Publications
Authors: Behzad Hamedi, Abhishek Saraswat, Jeff Warfford, Cameron Garman, William V. Mars & Saied Taheri
Published: 02/01/2026
Journal: Advances and Challenges in Computational Mechanics
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A Simulation-Based Framework for Designing Run-Flat Tires with Rim-Supported System
Abstract
Tire punctures pose significant challenges, particularly for critical applications like off-road vehicles. Run-flat tire (RFT) systems, including Self-Supporting Systems (SSS) and Rim-Support Systems (RSS), improve safety and operational efficiency by enabling mobility after pressure loss. This study focuses on RSS inserts, employing Finite Element Analysis (FEA) to evaluate fatigue life, thermal performance, and structural integrity under zero-pressure conditions. Preliminary designs for both s...
Tire punctures pose significant challenges, particularly for critical applications like off-road vehicles. Run-flat tire (RFT) systems, including Self-Supporting Systems (SSS) and Rim-Support Systems (RSS), improve safety and operational efficiency by enabling mobility after pressure loss. This study focuses on RSS inserts, employing Finite Element Analysis (FEA) to evaluate fatigue life, thermal performance, and structural integrity under zero-pressure conditions. Preliminary designs for both solid and hollow insert concepts are analyzed, with key indicators discussed. Validated through mesh convergence and sensitivity analyses, the model investigates parameters such as stress distribution, radial stiffness, strain energy density, temperature profiles, and contact patch behavior. Fatigue life and thermal performance are computed using the Endurica Solver, correlating insert design parameters with durability, deformation, and thermal management. Results indicate that insufficient insert support under zero-pressure conditions leads to tread warpage, uneven contact, and localized deformation, adversely affecting durability and handling. Critical metrics such as footprint area, pressure distribution, and displacement are identified as key optimization drivers. This simulation-driven framework provides valuable insights into developing durable, thermally efficient run-flat tires to meet real-world operational demands.
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Authors: William V. Mars, Thomas G. Ebbott, Ethan C. Steiner, Lewis B. Tunnicliffe, and James W. Kollar
Published: 10/12/2025
Journal: Tire Science and Technology
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Critical Plane Analysis of Surface-Proximal Fields for the Simulation of Thermo-Mechanical Wear
Abstract
A theory for multifield analysis of the consequences of sliding asperities on a rubber surface has been developed. The analysis considers (1) the multiaxial mechanical fields set up via the asperity contact, (2) the thermal field set up due to friction and heat generation, (3) the material property fields that evolve due to thermochemistry, and (4) the growth of crack precursors near the sliding interface. The theory considers two distinct Eulerian directions: the first direction considers strai...
A theory for multifield analysis of the consequences of sliding asperities on a rubber surface has been developed. The analysis considers (1) the multiaxial mechanical fields set up via the asperity contact, (2) the thermal field set up due to friction and heat generation, (3) the material property fields that evolve due to thermochemistry, and (4) the growth of crack precursors near the sliding interface. The theory considers two distinct Eulerian directions: the first direction considers strain history along streamlines oriented in the direction of sliding, and the second direction considers the progression of material toward the wear surface as material is removed. Considering the mechanical and thermal fields set up around an asperity, the theory simplifies what would otherwise be a large and complex analysis. The theory produces an estimate of the variation with depth of fatigue damage (residual life; as calculated via critical plane analysis), from which may be derived the wear rate for a particular surface sliding under a given set of conditions. Results of the calculation for two cases (two-dimensional sine wave and square wave asperity surfaces) with varying normal contact pressure are compared with Gent and Pulford’s blade abrader experiments.
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Authors: Nikolas Ryzí, Radek Stoček, Jakub Pawlas, William V. Mars, and Thomas G. Ebbott
Published: 04/07/2025
Journal: International Journal of Fracture
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Test parameter sensitivity of the Lake-Yeoh cutting method for measurement of intrinsic strength of rubber: Nikolas Ryzí et al.
Abstract
The intrinsic strength of rubber, T0 is one of the key parameters when describing fracture behaviour of elastomer because it is at this specific value of energy that crack growth initiates within loaded rubber material. The Coesfeld Intrinsic Strength Analyzer (ISA) has been established as the most efficient equipment to directly analyse T0 for various rubber materials. However, to obtain the most reliable and reproducible results it is crucial to understand the influence of boundary conditions ...
