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Uniaxial tension tests on dumbbells are routinely used to determine the stress–strain response of engineering materials. The simplest way to calculate strain is from grip displacement during extension, but this introduces significant error when dumbbells are gripped at the wider end sections to avoid the sample breaking prematurely in the grips. Mechanical and optical extensometers alleviate this problem by directly measuring strain in the gauge section. However, the equipment introduces significant additional hardware and software costs, and some experimental setups obstruct or prevent direct measurement of strain. The strain following systems also struggle both with the loss in mark intensity and changes of the shape of the marked point as the strain level is increased. To address these shortcomings, a novel analytical model to correct stress–strain data based on grip displacement is proposed. The model is implemented in Fortran and applied to hyperelastic materials which are assumed isotropic, but in principle the method is not restricted to elastomers. The model is validated with three studies on dumbbells: (i) a finite-element analysis for strains up to 660%; (ii) an experimental test with unfilled natural rubber up to 300% strain using a video extensometer; and (iii) a high temperature experimental test to fracture where the strain is corrected for a filled rubber. The model errors range from 2.2% to 3.1%, which is well within material and experimental uncertainties; hence, the model provides an accurate, inexpensive means of determining stress–strain behavior from grip displacement.

The introduction of dynamic bonds capable of mediating self-healing in a fully cross-linked polychloroprene network can only occur if the reversible moieties are carried by the cross-linker itself or within the main polymer backbone. Conventional cross-linking is not suitable for such a purpose. In the present work, a method to develop a self-healable and recyclable polychloroprene rubber is presented. Dynamic disulfide bonds are introduced as part of the structure of a crosslinker (liquid polysulfide polymer, Thiokol LP3) coupled to the polymer backbone via thermally initiated thiol-ene reaction. The curing and kinetic parameters were determined by isothermal differential scanning calorimetry and by moving die rheometer analysis; tensile testing was carried to compare the tensile strength of cured compound, healed compounds and recycled compounds, while chemical analysis was conducted by surface X-ray Photoelectron Spectroscopy. Three formulations with increasing concentrations of Thiokol LP-3 were studied (2, 4, 6 phr), reaching a maximum ultimate tensile strength of 22.4 MPa and ultimate tensile strain of 16.2 with 2 phr of Thiokol LP-3, 11.7 MPa and 10.7 strain with 4 phr and 5.6 MPa and 7.3 strain with 6 phr. The best healing efficiencies were obtained after 24 h of healing at 80 °C, increasing with the concentration of Thiokol LP-3, reaching maximum values of 4.5% 4.4% 13.4% with 2 phr, 4 phr and 6 phr, respectively, while the highest recycling efficiency was obtained with 4 phr of Thiokol LP-3, reaching 11.2%.

Strain energy functions (SEFs) are used to model the hyperelastic behavior of rubberlike materials. In tension, the stress–strain response of these materials often exhibits three characteristics: (i) a decreasing modulus at low strains (200%). Fitting an SEF that works in each regime is challenging when multiple or nonhomogeneous deformation modes are considered. The difficulty increases with highly filled elastomers because the small strain nonlinearity increases and finite-extensibility occurs at lower strains. One can compromise by fitting an SEF to a limited range of strain, but this is not always appropriate. For example, rubber seals in oilfield packers can exhibit low global strains but high localized strains. The Davies–De–Thomas (DDT) SEF is a good candidate for modeling such materials. Additional improvements will be shown by combining concepts from the DDT and Yeoh SEFs to construct a more versatile SEF. The SEF is implemented with user-defined material subroutines in Abaqus/Standard (UHYPER) and Abaqus/Explicit (VUMAT) for a three-dimensional general strain problem, and an approach to overcome a mathematically indeterminate stress condition in the unstrained state is derived. The complete UHYPER and VUMAT subroutines are also presented.

The viscoelastic behavior of elastomers manifests itself in numerous ways depending on the application. In seals, the viscoelastic response of an elastomer is complex as it depends upon the specifi...

After a brief but systematic discussion on the key aspects of pyroresistivity in conductive polymer composites, this paper gives a perspective on the most promising commercial applications, in particular in batteries safety, as temperature sensors and self‐regulating heaters.

