Development Of An Innovative Instrument For Non-
Destructive Viscoelasticity Characterization: VESevo
Flavio Farroni1, Andrea Genovese1, Antonio Maiorano1, Aleksandr Sakhnevych1 and
1 University of Naples Federico II
Abstract. The evaluation of the viscoelastic properties is a key topic for the anal-
ysis of the dynamic mechanical behaviour of polymers. In vehicle dynamics field,
the knowledge of the viscoelasticity of tread compound is fundamental for tire-
road contact mechanics modelling and friction coefficient prediction for the im-
provement of vehicle performance and safety, i.e. motorsport field. These prop-
erties are usually characterised by means of Dynamic Mechanical Analysis,
which implies testing a compound sample obtained by destroing the tire of inter-
est or a slab manufactured in different conditions respect to the final product pro-
vided by tiremakers. In this scenario, the non-destructive procedures are an ad-
vantageous solution for the analysis of the tread viscoelasticity, whitout affecting
the tire integrity, allowing a great number of tests in the shortest possible time.
For this reason, the authors propose an innovative instrument, called VESevo, for
viscoelasticity evaluation by means of non-destructive and user-friendly tech-
nique. The purpose of the following work is the preliminary analysis of the dy-
namic response of the tires tested employing the VESevo in order to determine
viscoelastic behaviour indexes for mechanical properties evaluation.
Keywords: Non-Destructive Testing, Tire Viscoelasticity, Vehicle Dynamics
The evaluation of tire tread viscoelasticity is a fundamental topic in a wide range of
activities concerning the development of polymers for innovative compounds, the par-
ametrization of physical contact models and the optimization of vehicle performance
and road safety.
In these applications, the viscoelastic properties determination of tire block, which
depends on rubber temperature and frequency solicitation of bitumen asperities, is es-
sential for contact mechanics modelling and the prediction of the limit value of the local
friction coefficient –.
IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . . 1
The Dynamic Mechanical Analysis (D.M.A.) is widely employed into the character-
ization of viscoelasticity in order define the hysteretic behaviour of the compound fol-
lowing the Time-Temperature Superposition principle . On one hand, this testing
approach perfectly fits with polymer specimens manufactured with specific dimension
for the D.M.A. and it cannot be always applied for tread characterization because of the
need to destroy the tire; on the other hand, these common testing procedures involve
complex and very expensive machines for the analysis of a generic compound sample.
Regarding the evaluation of the parameters of contact and friction models, the avail-
ability of thermal and structural properties of the effective tread compound provides an
increase in in reliability of the prediction of magnitudes of interest by means of the
proposed models. The chance to determine the viscoelasticity by means of non-invasive
testing would allow to preserve the tire integrity and to exclude the boundary effects
due to testing specimen of specific dimensions.
For these reasons, the development of innovative methodologies, as well as the non-
destructives, are an attractive solution replacing the standard test methods involving
complex and expensive benches for the investigation of a compound specimen manu-
factured in different conditions respect to the final product provided by tiremakers .
Further, Motorsport racing teams use to face with the restrictions due to the employ-
ment of confidential tires and not available to invasive testing. Therefore, an innovative
procedure for the acquisition of the data for tire viscoelasticity characterization within
the working thermal range could be very useful for vehicle setup optimization and def-
inition of vehicle simulation tools .
Hence, the Vehicle Dynamics research group of the Department of Industrial Engi-
neering of the University of Naples Federico II has designed and developed an innova-
tive and portable device, defined as Viscoelasticity Evaluation System Evolved
(VESevo), which allows users to characterise the tire tread viscoelasticity and its vari-
ations due to cooling or heating, due to wear phenomena , aging or different
compounding  depending on vehicle applications. Thus, engineers, especially Mo-
torsport ones, will be capable of analysing more useful information about confidential
tires and improving the vehicle performances and safety.
In the current work, the authors describe the development of the prototypal device
VESevo and the preliminary experimental activity aimed to analyse the viscoelastic
tires tread response taking into account the signals of interest. Therefore, the main task
of the paper is the employment of this innovative device for the extrapolation of the
parameters which mostly match with the viscoelasticity behaviour .
