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CONFLUENCE OF SCIENCE, ENGINEERING, ART
Time: Dec 15th 2017 Copy editor: Tyrefull
A pioneering engineering researcher in multibody dynamics and vehicle dynamics, Dr. Corina Sandu has done ground-breaking work in tyre modelling, terramechanics, and simulations that are aimed at improving the design of tyres and vehicles. In an interview to Tyre Asia, this Professor in the Department of Mechanical Engineering at Virginia Tech and Director of its Advanced Vehicle Dynamics Laboratory talks about her research and academic work. Author of about 70 peer-reviewed journal articles, 102 proceedings papers, six book chapters, and over 250 other papers, reports, posters,and presentations, she is also the Editor-in-Chief of the SAE International Journal of Commercial Vehicles and Associate Editor of the ASME Journal of Computational and Nonlinear Dynamics and of the Journal of Mechanics Based Design of Structures and Machines. She serves as the Chair of the ASME Design Engineering Division (DED) and as the Vice-President of the International Society for Terrain-Vehicle Systems (ISTVS). Dr.Sandu has been an ASME Fellow since 2011 and has been elected SAE Fellow in 2017.
When it comes to R&D in tyres and vehicle dynamics, one can turn to Dr. Corina Sandu for an update on current research in these fields where she has done breakthrough research. As a Professor in the Department of Mechanical Engineering at Virginia Tech and Director of its Advanced Vehicle Dynamics Laboratory and past Chair of the ASME Vehicle Design Committee and of the SAE Chassis Design and Vehicle Dynamics committee, she has taken up several research projects and supervised dozens of PhD and MS students giving her opportunities to remain on top of cutting edge technology. Her work has enhanced the knowledge of tyre designers worldwide.
Dr.Sandu says that there are many challenges before tyre designers in the context of expected proliferation of autonomous drive vehicles by 2020. “Tyres are fascinating and complex systems that are critical to the mobility and performance of wheeled ground vehicles. In addition to the chassis, tyres are probably the only vehicle components where science, engineering, and art meet,” she says.
Given their basic functions of providing traction, road holding, and suspension, tyres will continue to stay extremely relevant for future vehicles. “In fact, I think that tyres will play an increasing role with the proliferation of autonomous drive, as they will be an excellent but so far less explored venue to add more intelligence to the vehicles.”
She thinks that the tyre designers will face the challenge of improving the traditional performance of the tyres and of making them more energy efficient, while also incorporating into their design new and sophisticated sensor systems to aid in the autonomous driving.
Commenting on the critical role of tyre tread design and compounds to address issues such as friction and noise, Dr. Sandu stressed their importance. “Tyre tread design and rubber compounds are of critical relevance in addressing the tyre-road friction and the noise generated by the tyre-pavement interaction,” says she.
“I will address the friction part first: Part of our ongoing research in the Advanced Vehicle Dynamics Laboratory at Virginia Tech focuses on investigating the tractive performance of tyres on various types of surfaces and terrain types.Specifically, we are interested in understanding the fundamental principles involved in the tyre- terrain contact, explaining it in scientific terms, and using this knowledge to build tyre (and tyre- terrain contact) models, which can be used for predicting tyre and vehicle performance.”
For collecting experimental data on tyre tractive and braking performance on various surfaces and terrain types, Dr Sandu developed with her students an indoor single tyre test rig, called the Terramechanics Rig. “Our research indicates that there are multiple tyre design features, material properties, or operational parameters influencing the traction and braking capabilities of tyres.”
For hard surfaces, the researchers typically focus on the friction at the tyre-road interface as a key element in predicting the tyre performance. In this regard, her research looked at the traction of pneumatic tyres on ice, which continues to be a challenging scenario.
The static coefficient of friction used in her laboratory for the ice was between 0.15 and 0.18. Her team has done conclusive studies substantiating the fact that the tractive performance of a pneumatic tyre is dependent on the height of the tread (reduce tread height leading to reduced traction capability), as well as on the tyre inflation pressure, normal load, and ice/tyre temperature.
Higher friction levels were observed on dry ice compared to wet ice, leading to a level of traction about three times larger. Furthermore, tyres tested using different aggregates on the ice surface (salt, sand, etc.) indicated an increase in the friction levels with an increase in the adhesion capability of the particles to ice surface.
“We also distinguished differences, of course, between the traction of tyres with all season tread patterns versus winter tyres. More research must be conducted to be able to clearly assess and quantify the effort of specific tyre tread design parameters on the friction/tractive/ braking capacity of a pneumatic tyre.”
