Arithmetic Mean Surface Roughness Research Articles

Impacts of Material and Machine on the Variation of Additively Manufactured Cooling Channels

Abstract While additive manufacturing (AM) can reduce component development time and create unique internal cooling designs, the AM process also introduces several sources of variability, such as the selection of machine, material, and print parameters. Because of these sources, wide variations in a part's geometrical accuracy and surface roughness levels can occur, especially for small internal cooling features that are difficult to post-process. This study investigates how the selection of machine and material in the AM process influences variations in surface quality and deviations from the design intent. Two microscale cooling geometries were tested: wavy channels and diamond-shaped pin fins. Test coupons were fabricated with five different additive machines and four materials using process parameters recommended by the manufacturers. The as-built geometry was measured non-destructively with computed tomography scans. To evaluate surface roughness, the coupons were cut open and examined using a laser microscope. Three distinct roughness profiles on the coupon surfaces were captured including upskin, downskin, and channel walls built at 90 deg to the build plate. Results indicated that both material and machine contribute to producing different roughness levels and very different surface morphologies. The roughness levels on the downskin surfaces are significantly greater than on the upskin or sidewall surfaces. Geometric analysis revealed that while the hydraulic diameter of all coupons was well captured, the pin cross section varied considerably. Along with characterizing the coupon surfaces, cooling performance was investigated by experimentally measuring friction factor and heat transfer. The variations in surface morphology as a function of material and machine resulted in heat transfer fluctuating by up to 50% between coupons featuring wavy channels and 26% for coupons with pin fin arrays. Increased arithmetic mean surface roughness led to increased heat transfer and pressure drop; however, a secondary driver in the performance of the wavy channels was found to be the roughness morphology, which could be described using the surface skewness and kurtosis.

Evaluation of the Loss of Surface Roughness Following the Use of Four Different Instruments for Mechanical Debridement of Dental Implants: An In-vitro Pilot Study

To compare the dental implant surface properties such as mean surface roughness, roughness depth, and the surface loss produced by different prophylactic instrument types. Twenty-four surfaces of twelve dental implants were treated using titanium curettes, titanium-coated curettes, an air abrasion unit, and titanium brushes. The dental implants were inserted partially into a Styrofoam base, exposing one-third to simulate cases of peri-implantitis. The exposed surface was coated with artificial dental calculus (ADC) and divided into four groups for treatment. The arithmetic mean surface roughness (Ra) and the mean roughness depth (Rz) were assessed using the confocal microscope, and the surface loss (SL) area was calculated from the scanning electron microscopic images using an image analysis software. The Ra value varied between 1.08 to 0.29 µm, the Rz value between 10.3 to 70.5 µm, and the mean surface loss area between 154 to 9410 µm2. The One-way ANOVA analysis showed a statistically significant difference between the four groups (P < 0.05). The air abrasion unit showed the highest mean roughness value of 1.08 ± 0.14 µm, mean roughness depth of 70.5 ± 2.21 µm, and a minor surface area loss of 154 ± 132 µm2. In comparison, the titanium brushes showed the least Ra and Rz of 0.29 ± 0.05 µm and 10.3 ± 2.32 µm, respectively, whereas the titanium-coated curettes showed the highest loss of surface area 9410 ± 91.6 µm2. The air abrasion unit was shown to have the least detrimental effect on the implant surface when removing the artificial dental calculus compared to the other three methods.

Pool boiling heat transfer of Novec 649 on sandblasted surfaces

Pool boiling represents a potentially efficient mechanism for thermal management of power electronic components. The present study investigates pool boiling heat transfer using Novec 649 on copper substrates with varying surfaces. Sandblasting, which is a relatively simple surface modification technique, has been used to obtain different copper surface roughness levels ranging from 0.1 µm to 9 µm arithmetic mean surface roughness values. The effects of surface modifications and orientation on boiling heat transfer coefficient (HTC), and critical heat flux (CHF), of Novec 649 have been experimentally investigated by performing pool boiling experiments at atmospheric pressure and saturation pool temperature. The experimental results showed that the size and orientation of the boiling surface do not have a significant impact on the CHF, whilst the HTC improves in the nucleate boiling regime with vertical orientation. In addition, for the range of surface roughness investigated improvements of ∼3X and ∼1.5X in HTC and CHF, respectively, were found relative to the original smooth surface. The HTC in the film boiling regime relative to the nucleate boiling regime was also quantified and found to be ∼20X for our geometries.