2 Viscoelasticity Properties and Characterization Methods
The Viscoelasticity Evaluation System Evo, also called VESevo, is a prototypal de-
vice developed by Vehicle Dynamics Research Group of the Department of Industrial
Engineering of the university of Naples Federico II. The principal aim of this device is
the evaluation of viscoelastic response of materials by means of a non-destructive
2 IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . .
A viscoelastic material exhibits a mechanical behaviour depending on time and tem-
perature. Particularly, it halfway behaves between a purely elastic (Hookean Solid) and
a purely viscous one (Newtonian Liquid) . Therefore, a phase angle between 0° and
90° occurs comparing the stress and the corresponding strain (Fig. 1).
Fig. 1. Stress-strain phase delay for a viscoelastic material
This means that the stress-strain relationship is defined by a complex dynamic mod-
ulus as amount of the overall resistance to deformation of the compound:
The complex modulus is characterised by a real and an imaginary party. The first
one is defined Storage Modulus E’ and is a of the elasticity of the material linked to the
ability to story energy, the second one is the Loss Modulus E” is associated with the
aptitude of the compound to dissipate energy as heat. The ratio of the Loss Modulus to
the Storage Modulus defines the Loss Factor which is an index of the material overall
These viscoelastic properties of polymers, such as the tire tread compound, are usu-
ally determined by means of Dynamic Mechanical Analysis (D.M.A.). This method
requires testing a polymeric specimen of suitable dimension within a frequency range
from 0.1 Hz to 100 Hz . Furthermore, the D.M.A. is carried out by means of expen-
sive rheometers distinguished in three point bending and dual cantilever for dynamic
modulus E* evaluation or torsional plates for shear modulus G*.
Fig. 2. Dual Cantilever Clamp (a), 3 Point Bending Clamp (b), Shear Sandwich Clamp (c)
The Dual Cantilever Clamp (Fig. 2, a) is suitable for testing highly damped materials
and it is the best mode for evaluating the cure of supported ones; the 3 Point Bending
Clamp (Fig. 2, b) is the best way for measuring medium to high modulus materials and
it guarantees the purest deformation mode since clamping effects are defected rather
IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . . 3
than Dual Cantilever; the Shear Sandwich Clamp (Fig. 2, c) is good for evaluating
highly damped soft compounds.
Tipical trend of the Storage and Loss Moduli depending on solicitation frequency is
shown in Fig. 3. At very low frequency range, the compound behaves as a pure viscous
solid (rubbery plateau region), whereas the behaviour is similar to a glassy solid (glassy
region plateau) at high stress frequency values. Considering the frequency range match-
ing with piece of curve between these regions, the compound behaviour is viscoelastic
and the maximum energy dissipation occurs.
Fig. 3. Viscoelastic properties with the respect the solicitation frequency
The viscoelastic curves shown in Fig. 3 match with a reference temperature at which
the frequency sweep characterization is carried out. The same trend can be analysed
taking into account the temperature dependence, as shown in Fig. 4. On one hand, the
compound behaviour at lower temperature values is the same at high frequency ones
(glassy region); on the other hand, the same rubbery plateau region of low frequencies
occurs at high temperature ranges.
Fig. 4. Viscoelastic properties with the respect the compound temperature
The above diagrams exhibit the equivalence between temperature and time effects
on viscoelastic properties of viscoelastic material. This means that the Time-Tempera-
ture superposition principle is satisfied and the viscoelastic curves can be generated by
means of William-Landel-Ferry equation starting from the master curve :
4 IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . .
In equation 2, C1 and C2 are fitting coefficients of the William-Landel-Ferry rela-
tionship, T0 is the reference temperature of the master curve and aT is the shift factor
that satisfies the following relationship:
All the viscoelastic materials whose behaviour is in accordance with equations 2
and the Time-Temperature superposition principle are defined simple thermoreologi-
3 Prototypal device description
The Dynamic Mechanical Analysis described in the previous paragraph requires
very expensive and complex machines to determine the viscoelastic properties of a
compound of interest. Furthermore, this procedure only involves test on specimen of
standard dimension depending on the clamp system (Fig. 1). Thus, the viscoelasticity
characterization cannot be carried out on systems that do not allow the realization of
the samples required, such as a piece of tread compound of a Motorsport confidential
In this scenario, a prototypal device, called VESevo, has been developed by UniNa
Vehicle Dynamics research group with the aim to overcome the limits of traditional
D.M.A. testing and extrapolate the viscoelastic properties of the system of interest by
means of a non-destructive procedure.
