Tomasz Liskiewicz

Synovial joint lubrication — does nature teach more effective engineering lubrication strategies?

Abstract Nature shows numerous examples of systems which show energy efficiency, elegance in their design and optimum use of materials. Biomimetics is an emerging field of research in engineering and successes have been documented in the diverse fields of robotics, mechanics, materials engineering, and many more. To date little biomimetics research has been directed towards tribology in terms of transferring technologies from biological systems into engineering applications. The potential for biomimicry has been recognized in terms of replicating natural lubricants but this system reviews the potential for mimicking the synovial joint as an efficient and durable tribological system for potential engineering systems. The use of materials and the integration of materials technology and fluid/surface interactions are central to the discussion.

Review of recent progress in nanoscratch testing

Abstract Nanoscratch testing, as an important technique for the assessment of the mechanical failure behaviour and adhesion strength of ceramic coatings and a simulation tool of single asperity contact in tribological experiments, is increasingly becoming an established nanomechanical characterisation method. This paper reviews recent work in nanoscratch testing in different engineering applications including thin ceramic films, automotive organic coatings, chemical–mechanical polishing and biomaterials. In the main part of the paper, nanoscratch results from experiments performed using NanoTest systems fitted with tangential force sensors and spherical indenters as scratch probes are presented and discussed. The types of nanoscratch tests described include constant load nanoscratches, ramped load nanoscratch tests and multipass repetitive unidirectional constant load nanoscratch tests (nanowear). The results are discussed in terms of critical load sensitivity to intrinsic and extrinsic factors, impact of scan speed and loading rate, influence of probe radius and geometry, estimation of tip contact pressure, influence of surface roughness and film stress and thickness, and finally role of ploughing on friction evolution.

Wet adhesion for a miniature mobile intra-abdominal device based on biomimetic principles

Abstract An assessment of adhesion between the peritoneum and various micro/ nanopatterned polymer surfaces is presented as a key step in the design of a miniature intra-abdominal device for use in minimally invasive surgery practices. Of particular interest is the gathering of necessary information concerning understanding and quantifying the forces required to enable such a device to adhere to, move over, or detach and reattach to surface tissue without any damage to the latter. A micro-tribometer apparatus is used for this purpose, and results show that the adhesion force generated between the polymer and peritoneum does not scale linearly with nominal contact area. It is found that a non-optimized polymer surface patterned with a homogeneous micro-pillar structure, having an area of 113 mm2, when in contact with the peritoneum, is able to generate an adhesive force of 70 mN; six to eight such pads would in principle be capable of supporting a device/payload weighing 40–50 g. A discussion is provided of the mechanism(s) by which the adhesion is achieved and how the findings may impact on the eventual design and subsequent manufacture of a working intracorporeal device.

Effect of tribological factors on wet adhesion of a microstructured surface to peritoneal tissue.

Bio-inspired microstructured surfaces have been developed that attach effectively to a wet surface. However, little is known about the associated tribological and adhesion properties involved. In this paper, the adhesion of a microstructured surface to peritoneal tissue is investigated as a function of preload, speeds of approach and angle of tilt to the horizontal. Results show that within a critical range of preload and speed of approach of the microstructured surface to the tissue result in good adhesion characteristics at the micro-structured surface/tissue interface. The microstructured surface adhesion to the tissue and the payload supported against gravity depend significantly on the tilt angle to the horizontal. Furthermore, a wet adhesion model was used to elucidate the adhesion mechanism of the microstructured surface to a wetted glass. These tests provide significant initial data for the design of a miniature mobile intra-abdominal device which drives the need for this adhesion study.

Impact of Corrosion on Fretting Damage of Electrical Contacts

Electrical contacts are used in a large number of industrial applications, this includes all sorts of modern transportation: airplanes, trains and automobiles. Mechanical assemblies are subjected to vibrations and micro-displacements between mating surfaces are observed leading to fretting wear. Mechanical degradation can additionally be accelerated by a corrosive factor caused by variable humidity, temperature and corrosive gas attack. Fretting-corrosion leads to an increase of contact resistance or intermittent contact resistance faults as corrosion products change the nature of the interface primary through a range of film formation processes. In this work the impact of a corrosion product film formed on copper and gold surfaces on the electrical contact fretting behavior is shown. It has been observed that modification of the interface by the formation of the surface layer can surprisingly lead to increase of the electrical contact durability.

