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.
Soiling of Photovoltaic (PV) modules is a growing area of concern due to the adverse effect of dust accumulation on PV performance and reliability. In this work, we report on four fundamental ...adhesion forces that take place at the first stage of soiling process. These are capillary, van der Waal, electrostatic and gravitational forces. It is found that under high relative humidity, the adhesion mechanism between dust particles and PV module surfaces is dominated by capillary force, while van der Waal force dominates under dry conditions. Moreover, real field data for long soiling periods over solar panels in Qatar were investigated and resulted in proposing a novel modified sigmoid function that predicts a relative humidity inflexion value at which transition in the particulate matter deposition rate takes place from low to high values. Moreover, the effect of surface roughness was investigated by measuring adhesion force over clean glass versus substrates that are coated with in-house developed anti-dust titania thin films.
•Capillary adhesion force dominates under high relative humidity.•Gravitational adhesion force is negligible for small dust particles.•Novel modified sigmoid function of 18 months of real field data supports domination of capillary force at high RH.•Surface roughness reduces adhesion force.•Anti dust coatings reduces adhesion force.
•A realistic theory for damped vehicle moving over simple bridge.•Derive a new procedure for calculating the contact point (CP) response.•Being free of vehicle frequency, CP response is good for ...obtaining higher bridge frequencies.•CP response is less affected by vehicle damping compared with the vehicle response.•Ongoing traffic is positive to deal with the negative effect of road roughness.
By the vehicle scanning method, an instrumented test vehicle is used to scan the frequencies of vibration of the underlying bridge. In this paper, a realistic theory is proposed considering the damping effect of the test vehicle, which was not well studied previously. Bridge damping is ignored since the bridge vibration sensed by the moving vehicle is transient in nature. The vehicle response was criticized for the presence of vehicle frequency, which renders "scanning" less effective. In contrast, the response of the vehicle's contact point (CP) with the bridge is free of the vehicle frequency and enables us to extract more bridge frequencies. For the model adopted, closed-form solutions are firstly derived for both the vehicle and CP responses, with their transmissibility discussed. Through the numerical simulations and field test, the following are concluded: (1) The improved procedure for the CP response is reliable for scanning the first few bridge frequencies; (2) the effect of vehicle damping on the CP response can be ignored; (3) the performance of the CP response is always better than the vehicle response for each scenario studied; and (4) ongoing traffic is a positive effect that can outbalance the negative effect of surface roughness.
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In recent years, advances in nanotechnology have been positively reflected in the manufacturing industry, as in many other fields. Owing to their physical and chemical aspects, the nano-sized solid ...lubricants can help to improve the tribological and thermal properties when added to aerosols, suspensions and emulsions. In order to achieve high efficiency in machining operations, this phenomenon provides an opportunity to perform the tasks expected from a coolant/lubricant. Therefore, this study aimed to investigate the influence of cutting fluid reinforced by multi-walled carbon nanotubes (MWCNTs) into vegetable based cutting fluid on machinability characteristics of PH 13-8 Mo stainless steel that has excellent mechanical properties. For this, Taguchi's L27 (33) orthogonal array involving three factors and their three levels such as cutting speed of 120, 180, 240 m/min, feed rate of 0.1, 0.15 and 0.2 mm/rev and three C/L environment i.e., dry, pure-MQL (0 vol% of nano-additives) and MWCNTs mixed nanofluid-MQL were taken as process parameters. In this experimental design, surface roughness and peak temperature in cutting zone were considered as responses. Moreover, to analyze only the influence C/L environment on tool wear, wear mechanisms and surface topography, a series of experiments were conducted by preserving other machining parameters. As a result, approximately 5% and 12% lower surface roughness was achieved with pure-MQL and nanofluid-MQL, respectively. The reduction in flank wear was found to be 40.2% and 69% under cutting environment, i.e., pure-MQL and MWCNTs mixed nanofluid-MQL.
•Dry, pure-MQL and MWCNTs mixed nanofluid-MQL were used in experiments.•PH 13-8 Mo stainless steel was machined under different C/L environment.•The wear behavior of the PVD TiAlN-(AlCr)2O3 was investigated.•Surface roughness, surface topography and temperature were investigated.•The use of MWCNTs based nanofluid-MQL resulted in better performance than others.
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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.
