Coefficient Rate Research Articles

Research on the air-infiltration rate shelter coefficient of building complexes based on building parameter clustering

The configuration of a building complex can significantly influence the air-infiltration rate, which subsequently affects the energy consumption for heating and cooling. Given the diversity of parameters associated with a building complex, it is challenging to study all combinations. This study proposed the k-means clustering method to identify representative building clusters, thereby facilitating the derivation of correction coefficient for the air-infiltration rate within a complex. Initially, data pertaining to district characteristics, such as the complex density, height, and building aspect ratio, were collected and clustered to obtain several representative groups of building clusters. Subsequently, a validated computational fluid dynamics program with the renormalization group (RNG) k–ε turbulence model was employed to investigate the spatial characteristics of the pressure coefficient (Cp) on building surfaces across various groups within the complex. Finally, the shelter coefficient (SAIR), which represents the ratio of an individual building to those in different groups, was determined to correct for the air-infiltration rate in diverse district types. The results show that SAIR varies considerably (from 0.15 to 0.53) owing to the different densities, heights, and layouts between buildings. The applicability of SAIR was further demonstrated and verified in a case study of a building in Dalian, China. The research results can provide a method for predicting the air-infiltration rate of building complex.

Tribological behavior and biocompatibility of novel Nickel-Free stainless steel manufactured via laser powder bed fusion for biomedical applications

Due to the risk of releasing carcinogenic nickel ions from conventional 316L stainless steel under a corrosive human body environment, a new variant of steel termed nickel-free stainless steel (NiFSS) has been investigated. The present study investigates the tribological properties and biocompatibility of NiFSS manufactured via laser powder bed fusion (PBF-LB/M). The ferritic NiFSS exhibited significantly lower coefficient of friction (0.08 to 0.28) and wear rate (1.60 × 10-6 mm3/Nm to 6.60 × 10-6 mm3/Nm) compared to reported values for austenitic 316L SS, under both dry and simulated body fluid (SBF) conditions and various sliding geometries. This improvement is attributed to the superior hardness (3.394 ± 0.1340 GPa) and elastic modulus (238 ± 9.0797 GPa) of NiFSS. To assess the biocompatibility, the viability of mouse pre-osteoblastic MC3T3-E1 cells was evaluated with an Alamar Blue assay when the cells were cultured on top of PBF-LB/M built NiFSS and 316L SS samples. The results indicated that even though cell growth was most optimal on regular cell culture plastic, cell viability was better maintained on PBF-LB/M built NiFSS compared to 316L SS. Therefore, the results of the present study propose that PBF-LB/M fabricated NiFSS holds promise for application in biomedical devices for joint arthroplasty.

Effect of milling time on structural, mechanical and tribological properties of nanostructured HIPed near type Ti-15Mo alloys

The study aimed to analyze how milling time (2 h-24 h) affects structural, mechanical, and tribological properties of Ti-15Mo alloys, these last has evaluated by using XRD, SEM, and a ball-on-disk tribometer. The wear tests were carried out under applied, loads of 2, 8 and 16 N respectively. Results revealed that crystallite size decreased to, 25.5 nm, while lattice parameter increased to 5.34 Å, and porosity reduced to 0.07%, Conversely, mean pore size decreased to 31 nm after 24 h. Moreover, relative density, and Young's modulus increased with prolonged milling. Coefficient of friction, wear, volume, and rate increased with applied load (2–16 N) but decreased with milling time, especially in binary titanium alloys under 16 N load. Optimal conditions were identified, at 24 h milling and 16 N load

Mixed Convection Flow of a Casson Fluid Past a Thin Needle

Mixed Convection Flow of a Casson Fluid Past a Thin Needle

Coronavirus Infection Caused by the Omicron Variant and its Daughter Genovariants in Russia (2022–2023)

