By Sunish Vadakkeveetil, Mehran Shams Kondori, and Saied Taheri

Center for Tire Research (CenTiRe), Virginia Tech

 

 

 

 

 

 

 

 

Rubber, mainly because of its viscous nature, is a widely used material for most contact applications such as, seals, tyres, footwear, wiper blades, bushings etc. The material possesses the property of both a liquid (viscous) and a solid (elastic). Hence, rubber frictional losses at the contact interface is classified into three mechanisms as shown in Figure 1. Hysteresis  (μ_hys ) – Energy dissipated due to internal damping of rubber caused by undulation in the surface. Adhesion (μ_adh ) – Due to intermolecular or Vander Waals attraction at the contact interface. It vanishes in the presence of contaminants or lubricants on the surface. Viscous (μ_visc ) – Due to hydrodynamic resistance caused by the fluid in the contact interface. It mainly occurs under the presence of lubricant or fluid in between the contact interface.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Friction as a concept has evolved, as shown in Figure 2 from a simple empirical relation, developed by Amonton’s (1699) and Columb (1785) to more complex representations by considering these different mechanisms of friction. Initial experimental observations by Bowden and Tabor [1] observed the microscopic behaviour of the contact and obtained that the real area of contact is only a part of the nominal contact area. Grosch & Schallamach [2] performed experimental observation to determine the influential factors and obtain a relation between temperature and velocity-dependent friction to frequency-dependent viscoelastic behaviour. Savkoor[3] considers the frictional losses due to adhesive mechanism at the contact interface using a rudimentary theory where the interaction is considered as a series of processes from the growth of contact area in the initial stage to initiation and propagation of crack in the final stage.

Heinrich [4] developed an analytical representation to estimate the hysteretic component of friction by considering the energy losses at the contact interface to the internal damping of rubber from the undulations of the surface. The energy loss thus obtained is related to the frictional shear stress by the energy relation given by Eq. (2).

            ΔE=∫d^3 x dt u ̇ . σ (1)

           σ_f=ΔE/(A_0 v t)     (2)

Persson and Klüppel [5] extended the theory to consider the effect of the surface roughness by assuming the surface to behave as a fractal nature and obtaining the total energy loss being the sum over the different length scales. Klüppel considers the GW theory to consider the contact mechanics where Persson developed a stochastic based contact mechanics theory assuming the rubber deformations to follow the surface asperities, the results are as shown in Figure 3. To consider the actual deformation profile of rubber, an affine transformation approach [6] is considered to obtain the actual deformation of rubber contact. The results are as shown in Figure 4.

 

 

 

 

 

 

 

In addition to analytical methods, computational approaches are also considered to estimate deformation behaviour of a rubber block on a rough substrate (Figure 5). The numerical model [7] is validated using indentation experiment and compared against a single asperity model as shown in Figure 6. This is later being extended to obtain friction and wear characteristics of rubber at the contact interface by considering the deformations at the contact interface and obtaining the frictional force [5], [8].

 

 

 

 

 

 

 

 

 

 

Figure 6: FE Model Of Single Asperity Model & Comparison Of Results With Experimental & Analytical Approach

Wear is mainly due to the frictional shear stress generated at the contact interface leads to energy dissipation at the rubber – substrate contact interface that is either transformed into heat or responsible for crack initiation and propagation eventually leading to material removal. The major contribution of the wear occurs either due to the interaction of smooth asperity and rubber surface (adhesive wear), Figure 7 (a) instantaneous tearing of rubber by sharp asperities (abrasive wear), Figure 7 (b) or due to repeated cyclic contact stress (fatigue wear, Figure 7 (c)).

Due to the importance and complexity of the wear problem, it has been a vital topic of interest studied by many researchers [2]. Numerical techniques and empirical approaches have seen their light in the midst of the expensive and cumbersome experimental observations [9], [10]. Archard’s law states that “the volume rate of wear (W) is proportional to the work done by the frictional forces” as given by Eq. (3), where τ_f is the frictional shear stress and v is sliding velocity.

