Roughness Grooves Research Articles

Pull-out behavior of cluster stud-post pouring UHPC connectors in prefabricated steel-concrete composite beam

The use of ultra-high performance concrete (UHPC) as a connection material for cluster studs of prefabricated steel-concrete composite beams can achieve higher connection strength and less space for reserved holes. However, in addition to bearing the shear force, the studs need to bear the pull-out force to counteract the vertical relative separation between the steel and concrete. The pull-out behavior for cluster stud-post pouring UHPC connectors is complex and has not been clarified completely. Thus, a total of 30 cluster stud pull-out tests in 10 groups were carried out in this study, and the interface type, length-to-diameter ratio of the stud, transverse spacing of stud group, dimensions of the reserved holes, and type of post pouring concrete were considered. The results showed that the pull-out behavior of the cluster studs was different from that of studs embedded in cast-in-place intact UHPC slabs due to the UHPC conical integrity having been reduced significantly by the old-to-new concrete interface. The rough groove interface and UHPC as a post pouring material significantly improved the pull-out capacity and stiffness of the cluster studs. The stud fracture belongs to ductile failure, whereas UHPC and normal concrete (NC) cone failures are brittle. The bearing capacity of the UHPC cone is observed to increase with the effective embedment depth of the stud, the transverse spacing, and the dimensions of the reserved holes. The angle of the UHPC conical failure surface is 70° based on 3D laser scanning. Finally, the theoretical equations for predicting the pull-out capacity of stud-post pouring UHPC connectors with a rough groove interface were proposed, and the critical length-to-diameter ratio of the stud was calculated for different combinations of stud and UHPC strength.

Enhanced hydrogen adsorption capability of 2:17-type Sm-Co strips via microstructure modification

The hydrogenation kinetics of Sm26.2CobalFexCu4.0Zr2.3 (x = 23, 27 in wt%) strips (Fe23 and Fe27 strips) has been investigated. The phase composition, morphology, surface roughness and the inner pores of the strips also have been studied by XRD, SEM, optical profilometer and non-destructive micro-computerized tomography. Compared to Fe23 and Fe27 strips, heat-treated strips (H-Fe23 and H-Fe27) and corrosion heat-treated strips (HC-Fe23 and HC-Fe27) exhibit a relatively higher hydrogen absorption capability. Fragmentation behavior occurs in HC-Fe23, H-Fe27 and HC-Fe27 strips during hydrogenation. After heat treatment, the grain size and inner pore size increase, leading to the disappearance of fine crystal strengthening and the concentration internal stress. For corrosion-treated strips, increased surface roughness and deeper grooves result in the formation of surface stress concentration, ultimately leading to an increased susceptibility to hydrogen embrittlement. Accordingly, the increase of grain size, inner pore size and rougher surface is beneficial for hydrogenation and hydrogen embrittlement.

Gradient-Pattern Micro-Grooved Wicks Fabricated by the Ultraviolet Nanosecond Laser Method and Their Enhanced Capillary Performance.

Capillary-gradient wicks can achieve fast or directional liquid transport, but they face fabrication challenges by traditional methods in terms of precise patterns. Laser processing is a potential solution due to its high pattern accuracy, but there are a few studies on laser-processed capillary-gradient wicks. In this paper, capillary step-gradient micro-grooved wicks (CSMWs) were fabricated by an ultraviolet nanosecond pulsed laser, and their capillary performance was studied experimentally. The CSMWs could be divided into three regions with a decreasing capillary radius. The equilibrium rising height of the CSMWs was enhanced by 124% compared to the non-gradient parallel wick. Different from the classical Lucas-Washburn model describing a uniform non-gradient wick, secondary capillary acceleration was observed in the negative gradient direction of the CSMWs. With the increase in laser power and the decrease in scanning speed, the capillary performance was promoted, and the optimal laser processing parameters were 4 W-10 mm/s. The laser-enhanced capillary performance was attributed to the improved hydrophilicity and reduced capillary radius, which resulted from the increased surface roughness, protrusion morphology, and deep-narrow V-shaped grooves induced by the high energy density of the laser. Our study demonstrates that ultraviolet pulsed laser processing is a highly efficient and low-cost method for fabricating high-performance capillary gradient wicks.

