Pradeep L. Menezes

Mechanical, physical and tribological characterization of nano-cellulose fibers reinforced bio-epoxy composites: An attempt to fabricate and scale the 'Green' composite.

The development of bio-based composites is essential in order to protect the environment while enhancing energy efficiencies. In the present investigation, the plant-derived cellulose nano-fibers (CNFs)/bio-based epoxy composites were manufactured using the Liquid Composite Molding (LCM) process. More specifically, the CNFs with and without chemical modification were utilized in the composites. The curing kinetics of the prepared composites was studied using both the isothermal and dynamic Differential Scanning Calorimetry (DSC) methods. The microstructure as well as the mechanical and tribological properties were investigated on the cured composites in order to understand the structure-property correlations of the composites. The results indicated that the manufactured composites showed improved mechanical and tribological properties when compared to the pure epoxy samples. Furthermore, the chemically modified CNFs reinforced composites outperformed the untreated composites. The surface modification of the fibers improved the curing of the resin by reducing the activation energy, and led to an improvement in the mechanical properties. The CNFs/bio-based epoxy composites form uniform tribo-layer during sliding which minimizes the direct contact between surfaces, thus reducing both the friction and wear of the composites.

New Emerging Self-lubricating Metal Matrix Composites for Tribological Applications

Self-lubricating metal matrix composites (SLMMCs) are an important category of engineering materials that are increasingly replacing a number of conventional materials in the automotive, aerospace, and marine industries due to superior tribological properties. Implementing self-lubricating composites into different operating systems is a solution to reduce the use of external toxic petroleum-based lubricants at sliding contacts in a way to help the environment and to reduce energy dissipation in industrial components for strategies toward energy efficiency and sustainability. In SLMMCs, solid lubricant materials including carbonous materials, molybdenum disulfide (MoS2), and hexagonal boron nitride (h-BN) are embedded into the metal matrices as reinforcements to manufacture a novel material with an attractive self-lubricating properties. Due to their lubricious nature, these solid lubricant materials have attracted researchers to synthesize lightweight self-lubricating metal matrix composites with superior tribological properties. This chapter focuses on the recent development in tribological behavior of self-lubricating metal matrix (aluminum, copper, magnesium, and nickel) composites. It is important to note that the tribological parameters, such as normal load, sliding speed, and temperature vary on a wide range and also the counterface materials differ in different experimental tests, comparing the results of tribological behavior of different self-lubricating composites is extremely difficult. In this chapter, attempts have been made to summarize the tribological performance of various SLMMCs as a function of several tribological parameters. These parameters include material parameters (size, shape, volume fraction, and type of the reinforcements), mechanical parameters (normal load and sliding speed), and physical parameters (temperature and environment). The mechanisms involved for the improved mechanical and tribological performances are discussed.

Advancements in Eco-friendly Lubricants for Tribological Applications: Past, Present, and Future

This chapter highlights the evolution of eco-friendly lubricants derived from natural oils and fats to green lamellar solid additives to a new class of “greener” functional fluids known as room temperature ionic liquids (RTILs). The attraction to these bio-based lubricants began with vegetable oils due to their low friction and wear properties. These superior tribological characteristics are a result of their chemical composition of triacylglycerol molecules made up of esters derived from glycerol and long chains of polar fatty acids. It is these fatty acids within the natural oils that establish monolayers that enable high lubricity in boundary-lubricated regimes. Despite these accolades, vegetable oils suffer from thermal-oxidative instability, high pour points, and inconsistent chemical compositions. To improve upon the tribological properties, vegetable oils were subjected to additives such as lamellar solid powders to establish more resilient transfer layers to mitigate wear and surface damage. Currently, RTIL lubricants derived from bio-based feedstock represent a promising potential solution to many of the problems associated with previous eco-friendly lubricants. An investigation into RTILs begins with a discussion on the history of ionic liquids and an assessment on their tribological properties. The chapter also includes a case study on the use of RTILs as additives in vegetable oils and as neat lubricants as well as exploring the effects of cation-anion moiety exchange within ionic liquids themselves. Ultimately, the RTILs are compared to more traditional bio-based lubricants for their tribological performance as a new class of eco-friendly lubricants and their potential as a future lubrication technology.

