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.

 

The Association of Natural Rubber Producing Countries (ANRPC) published its Monthly Natural Rubber Statistical Report for August 2026, noting firmer prices in several markets. Supply constraints, stable downstream demand and persistent geopolitical and macroeconomic uncertainty shaped the month. Renewed conflict and disruptions to major shipping routes added further pressure.

Physical prices for major grades moved in different directions. SMR-20 in Kuala Lumpur averaged USD 2.31 per kg, up 4.25 percent from July, while STR-20 in Bangkok rose 1.40 percent to USD 2.39 per kg. RSS-3 dropped 4.18 percent to USD 2.80 per kg, but RSS-4 in Kottayam gained 0.57 percent to USD 2.92 per kg. Latex-in-bulk fell 4.73 percent to USD 1.73 per kg. Brent crude averaged USD 91.08 per barrel, driven by concerns over possible restrictions on oil shipments through the Strait of Hormuz and wider Middle East instability, which raised energy supply risks and strengthened the oil market risk premium.

On trade, China's imports climbed 3.39 percent month-on-month, while India fell 10.18 percent and Malaysia dropped 8.24 percent; Viet Nam rose 5.08 percent. Exports advanced 5.63 percent in Viet Nam but declined in Thailand (-5.24 percent), Indonesia (-5.36 percent), Malaysia (-1.48 percent) and Cambodia (-1.88 percent).

Global production is projected to rise 0.6 percent to 15.039 million tons in 2026 from 14.952 million tonnes in 2025, after revisions to Thailand's 2025 output and updated 2026 estimates for Thailand, Malaysia and Indonesia. Weather, including erratic rainfall and drier Southeast Asian conditions, affected output. August 2026 production was estimated at 1.396 million tonnes, down 4.51 percent from 1.462 million tonnes a year earlier. Demand is forecast to grow 0.4 percent to 15.356 million tonnes in 2026 from 15.301 million tonnes, with the largest consumption gains expected in China, Malaysia and Cambodia. Prospects depend on vehicle sales, tyre production, shipping conditions and weather-related supply disruptions, while steady EV-linked demand supported modest growth led by China and India. The ringgit traded between RM4.02 per USD and RM4.09 per USD, and the baht between 32.68 and 33.34. The SHFE January 2027 contract averaged 18,109 CNY per tonne, up 7.78 percent month-on-month, while the SGX November 2026 contract averaged USD 2.24 per kg, up 4.32 percent.

Epsilon Carbon Pvt. Ltd., a global speciality carbon and carbon black manufacturer, has broadened its emissions accounting to include value chain impacts beyond its direct operations. The move advances measurement and management of Scope 3 emissions across its supply and distribution network, according to the company.

The initiative spans Epsilon Carbon’s integrated carbon complex in Vijayanagar, Karnataka. That site has a production capacity of 500,000 tonnes per annum of speciality carbon and 215,000 TPA of carbon black. It combines carbon manufacturing with energy circularity efforts in one integrated ecosystem. The company assessed material Scope 3 categories under GHG Protocol guidelines.

Scope 3 emissions are indirect and arise from purchased goods and services, transportation, business activities and downstream product use where relevant. The assessment gives Epsilon Carbon clearer visibility into emissions outside its direct control and a foundation for spotting reduction opportunities. It builds on existing operational emissions and energy efficiency work.

The company previously reported a 98 percent Scope 2 reduction against its baseline year. A 17 MW captive power plant uses waste heat from carbon black operations, energy consumption intensity fell 6 percent from baseline, and 77 percent of energy needs came from waste heat recovery, avoiding over 89,000 tonnes of CO₂. Epsilon Carbon now emphasises supplier engagement, data transparency and circularity, aligning disclosures with global sustainability frameworks to track value chain emissions consistently and develop measurable reduction initiatives.

Vikram Handa, Managing Director, Epsilon Carbon, said, “Meaningful climate action requires us to look beyond the boundaries of our operations and understand the impact of the entire value chain. Scope 3 measurement gives us greater visibility into the emissions and enables deeper engagement with our partners and suppliers. Building this visibility will help us make more informed decisions as we scale our operations and advance our decarbonization plans.”

HS HYOSUNG has formalised a memorandum of understanding (MoU) with the State Government of San Luis Potosí, with the signing taking place at the World Trade Center Mexico City. The event formed part of the Korea-Mexico Business Forum, held alongside the Korean economic delegation's visit to Mexico.

Attending officials included Marcelo Ebrard, Mexico's Secretary of Economy, and Mario García Valdez, Secretary of Economic Development of San Luis Potosí. The two sides confirmed their shared resolve to back the company's local investment and regional growth. Separately, HS HYOSUNG's leadership met bilaterally with Secretary Ebrard to elaborate on its strategic vision and investment plans.

The agreement sets out a phased expansion of HS HYOSUNG's investments in San Luis Potosí beginning in 2027, with the goal of creating a major advanced materials production hub that bolsters supply for North American and wider global markets. The company's advanced materials span tyre cord, a flagship world-leading product, along with mobility, energy, aerospace and defence applications. Its North American operations, spanning Mexico and the United States, turn out tyre cord, airbag materials and mobility interior components for global leaders such as General Motors and Goodyear, underpinned by a highly dependable global supply chain.

Nak-yang Sung, CEO, HS HYOSUNG ADVANCED MATERIALS, said, “This investment goes beyond establishing a simple manufacturing base – it reflects our strategy to turn Mexico into a pivotal hub connecting North America with global supply networks. We are also committed to strengthening local supply chains and creating high-quality jobs to contribute directly to the region's industrial ecosystem.”

Kumho Petrochemical Group is steering its business towards research-driven, higher-value outputs as oversupply and soft demand continue to weigh on the worldwide petrochemical sector. The Seoul-based group outlined plans to boost spending on speciality chemicals, sustainable materials and novel production methods, a push intended to lift profits while building a foundation for future expansion.

Underlying the move is a deliberate evolution in the group's identity, from a bulk materials vendor to a provider of technology-backed solutions that address shifting customer requirements and stricter environmental rules. A central element of that effort involves widening the speciality lineup, exemplified by added capacity for solution styrene butadiene rubber, a synthetic rubber that enhances durability, rolling resistance and tread wear in high-performance electric vehicle tyres.

Environmental initiatives form another pillar. Facilities built by the company can trap approximately 76,000 metric tonnes of carbon dioxide each year, while separately developed technology turns recycled acrylonitrile butadiene styrene sourced from scrapped household appliances into automotive-grade interior components that satisfy performance standards and generate fewer emissions than conventional methods. The group has also joined forces with POSCO Future M and BEI on anode-free lithium-metal battery development.

Parallel technology-focused programmes are underway at affiliated units. Kumho P&B Chemicals is formulating water-based epoxy resins that curb volatile organic compound releases while incorporating more bio-based inputs to reduce carbon intensity. Kumho Mitsui Chemicals is advancing bio-based polyurethane systems and electric vehicle materials, alongside debottlenecking work to add 100,000 tonnes of annual methylene diphenyl diisocyanate capacity. Kumho Polychem, meanwhile, is targeting ethylene propylene diene monomer through low-temperature polymerisation paired with energy-efficiency improvements.