For vehicles operating in off-road conditions, such as tractors, military vehicles, SUVs, etc., in addition to the resistance due to the friction force at the interface between the tyre and the terrain (namely the shear force for deformable terrains), additional resistance will appear due to the sinkage of the tyre in the soil, as well as the resistance created due to soil accumulation (bulldozing effect).
These effects compound the challenge of evaluating the influence of various tyre parameters on the vehicle performance with the influence of the soil/terrain being negotiated.
Rubber compound
Regarding the effect of the rubber compound on the tyre-road friction, she said this is part of her on-going research on which her team may be able to report in the near future. Being mechanical engineers, her team’s investigation looks into this effect at the system level i.e., the full tyre.
“Once the experimental results are obtained for the performance of tyres with different rubber compounds in our laboratory, we plan on collaborating with material scientists to closely correlate the tyre performance with specific parameters for each compound,” Dr. Sandu said.
Regarding the tyre-pavement noise, she explained that the noise generated due to the tyre-pavement interaction is the main source of noise for passenger cars at speeds exceeding 40 km/h and for trucks exceeding 70 km/h.
“At Virginia Tech, we conducted studies in collaboration with Prof. Ricardo Burdisso’s laboratory on experimental measurement of the tyre-pavement noise for forty-two tyres over a range of speeds of 72-105 km/h, on a non-porous asphalt pavement. It has been shown that tyres with different tread pattern and construction generate noise of different levels and frequencies.”
Furthermore, she said, based on the experimental noise data collected, two artificial neural networks (ANN) were developed to predict the tread pattern and, respectively, the non-tread pattern noise components, separately.
“From our study, we concluded that on the non-porous asphalt tested, for the summer and all-season tyres tested, the tread pattern noise represents less than 5% of the total noise. In the same time, for some snow tyres and some directional tyres, the tread pattern may contribute up to 10~50% of total tyre-pavement noise.”
Dr. Sandu conducted several projects at AVDL with the scope of modelling the tyre-road (or off-road) contact and the performance of tyres under various conditions.”
In one of these studies, conducted in cooperation with Prof. Saied Taheri’s laboratory, their team has investigated the development of a physics-based multiscale rubber-road friction model that can predict the effectiveness of the tyre as it interacts with the vehicle and the pavement.
The study proved that a local fractal parameter and three other texture parameters can distinguish between road profiles that have different friction characteristics. “Our research has led to an in-depth understanding of contact mechanics and of the effect of the diverse factors that influence friction,” she said.
Elaborating on the dynamic mechanical analysis, she mentioned that new equipment has been developed as part of this project to measure the friction between a rubber sample and synthetic road surface to provide data for the multiscale rubber-road friction model. The result is the development of the Dynamic Friction Test apparatus by a graduate student whom Dr. Taheri and Dr.Sandu co-advised. It was also done in collaboration with other students at the
Center for Tire Research.
The equipment is able to measure the horizontal tractive friction force of surface-rubber braking traction and the dynamic vertical load on the test sample. The system consists of a rotating disk, to which an arbitrary surface simulating the road is attached.
The rubber tread sample to be tested is mounted on a measuring arm, which also holds the load cell that measures the vertical load. The measuring arm is constrained in the longitudinal and axial directions. The speed of the rotating disk and the speed of the rubber sample can be controlled, thus allowing measurements of the rubber sample-disk at various slip ratios.
Future research
Dr Sandu’s recent tyre-pavement interaction noise study conducted in collaboration with Dr.Burdissoon was on passenger car radial (PCR) tyres with different tread patterns. It has brought out many interesting points. While the results obtained so far suggest focusing future research on reducing the non-tread pattern noise, for some of the tyres studied on the non-porous asphalt pavement tested, the tread pattern noise is still dominant at certain frequencies above the non-tread pattern noise. One way the tyre designers could reduce this effect could be by spreading the tread pattern noise to a wider frequency range.
When asked what parameters tyre designers should take into consideration while working on developing tyre tread patterns that would improve rolling resistance and enhance safety/grip, Dr.Sandu says that this is a field where further research is needed.
“I would like to emphasize that one of the most important aspects to consider would be the type of environment in which the respective tyre will operate. While improving rolling resistance and enhancing safety is a common goal, the way to achieve this is dependent on the type and characteristics of the road/ terrain on which the tyre will perform.”
Dr. Sandu said the operational parameters of the tyre and vehicle also have a great influence, of course. A systematic approach in identifying the most important tyre tread pattern parameters for improving rolling resistance and grip on each of the surfaces of interest is needed to provide an accurate response.
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