Relevance. Surveillance of new genetic variants and manifestations of the epidemic process in SARS-CoV-2 is relevant for predicting the epidemiological situation and timely introduction of anti-epidemic measures. Aim. To evaluate changes in the intensity of the epidemic process during the long circulation of the «omicron» variant and its daughter genovariants. Materials and methods. The analysis of the computer database of the WHO National Center for morbidity, hospitalization and deaths from COVID-19 of the population as a whole and by age groups of 54 cities of the Russian Federation was carried out. Results. Since the appearance of COVID-19 in Russia in 2020, the maximum intensity was the V (winter–spring) wave of 2022. The intensity of the VI (autumn) and VII (winter–spring) waves was lower. In the VI wave, the incidence and mortality from COVID-19 of the population of the RF as a whole decreased by 2.5 and 6.5 times, St. Petersburg – by 2.6 and 29.7 times, and Moscow by 1.6 and 26.6 times. In the VII wave, compared with the VI wave, the decrease in morbidity was less. By age groups, the incidence decreased more among children aged 7–14 years (4.3 times in the VI wave) and less among children 0 –2 and people over 65 years (2.0 times), there was a tendency to increase the proportion of people over 65 years from 18% to 27%. The incidence rates of COVID-19 in the population as a whole and in age groups were higher in 4 FD (North-West, Far East, Siberia and the Center). In 2022, an interepidemic period was revealed for the first time in Russia, the duration of which was in megacities for 9 and FD – from 11 to 13 weeks. In the interepidemic period, the incidence was less than in the minimum VII (winter-spring) wave in the RF as a whole – by 4.6 times, in St. Petersburg – by 7.1 times and in Moscow – by 15 times. There were no deaths among children in the observed cities, and an increase in the total coefficient of mortality rate is associated with mortality among people over 65 years of age. Conclusion. The decrease in the intensity of the epidemicprocess in the VI and VII waves is caused by the prolonged circulation of omicron and its daughter genovarians.

Dry Sliding Wear Behavior of Experimental Low-Cost Titanium Alloys

The high cost and potential toxicity associated with the common commercial Ti-6Al-4V alloy are major concerns against its continued use in the biomedical industry. Low-cost, less toxic titanium alloys have been developed as a possible alternative to Ti-6Al-4V. Because of the various wear processes that take place in the human body, it is imperative to have a good understanding of the wear properties and wear resistance of these alloys. This study, therefore, investigated the resistance to wear of the low-cost Ti-3Fe, Ti-4.5Al-1V-3Fe, and Ti-4.5Al-1V-3Fe alloys under dry sliding conditions in contrast to the common commercial alloy, Ti-6Al-4V. The findings revealed that among the tested alloys, Ti-3Fe exhibited the lowest resistance to wear as it displayed the highest coefficient of friction (0.55) and wear rate (5.55E-06 mm3/Nm). The Ti-4.5Al-1V-3Fe alloy demonstrated superior wear resistance compared to the rest of the alloys, including Ti-6Al-4V, as it had the lowest wear rate (4.27E-06 mm3/Nm) and wear volume (0.0026 mm3). Overall, the experimental alloys displayed very similar wear resistance to Ti-6Al-4V, making them promising commercial alloys that can replace Ti-6Al-4V in bioimplant applications.

Turbulence modeling of stratified turbulence using a constrained artificial neural network

For large eddy simulations (LES) of stratified turbulence in the strongly stratified regime, an artificial neural network (ANN) with five hidden layers is used to construct a sub-grid scale (SGS) model. The ANN is assessed by comparing it to the Smagorinsky model, the dynamic Smagorinsky model, the gradient model, and filtered direct numerical simulation data. In the a priori test, the SGS model using ANN performed better than the Smagorinsky model and the gradient model in terms of the correlation coefficient and relative error of the energy transfer rate. However, the ANN does not provide sufficient energy dissipation when it is applied to LES with a larger filter width because it overpredicts backscatter. To address this problem, we also trained a constrained ANN using a custom loss function that penalizes excessive backscatter. It is shown that the constrained ANN successfully predicts less backscatter, maintaining the high correlation coefficient without ad hoc clipping. These results show that ANN is a promising tool for realizing a highly accurate and stable SGS model for stratified turbulence.