Effect of In-situ Processing Parameters on the Mechanical and Tribological Properties of Self-Lubricating Hybrid Aluminum Nanocomposites

In the present investigation, aluminum/TiB2/Al2O3 metal matrix composite was fabricated using the liquid metallurgy route. The transmission electron microscopy study was conducted in order to investigate the microstructure of the in-situ processed composites. X-ray diffraction analysis of the composite was performed to investigate the various phases present in the composite. Dry sliding tests were conducted using pin-on-disk tribometer in order to understand the self-lubricating behavior of developed composite. The microstructural characteristics revealed formation of in-situ phases and uniform dispersion of the reinforcement phases throughout the composite. The developed hybrid self-lubricating nanocomposites showed superior mechanical and tribological properties. The superior tribological properties of hybrid composite are attributed to the formation and synergetic effect of TiB2 and Al2O3 particles in the composites. The Al2O3 hard ceramic particles act as the obstacles to the movement of dislocation and thus enhance the mechanical properties. The oxidation of TiB2 on the surface forms H3BO3 and TiO2 tribolayer resulting in superior tribological properties.

Advances in Bio-inspired Tribology for Engineering Applications

Bio-inspired tribology is an interdisciplinary field of science where scientists and engineers seek to investigate and incorporate tribological properties encountered in biological beings into engineering applications. In this paper, bio-inspired tribological research that are speculated to have a huge impact on tribological applications have been reviewed. These research involve (1) investigations related to replication of lubricin found in synovial fluids of mammalian joints which have super-low friction values that can be utilized in IC engines, (2) surface replication concerning to superhydrophobic properties of gecko skin which is seen to have anti-wetting and self-cleaning properties, (3) friction-reducing shark skin through specialized nanoparticle coatings that is seen to give a different perspective on surface texturing, (4) new techniques, such as soft lithography to replicate surfaces of lotus leaf and air lubrication phenomenon inspired by emperor penguins that is being applied to propel boats, ships, and torpedoes faster by reducing skin friction underwater. Further, an investigation in self-healing materials inspired from pitcher plant that has led to the innovation of self-healing and slippery liquid-infused porous surfaces has been discussed. These research works reviewed not only provide a deep insight into the current advances in bio-inspired tribology but also helps understand the plausibility of the research applications in the future and the practicality of innovations possible.

A Review on the Science and Technology of Natural and Synthetic Biolubricants

Bio-based lubricants have gained prominence over conventional petroleum-based oils, progressively over the last two decades as biolubricants. This trend is observed in almost every industry that has been dependent on lubricants and oils irrespective of their applications. Factors that initiated and fueled this trend vary from stringent government regulations over petroleum-based oils to the high passed depletion of oil reserves. But the most concerning factor that has fast-tracked the need for biolubricants is the toxic and harmful effect of used petroleum oils has on the environment and ecological factors. It is estimated that nearly 50% of all lubricants produced are introduced to the environment which has spurred the interest in biolubricants. This review discusses various types of eco-friendly bio-lubrications that will become a sustainable and economical alternative to the conventional petroleum-based lubricants by being sourced from renewable resources. Biolubricants are seen to be feasible and versatile lubricants with higher lubricity, lower volatility, higher shear stability, higher viscosity index, higher load-carrying capacity, and superior detergency and dispersancy when compared to petroleum-based lubricants. The review also investigates in detail the poor thermal-oxidative stability, biological deterioration, their poor solidification at low temperatures, and hydrolytic instability as well as mechanical and chemical enhancements that seek to rectify these issues. Furthermore, economical and legislative landscape of biolubricants is discussed.

