matrix. They had a very clear impact on the dielectric properties of the composites and on the improvement efficiency. There was an insulator-to-conductor transition with the as-prepared MWNTs at 0.5 wt%. Regarding the mechanical properties, the addition of MWNTs increased the Young's modulus and reduced the fracture strain. In that case, the pre-treatment on MWNTs, however, had a much more moderate effect on the improvement efficiency.