Dynamics of energy transport on hydromagnetic Casson slippery nanoflow over curved surface

The study of fluid flow over curved surfaces is crucial in various engineering applications, such as designing aircraft wings, turbines, and submarines. Curved surfaces are being explored in various biomedical applications, such as designing stents for blood vessels and implants for bones and joints. Concerning the present applications of curved stretching sheets on fluid dynamics along with trihybrid nanofluids, this study is unique and fills the research gaps and offers solutions to several issues. This work looks at the flow through the boundary layer of an electrically conductive trihybrid nanofluid and the convection heat exchange of a Casson fluid across a curved stretched surface encircled within a circle of radius R. The study considers the effects of thermal radiation using the non-linearized Rosseland approximation, as well as a magnetic field, and hydromagnetic slip. The flow as well as the transfer of heat problem is mathematically described by curvilinear coordinates. Using the combination of the shooting technique and the Runge-Kutta method, similar solutions to the modeled partial differential equations are produced, and the set of non-linear ordinary differential equations with a boundary value solver is implemented through the MATLAB program. The study finds the influence of several limits on critical characteristics such as fluid velocity, coefficient of skin friction, pressure, temperature, and rate of heat exchange over a surface. The findings are shown in tables and graphs. Additionally, a comparative analysis between the current findings and those found in the literature is provided. Blood-containing nanoparticles (GO-SWCNTs-MWCNTs) on curved surfaces could improve drug delivery effectiveness, growth of synthetic tissues or organs with complex structures and effective cancer therapy treatment.

Study of Cu-doped zirconia toughened alumina ceramics (Cu-ZTA) subject to lubrication behaviors for arthroplasty

Zirconia-toughened alumina (ZTA) is widely applied in total hip arthroplasty (THA). However, problems with insufficient fracture toughness and lubrication remain, leading to wear, squeaking, and fracturing. In this study, the Cu doping of ZTA (Cu-ZTA) is proposed to solve these problems. To further promote the use of Cu-ZTA, the role of Cu doping on its tribological properties must be studied. In this study, the microstructure, mechanical properties, and stability capacity in a physiological environment, as well as the tribological behaviors of Cu-ZTA in phosphate-buffered saline (PBS) and bovine serum albumin (BSA), were systematically studied with varying amounts of Cu. The results demonstrated that holes and soft Cu-rich phases appeared, and grains grew after Cu doping, causing a decrease in hardness. The fracture toughness increased after Cu doping because the Cu-rich particles formed “bridges” during crack propagation and release energy. The incorporation of Cu improved the stability of ZTA in physiological environments, which enhanced the long-term stability of Cu-ZTA. The protein adsorption results indicated that a higher hydrophobicity and roughness contributed to a greater protein adsorption on the Cu-ZTA surfaces after Cu incorporation. In the BSA solution, the 5.0 wt% Cu-ZTA ceramics achieved a lower coefficient of friction (COF) and wear rate compared to ZTA, and a higher protein adsorption and formation of the denatured protein layer catalyzed by Cu ions in the wear track during friction, thus clearly improving the tribological properties of the Cu-ZTA.

Analysis of Carbon Black Proportion on Durability and Wear Behavior of EPDM Rubber

This study aims at understanding the effect of carbon black on mechanical properties of EPDM rubber. For this we select combination of carbon blacks N330 and N550 with standard curing procedure to minimize the wear rate and maximize durability. The EPDM rubbers were characterized using hardness, tensile, wear and durability tests. The coefficient of friction (COF), volume loss and wear rate of the EPDM rubbers were determined. It was found that with increasing CB content all above characteristics were reduced. Result shows that by using optimum combination of carbon black we can enhance wear performance and durability of EPDM rubber.

