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Volume 19 / 2022

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www.hennecke-group.com• Interview:

R. Apenburg,
A. Mander­scheid, Cannon• Chemical
recycling• Microcellular
elastomers• High-damping
elastomers

01
2022

Beating noise, vibrations
and impacts withpolyurethane pads
Applications in railway constructions& industry and the materials chemistry behind

Elastomers are defined by their reversible deformation
behaviour: Consider a specimen underlying an external
force. Once this force vanishes, its initial geometry will be
restored. In the case of ideal-elastic materials this happens
nearly instantly, while so-called viscoelastic materials needsome time to restore the initial geometry. Depending on theapplication, engineers make use of one or the other classof elastomers. For example, almost ideal-elastic materials
are the best choice to isolate vibrations in, e. g., building
industry and railway engineering. In contrast, viscoelastic
elastomers allow damping of impacts as well as damping of
the amplitude of vibrations. For such applications, Getzner
Werkstoffe offers a material series named Sylodamp. This
article describes the basic physical and chemical principles
that make it possible to develop materials with pre-defined
damping characteristics.
By M. Heim, M. Seidl-Nigsch, H. Loy

1	Introduction: Impacts and resonance in the caseof periodic forces
Getzner Werkstoffe develops and produces foamed materials
made from polyurethane. These materials are used to reduce
structure-borne noise and to protect components. They areused in the railway, construction and industry sectors. Depending on the individual application they may be highly elastic orplastic. An example for the use of a pronounced viscoelastic
and, thus, dampening rail pad to reduce the vibration of rails
and sleepers and, therefore, noise emanating from the railway
superstructure is illustrated in figure 1.
When employed in technical systems such as rail superstructures, building foundations and machine bearings, Getzner’selastic materials act primarily as springs, isolating vibrations andthus protecting buildings from structure-borne noise. Generally
speaking, structure-borne noise is generated by dynamic-periodic forces or impact loads. Elastic bearings either decouple
the source of the noise from the environment – as in the caseof railway tracks – or they separate a vibrating environment
from the object to be protected, such as a building.
At their simplest, systems like these are described as single massoscillators with a mass m (fig. 2). In reality, the spring element
is not an ideal-elastic material. The physical equivalent model
therefore more closely resembles that of a spring and a damper
connected in parallel. The stiffness of this spring-damper combi-

32

Source: Vincent Scherer - stock.adobe.com

nation under dynamic loading depends on the frequency f. The
dynamic modulus of elasticity Edyn (f) of the material is a measure of this stiffness and determines – in conjunction with othervariables – the natural frequency f0 of the single mass oscillator:

(1)where A represents the bearing area and d the bearing thickness. In addition to the stiffness of the material (Edyn), thedesign of the bearing (full-surface, strip or discrete; A,d) andthe mass also affect the natural frequency. When designing abearing, the engineer must coordinate the various parameters
to produce the desired natural frequency – bearing in mind
that there are usually constraints on the parameter values thatcan be employed. For example, the bearing thickness is limited
and the mass is fixed in advance.
PU MAGAZINE – VOL. 19, NO. 1 – March 2022