Influence of Cold Work on the Efficiency of Vibratory Machining

The aim of the article was to determine the impact of crushed condition (work hardening) on the effectiveness of the vibratory machining. The vibratory machining processing was carried out in two steps. The first step consisted of mechanical abrasion and remove oxides from the surface of the workpieces with abrasive media. While in the second step, smoothing - polishing with metal media was performed. Vibratory polishing also strengthened the treated surfaces. The test results were compared for samples in the crushed state (work hardening, plastic processing) and samples subjected to recrystallization annealing heat treatment. Mass losses, changes in the geometric structure of the surface and changes in the hardness of the machining surfaces were analyzed. Samples subjected to recrystallization, as compared to the samples in the state after work hardening-plastic working, are characterized by a slightly higher arithmetic mean surface roughness and lower surface hardness than for analogous processes for samples not subjected to heat treatment. Heat treatment of annealing allows to remove the effects of crushing and thus it is possible to obtain larger mass losses. Smaller burrs dimensions were obtained for samples after the heat treatment – annealing than after work hardening.

Optimization of Dry Turning of Inconel 601 Alloy Based on Surface Roughness, Tool Wear, and Material Removal Rate

In this work, the dry turning of Inconel 601 alloy in a dry environment with PVD-coated cutting inserts was studied. Turning was performed at various cutting speeds, feeds, insert shapes, corner radii, rake angles, and approach angles. After machining, arithmetic mean surface roughness (Ra) and flank wear (VB) were measured, and the material removal rate was also calculated (MRR). An analysis of variance (ANOVA) was performed to determine the effects of the turning input parameters. For the measured values, the turning process was modeled using an artificial neural network (ANN). Based on the obtained model, the process parameters were optimized using a genetic algorithm (GA). The objective function was to simultaneously minimize Ra and VB and maximize MRR. The accuracy of the model and the optimal values were further validated by confirmation experiments. The maximum percentage errors, which are less than 2%, indicate the possibility of practical implementation of the hybrid approach for modeling and optimization of dry turning of Inconel 601 alloy.

Drilling Response of Carbon Fabric/Solid Lubricant Filler/Epoxy Hybrid Composites: An Experimental Investigation

Carbon-fiber-reinforced epoxy composite (CEC) has gained widespread acceptance as a structural material in various applications. Drilled holes are essential for assembling composite material components. Reducing drilling-induced damage and temperature effects is crucial for improved surface quality and integrity of the drilled composite. In the present work, drilling experiments were conducted on CEC, hexagonal-boron nitride (h-BN) dispersed CEC, and molybdenum disulfide (MoS2) dispersed CEC at three different levels of spindle speed, feed, and drill diameter using solid carbide twist drills. The filler concentrations used in this study were 4, 6, and 8 wt%. Analysis of variance (ANOVA) was used to determine the significance of input factors (feed, spindle speed, drill diameter, and filler concentration) on the drilling responses such as thrust force, temperature, arithmetic mean surface roughness (Ra), and push-out delamination factor (DFexit). The average drilling temperature, Ra, and DFexit of MoS2 dispersed CEC were reduced by 24.7, 46.5, and 11.3%, respectively, when compared to neat CEC. In h-BN dispersed CEC, the average drilling temperature, Ra, and DFexit were reduced by 25.2, 40.9, and 13.2%, respectively, compared to neat CEC. The lubricating properties and high thermal conductivity of filler added to epoxy are responsible for the lower temperature and improved hole surface finish. The improved delamination resistance in filler-loaded CEC is due to the strengthening of the matrix and fiber–matrix interface. Scanning electron microscopy (SEM) was used to examine the morphology of the drilled composite surface. The spindle speed of 5500 rpm, feed of 0.03 mm.rev−1, and filler loading of 4 wt% produced the minimum Ra and DFexit. The response surface method (RSM) was applied to determine the input parameters based on multi-response optimum criteria.