Improve the thermal properties of oil‐loaded polysulfone microcapsules by optimizing copper layer for self‐lubricating polyamide

AbstractThis work reports polymer/metal double‐shell microcapsules with polysulfone (PSF) and copper as walls for application in self‐lubricating polymer. First, polyalphaolefin 40 (PAO40) was selected as lubricant oil, and PAO@PSF single shell microcapsules were prepared. A critical issue for the formation of copper layer is the sensitization of PSF shell, which can affect not only the adhesion between PSF shell and copper layer, but also the density of copper layer. The sensitization conditions were discussed in detail, and the corresponding effect on the formation of copper layer was evaluated. PAO@PSF/Cu microcapsules obtained under optimal sensitization condition were characterized by scanning electron microscopy (SEM), thermogravimetric analyzer (TGA), x‐ray energy dispersive spectrometer (EDS) and fourier transform infrared spectroscopy (FTIR). A uniform and compact copper layer improved the thermal properties of microcapsules. PSF/Cu microcapsules maintained relatively complete spherical shape when were heated to 300°C, while the PSF microcapsule softened and deformed at 200°C. The self‐lubricating polyamide 6(PA6) composites containing PAO@PSF/Cu microcapsules were fabricated at 230°C, microcapsules maintained complete structure and uniform distributed in the polymer matrix. Coefficient of friction (COF) and wear rate of PA6 composites were tested under different friction conditions. Compared with pure PA6, 15 wt.% PAO@PSF/Cu microcapsules could reduce the COF by 79.5%, and the wear rate was decreased by 98.3% under 300 rpm sliding speed and 50 N friction load.Highlights PSF/Cu double‐shell oil‐loaded microcapsules were designed and prepared. The copper layer effectively improved the thermal properties of microcapsules. The self‐lubricating PA6 composite exhibited excellent tribological properties.

Meta-analysis of temperature, heat release rate, delamination and auto-extinction of timber compartments

A meta-analysis was conducted on 100 structural mass timber compartment fire experiments. The analysis investigated temperature, heat release rate, auto-extinction and delamination. Dissimilarities in the compartment geometry, ventilation, and exposed timber surfaces of these experiments could be accounted for using two parameters, α and %AO (applicable to near cubic, ventilation-controlled compartments) defined as the shape-modified ventilation factor and opening ratio. The correlation coefficient for the total heat release rate (HRR) with the area of timber for the large and medium scale data was 0.97 and 0.74, respectively. Similarly, the correlation of medium scale data for the contribution of timber to the heat release rate was 0.90. A statistical analysis revealed a higher probability for auto-extinction to occur for exposure levels below 20%. Above 20% exposure, the risk for sustained flaming and delamination increase substantially. Auto-extinction was shown to depend strongly on delamination, with a 93% probability of occurrence given no delamination. The use of PUR HBS adhesive was shown to cause delamination in 73% of the cases, with PUR HBX delaminating in 33% of cases.

Braking Performance of Fe-Based and Cu-Based Powder Metallurgy Pads Paired with C/C-SiC Disk on Full-Scale Dynamometer

In this study, the friction performance of copper-based (Cu-PM) and iron-based (Fe-PM) powder metallurgy pads was systematically compared and analyzed by performing a braking test paired with a C/C-SiC disk on a full-scale flywheel brake dynamometer, including coefficient of friction (COF), wear rate (Wr), and worn surface under dry and wet tests. The test procedure simulated the braking conditions on high-speed trains with initial brake speeds (IBS) from 50 km/h to 200 km/h, as well as under various brake clamping forces (FB). During dry tests, both pads exhibited high levels of COF. The mean value of average COF (µm) for the Cu-PM pad was 0.371, which was slightly higher than that of 0.358 from the Fe-PM pad. The stability of µm over the IBS ranged from 68% to 82% for Cu-PM pads under different FB, while it was from 82% to 85% for Fe-PM pads. However, during the wet tests, the mean value of µm dropped to 0.207 for Cu-PM pads, and with the minimum µm of 0.062; whereas, they were 0.344 and 0.188 for Fe-PM pads, respectively, showing a significant difference in the friction performance between the two pads. Additionally, the Wr of the Cu-PM pad was 0.110 cm3/MJ during dry tests, which was 17.3% lower than that of 0.133 cm3/MJ observed for the Fe-PM pad. After the brake test with the Cu-PM pad, the friction film primarily covered the Si/SiC-rich region of the disk, effectively inhibiting the plowing of SiC hard asperities onto the pad surface. However, the friction film predominantly covered the fiber-rich region of the disk after the test with the Fe-PM pad, and the exposure of hard Si/SiC-rich asperities would continuously plow the pad during braking and resulted in furrows on the surface of the Fe-PM pad. In terms of wear mechanisms, adhesion wear was the primary mechanism on the contact surfaces of the Cu-PM pad and the C/C-SiC disk, while abrasion dominated the interaction between the Fe-PM pad and the C/C-SiC disk. This study provides valuable insights for the application of C/C-SiC brake disks on trains.