High-damping
elastomers
the vibrating element. The ideal material for vibration protection therefore exhibits as small a dynamic modulus of elasticity
Edyn as possible (equation 1). This is why minimising the modulus
of elasticity, and hence the transfer coefficient L, is often theobjective when developing new materials. (In general, however,application-specific requirements – for example with regard to
long-term stability – transform minimising into optimising.)
On the other hand, there are some applications that require
the bearing material to fulfil specific requirements in terms ofvibration amplification (f/f0 <√2). In situations where, for example, a machine that requires a relatively long period of time tostart up or reach its operating frequency f is to be decoupled,the material will have to reduce the resonance phenomenon
at f/f0 = 1 (fig. 3).
The transfer function maximum in the case of ideal-elastic materials is very high; in the physical equivalent model it corresponds
to the spring element (cf. fig. 2). By contrast, in the case of
so-called viscoelastic materials a component of the deformation
is delayed, which results in damping of the vibrations; this corresponds to a parallel connection of the spring and damper (fig. 2).
The extent of the damping is an expression of the mechanicalloss factor η: the larger the loss factor, the smaller the highest(positive) value of the transfer function (fig. 3).
If a material is intended to dampen load peaks in the event of
impact loading and, thus, requirements exceed the restrictionof resonance phenomena that occur in the case of periodic
forces, then its loss factor will have to be very high. With Sylodamp, Getzner Werkstoffe has developed the ideal material
for such applications. This paper explains both the physical andchemical relationships that underlie the design of Sylodamp –and it describes applications that are already using the material.
Finally, we take a look into the near future and discuss thepotential of highly damping polyurethane elastomers for products that are intended to protect against railway noise (fig. 1).
The natural frequency of a spring-mounted system is its central
parameter, as it is this that determines the effectiveness of thesound control measures, since the (always incomplete) decoupling of the element vibrating at a frequency f depends on theratio f/f0. The transfer coefficient L quantifies this relationship:
η
η

(2)
where η is referred to as the mechanical loss factor.
Bearings are designed such that f/f0 >√2, as only then will decoupling – even if incomplete – of the dynamic forces actually takeplace (negative value of L, fig. 3). The larger f/f0 or the smaller f0
is, then the smaller L will be, and the better the bearing isolates

2

Theory of viscoelastic materials

2.1 Loading, deformation and time
Mechanical deformation is reversible with elastic materials. Test
bodies or components made of ideal-elastic material return totheir original geometry immediately once the load is removed;
those made from a viscoelastic material do so as well, but
require a finite period of time – the (recovery) deformation isdelayed following a change in load (fig. 4).
This delay is the macroscopic consequence of damping movements at an atomic level (parallel-connected damper in thephysical equivalent model shown in figure 2). A viscous deformation component is also present if the deformation is notcompletely reversible. This corresponds to a series-connected

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Fig. 1: L eft: The railway superstructure emits noise due to vibrating rails and sleepers. Right: Dampening rail pads (orange) placed between rails and sleepers reduce the amplitude of vibrations
and, thus, reduce noise.

damper in the equivalent model. Creeping is a special type ofviscous deformation. It takes place slowly and hence requires
an extended period of loading. It resembles the flow of a poly­
mer melt.
Both damping components of the total deformation (viscoelastic and viscous) correlate with the rearrangement of sections of
the polymer chains, with the migration of side chains throughthe surrounding polymer matrix and other – potentially irreversible – movements [1b]. The material heats up as the resultof microscopic frictional effects (energy is dissipated) so that
only one – more or less large – part of the work performed by
the external force is stored as potential energy.
By contrast, the ideal-elastic component of the total deformation (spring in figure 2) correlates to the change in interatomic
distances and the distortion in the valence bond angles [1b].
The respective movements are associated with hardly any
heat loss as the change in the spatial coordinates of the atoms
involved is small.

2.2	Mechanical loss factor
and dynamic modulus of elasticity
In the event of periodic-dynamic loading, the shift between
the deformation and load curves – quantified using the angle
Fig. 2: P hysical equivalent model for vibration-prone mechanical systems. In the case of periodic loading with the frequency-dependent force F(f), the spring-damper combination
exhibits a dynamic stiffness that corresponds to the dynamic modulus of elasticity Edynof the material being used.

