Roughness Patterns Research Articles

Enhanced interfacial bonding strength between metal and polymer via synergistic effects of particle anchoring and chemical bonding

To enhance the performance of metal-polymer joint, surface modification is normally applied. Different from the common methods of increasing roughness or manufacturing complicated patterning, a new strategy of microscale morphology design of low roughness surface was introduced in this work, for improving the interfacial bonding strength between Ti6Al4V titanium alloy (TC4) and polyethylene terephthalate (PET) joined by hot pressing method. Low-roughness (R a = 0.18 μm) surface achieved by HF etching can also significantly enhance the interfacial bonding strength of TC4-PET joint by 133%, from 4.5 MPa (as-polished) to 10.5 MPa, as high as the joint strength achieved by sandblasting (11 MPa) with much higher roughness (R a = 3.7 μm). The bonding mechanisms in joints with different surface treatments were investigated and compared, showing that a new effect of surface particle anchoring played a key role in enhancing the interfacial bonding. Based on the characterization results and analyses, the crack propagation paths of HF and HNO 3 -HF treated samples were clarified and illustrated. This study indicated that roughness is not the only decisive factor of joint strength and demonstrated a new effective strategy via synergistic effects of surface particle anchoring and chemical bonding to improve interfacial bonding of metal and polymer from both theoretical and practical points of view.

A study of drag reduction with textile roughness on a cyclist model

Efforts were made to examine the effect of textile roughness for the reduction of aerodynamic drag experienced on a cyclist model. First of all, flow visualization experiments were conducted in a water channel with a 1/5 scale cyclist model to identify the flow separation lines on the contoured surface. Subsequently, based on the information learned, the idea of delaying flow separation on the model surface was implemented by means of sport suits. Seven sport suits featuring different textile materials and local roughness patterns were tested on a full-scale cyclist model in wind tunnel experiments, in addition to a reference case without a sport suit. From the CD data deduced, we identified a critical condition in most of the cases studied, featuring a least drag coefficient occurred at a Reynolds number within the flow speed range studied. For the best case found, the drag coefficient is amounted 7.5% less than that of the reference case at the same Reynolds number. Furthermore, the Cp and Cprms values reduced from the pressure measurements on the cyclist model with the sport suits unveil a trend that the reduction of drag actually infers the retreat of the local flow separation lines toward the rear side of the body accompanied with less severe the flow unsteadiness.

Controlling of RuO2 Nanostructures by Deposition Temperature and Its Effect on Structural, Morphological and Electrochemical Properties

Nanostructured ruthenium oxide electrodes materials were synthesized on stainless steel substrate at 473 K–773 K temperatures with 100 K intervals using automatic spray pyrolysis technique via an aqueous route. The physical and supercapacitive properties of the deposited electrodes were characterized thoroughly. Deposited electrodes show an amorphous structural property. Electrodes deposited at various temperature shows various morphologies such as rough porous interconnected pattern like granular morphology and well-covered dense sheet-like morphology. Electrode deposited at 673 K shows superior electrochemical properties viz highest specific capacitance of 524.9 F g−1 at 5 mV s−1, specific energy 128.2 Wh kg−1, specific power 256 kW kg−1, and columbic efficiency 94% in 1 M H2SO4 electrolyte. Electrochemical impedance spectroscopy reveals the capacitive behavior of the electrode. Electrode shows 3.39Ω combined internal resistance. Overall results demonstrate that spray deposited RuO2 at 673 K can be excellent electrode material for next-generation energy storage applications.

Effect of CO2 laser treatment on the leather surface morphology and wettability

The aim of this research was to determine the influence of pulsed CO2 laser treatment on crust leather surface morphology and wettability. The obtained results revealed that pulsed CO2 laser engraving can be used as an effective tool for crust leather surface treatment. Pulsed CO2 laser treatment only negligible affects the macrostructure of leather, while the morphology and wetting of the leather surface after treatment were changed. It was found that an increase of laser pulses number increases the initial water contact angle value and intensifies the water droplet relaxation process. After laser treatment, the water droplet contact angle relaxation rate increases twofold compare to those for untreated leather. SEM micrographs showed increased defectiveness with rough surface patterns, thermally affected areas, and change of microstructure. The EDX analysis revealed that the engraved leather surface contains a significantly higher amount of carbon but smaller quantities of oxygen compared to those of untreated samples. It was found that only after laser treatment chromium and sulfur in the EDX spectra appear while for untreated samples these elements on the surface were not observed. The results indicate that for investigated samples laser engraving does not affect the concentration of hexavalent chromium and are in accordance with EU requirements.