Spatial Trends and Distribution Patterns of Toxic Heavy Metal Contamination in an Urbanized Watershed

Rapid urban growth in developing nations exacerbates pressures on water resources through increased pollution loading if management practices cannot adapt efficiently. This study evaluated industrial effluent impacts on river systems in Nigeria contaminated by discharge from beverage, oil and biscuit manufacturing plants. Physicochemical parameters and heavy metal concentrations were monitored at sites upstream and downstream from waste outfalls during wet and dry seasons. Results demonstrated exceedances of national water quality standards for indicators of organic pollution like biochemical oxygen demand and chemical oxygen demand. Notably, highly toxic heavy metals exceeded World Health Organization limits by over 100 times, posing serious public health concerns through various exposure pathways. Seasonal variations reflected changes in pollution inputs. Spatial trends showed metal levels decreasing with distance, though remaining well above safe levels 100m downstream. A predictive transport model was formulated based on field measurements incorporated into the advection-dispersion equation. Key coefficients for the dispersion rate and velocity/dispersion ratio were quantified, allowing simulation of concentration changes under differing scenarios. Model predictions closely aligned with observed metal distribution patterns. Findings highlight the need for upgraded wastewater treatment and emissions controls to mitigate pollution over-burdening natural assimilative capacity. Continuous monitoring programs should track remediation effectiveness. This study provides insights to help authorities balance rapid industrialization, environmental protection and sustainable development goals through evidence-based regulatory strategies ensuring public health.

An improved technology for monitoring groundwater flow velocity and direction in fractured rock system based on colloidal particles motion.

The colloidal borescope, using colloidal particle motion, is used to monitor the flow velocities and directions of groundwater. It integrates advanced techniques such as microscopy, high-speed photography, and big data computing and enjoys high sensitivity at the micron level. However, In the same well, the groundwater flow velocity monitored by colloidal hole mirror is varies greatly from that obtained by conventional hydrogeological monitoring, such as pumping test. In order to solve this problem, the stability catcher and stratified packer are designed to control the interference of the vertical flow in drilling, and to monitor the flow velocity and direction of groundwater velocity at the target aquifer and target fracture. Five wells with different aquifers and different groundwater types were selected for monitoring in south-central China. The instantaneous velocity and direction are converted into east-west component and north-south component, the average velocity and direction is calculated according to the time of 10min, and the particle trajectory diagram is established. Based on these results, it proposed a concept of cumulative flow velocity. Using curve-fitting equations, the limits of cumulative flow velocities as the monitoring time tends to infinity were then calculated as the actual flow velocities of the groundwater. The permeability coefficient of aquifer is calculated by using the fissure ratio of aquifer, hydraulic slope and flow velocity, and compared with the permeability coefficient obtained by pumping test. The results are as follows: (1) The variation coefficient of the instantaneous flow velocity measured at the same depth in the same well at different times is greater than that of the time average flow velocity and greater than that of the cumulative flow velocity. The variation coefficient of the actual velocity is the smallest, indicating that the risk of using the actual flow velocity is lower. (2) The variation coefficient of the flow rate monitored at different depths in the same well is mainly controlled by the properties of the aquifer. The more uniform water storage space in the aquifer, the smaller the variation coefficient. (3) The comparison between the permeability coefficient obtained by monitoring and the permeability coefficient obtained by pumping test shows that the flow of structural fissure water controlled by planar fissure is more surface flow, and the results are consistent. When the groundwater flow is controlled by pores and solution gaps, the flow channel is complicated, which is easy to produce turbulent flow, and the result consistency is poor. (4) According to different research accuracy requirements, different monitoring and calculation methods can be selected for different aquifers and groundwater types. Researches show that, the permeability coefficient calculated for the actual flow velocity in well DR01 is the same as that calculated for the pumping test. The aquifer characteristics reflected by the coefficient of variation of the actual flow velocity in the same aquifer are more realistic. The pumping test method obtains the comprehensive parameters of a certain aquifer, and this method can be used to monitor a certain fissure. In this paper, the new technology developed for monitoring, and the new algorithm established for data processing, can accurately obtain the flow velocity and direction of groundwater, using capsule hole mirror monitoring method. The key parameters of hydrogeology can be obtained by using one well, which can reduce the time and cost input and improve the work efficiency.