δ (fig. 4) – is a suitable measure for characterising the dampingof the material. The so-called phase shift δ is a consequence ofthe time difference ∆t between the changes in deformationand load. Therefore, δ is large if the viscoelastic (and/or viscous)
component of the deformation is large, too. It is worth using
the tangent of the phase shift, as this represents both therelationship of dissipative to potential energy as well as therelationship between the loss modulus and the storage modulus. At the same time, we are already familiar with this variablefrom the introduction, as it is the mechanical loss factor η:d(3)where T is the temperature, f the frequency, δ the phase shift,
ED the dissipative energy (thermal energy), Epot the potential
energy, σ0 the tension, ε0 the deformation, E’’ the loss modulus
and E’ the storage modulus.
The term loss factor indicates that the energy that is converted
into heat is related to the recoverable deformation energy(which is the stored potential energy). It needs to be made clear
at this point that the parameters used to describe the dampingof vibration-prone systems or components (damping constant,damping coefficient, Lehr’s damping ratio, logarithmic decrement, etc.) have to be distinguished from the variables used
to characterise damping materials.
Fig. 3: T ransfer coefficient L as a function of the relationship between the frequency f of the
dynamic force and the natural frequency f 0. The mechanical loss factor η determines
the actual shape of the curve.
20

Transfer coefficient L / dB

15
resonance

10
5

√2,0

0
-5

high η

-10

low η

-15
-20

amplification

isolation

-25
-30

0

1

2

3

4

5

Frequency ratio f / f0

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PU MAGAZINE – VOL. 19, NO. 1 – March 2022

High-damping
elastomers
The quantitative relationship between the deformation andload curves (fig. 4) denotes the stiffness of the material – in thecase of the relative deformation and tension this is the dynamic
modulus of elasticity Edyn (a complex variable):(4)where the correlation E’’=η∙E’ has been used.
Edyn (in conjunction with other variables) determines the natural frequency f of the single mass oscillator (equation 1). The
absolute value is expressed as:(5)where σA is the tension amplitude and εA the deformation
amplitude (fig. 4).
Both the dynamic modulus of elasticity and the loss factor of anelastomer depend on the temperature and frequency. Furthermore, they are also a function of the pre-load and the tension
amplitude (force-controlled measurement). The temperaturedependency of the specified variables is at the heart of thedevelopment of an elastomer, as it is very pronounced due tovarious physical-chemical states: the curves E’(T) and Edyn (T)show a step and the curve η(T) has a maximum (fig. 5). The
properties of the material in the energy elastic range differ
markedly from those in the entropy elastic range. For example,
the modulus of elasticity of the two states can diverge by afactor of between ten and one thousand [1d].
In the energy elastic range – in other words at a low temperature – the mobility of the polymer chains is so limited that theycannot follow periodic-dynamic loading with the frequency f.
The deformation associated with the loading therefore only
Fig. 4: Relationship between sinusoidal, dynamic loading σ and the deformation ε as response
signal in the case of a viscoelastic material according to [1a]. ωt is the phase angle, ω
the angular frequency given by 2π∙f and δ the so-called phase shift.

correlates with the change in the interatomic distances andthe distortion of valence angles, which explains why the deformation is small and the modulus of elasticity high. The material is also hard and brittle. The deformation work is stored as
potential energy, resulting in a very high ideal-elastic component of deformation and a very small loss factor. When theloading decreases, the interatomic potential – in other words
the interaction energy between the atoms – causes the microscopic forces that are responsible for the observable macroscopic recovery. This is why this state is known as the energy
elastic state.
By contrast, in the entropy elastic range – that is, at a hightemperature – the mobility of the polymer chains is very high.
The rotation and rearrangement of chain segments and any
existing side chains take place on a time scale that is short
relative to the frequency f of the periodic-dynamic loading.
The deformation curve of the material is therefore only shiftedslightly compared with the load curve (fig. 4). For this reason,
the mechanical loss factor in this temperature range is small.
Due to the microscopic movements, the material is soft andthe modulus of elasticity is therefore low. In the entropy elastic
state, in contrast to the energy elastic state, energy is not thevariable that makes the deformations reversible, but entropy:
in a load-free state, the polymer chains exist as bundles. Thisis because, unlike extended chains, they result in less Gibbs
energy due to the larger entropy term. Under load, the polymer
chains are extended and the deformation energy is stored in
the form of less entropy (or more Gibbs energy).