Previous research into the friction behaviour of elastomers has typically focused on the effects of velocity, contact pressure, counter surface and lubrication on the coefficient of friction. O-ring type elastomer seals are common in many different industries. Friction plays a critical role during the setting and in service of these components. An experimental O-ring friction testing rig has been developed that can measure the effects of sliding speed and hydrostatic pressure on elastomer friction. Finite element analysis (FEA) packages can adopt fixed friction coefficients or ones that are pressure dependent. For the latter case, the dependence of the frictional behaviour is typically obtained from the instantaneous stress response at any given pressure and then related to the normal force response. The friction rig described in this paper uses industry standard dimensions for the O-ring gland, the pre-compression levels, extrusion gap size and pressure rating. The coefficient of friction is derived by dividing the measured friction force by the normal force, which was determined using an FEA modelling approach, as it could not be measured directly. Finally, a relationship between the frictional velocity and surface roughness is obtained in order to provide a frequency dependent Coefficient of Friction (CoF) that is easily translatable between surfaces.

Component design of rubber-based anti-vibration devices remains a challenge, since there is a lack of predictive models in the typical regimes encountered by anti-vibration devices that are deformed to medium dynamic strains (0.5 to 3.5) at medium strain rates (0.5/s to 10/s). An approach is proposed that demonstrates all non-linear viscoelastic effects such as hysteresis and cyclic stress softening. As it is based on a free-energy, it is fast and easily implementable. The fitting parameters behave meaningfully when changing the filler volume fraction. The model was implemented for use in the commercial finite element software ABAQUS. Examples of how to fit experimental data and simulations for a variety of carbon black filled natural rubber compounds are presented.

In this paper, the relationship between the tearing energy and the far-field cracking energy density (CED) is evaluated for an embedded penny-shaped flaw in a 3D elastomer body under a range of loading modes. A 3D finite element model of the system is used to develop a computational-based fracture mechanics approach which is used to evaluate the tearing energy at the crack in different multiaxial loading states. By analysing the tearing energy’s relationship to the far-field CED, the proportionality parameter in the CED formulation is found to be a function of stretch and biaxiality. Using a definition of biaxiality that gives a unique value for each loading mode, the proportionality parameter becomes a linear function of stretch and biaxiality. Tearing energies predicted through the resulting equation show excellent agreement to those calculated computationally.

The possibility of electrically tuning the scattering of light from surfaces by dynamically varying their properties is desirable for controllable transparency devices and diffusion filters. As a difference from state-of-the-art approaches where scattering is changed isotropically, this paper presents the first smart-material-based technology enabling electrical modulations in a single or multiple directions, which can be selected dynamically. The effect is achieved from thin soft membranes with transparent PEDOT:PSS coatings, which are electrically deformed along a single or multiple axes, using dielectric elastomer actuation. Anisotropic scattering is induced by electrically tuning the formation of directional surface wrinkles. As a proof of concept, a bi-directional device is obtained by overlapping two 90°-shifted mono-directional layers that can be controlled independently. According to the activation of the layers, light can be scattered along either direction, as well as both of them. Prototypes made of an acrylic elastomer were demonstrated with mono- and bi-directional operations. Devices with a window-to-total area ratio of 1:4 also showed a maximum electrical reduction of optical transmittance from 75% to 4%. This functionality and possible extensions to more than two controllable directions suggest applicability as electrically controllable anisotropic light diffusers for dynamic light shaping, as well as tunable transparency surfaces.

Smart self-sensing composites with integrated damage detection capabilities are of particular interests in various applications ranging from aerospace and automotive structural components, to wearable electronics and healthcare devices. Here, we report a straigthforward methodology to introduce and localise conductive nanofillers into existing elastomeric coatings of reinforcing cords for interfacial damage detection in cord-rubber composites. A simple swelling and infusion method was developed to incorporate carbon nanotubes (CNTs) into the elastomeric adhesive coating of glass cords. Conductive CNT-infused glass cords with good self-sensing functions were achieved without affecting the bonding provided by the coating with the rubber matrix. The effectiveness of using these smart cords as interfacial strain and damage sensors in cord-rubber composites was established under static and cyclic loading and demonstrated its potential in identifying both reversible deformation and irreversible interfacial damage. The simplicity of the proposed swelling and infusion methodology provides great promise for large-scale industrial implementation or the modification of existing elastomeric products.

