Compressive Surface Research Articles

Impact of cholesterol on the structure and phase separation of DPPC Langmuir monolayers: Experiments and simulations

Cholesterol is a lipid that plays a key role mainly in the plasma membrane of animal cells, determining their structural and mechanical properties. While Langmuir monolayers have been a traditional model for studying these membranes, they may not fully capture microscopic phenomena. We studied mixed Langmuir monolayers of DPPC and cholesterol in various proportions, using a Langmuir trough for surface compression isotherms and micro-Brewster Angle Microscopy (MicroBAM) for imaging. Furthermore, atomistic Molecular Dynamics (MD) simulations were used to examine molecular distributions, geometric conformations, and emergence of a gas phase in the monolayers. Both experimental and simulation results were compared to obtain a comprehensive understanding. The results reveal strong attraction between DPPC tails and cholesterol, increasing monolayer stiffness and density. These interactions align the lipid tails more perpendicularly to the water surface, effectively minimizing their projected area and preventing tail entanglement. Consequently, the reduced flexibility triggers a phase separation in the monolayer at smaller areas per lipid, with low-density voids and denser regions, as observed in both MicroBAM and simulations. These outcomes emphasize the critical role of cholesterol in biological membranes. Finally, the consistency of MD simulations with experiments validate them as a valuable tool for investigating lipid monolayer behavior.

Influence of the Surface Topography of Titanium Dental Implants on the Behavior of Human Amniotic Stem Cells.

The dental implant surface plays a crucial role in osseointegration. The topography and physicochemical properties will affect the cellular functions. In this research, four distinct titanium surfaces have been studied: machined acting (MACH), acid etched (AE), grit blasting (GBLAST), and a combination of grit blasting and subsequent acid etching (GBLAST + AE). Human amniotic mesenchymal (hAMSCs) and epithelial stem cells (hAECs) isolated from the amniotic membrane have attractive stem-cell properties. They were cultured on titanium surfaces to analyze their impact on biological behavior. The surface roughness, microhardness, wettability, and surface energy were analyzed using interferometric microscopy, Vickers indentation, and drop-sessile techniques. The GBLAST and GBLAST + AE surfaces showed higher roughness, reduced hydrophilicity, and lower surface energy with significant differences. Increased microhardness values for GBLAST and GBLAST + AE implants were attributed to surface compression. Cell viability was higher for hAMSCs, particularly on GBLAST and GBLAST + AE surfaces. Alkaline phosphatase activity enhanced in hAMSCs cultured on GBLAST and GBLAST + AE surfaces, while hAECs showed no mineralization signals. Osteogenic gene expression was upregulated in hAMSCs on GBLAST surfaces. Moreover, α2 and β1 integrin expression enhanced in hAMSCs, suggesting a surface-integrin interaction. Consequently, hAMSCs would tend toward osteoblastic differentiation on grit-blasted surfaces conducive to osseointegration, a phenomenon not observed in hAECs.

A Numerical Hydration Model to Predict the Macro and Micro Properties of Cement–Eggshell Powder Binary Blends

This study aims to propose a hydration kinetic model for the cement–eggshell powder binary system and predict the performance development of composite concrete through this model. The specific content and results of the model are as follows. First, based on the cumulative hydration heat of the cement and eggshell powder binary system in the first seven days, the parameters of the cement hydration model and the eggshell powder nucleation parameter are calibrated. These parameters remain constant regardless of the mix ratio. Secondly, the hydration heat of the cement–eggshell powder binary system over 28 days is calculated using the hydration model. The results show that at 28 days, for specimens with 0%, 7.5%, and 15% eggshell powder substitution, the cement hydration degrees are 0.832, 0.882, and 0.923, respectively. The hydration heat per gram of cement is 402.69, 426.88, and 446.73 J/g cement, respectively, while the hydration heat per gram of binder is 402.69, 394.86, and 379.72 J/g binder, respectively. Additionally, the hydration model is used to calculate the chemically bound water and calcium hydroxide content of the cement–eggshell powder binary system. At 28 days, for samples with 0%, 7.5%, and 15% eggshell powder, the chemically bound water content is 0.191, 0.188, and 0.180 g/g binder, respectively, and the calcium hydroxide content is 0.183, 0.179, and 0.173 g/g binder, respectively. Finally, a power function is used to regress the calculated hydration heat with experimentally measured compressive strength and surface electrical resistivity. The correlation coefficients for compressive strength and surface electrical resistivity are 0.8474 and 0.9714, respectively. This is because the strength weak point effect of eggshell powder has minimal impact on hydration heat and surface electrical resistivity experiments but significantly affects the strength experiment.