            W∝τ_f  v       (3)

 

 

 

 

 

 

 

 

 

 

 

In the case of road surfaces, the removal of rubber particles can be considered as a process of nucleation and propagation of crack like defects until it is detached to form a wear particle, as shown in Figure 8. Based on this mechanism of crack propagation, a physics-based theory assuming the crack propagates (Figure 9 & Figure 10) from already present defects or voids on the rubber surface was considered and then later compared with experimental methods performed using Dynamic Friction Tester (Figure 11) [6], [11], [12]. Future studies are being performed using analytical and computational approached to estimate the wear characteristics of a rubber material considering damage mechanics [8] and crack propagation theory considering the effect of surface roughness. An experimental technique is also being developed based on the Leonardo Da Vinci concept to experimental test the friction and wear characteristics of a rubber block under pure sliding.

 

References:

[1]       D. Bowden, F. P., & Tabor, The friction and lubrication of solids. Oxford university press., 2001.

[2]       A. Gent and J. Walter, The Pneumatic Tire, no. February. 2006.

[3]       A. R. Savkoor, “Dry adhesive friction of elastomers: a study of the fundamental mechanical aspects,” 1987.

[4]       H. Gert, “Hysteresis friction of sliding rubber on rough and fractal surfaces,” Pochvozn. i Agrokhimiya, vol. 25, no. 5, pp. 62–68, 1990.

[5]       S. Vadakkeveetil, “Analytical Modeling for Sliding Friction of Rubber-Road Contact,” Virginia Tech, 2017.

[6]       A. Emami and S. Taheri, “Investigation on Physics-based Multi-scale Modeling of Contact, Friction, and Wear in Viscoelastic Materials with Application in Rubber Compounds,” Virginia Tech, 2018.

[7]       S. Vadakkeveetil, A. Nouri, and S. Taheri, “Comparison of Analytical Model for Contact Mechanics Parameters with Numerical Analysis and Experimental Results,” Tire Sci. Technol., p. tire.19.180198, May 2019.

[8]       S. Vadakkeveetil and S. Taheri, “MULTI – LENGTH SCALE MODELING OF RUBBER TRIBOLOGY FOR TIRE APPLICATIONS,” Virginia Tech, 2019.

[9]       K. R. Smith, R. H. Kennedy, and S. B. Knisley, “Prediction of Tire Profile Wear by Steady-state FEM,” Tire Sci. Technol., vol. 36, no. 4, pp. 290–303, 2008.

[10]    B. W. and R. N. D. Stalnaker, J. Turner, D.Parekh, “Indoor Simulation of Tire Wear: Some Case Studies,” Tire Sci. Technol., vol. 24, no. 2, pp. 94–118, 1996.

[11]    A. Emami, S. Khaleghian, C. Su, and S. Taheri, “Comparison of multiscale analytical model of friction and wear of viscoelastic materials with experiments,” in ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), 2017, vol. 9.

[12]    M. Motamedi, C. Su, M. Craft, S. Taheri, and C. Sandu, “Development of a Laboratory Based Dynamic Friction Tester,” in ISTVS 7th Americas Regional Conference, 2013.

 

Orion Engineered Carbons, a specialty chemical company, started commercial sales in Italy from the first new reactor for carbon black production to be commissioned in the European Union in over 40 years. 

The new 25-kiloton line at the facility in Ravenna, in the northern region of Emilia-Romagna, produces both specialty and technical rubber carbon blacks, primarily for the European market, the company said in a release. 

Corning Painter, CEO, Orion, said, “The new line offers customers seeking long-term solutions a unique strategic opportunity to align with a dependable plant that has been operating for more than 60 years in Europe.” 

Additional investments at the plant include a new co-generation facility to convert waste heat into electricity, generating up to 120 MWh of electricity per year. Seventy percent of the electricity is supplied to the national grid, serving about 30,000 households. Orion is a net exporter of electricity in Europe and worldwide. (TT)  

Shin-Etsu Chemical, a leading chemical company, plans to invest $702 million in its silicone portfolio, a key component of its functional materials business segment.

This latest investment follows a plan announced in February 2022, worth $562 million, to meet the surging demand for advanced functional silicone products. However, due to the continuous growth in need, especially for eco-friendly options that align with the global goal of carbon neutrality, the company has decided to expand the applications of its silicone products. The company will also focus on enhancing the advanced functionality of its product lineup and further developing environmentally friendly silicones.

