Rubber Samples Research Articles

Effect of surface roughness on flashover characteristics of silicone rubber

To study how the flashover voltage of silicone rubber depends on surface roughness, we prepared samples of silicone rubber of varying surface roughness to explore the relationship between surface roughness and the hydrophobicity of silicone rubber. We investigate the surface-flashover voltage of these samples. The results show that an increase in surface roughness leads to a decrease in the hydrophobicity of silicone rubber. The-dry flashover voltage of a sample with high surface roughness increases with surface roughness, and the wet-flashover voltage is reversed. The flashover characteristics for a attached water droplet depend mainly on the length of the water droplet.

Estimation of thermal properties using only one surface by means of infrared thermography

In this work was used infrared imagery to estimate thermal properties of solid materials. The Two Superficial Hot Points Technique (TSHP) was proposed and it uses heat flux and temperatures measured from a single surface of the sample to estimate the thermal diffusivity and conductivity of the material. By definition, the two parameters to be estimated are correlated and for this reason the gain ratio function concept was used to nullify this correlation, creating two independent objective functions, one for each parameter to be estimated. The gain ratio concept was extended to a three-dimensional semi-infinite model and the surface temperature was measured with infrared thermography. Associated with infrared thermography, the use of a semi-infinite mathematical model creates versatility and the possibility of estimating the properties by assessing only the region where the heat flux was applied. In other words, the geometric and boundary conditions of the sample do not need to be considered in the thermal properties estimation. The TSHP technique takes less than four minutes for temperature monitoring, it is non-destructive and uses only superficial measurements allowing, perhaps, countless in situ applications. In the present work, the thermal properties of a pipe made of Polyvinyl Chloride (PVC) were successfully estimated. In addition, a silicone rubber and copper sample were also tested. The results obtained are in good agreement with the results reported in the literature.

Testing of modified primary stiffness for heavy-haul locomotives operating on sharper-radius curves

For the typical wheelset drive subsystem with axle-suspended motor, the coupled vibration differential equations of wheelset and axle hung motor are derived. The mechanical model of traction rod is established. The subsystems are integrated into a whole locomotive-track coupled dynamic model which is verified from the aspects of load transfer and curving negotiation performance. To reduce the wheel–rail dynamic interaction of six-axle heavy-haul locomotive passing through curves in old existing lines, the parametric optimization flow of primary rubber joint is presented. The stiffness of 12 new rubber joints equipped in drawbars is tested and the stiffness dispersions are investigated. The research results show that, for a single rubber joint, the maximum and minimum values of radial stiffness can, respectively, increase and reduce by 16.2% and 33% with respect to the test mean value. For the assembled axle-box with upper and lower drawbars, the test longitudinal and lateral stiffness increase by 18% and 46%, respectively, relative to the designed values. A distinct dispersion phenomenon in the stiffness distributions of rubber samples is found. By combining with the numerical simulation results, the primary longitudinal stiffness is optimized from 199 MN/m to 52 MN/m, as the lateral stiffness changes from 6.89 MN/m to 2.6 MN/m. The final running test indicates that the optimized parameters can reduce the wheel–rail lateral force by 12% in the 300 m radius curve. The ride comfort could still keep in the same level, and the running stability has not been deteriorated.

From Devulcanization to Revulcanization: Challenges in Getting Recycled Tire Rubber for Technical Applications

For a sustainable development, recycling is a very important step, which, beyond saving the use of natural resources can also be a solution for low-income families, providing them earnings. Recycling is also considered a category of green chemistry, and contributes to the reduction of pollution, bringing the improvement to the public health. However, recycling of a material trying to contribute to the environment will not bring positive results if the final properties of the recycled material do not point to an application that is viable. In this sense, the aim of this work is to present a comprehensive study of the revulcanized ground tire rubber (GTR) samples, previously devulcanized by the action of the microwaves under different exposure times. It is extremely important to know in depth the modifications occurred in the recycled material during all the stages of the recycling process to which the material was subjected, in order to select the ideal application for the recycled material. The obtained r...