Fatigue testing of cord-rubber composites is of significant interest as components manufactured from these materials are typically subjected to repeated loading during service. In this work, initial fatigue tests on a single carbon cord reinforced hydrogenated nitrile butadiene rubber (CC-HNBR) model composite were undertaken using conventional wedge grips which are routinely employed for fatigue testing of cord-rubber composites. Damage evolution was monitored using thermal imaging, while post-failure modes were evaluated using scanning electron microscopy (SEM). Finite element analysis (FEA) was performed to understand the stress state in the gripping region. The observed failure mode in wedge grips based testing was found to be interfacial debonding as a consequence of shear stress concentrations induced by the grips, leading to a significant underestimation of fatigue life. Consequently, an alternative bollard based test methodology was developed for cord-rubber composites. Fatigue data generated using this novel bollard test set-up was compared with data obtained by using conventional wedge grips. Bollard-based testing resulted in tensile fatigue behaviour dominated by cord failure rather than failure by interfacial debonding during accelerated laboratory fatigue testing, making the developed test methodology better suited for the characterisation of intrinsic fatigue behaviour of cord-rubber composites.

Full-page (multiple-lines), electrically refreshable, portable and affordable Braille displays do not currently exist. There is a need for such an assistive technology, which could be used as the Braille-coded tactile analogue for blind people of the digital tablets used by sighted people. Turning those highly desirable systems into reality requires a radically new technology for Braille dot actuation. Here, we describe standard-sized refreshable Braille dots based on an innovative actuation technology that uses electro-responsive smart materials known as dielectric elastomers. Owing to a significantly reduced lateral size with respect to conventional Braille dot drives, the proposed solution is suitable to array multiple dots in multiple lines, so as to form full-page Braille displays. Furthermore, a significant reduction also of the vertical size makes the design suitable for the development of thin and lightweight displays, thus enabling portability. We present the first prototype samples of these new refreshable Braille dots, showing that the achievable active displacements are adequately close to the standard Braille requirements, although the force has to be further improved. The paper discusses the remaining challenges and describes promising strategies to address them.

The possibility to electrically tune the optical transparency of thin membranes is of significant interest for a number of possible applications, such as controllable light diffusers and smart windows, both for residential and mobile use. As a difference from state-of-the-art approaches, where with an applied voltage the transparency can only increase or decrease, this paper presents the first concept to make it electrically tuneable to both higher and lower values, within the same device. The concept is applicable to any soft insulating membrane, by coating both of its surfaces with a circular transparent stretchable conductor, surrounded by a stretchable annular conductor. The two conductors are used as independently addressable electrodes to generate a dielectric elastomer-based actuation of the membrane, so as to electrically control its surface topography. We show that the optical transmittance can electrically be modulated within a broad range, between 25% and 83%. This approach could be especially advantageous for systems that require such a broad tuning range within structures that have to be thin, lightweight and acoustically silent in operation.

A model for the characterization and prediction of the adhesional friction experienced by a rough rubber surface sliding against a smooth rigid surface using fracture mechanics based peeling behavior is supported by experimental results. The friction is characterized by the strain energy release rate associated with the unpeeling of the asperities. This peeling energy of the rubber and rigid surface interface is used to derive a general relation for the frictional shear stress. Peeling characteristics are first found using rolling experiments, then this information is used to predict the results of sliding experiments. The velocity dependence of the friction is explained by relation to the dynamic viscoelastic properties of the rubber. The experiments compare favorably with the theoretical prediction derived using the model.

The elastic-viscous transition of tear fracture of rubber consists of three different fracture zones, the elastic-brittle fracture zone, the viscous-ductile fracture zone and the intermediate transition zone accompanied with stick-slip motion and a corresponding velocity jump at a constant strain energy release rate. Following the previous paper where the fundamental concept named the elastic-viscous transition for the velocity jump was newly introduced, here in addition the authors propose another new physical concept for the mechanism of the elastic-viscous transition in comparison with the phase transition of water. The vibrational energy caused by the stick-slip motion converted from the external strain energy works as a driving force for the velocity jump, being similar to the situation when the latent heat converted from an external heating source causes a volume jump in the phase transition of water. The greatly increased vibrational energy might be consumed to accelerate the ductile fracture of the newly induced fraction of the glassy state in the transition process from the rubbery to glassy state around the glass transition region, resulting in the velocity jump at the elastic-viscous transition. It is the purpose of this paper to answer the essential question why the abrupt and significant velocity change occurs under circumstances where the input strain energy release rate is kept constant.

Change in the free volume of an elastomer is modelled to predict the physical ageing of filler reinforced rubber by a nonlinear, fractional differential equation as a function of physical ageing te ...