In alignment with its newly announced silicones investment plan, Shin-Etsu Chemical will make investments not only in its central production hub in Japan, the Gunma Complex in Gunma Prefecture, but also in its Naoetsu Plant in Niigata Prefecture, Takefu Plant in Fukui Prefecture, and the Group company plant in Thailand, where silicone monomer and polymer production is conducted. The company will also invest further in existing silicone plants across other Asian countries, the United States, and Hungary. Simultaneously, Shin-Etsu Chemical will accelerate efforts to achieve carbon neutrality by embracing greener manufacturing processes.

Klean Industries Inc has announced that its partner Pyrolysis Hellas SA has completed Phase II of the Detailed Feasibility Study to design and build a tyre pyrolysis plant in Greece. Greek Authorities gave permits to its final Phase, the company said in a release. The company, while terming it as a significant milestone for the PHS project, claimed that it was the first tyre pyrolysis and carbon upgrading project in Greece to receive full authorizations.

Klean Industries Inc has announced that its partner Pyrolysis Hellas SA has completed Phase II of the Detailed Feasibility Study to design and build a tyre pyrolysis plant in Greece. Greek Authorities gave permits to its final Phase, the company said in a release. The company, while terming it as a significant milestone for the PHS project, claimed that it was the first tyre pyrolysis and carbon upgrading project in Greece to receive full authorizations.

Klean Industries Inc has announced that its partner Pyrolysis Hellas SA has completed Phase II of the Detailed Feasibility Study to design and build a tyre pyrolysis plant in Greece. Greek Authorities gave permits to its final Phase, the company said in a release. The company, while terming it as a significant milestone for the PHS project, claimed that it was the first tyre pyrolysis and carbon upgrading project in Greece to receive full authorizations.Klean Industries Inc has announced that its partner Pyrolysis Hellas SA has completed Phase II of the Detailed Feasibility Study to design and build a tyre pyrolysis plant in Greece. Greek Authorities gave permits to its final Phase, the company said in a release. The company, while terming it as a significant milestone for the PHS project, claimed that it was the first tyre pyrolysis and carbon upgrading project in Greece to receive full authorizations.

Each year, over 1.5 billion tyres are sold worldwide, representing more than 26 million metric tonnes, and just as many tyres each year also fall into the category of end-of-life tyres providing a large and partially untapped potential for resource and material recovery. Today, most traditional ELT treatment processes are not circular and do not result in any production of raw materials that are suitable to be reused in the tyre manufacturing industry. Without such ELT solutions in the EU, more than half of the EU end-of-life tyres and secondhand tyres are landfilled or are exported as tyre derived fuels for use into furnaces as an industrial fuel. The PHS project intends to reverse these trends and create a vibrant addition to advancements being made in the tyre recycling sector, the release said.

The PHS project is co-owned by Karabas European Hellenic Recycling. Currently, KEHR collects and recycles all types of scrap vehicle tyres and recycles them through traditional methods by shredding tyres into rubber granules, rubber powder & shock-absorbent surfacing slabs.

PHS has partnered with Klean Industries to build a modern tyre recycling facility that encompasses a state-of-the-art scrap tyre pyrolysis plant to recycle 20,000 TPA of waste tyres into valuable chemical products.

PHS proposes to construct and operate the Waste Tyre Pyrolysis Plant in Moulkia, a seaside town near Skala, Greece. It is located at an existing industrial site that is owned by KEHR, the release added. (TT)

ResiCare, an adhesive manufacturing subsidiary of Michelin, has found commercial use in Allin's plywood manufacturing unit, R'PLY. Allin and Michelin have been in collaboration since 2018.

The company claims that R'Ply is the first responsible plywood made using certified Poplar wood and integrating a ResiCare resin that is kinder to human health as well as the environment. The R’Ply is a high-performance plywood which can be used for multiple applications, according to the company. The plywood can be used for boat-building or in the building trade and will be available at certain DIY stores soon.

Michelin had set up a mobile ResiCare production unit at its Olsztyn site in May 2021. The company hopes to replace more than 80 percent of the usual adhesive used in its tyre textile reinforcement with the new ResiCare adhesive, which is free from any substances of very high concern for health (SVHC), by 2025. The company further plans to set up mobile production units similar to the one in Europe and Asia in the coming months. (TT)