Natural Adhesion System Leads to Synthetic Adhesives

Nature has developed multi-functional geometric structures, and surface textures with excellent tribological characteristics, such as feet of geckos. Geckos have extraordinary abilities to climb walls and even upside down on the ceiling. Studies have revealed that hierarchical structure of gecko’s feet can bear the weight of two humans and this strong adhesion force is mainly generated by weak van der Waals force. This paper reviews the mechanisms and the forces responsible for gecko’s adhesion, and the effect of humidity on adhesion against different hydrophobic/hydrophilic surfaces. The excellent adhesive and frictional properties of gecko adhesion system have inspired many researchers to develop gecko-inspired synthetic adhesives. In this paper, recent development of gecko-inspired synthetic adhesives has been presented in terms of various fabrication methods, different tip structures, and the effect of counter surface roughness as well as design criteria to avoid bunching of nano-structures. The application of synthetic adhesives is also discussed for wall climbing robots and novel applications in the field of space, biomedical and sports accessories.

Performance Analysis of Retrofitted Tribo-Corrosion Test Rig for Monitoring In Situ Oil Conditions

Oils and lubricants, once extracted after use from a mechanical system, can hardly be reused, and should be refurbished or replaced in most applications. New methods of in situ oil and lubricant efficiency monitoring systems have been introduced for a wide variety of mechanical systems, such as automobiles, aerospace aircrafts, ships, offshore wind turbines, and deep sea oil drilling rigs. These methods utilize electronic sensors to monitor the “byproduct effects” in a mechanical system that are not indicative of the actual remaining lifecycle and reliability of the oils. A reliable oil monitoring system should be able to monitor the wear rate and the corrosion rate of the tribo-pairs due to the inclusion of contaminants. The current study addresses this technological gap, and presents a novel design of a tribo-corrosion test rig for oils used in a dynamic system. A pin-on-disk tribometer test rig retrofitted with a three electrode-potentiostat corrosion monitoring system was used to analyze the corrosion and wear rate of a steel tribo-pair in industrial grade transmission oil. The effectiveness of the retrofitted test rig was analyzed by introducing various concentrations of contaminants in an oil medium that usually leads to a corrosive working environment. The results indicate that the retrofitted test rig can effectively monitor the in situ tribological performance of the oil in a controlled dynamic corrosive environment. It is a useful method to understand the wear–corrosion synergies for further experimental work, and to develop accurate predictive lifecycle assessment and prognostic models. The application of this system is expected to have economic benefits and help reduce the ecological oil waste footprint.

Ionic Liquids: A Plausible Future of Bio-lubricants

AbstractThis paper reviews the development of bio-lubricants from conventional impeller pressed natural oils to a new class of green bio-lubricants referred to as ionic liquids (ILs) at room temperature. The attraction to bio-lubricants began with natural oils due to their low friction and wear characteristics owing to high lubricity. To better control the tribological behavior, natural oils were introduced to additives, such as lamellar solid powders. Looking to the future, room-temperature IL lubricants derived from biological feedstock are seen as prospective alternatives and solutions to the issues associated with currently available bio-lubricants. Hence, a comprehensive investigation on the tribological properties of novel bio-based IL lubricant is carried out. A simplistic IL feasibility study has also been performed wherein pin-on-disk tests were conducted to analyze the friction and wear behavior under ambient conditions. The ILs demonstrate improved tribological performance when compared to conventional petroleum-based and bio-based lubricants in their purified forms at various levels. The mechanisms concerning the chemical composition of the ILs and their tribological properties imbibed by the bio-lubricants are discussed while highlighting its plausible industrial application.

Comparative Analysis of Two Methods for Evaluating Wear Rate of Nanocrystalline Diamond Films

The study deals with the calculation of the wear rate of nanocrystalline diamond (NCD) films. The NCD films were grown by microwave plasma enhanced chemical vapor deposition (MW-PECVD) on (100)-oriented Si wafers. Reciprocating sliding tests with different loads and test durations were conducted. The depth profiles of wear scars were analyzed by the mechanical (stylus) profilometer and the wear rate was evaluated. The NCD films were broken across the wear scars and the wear rate was estimated by the measurement of the area of wear scar using the scanning electron microscopy (SEM) cross-sectional image. A good agreement was found between two methods.