2.3 High-damping elastomers
For technical applications – as well as for general use – elastomers are almost always found in their entropy elastic state.
It is in this state that they possess the properties that a springelement, for example, needs in order to provide vibration isolaFig. 5: Storage modulus E’, loss modulus E’’ and mechanical loss factor η of an elastomer withperiodic loading (with constant frequency f) as a function of temperature accordingto [1c]. The stepped section of the storage modulus/the peak of the loss modulus
define the glass transition range. The energy elastic range lies on its low temperatureside, with the entropy elastic range on its high temperature side. The glass transition
temperature Tg describes the position of the glass transition range; here, it is defined as
the inflection point in the E’ curve.

δ

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35

Fig. 6: The Sylodamp series consists of materials with six varying degrees of stiffness.

tion: Edyn and η are small; consequently the transfer coefficient
L in the range f/f0 >√2 is also small (fig. 3).
High damping elastomers – in other words those that absorb
energy – are an exception: at service temperature, they haveto exist in a transition state between the energy elastic andentropy elastic states. This is namely where elastomers transform deformation work into heat to absorb a large amount of
the introduced energy. The temperature window associatedwith this transition state is known as the glass transition range,
since the at least partially amorphous (glassy) solid softens
when heat is applied. Because its chemical structure is based on
macromolecules in the case of elastomers, the amorphous solidstate is not converted immediately into a liquid state. However,
the mobility of the chain segments and side chains is reminiscent of how they move in a polymer melt (which in the case ofthermoplastics is in fact achievable through further heating).
In the entropy elastic state, the polymer chains relax quickly
relative to the frequency f of the periodic-dynamic loading. In
the energy elastic state, by contrast, they relax very slowly. In
both cases, their microscopic movements are therefore decoupled from the macroscopic deformation. The consequence ofFig. 7: Mechanical loss factor of the six types of Sylodamp as a function of temperature(dynamic-mechanical analysis of a static loading below the upper limit of the static
range of use, sinusoidal excitation with a speed level of 100 dB at a reference value of5 ∙ 10 -8 m/s and a frequency of 10 Hz, shape factor 3).

36

this is that in the transition range between the two states,
the movements of the chain segments (and any existing side
chains) are not decoupled from the external deformation. The
frequency f therefore determines the position of the transition
range, while the coupling itself determines the properties ofthe elastomer in the corresponding temperature window. In
much the same way as vibration-prone mechanical systems(fig. 2), the polymer chains move more or less in phase withthe periodic loading. In extreme cases, resonance occurs, aswith macroscopic systems (fig. 3). This situation usually occurs
when the frequency f and the reciprocal of the relaxation time
1/τ(T) are the same. The closer f∙τ(T) is to 1, the greater the
coupling and the larger the loss modulus E’’(T). The glass transition range therefore marks a peak in the curve E’’(T) (fig. 5).
Due to the relation η(T)=E’’(T)/E’(T), the mechanical loss factor
also exhibits a peak. While resonance in mechanical systems
results in an amplification of the vibration amplitude (fig. 3),
it has a damping effect in elastomers (fig. 5).
The free volume theory of glass formation [1e, 2, 3] provides an
explanation for the large loss modulus in the transition range:
The volume of a test specimen decreases as it cools, causing
the free volume between the polymer chains to decrease as
well. At the same time, the interactions between the chains
increase, since the interatomic distances become smaller. Even
though the chain segments and side chains are still able tomove, microscopic friction effects convert some of the macroscopic deformation work into heat. The corresponding energy
component is lost and is hence no longer available to restore
the original geometry of the test specimen, which delays thedeformation with respect to the loading (fig. 4).
The peak of the curves E’’(T) and η(T) is broad in the case ofpolymers as they are characterised by a wide range of relaxation times. Every difference in the chemical structure of individFig. 8: D ynamic modulus of elasticity of the six types of Sylodamp as a measure of thestiffness of the materials as a function of temperature (dynamic-mechanical analysis ofa static loading below the upper limit of the static range of use, sinusoidal excitation
with a speed level of 100 dB at a reference value of 5 ∙ 10 -8 m/s and a frequency of 10
Hz, shape factor 3).

