High Friction Research Articles

Effectiveness of Mangifera Indica, Carica Papaya, and Citrus Limon Peels as Bio-Floor Wax for Classroom Use in the Philippines

The Philippines has a tradition of using floor wax to enhance the shine and durability of floors. However, commercial floor wax often contains harmful chemical substances that pose significant health risks. The study evaluated the potential of Mangifera indica, Carica papaya, and Citrus limon as bio-floor wax. Using a quantitative research approach, the research examined the odor, shininess, friction, and water resistance properties of these fruit peels. An antimicrobial sensitivity test was also conducted, and the mango extract had the highest average inhibition zone, while the combined extract had the lowest. The results showed that lemon peels have the highest friction on ceramic tiles, while papaya peels performed best on wood flooring. Mango peels showed the highest shininess on scarlet oak surfaces. The water resistance test showed no significant differences across different tiles. The results showed that the fruit peels could be a viable option for bio-floor wax in Philippine classrooms. Further research is recommended to develop formulations suitable for broader applications and to validate the product’s performance under different environmental conditions.

The Role of Ceramic Materials in Surface Modification of Cutting Tools - A Review Paper

A modification cutting tool is a type of cutting tool that can be altered or adjusted to change its cutting properties. This can include changing the angle or shape of the cutting edge, adjusting the depth of cut, or modifying the material or coating used on the tool. These modifications allow for greater precision and efficiency in cutting operations, particularly in industries for manufacturing and construction different products. Ceramic materials can be used in coatings to provide a variety of benefits, such as corrosion, wear resistance , and thermal insulation. They also offer high hardness, low friction, and chemical stability. Ceramic coatings can be applied to various substrates including metals and ceramic. Modification of cutting tools using nanomaterial deposition is a promising approach to enhance their performance and durability. The process involves depositing one or more layer of nanosized particles onto the surface of the cutting tool, which can improve its mechanical, thermal, and tribological properties. Keywords: Ceramic materials ; coating ;cutting tools; coating process.

Fracture Pre-propping and Temporary Plugging for Formation Damage Control in Deep Naturally Fractured Tight Reservoirs

Summary To address the challenges of formation damage related to drill-in fluid loss into deep reservoir fractures during the drill-in process, we propose pre-propping and temporary plugging (PPTP) technology as an integrated solution in this paper. The PPTP approach combines high-strength bridging (HSB) materials with self-degrading filling (SDF) materials for efficient fracture plugging during lost circulation and effective fracture propping during oil and gas production from deep naturally fractured reservoirs. HSB material with good mechanical properties and SDF material with a controllable degradation cycle are developed and systematically evaluated. Fracture plugging tests and stress sensitivity experiments are conducted to evaluate the transformation effect of fracture plugging zones on fracture propping zones. Research results show that the developed HSB material exhibits a high compressive capacity and friction coefficient, which maintains a crushing rate below 3% under 60 MPa pressure and an average friction coefficient of 1.56. The degradation ratio of SDF material increases with temperature and pH value. The degradation cycle can reach up to 168 hours under the conditions of 120°C and pH = 13, which ensures continuous stable fracture plugging and lost-circulation control during the drill-in process. The PPTP technology, combining HSB and SDF components, efficiently plugs fractures with widths ranging from 1.0 mm to 3.0 mm, with a maximum plugging pressure of up to 10.16 MPa. HSB material props the fractures after SDF degrades, preventing fracture closure and converting the fracture plugging zone into a propping zone. The stress sensitivity damage of reservoir fractures can be effectively mitigated, preserving and enhancing fracture conductivity. Thus, the PPTP technology shows great potential for the integration solution of drill-in fluid loss and formation damage in deep naturally fractured reservoirs.