External gas-assisted mold temperature control and optimization molding parameters for improving weld line strength in polyamide plastics.

In this study, we present a novel approach to injection molding, focusing on the strength of weld lines in polyamide 6 (PA6) composite samples. By implementing a mold temperature significantly higher than the typical molding practice, which rarely exceeds 100°C, we assess the effects of advanced mold temperature management. The research introduces a newly engineered mold structure specifically designed for localized mold heating, distinguishing it as the 'novel cavity.' This innovative design is compared against traditional molding methods to highlight the improvements in weld line strength at elevated mold temperatures. To optimize the molding parameters, we apply an Artificial Neural Network (ANN) in conjunction with a Genetic Algorithm (GA). Our findings reveal that the optimal ultimate tensile strength (UTS) and elongation values are achieved with a filling time of 3.4 seconds, packing time of 0.8 seconds, melt temperature of 246°C, and a novel high mold temperature of 173°C. A specific sample demonstrated the best molding parameters at a filling time of 3.4 seconds, packing time of 0.4 seconds, melt temperature of 244°C, and mold temperature of 173°C, resulting in an elongation value of 582.6% and a UTS of 62.3 MPa. The most influential factor on the PA6 sample's UTS and elongation at the weld line was found to be the melt temperature, while the filling time had the least impact. SEM analysis of the fracture surfaces revealed ductile fractures with rough surfaces and grooves, indicative of the weld line areas' bonding quality. These insights pave the way for significant improvements in injection molding conditions, potentially revolutionizing the manufacturing process by enhancing the structural integrity of the weld lines in molded PA6 samples.

Identifying the features of surface roughness and H2 bubble production on the super-hydrophobic properties of Al2O3 and Mg membranes

This research investigates Alumina (Al2O3) and Magnesium nano membrane layers using hybrid technology. Hybrid is a concept of combining two or more materials/elements to achieve something better. Hybrid technology was developed because of the possibility of combining materials/elements which, if used simultaneously, has more advantages than if used independently. The problem to be solved is to find the best composition of Alumina and Magnesium hybrid membranes. Superhydrophobic properties of the membrane are achieved at a percentage of Mg: 50 %, Al2O3:50 %. At a composition below 50 % Mg, the small surface roughness has a low surface tension, while the H2 production reaction by Mg is also low, so the surface tension carrying capacity of the gas and the roughness of the droplets is not strong, which causes the hydrophobicity to be low. In compositions above 50 % Mg, H2 production by high Mg makes bubbles cover the roughness peaks so that the surface tension is lower and changes the superhydrophobic to hydrophobic properties. At a high Mg percentage, H2 production is very large, while surface roughness decreases due to minimal Al2O3. As a result, the roughness grooves are unable to accommodate H2 gas bubbles, the bubbles completely cover the roughness peaks which are the source of surface tension so that the hydrophobic properties become hydrophilic. The results of this best hybrid composition can be used as a guide in making superhydrophobic membranes on Alumina (Al2O3) and Magnesium alloys. This membrane application is used as a filtration membrane in the water purification process. Superhydrophobic membranes are widely applied in membrane distillation, membrane gas absorption and pervaporation

Micro-grooves machining and optimizing on SiC/SiC composites by femtosecond laser-based on response surface methodology

This study applied femtosecond laser processing technology to prepare microgrooves on the surface of SiC/SiC ceramic matrix composites (CMCs). The corresponding parameter ranges for response surface optimization were determined through single-factor experiments. Additionally, four quadratic regression models were established to predict surface roughness, groove width, groove depth, and volume material removal rate. The Analysis of Variance (ANOVA) revealed that the developed model was reliable. Additionally, the study investigated the effects of laser parameters such as power, scanning speed, and defocusing amount, as well as their interactions, on various outcome measures, including the roughness average (Ra), groove width, groove depth, and volume material removal rate (VRR). To optimize the process parameters, the response surface method was employed to achieve maximum VRR and minimum Ra. After conducting the analysis, the optimal processing parameters were determined to be a laser power of 36 W, a scanning speed of 24 mm/s, and a defocusing amount of −1.17 mm. The developed model accurately predicts groove depth, width, volume material removal rate, and surface roughness in SiC/SiC-CMCs processing. The relative deviations between the actual and expected values fall within the acceptable range, affirming model's reliability. This indicates that the model improves precision in predicting these parameters for SiC/SiC-CMCs processing. The findings of this study have significant implications for improving the processing quality and efficiency of SiC/SiC-CMCs and establishing a relationship between processing parameters and responses. These insights can inform future research efforts to optimize these complex materials' manufacturing processes.

