Rubber Samples Research Articles

Occlusal load modelling significantly impacts the predicted tooth stress response during biting: a simulation study

Computational models of the masticatory system can provide estimates of occlusal loading during (static) biting or (dynamic) chewing and therefore can be used to evaluate and optimize functional performance of prosthodontic devices and guide dental surgery planning. The modelling assumptions, however, need to be chosen carefully in order to obtain meaningful predictions. The objectives of this study were two-fold: (i) develop a computational model to calculate the stress response of the first molar during biting of a rubber sample and (ii) evaluate the influence of different occlusal load models on the stress response of dental structures. A three-dimensional finite element model was developed comprising the mandible, first molar, associated dental structures, and the articular fossa and discs. Simulations of a maximum force bite on a rubber sample were performed by applying muscle forces as boundary conditions on the mandible and computing the contact between the rubber and molars (GS case). The molar occlusal force was then modelled as a single point force (CF1 case), four point forces (CF2 case), and as a sphere compressing against the occlusal surface (SL case). The peak enamel stress for the GS case was 110 MPa and 677 MPa, 270 MPa and 305 MPa for the CF1, CF2 and SL cases, respectively. Peak dentin stress for the GS case was 44 MPa and 46 MPa, 50 MPa and 63 MPa for the CF1, CF2 and SL cases, respectively. Furthermore, the enamel stress distribution was also strongly correlated to the occlusal load model. The way in which occlusal load is modelled has a substantial influence on the stress response of enamel during biting, but has relatively little impact on the behavior of dentin. The use of point forces or sphere contact to model occlusal loading during mastication overestimates enamel stress magnitude and also influences enamel stress distribution.

Experimental Investigation and Simulation of Aircraft Tire Wear

ABSTRACT Not only in the automotive sector, but also in the field of aircraft tires, the topic of abrasion is of great importance. The aircraft tire manufacturers provide criteria for the permissible degree of wear. If these limits are exceeded, the tire must be replaced or retreaded. By this time, the tire should withstand as many takeoff and landing cycles as possible. Abrasion models should help to predict the wear behavior in preflight modeling. At the Institute of Dynamics and Vibration Research, quasi-steady abrasion tests are performed using tread block samples from an aircraft tire. For various pressures and sliding speeds, the abrasion is determined by recording the mass loss of the rubber sample. Based on these measurement data, a wear model is derived as a function of coefficient of friction, contact pressure, and sliding speed for different ambient temperatures. The well-known brush model forms the basis for the wear simulations. With parameters validated on the aircraft tire, such as contact length, stiffness, and friction coefficient, the resulting mechanical forces within the contact area are calculated. Finally, the classic brush model is extended by the abrasion calculation. The tire wear is determined during unsteady load and slip conditions by use of the quasi-steady wear maps derived from our experiments. Within a measurement campaign on the complete tire, the tread depth is measured after various driving maneuvers and is in good agreement with the simulation results.

Thermal aging analysis of carbon black and silica filled natural rubber based on terahertz dielectric spectroscopy

Two main types commonly used modified natural rubber, carbon black filled and silica filled, are studied using terahertz (THz) dielectric spectroscopic technique during their thermal aging. Standard artificial thermal aging is applied to the tailor-made rubber samples and THz time-domain spectroscopy (THz-TDS) system is employed to measure their complex THz dielectric permittivity at regular intervals during the entire span of thermal aging. Experimental results show that there are obvious differences in THz dielectric permittivity of carbon-black-filled and silica-filled natural rubber. And more importantly, THz technology can distinguish the rubber samples’ aging states, and the rules between THz dielectric permittivity and the thermal aging states are different for these two kinds of modified natural rubber.