Comparative Evaluation of the Mechanical and Physical Properties of Mineral Trioxide Aggregate vs. Bacterial Cellulose Nanocrystal-Reinforced Mineral Trioxide Aggregate: An In Vitro Study.

This study aims tocompare and assess the compression strength, microhardness, and surface texture of two sets of materials: mineral trioxide aggregate (MTA) PlusTMand bacterial cellulose nanocrystal (BCNC)-reinforced MTA PlusTM. According to the ASTM E384 standard, the cylindrical molds made of plexiglass with an internal diameter of 6 mm and a height of 4 mm were fabricated using computer numerical control laser cutting. A total of 20 samples (n=10) in each group were considered in this experimental study: Group I (control group) MTA PlusTM (Prevest DenPro Limited, India)and Group II (experimental group) BCNC (Vedayukt India Private Limited, India)-reinforced MTA PlusTM. After preparation, the molds were incubated at 37°C in a fully saturated condition for about 24 hours, and then the compression strength, microhardness, and scanning electron microscopy analyses were performed at different magnifications. The obtained data were then statistically analyzed. Quantitative analysis revealed that there is a statistically significant difference between MTA PlusTM and BCNC-reinforced MTAPlusTM (p<0.002). The Wilcoxon signed-ranktest and Mann-Whitney U-test revealed that BCNC-reinforced MTA PlusTM showed significantly higher compression strength (33.80±3.83 MPa, p=0.00) and surface microhardness (642.85±24.00 μm, p=0.00) than the control group. Based on ourfindings, it was concluded thatthere is a statistically significant difference between both study groups. Thus, incorporating BCNC into the MTA PlusTM significantly increased the compression strength and surface microhardness of the MTA PlusTM cement. Numerous dental applications have been investigated for bacterial cellulose. Many benefits of bacterial cellulose are available, which includeits effects on moldability, low cost, high water retention capacity, biocompatibility, and biodegradability. Furthermore, the addition of BCNC to MTA PlusTM accelerates the material's hardening process and decreases its setting time, which in turn shortens clinical chairside procedural timing and thereby improves patient satisfaction.

Microstructural characterization and equibiaxial flexural strength of CeO2 and Ti-doped CeO2

In this study, the synthesis of CeO2 and titanium dioxide (TiO2) doped CeO2 (TDC) monoliths are investigated, and their fracture strength is assessed using an equibiaxial flexure testing technique at room temperature. Pellets were synthesized using conventional powder processing and sintering methods to produce the desired characteristics. The TiO2 dopant concentration was optimized at 0.1 wt % TiO2 to obtain dense, solid-solution pellets with an enhanced grain microstructure. A ball-on-ring fixture was used to obtain the TRS and Weibull parameters of over 30 pellets for CeO2 and 0.1 wt % TDC to compare fracture behavior. The TRS of CeO2 pellets ranged from 88 to 160 MPa and the TRS of 0.1 wt % TDC pellets ranged from 102 to 171 MPa, both being consistent with published values. Weibull parameters, such as characteristic strength and Weibull modulus, were extracted as 129 MPa and 8.5 for CeO2 and 150 MPa and 9.3 for 0.1 wt % TDC, respectively. Although Hertzian contact damage was observed on compressive surfaces, failure initiation occurred on the tensile surfaces of both types of samples. Fracture surface analysis for CeO2 indicated a predominantly intergranular fracture while 0.1 wt % TDC had a predominantly transgranular fracture mode. The TRS of 0.1 wt % TDC resulted in increased Weibull parameters when compared to CeO2, indicating sample chemistry and microstructure impact mechanical behavior for these samples.