Analysis of Different Mould Section Sizes to Optimize the Submerged Entry Nozzle to Measure the Meniscus Fluctuation in a Continuous Casting Mould

An experimental investigation has been carried out to analyse different mould section sizes to measure the meniscus fluctuation by varying different liquid flow rates and different submerged entry nozzle port angles, i.e., 0° port angles, 15° downward and 15° upward port angles. The terms of maximum surface wave fluctuation and standard deviation have been analysed for the above mentioned parameters. It was observed that a submerged entry nozzle with 0° port was found to be superior when it was compared with a 15° downward and 15° upward port nozzle. By conducting an experiment, it was observed that as the water flow rate increased, the maximum wave amplitude was found to be increasing, which results in more turbulence. Different mould section sizes were analysed to provide background information to the steelmaker to analyse the behaviour of fluid flow pattern. The operating parameters of the result obtained from the present setup were compared with the published literature, and a scale down of slab moulds can be justifiedregarding the rough flow pattern in the mould but can lack accuracy. The reason behind this statement is that the integral length scales of the turbulent flow between scaled down and full scale models can be different. Therefore, details of the flow pattern can become great differences between both types of models.

Effect of Al2O3 nanoparticle additives on the performance characteristics of rough journal bearings

This paper investigates the influence of Al2O3 nanoparticle additives on static and dynamic characteristics of water-lubricated rough journal bearings under thermo-hydrodynamic lubrication (THL). The time-dependent modified Reynolds equation and the approximated adiabatic energy equation have been formulated and solved numerically with boundary conditions and initial conditions. The results are presented for dimensionless maximum film pressure, dimensionless maximum film temperature, dimensionless minimum film thickness, eccentricity ratio, attitude angle, dimensionless friction force, spring constants, damping coefficients and mass parameters for both journal bearings with transverse roughness patterns and with longitudinal roughness patterns under a dimensionless load of 7. The results show that journal bearings with Al2O3 nanoparticle additives tend to significantly increase load carrying capacity and minimum film thickness by decreasing both the eccentricity ratio and temperature rise for longitudinal roughness patterns. For journal bearings with longitudinal roughness patterns and lubricated with Al2O3 nanoparticle additives, the stability region tends to increase.

Rough Set Neural Network Feature Extraction and Pattern Recognition of Shaft Orbits Based on the Zernike Moment

In the shaft axis monitoring of hydrogenerating unit condition monitoring and fault diagnosis, the shaft orbit is intuitive and comprehensively reflects the unit operation state, and different shaft orbits correspond to different fault types, which can accurately indicate a system vibration fault. Shaft orbit identification has important significance for vibration fault diagnosis. In getting the feature extraction and pattern recognition of a shaft orbit, the Zernike moment is better than the Hu moment; it has the advantages of a small calculation error and a high recognition rate. A rough set neural network (RS-BP hybrid model) of shaft orbit recognition is established, which uses just 13 moment eigenvalues reserved by the rough set feature selection algorithm as input variables; it has the same calculation error and recognition rate and reduces the calculation time step. The simulation of the recognition of shaft orbits shows that the hybrid model has achieved good results in the identification of shaft orbits.

Modeling and exploiting the strip tension influence on surface imprinting during temper rolling of cold-rolled steel

To produce cold-rolled steel strips with specific mechanical properties and surface roughness typically temper rolling is adopted. In most cases, a uniform roughness pattern on the strip surface is mandatory. Due to the wear of the textured work rolls, their surface roughness (Ra) continuously reduces during the process, which should be accounted for process control. However, conventional temper rolling systems fail to guarantee a uniform surface roughness. In this work, the influence of strip tension on the imprinting of surface roughness during temper rolling is analyzed based on a multi-scale FE modeling concept to explore new ways for surface roughness control. This is done in simulation where, a macroscopic rolling model incorporating strip tension is coupled to a mesoscopic imprinting model and both models are validated using copper rolling trials. The influence of different thickness reductions, strip tensions and incoming strip's surface roughness on imprinting is modeled and compared. The numerical results reveal that a higher strip tension decreases the roughness transfer, which presents potential to control the roughness transfer ratio without changing other process parameters like the prescribed thickness reduction in the future.