Micromechanical modelling of complex shear modulus of crumb rubber modified bitumen

Crumb rubber modified bitumen (CRMB) can be considered as a binary composite system where rubber particles are embedded in the bitumen matrix. The bitumen-rubber interaction process (mainly swelling) significantly changes the mechanical properties of both bitumen and rubber phases. This study aims to predict the complex moduli of CRMB binders with more representative constituent parameters using micromechanical models. To achieve this goal, frequency sweep tests using a dynamic shear rheometer were performed on the liquid phase of CRMB and swollen rubber samples to represent the essential properties of bitumen matrix and rubber inclusion. In addition, the numerical swelling model was developed to estimate the effective volume concentration of rubber after swelling. Results show that the liquid phases of CRMB are stiffer and more elastic than the neat bitumen while the swollen rubber is softer and more viscous than the dry rubber. The effective volume concentration of rubber can increase to 2.126 times as the blend percentage based on the finite element analysis. Using the liquid phase of CRMB binder and swollen rubber properties as the micromechanical model inputs yield more accurate predictions. The used four micromechanical models predict well at higher frequencies while underestimating the complex modulus at lower frequencies.

Effect of Indian honey on expression of p53 and cyclin B1 in HeLa cells

Honey is a natural product collected from the nectar by honey bees and has a wide array of therapeutic important compounds called as phytochemicals. Cancer is one of the leading causes of death worldwide. Existing conventional cancer therapy which is mainly comprised of chemotherapeutic agents has side effects. Honey due to the presence of phytochemicals especially flavonoids and phenolic acids like apigenin, chrysin, quercetin and caffeic acid are found to inhibit the cancer growth. This effect varies among different honeys since they are dependent on the phytochemical composition and their concentrations in honey, which varies with respect to floral origin from which honey has been collected, geographical and climatic conditions. Thus, in the current study, phytochemical characterization of Jambhul, Rubber, Litchi and Drumstick honey samples along with their effect on the expression of proteins playing a vital role in the event of cell cycle and apoptosis i.e. Cyclin B1 and p53 proteins were determined by Flow cytometry. It was found that these honey samples contain apigenin, chrysin, quercetin and caffeic acid. These honeys exhibited an increase in expression of p53 whereas, expression of Cyclin B1 protein was reduced in HeLa cells treated with honey samples. The presence of phytochemical markers exhibiting promising anticancer potential along with the ability of alterations in the expression of these proteins proves that these honey samples have a potent anticancer activity which enhances the chances of these Indian honeys to be utilized in the treatment of cervical cancer.

Mechanical, thermal, electrical and crystallographic behaviour of EPDM rubber/clay nanocomposites for out-door insulation applications

ABSTRACTIn this study, the degradation of tensile properties is investigated by placing the neat ethylene propylene diene monomer (EPDM) rubber and different weight percentages (2 wt%, 4 wt% and 6 wt%) of MMT clay dispersed in the EPDM rubber samples in a humidity chamber for 0, 5, 7, 12 and 14 days. The thermal properties of neat EPDM rubber and its clay nanocomposites were studied by using different instruments, namely dynamic mechanical analyser (DMA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The viscoelastic properties are studied over the temperature range of −80°C to 80°C at different frequencies by using DMA. An increase in storage modulus and the decrease in loss tangent values are observed with the increase in clay content from 0 wt% to 6 wt% in EPDM rubber. Increase in storage modulus and glass transition temperature (Tg) values is observed with the increase in frequency from 1 Hz to 50 Hz. Also, the thermal stability and change in mass of these materials as a function of temperature and time are studied using TGA. It is found that EPDM/4 wt% clay composites exhibit the highest residual weight at 690°C while neat EPDM exhibits the highest weight loss compared to samples dispersed with other clay weight percentages. Using X-ray diffraction (XRD), 2θ value was measured and the crystal structure is investigated. Fourier transformed infrared spectroscopy (FTIR) was used to characterise the grafting of clay in the EPDM rubber. The dielectric constant and conductivity were studied for different frequencies and temperatures.