Establishment of urinary catheter materials antibacterial efficacy evaluation platform in pigs

Urinary catheters are one of the common invasive medical catheters, mostly composed of high-polymer materials such as polyurethanes. During clinical use, the high friction between the catheter material surface and tissues can lead to tissue damage, patient discomfort, and pain during insertion or removal. Moreover, due to the hydrophobic nature of the polymer material surface, there is a risk of urinary tract infections (CTIs) caused by problems such as protein adsorption and bacterial infection upon insertion into the body. Prolonged indwelling time of urinary catheters in the body increases the probability of other complications, potentially leading to life-threatening consequences and imposing medical burdens. Therefore, the purpose of this study was focused on the insertion of the Escherichia coli (E. coli, 1 × 105 CFU/mL)-coated urinary catheter to implant into a female pig’s urethra for establishing the urinary catheter materials antibacterial efficacy evaluation platform in pigs. Results were shown that during the experimental period, the week 1 and week 2 average pig’ body temperature were 39.4 ± 0.6°C and 39.1 ± 0.2°C, respectively. The average pig’s body temperature was normal and there was no significant differences in body temperature at week 1 and week 2 urinary catheter implanted-experiment period. Moreover, the clinical observation of the pigs showed that their vitality, appetite, and excretion were all normal, and they survived until the end of the experiment without presenting any abnormal clinical symptoms. In addition, E. coli in urine culture respectively showed 0.95 ± 0.03 × 105 CFU/mL, 1.23 ± 0.03 × 105 CFU/mL, 1.43 ± 0.04 × 105 CFU/mL, 1.75 ± 0.08 × 105 CFU/mL, and 1.91 ± 0.09 × 105 CFU/mL on day 0, 3, 7, 10, and 14 of urinary catheter implantation. As time progressed after urinary catheter implantation, there was an increasing trend in E. coli counts. Staining with crystal violet for urinary catheter showed that the urinary catheter wall was positive for crystal violet staining. E. coli isolation and counts from biofilm on inside and outside of urinary catheter respectively showed 5.10 ± 0.10 × 105 CFU/mL and 7.50 ± 1.08 × 105 CFU/mL on day 14 of urinary catheter implantation. As time progressed after urinary catheter implantation, there was an increasing trend in E. coli counts. Finally, the pathological interpretation of the urinary tract indicates that in the tissue morphology of the bladder, there is observed a localized mild shedding of superficial and intermediate layer cells in the transitional epithelium of the ureteral stent group, with only basal cells remaining connected to its submucosa. There are no significant pathological changes observed in the tissue morphology of the urethra and kidneys. According to the results of this study, a urinary catheter materials antibacterial efficacy evaluation platform in pigs has successfully established, which can be provided for R&D of urinary catheter antibacterial materials.

Adhesion-Lubrication Paradox of Articular Cartilage.

The friction of solids is primarily understood through the adhesive interactions between the surfaces. As a result, slick materials tend to be nonstick (e.g., Teflon), and sticky materials tend to produce high friction (e.g., tires and tape). Paradoxically, cartilage, the slippery bearing material of human joints, is also among the stickiest of known materials. This study aims to elucidate this apparent paradox. Cartilage is a biphasic material, and the most cited explanation is that both friction and adhesion increase as load transfers from the pressurized interstitial fluid to the solid matrix over time. In other words, cartilage is slippery and sticky under different times and conditions. This study challenges this explanation, demonstrating the strong adhesion of cartilage under high and low interstitial hydration conditions. Additionally, we find that cartilage clings to itself (a porous material) and Teflon (a nonstick material), as well as other surfaces. We conclude that the unusually strong interfacial tension produced by cartilage reflects suction (like a clingfish) rather than adhesion (like a gecko). This finding is surprising given its unusually large roughness, which typically allows for easy interfacial flow and defeats suction. The results provide compelling evidence that cartilage, like a clingfish, conforms to opposing surfaces and effectively seals submerged contacts. Further, we argue that interfacial sealing is itself a critical function, enabling cartilage to retain hydration, load support, and lubrication across long periods of inactivity.

