Micromechanisms Controlling the Structural Evolution of Tribosystems

The article presents a comprehensive analysis of technological processes in the manufacturing of parts for agricultural machinery, which significantly affect the reliability, stability, and service life of machines used in agro-industrial production. Particular attention is given to the study of requirements for the geometric parameters and physical and mechanical properties of structural materials, as these characteristics directly determine assembly precision, wear resistance, robustness, and durability of machinery components. Key parameters ensuring proper quality of parts are considered, such as tensile strength, resilient modulus, hardness, ductility, wear resistance, and corrosion resistance. Modern heat treatment methods are analyzed, including hardening, annealing, normalization, and tempering, as well as their influence on the internal structure of the metal and improvement of mechanical properties. Additionally, methods of steel alloying and chemical surface modification – such as carburizing, chromium plating, and the addition of alloying elements (manganese, boron, silicon) – are explored, as they enhance the resistance of parts to external loads and aggressive environments. A comparative analysis of different heat treatment regimens for steel grade L65 is provided using statistical methods, allowing the identification of optimal technological parameters. The study concludes that a comprehensive approach to the design and production of agricultural machinery parts – including the choice of manufacturing accuracy, treatment regimens, and material composition – can significantly increase the reliability and efficiency of machines under real operating conditions.

Influencing the Friction in Metal Forming Processes by Superimposing Ultrasonic Waves

In this work a variety of modifications of porous glass membranes are investigated considering their application in vanadium redox-flow batteries. Through 3D-printing technology a cell assembly was established that made replicable long-term testing of single glass membranes with a predefined geometry possible. Native as well as modified porous glass membranes with pore diameters in the range of 2 nm to 50 nm and thicknesses varying from 300 μm to 500 μm are electrochemically characterized (cf. Chapter IV). Pore surface modifications included the chemical bonding of sulfonic acid groups, propyl-N, N, N-trimethylene-ammonia-groups and propyl-pyridinium groups (cf. Chapter III). Membranes with large pore diameters and thus high porosity showed the highest performance concerning achievable current densities. However, self-discharge and selectivity are affected negatively in these membranes (cf. Chapter V). A newly developed point system identified the best performance of membranes with a thickness of 300 μm, a mean pore diameter between 5 nm and 10 nm and finely dispersed silica particles throughout the pore system. This corresponds with the membrane type 503FD. With this type a mean charging power density of 54.1 mA cm-2 at 1.8 V and a mean discharging power density of 71.7 mA cm-2 at 0.8 V was achieved during cycling. The maximum power density reached 75.3 mW cm-2 at a current density of 100.1 mA cm-2 and a voltage of 752 mV during discharge starting from a SoC of 100 %. Furthermore very high Coulomb Efficiencies (CE) of 98.1 % are possible with such membranes. Further surface modification of this membrane type does not lead to improvements of the performance. Although surface modifications contribute in reducing the self-discharge of the battery through cation crossover, other electrochemical characteristics suffer considerably. Given the additional work and expense of the process, modification of this membrane type is negligible (cf. Chapter VI). The overall performance of the investigated porous glass membranes and their modifications are still well below those of the referenced system of Nafion™ 117. This is explained by the relatively low porosity of the porous glasses. If it was possible to establish large-size, thin and stable glass membranes with high porosities and mean pore diameters in the range well below of 10 nm at reasonable prices, their longevity and aging resistance as well as the large variety of possible chemical surface modifications might lead to drastic performance and efficiency gains. Therefore porous glass membranes might become a real competition for the widespread use of polymer membranes in vanadium redox-flow batteries. The great potential of porous glasses in electrochemical applications is still to be developed in further studies. Their biggest advantage being that their chemical properties can be adopted to their very purpose through chemical modification. In summary the chemical stability and electrochemical performance of porous glass membranes provide very good preconditions for various long-term applications under the harsh conditions of redox flow-battery systems.

