Sequel to the fact that hybrid nanofluidic systems (e.g. scalable micro-/nanofluidic device) exhibit greater thermal resistance with increasing nanoparticle concentration, little is known on the ...significance of thermal radiation, surface roughness and linear stability of water conveying alumina and copper oxide nanoparticles. This study presents the effects of thermal radiation and surface roughness on the complex dynamics of water conveying alumina and copper oxide nanoparticles, in the case where the thermophysical properties of the resulting mixture vary meaningfully with the volume fraction of solid nanomaterials, as well as with the Brownian motion and thermophoresis microscopic phenomena. Based on the linear stability theory and normal mode analysis method, the basic partial differential equations governing the transport phenomenon were non-dimensionalized to obtain the simplified stability equations. The optimum values of the critical thermal Rayleigh number depicting the onset of thermo-magneto-hydrodynamic instabilities were obtained using the power series method and the Chock–Schechter numerical integration. The increase in the strength of Lorentz forces, thermal radiation and surface roughness has a stronger stabilizing impact on the appearance of convection cells. On the contrary, the stability diminishes with the increasing values of the volumetric fraction and diameter of nanomaterials. The partial substitution of the alumina nanoparticles by the copper oxide nanomaterials in the mixture stabilizes importantly the hybrid nanofluidic medium.
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In recent years, the aluminum alloys parts produced by Selective Laser Melting (SLM) are increasingly used instead of casting aluminum alloys parts in the automotive, aerospace and ...other fields. However, the high surface roughness of the vertical surfaces is a major issue influencing the application of SLM for aluminum. Moreover, most of the methods to reduce the surface roughness, such as polishing, bead blasting or machining, will increase the production delays and costs. The present study aims at evaluating the effect of linear energy density on the surface roughness of the vertical planes. Both deposited tracks and volumetric specimens were produced and the morphologies and the surface roughnesses were measured. The obtained results indicate that the surface roughness of the vertical planes was reduced to 4 μm from 15 μm when deposited a suitable linear energy density, reducing the surface roughness by more than 70%. The surface morphologies and the height change rate of the deposited tracks had a significant influence on the surface roughness. Furthermore, for experiments with the same linear energy density, the surface roughness was improved with higher laser power.
Selective Laser Melting (SLM) is an increasingly employed additive manufacturing process for the production of medical, aerospace, and automotive parts. Despite progresses in material flexibility and ...mechanical performances, relatively poor surface finish still presents a major limitation in the SLM process.
In this study an investigation of surface roughness and morphology is presented for Steel 316L alloy parts made by SLM. In order to characterise the actual surfaces at different sloping angles, truncheon samples have been produced and an analysis has been conducted at different scales, by surface profilometer and scanning electron microscope (SEM). The surface analysis has showed an increasing density of spare particles positioned along the step edges, as the surface sloping angle increases. When layer thickness is comparable to particle diameter, the particles stuck along step edges can fill the gaps between consecutive layers, thus affecting the actual surface roughness.
Classic models for roughness prediction, based on purely geometrical consideration of the stair step profile, fail to describe the observed trend of the experimental data. A new mathematical model is developed to include the presence of particles on top surfaces, in addition to the stair step effect, for the accurate prediction of surface roughness. Results show that surface roughness predicted by this model has a good agreement with the experimentally observed roughness. The paper investigates the key contributing factors influencing surface morphology, and a theoretical model for roughness prediction that provides valuable information to improve the surface quality of SLM parts, thus minimising the need of surface finishing.