PU MAGAZINE – VOL. 19, NO. 1 – March 2022

High-damping
elastomersa) Extent of the dampingb) Long-term mechanical stabilityc) Width of the glass transition range

Fig. 9: B earings of a compressor on parallel-connected cylinders made from Sylodamp andsteel springs, respectively.

ual chain segments, in the length of side chains, etc., and every
difference in the spatial environment of a segment results ina different relaxation time. The glass transition temperature
Tg is a measure for the position of the glass transition range.
There are various ways to define Tg, for example, as the temperature at which the curvature of the curve E’(T) changes its
sign (inflection point, fig. 5).

2.4	Design of viscoelastic polyurethaneswith pronounced damping
At service temperatures, products made of elastomers usually have a mechanical loss factor η of 0,1 to 0,2; their damping effect is therefore moderate. There are some elastomers
with η<0,1 on the market, for example Sylodyn from Getzner
Werkstoffe. Damping is very low with these materials. They
are therefore used in such cases where they are to fulfil thefunction of a spring with as little loss as possible. An example
is vibration protection, in which the transfer coefficient L in
the relevant range (f/f0 >√2) should be as small as possible. On
the one hand, the smaller η is, the smaller L will be (fig. 3). On
the other, L is a function of the natural frequency f 0∝√(Edyn ) of
the system. The smaller f0 (or Edyn) is, the larger the relationshipf/f0 – the x-axis in figure 3 – and the smaller the associatedtransfer coefficient L. Then again, the lower the loss modulus
E’’ and the loss factor η, the smaller the dynamic modulus ofelasticity Edyn (equation 5). Damping therefore increases thetransfer coefficient L (equation 2) directly through η and indirectly through the correlation chain E’’–Edyn –f0.

Regarding a): To achieve a loss factor ≥0,3, the specified service temperature has to lie close to the peak of the η(T) curve(fig. 5), in other words, within the glass transition range. The
position of the glass transition is, for this reason, a commandvariable. It depends on four structural features [1f]: interactions between individual chains/chain segments (Van der Waals
interactions, hydrogen bonds) and covalent bonds restrict themobility of the main chains. Physical and chemical crosslinking
therefore raises the glass transition temperature Tg. Moreover,Tg will be greater according to the extent to which the ability to rotate around the C–C bonds and the mobility of thechain sections with respect to each other are prevented. For
this reason, bulky side groups and ring structures in the main
chain increase the temperature of the glass transition range.
Different polymers exhibit very different values for Tg, ranging
from -70 °C (polyisobutylene) to 145 °C (polycarbonate) [1g].
Regarding b): Raw materials with damping structural features
not only increase the viscoelastic component of deformation
but also frequently the viscous component of deformation of
the material. This has a detrimental effect on the creep as wellas on the fatigue behaviour since the viscous deformation isirreversible, which reduces recovery ability. To fulfil the respective requirements of many technical applications, the recipemust therefore achieve the right balance between the conflicting material properties of damping and long-term mechanicalstability.
Regarding c): The service temperature – in other words thetemperature at which the materials must fulfil their function –is in fact a finitely wide range. In just about every application(installed in devices, inside buildings or outdoors), damping
products must therefore demonstrate the required degree ofenergy absorption within a certain temperature window. As
the service temperature has to lie close to the peak of themechanical loss factor η(T) (see point a)), the peak should be
as wide as possible. In this case, η(T) and energy absorption will
not depend so heavily on temperature, and damping will be
sufficiently high across the entire range of use. The broader therange of relaxation times, the broader the glass transition peak.
Fig. 10: Sylodamp protector to protect the body in the event of impact loading.