The intrinsic strength of rubber, T0 is one of the key parameters when describing fracture behaviour of elastomer because it is at this specific value of energy that crack growth initiates within loaded rubber material. The Coesfeld Intrinsic Strength Analyzer (ISA) has been established as the most efficient equipment to directly analyse T0 for various rubber materials. However, to obtain the most reliable and reproducible results it is crucial to understand the influence of boundary conditions of the ISA measuring methodology. Therefore, in this study sets of boundary conditions were chosen to be analysed through mechanical response of reference EPDM material with known T0 value. For the purposes of this study the effects of individual boundary conditions were compared through directly measured value of intrinsic cutting energy, S0 which is proportional to T0. Blade sharpness and geometry showed the greatest impact followed by repetition of blade and specimen milling direction whereas the relaxation time and number of measuring strains showed no significant influence. The results of this study show that the knowledge of blade micro-geometry is at its most importance during the T0 analyses. Moreover, the data clearly indicates possible future modification of boundary conditions to achieve a very efficient testing procedure with significantly reduced time required for the analyses.
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Authors: Behzad Hamedi a , Abhishek Saraswat b , Jeff Warfford c , Cameron Garman d , William V. Mars e , Saied Taheri f
Published: 01/07/2025
Journal: Engineering Failure Analysis
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A preliminary conceptual study for coupled thermo-mechanical and structural characterization of rim-supported run-flat tires
Abstract
Rim-supported inserts in run-flat tires (RSS RFTs) ensure extended mobility after a blowout, offering at least 50 miles of operation at 45 mph under zero-pressure conditions. However, excessive heat generation during deflation accelerates rubber aging and degrades performance. To address this, a validated 3D finite element model, coupled with Abaqus/CAE and Endurica co-simulations, is used to analyze strain distribution, contact patch characteristics, and thermo-mechanical behavior.
Results rev...
Rim-supported inserts in run-flat tires (RSS RFTs) ensure extended mobility after a blowout, offering at least 50 miles of operation at 45 mph under zero-pressure conditions. However, excessive heat generation during deflation accelerates rubber aging and degrades performance. To address this, a validated 3D finite element model, coupled with Abaqus/CAE and Endurica co-simulations, is used to analyze strain distribution, contact patch characteristics, and thermo-mechanical behavior.
Results reveal high strain and heat generation concentrated in the contact patch center, intensifying material degradation and the risk of premature failure. Strain redistribution mechanisms, shifting strain from the footprint and inner liner zones toward the sidewall, enhance durability and mobility under repeated loading or deflation scenarios. The methodology optimizes insert designs to mitigate localized stresses, deformation, sidewall warpage, and thermal issues, thereby extending fatigue life in deflated conditions.This study highlights critical design factors influencing the durability and performance of rim-supported run-flat tires (RSS RFTs). Simulation-driven methodologies are employed to evaluate and optimize key parameters such as durability, contact patch footprint area, pressure distribution, radial stiffness, and overall operational efficiency. A nonlinear FEA model in Abaqus/CAE accurately simulates large deformations, material behavior, and tire geometry, validated through mesh convergence studies, sensitivity analyses, and failure mechanism evaluations under diverse loading conditions. Predicted fatigue life and thermal performance align with prior studies, confirming the reliability of the approach and its potential for real-world application.
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Authors: Gobi Gobinath, Thomas Ebbott, Shannon Hughes
Published: 23/09/2024
Journal: Tire Science and Technology (2024) 52 (2): 93–122.
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Predicting Residual Casing Life of a Tire following an Impact Event
Abstract
By applying recognized engineering methods, including finite element analysis, the role of impact events on the service life of a tire was studied by varying three factors: speed of impact, treadwear, and angle of impact. The approach combines well-known finite element analysis methods to simulate a tire rolling over an obstacle with the calculation of damage at the tire belt edge imparted by the impact event by using recognized methods of rubber fatigue analysis. An efficient method is develope...