Unsteady flow characteristics in an over-under TBCC inlet during mode transition under unthrottled and throttled conditions

The study presents an experimental exploration into the mode transition of an over-under TBCC (Turbine-Based Combined Cycle) inlet, with a specific emphasis on the flow characteristics at off-design transition Mach number. A systematic investigation was undertaken into the mode transition characteristics in both unthrottled and throttled conditions within a high-speed duct, employing high speed Schlieren and dynamic pressure acquisition systems. The results show that the high-speed duct faced flow oscillations primarily dictated by the separation bubble near the duct entrance during the downward rotation of splitter, leading to the duct’s unstart under the unthrottled condition. During the splitter’s reverse rotation, a notable hysteresis of unstart/restart of the high-speed duct was observed. Conversely, hysteresis vanishes when the initial flowfield nears the critical state owing to downstream throttling. Moreover, the oscillatory diversity, a distinctive characteristic of the high-speed duct, was firstly observed during the mode transition induced by throttling. The flow evolution was divided into four stages: an initial instability stage characterized by low-frequency oscillations below 255 Hz induced by shock train self-excitation oscillation and high-frequency oscillations around 1367 Hz caused by the movement of separation bubble. This stage is succeeded by the “big buzz” phase, comprised of pressure accumulation/release within the overflow-free duct and shock motion outside the duct to retain dynamic flow balance. The dominant frequency escalated with the increase of the internal contraction ratio in the range of 280 Hz to 400 Hz. This was followed by a high-frequency oscillation stage around 453 Hz dominated by a large internal contraction ratio with low pulsating energy, accompanied by a continuous supersonic overflow. Lastly, as the splitter gradually intersected the boundary layer of the first-stage compression surface, the capture area and the turbulence intensity of the incoming flow underwent a sudden shift, leading to a more diverse flow oscillation within the duct, manifested as various forms of mixed buzz.

Effect of E-glass fibers addition on compressive strength, flexural strength, hardness, and solubility of glass ionomer based cement

BackgroundIn dentistry, glass-ionomer cements (GICs) are extensively used for a range of applications. The unique properties of GIC include fluoride ion release and recharge, chemical bonding to the tooth’s hard tissues, biocompatibility, a thermal expansion coefficient like that of enamel and dentin, and acceptable aesthetics. Their high solubility and poor mechanical qualities are among their limitations. E-glass fibers are generally utilized to reinforce the polymer matrix and are identified by their higher silica content.ObjectivesThe purpose of the study was to assess the impact of adding (10 wt% and 20 wt%) silane-treated E-glass fibers to traditional GIC on its mechanical properties (compressive strength, flexural strength, and surface hardness) and solubility.MethodsThe characterization of the E-glass fiber fillers was achieved by XRF, SEM, and PSD. The specimens were prepared by adding the E-glass fiber fillers to the traditional GIC at 10% and 20% by weight, forming two innovative groups, and compared with the unmodified GIC (control group). The physical properties (film thickness and initial setting time) were examined to confirm operability after mixing. The evaluation of the reinforced GIC was performed by assessing the compressive strength, flexural strength, hardness, and solubility (n = 10 specimens per test). A one-way ANOVA and Tukey tests were performed for statistical analysis (p ≤ 0.05).ResultsThe traditional GIC showed the least compressive strength, flexural strength, hardness, and highest solubility. While the GIC reinforced with 20 wt% E-glass fibers showed the highest compressive strength, flexural strength, hardness, and least solubility. Meanwhile, GIC reinforced with 10 wt% showed intermediate results (P ≤ 0.05).ConclusionUsing 20 wt% E-glass fiber as a filler with the traditional GIC provides a strengthening effect and reduced solubility.

Microstructure and performances of rigid polyurethane foam prepared using double‐effect baking powder as a foaming agent

AbstractThe preparation of rigid polyurethane foam with uniform pore size is extremely challenging. In this work, double‐effect baking powder was used as foaming agent, and rigid polyurethane foam with regular morphology was successfully prepared through semi‐prepolymerization. The rigid polyurethane foam apertures with regular morphology were controlled by the secondary release of CO2 when the content of baking powder is 0.30 part. Combined with theoretical calculation and experimental test, it is found that the particle size distribution, wall thickness, and hole shape are uniform, regular, thin, polygonal, and few broken holes. The compression strength, contact angle, and surface energy of the rigid polyurethane foam are 33.36 kPa, 109.6°, and 21.8 mJ/m2 after adding 0.20 part of double‐effect baking powder, respectively. By adjusting the amount of double‐acting baking powder, the porosity, mechanical properties and foam rate of the polyurethane foams could be significantly improved. Due to the molecular solvation effect, rigid polyurethane foams will deform in the water and oil due phase, but it can remain stable for a long time at room temperature without solvent. It provides a new method for the preparation of rigid polyurethane foam, which is expected to be widely used in transportation and other fields.Highlights Baking powder was firstly used as a foaming modifier for rigid polyurethane. Baking powder releases CO2 twice to ensure uniform structure of polyurethane cell. Rigid polyurethane foam has long‐term stability and regular, uniform cell holes. The porosity and mechanical properties of foams could be significantly improved. Foaming mechanism of rigid polyurethane using baking powder was firstly revealed.