Performance analysis of EDM electrode manufactured by direct metal laser sintering during machining of titanium alloy (Ti6Al4V)

Recently, additive manufacturing based rapid tooling (RT) is gaining popularity in manufacturing industries because tool fabrication time and cost can be substantially reduced. In this regard, an experimental investigation is made to explore the machining performance of AlSi10Mg tool electrode manufactured through direct metal laser sintering and compared with commonly used copper and graphite electrodes in electro-discharge machining (EDM) of titanium alloy work piece. The influence of EDM variables on performance measures like material removal rate, tool wear rate, arithmetic mean surface roughness, surface crack density, white layer thickness and microhardness has been analyzed. The machined surface generated with the usage of different electrodes is inspected by scanning electron microscopy to study the surface integrity. It is observed that superior surface integrity can be attained utilizing AlSi10Mg DMLS electrode at lower setting of machining parameters. Energy dispersion X-ray spectroscopy analysis reveals that transfer of tool electrode elements onto the machined surface occurs along with increase in percentage of carbon and oxygen on the machined surface. From the X-ray diffraction analysis, it is found that metal carbides like titanium carbide and vanadium carbide are formed on the machined surface leading to increase in microhardness of the surface.

A Study on Electrochemical Polishing of Additively Manufactured Ti6Al4V Complex Parts and Its Influence on Corrosion Behavior

Nowadays, metal additive manufacturing (AM) has become popular for creating complex geometries that are impossible to create with conventional manufacturing methods. However, the surface quality of as-built AM parts is typically not (uniformly) smooth. Among different imperfections leading to irregular surface morphology, we can mention the staircase effect due to the layer-by-layer nature of the deposition techniques, partially fused feedstock material, balling effects, spatter, and inadequate fusion, where each impact on surface finish depends on the deployed AM process method. Typically, the surface quality of an as-built part is not satisfactory for functional biomedical applications. To address this issue, many research studies are focusing on optimizing part production variables, such as feed stock material, design of the part, AM process parameters and condition of fusion deposition and binding. However, in most cases, to meet the final part requirements, post-processing after AM production is necessary. Different post-processing methods such as abrasive polishing, laser polishing, chemical etching, and electrochemical polishing are established over the years. Among others, electrochemical polishing (ECP) is a suitable post-processing method for metal additive manufactured parts, particularly those with complicated geometry and inaccessible surfaces such as lattice structures. Titanium and its alloys are commonly used in biomedical applications because of their fracture toughness, corrosion resistance, and biocompatible properties, as well as their fatigue strength. Therefore, Ti-6Al-4V is selected as AM feedstock material for lattice structure fabrication in this work.The principal objectives of this study are 1) to characterize the surface of the lattice structure’s struts to observe the influence of post-processing on the core of the lattice and ensure achieving a uniform lattice structure; and 2) to study the influence of electrochemical polishing (ECP) on corrosion behavior of AM lattice structures as well as on AM flat surfaces.In a first step (Figure 1a), the best ECP condition, based on a Taguchi method design of experiment (DOE), on a flat additively manufactured titanium surface is established. The applied potential, electrochemical polishing time, and the electrode distance (the distance between working and counter electrode) are considered as the ECP parameters in the DOE, and for each parameter two levels are considered. Therefore, four experiments are designed, and two samples are polished for each experiment. In order to observe the effect of each experiment, a Confocal characterization is performed (Figure 1b), and based on the results, the experiment with the highest improvement in roughness is selected to polish a part with lattice-like structure (Figure 1C).In a second step, it is necessary to characterize the internal struts of the lattice structures to observe the influence of post-processing on the core of the lattice and ensure achieving a uniform lattice structure after ECP. This can be accomplished by cutting the part followed by profilometry or confocal microscopy, which are destructive methods. As a non-destructive method, X-ray computed tomography (XCT) can be used to asses the internal parts of a lattice structure. However, in most literature, it is used as a qualitative tool to evaluate the uniformity of lattice structure after post-processing. In this study, the XCT output are analyzed using a novel method, which could quantitatively measure the surface roughness of internal struts and assess its improvement by ECP, in a non-destructive manner.In spite of the fact that corrosion resistance of lattice structure AM parts is important for many practical applications, few studies specifically report corrosion rates before and after post-processing of AM lattice parts. In this paper the influence of ECP on corrosion behavior of AM lattice structures and AM plane surfaces are studied. To evaluate the impact of ECP on the corrosion behavior of AM parts, linear polarization is conducted to measure both the corrosion potential and corrosion rate (Figure 1d).According to the obtained results, the highest improvement of in surface roughness is obtained in the second experiment (sample P03, P04), which contains the higher level in each parameter (20 min polishing time and 20V applied voltage). By ECP of the Ti-6Al-4V AM surface, we have proven that we can decrease the arithmetic mean surface roughness value - Sa – by 70%. Using the ECP process, we reduced the initial roughness of 12.3 μm to a polished surface of 3.5 μm.Further experiments are being conducted on the ECP of lattice structures and the evaluation of their corrosion behavior. Figure 1