By applying recognized engineering methods, including finite element analysis, the role of impact events on the service life of a tire was studied by varying three factors: speed of impact, treadwear, and angle of impact. The approach combines well-known finite element analysis methods to simulate a tire rolling over an obstacle with the calculation of damage at the tire belt edge imparted by the impact event by using recognized methods of rubber fatigue analysis. An efficient method is developed and used to demonstrate that across a range of impact conditions, some conditions can cause substantial internal damage, whereas other conditions can cause very little damage. The area of investigation is the tire belt edge; thus, although significant internal damage may have occurred, it might not be visually perceptible in the normal operation of a vehicle. In some cases, the nondetectable damage is shown to propagate to a point where the tire loses its structural integrity before reaching its normal operating life defined by treadwear. This study includes the role of mechanical, temperature, and rate effects.
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Authors: William V. Mars, Ph.D., P.E. and Thomas G. Ebbott, Ph.D.
Published: 11/09/2024
Journal: Advances in Understanding Thermal Effects in Rubber
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A Review of Thermal Effects on Elastomer Durability
Abstract
A chapter in the book Advances in Understanding Thermal Effects in Rubber, Pages 251-324
Authors: William Mars, Kevin Barbash, Matthew Wieczorek, Scott Braddock, Joshua Goossens, Ethan Steiner
Published: 09/04/2024
Journal: Society of Automotive Engineers
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Durability of Elastomeric Bushings Computed from Track-Recorded Multi-Channel Road Load Input
Abstract
The qualification requirements of automakers derive from track testing in which road load and moment inputs to a part in x, y and z directions are recorded over a set of driving conditions selected to represent typical operation. Because recorded histories are lengthy, often comprising many millions of time steps, past industry practice has been to specify simplified block cycle schedules for purposes of durability testing or analysis. Simplification, however, depends on imprecise human judgemen...
The qualification requirements of automakers derive from track testing in which road load and moment inputs to a part in x, y and z directions are recorded over a set of driving conditions selected to represent typical operation. Because recorded histories are lengthy, often comprising many millions of time steps, past industry practice has been to specify simplified block cycle schedules for purposes of durability testing or analysis. Simplification, however, depends on imprecise human judgement, and risks fidelity of the inferred life and failure mode relative to actual. Fortunately, virtual methods for fatigue life prediction are available that are capable of processing full, real-time, multiaxial road load histories. Two examples of filled natural rubber ride bushings are considered here to demonstrate. Each bushing is subject to a schedule of 11 distinct recorded track events. Endurica EIETM map building procedures are first used together with a finite element solution to map the 6 channel loading space and to obtain stress/strain solutions at each gridpoint in the load space. EIE is then used with the recorded histories to interpolate from the recorded road load inputs on the bushing to stress-strain history at each element centroid in the finite element model. The interpolated stress-strain histories are then used to compute damage accrual and fatigue life across all 11 events. The computational requirements of this workflow are benchmarked with the outcome that the entire schedule in full detail can be analyzed on a timescale well suited for use at the earliest stages of business development and engineering.
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Authors: Lewis B. Tunnicliffe, Christopher G. Robertson, William V. Mars
Published: 30/12/2023
Journal: Rubber Chemistry and Technology
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A Microscopy Investigation of Rubber Compound Crack Precursors and Tensile Fracture Surfaces
Abstract
Tensile stress–strain testing is used to investigate the fracture behavior of carbon black–reinforced styrene–butadiene rubber, using 50 replicate specimens. Four vulcanized rubber compounds are studied: a CB-filled SBR with standard mixing conditions (control), the same formulation with intentional poor mixing of the CB, and materials identical to the control material but formed by adding minor amounts of 0.5-mm-diameter glass microspheres (beads)—serving as large model defects/inclusio...