Influence of Yarn and Fabric Properties on Mechanical Behavior of Polymer Materials and Its Retention over Time.

The mechanical properties of textile materials play a crucial role in determining their comfort, functionality, performance, safety, and aesthetics. Understanding and optimizing these properties is essential to meet consumer demands. Key aspects of mechanical properties, such as surface roughness, abrasion resistance, and compression, have a significant impact on the touch and durability of the material, as demonstrated by various research studies. This study focuses on analyzing the mechanical properties of materials produced of different polymer yarns and their changes under combined aging factors. The findings emphasize the significance of textile abrasion resistance and surface roughness measurement, particularly for aged materials. Although the use of recycled polyester yarn is sustainable and offers advantages such as higher tensile strength, the results have shown that the use of conventional polyester yarn is more advantageous overall as it has higher abrasion resistance, a smoother surface texture, and better elasticity retention after aging. The insights presented are vital for designing high-performance sportswear, which is crucial in today's competitive environment.

Characterization of hygrothermal, gas pressure and stress characteristics for poplar wood during unilateral surface densification

Unilateral surface compression in wood presents notable benefits, including reduced wood volume loss and energy consumption, rendering a highly promising and extensive utilization. However, shortcomings in compressed wood arise due to unclear gas pressure, temperature, and moisture content distribution within the wood during hot pressing. In this paper, the temperature and pressure distribution were analyzed utilizing an optical fiber temperature and pressure measurement system within the wood during hot pressing. Moreover, the moisture content, stress and strain in each layer at the end of hot pressing were discussed extensively. The results showed that the wood surface layer (SL) and subsurface layer (SSL) maximum temperature values were similar even with different layer thicknesses. Under sealing conditions, SL and SSL temperatures were generally 6 ℃ to 7 ℃ higher compared to unsealing conditions. The gas pressure maximum value exhibited an opposite order, gradually transferring to the core layer (CL) and declining as the processing time extended. During compression treatment, moisture migrated from the hot end to the cold within the wood. The moisture content displayed significant differences between the middle and end parts of the wood under unsealed conditions, with the disparity becoming more pronounced further away from the hot end. The transition region of the compressed wood served as a stress concentration area, experiencing the highest levels of stress. The dense region followed with the second highest stress levels, while the un-densified region exhibited the least amount of stress. Under the same process parameters, the thickness had little influence on the distribution of dense layers.

Extended discharge time of ready-mixed concrete: Myth or necessity?

A significant volume of pre-mixed concrete is frequently sent back to batching plants for disposal due to various factors such as excessive slump loss during transportation, overproduction, and experimentation with new batches. It is estimated that approximately 3 % of the total concrete production becomes waste. Rejecting numerous truckloads of concrete is typically based on strict adherence to the concrete discharge 90-minute time limit. This study investigates the effects of extending the discharge time on the properties of fresh and hardened ready-mixed concrete, as well as its durability. To emulate typical field construction conditions, we formulated representative concrete mixtures and sourced, batched, and poured them from a local ready-mix concrete supplier. To maintain the concrete's workability without altering the mix design, high-range water reducer (retarder or stabilizer), and air-entrainment admixtures were incorporated as needed. The fresh and hardened concrete properties were evaluated at batching and at time intervals of 60, 90, 120, and 150 minutes for three different concrete mixtures. Fresh concrete properties included air content, slump, and temperature, while hardened concrete properties encompassed compressive strength, freeze-thaw resistance, and surface resistivity. Remarkably, the discharge time had no significant impact on the fresh and hardened concrete properties even up to 150 minutes. This indicates that the strict discharge time limit is overly cautious. Embracing an extended discharge time offers numerous economic and sustainable advantages.