To improve the lubrication and wear resistance of nickel composite moulds, nano-sized polytetrafluoroethylene (PTFE) particles were co-deposited with nickel. This work reports the effect of using micro-sized and nano-sized PTFE particles on the surface, mechanical and tribological properties of Ni composite moulds. The experimental results indicate that using nano-sized PTFE particles is significantly more effective than micro-sized PTFE particles in improving the lubrication, mechanical and tribological properties of the composite moulds. The microhardness of the composite mould increases by 2.5 times to 483 Hv for a Ni-PTFE nanocomposite mould, along with the COF against polymethyl methacrylate (PMMA) decreasing by 52.2% to 0.22. Using micro-sized PTFE particles serves to roughen the mould surface, which results in faster adhesive wear. In comparison, the Ni-PTFE nanocomposite mould has a low surface roughness and enhanced wear resistance against PMMA, while the tool lifetime increases by 11.5 times. Finally, a Ni/PTFE nanocomposite mould was successfully fabricated via UV-LIGA, and its lubricating properties were validated by producing high-quality PMMA replicas via micro hot embossing.

Inorganic nanoparticles such as silica, and titanium oxide, are widely used industrially as fillers and pigments for polymer materials, because inorganic nanoparticles have excellent properties such as chemical, heat and weather resistance, lightweight, thermal conductivity and low thermal expansion. On the other hand, nanocarbons, such as carbon black, nanodiamond, and carbon nanotube, are well known as one of the industrially important carbon materials. Carbon materials also have outstanding properties such as electro-conductivity, heat-resistance, biocompatibility, and chemical-resistance. Carbon nanotubes in particular have attracted attention as nanotechnology related materials. In general, dispersing inorganic nanoparticle and nanocarbons uniformly into a polymer or an organic solvent is very difficult because of aggregation. In addition, the mechanical properties of polymer composite from nanoparticles and nanocarbons are considered to depend on not only the mechanical properties of the polymer matrix but also on the properties of interfacial regions between surface of nanoparticles and matrix polymers. The chemical and physical modifications of inorganic nanoparticle and nanocarbon surfaces, therefore, have been extensively studied. The chemical modification of surfaces is permanent, but physical modification is temporary. We have pointed out that the dispersibility of silica nanoparticles and nanocarbons is extremely improved by surface grafting of polymers, namely, chemical binding of polymers, onto nanoparticle and nanocarbon surfaces (Tsubokawa, 1999; Tsubokawa, 2002; Tsubokawa, 2007). In addition grafting of polymers onto these surfaces interests us for designing new functional composite materials which have the excellent properties both of nanoparticles as mentioned above and of grafted polymers, such as photosensitivity, biorepellent activity, antibacterial activity, and pharmacological activity (Tsubokawa, 2007). We have succeeded in the grafting of various polymers such as vinyl polymer (Tsubokawa et al., 1988a; Tsubokawa et al., 1990; Fujiki et al., 1990; Tsubokawa et al., 1992a), polyester (Tsubokawa et al., 1982; Tsubokawa et al., 1983), polyether (Tsubokawa et al., 1986; Tsubokawa et al., 1988b), poly(organophosphazene) (Tsubokawa et al., 1992b), and poly(dimethysiloxane) (Tsubokawa et al., 1992c) onto silica nanoparticle and carbon black surfaces using surface functional groups as grafting sites. Furthermore, many experimental attempts by other researchers also have been made to graft polymers onto silica nanoparticle and carbon black surfaces.