Turning performance analysis and optimization of processing parameters using GRA-PSO approach in sustainable manufacturing

The main aim of this research work is to examine the impact of input process factors (cutting speed, feed rate, and depth of cut) on machining characteristics (arithmetic mean surface roughness, tool flank face wear and tool chip interface temperature) and further to optimize during turning of Incoloy alloy 800. The cutting tool used was PVD multilayer coated (TiAlN-TIN) carbide insert. The experiment was performed based on Taguchi L27 methodology with a focus on the sustainability of turning. Sustainable manufacturing is considered for accomplishing overall efficiency with regard to economic, environmental and social aspects. The ANOVA (Analysis of Variance) was employed to assess the contributions of input process variables on cutting variable outputs. Further, the main effect diagrams exemplified the influences of main parameters on response variables. ANOVA analysis results demonstrated that the feed rate was the most leading factor that affects average surface roughness. The relationship(s) among input process factors and the evaluated measured outputs are determined using a quadratic regression model. Taguchi grey relational analysis has been implemented to trial results so as to optimize responses. The results revealed that the grey relational grade is significantly improved (0.308) through the setting of optimal parametric combinations. This integrated Grey–Taguchi approach was established quite effectual for simultaneously optimization of multifaceted machining output responses of turning process. This study provides a novel strategy to develop the machining efficiency of Incoloy 800 steel toward the improvement of sustainable processes and provide suitable applications in aerospace industry.

The Use of a High-Pressure Water-Ice Jet for Removing Worn Paint Coating in Renovation Process.

The paper presents the results of investigations into the possibility of using ahigh-pressure water-ice jet as a new method for removing a worn-out paint coating from the surface of metal parts (including those found in means of transportation) and for preparing the base surface for the application of renovation paint coating. Experimental investigations were carried out in four stages, on flat specimens, sized S × H = 75 × 115 mm, cut from sheet metal made of various materials such as steel X5CrNi18-10, PA2 aluminium alloy and PMMA polymethyl methacrylate (plastic). In the first stage, the surfaces of the samples were subjected to observation of surface morphology under a scanning electron microscope, and surface topography (ST) measurements were made on a profilographometer. Two ST parameters were analysed in detail: the maximum height of surface roughness Sz and the arithmetic mean surface roughness Sa. Next, paint coatings were applied to the specimens as a base. In the third stage, the paint coating applied was removed by means of a high-pressure water-ice jet (HPWIJ) by changing the values of the technological parameters, i.e., water jet pressure pw, dry ice mass flow rate , distance between the sprinkler head outlet and the surface being treated (the so-called working jet length) l2 and spray angle κ for the following constants: the number of TS = 4 holes, water hole diameter φ = 1.2 mm and sprinkler head length Lk = 200 mm. Afterwards, the surface morphology was observed again and the surface topography of the specimen was investigated by measuring selected 3D parameters of the ST structure, Sz and Sa. The results of investigations into the influence of selected HPWIJ treatment parameters on the surface QF removal efficiency obtained are also presented. Univariate regression functions were developed for the mean stripping efficiency based on the following: dry ice mass flow rate , working jet length l2 and spray angle κ. Based on these functions, the values of optimal parameters were determined that allow the maximum efficiency of the process to be obtained. A 95% confidence region for the regression function was also developed. The results demonstrated that HPWIJ treatment does not interfere with the geometric structure of the base material, and they confirmed the possibility of using this treatment as an efficient method of removing a worn paint layer from bases made of various metal and plastic materials, and preparing it for applying a new layer during renovation.