The effect of cleaning and repainting on the ship drag penalty

Although the hull of a recently dry-docked large ship is expected to be relatively smooth, surface scanning and experimentation reveal that it can exhibit an “orange-peel” roughness pattern with an equivalent sand-grain roughness height = 0. 101 mm. Using the known value and integral boundary layer evolution, a recently cleaned and coated full-scale ship was predicted to experience a significant increase in the average coefficient of friction and total hydrodynamic resistance during operation. Here the report also discusses two recently reported empirical estimations that can estimate ks directly from measured surface topographical parameters, by-passing the need for experiments on replicated surfaces. The empirical estimations are found to have an accuracy of 4.5 − 5 percentage points in

Characteristics of drag due to streamwise inhomogeneous roughness

Characteristics of the skin friction due to streamwise inhomogeneous roughness are investigated by modeling it in a simplified manner using step changes in equivalent sand grain roughness height ks, denoted as P (ks = 81.25 μm), Q (ks = 325.00 μm) and R (ks = 568.75 μm). The selected ks values represent the common ship-hull roughness, i.e., from light slime to about small calcareous fouling. RANS simulations are performed to study the friction characteristics of various rough surfaces formed by a trio-combination of P, Q and R roughnesses on flat plates with streamwise lengths of 30, 60, 120 and 240 m. The three combinations of roughnesses form either homogeneous (PPP, QQQ or RRR) or inhomogeneous (PQR, PRQ, QPR, etc.) rough walled turbulent boundary layer flow. A step change in roughness height results in a sudden change of the local skin friction coefficient in the form of overshoot or undershoot, followed by a relaxation where the inhomogeneous local skin friction is slowly returning to the homogeneous local one. The sequence of roughness arrangement in a streamwise inhomogeneous roughness pattern plays a key role in the resulting overall skin friction with value increasing in the following order: PQR < PRQ < QPR < QRP < RPQ < RQP. The similarity laws hold for both homogeneous and inhomogeneous rough surfaces.

Turning parameters effects in residual stresses of AISI 1045 steel

The main objective of this work was to evaluate the influence of turning parameters on the generation of residual stresses in AISI 1045 steel bars. Therefore, effects of four main parameters as feed rate, cutting velocity, tool nose radius, and rake angle were analyzed. Residual stresses investigation through X-ray diffraction (XRD) was carried out at different depths (surface, 5, 10, 20, 50, and 75 μm). As the samples showed distinct roughness patterns with variable amplitude and shape, and based in a previous work, samples were classified in two main groups accordingly with surface finishing (regular and irregular). The current results showed that feed rate and cutting speed played the major influence on residual stress distributions. Moreover, the tool nose radius affected surface residual stresses, whereas the rake angle did not significantly change it. Finally, samples could be divided in two residual stress groups, showing a direct relation of surface finishing quality and residual stresses.

Biomimetic surfaces prepared by soft lithography and vapour deposition for hydrophobic and antibacterial performance

ABSTRACT This study demonstrates the synthesis of a bioinspired surface exhibiting hydrophobic and antibacterial functionalities using a two-stage synthesis approach which involves soft lithography and initiated chemical vapour deposition (iCVD). Sandpapers, which are inexpensive and available with desired grit size, were used as the moulds in soft lithography to transfer the rough surface patterns to the PDMS replica surfaces. The antibacterial surface modification of the PDMS replicas was done through vapour-phase deposition of thin poly(diethylaminoethyl methacrylate-vinylbenzyl chloride) (P(DEAEMA-VBC)) films by iCVD method from the corresponding monomers. FTIR analysis of the as-deposited films showed a high retention of the chemical functionalities. The hydrophobicity and antibacterial performances of the flat and rough surfaces were examined as a function of surface roughness. The antibacterial activities were tested against gram-negative E. coli and gram-positive S. aureus. It was found that obtained replicas achieved up to a 7-log reduction in bacterial population and showed high hydrophobicity.

Modelling the combined effect of surface roughness and topography on bacterial attachment