Numerical study of two types of rough groove in suppressing the tip clearance cavitation

Tip clearance cavitation (TCC) which is consisted of tip leakage vortex (TLV) cavitation and gap cavitation (occurs inside the gap region) is a common phenomenon in the gap flow filed in axial turbomachinery, and can trigger a series of negative effects. Based on the suppression mechanism of a type of prototypical horizontal casing groove, two types of rough groove structures are proposed in this paper aiming at enhancing the suppression effect on the TCC by utilizing the Coanda effect of the gap leakage jet. The gap flow field is generated via a NACA0009 hydrofoil and a solid wall. The gap size is fixed as 2 mm. The numerical simulation method is adopted. The results show that combining the detached-eddy simulation (DES) approach, SchnerrSauer cavitation model and a type of varRhoTurbVOF method on the OpenFOAM platform, accurate numerical results of cavitating gap flow fields under the small gap conditions can be obtained. The gap flow field analysis reveals that the control ability of the grooves on the leakage flow is enhanced via divergent–convergent flow passage in the roughness groove cases. The leakage rate is reduced while the local turbulence intensity is increased, which weakens the TLV and the tip separation vortex (TSV) dramatically. The rough casing grooves show a superior suppression effect on the TCC. The present work can inspire new casing treatment method for improving the anti-cavitation performance in the axial-flow hydraulic machinery.

Ultrashort Laser Texturing of Superelastic NiTi: Effect of Laser Power and Scanning Speed on Surface Morphology, Composition and Wettability

Among metallic biomaterials, near-equiatomic NiTi is one of the most promising intermetallic system applicable for biomedical applications, thanks to its high biocompatibility and unique superelasticity (or pseudoelasticity), offering a complete recoverable strain up to 8%. In the prospective uses for bio-devices, the surface processing of NiTi medical components plays a fundamental role for guaranteeing both a Ti oxide passivizing layer for avoiding Ni ion release into the human body and surface morphology for controlling the cell proliferation. Mechanical polishing, thermal, chemical or electro-chemical treatments are typically performed for surface modifications. Recently, laser texturing has been successfully applied for different materials, included NiTi shape memory alloys, and also for tuning the surface properties, such as wettability. In the present work, ultrashort laser surface modification was carried out, through the use of a femtosecond laser, for the surface texturing of commercial superelastic NiTi plates. The main goal is to investigate the correlation among morphology, chemical composition and wettability with the principal process parameters, such as average power and scanning velocity in high power ultrashort laser texturing. Laser patterned surfaces were characterized by means of scanning electron microscopy, 3D-profilometry, XPS analysis and wetting measurements. After the laser treatments, both surface morphology and Ni/Ti ratio were largely modified from the initial surface, depending on the adopted process parameters. The wettability of the laser textured surfaces can be also varied with respect to the initial surface, due to the roughness values and grooves induced by the laser beam scans. The laser texturing process induced a combination between micro and nano structures, depending on the input energy. In details, the surfaces were tuned to lower roughness values (from 0.4 μm to 0.3 μm) with a laser power of 1 W, while it was increased up to 0.65 μm with a laser power of 13 W. The laser surface modification promoted a change of the contact angle from 70° of the untreated condition up to 135° to the surface laser treated with a power of 13 W.