Tribological properties of swollen nitrile rubber under dry and wet sliding conditions

When nitrile rubber contacting with water under the external force during the service life, swelling and sliding wear occur. Since nitrile has similar polarity to water, the interaction between water and nitrile rubber and its influence on mechanical and tribological behaviors of the nitrile rubber play an important role in rubber performance, which is extremely necessary to be studied systematically. In this study, immersion experiments were conducted on three nitrile rubber samples which contained different acrylonitrile weight percentages of 18%, 26% and 41% (i.e. N18, N26, and N41) respectively. The hardness, tensile, dry and wet unidirectional sliding wear tests were further conducted. To reveal the mechanisms, the nuclear magnetic resonance (NMR) analysis and scanning electron microscopy (SEM) analysis were performed and interpreted accordingly. The results showed that cross-linking break based structural damage, substance dissolution and surface layer defects occurred after swelling, resulting in decreases in hardness and tensile strength and increases in permanent deformation fracture rates of the nitrile rubbers. The friction coefficient value of the un-swollen NBRs was positively related to the wear loss and decreased with the increase of the acrylonitrile content. During the wear process under dry conditions, the un-swollen rubbers presented hardening in aging while the swollen samples softened along with the deterioration of adhesive wear with higher steady-state friction coefficient value and wear loss. Under wet friction conditions, the susceptible wear behavior of the swollen rubbers induced reductions in friction coefficient and increases in wear loss. The swelling degree and its effects on mechanical and tribological behavior decreased with the increase of the acrylonitrile content. The swelling influences on the tribological behavior of nitrile rubber affected and acted on the entire wear process.

The Preparation and Research on the Electromagnetic Shielding Effectiveness of T-ZnO@Ag/Silicone Rubber Composites

This study first conducted surface modification of Ag-plated Tetrapod-like zinc oxide (T-ZnO) whiskers with the use of dopamine and prepared Ag-plated T-ZnO whiskers (T-ZnO@Ag) by means of chemical plating, in which AgNO3 solutions with different concentrations were used during the preparation. Micro-structures of the prepared T-ZnO@Ag powders were examined to evaluate the effect of AgNO3 concentration on Ag plating performance. Subsequently, conductive Si rubber samples were prepared, the T-ZnO@Ag powders were used as fillers, and the effectiveness of the related electromagnetic shielding was investigated in detail. The results showed that using AgNO3 solution with a concentration of 20 g/L, a continuous Ag coating-layer was observed on the surface of T-ZnO whiskers. It was evident that, when used as fillers, T-ZnO@Ag has a conductive threshold and when the mass fraction of the fillers exceeded 50 %, the T-ZnO@Ag whiskers that were uniformly dispersed in the matrix formed interconnected conductive paths. In this condition, the electromagnetic shielding effectiveness of the prepared T-ZnO@Ag/Si rubber composite reached up 90 dB.

Instrumented indentation of an elastomeric material, protocol and application to vulcanization gradient

Instrumented Indentation Testing is applied on a fluoroelastomer so as to get information about the local mechanical response of such a rubbery material. Due to their viscoelasticity, elastomers exhibit a time-dependence, responsible for a variation in their behavior as a function of the stress or strain rate. A few studies highlight modifications of the indentation hardness H and modulus Er when the load function varies. However, these works concern polymers and, to our knowledge, such an investigation has not yet been carried out on elastomeric materials. Results about the influence of the loading-unloading procedure on Er are presented here. They show elastic modulus' variations depending on the chosen protocol's time scale and reported evolutions are consistent with the expected behavior of viscoelastic materials. Furthermore, in preparation of this main study, preliminary verifications were necessary since sources of error are known to distort indentation results. A focus on the microstructure and roughness is presented in this paper and reveals, in particular, a non-negligible improvement of indentation curves (load-displacement hystereses) with an appropriate sample preparation and surface finish. These results have finally been used as a basis for the study of local gradients within a rubber sample. This study revealed a gradient (i.e. an increasing modulus) from the outer part of the sample to the inner one, attributed to thermal effects during the molding.