The influence of occupational footwear on slip responses

This study investigated how walking in occupational footwear (OF) affects slip outcome and slip recovery strategies in response to an unexpected slip. Participants walked along a walkway while either barefoot (BF; n = 13) or in OF (n = 12). The first five walking trials consisted of the no-slip condition, where a high friction sheet was placed halfway down the walkway to ensure a low probability of a slip. Prior to the sixth walking trial and without the participant’s knowledge, the sheet was replaced with a low friction surface to induce an unexpected slip. Results obtained during the no-slip trials indicated that compared to the BF group, the OF group walked with a 15% smaller required coefficient of friction (p = 0.04), a 12° greater dorsiflexion at heel strike (p = 0.007) and a 7° more extended knee position at 100 ms following heel strike (p = 0.008). The OF group also demonstrated greater electromyographic (EMG) activity in the hamstrings of the stance limb and the gastrocnemius of the contralateral limb prior to and after heel strike. When the low friction surface was unexpectedly encountered, a slip was induced in both groups. But compared to the BF group, the OF group experienced a less severe slip, with the slip being 42% shorter (p = 0.004) and 75% slower (p < 0.001), and exhibited a 19–71% lesser EMG activation when responding to the slip. Although these results provide initial evidence for the benefits of wearing OF to minimise the consequence of a slip in the workplace, further research is needed to determine whether the altered walking patterns associated with wearing OF (e.g., greater dorsiflexion, reduced knee range of motion, etc.) may have contributed to the decrease in slip severity.

Photogrammetric analysis of limb joint angles in cows with normal gait before and after hoof trimming

The aim of this study was to evaluate the effect of hoof trimming on overall limb movements by comparing the changes in 8 limb joint angles before and after one week of hoof trimming. Seventeen Holstein-Friesian dairy cows that were able to move freely and had no history of hoof diseases were included in the study. The cows were walked on a rubber mat with a high friction coefficient (HFM) and a low friction coefficient by the spraying of sodium polyacrylate (LFM). A high-speed camera was set to 200 fps on the image analysis software, and the images of the cows that were given 15 reflective markers on their right side were captured while walking on the test mat. The tests were conducted before and after one week of hoof trimming, and the cows were trimmed by the functional hoof trimming method. With image analysis software, video clips of walking cows were confirmed visually and tracked during one gait cycle by each reflective marker attached to the hoof of the forelimb and hindlimb, after which the stance phase and swing phase were identified. The durations of the stance phase and swing phase of the forelimb and hindlimb, respectively, and the maximum, minimum, and range of motion (ROM) values of the 8 joint angles, shoulder joint, elbow joint, carpus joint, forelimb fetlock joint, hip joint, stifle joint, hock joint and hindlimb fetlock joint during one gait cycle were included in the analysis. The maximum and minimum angles of the hip and stifle joints were narrower after hoof trimming than before, although the ROM did not change and was clearer for HFM than for LFM. It was thought that the flexion of the proximal hindlimb would progress smoothly during walking after trimming.

Development and characterization of high friction polyurethane bearings for bridge engineering applications

In this study, a high friction polyurethane (HFPU) was prepared using PCL-210 N, MOCA, TDI, and silicone diols. HFPU bearings for bridges were manufactured by casting HFPU in layers onto steel plates. The chemical composition, microstructure, crosslinking strength, and viscoelastic properties of HFPU were characterized. The results demonstrated that HFPU possesses excellent mechanical properties and surface roughness. Mechanical tests showed that HFPU has a hardness of 84 HA, a tensile strength of 35.05 MPa, residual deformation of less than 5 %, and a shear modulus of 2.57 MPa. The HFPU bearings also exhibited excellent vertical load-carrying capacity, horizontal deformation resistance, and recovery capability. Additionally, the Bouc-Wen model accurately simulated the hysteretic behavior, indicating that the HFPU bearings can provide seismic damping effects in bridge structures. The high friction characteristics, characterized by both the Bouc-Wen and Dahl models, showed that the HFPU bearing could work stably within 0–250 % strain.