Dry sliding wear behavior of aluminum alloy 6082 - SiC composites through ex-situ casting process

The applications of AA6082 alloys in the structural and transport are found to be more due its light weight. To improve strength to weight ratio and stress resistance, the carbides/oxides are added and this will leads to improvement in the mechanical properties and high stress sustainability. In this research work, AA6082 Metal Matrix Composite (MMC) is manufactured through the ex-situ casting process with the Silicon Carbide (SiC) reinforcements of 2.5 & 5 wt% and the microstructure evolution, hardness, dry sliding wear behavior and tensile properties of MMCs are investigated. As-cast AA6082 showed the dendritic microstructure with intermetallic eutectics. The presence of SiC particulates in AA6082 resulted in decreased grain size and equixed grains. The hardness of the tested as casted AA6082 samples was found to be 81 HV which has been increased to 93 HV and 107 HV and the tensile strength of AA6082 is increased by 16% and 41% by addition of 2.5 wt% SiC and 5 wt%SiC respectively due to the presence of the SiC particulates. At the same time coefficient of friction of AA6082 is found to be decreased by 11.8% and 20.5% for the testing load of 10N and the corresponding decrease in wear rates were found to be 50.8% and 70.3% respectively. The worn surface showed the continuous groove parallel to sliding direction with short cracks, bidirectional rough grooves with peeled-off SiC, unidirectional smooth scratches along the sliding surfaces for as-cast AA6082, AA6082-2.5 wt SiC and AA6082-5 wt SiC respectively that indicates the significant effects of SiC particulates on wear mechanism.

Plastron replenishment on superhydrophobic surfaces using bubble injection

While the air lubrication by bubble injection and superhydrophobic (SHPo) surfaces have been investigated vigorously for flow control, for example, underwater drag reduction, further advancement seems to be delayed. For the former, large air flow rate is required for the meaningful performance, and furthermore, the injected bubbles do not stay over the surface willingly. Depletion (diffusion) of the trapped air pockets on the SHPo surface is a critical issue for the latter. In the present water-tunnel experiments, we show that the above-mentioned challenges can be successfully overcome by combining the two methods; that is, the plastron on SHPo surfaces can be replenished in turbulent flows with a very small amount of air, even after the surface is fully wetted. To analyze the phenomena, the bubble–plastron interaction is visualized and quantified while introducing bubbles over the SHPo surfaces (with random roughness or longitudinal grooves) in the turbulent boundary layer flow of ReL=0.3−1.1×106. The plastron on SHPo surfaces with longitudinal grooves is retained in a film-like shape with a quite smaller amount of air than that with random roughness. By quantifying the light intensity from the surface, we suggest a scaling relation between the effective plastron thickness and surface light intensity, which would serve as a criterion for the successful plastron replenishment. Finally, the morphology of the plastron is classified into different regimes, depending on the Reynolds number, air flow rate, and surface roughness types.

Bending Performance of Epoxy Adhesive Joints of Prefabricated Concrete Elements

The assembly construction of prefabricated UHPC elements can well balance quality reliability and construction convenience, thus it has excellent application prospects in bridge engineering. The joints between prefabricated elements are the key to ensuring the overall force performance of the structure, which directly determine the load-bearing capacity and the life of structure. To clarify the bending behavior of epoxy adhesive joints between prefabricated UHPC elements, four groups of 12 bending tests were carried out with different interface treatment forms as parameters. The failure modes, load-deflection curves, and ultimate bending strength of the interface were investigated. The results reveal that the interfacial failure modes mainly include the interfacial stripping failure of epoxy-UHPC surface, steel fibers and fine aggregates into UHPC surface by pulling out, and tensile damage of UHPC at the root of key teeth on the side of the keyway interface. The load-deflection curves of all specimens exhibit the two-fold lines form. The load tends to rise linearly during the loading phase, and there is no yielding phase before the failure. The load-carrying capacity of the specimen is lost immediately after the failure, and no reliable residual strength is available except for the keyway interface. In addition, the bending strength of rough interface, groove interface, and keyway interface are respectively improved by −24.02, 2.34, and 4.64%, compared with the natural interface. So it is recommended that the joint between prefabricated UHPC elements take the form of keyway interface. Finally, a simplified force model of the keytooth adhesive joint is proposed, and a calculation formula for the flexural bearing capacity is established based on the principal of Mohr’s circle, based on the experimental results and theoretical analysis. The mean ratio of the proposed adhesive joint calculation equation to the experimental results was 0.925 with a standard deviation of 0.065.