Effect of different buried depth on the disintegration characteristic of red-bed soft rock and the evolution model of disintegration breakage under cyclic drying-wetting

The disintegration of red-bed soft rock exhibits a strong correlation with various geological disasters. However, the investigation into the evolutionary mechanisms underlying disintegration breakage has not yet received extensive exploration. In order to comprehensively examine the disintegration characteristics of red-bed soft rock, the slake durability tests were conducted to red-bed soft rocks of varying burial depths. Subsequently, an investigation was carried out to examine the disintegration characteristics and the evolution of disintegration parameters, including the coefficient of uniformity (Cu), coefficient of curvature (Cc), disintegration rate (DRE), disintegration ratio (Dr), and fractal dimension (D), throughout the disintegration process. Finally, employing the energy dissipation theory, an energy dissipation model was developed to predicate the disintegration process of samples at various burial depths. The findings demonstrate a decrease in the abundance of large particles and a concurrent increase in the abundance of small particles as the number of drying-wetting cycles increases. Furthermore, as the number of drying-wetting cycles increases, a significant alteration is observed in the content of particles larger than 10 mm, whereas the content of particles smaller than 10 mm undergoes only minor changes. The disintegration parameters, including the curvature coefficient, non-uniformity coefficient, disintegration rate, and fractal dimension, exhibit a positive correlation with the number of drying-wetting cycles. Conversely, the disintegration index demonstrates a decreasing trend with the increasing number of cycles. Nevertheless, as the burial depth increases, a notable trend emerges in the disintegration process, characterized by a gradual increase in the content of large particles alongside a progressive decrease in the content of small particles. Concurrently, the curvature coefficient, non-uniformity coefficient, disintegration rate, and fractal dimension exhibit a gradual decline, while the durability index experiences a gradual increase. In addition, based on the principle of energy dissipation, it is revealed that the surface energy increment of red-bed soft rock increases with the increase of the number of drying-wetting cycles, but decreases with the increase of burial depth. Ultimately, by leveraging the outcomes of energy dissipation analyses, a theoretical model is constructed to elucidate the correlation between surface energy and both the number of drying-wetting cycles and burial depth. This model serves as a theoretical reference for predicting the disintegration behavior of samples, offering valuable insights for future research endeavors.

Magnesium Addition and Treatment of Reinforcement Particles in Al6061 – Sea Sand Composite on Coefficients Friction and Wear Rate

Aluminium matrix composite is a composite material that can be used as reinforcement to increase the tribological properties of composite. The process of manufacturing the Al6061-Sea sand composite used the stir casting method with stirring time of 10 minutes and speed of 600 rpm. Stir casting specimens were manufactured with height dimension of 20 mm and diameter of 10 mm. After that, the specimen was friction tested using the pin on disc method. The highest coefficient of friction was the specimen without electroless coating with the addition of 2 wt% Mg of 0.634. The more mass fraction of sea sand, the higher the porosity, and the lower the density. An electroless coating process can be carried out on reinforcing particles. This study aims to determine the effect of addition of Mg and treatment of reinforcing particles on the Al6061-Sea sand composite on the coefficient of friction and wear rate. The coefficient of friction, the specimen density increased, the porosity and the wear rate, decreased. This occurred because the reinforcement particle size of sea sand bonded strongly to aluminium matrix. The highest coefficient of friction was the electroless coating with the addition of 2 wt% Mg of sea sand, which was 0.646.