The device VESevo has been designed taking into account a gun-shape handle. Thus,
the ergonomics of the instrument allows a high number of tests with a satisfying repeat-
ability (see Fig. 5).
Fig. 5. 3D representation of the prototypal device VESevo
The inner structure of the device is characterised by a steel rod with a semi-spherical
indenter. This rod is free to bounce on the surface of the compound of interest sliding
inside a suitable guide so that the damping phenomenon during the rod motion inside
the case can be neglected. A spring is arranged in the system in order to guarantee a
The motion of the rod always starts from the same initial position thanks to an in-
novative system based on an magnet: this magnet is mounted on a suitable slider and
IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . . 5
it is capable of holding the upper plate of the rod and lifting it up to the maximum ascent
point. The described system has been patented by the Vehicle Dynamics research group
of the University of Naples Federico II .
During each test, the motion of the rod starting from initial position against the
compound surface needs to be analysed. To acquire properly the displacement signal,
an optical sensor has been chosen for its compact dimensions and very high frequency
response rather than others commonly available in similar devices, such as LVDT.
The temperature of the compound during a single test has to be acquired together
with the displacement data. Therefore, a compact IR pirometer has been chosen and set
up in the suitable sensor housing in order to analyse the signals at different viscoelastic
behaviour of the specimen of interest.
4 Signal acquisition and processing
The signal acquisition of the VESevo needs a suitable case containing the data ac-
quisition devices, i.e. a National Instrument data logger and the conditioning devices
for the optical sensor and IR pyrometer provided by the corresponding manufacturers.
Furthermore, a self-made customized software for raw data acquisition has been de-
veloped in LabVIEW environment to find out any acquisition anomalies and check the
goodness of the whole test session.
A typical raw signal of the displacement curve during a single test is shown in Fig.
6. The signal is acquired within a time range of 0.1s. The compound temperature is
determind as the average of the values acquired before the first impact of the road on
the sample of interest.
Fig. 6. Displacement raw signal of the rod testing a compound at 30°C
In a single acquisition, the rod bounce exhibits three different phases which are es-
sential for the evaluation of the indexes connected with the viscoelastic behaviour :
• The first one is characterised by the impact of the sensor rod on the tire surface
and it matches with the minimum point of the acquired curve;
6 IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . .
• During the second phase, the rod bounces to the maximum point of the curve
because of its interaction with the external tire rubber layer; particularly, different
bounces could occur after the first one depending on surface temperature and
• The last phase is characterised by a stabilized rod displacement value established
within the contact at the end of transient reciprocal dynamics.
In order to characterise the tire tread compound within the temperature range of -
20°C to 100°C, a heating gun and a climatic cell (Fig. 7) were used. Thus, the glass
transition phenomenon could be identified for the compound of interest, with the po-
tential advantage to improve the evaluation of grip coefficient by means of specific
physical models .
During the test session, the tread surface is cooled and heated without degradation
until its temperature stabilises; then, three consecutives acquisitions at the same tem-
perature are stored in order to have a suitable amount of data for statistical processing.
The data are acquired by means of a self-made customized software developed in Lab-
Fig. 7. Instruments employed in the experimental characterization procedure
Taking into account the typical shape of the signals provided by the VESevo (Fig.
6), a set of indicators of the viscoelastic behaviour of the compound can be estimated
for the time-temperature characterization.
IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . . 7
Fig. 8. VESevo data acquisition on passenger tire A at different tread temperatures
In Fig. 8, the data acquired on a passenger tire compound (named A) at different
temperatures are shown. Particularly, increasing the temperature, the motion of the rod
changes due to different material responses. The signal is characterised by small am-
plitudes and reduced number of bounces within a low temperature range; on the con-
trast, more bounces with substantial amplitudes values occur at high temperatures. This
phenomenon is strictly depending on the viscoelasticity changes due to temperature
effect : when the tread compound is solicited at lower temperatures, the strain en-
ergy loss peak occurs and the rod cannot reach the maximum amplitude during the
Taking into account the equation 2, the loss factor master curves with respect the
frequency at different test temperatures can be analysed. As observable in Fig. 9, the
maximum loss factor values occur in the frequency range of 500-5000 Hz, which
matches with the VESevo solicitation one, and between -15° and 15°C. This data are
in accordance with the phenomena described in Fig. 8.