Laser Processing of Polymers for Surface Energy Control of Biomedical Implants

Poly (etheretherketone) (PEEK) is a high-performance rigid polymer that combines excellent chemical resistance, mechanical strength, and dimensional stability. PEEK is mostly used in the biomedical field for the manufacture of implants. However, the inherently bioinert PEEK surface poses a challenge in terms of adhesion at the implant-tissue interface. Effective enhancement of the adhesive properties of PEEK can be achieved by modifications of surface wettability and free energy. Although many studies investigate the influence of laser parameters on wettability and topography of PEEK, there is scarce information in literature on surface treatment with CO2 laser of neat PEEK. Furthermore, there is no detailed literature report on impact of various laser parameters on the biomechanical properties of PEEK relevant for implants. Therefore, this work focuses on enhancing surface functionality of PEEK through surface energy control. Samples treated at various laser power, fluence, beam pitch and number of passes were characterized with 3D profilometry, Rockwell hardness test, compression tests and contact-angle measurements. Generally, CO2 laser treatment of PEEK did not result in unfavorable changes in its bulk mechanical properties, namely, yield strength and elastic modulus only above the ablation threshold. At a fluence of 14 J/cm2, a significant reduction in hardness (98.03 HRM) was recorded with a single-pass processing. A positive correlation was observed between roughness parameters, groove geometries and laser fluence. More intense surface changes were achieved via ablative mechanism with single-pass processes at a lower total fluence in comparison to double-pass ones. Overall, all increases in roughness resulting from non-ablative processes led to improved wettability.

The unrecognized importance of roughness directionality to polymer wear

Effects of various counterface roughness components (i.e., magnitude, density, direction) on polymer wear and transfer film are strongly coupled and difficult to isolate and test. Previous works found counterface roughness grooves and ridges perpendicular to the direction of sliding were generally beneficial to debris retention and tribofilm formation, but the effect was competing with a decrease in debris retention caused by in-situ generated furrows parallel to the direction of sliding. To further study the effect of roughness directionality on polymer wear, a model polymer solid lubricant (5 wt% Al2O3-PTFE) was slid against counterfaces with laser-textured grooves parallel to the direction of reciprocated sliding and a 2 × 3 variable matrix of groove depth and density. The results found: (1) all textures yielded higher polymer wear than the untextured surface did, (2) counterface with the deepest, densest grooves had the highest polymer wear rate and transient wear volume (wear volume during run-in sliding), (3) shallow groove textures generally produced less wear of the counterface and polymer, stronger tribofilm IR signature and more continuous and complete tribofilms than deep groove textures did. A new roughness parameter (IRa) was defined as a single, unified and comprehensive metric for counterface roughness directionality. By comparing with a previous study, the results found a general correlation between IRa and polymer transient wear volume and suggested strong beneficial effects of perpendicular grooves on debris retention and parallel grooves on debris ejection. A simple framework was postulated to illustrate the interrelations between texture parameters, roughness directionality and debris mobility. It was further supported by analyzing results of a closely relevant work. Although being strongly limited to the model polymer solid lubricant, this study provides perhaps some useful tools for advancing our understanding of the complex relations between roughness directionality, debris mobility (e.g., ejection, retention) and wear of polymer solid lubricant.

Simultaneous removal of ammonium and phosphate in aqueous solution using Chinese herbal medicine residues: Mechanism and practical performance

Excessive ammonium (NH4+) and phosphate (PO43−) in aquatic environments can cause serious eutrophication. Agricultural waste is an efficient adsorbent for nutrients removal and has good potential for comprehensive utilisation of resources. In this study, two Chinese medicinal herbal residues, Rhizoma Typhonium Gigantei (ZB) and Radix Glycyrrhizae Preparata (ZG), were implemented to simultaneously remove NH4+ and PO43− from water. Parameters such as adsorbent dosage, solution pH, contact time and initial concentration that influenced the adsorption process onto adsorbents, along with removal mechanism and practical performance were investigated. The microstructure of ZB was irregular with numerous spherical particles, while ZG displayed an uneven flaky structure with few rough grooves. The nutrients adsorption was significantly influenced by pH. The maximum adsorption capacity by ZB was 91.84 N mg g−1 and 71.81 P mg g−1. In addition, the maximum adsorption capacity recorded by ZG was 100.86 N mg g−1 and 89.51 P mg g−1 (pH, 8.0; dosage, 0.2 g L−1; initial concentration, 60 mg L−1; and contact time, 180 min, for both the herbal residues). The adsorption of NH4+ and PO43− was well described by the pseudo-second-order and intra-particle diffusion models, respectively. The Langmuir isotherm model is the best fit model for the adsorption equilibrium data, suggesting monolayer adsorption of NH4+ and PO43− by the two adsorbents. In addition, NH4+ was predominantly adsorbed by electrostatic attraction, ion exchange and complexation, whereas PO43− was predominantly adsorbed by intra-particle diffusion and ligand exchange. Practical application analysis demonstrated that ZG could remove and recover more NH4+ and PO43− from swine wastewater than ZB. Therefore, ZG exhibited a more significant potential to simultaneously remove and recover NH4+ and PO43− from wastewater.