A new biomimetic stimuli-responsive adaptive elastomeric material, whose mechanical properties are altered by a water treatment is reported in this paper. This material is a calcium sulphate (CaSO4) filled composite with an epoxidized natural rubber (ENR) matrix. By exploiting various phase transformation processes that arise when CaSO4 is hydrated, several different crystal structures of CaSO4·xH2O can be developed in the cross-linked ENR matrix. Significant improvements in the mechanical and thermal properties are then observed in the water-treated composites. When compared with the untreated sample, there is approximately 100% increase in the dynamic modulus. The thermal stability of the composites is also improved by increasing the maximum degradation rate temperature by about 20 °C. This change in behavior results from an in situ development of hydrated crystal structures of the nanosized CaSO4 particles in the ENR matrix, which has been verified using Raman spectroscopy, transmission electron micros...

The holy grail of reconfigurable optics for microscopy, machine vision and other imaging technologies is a compact, in-line, low cost, refractive device that could dynamically tune optical aberrations within a range of about 2–5 wavelengths. This paper presents the first electrically reconfigurable, fully elastomeric, tuneable optical lenses with motor-less electrical controllability of astigmatism in the visible range. By applying different voltage combinations to thin dielectric elastomer actuator segments surrounding a soft silicone lens, we show that the latter can be electrically deformed either radially or along selectable directions, so as to tune defocus or astigmatism, up to about 3 wavelengths. By mounting the new lenses on a commercial camera, we demonstrate their functionality, showing how electrically reconfiguring their shape can be used to dynamically control directional blurring while taking images of different targets, so as to emphasize directional features having orthogonal spatial orientations. Results suggest that the possibility of electrically controlling aberrations inherent to these smart lenses holds promise to develop highly versatile new components for adaptive optics.

Flexible and controllable self-regulating heating devices with positive temperature coefficient (PTC) behaviour are potentially excellent candidates in applications like healthcare, soft robotics, artificial skin and wearable electronics. Although extensive studies have been carried out in this field to understand the mechanism of PTC effect, rather limited conclusions have been reached. Many controversies remain on the dominating factors that influence the PTC performance of composites, hence limiting their design and broader applications. Herein, we propose a systematic study to explore the PTC phenomenon and the underlying mechanism, from a conductive network viewpoint, taking account of both conductive fillers and polymer matrices. Three representative conductive fillers with distinct dimensions and shapes (0D silver coated glass spheres, 1D carbon nanotubes and 2D graphene nanoplatelets), in combination with three different polymer matrices (high density polyethylene, thermoplastic polyurethane and polycarbonate) were selected to elucidate the effect of the “robustness” of different conductive networks on PTC behaviour in conductive polymer composites (CPCs). The desired conductive network can be obtained by selecting preferentially larger filler size, lower filler aspect ratio and/or selective distribution of filler (e.g. in the amorphous region of semi-crystalline polymers). The highest PTC intensity was observed around the “critical” percolation threshold, in correspondence of networks with the lowest number of inter-particle contacts. This study can serve as a guideline in the selection of the most appropriate conductive filler and polymer matrix for various self-regulating heating requirements and final applications.

The strain and thermal dependence of the dynamic mechanical properties of carbon black filler networks underpin the performance of many rubber components. These effects are examined by varying the surface energetics of carbon black. This has a profound influence on the level of flocculation of the carbon black network in the final crosslinked compounds. Filler networks comprised of thermally deactivated carbon blacks are significantly more strain-sensitive – shifting the onset of the Payne effect to smaller dynamic strains. Using free vibration equipment to precisely probe the thermal sensitivity of the linear viscoelastic properties of the filled compounds, it is shown that carbon black deactivation results in carbon black networks which are more thermally sensitive than corresponding unmodified carbon black networks. Increased thermal dependence of the dynamic moduli results in the appearance of a secondary increase in tan δ as a function of increasing temperature well above the rubber Tg – which is not correlated with any thermal transitions in calorimetric experiments. Such effects are prevalent in the relevant literature for various rubber–filler combinations but their physical origins are often misinterpreted or unexplained. A rationalization of these effects based on the dynamics of the filler network is presented.

The nature of filler–polymer and filler–filler interactions in rubber composites under strain remains an open question in soft matter physics. These interactions are key to explaining the rich variety of complex behavior exhibited by particle-filled rubber products. In this paper we demonstrate a simultaneous dielectric/dynamic mechanical analysis technique (SDMS) which provides new insights into the structure–property relationships of filled rubbers. The complex permittivity of carbon black filled natural rubber has been characterized under a simultaneous tensile strain field (from 0.1% to 50%). The complex permittivity exhibits a dramatic nonlinear dependence on strain coupled with features which are analogous to mechanical strain softening and strain history, namely the “Payne” and “Mullins” effects. The sensitivity of the complex permittivity to such effects is several orders of magnitude greater than in corresponding, traditional mechanical tests. In addition, we demonstrate for the first time that i...