Bacterial attachment is a complex process affected by flow conditions, imparted stresses, and the surface properties and structure of both the supporting material and the cell. Experiments on the initial attachment of cells of the bacterium Streptococcus gordonii (S. gordonii), an important early coloniser of dental plaque, to samples of stainless steel (SS) have been reported in this work. The primary aim motivating this study was to establish what affect, if any, the surface roughness and topology of samples of SS would have on the initial attachment of cells of the bacterium S. gordonii. This material and bacterium were chosen by virtue of their relevance to dental implants and dental implant infections. Prior to bacterial attachment, surfaces become conditioned by the interfacing environment (salivary pellicle from the oral cavity for instance). For this reason, cell attachment to samples of SS pre-coated with saliva was also studied. By implementing the Extended Derjaguin Landau Verwey and Overbeek (XDLVO) theory coupled with convection-diffusion-reaction equations and the surface roughness information, a computational model was developed to help better understand the physics of cell adhesion. Surface roughness was modelled by reconstructing the surface topography using statistical parameters derived from atomic force microscopy (AFM) measurements. Using this computational model, the effects of roughness and surface patterns on bacterial attachment were examined quantitatively in both static and flowing fluid environments. The results have shown that rougher surfaces (within the sub-microscale) generally increase bacterial attachment in static fluid conditions which quantitatively agrees with experimental measurements. Under flow conditions, computational fluid dynamics (CFD) simulations predicted reduced convection-diffusion inside the channel which would act to decrease bacterial attachment. When combined with surface roughness effects, the computational model also predicted that the surface topographies discussed within this work produced a slight decrease in overall bacterial attachment. This would suggest that the attachment-preventing effects of surface patterns dominate over the adhesion-favourable sub-microscale surface roughness; hence, producing a net reduction in adhered cells. This qualitatively agreed with experimental observations reported here and quantitatively matched experimental observations for low flow rates within measurement error.

The effect of Fit-checking material and various subsequent cleaning methods on the wettability of the dentin surface: an in vitrostudy

Background: GC Fit-checker is a modified polyvinyl siloxane impression material exclusively used to check the internal fit and improve the marginal fit of indirect restorations. An unpolymerized organic film is known to be leftover on the bonding surfaces after the silicone disclosing procedure. Residual silicone film being hydrophobic may alter the wettability of the cement to the tooth/metal surface, thus having a detrimental effect on the bond strength and retention of the restoration. Aim: This study aimed to evaluate the wetting of luting liquid (GIC) to tooth dentin surface after application of Fit-checker and evaluate the efficiency of various surface treatments in removing the residual silicone film. Materials and Methods: Extracted human molars were mounted on the acrylic block, and the tooth occlusal surface was ground flat till the dentin exposure. All the specimens were assigned into five groups: Group 1: without application of Fit-checker (control group); Group 2: without any surface treatment after peeling off Fit-checker; Group 3: surface treatment with wet pumice; Group 4: 37% phosphoric acid treatment; Group 5: 10% polyacrylic acid treatment. Later, Type 1 Glass Ionomer Cement (GIC) liquid drop was placed on the dentin and photographs were made horizontally using a standardized procedure. Contact angles were measured using AUTOCAD software. Obtained values were statistically analyzed using the One-way ANOVA test and Tukey’s Post hoc test. Samples of each group were examined using the scanning electron microscope. Results: Statistically significant difference was observed among all the groups except between Group 4 and Group 2 (p > 0.05). SEM images of various groups showed a significant difference in roughness patterns. Conclusion: Surface treatment with pumice and the rotary brush was an effective method among the three in cleaning the residual silicone film.

Dynamic characteristics and growth curve of rail corrugation at saturation stage

Rail corrugation, which causes the vibration and the noise, is a phenomenon in which roughness patterns of approximately regular wavelengths are formed on the rail running surface by trains running. In the previous paper, we have already explained the growth mechanism and the wavelength determination mechanism of the rail corrugation from the dynamic point of view and that there are three stages in the evolution process of the corrugation: formation, growth and saturation. In this paper, we analyze the dynamic characteristics of the track and vehicle in the saturation stage, propose a growth curve of corrugation, and verify them based on measured data obtained on commercial lines. As a result, it is confirmed that when the roughness amplitude grows and exceeds the critical roughness amplitude, there are two characteristics: the significant increase of the contact force fluctuation and the acceleration of the rail and wheel, formation of higher-order roughness components of the corrugation. The growth curve of the corrugation can be approximated by a logistic function.

High-resolution and scalable printing of highly conductive PEDOT:PSS for printable electronics

Topographical discontinuous dewetting (TDD) and liquid bridge transfer (LBT) was used for submicron resolution, R2R-compatible, high thickness, low line edge roughness patterning of PEDOT:PSS. High conductivities up to ∼2590 S cm−1 were achieved.

Experimental analysis of tip vortex cavitation mitigation by controlled surface roughness

This study presents results of experiments where roughness applications are evaluated in delaying the tip vortex cavitation inception of an elliptical foil. High-speed video recordings and laser doppler velocimetry (LDV) measurements are employed to provide further details on the cavitation behavior and tip vortex flow properties in different roughness pattern configurations. The angular momentum measurements of the vortex core region at one chord length downstream of the tip indicate that roughness leads to a lower angular momentum compared with the smooth foil condition while the vortex core radius remains similar in the smooth and roughened conditions. The observations show that the cavitation number for tip vortex cavitation inception is reduced by 33% in the optimized roughness pattern compared with the smooth foil condition where the drag force increase is observed to be around 2%. During the tests, no obvious differences in the cavitation inception properties of uniform and non-uniform roughness distributions are observed. However, the drag force is found to be higher with a non-uniform roughness distribution.