Facile and environmentally-friendly fabrication of underwater superaerophobic and superaerophilic metallic surfaces through laser ablation and heat treatment

Underwater superaerophilic and superaerophobic metallic surfaces have gained increasing interest due to their significance in both academic research and industrial applications. However, surface chemical modifications with low-surface-energy reagents are usually demanded to fabricate the underwater superaerophilic metallic surfaces, which would increase production cost, operation difficulty, and environmental risk. In this work, we developed a facile and environmentally-friendly method to fabricate underwater superaerophobic and superaerophilic surfaces on aluminum, H59 brass, 304 stainless steel, and titanium substrates through laser ablation and low-temperature heat treatment. After the laser ablation, the metallic surfaces exhibited underwater superaerophobicity since the great affinity of the surfaces with water makes the gaps of the micro/nano structure be filled with water, which repels the bubbles in water. While, after the heat treatment, the laser ablated metallic surfaces became underwater superaerophilic because the hydrophobic airborne organic compounds adsorbed on the laser ablated metallic surfaces prevent water entering into the roughness grooves and make the gaps of the micro/nano structure be occupied by air, which can absorb the bubbles in water. Additionally, it was demonstrated that such underwater superaerophobic and superaerophilic metallic surfaces can be used to control the passage of the underwater bubbles by combining with fabricating the micro-holes structure.

CHEMICAL MODIFICATION AND CHARACTERIZATION OF CHITOSAN FOR PHARMACEUTICAL APPLICATIONS

Nine crosslinked chitosan derivatives (CLCS) were prepared using three different types of crosslinkers: glutaraldehyde, glyoxal and terephthaldehyde. The prepared CLCS were used to control the acyclovir (ACV) release in order to improve its oral bioavailability. The CLCS were prepared by Schiff based reaction and characterized by means of infrared spectroscopy (FTIR), x-ray diffraction measurements, thermogravimetric inspection, differential scanning calorimetry, and scanning electron microscopy (SEM). Establishment of an imine (C=N) bond was evidenced in FTIR. Compared to raw chitosan, the crosslinked chitosan derivatives showed more amorphous structure and exhibited more water holding capacity that increased with raising the crosslinking percent. In SEM, the CLCS demonstrated areas with rough surfaces and grooves that did not present in the smooth chitosan surface. The difference in swelling degree with varying crosslinker amount was also examined. The crosslinked chitosan displayed less swelling and the degree of swelling decreased with increasing the density of crosslinking agent. The CLCS investigated in controlling the release of acyclovir by being incorporated with ACV in granules formulations. In vitro drug release results exhibited sustained release of ACV affected by the type and percent of crosslinker.

Influence of nanostructure morphology on the heat transfer and flow characteristics in nanochannel

Based on the molecular dynamics principle, the convective heat transfer of the fluid through nanochannel with various rough nanostructure morphologies is investigated. The influences of nanostructure free shear ratio, morphology period and nanostructure depth on the flow and heat transfer characteristics are probed. A comprehensive evaluation on the convective heat transfer in rough nanochannel considering the flow resistance is performed. The result shows that the temperature jump and velocity slip dominate the heat and momentum exchange between the channel wall and fluid. Under the weak wall-fluid interaction, the smaller the nanostructure free shear ratio, the better the heat transfer performance as well as drag reduction characteristic. In contrast, the smaller the nanostructure morphology period, the better the heat transfer performance, the greater the flow resistance. Therefore, the wall rough morphology with small free shear ratio and sparse nanostructures is conducive to heat transfer augmentation and drag reduction jointly. The deeper rough nanostructure groove is unfavorable to reduce the flow resistance. The combination of rough nanostructure morphology and weak wall-fluid interaction is crucial, which will bring about a favorable impact on the heat transfer and flow resistance in nanochannel. Specifically, the nanostructure free shear ratio with ϕa=0.1875 is a favorable rough morphology to obtain optimum heat transfer and drag reduction characteristics in nanochannel.