Effect of temperature on the tribological behavior of additively manufactured tool materials in reciprocating sliding against cemented carbide

Additive manufacturing (AM) of ferrous alloys has achieved a technological maturity level that allows for the production of high-performance steel components. Among these alloys, tool steels and maraging steels can be used in die manufacturing for different hot forming processes as both materials have good mechanical properties and thermal stability. In recent years, several works have successfully produced these alloys through selective laser melting, focusing on the optimization and characterization of their microstructure and mechanical properties. However, few studies look into the tribological aspects of these newly produced materials and even fewer consider high temperature friction and wear performance. Therefore, there is a need to understand the high temperature tribological response of tool materials produced by additive manufacturing. In this context, the aim of this work is to investigate the tribological behavior of a tool steel and a maraging steel, both produced by selective laser melting, at different elevated temperatures. A conventionally produced tool steel was used as reference. A reciprocating sliding tribometer was used to perform tests at 40 °C, 200 °C and 400 °C. The counter-body was a WC-Co cemented carbide. Friction and wear of the AM tool steel and reference tool steel were very similar, thus no signs of the AM route having an impact on the tribological behavior were observed. Both tool steels showed reduced wear volume with increasing temperature, while the opposite was observed for their respective WC-Co counter-bodies. Higher temperature also resulted in increased amount of W transferred onto the tool steel wear scars. AM maraging steel showed higher and more unstable friction level, as well as a much larger wear volume at all temperatures; material transfer onto WC-Co was observed at certain temperatures. Overall, tribolayer formation (or lack thereof) was the dominant aspect in the tribological responses.

Performance of optimized composition of epoxy resin adhesive used in High Friction Surface Treatment

The High Friction Surface Treatment (HFST) paving technique is widely employed in engineering practices globally, serving to enhance the long-term anti-skid performance of pavements. However, there still exist significant gaps in research regarding the modified and optimized composition and corresponding content of the polymer binding materials used in HFST, as well as the performance of the pavements laid with modified and optimized blended aggregates during service. To address these issues, this research first modified and optimized the composition ratio of traditional epoxy resin materials. Subsequently, a toughened, high-flow epoxy bonding system suitable for the maintenance of concrete pavements was prepared. Additionally, the study explored the bonding performance of this system with both the cement base surface and aggregates. The results established that the optimal ratio range for the modified epoxy adhesive system is E51 epoxy resin to curing agent to toughening agent to diluent in the proportions of 100: 30–35: 20–30: 5. The experimental group used a high-flow epoxy resin adhesive ratio of E51 epoxy resin: curing agent: toughener: diluent = 100:30:20:5. For control group 1, the ratio of epoxy resin adhesive was E51 epoxy resin: curing agent = 100:30, and for control group 2, the ratio was E44 epoxy resin: curing agent = 1:1. Compared with control groups 1 and 2, the modified epoxy system with the cement base demonstrated a 149 % increase in average pull-off strength and an 18 % increase in average shear strength. Similarly, in comparison with control groups 1 and 2, the modified epoxy system with aggregates exhibited a 174 % increase in average pull-off strength and a 541 % increase in average shear strength. Based on the pull-off and shear test results, it was ultimately determined that the dosage of modified epoxy binder for HFST mixtures should be controlled at 1.0–1.2 kg/m2, and the dosage of aggregate should be controlled at 3.3–4.3 kg/m2. These findings provide valuable insights into optimizing HFST pavement compositions for improved performance and longevity.

DLC coatings in biomedical applications – Review on current advantages, existing challenges, and future directions

This review explores the intricate realm of DLC (Diamond-like carbon) coatings in biomedical applications, providing a thorough analysis of their biocompatibility and hemocompatibility. The investigation delves into the diverse types of DLC coatings, scrutinizing the influence of their sp3/sp2 ratio and impact of hydrogenation on the coatings' performance. Besides presenting an overview about deposition methods, the application of DLC coatings in orthopedics, tribology, and anti-corrosion within the biomedical context is discussed based upon state-of-the-art literature. The results of the literature survey suggested that DLC-coated joint replacements and prosthetic devices exhibited an improved durability and longevity in orthopedics. Similarly, in cardiovascular interventions, DLC-coated stents demonstrated reduced wear and decreased risk of restenosis thus making them beneficial for applications subject to high mechanical stress and friction. DLC coatings have demonstrated a remarkable biocompatibility with biological tissues, fostering an improved integration and reduced adverse reactions. Moreover, DLC coatings exhibited a notable corrosion resistance enhancing their durability of biomedical devices and implants in physiological environments. Our review does not only illuminate the advancements made but also highlights the challenges encountered in utilizing DLC coatings in biomedical applications, which relates to their robust adhesion to substrate materials, as delamination can compromise the performance and longevity of biomedical devices. Furthermore, there is less information on the long-term stability of DLC coatings in dynamic physiological environments such as joint articulation, which require further studies to ensure sustained performance over the lifespan of biomedical implants.