Elastomers with η≥0,3 are strongly damping and are used asenergy absorbers in impact load situations or to limit the resonance phenomenon in the case of periodic loading (fig. 3).
When synthesising suitable polyurethane materials, the developer has to establish a recipe that is able to satisfy a range ofdifferent requirements in the best possible way:

PU MAGAZINE – VOL. 19, NO. 1 – March 2022

37

From a structural point of view, the material must therefore
be heterogeneous, and the individual, local structures should
all be present to about the same extent.
The diverse goals with respect to the properties of a new elastomer with high levels of damping and the chemical-physicalcorrelation between these properties constitute a complex situation. Accordingly, the value of both theoretical and practicalexperience as a resource for companies that are developing
their own recipes has to be strongly emphasised.

3

Sylodamp

Sylodamp is a highly damping polyurethane material fromGetzner Werkstoffe. The characteristics profile of the material is the result of an optimisation process that takes accountof all the requirements placed on a damping elastomer (seeabove). What it is definitely not is the result of maximising aparticular property (damping, for example). Instead, it achieves
a balance between a high loss factor (η≥0,45) and long-term
mechanical stability.

3.1 Properties
Sylodamp is available in six varying degrees of stiffness, eachof which is indicated by a particular colour (fig. 6). The varying degrees of stiffness enable an efficient construction fordifferent static loads in the range 0.005 N/mm2 to 0.5 N/mm2.
Depending on the type used, Sylodamp is able to tolerate load
peaks that can be as much as ten to fifty times larger thanthe upper limit of the static range of use. The compression
set is less than 5 % (test conditions: 25 % compression, 23 °C,
72 hours; examination 30 minutes after removal of the load).
In the case of classical elastomers, practically the whole glasstransition range lies below room temperature. Thus themechanical loss factor at room temperature is low: 0,1 to 0,2.
By contrast, it is ≥0,45 for the types of the Sylodamp series,
as in their case the peak of the curve η(T) lies close to room

temperature, and is therefore in the service temperature range(fig. 7). At the same time, the width of the η(T) peak, andhence the glass transition range, are so large that the damping
characteristics of the material within the range of use are not
too dependent on the temperature.
The rebound resilience of 13 % to 16 % and the (with respect
to the weight per unit volume) relatively high dynamic stiffness(fig. 8) reflect the pronounced damping response of Sylodamp.

3.2 Applications
Sylodamp reduces the extent of resonance phenomena in applications with periodic loading (fig. 9). In the event of an impact,
it isolates structure-borne noise and causes a fast decay of thevibration’s amplitudes. It also protects mechanically stressedcomponents, sensitive electronics and people (fig. 10) fromexcessive forces – for example when used as a material for thefeet of punching machines, as impact protection, etc.
Engineers can optimise the required effect (vibration isolation,
vibration damper, reduction in maximum force) by combining
the materials with differing spring or damping characteristics inparallel or in series (fig. 9). Carrying out local structure-borneor airborne noise measurements helps optimise the applicationin question and select the materials in the best possible way.

4

Noise and vibration reduction in railway

The characteristics profile of Sylodamp maintains a balance
between the conflicting material properties of damping andlong-term mechanical stability. As a result, the material willbring about improvements to products in many ranges of usethat do not have extreme specifications.
However, if the requirements with respect to the fatigue
behaviour are exceptionally high – as it will be in the railway
industry for instance – the formulation of the recipe realised

Fig. 11: Noise caused by railway traffic: the interaction between the wheel and the rail causes the wheels, rails and sleepers to vibrate [5], generating airborne noise.