Coupled analysis on hyper-viscoelastic mechanical behavior and macromolecular network alteration of rubber during thermo-oxidative aging process

This paper synergistically addressed the microstructure alteration and the mechanical behavior of rubber during thermo-oxidative aging process from both experimental and numerical modeling aspects. Through the FTIR spectra analysis, equilibrium swelling experiment, low-field NMR measurement and mechanical tests of styrene-butadiene rubber (SBR) samples, a macromolecular network alteration mechanism was introduced. The mechanism is related to the variation of the crosslinking network and dangling chain ends of SBR during aging. A finite deformation based hyper-viscoelastic constitutive model was then established to capture the mechanical behavior of SBR during aging. Based on the interpretation of the microscopic mechanism, the above-mentioned network alterations during aging were considered in the model. After the implementation by means of the finite element simulation software ABAQUS, the accuracy of the established model was checked via the comparison of the numerical results with the corresponding data obtained from mechanical tests. The work is helpful for estimating rubber mechanical performance during aging process.

Artificial turf: chemical flux and development of silicone wristband partitioning coefficients

This work uses passive samplers to identify PAHs and OPAHs not previously associated with artificial turf, and to provide the first quantitative measure of in situ flux of semi-volatile contaminants on artificial turf fields. Both air (1.5-m height) and turf air (immediately above turf surface) were sampled using two sampling materials: low-density polyethylene and silicone. Utilizing a broad targeted screen, we assess both artificial turf and samples of crumb rubber for over 1530 chemicals including pesticides, phthalates, and personal care products. We report the presence of 25 chemicals that have not yet been reported in artificial turf literature, including some with known human effects. The samplers were also quantitatively analyzed for polycyclic aromatic hydrocarbons yielding gas-phase concentrations at breathing height and surface level—the first such report on an artificial turf outdoor field. Turf pore-air and air chemicals were highly correlated at all sites, and particularly at the recently installed indoor site. Flux of chemicals between air and turf surface appear to follow field age although more research is needed to confirm this trend. The thermal extraction process and silicone passive samplers used are suitable for larger-scale environmental sampling campaigns that aim for less solvent and sample processing. By co-deploying silicone passive samplers and conventional low-density polyethylene, partitioning coefficients are derived that can be used for future silicone passive air sampling environmental assessment. This study provides an initial demonstration that passive samplers can be used to quantify volatile and semi-volatile organic chemicals from artificial turf.

Gamma radiation induced compressive response of silicon rubber foam: Experiments and modeling

Abstract

A Quick Classifying Method for Tracking and Erosion Resistance of HTV Silicone Rubber Material via Laser-Induced Breakdown Spectroscopy.

Silicone rubber material is widely used in high-voltage external insulation systems due to its excellent hydrophobicity and hydrophobicity transfer performance. However, silicone rubber is a polymeric material with a poor ability to resist electrical tracking and erosion; therefore, some fillers must be added to the material for performance enhancement. The inclined plane test is a standard method used for evaluating the tracking and erosion resistance by subjecting the materials to a combination of voltage stress and contaminate droplets to produce failure. This test is time-consuming and difficult to apply in field inspection. In this paper, a new and faster way to evaluate the tracking and erosion resistance performance is proposed using laser-induced breakdown spectroscopy (LIBS). The influence of filler content on the tracking and erosion resistance performance was studied, and the filler content was characterized by thermogravimetric analysis and the LIBS technique. In this paper, the tracking and erosion resistance of silicone rubber samples was correctly classified using principal component analysis (PCA) and neural network algorithms based on LIBS spectra. The conclusions of this work are of great significance to the performance characterization of silicone rubber composite materials.

Differentiation of Rubber Cup Coagulum Through Machine Learning

Abstract A support vector machine classification algorithm was formulated to differentiate rubber cup coagulum according to the type of acid coagulant used. Two classification models were established, a binary classification algorithm and a model that can identify if formic, acetic, sulfuric acid, or no acid was used to induce coagulation. The models were based on the properties of the rubber cup coagulum that are easy to measure, such as tensile strength, water contact angle, and density. The binary classification model, which differentiates the industry-accepted formic acid-coagulated rubber cup coagulum from those which are not, exhibited satisfactory reliability, as evidenced by a 92% overall prediction accuracy and 71.4% cross-validation accuracy. Moreover, it was also determined that the rubber properties density, and water contact angle were important contributors for the classification. Acid-induced rubber coagulation is an important post-harvest process that influences the resulting rubber quality. Thus, the accurate differentiation of the rubber samples is useful for quality assurance purposes, as well as in policy enforcement.