A spherical hinge structure is a key swivel bridge element that must be considered when evaluating friction characteristics and lubrication properties to meet the rotation requirement. Polytetrafluoroethylene (PTFE)-based spherical hinge sliders and lubrication coating have been employed for over 20 years, but with the growing tonnage of swivel bridge construction, their capacity to accommodate the required lubrication properties can be exceeded. In this manuscript, the optimal friction coefficient of the spherical hinge is obtained through the finite element analysis method. Four lubrication coatings and four spherical hinge sliders are prepared and tested through a self-developed rotation friction coefficient test, four-ball machine test, dynamic shear rheological test, and compression and shear performance test to evaluate the lubrication and friction properties of the spherical hinge structure. The results of the finite element analysis show that the optimum rotation friction coefficient of the spherical hinge structure is 0.031–1.131. The test results illustrate that the friction coefficient, wear scar diameter, maximum non-seize load, phase transition point, and thixotropic ring area of graphene lubrication coating are 0.065, 0.79 mm, 426 N, 14.6%, and 64,878 Pa/s. The graphene lubrication coating has different degrees of improvement compared with conventional polytetrafluoroethylene lubrication coating, showing more excellent lubrication properties, bearing capacity, thixotropy, and structural strength. Compressive and shear tests demonstrate that polyether ether ketone (PEEK) has good compressive and shear mechanical properties. The maximum compressive stress of PEEK is 87.7% higher than conventional PTFE, and the shear strength of PEEK is 6.07 times higher than that of PTFE. The research results can provide significantly greater wear resistance and a lower friction coefficient of the spherical hinge structure, leading to lower traction energy consumption and ensuring smooth and precise bridge rotation.

Hybrid composites prepared by the incorporation of two or more different types of fibres into a single polymer matrix deserve much attention. This method of hybridisation of composites offers a profitable procedure for the fabrication of products while the resulting materials are noted for their high specific strength, modulus and thermal stability. The influence of the relative composition of short sisal/glass fibres, their length and distribution on the tensile properties of short sisal/glass intimately mixed polyethylene composites (SGRP) was examined. Different compositions of sisal and glass such as 70/30, 50/50 and 30/70 have been prepared with varying fibre lengths in the range of 1–10 mm. Emphasis has also been given to the variation of fibre–matrix adhesion with several fibre chemical modifications. Chemical surface modifications such as alkali, acetic anhydride, stearic acid, permanganate, maleic anhydride, silane and peroxides given to the fibres and matrix were found to be successful in improving the interfacial adhesion and compatibility between the fibre and matrix. The nature and extent of chemical modifications were analysed by infrared spectroscopy while improvement in fibre–matrix adhesion was checked by studying the fractography of composite samples using a scanning electron microscope. Assessment of water retention values has been found to be a successful tool to characterize the surface of the stearic acid modified fibres. It was found that the extent of improvement in tensile properties of SGRP varied with respect to the nature of chemical modifications between fibre and matrix. Improved mechanical anchoring and physical and chemical bonding between fibre and polyethylene matrix are supposed to be the reasons for superior tensile strength and Young's modulus in treated composites. Several secondary reasons such as high degree of fibre dispersion and reduced hydrophilicity in chemically modified fibres also are believed to play a role. Among the various chemical modifications, the best tensile strength and modulus was exhibited by the SGRP with benzoyl peroxide treated fibres. This is attributed to the peroxide‐initiated grafting of polyethylene on to the fibres. Copyright © 2004 Society of Chemical Industry

Background: The wound-healing process incorporates a spectrum of periodontal therapeutic interventions that strive to restore the health and function of the periodontium. Fibroblasts play pivotal roles in tissue repair and regeneration. Extensive research has been focused on mechanical and chemical root surface modifications to enhance fibroblast adhesion, which is crucial for successful wound healing.Purpose: This study aimed to assess the combined efficacy of mechanical and chemical root surface modifications in promoting fibroblast viability to root surfaces affected by periodontitis in comparison to chemical modifications alone.Materials and methods: Root samples were collected from healthy individuals and those with advanced periodontitis. The specimens were prepared, and the experimental groups were categorized based on the type of surface modification with mechanical and/or chemical materials, including hyaluronic acid (HA), ethylenediaminetetraacetic acid (EDTA), enamel matrix derivatives (EMD), and EDTA/EMD. Fibroblasts were seeded onto previously treated root samples. Cell adhesion was assessed using a viability assay.Results: Fibroblast viability was significantly higher on root surfaces treated with chemical agents than on those treated with mechanical and chemical modifications. Long-duration EDTA and short-duration EMD treatments were significantly effective in enhancing cell viability. EDTA/EMD surface treatments resulted in significantly higher cell viability in all groups compared to the periodontitis root surfaces.Conclusion: EDTA, EMD, and their combined application can potentially ameliorate periodontitis-induced surface structural impairments. Mechanical surface debridement can significantly affect the effectiveness of EDTA and EMD root conditioning agents.