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PU MAGAZINE – VOL. 19, NO. 1 – March 2022

High-damping
elastomers
in Sylodamp will need to be modified. During the optimisation process, the long-term stability factor will receive greater
weight, and raw materials that match the target properties ofthe final product will be used. Railway-specific products madefrom polyurethane materials with high levels of damping havehuge potential, since they extend the service life of the railway
superstructure [4] and can also reduce railway noise. The latteris steadily increasing due to the heavier utilisation of railway
tracks – as is the noise pollution that affects human’s health.
It is the vibration of rails and sleepers that causes the noise emanating from the railway superstructure (fig. 11). High-damping
rail pads could reduce these vibrations and hence help reducenoise levels. Rail pads normally act as elastic elements between
the rail and the sleeper. They cause the load of the train to
be distributed across several sleepers, thus protecting thesuperstructure and reducing how often it needs maintenance.
Conventional rail pads made of elastic materials with small
mechanical loss factors fulfil this requirement very well, buthave practically no effect on the vibrations from the rails andsleepers and the associated noise emissions. By contrast, viscoelastic, high-damping rail pads (fig. 12) have the potential tolower vibration amplitudes and hence the emitted noise level.

Fig. 12: Sample of a high-damping rail pad made of viscoelastic polyurethanerail pads in the railway superstructure can reduce the vibrationsof wheels, rails and sleepers, and thus lower noise emissions.
To satisfy the rail industry’s requirement concerning fatigue
behaviour within the development of an innovative damping
rail pad, the formulation used for Sylodamp is to be modified
to give greater weight to the long-term stability factor.

6

Literature[1]	G. W. Ehrenstein, „Polymer Werkstoffe. Struktur, Eigenschaften,
Anwendung“, [Polymer materials: structure, properties, applica-5

Summary

High-damping elastomers are viscoelastic materials. As they
deform, they absorb motion energy due to friction between
the chain segments in the polymer matrix. Engineers thereforeuse damping elastomers to reduce load peaks resulting from
impacts and to limit resonance phenomena in the case of periodic forces. With Sylodamp, Getzner Werkstoffe has developeda range of materials for such applications. At room temperature, it has a pronounced damping effect: the mechanical loss
factor for all six types of Sylodamp is ≥0,45.
To achieve such a high loss factor, the viscoelastic component of
deformation has to be very large. Sylodamp is therefore basedon chemical structures that cause the material to exist at roomor service temperature in the glass transition range, where thepolymer chains move more or less in phase with the periodic
loading; at the same time, the free volume available for thesemicroscopic movements is low. Both cause microscopic friction
so that energy is dissipated.
The characteristics profile of Sylodamp is the outcome of a physical-chemical optimisation process that results in both a highloss factor and a high long-term mechanical stability of thematerial. It is therefore ideal for a broad range of applications
in which people, sensitive electronics or mechanically stressedcomponents have to be protected from excessive forces.
Moreover, high-damping polyurethane elastomers have huge
potential as protection against noise. For example, dampingtion] Carl-Hanser-Verlag, Munich, 2011, a) p. 181, b) p. 36, c) p. 183,d) p. 34, e) p. 82f & 192–195, f) pp. 199–201, g) p. 203.
[2]	M. H. Cohen and D. Turnbull, “Molecular transport in liquids andglasses”, J. Chem. Phys. 31 (1959), 1164.
[3]	M. D. Ediger, C. A. Angell and S. R. Nagel, “Supercooled liquids
and glasses”, J. Phys. Chem. 100 (1996), 13200.
[4]	H. Loy and A. Augustin, “Pushing the limits of ballasted heavyhaul railway track by means of high-strength under-sleeper pads
made of a specially developed PUR”, Rail Engineering International
Edition 2015, Number 4 (2015), 3.
[5]	D. J. Thompson and C. J. C. Jones, “A review of the modelling ofwheel/rail noise generation”, J. Sound Vib. 231 (2000), 519.

AUTHORS:
Markus Heim 1
markus.heim@getzner.com
Research and Development, Railway Division
Dr. Markus Seidl-Nigsch 1
markus.seidl-nigsch@getzner.com
Materials Development
Dr. Harald Loy 1, 2
harald.loy@getzner.com
Head of Research and Development, Railway Division1

 Getzner Werkstoffe GmbH
Buers, Austria
www.getzner.com

2

 Department of Infrastructure,
Unit of Intelligent Transport Systems
University of InnsbruckInnsbruck, Austria

All figures and tables, unless otherwise stated, havebeen kindly provided by the authors.

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