PLENARY AND KEYNOTE SPEAKERS

Friction is generally described by a single degree of freedom, a ‘friction coefficient’. We experimentally study the space-time dynamics of the onset of dry and boundary lubricated frictional motion when two contacting bodies start to slide. We first show that the transition from static to dynamic sliding is governed by rupture fronts (closely analogous to earthquakes) that break the contacts along the interface separating the two bodies. The structure of these ‘laboratory earthquakes’ is given by singular solutions describing rapid shear cracks. This framework establishes a new (and fruitful) paradigm for quantitatively describing friction onset, earthquake’ motion and arrest.

The aim of this presentation is to review the role of friction in cell and tissue mechanics at various scales: at the molecular scale of the proteins, at the cellular scale and at the more macroscopic scale of a tissue.

Cartilage is an extraordinary material that allows our joints to move with low friction and wear, often for many decades. Imitating cartilage with polymer brushes and gels has a number of purposes: It can help us understand more about the lubrication mechanism of cartilage itself; it is a necessary step for the development of improved replacement materials for cartilage that is damaged; and finally, the soft, highly lubricious materials developed can have many potential applications in industry and medicine.

Inspired by the excellent surface hydration lubrication mechanism, typical layered biochemical feature and the adaptive load-bearing/stress dissipation route of natural articular cartilage, a series of novel layered cartilage lubrication materials have been designed by soft/hard combination strategy. These novel materials exhibit high load-bearing, low friction and excellent wear-resistance properties, as well as remarkable lubrication performance of cartilage. Those novel design, inspired by nature would provide new route for the development of high-performance water-based lubrication materials.

The increasing demand for sustainable tribology has accelerated the development of environmentally friendly lubrication solutions such as water-related lubricants in combination with carbon or ceramic surfaces under boundary lubrication conditions. Atomistic simulations reveal superlubricity mechanisms for glycerol- lubricated tetrahedral amorphous carbon (ta-C) [1] and Si3N4 [2]. In our quantum molecular dynamics (MD) simulations glycerol concurrently chemisorb on both tribopartners and bridge the tribogap. Sliding-induced mechanical strain triggers complete fragmentation of the lubricant. In the case of ta-C surfaces, superlubric graphenoid passivation layer forms. For Si3N4 surfaces, glycerol’s oxygen reacts with Si to silica, while the carbon forms superlubric disordered graphene-nitrides. Both results are supported by experiments.

Wear of materials remains to be one of the most costly failures of products. This is particularly so for systems in motion, such as total joint replacement, passenger cars, and manufacturing machines where mechanical impacts and environmental attack pose challenges to rubbing components. However, the current design of structural materials has been primarily focused on the hardness as the sole property. The increased hardness associates with brittle fracture that leads to severe loss of materials. In this presentation, discussion will be given on the nature of conflicts between hardness and toughness of materials. This leads to the advantages in composites and multi-phase materials. Further discussion will be about the microstructural design of quasicrystal alloys and their effects on mechanical properties and wear performance. It will be revealed that by microstructural design and adding toughness in certain phases, it is possible to predict the failure and to achieve ultimate resistance to wear.

The lecture presents measurements of leakage and dynamic force coefficients for six distinct annular pressure seals operating with an air in oil mixture ranging from pure liquid to just air. The comprehensive test campaign reveals the salient characteristics of various annular pressure seal configurations, thus aiding to better design multiple-phase flow centrifugal pumps.

TotalEnergies is a broad energy company committed to providing energy that is ever more affordable, cleaner, more reliable and accessible to as many people as possible. We therefore face the dual challenge of producing more energy to meet growing demand, while reducing our GHG emissions in line with our ambition to achieve carbon neutrality by 2050 with society. In this context, tribology is an essential tool for the research and development of products combining maximum performance and minimum environmental impact, particularly in the fields of industry and mobility.

Already back in 2017, Holmberg et al laid out how 20% of all power produced globally is used to overcome friction and other losses in bearings, cams, gears, seals and the like. They also showed how half of these losses could be removed by 2030 by making use of then state-of-the art knowledge in tribology. Today, with the UN Sustainable Development Goals and the Science Based Targets committed to by many industrial companies, these insights have found a new audience and become the frontier in mechanical engineering. Design for circular is the buzz word of engineering students today, and zero emissions is the norm. But how will this actually happen - in the short time we have? If the knowledge was there in 2017, why did not more happen already?
This presentation will deal with some of the blockers and discussion ways around and solutions. Hopefully we can use the conference for driving action towards a Net Zero carbon world.