Fatigue and failure mode analyses of glass infiltrated 5Y-PSZ bonded onto dentin analogues

The purpose of this study was to evaluate the fatigue survival of 5Y-PSZ zirconia infiltrated with an experimental glass and bonded onto dentin analogues. Disc-shaped specimens of a 5Y-PSZ (Katana UTML Kuraray Noritake) were cemented onto dentin analogs (NEMA G10) and divided into four groups (n = 15): Zctrl Group (control, without infiltration); Zglz Group (Glaze, compression surface); Zinf-comp Group (Experimental Glass, compression surface); Zinf-tens Group (Experimental Glass, tension surface). Surface treatments were varied. Cyclic fatigue loading, oblique transillumination, stereomicroscope examination, and scanning electron microscopy were performed. Fatigue data were analyzed (failure load and number of cycles) using survival analysis (Kaplan–Meier and Log-Rank Mantel–Cox). There was no statistically significant difference in fatigue survival between the Zglz, Zctrl, and Zinf-comp groups. The Zinf-tens group presented a significantly higher failure load when compared to the other groups and exhibited a different failure mode. The experimental glass effectively infiltrated the zirconia, enhancing structural reliability, altering the failure mode, and improving load-bearing capacity over more cycles, particularly in the group where the glass was infiltrated into the tensile surface of the zirconia. Glass infiltration into 5Y-PSZ zirconia significantly enhanced structural reliability and the ability to withstand loads over an increased number of cycles. This approach has the potential to increase the durability of zirconia restorations, reducing the need for replacements and save time and resources, promoting efficiency in clinical practice.

Probing the microstructure and deformation mechanism of an FeCoCrNiAl0.5 high entropy alloy during nanoscratching: a combined atomistic and physical model study.

High entropy alloys (HEAs) exhibit superior mechanical properties. However, the nanoscratching properties and deformation behaviour of FeCoCrNiAl0.5 HEAs remain unknown at the nanoscale. Here, we investigate the effect of scratching depth on the microstructural and tribological characteristics of an FeCoCrNiAl0.5 HEA using molecular dynamics simulations combined with a physical model. The scratching force increases significantly as the scratching depth increases. In the lower part of the scratching region, there is a clear atomic movement process, with the load generated in the normal direction causing the atoms to shift downwards. Noticeable shear bands are formed in the subsurface area, and they are both small and narrow compared with the pure Ni. The plastic deformation mechanism of the compressed surface is mainly governed by the formation and expansion of stacking faults during the subsurface evolution process. The evolution process of screw dislocations is similar to that of edge dislocations. In addition, the high strength and deformation resistance of FeCoCrNiAl0.5 HEAs are further evaluated by establishing a microstructure-based physical model. The combined effect of the lattice distortion strengthening and dislocation strengthening promotes the high strength of the FeCoCrNiAl0.5 HEA, which is significantly better than the single strengthening mechanism of pure metals. These results accelerate the understanding of the mechanical properties and deformation mechanisms of HEAs.

Transient Nucleate Boiling and Its Use for Thermomechanical Technologies Development

In the paper high temperature and low temperature intensive thermomechanical treatment is discussed. It is based on recently discovered new three physical principles that belong to the transient nucleate boiling process taking place in cold fluids. Such processes are considered in conditions when any film boiling during quenching in cold fluids is completely absent. That makes nucleate boiling very intensive, i.e. . The discoveries are used for direct quenching articles after forgings. The first is intensive high-temperature thermo-mechanical treatment (HTTMT). It is used for low and middle-carbon alloy steels. Forged steel parts are intensively quenched with a cooling interruption at the proper time to form surface compression residual stresses and fine bainitic microstructure at the core that increases radically surface life of forgings. The second method includes high-temperature and low temperature intensive thermo - mechanical treatment (LTTMT) of high carbon alloy steels with delaying martensitic transformation to make low-temperature thermo - mechanical treatment (LTTMT) possible. Then, after high temperature and low-temperature thermomechanical treatment, the steel goes to immediate tempering to create highly strengthened fine bainitic microstructure throughout the section of the steel part. A modified method of cooling time calculation, suitable for any size and form of steel part, is widely discussed in this paper.

Hydrogen charging can relax compressive residual stresses caused by shot peening

Surface engineering to generate compressive stresses via processes such as shot peening is commonly employed to mitigate fracture or fatigue failures in metallic systems. Localized plastic deformation is used to generate the generally biaxial compressive elastic stresses. This study examined the residual stress conditions and local mechanical performance of medium carbon steel in a quenched and tempered state. Electrolytic hydrogen charging of peened samples led to a permanent reduction in the compressive surface stress while concurrently hardening the surface. Slight changes in elastic modulus when solute hydrogen was present could not explain the resulting change in the measured residual stress; a reduction in X-ray peak breadth suggests that the combined effects of elastic stresses and solute hydrogen caused local dislocation annihilation and re-organization of the dislocation structure in the severe plastically deformed layer, leading to a lower magnitude and shallower depth of compressive residual stress on the peened surface after hydrogen charging.