Fig. 9. Loss factor viscoelastic master curves at different reference temperatures
A further analysis on the viscoelastic behvior of the tested tire compound can be
carried out considering the velocity signals of the rod motion (Fig. 10). Particularly, the
8 IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . .
slope of the displacement curve before and after the maximum indentation depth
changes due to the rebound on a viscoelastic surface. Thus, two different velocity val-
ues for each test next to the indentation area can be identified.
Fig. 10. VESevo velocity signals on passenger tire A at different tread temperatures
A preliminary experimental test session has been carried out on other tire com-
pounds, identified as tire B and tire C, whose viscoelastic behaviour is different in ac-
cordance with their vehicle dynamics application . These compounds mostly differ
in percentage of fillers, silica, carbon filler and other chemicals added to the standard
stirene butadiene rubber.
Aspreviously described, the VESevo testing procedure requires warming and cool-
ing the tire by means of a professional heating gun (Fig. 7) or a climatic cell. The sur-
face tread temperature is measured through the IR pirometer set-up in the special hous-
ing built-in the device. Both temperature and displacement signals can be real-time an-
alysed through the customized acquisition software.
Fig. 11. Viscoelastic index at 1 Hz for the tested tire compounds
IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . . 9
Thus, a preliminary index of viscoelastic behaviour has been estimated as the varia-
tion of kinetic energy of the rod pre- and post- the first indentation, within the temper-
ature range of interest for each tested tire. The kinetic energy variation due to the
bounce on a viscoelastic sample is expressed as follows:
where is the mass of the indenter, and the velocity pre- and post- the
first indentation. Such index has been chosen for this preliminary analysis because of
its physical coherence with the intrinsic concept of dissipation due to viscoelasticity
and for the good fitting with the available loss factor data, coming from D.M.A. analysis
carried out at 1Hz, once properly re-scaled. In Fig. 11, the viscoelastic index of the
tested tire compounds (A, B and C) as function of the temperature together their fit
curves are plotted. Each marker of a single curve corresponds to 1 Hz solicitiation fre-
quency for the compound. These iso-frequency curves have been generated shifting the
acquired temperature through eq. 2 and considering the fitting coefficients provided by
the tiremaker .
As noticeable in these diagrams, the index trend looks similar to loss factor one,
exhibiting a peak matching with the glassy transition temperature at which occurs the
maximum energy loss. Moreover, a difference between the tested compounds can be
appreciated: on one hand, the tire C seems to be characterised by a higher loss factor
peak rather than the others; on the other hand, the tire B exhibits the lowest glassy
transition temperature. Consequently, this preliminary analysis, taking into account the
viscoelastic index, can provide suitable information concerning the viscoelastic behav-
iour among the tested tread compounds.
Fig. 12. Normalised loss factor 1 Hz D.M.A. master curves
The previous analysis results can be compared with the normalised values of the loss
factor determined by temperature sweep tests carried out in dual cantilever at 1 Hz. The
diagrams shown in Fig. 12 are mostly in accordance with the results described in Fig.
11. Actually, the tire C exhibits the maximum dissipation peak among the considered
10 IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . .
ones; whereas the compound B is marked by a low glassy transition temperature as
expected. Besides, the glassy transition temperature values, which are estimated by
means of VESevo acquisitions, are compared with D.M.A. ones in Table 1. As shown,
the results are very similar proving the goodness of the non-destructive method.
Table 1. Glassy transition temperature comparison
A prototypal device, called VESevo, has been proposed and described by the Vehi-
cle Dynamics research group of the University of Naples Federico II in the following
work. This device has been designed with the aim to perform a viscoelastic behaviour
analysis through an innovative and non-invasive testing approach.
Actually, the employment of the VESevo can provide a fast and accurate preliminary
evaluation of the viscoelasticity whitout using expensive rheometers and specific com-
pound samples, as traditional D.M.A. requires.
For these reasons, the VESevo could be very useful in Vehicle Dynamics field,
where the knowledge of viscoelastic properties of the tire tread compound could pro-
vide further information concering motorsport, truck or passenger vehicle applications.
Since the preliminary experimental activity carried on three different tire compounds
showed results in agreement with the expected D.M.A., the authors will focus on the
development of an algorithm capable of evaluating the viscoelastic properties, in terms
of Storage and Loss moduli, starting from the main index connected with the material
behaviour. Thus, the VESevo will be useful for monitoring the tread status by a non-
invasive approach, for analysing the dynamic behaviour of confidential motorsport tires
and for comprehending when changing tires configuration could be necessary.