A mechanistic understanding of adhesion in soft materials is critical in the fields of transportation (tires, gaskets, and seals), biomaterials, microcontact printing, and soft robotics. Measurements ...have long demonstrated that the apparent work of adhesion coming into contact is consistently lower than the intrinsic work of adhesion for the materials, and that there is adhesion hysteresis during separation, commonly explained by viscoelastic dissipation. Still lacking is a quantitative experimentally validated link between adhesion and measured topography. Here, we used in situ measurements of contact size to investigate the adhesion behavior of soft elastic polydimethylsiloxane hemispheres (modulus ranging from 0.7 to 10 MPa) on 4 different polycrystalline diamond substrates with topography characterized across 8 orders of magnitude, including down to the angstrom scale. The results show that the reduction in apparent work of adhesion is equal to the energy required to achieve conformal contact. Further, the energy loss during contact and removal is equal to the product of the intrinsic work of adhesion and the true contact area. These findings provide a simple mechanism to quantitatively link the widely observed adhesion hysteresis to roughness rather than viscoelastic dissipation.
Through silicon via (TSV) is the key technology for 3-D integrated circuits (3-DICs) which could vertically stack homogeneous or heterogeneous dies with the high performance and density. To evaluate ...the electrical characteristics of TSV at the high-frequency transmission, the skin effect and surface roughness effect are necessary to be considered. However, these effects would significantly result in the TSV equivalent resistance under the high operating frequency. Thus, it is important to investigate the carbon nano tubes (CNTs) TSV which has less skin effect intrinsically. In this work, we analyze the advantage of CNTs as TSV compared to the conventional filling materials such as copper (Cu). Furtherly, we also propose the equivalent circuit model of TSV and its multi-layer structure to simulate the electrical behaviors with different TSV pitch, height, diameter, and stacking layers by using ANSYS designer and high-frequency structure simulator (HFSS). Based on the frequency-domain analysis, it can be found that CNTs TSV has the lower frequency-dependent loss than Cu due to the lower equivalent resistance. In a summary, CNTs could be a promising TSV filling material at the high-speed transmission frequency based on our study.
•Effect of hot isostatic pressing (HIP) on multiaxial fatigue of AM Ti-6Al-4V.•Build orientation effect on multiaxial fatigue of AM Ti-6Al-4V.•Surface roughness effect on multiaxial fatigue of AM ...Ti-6Al-4V.•Damage mechanism and effect of defects in multiaxial fatigue of AM Ti-6Al-4V.
Additive manufacturing (AM) technology has gained significant attention in recent years due to several important advantages. However, design of critical load carrying parts using this technique is still at its infancy, partly due to the inferior performance and lack of sufficient understanding of cyclic deformation and fatigue behaviors of AM metals as compared to their wrought counterparts. Similar to most other components in different industries, AM parts typically undergo cyclic loadings through their service life; therefore, fatigue performance is a key performance criterion. In addition, due to common presence of multiaxial stress states at fatigue critical locations, multiaxial fatigue is of special interest. In this study, thin-walled tubular specimens made of Ti-6Al-4V alloy fabricated with powder bed fusion (PBF) process were used to investigate their cyclic deformation and fatigue behaviors. The main focus of this study was on the effect of hot isostatic pressing (HIP) on fatigue performance under uniaxial, torsion, combined in-phase, and 90° out-of-phase axial-torsion loads. To study build orientation effect, both vertically built and diagonally built (at 45°) specimens were included. However, no substantial difference on the fatigue behavior of vertical and 45° built specimens was observed. Although the majority of specimens had a machined surface, some torsional tests with as-built surface were also included to evaluate surface roughness effect. It was found that even after HIP treatment, the rough surface is the dominant factor in shortening the fatigue life. In addition, to evaluate the effectiveness of the HIP treatment, torsion fatigue performance of the HIPed specimens were compared to torsion fatigue performance of annealed AM specimens, as well as to the multiaxial fatigue behavior of the conventional wrought material. Fatigue failure mechanism of the HIPed material was shear, similar to the wrought material, and fatigue performance was found to be similar to the wrought alloy. Fatigue test results were correlated well using a shear-based critical plane parameter approach, also similar to the wrought material. Comparison of multiaxial fatigue data in this study and a similar previous study by the authors indicates that fabrication machine-to-machine and the associated build parameter differences can result in substantial differences in the observed defect size and population, resulting in different failure mechanisms and subsequently different fatigue performance.
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