This paper investigates a long-standing question about the effect of surface roughness on turbulent flow: What is the equivalent roughness sand-grain height for a given roughness topography? Deep ...neural network (DNN) and Gaussian process regression (GPR) machine learning approaches are used to develop a high-fidelity prediction approach of the Nikuradse equivalent sand-grain height $k_s$ for turbulent flows over a wide variety of different rough surfaces. To this end, 45 surface geometries were generated and the flow over them simulated at ${Re}_\tau =1000$ using direct numerical simulations. These surface geometries differed significantly in moments of surface height fluctuations, effective slope, average inclination, porosity and degree of randomness. Thirty of these surfaces were considered fully rough, and they were supplemented with experimental data for fully rough flows over 15 more surfaces available from previous studies. The DNN and GPR methods predicted $k_s$ with an average error of less than 10 % and a maximum error of less than 30 %, which appears to be significantly more accurate than existing prediction formulae. They also identified the surface porosity and the effective slope of roughness in the spanwise direction as important factors in drag prediction.
Aluminum alloys processed using laser powder bed fusion are attracting industrial and research efforts striving to achieve the lightweighting potential and combination of good mechanical and ...corrosion properties. In this study, border parameter optimization for F357 (AlSi7Mg) alloy processed using LPBF was performed with the aim of reducing the as-fabricated surface roughness. The optimization revealed that laser power and scanning speed can significantly influence the surface roughness of cube vertical surfaces. Measured areal average surface roughness (Sa) for cube samples varied from 15 to 24 µm. The cube-based optimized parameters were used to fabricate angled wall samples with angles ranging from 45° to 90°. The surface roughness reduced when the built angle increased from 45° to 75°, while for 75–90°, the surface roughness values remained constant.
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•Uniaxial strain- and force-controlled fatigue tests are conducted on LB-PBF 304L SS.•Specimens in machined/polished and as-built surface conditions are characterized.•Locational and ...directional effects on surface roughness of specimens are minimal.•The effect of surface roughness is more significant on stress-life behavior.•Fatigue life of as-built specimens can be estimated using their surface topography.
The fatigue strength of additively manufactured metallic parts in their as-built surface condition is mainly dominated by the surface roughness. Post-processing is often inevitable to reduce surface roughness effects even though post-processing diminishes the main advantage of additive manufacturing, which is net-shaped direct-to-service production. This study investigates the underlying mechanisms responsible for fatigue failure of additively manufactured 304L stainless steel parts in as-built and machined/polished surface conditions. Both strain- and force-controlled, fully reversed fatigue tests were conducted to gain a comprehensive understanding of surface roughness effects on fatigue behavior. The sensitivity to surface roughness is shown to be dependent on the control mode, with stress-based fatigue tests showing greater sensitivity than strain-based fatigue tests. Moreover, the fatigue life estimation for as-built specimens was performed based on surface roughness parameters as well as the fatigue properties of the specimens in machined/polished surface condition of the material without using any fatigue data of specimens in as-built surface condition. Accordingly, the effect of surface roughness on the fatigue behavior could be estimated reasonably well in both strain-life and stress-life approaches.
Selective Laser Melting (SLM) and Electron Beam Melting (EBM) are powder bed fusion processing which allows to build-up parts by successive addition of layers using 3D-CAD models. Among the ...advantages, are the high degree of freedom for part design and the small loss of material, which explain the increase of Ti-6Al-4V parts obtained by these processes. However, Ti-6Al-4V parts produced by SLM and EBM contain defects (surface roughness, porosity, tensile residual stresses) which decrease significantly the High Cycle Fatigue (HCF) life. In order to minimize the porosity and tensile residual stresses, post-processing treatments like Hot Isostatic Pressing (HIP) and Stress Relieving are often conducted. But the modification of the surface roughness by machining is very costly and not always possible, especially for parts with complex design. The aim of this work is to evaluate the effect of the surface roughness and microstructure of Ti-6Al-4V parts produced by SLM and EBM on the HCF life. Five sets of specimens were tested in tension-compression (R=-1; f=120Hz): Hot-Rolled (reference); SLM HIP machined; SLM HIP As-Built; EBM HIP machined; EBM HIP As-Built. For each condition, microstructure characterization, observation of the fracture surface of broken specimens and surface analysis were carried out respectively by Optical Microscope (OM), Scanning Electron Microscope (SEM) and 3D optical profilometer. Results of fatigue testing show a significant decrease of the HCF life mainly due to the surface roughness. Along with experimental testing, numerical simulations using FEM were conducted using the surface scans obtained by profilometry. Based on extreme values statistics of the crossland equivalent stress averaged on a critical distance, a methodology is proposed to take into account the effect of the surface roughness on the HCF life.
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