The influence of frequency and R ratio on tensile fatigue of carbon cord reinforced HNBR composites has been studied. Frequency was found to have negligible effect on fatigue life, due to minimal heat build-up even at the highest frequency. Longer fatigue life at higher R ratios at a given maximum cyclic stress level was associated with the dynamic process of forming and melting of crystallites during loading and unloading, leading to a crack-arresting effect. The applicability of various analytical constant life diagram (CLD) models showed that the modified Harris’s CLD and piecewise linear CLD gave a reasonably good agreement with experimental fatigue data.

The authors propose a new philosophy and theory for rubber friction and wear that are significantly different from the existing classical theories. Several distinctive features of rubber friction such as the exceedingly high friction coefficient and the intense stick-slip motion during frictional sliding all result from the sticky surface behavior exhibited by a cross-linked rubber, where there is a meniscus force brought about at the interface between the rubber and the rigid surface. The total friction coefficient μall incorporates three factors including an adhesion term μadh, a deformation term μdef and a crack formation term μcrac. This generates an equation μ all = μ adh + μ def + μ crac ≒ K 1 ηv [ 1 + K 2 ( tanδ 2 ) + 2 K e c ) E - 7 / 6 W 1 / 6 ] where η is the viscosity of the uncross-linked phase, E the modulus of the cross-linked rubber, v sliding velocity, c crack length, W normal load, K1, K2, Keare all coefficients whose characteristics also govern rubber wear. The adhesion term is the most dominant factor during rubber friction, which roughly contributes about 70–80% of the total friction coefficient according to a very rough estimation. The close relationships between the observed stick-slip motion, abrasion pattern formation and wear have been verified experimentally. The abrasion pattern is initiated by the high frequency vibration and the steady abrasion pattern together with steady wear is promoted by the stick-slip motion. Steady wear rate V ˙ could be estimated theoretically as a function of the steady abrasion pattern distance Dab using an equation V ˙ = k’Dab3, which indicates that many of the characteristics observed in rubber wear are also fundamentally governed by the intense stick-slip motion induced by the sticky rubber surface.

With the ever increasing demand for energy reduction to stimulate sustainable development, new energy efficient manufacturing processes for advanced fibre-reinforced plastics (FRPs) are of great interest to overcome limitations of conventional autoclave or oven based manufacturing processes such as high energy consumption and size restrictions. Herein, a highly energy efficient and safe out-of-oven curing method is presented by integrating a pyroresistive surface layer with intrinsic self-regulating heating capabilities, into a composite laminate. This surface layer consists of a nanocomposite film based on graphene nanoplatelets (GNPs) and high density polyethylene (HDPE) and possesses self-regulating Joule heating capabilities, which can be used to cure epoxy based composites at a desired temperature without the risk of over-heating. Moreover, the thermoplastic nature of the surface layer enables easy fabrication with good flexibility for complex shapes. Compared to state-of-the-art out-of-autoclave oven curing, the proposed out-of-oven Joule heating approach consumed only 1% of the energy required for curing, with no effect on mechanical performance and glass transition temperature (Tg) of the final composite. Moreover, the integration of the self-regulating heating layer offers additional functionalities to the cured composites, like strain or damage sensing as well as the potential of de-icing without affecting the internal structure and performance of the laminate. The presented smart heating layer provides a novel solution for sustainable manufacturing as well as real-time structural health monitoring (SHM) throughout the components’ life for multifunctional composite applications in the field of renewable wind energy and aerospace.

Modelling the viscoelastic behavior of rubber for use in component design remains a challenge. Most of the literature does not consider the typical regimes encountered by anti-vibration devices that are deformed to medium dynamic strains (0.5 to 3.5) at medium strain rates (0.5/s to 10/s). Previous studies have either focused on the behaviour at small strains and small strain rates or in fast loading conditions that result in low cycle fatigue or tearing phenomena. There is a lack of understanding of the dynamic response of natural rubber suspension components when used in real vehicle applications. This paper presents a review of popular viscoelastic nonlinear constitutive models and their ability to model the mechanical behaviour of typical elastomer materials such as Natural Rubber (NR) incorporating different PHR (Parts per Hundred Rubber, XX) of carbon black. The range of strain and strain rate are typical for the materials used in rubber suspensions when operating in severe service operating conditions, such as over rough terrain or over pot-holes. The cyclic strain is applied at different amplitudes and different strain rates in this medium strain range. Despite the availability of many models in the literature, our study reports that none of the existing models can fit the data satisfactorily over a wide range of conditions.