Effect of uncertainties in cable corrosion and material strength on seismic fragility of long-span cable-stayed bridges in marine environments

This paper presents an investigation into the seismic fragility of cable-stayed bridges and considers the complex uncertainties in cable corrosion and material strength. Under certain assumptions and using the limited measured data available for steel corrosion, a cable corrosion model is established. The probability distribution of several parameters, including the corrosion rate, corrosion initiation time, chloride concentration, and cable replacement in the corrosion model, is considered. In addition, the influence of the stress level of cables is also considered in the model by the amplification coefficient of the corrosion rate. To consider the effect of the uncertainties in cable corrosion and material strength on the seismic fragility of this bridge, the uniform design (UD) method is used to generate reasonable bridge samples and to build probabilistic seismic demand models. The results indicate that cable corrosion has a significant impact on the seismic fragility of cable-stayed bridges. The seismic fragility of girders and piers are the smallest and the highest among all bridge components, respectively. The material strength uncertainties have a significant influence on the seismic fragility of bridge components. The coupling between the uncertainties in cable corrosion and material strength does not increase the seismic fragility of the bridge components in most cases because of the cancellation effect of the two uncertainties to some extent. In addition, cable replacement has a significant influence on the seismic fragility of bridge components. In order to correctly evaluate the performance of cable-stayed bridges in service, it is necessary to consider the uncertainties in cable corrosion and material strength in a seismic fragility analysis of long-span cable-stayed bridges with different service periods.

Enhancement of tribological properties of carbide cutting tools by ceramic coating deposition

ABSTRACT Coating by sol–gel deposition to modify the tribological properties of K10 carbide cutting insert was performed. The study examines the thermal and tribological characteristics of uncoated cutting inserts and the cutting inserts coated with TiO2/8YSZ and TiO2/15YSZ layers respectively. The TiO2/8YSZ and TiO2/15YSZ coatings had a hardness of 1151.6 and 1678.9 HV, respectively, and the TiO2/8YSZ and TiO2/15YSZ coated inserts had scratch hardness of 2.73 and 22.98 GPa respectively. Among the uncoated and coated inserts, the TiO2/15YSZ coated inserts had the lowest coefficient of friction and rate of wear. The TiO2/8YSZ coated insert had a lower thermal conductivity when compared to TiO2/15YSZ coated insert and uncoated carbide cutting insert (10.3 vs. 14.1, and 41.8 W/m.K). The thermal expansion coefficients of the 8YSZ layers, 15YSZ layers, and carbide cutting tool were 3.66*10−6, 3.546*10−6 and 14*10−6 K−1, respectively. The reasons for the enhancement of the tribological properties of the carbide cutting tools by the ceramic coatings are discussed.

Observation of anomalous low friction and wear behavior of polyimide in alkaline environment under high load

Polyimide (PI) was first discovered to exhibit excellent tribological properties in alkaline environments. PI is widely used because of its low thermal expansion coefficient, excellent mechanical properties, and resistance to high and low temperatures. The high manufacturing cost of PI makes its waste recycling a hot topic. The most common way of recycling is to hydrolyze PI in strong alkaline environments (C(OH−)>2 mol/L). Therefore, the intuition is that the friction performance of PI decline in highly corrosive environments. However, this paper found a counter-intuitive phenomenon. PI exhibits excellent tribological properties in alkaline environments. This paper studied the behavior of ball-on-disk contact between ceramic ball and PI disk tribopair in an alkaline environment. Results show a very low coefficient of friction (COF, 0.013) and wear rate (1.4 × 10−6 mm3/NM) in sodium hydroxide (NaOH) solution with pH = 13 under the average Hertzian contact pressure of 60 MPa. The COF and wear rate decreased by 80% and 63.4%, respectively, compared with those in solutions with pH = 7. The worn surface was characterized to explore the tribological mechanism. NaOH reacts with PI to form a polymer containing sodium ions during the friction process. The polymer adheres to the friction surface and improves the friction performance of PI. The chemical reaction breaks the C–N–C chemical bond of PI, thereby reducing the molecular rigidity and improving the adhesion of the PI surface. This paper provides a new modification method for improving the tribological properties of PI.