Application of Machine Learning to Evaluate Insulator Surface Erosion

This article proposes a new automated inspection system that can estimate erosion in silicone rubber (SIR) samples using a computer vision-based method. In this work, we used SIR samples that were damaged under laboratory conditions. The proposed work is expected to classify SIR samples into one of three classes based on the degree of erosion following the IEC-60587 standard in defining failed samples. We use various preprocessing and feature extraction methods and classify using the artificial neural network (ANN) and deep convolutional neural network (CNN). We compare their performance and find that the best results were achieved using a deep CNN architecture. This work serves as a proof of concept and can be further extended to outdoor on-field test cases.

Friction and Wear between Polymer and Metal in the Mixing Process.

In order to obtain a longer mixing chamber life, a layer of hard alloy coating is generally welded on the surface. However, when the mixing chamber is used for a long time, the surface will be worn due to friction with small fillers and rubber. As a result, there will be a large gap between the mixing chamber and the rotor, which will further affect the quality of the mixed rubber. In this paper, the dispersion process of the reinforcing system is simulated at first, and the mixed rubber samples are obtained from different dispersion stages in preparation for experiments with the chamber material. On this basis, the friction experiment is carried out with the same material as the mixing chamber on the friction experiment machine employed in the improved test part. The experiment shows that the friction and wear between the mixture and metal produced in each mixing stage are different. The wear in the stage with high friction is not necessarily large. The wear will be intensified in the middle and later mixing periods, while the friction will tend to be stable. In this paper, besides the exploration on the friction of fillers and rubber on the mixing chamber in different mixing stages, the most important thing is to change the mixing process of rubber formula, so as to extend the service life of the mixing chamber without changing the comprehensive physical properties of the mixing rubber.

Study on the Influence of Activated Carbon Nanotubes on the Tribological Properties of Frost-Resistant Rubber

This article presents results on studying effect of multi-walled carbon nanotubes (CNTs) on the tribological properties of frost-resistant rubber based on epichlorohydrin rubber. The sliding friction coefficient has been determined using a laboratory tribometer according to the “rubber ring-smooth steel disk” contact scheme. Rubber samples have been tested under conditions of dry friction for ranges of normal pressures of 0.1 … 0.4 MPa, sliding velocities of 1 … 100 mm/s for two values of the bulk temperature: 23 and −25° C. The wear rate of the samples has been determined at a temperature of 23° C, pressure of 0.4 MPa, and sliding speed of 10 mm/s. As a counterbody in experiments on the wear resistance assessment, sandpaper made of silicon carbide with a grain size of 120 and 250 microns has been used. It has been found that using CNTs as a filler for studied rubbers leads to an increase in their wear resistance. There is a multiple decrease in the wear rate when filling rubber with a small amount of CNTs (1–2 pts. wt. per 100 pts. wt. of rubber). Moreover, an improvement in physical and mechanical characteristics while maintaining high frost resistance is established. The addition of CNTs to the studied rubbers does not affect the static coefficient of friction.

Research on property variation of silicone rubber and EPDM rubber under interfacial multi-stresses

In this paper, silicone rubber (SR) and ethylene propylene-diene monomer (EPDM) rubber used in 110 kV prefabricated joints of XLPE cables were chosen as subjects, and a multi-stress experimental device was set up to simulate the insulation interface. Different mechanical tensions and/or AC electrical stresses were applied to the rubber samples at the interface composed of XLPE and SR/EPDM. After preset times, microscopic observations, together with measurements of mechanical properties, volume resistivity, crosslinking degree, attenuated total reflectance Fourier infrared spectrum and X-ray photoelectron spectroscopy were performed. It is shown that for both materials, molecular chains are partly broken by electron or ion bombardment from the discharges under electrical stress, and micro-molecules and oxides are formed on the sample surfaces. The mechanical stress facilitates this process without changing the reaction essence. The volume characteristic parameters of SR samples degraded with aging, while those of EPDM samples remained relatively stable. It is shown that under the same interfacial electrical-mechanical stresses, SR samples shows degradation of the overall performance; while for EPDM samples, the damage occurs mainly on the surface. This is due to the different chain structures, filler types and content in the materials.