Stress relaxation behavior and life prediction of gasket materials used in proton exchange membrane fuel cells

Silicone rubber gaskets are employed to keep fuel gases and oxidation in their own zones. Due to the viscosity and elasticity, the assembly force could relax when the silicone rubber is compressed in a proton exchange membrane fuel cell. In this work, the stress relaxation behavior of silicone rubber samples is studied under different temperatures and simulated operating conditions. The results show that the stress relaxes exponentially with time at 25% strain level, especially at higher temperature or with higher acid concentration solution. The three-term Prony series can simulate the viscoelastic behavior well, and the Master curves are established by applying a time-temperature superposition method to estimate the life of the samples. It can save approximately 50% and 78% of the test time when an operating temperature and acid solution are chosen appropriately.

Experimental investigation and constitutive modeling of uncured carbon black filled rubber at different strain rates

The tensile behavior of uncured carbon black filled rubber is investigated under different loading scenarios and strain rates. A non-contact optical measurement technique, Automated Grid Method, is applied to the tensile tests to capture the full-field large deformation of uncured rubber samples, and then their accurate stress-strain curves are obtained. Based on the test results, the deformation mechanisms of elastic, inelastic, hysteresis and softening behaviors at different strain rates are revealed and discussed. On the other hand, a three parallel network model comprising a hyperelastic part and two elastic-viscoplastic parts is proposed to characterize the constitutive mechanics behavior of uncured rubber. By using this new proposed model, the distinct characteristics of the cyclic tests can be captured well at four different strain rates. Moreover, the model predictions for the multistep tensile relaxation process are found to be consistent with the experimental observations, which provide a physical framework to describe the underlying deformation mechanisms of uncured rubber.

Evolution of coefficient of friction between tire and pavement under wet conditions using surface free energy technique

The interaction between tire rubber and pavement surface depends upon their surface characteristics and physical properties. Presence of water on the pavement surface aggravates the interaction and decreases the skid resistance drastically. Due to the interfacial water, the real contact area between pavement and tire decreases, which leads to decreased Coefficient of Friction (CoF). It is reported that CoF in this triphasic system (tire- water – pavement) can be derived from three components: hysterical, dry adhesion (tire-pavement) and wet adhesion (tire- water – pavement). The present study analyses a mechanistic-empirical model to evaluate the CoF between pavement and tire in wet conditions considering Surface Free Energy (SFE) characteristics of materials. The present study was conducted on five distinct types of rubber samples prevalent in Indian condition with basalt rock chosen as the surface mimicking pavement. Physical properties of the rubber samples (Hardness, material yield strength and tan delta values) were determined according to the ASTM standards. SFE parameters were calculated by measuring the contact angles using Sessile drop method. Surface roughness of basalt aggregate was measured using a Zeta Profilometer. Actual friction coefficient was measured using British pendulum (BP) tester under wet conditions. Further, theoretical CoF was calculated by inputting the experimental material properties into mathematical model. The results showed that the wet adhesive friction was the main contributor to the theoretical CoF, whereas dry adhesive friction was the least. Also, the correlation between actual CoF and the material properties was tried. The actual CoF showed fairly good correlation with the hardness of the rubber samples (R2 = 0.95). The study concludes that the SFE based model to determine friction coefficient between wet pavement and road shows potential to ascertain the frictional interactions taking place between the two surfaces.

Parameter estimation of butyl rubber aided with dynamic mechanical analysis for numerical modelling of an air-inflated torus and experimental validation using 3D-laser Doppler vibrometer

Over the few decades, there has been an exponential growth in the application of inflated torus system in the field of space deployable antenna design, solar propulsion, and aerodynamic deceleration system. However, such a system is inherently susceptible to mechanical vibration and hence requires precise modal analysis to produce stable inflatable structures. This paper summarizes all the necessary steps to be followed for dynamic analysis of inflatable structures. With this objective, a butyl rubber-based inflated torus system with dynamic material properties has been considered in this work. On performing mechanical tests of the rubber sample, properties like Prony series parameters, complex modulus, and damping values were obtained. Using laser Doppler vibrometry, the modal behavior of a butyl rubber-based air-inflated torus with free–free boundary condition was studied. The results achieved from experimental modal analysis and simulation involving fluid–structure interaction were found to be in close proximity. It is envisaged that the test template integrated with numerical validation can lay the foundation for designing complex inflatable torus structures.