A Hydration-Based Integrated Model to Evaluate Properties Development and Sustainability of Oyster Shell Powder–Cement Binary Composites

Currently, oyster shell powder (OSP) is becoming more widely used in the production of cement-based materials. The purpose of this study is to propose a predictive model that can predict the properties of concrete materials incorporating oyster shell powder. The methods of this prediction model are given as follows. First, based on the measurement results of the heat of hydration in the first 7 days, the prediction parameters of the hydration model are obtained. Secondly, based on the hydration model, the measured results of the heat of hydration were extrapolated, and the heat of hydration from the start of stirring to day 28 was calculated. From the calculation results, the developments of compressive strength, ultrasonic velocity, and surface electrical resistivity were estimated. Finally, we evaluated the CO2 emissions of concrete incorporating oyster shell powder. The CO2 emissions corresponding to unit compressive strength and unit surface electrical resistivity were calculated. The important conclusions of the prediction model are given as follows. First, for different substitution amounts of oyster shell powder, the model result shows that the ultimate value of the heat of hydration corresponding to the unit cement mass is the same, i.e., 454.27 J/g. While the substitution amount of oyster shell powder increases from 0% to 30%, the model result shows that the cumulative 28-day hydration heat for 1 g cement increases the powder amount from 405.7 J/g to 419.3 J/g. Secondly, as the amount of substituted oyster shell powder increases from 0% to 30%, the model result shows that the cumulative 28-day heat of hydration per gram of cementitious material decreases this amount from 405.7 J/g to 293.4 J/g. Compressive strength, ultrasonic pulse velocity, and surface electrical resistivity can all be expressed as exponential functions of the heat of hydration. For compressive strength, ultrasonic pulse velocity, and surface electrical resistivity, the coefficients of determination for the simulation results and experimental results are 0.8396, 0.7195, and 0.9408, respectively. Finally, as the amount of substituted oyster shell powder increases from 0% to 30%, the model result shows that the CO2 emission per unit of compressive strength increases from 10.18 kg/MPa to 16.51 kg/MPa. As the amount increases from 0% to 30%, the model result shows that the CO2 emission corresponding to the unit surface electrical resistivity does not change significantly. In summary, the importance of this model is that it can predict various properties of concrete mixed with oyster shell powder, reduce the number of experiments, and promote the engineering application of oyster shell powder concrete.

Evaluation of Tactile and Thermophysiological Comfort in Reusable Surgical Gowns Compared to Disposable Gowns

Though the transition from disposable to reusable surgical gowns holds substantial promise, successful implementation faces challenges. This study investigated tactile and thermophysiological comfort in surgical reusable gowns, comparing them with their disposable counterparts. Parameters such as surface roughness, compression, heat flux, and material rigidity were tested using a Fabric Touch Tester. Additionally, the water vapour permeability and static charge of the gowns were assessed. Thermophysiological comfort of the gowns was evaluated by measuring the temperature and relative humidity (RH) on test subjects during wear trials where they were engaged in an activity that mimics a surgeon’s performance. Skin temperature was monitored using iButton sensors and a thermal camera, and the impact on heart rate during the task was analysed. Following each test, participants provided subjective feedback through a questionnaire. The results indicated that reusable gowns boasted a smoother texture, translating to reduced friction on the skin and better heat transfer compared to the disposable fabrics, as indicated using FTT. They also exhibited higher water vapour permeability compared to their disposable counterparts. The wear trials revealed minimal differences in comfort between disposable and reusable gowns. While performing the activity, an increase in body temperature led to decreased RH, yet this rise did not adversely affect subject comfort, as validated using heart rate and questionnaire survey data. From a comfort point of view, switching from disposable to reusable gowns would not have drawbacks, meaning hospitals should be able to switch provided logistics and costs can be managed.