Aging Properties of Nitrile Rubber in Medium under High-Low Cyclic Temperature Environment

To obtain the aging mechanism of a certain kind of missile sealing nitrile rubber material under high and low-temperature cycle conditions, the nitrile rubber sealing ring was subjected to the accelerated aging test of high and low temperature circulating oil medium. The changes of compression set, mechanical properties, microstructure, molecular structure and dynamic mechanical properties under the condition of temperature-changing oil medium were studied. The dissociation energy of several important chemical bonds of nitrile rubber molecules was calculated. The test results show that the maximum tensile strength and elongation at break of special nitrile rubbers decrease with the increase of the number of cycles, and the compression set rate of nitrile rubber samples stored in oil medium increases gradually in the early stage of aging. Large, slightly restored in the late stage of aging, as the aging time increases, the side groups of the nitrile rubber molecules decompose and the main chain flexibility increases.

Study of the physical-chemical characteristics of non-food solid waste combustion

The ignition and combustion processes of six non-food municipal solid waste (MSW) samples of different type were studied. The samples of wood waste, rubber, leather, cardboard, textile and plastic were put into the combustion chamber at a temperature of 600 °C in air medium at atmospheric pressure. The observations were carried out by means of high-frequency video imaging of the combustion process. Based on the obtained results the characteristic times of the ignition delay, combustion of volatiles and carbon residue were defined. The highest values of ignition delay and combustion of the carbon residue times were obtained for rubber sample and were 11.3 and 285 s, respectively. Significant correlation was found between the time of volatiles and carbon residue combustion and the fixed carbon content of the sample: the higher the Cd content, the higher value of respective time. The concentration peaks of the gas-phase products release during combustion of non-food MSW were presented as well.

Environmentally Sustainable Cement Composites Based on End-of-Life Tyre Rubber and Recycled Waste Porous Glass.

In this paper, environmentally sustainable cement mortars were prepared with end-of-life tyre rubber (TR) and recycled waste porous glass (PG) as aggregates in order to obtain lightweight products characterized by renewable and not-pretreated materials specifically for indoor applications. The secondary raw materials were added as partial and/or total replacement of the conventional sand aggregate. The resulting lightweight specimens were characterized by rheological, mechanical, thermal, microstructural and wettability tests. Fine tyre rubber aggregates affected the cohesiveness of the composites, as opposite to coarse tyre rubber and porous glass. The flexural and the compressive strengths of the porous glass samples were higher than the tyre rubber samples because of the higher stiffness and good adhesion of the glass to the cement paste as observed by microstructural observations. On the contrary, an unfavorable adhesion of the tyre aggregates to the cement paste was observed, together with discrete cracks after failure without separation of the two parts of the specimens. The latter result can explain the best results obtained by tyre rubber mortars in the case of impact compression tests where the super-elastic properties of the elastomeric material were evidenced by a deep groove before complete failure. Moreover, the thermal conductivity decrease of the lightweight porous TR and PG composites was in the range of ~80–90% with respect to the sand-based samples, which suggests that they can be used as plasters and masonries, and, in the case of tyre rubber specimens, outside applications are not excluded as observed from the wettability tests.