Fine-tuning of chemical and physical polymer surface modifications by atmospheric pressure post-discharge plasma and its correlation with adhesion improvement

The study objective is to increase the information value, accuracy and reliability of the experimental assessment results of extreme pressure and antifriction properties of the tested materials. A brief analysis of the work on the creation of test tribo-technical equipment is given. The difference between the designs of friction machines for testing using Reichert and Timken tests is shown. The design of an upgraded friction machine for determining extreme pressure, antifriction and anti-wear properties of lubricants is presented. In the proposed installation, the radial force on the friction unit ("roller - ring" or "bar – ring") is generated by a mechanism of even loading, and the assessment of extreme pressure lubricants is determined at the moment of gripping the rubbing samples, at which the motor shaft stops. As a result of upgrading the machine, it became possible to measure the friction force, the normal load and to read the friction factor, both for the lubricants under study and for friction pairs consisting of structural and instrumental materials. The results of comparative tests on the upgraded friction machine for lubricating and cooling liquids with different contents of extreme pressure, antifriction and anti-wear additives are presented. 
 A new friction machine design based on Reichert machine is developed, which allows testing structural and lubricating materials for friction and wear using both Reichert and Timken tests. At the same time, the accuracy of determining tribo-engineering characteristics of the tested materials is increased. It is found that as a result of equipping the friction machine with an even loading system and force measuring sensors, it becomes possible to determine extreme pressure and anti-friction properties of lubricants and structural materials, as well as to estimate the value of the friction factor.

Control of wettability of hydrogenated amorphous carbon thin films by laser-assisted micro- and nanostructuring

Chapter 8 Chemical modification of silica: applications and procedures

Considered modern technologies for the formation of composite detonation crystalline and amorphous-crystalline coatings, their friction and wear under the conditions of the presence and absence of lubricant, compatibility with structural and antifriction materials, as well as the influence of the stress state on their formation. The monograph consists of six chapters. Chapter 1 discusses the general issues of friction and wear research of composite detonation coatings in the absence of lubricant. It is shown how the sliding speed affects the wear of the friction surfaces. The evaluation of the features of wear in conditions of heavily loaded contact and the formation of coatings in conditions of elevated temperatures is given. Chapter 2 shows how the presence of lubricant affects the wear of composite detonation coatings. The role of tribochemical processes in the formation of wear-resistant surface structures and the wear resistance of coatings in the presence of lubricant in contact, the influence of elemental-organic additives on the processes of friction and wear are revealed. Chapter 3 deals with the compatibility of coatings with antifriction and structural materials. On the basis of the obtained results, friction pairs from structural and antifriction materials were selected, as well as the operational stability of detonation coatings in these friction pairs was studied. Chapter 4 describes the principles of forming amorphous and amorphous-crystalline coatings. The selection and justification of the components of the wear-resistant amorphous-crystalline coating, their influence of the nature of alloying elements on the properties of zirconium-based coatings are considered. The influence of technological parameters of detonation sputtering on the formation of detonation amorphous-crystalline coatings Chapter 5 presents the results of research on friction and wear of amorphous-crystalline coatings in the absence of lubricant. The wear resistance of amorphous-crystalline coatings in friction with tested coatings was studied. The wear resistance of amorphous-crystalline coatings with aircraft steels and the patterns of wear of amorphous-crystalline coatings with anti-friction materials were studied. Chapter 6 examines the features of the formation of the stress state of amorphous-crystalline detonation coatings. An assessment of the level of technological residual stresses in friction pairs and their effect on wear resistance was carried out. The influence of residual stresses on the wear resistance of the obtained coatings is shown. For researchers, engineers, as well as teachers, graduate students and students of higher educational institutions dealing with the problems of formation and research of detonation coatings.

Surface modification of poly(ethylene terephthalate) fibers induced by radio frequency air plasma treatment

Oleic-acid enhanced triboelectric nanogenerator with high output performance and wear resistance