High-Temperature Superlubricity in MoS2/Graphene van der Waals Heterostructures.

Achieving high-temperature superlubricity is essential for modern extreme tribosystems. Solid lubrication is the sole viable alternative due to the degradation of liquid ones but currently suffers from notable wear, instability, and high friction coefficient. Here, we report robust superlubricity in MoS2/graphene van der Waals heterostructures at high temperatures up to ∼850 K, achieved through localized heating to enable reliable friction testing. The ultralow friction of the MoS2/graphene heterostructure is found to be notably further reduced at elevated temperature and dominantly contributed by the MoS2 edge. The observation can be well described by a multi-contact model, wherein the thermally activated rupture of edge-contacts facilitates the sliding. Our results should be applicable to other van der Waals heterostructures and shed light on their applications for superlubricity at elevated temperature.

Frictional Fault Strength Analysis of Palu-Koro and Matano Faults, Sulawesi, Indonesia, from Earthquake Focal Mechanism Data

ABSTRACT Sulawesi’s complex tectonic setting generates active Palu-Koro and Matano faults. Understanding earthquake mechanic is important for mitigation purpose. We performed fault strength analysis by examining its friction, through joint stress inversion and stress magnitude estimation approach, using focal mechanism data from International Seismological Centre bulletin. Friction was analyzed in four segments of the Palu-Koro Fault and two segments of the Matano Fault. Bootstrap and Jack-knife are applied to assess its uncertainty. From north to south, the friction pattern increases at the Palu-Koro Fault segments: Donggala (0.35<μs <0.56) to Palu segment (0.59<μs <0.76); then decreases sequentially: at Saluki (0.49<μs <0.55), Moa segment (0.31< μs <0.35), and further at the Matano Fault segment (Pamsoa-Ballawai) (0.26<μs <0.3). Regarding the 2018 Mw 7.5 Palu earthquake rupture, high friction at the Saluki segment coincides with and indicates its rupture termination. Seismicity records from 1977 to 2011 showed that the largest event occurred at Matano Fault has Mw less than 7.5. Low friction observed at Matano Fault correlates with small magnitude events and low fault strength.

High-temperature tribological properties of (TiZrNbMoTa)N and (TiZrNbMoTa)CN ceramic coatings

As dry-cutting tool coatings, high-entropy ceramics (HECs) exhibit excellent hardness, toughness, and wear resistance properties. However, the hardening mechanism of HEC coatings and their mechanical and frictional properties under high-temperature conditions have not been studied. In this study, we successfully prepared (TiZrNbMoTa)N high-entropy nitride (HEN) and (TiZrNbMoTa)CN high-entropy carbon nitride (HECN) coatings using reactive magnetron sputtering technology. The strengthening mechanism and thermodynamic properties of HEN and HECN coatings were systematically studied using the Debye-Grüneisen quasi-harmonic approximation model combined with density functional theory (DFT) calculations. At room temperature (RT, 25 °C) and high temperature (HT, 500 °C), the microhardness of HECN is 62 % and 56 % higher than that of HEN, respectively. Especially at RT, the microhardness of HECN reaches 46.37 GPa. Through in-situ XRD, in-situ nanoindentation, and high-temperature friction and wear analysis, we conducted in-depth research on the phase stability, high-temperature mechanical properties, and high-temperature tribological properties of HECs coatings in high-temperature. XRD test results show that HEN and HECN coatings exhibit a single-phase FCC structure and maintain good stability under HT. DFT calculation results show that the M − C bond in HECN is stronger than the M − N bond in HEN, which is why the HECN coating is harder. At HT, the wear rate of HECN coating is only reduced by 10 % compared with HEN coating. Different from RT, under high-temperature conditions, the primary wear mechanism of the coating is oxidative wear. The coating's red hardness and friction coefficient (COF) have a limited impact on the coating's high-temperature anti-wear performance. This research provides a theory and technical basis for designing and preparing protective coatings with high hardness and low friction coefficient.