Identification of natural rubber samples for high-voltage insulation applications

Latex presents high variability due to inherent differences among varieties from different countries, producers or crop seasonality. Natural rubber formulations from natural latex, to be used in insulating materials intended for high-voltage applications, require a wide variety of compounding and multitude of industrial processes. These aspects make it very difficult ensuring the same dielectric properties of the final product. At manufacturing level, it is very important to apply strict control processes to ensure that the final product fulfills all quality specifications. In this paper, a promising approach was applied to automatically identify natural rubber samples with suitable dielectric behavior from those with unsuitable dielectric behavior. This approach is based on the study of FTIR spectral data by applying suitable multivariable methods, such as principal component analysis, canonical variate analysis and k-nearest neighbors. The accurate and fast results reported in this work prove the suitability and potential of the proposed approach.

Amazon Rubber, A Potential Yet to be Rediscovered

Natural rubber still has socioeconomic, environmental and technical importance, despite the production of several synthetic similar polymers in the last 70 years. The Amazon Rainforest, the genetic base of Hevea brasiliensis, harbors a great diversity of ecosystems that can result in differentiated latex and elastomer molecules, from trees of the same species or other species and varieties of laticifer plants. Even so, there is little research to compare latex and rubber properties produced from native trees and planted clones. In this work, rubber latex was collected from four locations in the Amazon, including the historical places of Boim and Belterra and the most cultivated clone in Brazil, the RRIM 600, from a hevea plantation in the Center-West of Brazil. The following colloid properties were determined: pH, viscosity, particle size, dry rubber content, total solids content, gel content, total lipids, and total proteins. The molecular weight and the main physical and mechanical properties of the rubbers were also determined. Some main results can be highlighted: the rubber sample from Acre, in the extreme Western part of the Amazon, presented the highest molecular weight, while the Belterra sample, from remaining plantations of the Ford Project in Amazon, showed the highest values for mechanical properties. On the other hand, the technical characteristics of the RRIM 600 clone are close to the results obtained for the Boim sample, in Para, of the micro-region from where Henry Wickham collected the 70,000 seeds in 1876, from which the species was internationally domesticated. The present work is one of the very few studies to have been carried out with latex and rubber of these ancient rubber trees.

Sliding friction characteristics of styrene butadiene rubbers with varied surface roughness under water lubrication

We investigated the effect of the surface topography of rubbers on their wet sliding friction characteristics. For six types of rubber samples with different viscoelastic properties, rubber specimens with five levels of surface roughness were prepared and slid against a rough rigid surface under water lubrication. The friction coefficient increased with increasing surface roughness for each of the rubber samples, and the rank of the friction coefficient of different samples varied depending on the surface roughness. These results indicate that the effect of hysteresis friction becomes more significant as the surface roughness of the rubber increases, and the effect of the inhibition of adhesion friction caused by lubrication becomes more significant as the surface roughness decreases. Our findings demonstrate the importance of rubber surface topography in determining the friction coefficient under water lubrication. The results of this study may lead to new design criteria for high-wet-grip rubber tires.

Mechanical properties of hot-mix asphalt using waste crumber rubber and phenol formaldehyde polymer

