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.

 

Leading global tyre manufacturer NEXEN TIRE has signed a long-term supply agreement with LD Carbon (LDC) for recovered carbon black (rCB) with an aim to boost the adoption of sustainable materials. This partnership is in line with the company's commitment to improving worldwide sustainable management standards.

In order to significantly reduce carbon emissions and encourage resource cycle, LD Carbon produces its recovered carbon black by pyrolysing end-of-life tyres in an oxygen-free atmosphere. Using recycled carbon black instead of petroleum-based carbon black is a smart move that preserves product performance and promotes environmental sustainability. The company has been using more recovered carbon black over time, and this agreement aims to hasten the shift to more ecologically friendly raw materials.

Recovered carbon black from manufacturing sites worldwide, such as those in China, the Czech Republic and Korea, will be used by NEXEN TIRE. In order to increase its global competitiveness, NEXEN TIRE is creating a circular resource structure that will provide a steady supply of recycled materials and integrate them into its global manufacturing chain. The use of sustainable materials in tyre manufacturing will be required under the European Union's proposed Ecodesign for Sustainable Products Regulation (ESPR), and NEXEN TIRE is in a strong position to increase its competitiveness by proactively creating a sustainable raw material supply chain, especially in Europe, where it accounts for almost 40 percent of total sales.

John Bosco (Hyeon Suk) Kim, CEO, NEXEN TIRE, said, “Expanding the usage of recovered carbon black is a strategic step that demonstrates our commitment to ESG management and proactive response to global environmental concerns. We will continue to accelerate the transition to eco-friendly materials and establish a tire manufacturing system that has a low environmental effect from production to disposal.”

LANXESS, a speciality chemicals company, has achieved the top score of ‘A’ in the Climate Change category of the CDP annual sustainability ratings. This is LANXESS’s eighth time in a row in the climate category on the A list by the global environmental non-profit organisation.

In the most significant investor questionnaire in the world, the non-profit CDP assesses the performance and openness of organisations in the categories of Climate Change, Water Security and Forests. Every year, it gathers and evaluates data and information on environmental consequences, goals and plans on behalf of investors. Participation is entirely voluntary.

LANXESS led the evaluation group of more than 24,700 businesses globally in the Climate Change area with the highest grade of A, secure a spot among the top two percent of all rated companies. These businesses, according to CDP, are distinguished by extensive and high-quality data that offers a thorough summary of environmental impacts and transformation goals. Additionally, LANXESS got an A- and reaffirmed its top spot in the Water Security area.

Hubert Fink, member of the Board of Management of LANXESS AG, said, “With our solutions and expertise, we are making a significant contribution to sustainable development. At the same time, we are helping our customers achieve their sustainability goals. CDP's renewed top rating underscores our commitment to climate protection and shows that we are on the right track.”

Bansal Wire Industries (BWIL)  unveiled its largest manufacturing facility in Dadri, bolstering India’s push to expand its manufacturing and infrastructure sectors. The 37-acre plant increases BWIL’s total manufacturing sites to five, with one in Bahadurgarh and three in Ghaziabad. The company’s production capacity has risen to 6 million metric tonnes per annum from 2.4 million tonnes previously.

The advanced facility produces specialised wires for diverse sectors, including agriculture, automotive, construction, power transmission, and general engineering. For the automotive industry, the plant manufactures steel wires, hose wires, and low-relaxation pre-stressed concrete steel strands used in bullet trains and metro systems.

The Dadri operation integrates industrial-scale processes with sustainability practices, including rainwater harvesting, solar power generation, acid-free wire cleaning and energy-efficient machinery. An on-site effluent treatment plant and landscaped areas are also featured. A new section for speciality wires was added this quarter, with IT/OT (Internal/Outer) wires coming soon.

Manufacturing Capabilities

The plant produces high-carbon steel wire, valued for its wear resistance and strength, making it suitable for door panels, vehicle frames, bushings, springs, and other automotive components. The facility also manufactures bead wire, a low-carbon wire with properties including weldability, ductility, high strength, fatigue resistance, adhesion to rubber, and malleability. Visible at the edge of a tyre, bead wire secures the tyre to the rim. Some wires receive zinc coating to increase corrosion resistance.