Double layer silica antireflective films with high strength and rub resistance prepared by sol gel method

The single-layer silica antireflective film with base catalysis prepared by sol gel method is an important part of the high-power laser facility for inertial confinement fusion, while the weak adhesion between the single-layer silica film and the substrate during the preparation process makes it susceptible to be contacted erasure and unable to be used. Double-layer silica antireflective (DLAR) films of different thicknesses were obtained using the base catalysis sol–gel method, in which the upper layer was coated with a relatively dense thin layer, and the performances of the films were characterized. The results showed that the transmittances of the DLAR films with different thicknesses were ˃99.0%, and in which one of the maximum transmittance peaks reached to 99.83% @ 1000 nm. The surface roughness of the DLAR films was < 2.0 nm, and the surfaces of the films were flat. The contact angles between DLAR films and water reached 118° and maintained stable in high humidity environment. The laser induced damage thresholds for different thickness DLAR films (peak transmittances @ 400, 600, 800, 1000 nm) were comparable to device requirements by 1-on-1 testing method, and the DLAR films exhibited high strength and good friction resistance.Graphical abstract

Effect of the combination of antioxidant and dispersant in traction oils on their interaction and lubricating property

Molecular dynamics simulation is utilized to reveal the interaction and lubricating property of polyisobutylsuccinimide-polyamine (PIB-PAM) dispersant and phosphorus compound (PAE3) antioxidant in two traction systems (JP1E, JP1EC). The content ratio of PIB-PAM to PAE3 is changed. The static self-assembly of additives is observed, while PIB-PAM molecules with strongly intermolecular entanglement displays a suppressive effect on the molecular diffusion. In the shear process, the adsorption of base oil on surfaces shows a non-wall-slip friction state, and the increasing shear rate causes the adsorption film thinning and the friction coefficient rise. The strong intermolecular interaction in lubricating system induces high friction resistance. The fundamental insights into the interaction mechanism of different additives are helpful for improving lubricant research and development.

Hyperbranched Vitrimer for Ultrahigh Energy Dissipation.

Polymers are ideally utilized as damping materials due to the high internal friction of molecular chains, enabling effective suppression of vibrations and noises in various fields. Current strategies rely on broadening the glass transition region or introducing additional relaxation components to enhance the energy dissipation capacity of polymeric damping materials. However, it remains a significant challenge to achieve high damping efficiency through structural control while maintaining dynamic characteristics. In this work, we propose a new strategy to develop hyperbranched vitrimers (HBVs) containing dense pendant chains and loose dynamic crosslinked networks. A novel yet weak dynamic transesterification between the carboxyl and boronic acid ester was confirmed and used to prepare HBVs based on poly (hexyl methacrylate-2-(4-ethenylphenyl)-5,5-dimethyl-1,3,2-dioxaborinane) P(HMA-co-ViCL) copolymers. The -type of macromonomers, the crosslinking points formed by the dynamic covalent connection via the associative exchange, and the weak yet dynamic exchange reaction are the three keys to developing high-performance HBV damping materials. We found that P(HMA-co-ViCL) 20k-40-60 HBV exhibited ultrahigh energy-dissipation performance over a broad frequency and temperature range, attributed to the synergistic effect of dense pendant chains and weak dynamic covalent crosslinks. This unique design concept will provide a general approach to developing advanced damping materials.