1. G. Carbone, B. Lorenz, B. N. J. Persson, and A. Wohlers, “Contact mechanics and rubber
friction for randomly rough surfaces with anisotropic statistical properties,” Eur. Phys. J. E,
vol. 29, no. 3, pp. 275–284, Jul. 2009.
2. B. Lorenz, B. N. J. Persson, G. Fortunato, M. Giustiniano, and F. Baldoni, “Rubber friction
for tire tread compound on road surfaces,” J. Phys. Condens. Matter, vol. 25, no. 9, p.
095007, Mar. 2013.
3. M. Klüppel and G. Heinrich, “Rubber Friction on Self-Affine Road Tracks,” Rubber Chem.
Technol., vol. 73, no. 4, pp. 578–606, Sep. 2000.
IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . . 11
4. F. Farroni, R. Russo, and F. Timpone, “Experimental Investigations on Rubber Friction
Coefficient Dependence on Visco-Elastic Characteristics, Track Roughness, Contact Force,
and Slide Velocity,” Tire Sci. Technol., vol. 45, no. 1, pp. 3–24, Jan. 2017.
5. K. P. Menard and N. Menard, “Dynamic Mechanical Analysis,” in Encyclopedia of
Analytical Chemistry, Chichester, UK: John Wiley & Sons, Ltd, 2017, pp. 1–25.
6. D. W. van. Krevelen, Properties of polymers : their correlation with chemical structure ; their
numerical estimation and prediction from additive group contributions. Elsevier, 1997.
7. F. Farroni, A. Sakhnevych, and F. Timpone, “Physical modeling of a dynamic dial indicator
for the non-destructive evaluation of tire tread viscoelastic characteristics,” in Lecture Notes
in Engineering and Computer Science, 2016.
8. F. Farroni, M. Russo, A. Sakhnevych, and F. Timpone, “TRT EVO: Advances in real-time
thermodynamic tire modeling for vehicle dynamics simulations,” Proc. Inst. Mech. Eng. Part
D J. Automob. Eng., vol. 233, no. 1, pp. 121–135, 2019.
9. C. Allouis, F. Farroni, A. Sakhnevych, and F. Timpone, “Tire Thermal Characterization:
Test Procedure and Model Parameters Evaluation,” in Lecture Notes in Engineering and
Computer Science: Proceedings of The World Congress on Engineering 2016, 2016, pp.
10. K. A. Grosch, “The Rolling Resistance, Wear and Traction Properties of Tread
Compounds,” Rubber Chem. Technol., vol. 69, no. 3, pp. 495–568, Jul. 1996.
11. F. Farroni, A. Sakhnevych, and F. Timpone, “Physical modelling of tire wear for the analysis
of the influence of thermal and frictional effects on vehicle performance,” in Proceedings of
the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and
12. S. Maghami, W. K. Dierkes, T. V. Tolpekina, S. M. Schultz, and J. W. M. Noordermeer,
“Role of material composition in the construction of viscoelastic master curves: silica-filler
network effects,” Rubber Chem. Technol., vol. 85, no. 4, pp. 513–525, Dec. 2013.
13. R. S. Lakes, Viscoelastic materials. Cambridge University Press, 2009.
14. J. Ferry, “Viscoelastic properties of polymers,” 1980.
15. R. F. Landel, “A Two-Part Tale: The WLF Equation and Beyond Linear Viscoelasticity,”
Rubber Chem. Technol., vol. 79, no. 3, pp. 381–401, Jul. 2006.
16. F. Farroni, A. Sakhnevych, F. Timpone, “Snap button device for non-destructive
characterization of materials,” PCT/I2019/050858, 2019.
17. V. L. Popov, “Thermal Effects in Contacts,” in Contact Mechanics and Friction, Berlin,
Heidelberg: Springer Berlin Heidelberg, 2010, pp. 199–205.
18. A. Genovese, F. Farroni, A. Papangelo, and M. Ciavarella, “A Discussion on Present
Theories of Rubber Friction, with Particular Reference to Different Possible Choices of
Arbitrary Roughness Cutoff Parameters,” Lubricants, vol. 7, no. 10, p. 85, Sep. 2019.
12 IFIT2020, 079, v1: ’Development Of An Innovative Instrument For Non-Destructive Visc. . .