Stretchable strain sensors with dentate groove structure for enhanced sensing recoverability

Stretchable strain sensors based on conductive polymer composites commonly utilize elastic polymers as the matrix. However, elastic polymers always show strong mechanical hysteresis effect leading to shoulder peak phenomenon and thereby poor recoverability of strain sensors. Herein, we design a stretchable rough filament strain sensor with dentate groove structure to eliminate the shoulder peak phenomenon and improve recoverability. The filament strain sensor is fabricated by the extrusion of poly(styrene-b-ethylene-b-butylene-b-styrene) (SEBS) filament constructing dentate groove structure and the subsequent ultrasonic treatment decorating carbon nanotubes (CNTs) on the surface of the SEBS filament. It is interesting to find that the strain sensing range of rough SEBS/CNTs filaments with dentate groove structure is wider than that of smooth filaments. More importantly, the rough filament strain sensors exhibit significantly enhanced recoverability without shoulder peak during the releasing process while the rough dentate groove structure has minor effects on the mechanical properties of SEBS filaments. The great improvement is ascribed to the uniform distribution of deformation because of the dentate groove structure, which induces reduction of the mechanical hysteresis effect and thereby decreases residual strain. Moreover, the rough filament strain sensors have a favorable integration of good stability, fast response time of 300 ms (0.5% strain is applied with a high strain rate of 500 mm/min) and excellent durability (1976 cycles at the strain of 50%). The rough filament strain sensors can accurately and stably monitor both large and subtle human motions (such as body motion, expression and phonation), showing broad application prospects in wearable devices.

Direct Shear Creep Characteristics and Microstructure of Fiber-Reinforced Soil

Fiber-reinforced soil is an excellent engineering material that has become a focus of research. Most studies focus on the conventional mechanical properties of reinforced soil, such as its tensile, compressive, and shear strength, and rarely study its creep-related mechanical properties. However, when such soil is used as backfill, the creep effect should not be ignored. This study explored the characteristics of creep mechanics in reinforced soil, the fiber-reinforcement mechanism, and the dynamics of microstructures before and after creep tests. Direct shear creep tests were carried out using a direct shear creep tester on soil reinforced with natural palm fibers of equal length (1.5 cm) in different amounts (0%, 0.2%, 0.6%, 1.0%). Microscale tests were carried out on the reinforced soil samples before and after the creep tests by polarized light and scanning electron microscopy. The results show that the fiber reinforcement can restrain the deformation and enhance the long-term strength of soil. However, a nonlinear relationship between the reinforcement effect and fiber content was found, with 0.6% being the optimal content. Palm fibers have rough surfaces, grooves, and independent pore chambers, which increase the effective contact area and interaction with the soil. With increases in fiber content, the fibers interweave to form a nestled network structure, which increases the strength and integrity of the soil. Fiber addition changes the microstructure of the soil pores; the proportion of large pores decreases and that of small pores increases. Under the effect of creep, the pore changes follow the principle of pore homogenization; large pores are destroyed and transformed into small pores, causing the porosity of reinforced soil to decrease faster and be less porous than unreinforced soil. This research can provide technical reference for the engineering application of palm fiber-reinforced soil.

Improvement of corrosion resistance of H59 brass through fabricating superhydrophobic surface using laser ablation and heating treatment

In this work, a superhydrophobic brass surface was fabricated by laser ablation followed by heating treatment, and corrosion resistance of this surface was studied by performing electrochemistry tests. The observed superhydrophobicity arises from the synergistic effect of the micro/nano hierarchical structure produced by the laser ablation and the adsorption of organic compounds from ambient air (mainly the nonpolar C−C/C−H groups) during the heating treatment. The superhydrophobic surface shows better corrosion resistance than polished brass surface because of the additional air film resistance and the decrease in the solid-electrolyte contact area caused by the air pockets trapped in the roughness grooves.