The bead wire production process follows multiple stages: procuring high-carbon steel rods, drawing high-tensile steel wire, passing through a lead bath, washing in an HCL tank, drying via heat treatment, applying zinc and copper coatings to form brass, wiping excess coating, cooling with chemical additives, collecting the wires and reducing them to thin filaments for those wires.

Each wire is drawn differently based on customer requirements before passing through Chinese and Indian furnaces. A 30-metre furnace operating at 980-1000°C restores wire properties after initial processing. After cleaning the HCL tank, zinc and copper coatings are applied. The chemical and subsequent stages occur in air-conditioned environments to maintain wire properties during separation into filaments. The 0.2mm filaments are combined to achieve 1.6-2.4mm thicknesses for commercial and TBR (Truck, Bus, and Radial) tyres.

The Dadri plant also produces hose wires and steel cords that enhance tyre strength, performance and stability. Additionally, it manufactures stainless steel wires that provide aesthetic appearance, corrosion and staining resistance, and low maintenance costs for automotive applications.

Business Performance

As a diversified wire manufacturer, BWIL reports 89 percent client retention and 20-25 percent year-on-year sales growth. Exports constitute 10-15 percent of total sales, with 75 percent destined for US and European markets. Pranav Bansal noted that despite China’s dominance in steel exports, India shows "tremendous positivity” for steel and stainless-steel wires.

He dismissed concerns about US reciprocal tariffs, explaining that with exports limited to 10 percent, the company maintains growth above 20 percent. BWIL’s revenue increased 52 percent in Q3FY25, and profits rose 171 percent.

Regarding price fluctuation, Pravin Bansal said, “We follow a cost + business model at BWIL. While the prices of steel change every month, the prices of stainless steel undergo change daily. The prices are revised as soon as there is a change, ensuring that there is no lag across 90 percent of products.”

He added, "Business works on quantity terms, not on revenue. Instead, revenue is a function of raw materials, and we’ve never given too much attention to the former.” However, he acknowledged that some automotive product prices fluctuate quarterly, creating a lag for products like bead wires and suspension spring wires, with costs passed on in subsequent quarters.

Expansion Plans

Pranav Bansal outlined the company's growth strategy: "Our business model is such that we can keep investing as per the needs of our customers. We don't need to wait for a specific capacity to be established before commencing business; we can expand on a to-go basis.”

For FY26, BWIL plans a 42-acre Sanand, Gujarat plant focused on low carbon and stainless steel wires. The INR 800-900 million facility will include 0.18 million tonnes of backward integration capacity and 60,000 tonnes of new wire production.

Currently serving 5,000 customers with 4,000 SKUs, BWIL's long-term strategy involves developing products with zero price fluctuation, which Pranav Bansal describes as "most helpful for the company’s supply chain cycle."

The company contributes to India's electric vehicle sector, which recorded sales of 1.94 million units by end-2024, with Tata Motors leading the market. BWIL's steel cords and specialised wires offer high tensile strength with reduced weight for EV applications. The company also produces copper-coated and aluminium-stranded wires for electric vehicles.

 

 Natural rubber prices declined in March amid significant market volatility, according to the latest monthly report from the Association of Natural Rubber Producing Countries (ANRPC).

The industry body said in its Monthly NR Statistical Report for March 2025 that the downward trend was attributed to multiple factors, including the postponement of the European Union Deforestation Regulation (EUDR), changes in US tariff policies, and falling oil prices.

Despite strong demand from China in early 2025, market sentiment was dampened by growing concerns over new US tariff measures, which analysts say could reshape global rubber trade flows.

The ANRPC, representing major producing nations including Thailand, Indonesia, Vietnam and Malaysia, projected global natural rubber production to grow by a modest 0.4 percent in 2025 compared to the previous year.

Meanwhile, global demand for natural rubber is forecast to increase by 1.5 percent this year, supported primarily by expansion in the electric vehicle market, according to data compiled from ANRPC member countries.

This growth comes despite concerns of a potential global economic slowdown and complications arising from new US trade policies that could hinder international trade.

Natural rubber, a critical raw material for tyre manufacturing and various industrial applications, has faced increasing price pressures as automotive production forecasts remain uncertain in key markets.