A Novel Machine-Learning-Based Procedure to Determine the Surface Finish Quality of Titanium Alloy Parts Obtained by Heat Assisted Single Point Incremental Forming

Single point incremental forming (SPIF) is a cheap and flexible sheet metal forming process for rapid manufacturing of complex geometries. Additionally, it is important for engineers to measure the surface finish of work pieces to assess their quality and performance. In this paper, a predictive model based on machine learning and computer vision was developed to estimate arithmetic mean surface roughness (Ra) and maximum peak to valley height (Rz) of Ti6Al4V parts obtained by SPIF. An image database was prepared to train different classification algorithms in accordance with a supervised learning approach. A speeded up robust feature (SURF) detector was used to obtain visual vocabulary so that the classifiers are able to group the photographs into classes. The experimental results indicated that the proposed predictive method shows great potential to determine the surface quality, as classifiers based on a support vector machine with a polynomial kernel are suitable for this purpose.

Tungsten-Copper Composites for Arcing Contact Applications

The study presents the research findings on electrical contact materials based on tungsten-copper (W-Cu) composites containing 72 ± 3 wt.% W, rest Cu, and up to 1.5 wt.% Ni. Cylindrical sintered parts with 57 ± 0.5 mm in diameter and 12 ± 0.5 mm in height were manufactured by pressing, sintering, and liquid infiltration route, then were mechanically polished and processed as complex shape protection rings used as arcing contacts in high voltage circuit breakers (HVCBs). The surface elemental composition of the sintered parts was determined by wavelength dispersive X-ray fluorescence spectrometry. The density was determined by hydrostatic weighing in ethanol. The arithmetic mean surface roughness was measured by contact profilometry. The microstructure was studied by scanning electron microscopy. The electrical conductivity was measured by eddy current method. The thermal diffusivity and specific heat were determined by laser flash analysis. Instrumented indentation testing and two computational methods (Oliver &amp; Pharr, and Martens hardness) were employed to study the mechanical properties under quadratic loading and continuous multi cycle (CMC) indentation mode. The functional behavior of the arcing contacts was assessed in terms of static and dynamic contact resistance in operation in minimum oil HVCBs of 110 kV. The properties investigation revealed highly dense contact parts with homogeneous microstructure, Vickers hardness of 260-374, elastic modulus of 185-311 GPa, as well as good electrical and thermal conductivity. The arcing contacts proved a good functional behavior. in service, too. The results endorse the developed sintered contact materials for implementation in practical applications.

Adhesion of streptococci to titanium and zirconia.

The purpose of this study was to evaluate the adherence of streptococci to disks of titanium (commercially pure titanium: CpTi) and zirconia (tetragonal zirconia polycrystals: TZP). CpTi and yttria-stabilized TZP disks with a mirror-polished surface were used as specimens. The arithmetic mean surface roughness (Ra and Sa) and the surface wettability of the experimental specimens were measured. For analyzing the outermost layer of the experimental specimens, X-ray photoelectron spectroscopy (XPS) analysis was performed. Streptococcus sanguinis, S. gordonii, S. oralis, and S. mutans were used as streptococcal bacterial strains. These bacterial cultures were grown for 24 h on CpTi and TZP. The number of bacterial adhesions was estimated using an ATP-bioluminescent assay, and scanning electron microscope (SEM) observation of the adhered bacterial specimens was performed. No significant differences in surface roughness or wettability were found between CpTi and TZP. In XPS analyses, outermost layer of CpTi included Ti0 and Ti4+, and outermost layer of TZP included Zr4+. In the cell adhesion assay, the adherences of S. sanguinis, S. gordonii, and S. oralis to TZP were significantly lower than those to CpTi (p < 0.05); however, significant difference was not observed for S. mutans among the specimens. The adherence to CpTi and TZP of S. mutans was significantly lower than that of S. sanguinis, S. gordonii, and S. oralis. These results were confirmed by SEM. S. sanguinis, S. gordonii, and S. oralis adhered less to TZP than to CpTi, but the adherence of S. mutans was similar to both surfaces. S. mutans was less adherent compare with the other streptococci tested in those specimens.

Analysis of the effect of surface roughness on fatigue performance of powder bed fusion additive manufactured metals

An important advantage of AM is to create net-shaped components with no need for further surface machining since it is usually very difficult for complex geometries. The effect of surface roughness on fatigue performance of powder bed fusion additively manufactured metals was evaluated in this work. The intrinsic rough surface of metal AM parts that could act like existing surface cracks and significantly affect fatigue performance is investigated. The effect of processing and post-processing conditions on surface roughness of AM parts are reviewed and the effect of surface roughness on fatigue performance is analyzed. The synergistic effect of internal defects and surface roughness on fatigue performance is also evaluated. Arithmetic mean surface roughness parameter Ra is used here as a representation of surface roughness, since this parameter has been presented in most of the studies dealing with metal AM surface roughness. Surface roughness effect on fatigue performance is shown to be dominant even in the presence of relatively large internal defects and various microstructures. Ra decreases with an increase in power. This consequently increases fatigue limit, although scatter is observed due to the secondary effect of internal defects and microstructure. For similar microstructures, considering synergistic effect of Ra along with average critical internal defect size in combination with the stress amplitude, resulted in improved correlation of the S-N fatigue data.