Hyperbranched Vitrimer for Ultrahigh Energy Dissipation

AbstractPolymers are ideally utilized as damping materials due to the high internal friction of molecular chains, enabling effective suppression of vibrations and noises in various fields. Current strategies rely on broadening the glass transition region or introducing additional relaxation components to enhance the energy dissipation capacity of polymeric damping materials. However, it remains a significant challenge to achieve high damping efficiency through structural control while maintaining dynamic characteristics. In this work, we propose a new strategy to develop hyperbranched vitrimers (HBVs) containing dense pendant chains and loose dynamic crosslinked networks. A novel yet weak dynamic transesterification between the carboxyl and boronic acid ester was confirmed and used to prepare HBVs based on poly (hexyl methacrylate‐2‐(4‐ethenylphenyl)‐5,5‐dimethyl‐1,3,2‐dioxaborinane) P(HMA‐co‐ViCL) copolymers. The ‐type of macromonomers, the crosslinking points formed by the dynamic covalent connection via the associative exchange, and the weak yet dynamic exchange reaction are the three keys to developing high‐performance HBV damping materials. We found that P(HMA‐co‐ViCL) 20k‐40‐60 HBV exhibited ultrahigh energy‐dissipation performance over a broad frequency and temperature range, attributed to the synergistic effect of dense pendant chains and weak dynamic covalent crosslinks. This unique design concept will provide a general approach to developing advanced damping materials.

The impact of the coupling relationship between projectile size and yarn dimension on the ballistic performance of plain weave fabric

Aramid fibers, due to their relatively high inter-yarn friction, high strength, high modulus, and other characteristics, have become a typical representative of flexible anti-ballistic materials in modern warfare. Current research on the anti-penetration of aramid fabrics mostly focuses unilaterally on the structure and performance of aramid fabrics or the shape and size of projectiles, with fewer studies on the coupled effect of both on ballistic performance. This study analyzes how the coupling relationship (or size effect) between the projectile and fiber bundle dimensions affects the fabric ballistic performance from a mesoscopic scale perspective. Taking plain weave aramid fabric as the research object, considering different diameter projectiles, through a large number of ballistic impact tests and numerical simulations, parameters such as ballistic limit velocity, average energy absorption of fabric, and specific energy absorption ratio (average energy absorption of fabric divided by projectile cross-sectional area) are obtained for ballistic performance analysis. The influence law of projectile size on the ballistic performance of high-performance fabrics is as follows: The relative range of fitted ballistic limit velocity at different target positions gradually decreases and then stabilizes as the projectile diameter increases, indicating that the fabric structure effect gradually disappears at a projectile diameter of 12 mm; The average ballistic limit velocity at three impact positions, P1, P2, and P3, provides the corresponding ballistic limit velocity for 1000D aramid fabric, which increases with projectile diameter but the rate of increase slows down at an inflection point, which in this study occurs where the fabric structure effect nearly disappears at a projectile diameter of 12 mm; The energy absorption ratio increases and then decreases as the projectile diameter increases from 4 mm to 20 mm, reaching a peak at the diameter of 12 mm due to the gradual disappearance of the fabric structural effect. The projectile diameter of 12 mm corresponds to the coupling size of 11.159, which provides a size design reference for the macroscopic-based continuum models of aramid plain weave fabrics.

Effect of humidity and oxygen on friction, wear and durability of a polymer-bonded molybdenum disulfide (MoS2)-based dry film lubricant (DFL) coating system in large amplitude fretting

Investigations into effects of humidity and oxygen on a polymer-bonded MoS2-based dry film lubricant (DFL) coating, on grit-blasted Ti–6Al–4V using a cylinder-on-flat configuration, are reported. Sustained low friction and low wear occurred in both low-humidity air and low-humidity argon, producing significant extension of fretting wear lifetimes. A cracked-paved structure was observed in low-humidity air which was not observed in low-humidity argon. The Mo-DFL coatings were observed to be highly sensitive to humidity. As humidity increased, a notable rise of friction and wear ensued which reduced the system lifetime. Different friction evolution was observed in high-humidity air and high-humidity argon before failure, with a short-lived but established low friction phase in high-humidity air and a consistent high friction phase in high-humidity argon. Although oxidation of the MoS2 to MoO3 is a key process of degradation of DFLs of this type, this oxidation reaction does not operate in the absence of humidity.