Microtribology: new tools to fill measurement gap

Abstract Microtribological experiments are currently becoming an important tool in the tribological practice by offering maximum experimental benefits with minimum technical complexity. In this perspective paper several microtribological case studies are presented to illustrate potential methodologies. Results are presented and discussed in relation to: nanoscratch and nanowear experiments, accelerated nanowear technique, nano-impact test and method of capturing topography and material phase features. Two commercially available systems are used in this study, namely, NanoTest Platform and MUST tester. A general classification of tribological techniques has been proposed distinguishing between classical tribometers, atomic force microscopy based techniques and microtribometers.

Designing new lubricant additives using biomimetics

Nature produces some complex nanocomposite structures having the following properties, self-healing capability, functional gradation and smartness. These properties are all required of tribofilms in the field of lubrication technology where their structure, formation and removal rate and smartness are key to their ability to maintain fuel economy and durability. In this paper the potential for using biomimetic principles in the field of tribology and specifically as a means of improving tribological performance in the boundary lubrication regime is investigated. The paper initially describes the challenges associated with operating tribological contacts in the boundary lubrication regime, assesses the need for new approaches to lubrication and gives a preliminary appraisal of biomimetic principles applied to this engineering problem.

Mechanical and tribological properties of Cr–Nb double-glow plasma coatings deposited on Ti–Al alloy

Abstract Double-glow plasma (DGP) coatings are recommended for metallic components to mitigate the damage induced by complex working conditions in previous studies. In this paper, Nb-rich (Cr–Nb4) and Cr-rich (Cr4–Nb) -alloyed layers were formed onto the Ti–Al substrate via a DGP process to enhance its wear resistance. Scratch and Nano-indentation tests were used to evaluate the mechanical properties of the coatings. The tribological behaviour of the coatings were investigated using a pin-on-disc tribometer by rubbing against the GCr15 ball. Results from surface analysis techniques showed that the coatings mainly comprised Cr, Nb and Cr2–Nb phases, and were well bonded to the substrate. The hardness of the Cr–Nb4 coating was 11.61GPa and the Cr4–Nb coating was 9.66 GPa which all higher than that of the uncoated Ti–Al which was 5.65 GPa. However, the critical load of the Cr4–Nb coating ~21.64 was higher than that of the Cr–Nb4 coating ~17.6. And the specific wear rate of Cr–Nb4 coating, Cr4–Nb coating and uncoated Ti–Al were 3.54 × 10−4, 0.01 × 10−4 and 1.53 × 10−4mm3 N−1 m−1, respectively. The low-wear mechanism of the coatings is discussed in detail in this paper.

Locomotion selection and mechanical design for a mobile intra-abdominal adhesion-reliant robot for minimally invasive surgery

Miniaturisation of surgical robots combined with bio-inspired adhesive material offer the possibility of a device able to move stably inside the body. In this paper a miniature adhesion-reliant robot is proposed as an alternative to current cumbersome, externally anchored surgical robots. An effective locomotion strategy is selected according to the specific working environment of this application. This environment is the ceiling of the insufflated human abdomen during laparoscopic surgery. Having chosen the most appropriate actuation technology in the market (piezo-electricity), the mechanical design to implement the former locomotion strategy is demonstrated.

Friction In Nature

Natural systems show efficient ways to minimise or maximise friction depending on the required function. Such a function is always achieved by a number of properties and mechanisms as no single solution exists in nature to tackle one problem. Nature shows solutions to provide ultra low friction in the case of lubricated systems, ultra high friction in the case of adhesives or in some cases even controlled adaptable friction performance. Frictional surfaces can be found on different scales in nature from a nanometre scale to a macro scale. From a wide variety of natural systems, synovial joints have probably attracted more research attention than other systems and this is fully justified as they are examples where an ideal synergy between the lubrication process and materials technology exists. Other examples include shark skin riblets providing drag reduction, hierarchical structures providing maximum adhesion or mucus and slime for an improved slip. In this contribution, a summary of natural frictional systems is presented. Several examples of the successful use of biomimicry for the manipulation of the interface to provide the desired functions are presented. Finally, directions of further exploitation of a biomimetic approach in tribology are discussed.