Improved flashover performance and tracking resistance of silicone rubber by direct fluorination

ABSTRACTSilicone rubber (SIR) samples are fluorinated using a F2/N2 mixture at different temperatures. Physicochemical characteristics are analyzed by attenuated total reflection infrared spectroscopy, X‐ray photoelectron spectroscopy, and scanning electron microscopy. Basic properties of the fluorinated surface layers are investigated, and the intrinsic alternating current (AC) flashover performance and tracking resistance of the surface fluorinated samples are evaluated. The flashover test results indicate that the fluorination leads to an improvement in AC flashover performance of the SIR material, as a result of the competition between the favorable effect of the increase in surface conduction and the adverse effect of a likely increase in surface layer permittivity. The increase in AC flashover voltage is associated with the voltage‐increasing mode of the flashover test. The flashover test results also show an improved tracking resistance of the SIR material by the fluorination, and the improvement is especially significant for the fluorinated surface layer that has less cleavage of SiC bonds or a good compactness as well as a large thickness. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48556.

Investigation of Surface Degradation of Aged High Temperature Vulcanized (HTV) Silicone Rubber Insulators

Polymeric composite insulators are subjected to varying work conditions like rain and heat, which create an impact on degradation during their long service period. Electrical tracking under the Alternating Current (AC) field plays a predominant role in surface degradation, which can be different for fresh and aged insulations. The tracking studies on the fresh and aged polymeric insulation therefore become significant. Motivated by this, an indigenous low-cost electrical tracking setup was developed, and the tracking studies were carried out as per International Electro technical Commission standard (IEC) 60587 on fresh, thermal-aged and water-aged silicone rubber samples. Contact angles of samples were measured to analyse the effect of ageing on hydrophobicity. Further, to analyse the influence of ageing on insulation integrity, tracking tests were conducted and parameters like leakage current pattern and magnitudes, tracking length and loss of weight in the material due to tracking were examined. The physicochemical impacts of ageing on the surface degradation of the samples were also analysed using X-ray diffraction analysis and Fourier Transform Infrared Spectroscopy analysis. The investigations added insight into the degradation mechanism of polymeric insulators in terms of their electrical performance and physicochemical changes in the material. Comparison of these changes showed that ageing could influence surface degradation of samples.

Study of impact of tribotechnical composition on rubber technical products to assess its applicability in wheeled transport engine

Tribotechnical coating helps to reduce the friction factor and improves the performance of the internal-combustion engine, but in the process, the generic components of the engine oil and other additives interfuse together. Besides, the coating mixture excretes acids and can destroy general mechanical rubber goods and metals. For this research the oil-gasoline-resistant rubber was used which is half-disk shaped with the dimensions of 27x7x2 mm. These samples of rubber have been heated to 110°C and exposed to generic components of engine oil, tribotechnical coating «ACTIVE PLUS» and strong acid H2SO4. In the total, the volume of the tribotechnical coating and engine oil was approximately 1 % of strong acid H2SO4. The article describes most common properties of aged rubbers such as rubber hardness, resilience, elasticity after exposure to generic components of engine oil and its additives. Results were obtained in the laboratory where samples of rubber were exposed to heat, engine oil, tribotechnical coating in conditions of absence of mechanical load. This study has identified an important issue according to which sulfuric acid destroys the system of oil-ultrafine particles in the absence of swelling of rubber.

Effect of phenyl content, sample thickness and compression on damping performances of silicone rubber: A study by dynamic mechanical analysis and impact damping test

The relaxation behaviors and impact damping effects of phenyl silicone rubber were investigated using dynamic mechanical analysis (DMA) and a home-designed impact damping test. The effects of rubber phenyl content, sample thickness and compression on the damping performance were evaluated. DMA results over a broad temperature and frequency range indicate that silicone rubber with higher phenyl content would overall exhibit better damping capacity owing to the increase in friction between molecular chains, and the impact damping performances agree well with the relaxation results. Besides, sample thickness and compression will also strongly influence the damping performances as directly evidenced by the impact damping tests. It is demonstrated that a combination of DMA and impact damping test is of critical use for designing rubber damping devices according to the frequency range of interest. This work will provide deeper insight into damping performances of rubbers and practical guidance for their engineering applications.