Molecular remnant of Nova 1670 (CK Vulpeculae)

CK Vul erupted in 1670 and is considered a Galactic stellar-merger candidate. Its remnant, observed 350 yr after the eruption, contains a molecular component of surprisingly rich composition, including polyatomic molecules as complex as methylamine (CH3NH2). We present interferometric line surveys with subarcsec resolution with ALMA and SMA. The observations provide interferometric maps of molecular line emission at frequencies between 88 and 243 GHz that allow imaging spectroscopy of more than 180 transitions of 26 species. We present, classify, and analyze the different morphologies of the emission regions displayed by the molecules. We also perform a non-LTE radiative-transfer analysis of emission of most of the observed species, deriving the kinetic temperatures and column densities in five parts of the molecular nebula. Non-LTE effects are clearly seen in complex species including methanol absorption against the cosmic microwave background. The temperatures are about 17 K in the inner remnant and 14 K in the extended lobes, both higher than excitation temperatures estimated earlier in an LTE approach and based on single-dish spectra. We find total (hydrogen plus helium) densities in the range of 104 − 106 cm−3. The column densities provide rough relative abundance patterns in the remnant which currently are not understood. Attempts to derive elemental abundances within the assumption of a chemical equilibrium give only loose constraints on the CNO elements. That the formation of many of the observed molecules requires a major involvement of circumstellar shocks remains the preferred possibility. The molecular gas could have formed 350 yr ago or more recently. The molecules are well shielded from the interstellar radiation field by the circumstellar dust. Their presence alone indicates that the unobservable central star cannot be a hot object such as a white dwarf. This excludes some of the proposed scenarios on the nature of CK Vul. The general characteristics of the molecular environment of CK Vul derived in this study resemble quite well those of some pre-planetary nebulae and asymptotic giant branch stars, most notably that of OH231.8+4.2.

Experimental and Numerical Investigation of the Extrusion and Deposition Process of a Poly(lactic Acid) Strand with Fused Deposition Modeling.

In the last decade, Fused Deposition Modeling (FDM) has gained popularity for allowing the fabrication of pieces with complex shapes. The final quality of the pieces is strongly linked to the shape, size and surface finish of the strands deposited successively, which themselves depend on the printing parameters and extruded material properties. In this work, we present an experimental characterization of an extruded and deposited single strand of Poly-Lactic Acid (PLA), by means of high-speed visualization of the bead region between the substrate and the nozzle, where the molten polymer is still in liquid phase. A Computational Fluid Dynamics (CFD) model proposed in literature, and, based on isothermal and viscous flow assumptions, is validated with this data in terms of strand height and meniscus shape. The characteristics of the printed layer are also confronted to the measurements of the solidified strands by microscopy, with a good agreement. The focus on high printing speeds allows extending the conclusions of previous studies. Regarding the surface finish, the roughness patterns detected on the printed strands are correlated to the velocity fluctuations of the printing head. The CFD model does not capture those thickness variations, however, due to not accounting for solidification.

Propeller tip vortex mitigation by roughness application

In this study, the application of surface roughness on model and full scale marine propellers in order to mitigate tip vortex cavitation is evaluated. To model the turbulence, SST k−ω model along with a curvature correction is employed to simulate the flow on an appropriate grid resolution for tip vortex propagation, at least 32 cells per vortex diameter according to our previous guidelines. The effect of roughness is modelled by modified wall functions. The analysis focuses on two types of vortices appearing on marine propellers: tip vortices developing in lower advance ratio numbers and leading edge tip vortices developing in higher advance ratio numbers. It is shown that as the origin and formation of these two types of vortices differ, different roughness patterns are needed to mitigate them with respect to performance degradation of propeller performance. Our findings clarify that the combination of having roughness on the blade tip and a limited area on the leading edge is the optimum roughness pattern where a reasonable balance between tip vortex cavitation mitigation and performance degradation can be achieved. This pattern in model scale condition leads to an average TVC mitigation of 37% with an average performance degradation of 1.8% while in full scale condition an average TVC mitigation of 22% and performance degradation of 1.4% are obtained.