Effect of sodium hydroxide treatment on dry sliding wear behavior of Phoenix sp. fiber reinforced polymer composites

In this work, the effect of various concentrations of sodium hydroxide treatment (5, 10, 15 and 20%) on tribological properties of Phoenix sp. fiber reinforced epoxy composites was investigated for the first time and reported. The composites were fabricated by using compression molding technique with optimized fiber length (20 mm) and fiber volume fraction (40%). The shore D hardness of the untreated and treated fiber reinforced composites was determined. The dry sliding wear test was conducted using pin-on-disk wear testing machine at different loads (10, 20 and 30 N), sliding speeds (1, 2 and 3 m/s) and sliding distances (1, 2 and 3 km). The arithmetic mean surface roughness of the samples was measured before and after the wear test. The outcomes revealed that the concentration of sodium hydroxide treatment significantly influenced the hardness and tribological properties and surface roughness value of the fabricated composites. In particular, the composites reinforced with 15% treated fiber composites showed higher wear resistance at all operating conditions and was suggested for fabricating the friction composites for automobile and machine tool applications. The morphology of the worn surfaces of the samples was examined using a scanning electron microscope to study the wear mechanisms.

Evaluation of the effects of polishing systems on surface roughness and morphology of dental composite resin.

Objectives The aim of this in vitro study was to evaluate the effects of five different two-step diamond impregnated polishing systems (Sof-Lex Spiral, Venus Supra, Komet Spiral, CompoMaster and Shapeguard) on the surface roughness and morphology of a submicron hybrid composite resin material (Brilliant Everglow).Materials and methods Two-hundred composite resin discs were prepared with 180 SiC paper to produce a uniform baseline surface. The samples were randomly assigned to one of five groups and polishing was completed by one operator. The arithmetic mean surface roughness (Ra) was measured using contact profilometry and the surfaces were examined under an SEM.Results Statistical differences (p <0.05) were identified between the surface roughness remaining after use of the polishers. Diatech Shapeguard (0.22 μm, SD 0.08) and Komet Spiral (0.26 μm, SD 0.09) polishers yielded the lowest Ra values, while the CompoMaster polishing system led to the highest surface roughness values (0.55 μm, SD 0.19).Conclusions Within the limits of this in vitro study of the efficacy of diamond impregnated two-step polishing systems, Diatech Shapeguard and Komet Spiral polishing systems produced the lowest surface roughness values. These polishing systems yielded acceptable surface roughness values with regards to oral health and patient comfort.Clinical relevance Similarly designed polishing systems do not produce comparable surface roughness levels and clinicians should be aware of this when considering polishing protocols for composite restorations.

Influence of Laser Energy Density on Acquisition and Wear Resistance of Bionic Semisolid Unit of 40Cr Steel

40Cr steel is one of the most common materials for manufacturing brake camshaft of trailer. The brake camshaft is subjected to extreme wear during its service life. In order to enhance wear resistance, medium frequency induction hardening (MFIH) treatment is usually conducted on the surface of brake camshaft. However, conventional MFIH technique requires heating of the entire surface, which has the drawbacks of more power consumption, high production cost and easy deformation. Therefore, inspired by the bionic theory, a process named as “laser bionic semisolid treatment” method accompanied by favorable surface roughness and minimum distortion has been proposed herein as an alternative to MFIH method. By this means, bionic units with different surface roughness, sizes microstructure and hardness were manufactured on the surface of 40Cr steel. Then, the wear resistance of 40Cr steel with various laser energy densities was experimentally investigated. The results demonstrated that when the laser energy density was $$ 18.00_{ - 3}^{ + 3} $$ J/mm2, the bionic semisolid unit was obtained with the arithmetic mean surface roughness Ra of 1046.81 nm. Moreover, there was a significant improvement in the wear resistance of 40Cr steel due to the microstructure and higher hardness compared with the untreated sample, and its weight loss ratio was decreased by 71.90%. The mechanism of wear resistance enhancement was also discussed.