Surface activity of Lupinus angustifolius (blue lupine) seed extracts

Surface tension (γeq) of the seed extracts of four lupine cultivars showed values in the range 44.9–46.4 mN/m. The surface compression elasticity (E') of the adsorbed layers and foaming capacity (FC) also showed similar values (E' ∼ 30 mN/m, FC ∼ 100%). The effect of defatting prior to extraction at pH 8.5 depends on the solvent employed – hexane and dichloromethane improved the subsequent protein extraction yield, while ethanol reduced it. The effect of defatting on surface tension could be positive (for hexane and ethanol) or negative (for dichloromethane). Generally, defatting improved the surface compression rheological and foaming parameters. On the other hand, fractionation of the extracts obtained at pH 8.5 from hexane-defatted seeds did not improve significantly the surface activity parameters. Some improvement with respect to the unfractionated extracts was observed only for the extracts of undefatted seeds. γeq, E', E" and FC isotherms confirm the surfactant-like behavior of the lupine seed extracts.

Composite effects of residual stress and hardness gradient on contact fatigue performance of rough tooth surfaces and optimization design of detailed characteristic parameters

Residual stress and hardness gradient significantly affect the contact fatigue failure process of rough tooth surfaces, and the meticulous design of their characteristic parameters can help improve the fatigue resistance of gears. In this paper, an efficient computational method for rough tooth surface contact is established based on the reconstruction modeling of asperities and mixed lubrication analysis. By comprehensively considering the effects of residual stress and hardness gradient, the Dangvan multiaxial fatigue criterion is adopted to predict and analyze the contact fatigue life of the gear surface. The correlation between the surface residual stress, maximum residual stress depth, surface hardness, and effective hardening layer depth, among other characteristic parameters, and the contact fatigue performance of tooth surfaces is established. The results show that: (1) Increasing the magnitude of surface residual compressive stress and surface hardness can significantly reduce the risk of fatigue failure in the near-surface layer of the gear. To achieve the same fatigue performance, there is a linear negative correlation between the design values of the two parameters. (2) Affected by the double stress peaks in the rough tooth surface stress field, the maximum residual stress depth significantly affects the depth at which the highest failure risk occurs. With changes in roughness, the optimal design value of the maximum residual compressive stress depth changes from about 0.5 times the Hertzian contact half-width depth in the subsurface layer (Sa < 0.2 μm) to about 15 μm in the near-surface layer (Sa > 0.4 μm). (3) Considering both process cost and gear surface fatigue resistance, the design threshold for the effective hardening layer depth should be greater than the Hertzian contact half-width. This paper establishes a composite correlation between the meticulous characteristic parameters of residual stress, hardness gradient, and the contact fatigue performance of tooth surfaces, providing theoretical support for optimal design of tooth surface anti-fatigue performance.

The effect of shot peening on the contact fatigue performance of C40 steel gears after laser surface melting

In this paper, shot peening (SP) was employed as a post-processing technique for the laser surface melted (LSMed) gear. The aim was to improve the contact fatigue performance of laser surface melting+shot peened (LSMSPed) gears. The microstructure, surface roughness, residual stress, microhardness of C40 steel gears before and after SP treatment were characterized using scanning electron microscopy, x-ray diffraction stress analyzer, contour measuring instrument, and hardness tester. Fatigue test of gear was carried out with a Forschungsstelle für Zahnräder und Getriebebau (FZG) testing machine. Following the laser surface melting (LSM) treatment, a molten layer was observed on the gear teeth surface. The experimental results indicated that SP induced a hardened layer with a certain thickness and plastic deformation on the surface of LSMed gears. Importantly, as the SP parameters increased, there’s a corresponding reduction in both the average grain diameter and the maximum grain diameter. The reduction was most pronounced when the shot diameter reached its maximum value. It’s worth noting that once the optimal threshold for SP parameters is surpassed, the residual compressive stress and microhardness on the LSMSPed gear surface do not exhibit a continuous growth trend. Furthermore, the rise in SP parameters resulted in a gradual increase in the surface roughness of LSMSPed gears, albeit to varying degrees. In light of the combined effects of grain refinement, residual compressive stress, microhardness, and surface roughness, the contact fatigue performance of LSMSPed gears improved with increasing SP parameters. Notably, when comparing the contact fatigue life of LSMed gears with that of LSMSPed gears, we observed a substantial enhancement. However, it’s essential to highlight that when the shot diameter reaches its maximum value, the contact fatigue life of the LSMSPed gear, somewhat unexpectedly, decreased. It emphasized to a certain extent the influence of surface roughness on the contact fatigue performance of LSMSP gears.