Tensile stress–strain testing is used to investigate the fracture behavior of carbon black–reinforced styrene–butadiene rubber, using 50 replicate specimens. Four vulcanized rubber compounds are studied: a CB-filled SBR with standard mixing conditions (control), the same formulation with intentional poor mixing of the CB, and materials identical to the control material but formed by adding minor amounts of 0.5-mm-diameter glass microspheres (beads)—serving as large model defects/inclusions—using a two-roll mill at two levels, corresponding to average values of 0.78 and 6.24 beads per gauge section region of the tensile test specimen. Microscopy analysis of the resulting fracture surfaces was conducted to complement our recent publication on Weibull failure statistics for distributions of tensile strength and crack precursor size. All 200 fractured specimens from tensile testing at 23°C were imaged with light microscopy and exhibited fracture surfaces characterized by relatively smooth planes perpendicular to the uniaxial loading direction. Most tensile failures originated from the edges of the dumbbell specimens, in line with expectations from fracture mechanics. Light microscopy revealed concentric fracture ring features of high specular reflectance emanating from crack precursors, which are a universal feature of the failure process for these compounds and independent of precursor type, size, or location. Noncontact interferometric microscopy confirmed that the rings resulted from variations in surface micro-roughness, proceeding outward from the precursor as rough–smooth–rough to the edge of the fracture surface. Fracture rings were also observed for tensile tests performed at 80°C. The variation in surface roughness of the fracture surface has parallels to the stick–slip tearing behavior seen for rubbers torn at medium to high rates. To the best of the authors’ knowledge, this is the first time that such striking features have been reported.
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Authors: Mars W.V. (2020)
Published: 03/12/2020
Journal: Heinrich G., Kipscholl R., Stoček R. (eds) Fatigue Crack Growth in Rubber Materials. Advances in Polymer Science, vol 286. Springer, Cham.
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Critical Plane Analysis of Rubber
Abstract
Durability is an essential feature of most elastomer products, directly linked to safety and to perceptions of brand quality. Product designers must therefore consider the impact on product durability of typical and abusive end-user loading scenarios. This can be accomplished using critical plane analysis (CPA). CPA starts by acknowledging that a small crack precursor might exist at any point in a part, and in any orientation, and that the potential development of all crack precursors must be ev...
Durability is an essential feature of most elastomer products, directly linked to safety and to perceptions of brand quality. Product designers must therefore consider the impact on product durability of typical and abusive end-user loading scenarios. This can be accomplished using critical plane analysis (CPA). CPA starts by acknowledging that a small crack precursor might exist at any point in a part, and in any orientation, and that the potential development of all crack precursors must be evaluated. The analysis produces a full accounting of which location and orientation maximizes crack growth (or, equivalently, minimizes fatigue life) at each point, the energy release rate history experienced, and of course the worst-case fatigue life across all possible orientations. This review provides an account of the development of the method over the last two decades and the validation case that has accumulated. This review also suggests directions for further development of the method.
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Authors: Robertson C.G., Stoček R., Mars W.V. (2020)
Published: 01/12/2020
Journal: Advances in Polymer Science
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The Fatigue Threshold of Rubber and Its Characterization Using the Cutting Method
Abstract
Below a limiting value of tearing energy called the intrinsic strength or fatigue threshold (T0), cracks will not grow in rubber due to fatigue; hence, this material characteristic is important to understand from both fundamental and practical perspectives. We summarize key aspects of the fatigue threshold, including the Lake-Thomas molecular interpretation of T0 in terms of fracture of polymer network chains in crosslinked elastomers. The various testing approaches for quantifying T0 are also d...
Below a limiting value of tearing energy called the intrinsic strength or fatigue threshold (T0), cracks will not grow in rubber due to fatigue; hence, this material characteristic is important to understand from both fundamental and practical perspectives. We summarize key aspects of the fatigue threshold, including the Lake-Thomas molecular interpretation of T0 in terms of fracture of polymer network chains in crosslinked elastomers. The various testing approaches for quantifying T0 are also discussed, with a focus on the classic Lake-Yeoh cutting method which was recently revived by the introduction of a commercial testing instrument that applies this procedure, the Intrinsic Strength Analyser (ISA). A validation of the cutting method is also given by demonstrating that a 2-h test on the ISA yields a value of T0 that is essentially identical to the T0 from near-threshold fatigue crack growth (FCG) measurements that require 7.5 months of continuous testing. Compound formulation effects – polymer type, crosslink density, type and amount of reinforcing fillers, and addition of oils/plasticizers – are examined based on the limited published research in this area and our new results. At the end, some insights are offered into using the fatigue threshold to develop highly durable rubber products.
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