Dielectric elastomers are widely investigated as soft electromechanically active polymers (EAPs) for actuators, stretch/force sensors, and mechanical energy harvesters to generate electricity. Although the performance of such devices is limited by the dielectric strength of the constitutive material, the electrical breakdown of soft elastomers for electromechanical transduction is still scarcely studied. Here, we describe a custom-made setup to measure electrical breakdown of soft EAPs, and we present data for a widely studied acrylic elastomer (VHB 4905 from 3M). The elastomer was electrically stimulated via a planar and a hemispherical metal electrode. The breakdown was characterized under different conditions to investigate the effects of the radius of curvature and applied force of the hemispherical electrode. With a given radius of curvature, the breakdown field increased by about 50% for a nearly 10-fold increase of the applied mechanical stress, while with a given mechanical stress the breakdown field increased by about 20% for an approximately twofold increase of the radius of curvature. These results indicate that the breakdown field is highly dependent on the boundary conditions, suggesting the need for reporting breakdown data always in close association with the measurement conditions. These findings might help future investigations in elucidating the ultimate breakdown mechanism/s of soft elastomers.

The role of filler particles in defining local changes to the dynamics of elastomer polymers – specifically in relation to the reinforcement of commercial elastomer systems – is as yet incompletely resolved. This work examines the glass transition of filled, crosslinked natural rubber in relation to filler reinforcement mechanisms using a variety of complimentary experimental techniques. Carbon black and precipitated silica filler particles with a wide range of surface areas, structures and surface activities are used as the reinforcing phase. No effect of the filler particles on the calorimetric glass transition is observed in terms of shifting, broadening or transition strength. Dielectric spectroscopy measurements show that the polymer relaxation times of the filled rubbers in the glass-to-rubber transition zone remain essentially equivalent to that of the corresponding unfilled material. Dynamic mechanical analysis demonstrates that the storage moduli of the filled elastomers are significantly amplified on the rubbery side of the glass transition. Elastic stiffening mechanisms are discussed in the context of contributions from filler networking. The reason for a distinct lack of evidence for filler-induced polymer modification may be due to the nature of polymer confinement associated with the imperfect dispersion state of the fillers in the sample and the fact that the fillers themselves are formed from aggregated primary particles rather than being true nanoparticulates.

The stress relaxation, creep and recovery behaviour of a cross-linked unfilled natural rubber has been investigated at moderate stresses in tension. The aim being to extend the idea, initially developed by Alan Gent in his seminal 1962 paper on the relaxation behaviour of rubber, in order to understand and examine the time dependent mechanisms that are present in elastomers under strain. A method based upon the Boltzmann superposition principle was used to compare the creep compliance with a measurement of its recovery after release from a range of constant loads held for different times. The creep behaviour was seen to exhibit the usual linear dependence on the logarithm of time. The recovery data was also seen to reduce onto a single recovery curve for any given applied tensile stress for a range of loading times using the Boltzmann superposition principle. The differences between the relative rates of the creep and the recovery behaviour can in part be attributed to the non-linearity in the stress–strain behaviour exhibited in tension of the elastomer.

Modelling the viscoelastic behaviour of rubber for use in component design remains a challenge. Previous reviews (Diani, Fayolle, & Gilormini 2009) and our studies presented in this paper highlight the issues of using of the most common viscoelastic non-linear constitutive models (Besdo & Ihlemann 2003; Bergstrom & Boyce 1998; Ogden & Roxburgh 1999). In detail, such models cannot reproduce or predict the experimental stress data for filled natural rubber loaded under the typical operating conditions. Examples of such conditions include cyclic strain history with constant strain rates and variable amplitude. This paper examines the behaviour of natural rubber elastomers filled with different percentages of carbon black. The elastomers chosen are typical of the materials used in vibration damping or automotive suspensions. We show that a constitutive model based on the fractional calculus can provide a good agreement for cyclic uniaxial tensile tests at a constant amplitude. The proposed model can capture, for example, the hysteresis and cyclic stress softening observed in the experimental data.