Surface texture influences friction during sliding. In the present investigation, various kinds of surface texture with varying roughness were produced on steel plates. Pins made of pure iron were then slid against the prepared steel plates using an inclined pin-on-plate sliding tester to understand the role of surface texture on coefficient of friction under both dry and lubricated conditions. The contact surfaces of both the pins and plates were observed using a scanning electron microscope (SEM). Surface textures of steel plates were characterized in terms roughness parameters using an optical profilometer. The data analysis showed that the coefficient of friction depends on the surface texture of the harder counterface under both dry and lubricated conditions. Further, a transfer layer of pure iron did not form on the steel plate surface. In addition, it was observed that the soft iron pin scratches the harder steel surface, and hence the coefficient of friction was observed to be independent of surface roughness parameters.
Ceramics are widely evaluated for their extreme hardness, high-temperature stability, and corrosion resistance, which enable applications in harsh service environments. However, these same properties, high melting points, brittleness, and low thermal shock resistance, make conventional manufacturing of complex ceramic components difficult and expensive. Traditional processes often require costly diamond tooling or energy-intensive sintering and tend to produce only simple geometries, with significant waste material and risk of defects. Additive manufacturing (AM) has recently emerged as a promising route to fabricate intricate, near-net-shape ceramic parts without these drawbacks. By building components layer by layer, AM reduces the need for extensive machining and enables the fabrication of geometrically complex, near-net-shape ceramic structures with reduced material waste, although challenges such as porosity, interlayer defects, and cracking during post-processing remain. Nonetheless, ceramic AM technologies lag behind their metal and polymer counterparts, and significant challenges remain in achieving fully dense parts with reliable mechanical properties. This review provides an in-depth overview of the state of the art in ceramics and ceramic composite additive manufacturing. We detail the most widely used AM processes (stereolithography, binder jetting, material extrusion, powder bed fusion, inkjet printing, and direct energy deposition) and typical feedstock formulations for each technique. We examine the resulting mechanical properties (strength, toughness, hardness, wear resistance) and functional properties (thermal stability, dielectric behavior, biocompatibility) of additively manufactured ceramics, and discuss their current and potential engineering applications in the aerospace, defense, automotive, biomedical, and energy sectors. Persistent challenges, including porosity, shrinkage and cracking during sintering, achieving uniform microstructures, high process costs, and scalability issues, are analyzed, and we highlight promising future directions such as multi-material grading, integration of machine learning for process optimization, and sustainable manufacturing approaches. Despite significant progress, challenges remain in achieving fully dense structures, improving process reliability, and scaling ceramic AM for industrial applications, highlighting the need for further research in process optimization, material design, and multi-material integration.
Tribology and Applications of Self-Lubricating Materials provides insight into the complex mechanisms behind the development of self-lubricating materials, which due to their ability to transfer embedded solid lubricants to the contact surface to decrease wear rate and friction in the absence of an external lubricant, make up an important part of engineering materials used today. This book emphasizes an understanding of the tribological nature of different composites such as metal, polymer, and ceramic matrix composites and discusses the compatibility of these composites with specific lubricants. The book also offers a view of advancements in the development of self-lubricating mechanisms and covers the latest technologies in the field.
Understanding the tribological interactions between shoe and floor materials is important in order to enhance shoe and floor design and to prevent slip and fall accidents during walking. In the present investigation, experiments were conducted using a custom developed pin-on-disk type tribometer to understand the influence of boundary and hydrodynamic properties on the shoe-floor materials’ coefficient of friction. Specifically, polyurethane shoe material was slid against vinyl floor material in the presence of varying lubricants (i.e., water, detergent, three diluted glycerol concentrations, and canola oil). The experiments were conducted for a range of biologically relevant sliding velocities from 0.05 m sec−1 to 1.0 m sec−1 at a contact pressure of 266.1 kPa under ambient conditions. The fluid chemical composition appeared to affect the boundary friction coefficient with longer-chain molecules resulting in a decreased coefficient of friction. As fluid viscosity increased, the rate of coefficient of friction decay increased with respect to increasing fluid entrainment velocity, suggesting less material contact and increased film thickness. The nondimensional film thickness under all conditions was calculated and the nondimensional film thickness consistently increased with increased viscosity and speed. Additionally, the effect of functionally achievable variations in polyurethane shoe roughness on the coefficient of friction was examined and found to have no statistically significant effect on boundary or hydrodynamic contributions to the coefficient of friction.