Construction is always a complex in the nature and especially flexible road pavement which is the most prerequisites for the smooth transportation. The country economic growth is linked with smooth and fast transportation network where major transportation carried through road network interconnected cities and now major countries. Durable road pavement structure is an essential but pavement infrastructure is more vulnerable to the several failures among rutting and permanent deformation is the most common. Trial based studies encouraged to reuse waste polymers which may enhance the asphalt pavement. Study has chosen waste crumb rubber and Bakelite to study themechanical properties by addition ratio of 4.0%, 8.0%, 12.0%, 16.0% and 20.0%. Bitumen penetration grade 60/70 and ACW-20 were selected after examine the bitumen and aggregate tests Marshall mixture were designed and tested for density, Marshall stability, flow, air voids and stiffness properties for the control, crumb rubber and Bakelite samples. The encouraging result shows that addition of crumb rubber and Bakelite by 12% significantly improve the properties of asphalt mixture almost double Marshall stability strength compare to the control sample, higher density, control flow within the recommended range and higher stiffness shows strong resistance against rutting and permanent deformation. Study concluded crumb rubber and Bakelite has potential to enhance the mechanical properties and between them Bakelite shows better result in term of higher strength and stiffness.

Fracture analysis of rounded-tip V-notched components made of rubber-like materials using averaged strain energy density criterion

Nowadays, hyperelastic materials such as rubbers and elastomers have become increasingly important in research and industry. However, the existence of any geometric discontinuities like a crack or notch will affect the behavior of rubbers. Thus, the prediction of rupture condition in these materials is of paramount importance. One of the energy-based criteria, which has attracted many attentions due to its convenience in use and high precision, is the averaged strain energy density (ASED) criterion. Based on this criterion, a limited amount of energy in a specified volume around the stress concentration region controls the fracture of components. This criterion, which was already utilized extensively for brittle materials, has been recently extended for being used in cracked components having non-linear behavior like rubbers. On the other hand, by examining the previous studies, it can be concluded that despite the importance of rounded V-shaped notch, no research has been carried out in the presence of this type of stress concentration in hyperelastic materials. As a consequence, this study is devoted to investigate the rupture of rubbers containing a round-tip V-shape notch using the ASED criterion. To this end, first, some experiments are performed for rounded-tip V-notched rubber samples. Afterwards and in order to utilize the ASED criterion for predicting the rupture loads of tested samples, some finite element modeling considering both geometric and material non-linearities are performed. The comparison between the estimations of the ASED criterion and the corresponding experimental data reveals the high efficacy of this criterion in hyperelastic materials weakened by round-tip V-shape notches.

Three-dimensional numerical simulation of mechanical properties of soil-tire mixture by discrete element method

Soil engineering properties can be improved employing different methods. Among them is mixing soil with tire derived additives (TDA). TDAs generally increase some parameters of mixture such as damping ratio, permeability, ductility and also in some cases shear strength. Various properties of TDAs from mechanical properties to their geometry can affect the mixture behavior. In this paper using the YADE platform, simulations of triaxial tests on sand tire mixtures are presented. To take compressibility into consideration, each rubber crumb particle is made of several spheres connected elastically to each other. For sand particle generation the clump technique was employed. Shapes of both sand and rubber particles are inspired from real grains. As properties of sand and rubber are different, especially Young modulus, rubber sand interaction is considered as soft rigid contact. Therefor harmonic average and arithmetic average was used to compute contact Young modulus (and then stiffness). The model was validated by comparison of results of triaxial tests simulation on pure rubber sample with literature ones which both exhibited linear stress-strain curve. Then triaxial tests with different sand to rubber ratio were simulated to see whether harmonic average or arithmetic average gives the best match to literature. The results show shear strength reduces by decreasing of sand to rubber ratio. This is the same as what is reported in literature.

Impact of carbon black aggregates on the optical properties of black rubber samples in the terahertz frequency range

We report on the optical responses of black rubber samples in the terahertz regime as a function of the carbon black (CB) concentration. We prepared samples with different CB concentrations and investigated their absorbance, birefringence, and the angle of the slow optic axis in the terahertz frequency range. A monotonic increase of the terahertz absorbance is observed with increasing CB concentration, which indicates that the density of the CB aggregates inside the black rubber plays a crucial role for controlling the absorbance. In addition, a systematic increase of the birefringence is observed with increasing draw ratio, while the spatial fluctuation of the angle of the slow optic axis systematically decreases. This simultaneous behavior indicates that the mechanical stretching of the black rubber sample induces an alignment of the CB aggregates along the stretching direction. These results provide the fundamentals to understand the correlation between the terahertz response and the condition of the CB aggregates inside the samples. The thorough understanding of this correlation is important for future applications.