Atomistic molecular dynamics simulation study on the mechanical behavior and dispersion of surface functionalized graphene/polypropylene nanocomposites

The effect of methyl surface functionalization of single-layer graphene on the mechanical behavior and interfacial load transfer of polypropylene (PP) nanocomposites is studied by using molecular dynamics simulations. In the molecular model, both pristine and 20 methyl-group-functionalized graphenes are embedded into an amorphous PP matrix to constitute unit cell models of transversely isotropic periodic nanocomposites. The stress–strain curves of nanocomposites under uniaxial tension and shearing are determined based on non-equilibrium ensemble simulations with a constant true strain rate. Due to the degradation of graphene by the methyl groups, the longitudinal Young’s modulus and in-plane shear modulus of the nanocomposites are degraded. On the other hand, the longitudinal shear moduli of the nanocomposites, which depend on the interfacial shear load transfer, are considerably improved upon methyl functionalization. To establish the relationship between the improved interfacial properties in nanocomposites and methyl functionalization, the intrinsic adhesion energy between graphene and PP matrix and the arithmetic mean surface roughness of graphenes are determined and compared. The dispersibility of graphenes are also studied in terms of the solubility parameters.

The effect of the chemical composition and structure of polymer films made from resorbable polyhydroxyalkanoates on blood cell response

Four PHA types were synthesized in the culture of Cupriavidus eutrophus B-10646 under special conditions, poly(3‑hydroxybutyrate) [P(3HB)] and of copolymers, which contained 3HB monomers and 4‑hydroxybutyrate (4HB), 3‑hydroxyvalerate (3HV), or 3‑hydroxyhexanoate (3HHx). All copolymers had the Mw of about 550–670 kDa, and the homopolymer P(3HB) had a significantly higher Mw – 920 kDa. P(3HB‑co‑4HB) and P(3HB‑co‑3HHx) had the lowest Cx (42 and 49%) while P(3HB‑co‑3HV) and P(3HB) exhibited higher Cx values (76%). Polymer films were prepared from different PHAs. Electron microscopy showed differences in the surface microstructure of the films. Films prepared from the P(3HB) were more hydrophobic and the arithmetic mean surface roughness of 71–75 nm, than the copolymer films, which were hydrophilic (57–60°) and had considerably higher roughness (158–177 nm). Blood parameters (hemoglobin and hemolysis) and response of the cells (erythrocytes, platelets, and monocytes) were studied in experiments with blood directly contacting the surface of the films of PHAs with different compositions. Cultivation of blood cells on polymer films did not cause any adverse effects on adhesion and morphology of all cell types. Results of studying blood cell response suggested that the films made from low-crystallinity copolymers containing 4‑hydroxybutyrate and 3‑hydroxyhexanoate were the best for contact with blood.

Optimization of Process Parameters for Anti-Glare Spray Coating by Pressure-Feed Type Automatic Air Spray Gun Using Response Surface Methodology.

The process of preparing anti-glare thin films by spray-coating silica sol-gel to soda-lime glass was exclusively and statistically studied in this paper. The effects of sol-gel deliver pressure, air transport pressure, and spray gun displacement speed on the gloss, haze, arithmetic mean surface roughness, and total transmittance light were analyzed. The experimental results indicate that the factors of sol-gel deliver pressure, air transport pressure, and displacement speed exhibit a significant effect on the haze, gloss, and Ra. In contrast, the variation of total transmittance light with these three factors are insignificant. Because the anti-glare property is predominantly determined by low gloss and high haze, we therefore aim to minimize gloss and maximize haze to achieve high anti-glare. Central composite design and response surface methodology are employed to analyze the main and interaction effects of the three factors through quadratic polynomial equations, which are confirmed by the analysis of variance and R2. The response surface methodology predict the lowest gloss and highest haze are 9.2 GU and 57.0%, corresponding to the sol-gel deliver pressure, air-transport pressure, and displacement speed of 250 kPa, 560 kPa, and 140 mm/s, and 340 kPa, 620 kPa, and 20 mm/s, respectively. Comparing the predicted optimal data with the real experimental results validates the applicability of the mathematical model. This study provides an important basis for the subsequent production of anti-glare glass with different specifications to satisfy the market demand.