In the present investigation, basic studies were conducted using Inclined pin-on-plate sliding Tester to understand the role of surface texture of hard material against soft materials during sliding. Soft materials such as Al-Mg alloy, pure Al and pure Mg were used as pins and 080 M40 steel was used as plate in the tests. Two surface parameters of steel plates — roughness and texture — were varied in tests. It was observed that the transfer layer formation and the coefficient of friction which has two components, namely adhesion and plowing component, are controlled by the surface texture of harder material. For the case of Al-Mg alloy, stick-slip phenomenon was absent under both dry and lubricated conditions. However, for the case of Al, it was observed only under lubricated conditions while for the case of Mg, it was observed under both dry and lubricated conditions. Further, it was observed that the amplitude of stick-slip motion primarily depends on plowing component of friction. The plowing component of friction was highest for the surface that promotes plane strain conditions near the surface and was lowest for the surface that promotes plane stress conditions near the surface.
In the present investigation, efforts were made to study the different frictional responses of materials with varying crystal structure and hardness during sliding against a relatively harder material of different surface textures and roughness. In the experiments, pins were made of pure metals and alloys with significantly different hardness values. Pure metals were selected based on different class of crystal structures, such as face centered cubic (FCC), body centered cubic (BCC), body centered tetragonal (BCT) and hexagonal close packed (HCP) structures. The surface textures with varying roughness were generated on the counterpart plate which was made of H-11 die steel. The experiments were conducted under dry and lubricated conditions using an inclined pin-on-plate sliding tester for various normal loads at ambient environment. In the experiments, it was found that the coefficient of friction is controlled by the surface texture of the harder mating surfaces. Further, two kinds of frictional response, namely steady-state and stick-slip, were observed during sliding. More specifically, stead-state frictional response was observed for the FCC metals, alloys and materials with higher hardness. Stick-slip frictional response was observed for the metals which have limited number of slip systems such as BCT and HCP. In addition, the stick-slip frictional response was dependent on the normal load, lubrication, hardness and surface texture of the counterpart material. However, for a given kind of surface texture, the roughness of the surface affects neither the average coefficient of friction nor the amplitude of stick-slip oscillation significantly.
Presented in this study is a new class of “greener” lubricants, room temperature ionic liquids, that represent a promising potential solution to many of the problems associated with both conventional lubricants and those based on natural oils. In this study, friction and wear tests were carried out using a pin-on-disk tribometer under ambient conditions to characterize the performance of the ionic liquids as lubricants. Specifically, ionic liquids consisting of salicylate, benzoate (common food additives) and saccharinate (an artificial sweetener) anions with conventional phosponium cations were evaluated as lubricants and compared to petroleum-based lubricants and natural oils in regards to structure and performance. The ionic liquids generally demonstrated better tribological performance than either the petroleum-based lubricants or natural oils. The mechanisms governing the chemical composition and improved tribological performance are discussed while highlighting possible industrial applications of this new class of lubricants.
Self-healing materials (SHMs) are a class of bio-inspired materials capable of autonomously repairing damage, similar to how living organisms heal wounds. The core motivation behind SHMs is to extend the service life of components while enhancing safety and reducing maintenance or replacement needs. SHMs can be broadly categorized into intrinsic systems, which rely on reversible internal bonds (dynamic covalent or supramolecular interactions) to heal repeatedly, and extrinsic systems, which embed external healing agents (e.g., microcapsules or vascular networks) that are released upon damage to effect repairs. Researchers have demonstrated self-healing behavior in diverse material families, including polymers, metals, ceramics/cementitious materials, and protective coatings, thereby improving crack resistance, fatigue life, and reliability across aerospace, automotive, civil infrastructure, energy storage, and microelectronics applications. Advances in material design and additive manufacturing have started integrating SHMs into practical structures. However, challenges such as scaling up production, maintaining mechanical performance, and ensuring long-term durability remain. Reported healing efficiencies in self-healing materials typically range from ~50% to near-complete recovery (~100%), depending on material systems and testing conditions, highlighting key trade-offs between healing performance, mechanical integrity, and scalability. Overall, SHMs represent a promising strategy for creating safer and more sustainable engineering systems, with ongoing developments aimed at overcoming current limitations and expanding their capabilities. This review highlights key trade-offs between healing efficiency, mechanical performance, and scalability, providing insights into the design and application of next-generation self-healing materials.
