In recent pre-season Formula 1 tests in Bahrain, some of the team’s technicians were spotted with a strange gun-shaped tool on the tires just before the cars hit the track.
The “weapon” was conceived and developed by the “Vehicle Dynamics” research group at the Federico II University of Naples. VESevo is the abbreviation for Viscoelasticity Evaluation System Evolved, but also derived from the Latin name of the ancient Vesuvius.
Vesevo collects information about the profile in order to understand the behavior of the tire on the track. With a data post-processing algorithm, technicians can analyze the physical properties of the tire. You get better information on internal temperatures, bond stiffness and wear. The data shown in the graphs (analyzed below) are used to understand the impact of tire temperature and road surface on tire performance and durability. This information can help teams choose the right compound for the race. Although the suppliers Pirelli in Formula 1 and Michelin in MotoGP provide information about the working range of the tires, it is not uncommon for the actual behavior of the tire to deviate from what is expected.
The weapon that is actually a hammer
The ergonomics of the weapon allow technicians to perform a large number of tests well and repeatedly. This is a necessary prerequisite for being able to compare the recorded data. Inside the instrument there is a sliding steel rod that is pretensioned by a spring. The end of the indenter that “pounds” the rubber is hemispherical in shape. similar to the Brinnel endurance test. The main difference is that VESevo does not leave permanent marks on the profile. The wave can bounce off freely after the impact, so that the damping can be neglected. The repeatability of the test is ensured by a sealing / release mechanism that can always position the top plate of the rod in the same starting position.
The signal of the Move of the rod is detected by an optical sensor, which is advantageous due to its small size. The profile for each individual test temperature can also be measured with an infrared pyrometer. The acquisition and subsequent analysis of data through processing algorithms enables technicians to characterize the viscoelastic behavior.
In addition to the patented hardware, the software was also developed internally (in the Lab View environment) by the research group. With personalization you can “clean up” the raw data of recording anomalies. During the test of the temperature of the rubber, three consecutive measurements are made at the same temperature in order to have sufficient data for statistical purposes.
If you analyze the two graphs above, you will see a different reaction of the rod when the temperature changes. On the left you can see that at At low temperatures, both the number of rebounds and the amplitude decrease. The viscoelastic effect of the profile has the opposite effect as the temperature rises. The graphic on the right shows depending on the speed of the shaft: a different slope of the curve before and after the maximum penetration into the tread. The reason is rebound on a viscoelastic surface, which changes the response to stress.
How does a tire made of viscoelastic material behave?
As just described, knowing the viscoelasticity of the joint enables a more accurate description of the asphalt tire model. This is also useful to: a Prediction of the coefficient of friction Aligned both in terms of road safety and performance on the route.
In motorsport, the supply of quota tires prevents technicians from performing invasive tests where the rubber can no longer be used. VESevo is a non-destructive tool and can be used immediately, expanding the prospects for optimizing vehicle dynamics directly on the racetrack. The “hammering” applied to the tread does not affect the performance of the tire itself.
A viscoelastic material has an intermediate behavior between a purely elastic, which respects Hooke’s law, and a purely viscous, which respects Newton’s law of viscosity. This means that the material Loads deform as a function of time and temperature. The response of the material is delayed out of phase with respect to the prompt. The answer analysis relationship that expresses Resistance to deformation, is a complex module Sum of two factors. The real part Memory module, indicates the ability to store energy during stress. The imaginary part, Loss modulus, shows the loss of energy in the form of heat. This provides an important aid in predicting grip and tread wear.
However, dynamic mechanical analysis (DMA), which is concerned with studying viscoelasticity, requires the use of material samples that have been tested on specific machines. This application cannot be used for tires as they are destructive tests. With VESevo, technicians can analyze the viscoelastic properties of the material as a function of temperature without having to cut the tires.
An example: three connections compared
A preliminary index of viscoelastic behavior can be defined by VESevo as Kinetic Energy Variation of the stem before and after the first imprint within the temperature range for each tire tested. Kinetic energy is the energy that a moving body possesses and is proportional to the square of its speed.
Megaride states that this index was chosen for this preliminary analysis because of its physical agreement with the intrinsic concept of dissipation due to viscoelasticity and for its good adaptation to the available reference curves the loss factor.
In the graph above, the viscoelastic index (the change in kinetic energy) of three tire reference compounds (A, B and C) is given as a function of temperature along with their fit curves. The trends show a good correlation with those of the loss factor. which are normalized for reasons of commercial confidentiality (graphic below).
There is a peak in correspondence with the glass transition temperature at which the maximum energy loss occurs. Compound C has a higher loss factor than the others. Tire B shows a lower glass transition temperature; the curve is shifted to the left compared to the other two.
Source: megaride.eu; VESevo: An innovative device for non-destructive characterization of viscoelasticity – Antonio Maiorano