Rubber Specimens Research Articles

Development of Crack Measurement Equipment for Rubber Specimens through Image Processing

Development of Crack Measurement Equipment for Rubber Specimens through Image Processing

Modeling the thermo-oxidative aging effects on fatigue life of natural rubber using a continuum damage mechanics approach

Thermo-oxidative aging (TOA) significantly impacts the fatigue life of rubbers by reducing the fatigue strength and modifying the slope of the Wöhler curve, rendering traditional time-temperature superposition methods inadequate. In this work, we aim to develop a model capable of predicting the effect of TOA on the fatigue properties of rubbers. For this purpose, dumbbell specimens of natural rubber (NR) were subjected to aging in an air-vented oven at different temperatures prior to mechanical testing. Tensile tests were conducted to quantify the aging effects on a microscale network parameter known as elastically active chains (EAC) density, along with determining ultimate properties such as the stress and strain at break. By using a time-temperature equivalence and the Arrhenius shift factor, master curves were constructed for both EAC density and ultimate properties. Subsequently, the fracture properties of the aged material were predicted using an energy limiter approach whose evolution follows that of EAC density. Furthermore, a relationship between the parameters of the continuum damage mechanics (CDM) approach (specifically, the power law parameters of the Wöhler curve) and the fracture properties was proposed, resulting in accurate estimates of the fatigue life regardless of the aging conditions. Satisfactory agreement was observed between the model predictions and the data for nine aging conditions encompassing four different temperatures. The CDM approach also allows assessing the evolution of mechanical damage within the material influenced by TOA. The novelty of this approach lies in establishing a direct relationship between fatigue and fracture properties. Moreover, this is the first time to the best of our knowledge that TOA has been explicitly incorporated into a fatigue life prediction model via the evolution of the EAC density.

Effect of Complex Well Conditions on the Swelling and Tribological Properties of High-Acrylonitrile Stator Rubber in Screw Pumps.

The effects of complex well conditions in shale oil wells on the swelling and tribological properties of high-acrylonitrile stator rubber used in screw pumps were investigated in this study. Tests were conducted considering the combined effects of immersion medium, temperature, and duration. The key parameters measured included mass change rate, volume change rate, hardness, elongation at break, tensile strength, surface micro-morphology of the rubber after thermal expansion and swelling, friction coefficient, and wear quantity. The results indicated that in the actual well fluids, the mass change rate of high-acrylonitrile rubber ranged from -1.08% to 1.29%, with a maximum volume change rate of 2.78%. In diesel oil, the greatest mass change rate of the rubber was 4.68%, and the volume change rate did not exceed ±1%, indicating superior swelling resistance. In both actual well fluids and diesel oil, the maximum decreases in hardness were 8.7% and 9.5%, respectively. Tensile strength and elongation at break decreased with increasing immersion temperature, with elongation at break in 80 °C diesel oil decreasing by over 50%, indicating a significant decline in the tensile properties of the rubber. The average friction coefficient of rubber specimens immersed in actual well fluids at three temperatures, as well as in diesel oil at 25 and 50 °C, decreased compared with the high-acrylonitrile rubber without thermal expansion and swelling. However, the average friction coefficient of rubber specimens immersed in diesel oil at 80 °C increased. The wear quantity of the rubber increased following immersion in both media. Additionally, the friction coefficient and wear quantity of the rubber increased with increasing immersion temperatures. The results of the study can offer valuable insights into assessing the durability of properties in high-acrylonitrile stator rubber under complex well conditions.

Accelerated fatigue bench test method for rubber vibration isolators based on load spectrum compilation

The present study is focused on the development of a novel method for compiling load blocks to accelerate the fatigue bench test of rubber vibration isolators. This approach involves three main steps: Firstly, a uniaxial tensile fatigue test is conducted on rubber specimens under a constant amplitude load. According to the fatigue test data, a rubber fatigue life prediction model is established. Secondly, the mount load spectrum is statistically analyzed, and the fatigue damage distribution of the mount is calculated using the rubber fatigue life prediction model. Lastly, following the principle of damage equivalence, the load spectrum is compiled into load blocks. The fatigue bench test of the mount is then conducted using both the load spectrum and the load block as loading data, respectively. The test results demonstrate that the fatigue failure locations of the mounts are essentially identical under both loading data types, verifying the effectiveness of the proposed load block compilation method.

Support medium development for 3D printing natural rubber latex via direct ink writing in the support bath technique

The direct manufacturing of rubber products from natural rubber latex through 3D printing, particularly extrusion in air, faces challenges in creating intricate shapes. Research suggests that utilizing 3D printing with extrusion in a support medium, known as direct ink writing (DIW), is effective for crafting complex-shaped rubber products. However, few studies have explored 3D printing natural rubber as a support medium. This study focuses on formulating a support medium for the DIW printing of natural rubber by incorporating triethanolamine (TEA) and alcohol in varying proportions. Key characteristics, such as viscosity, were assessed for each formulation, along with essential printing parameters, such as speed and flow rate. A suitable support liquid consisting of TEA (2.5 g), alcohol (160 g), Carbopol (1.5 g), and water (200 g) was determined for DIW printing natural rubber. The optimal settings were determined to be a nozzle size of 0.85 mm, a speed of 30 mm/s, and a flow rate of 30 mm3/s. Comparative results from the forming process indicate that 3D-printed rubber specimens exhibit poorer mechanical properties than traditionally molded specimens, owing to material uniformity. The vulcanized rubber system with the EV pattern exhibited superior mechanical characteristics. The developed support medium for DIW printing shows potential for use in intricate natural rubber products; however, further exploration of additional parameters is crucial for advancing complex-shaped natural rubber manufacturing using 3D printers.

Rubber tracks and tyres: a detailed insight into force analysis during obstacle negotiation

The contact of a rubber track or a tyre tread with an edge corner is a process involved in many practical applications, i.e. traversing rough terrain and stair climbing. This paper presents a rigorous analysis along with experimental results to study what happens during the contact between a running gear and an edge corner as well as what forces are exchanged between these two elements by providing also a comparison between existing theoretical methods to assess which one is the most accurate. A testbed has been specifically developed for this research work to analyse the behaviour of a rubber specimen in contact with a step-like obstacle. The experimental results highlighted that the forces exchanged between a belt and a corner edge depend only on the relative inclination between the two sides of the belt and on the coefficient of friction while a pneumatic tyre patch behaves similarly to a belt when it is in contact with a step corner edge.

Utilization of Silica Fume and Sodium Hydroxide in Treated Crumb Rubber for Cement Mortar

Cement mortar offers an excellent replacement for materials such as fine aggregate with tire rubber waste in the form of crumbs. It provides excellent environmental and technical benefits to concrete production using recycled materials. As such, it contributes to the sustainable development of the construction industry. This paper mainly emphasizes the strength of untreated and treated crumb rubber from waste tires in cement mortar. Crumb rubber that has been pre-treated with Silica fume (SF) and sodium hydroxide (NaOH) to improve the strength of the mortar mix. This research used a cement-aggregate mix ratio of 1:4 and a water-cement ratio of 1:2. Five different percentages of fine aggregate replacement (0, 3, 6, 9, and 12%) was selected. The compressive strength, density, and water absorption of the mortar were measured at 28 days to find optimum strength. The compressive strength of the cement mortar mixed with treated crumb rubber showed significantly higher values, with an increase of 92% for 12% treated crumb rubber by sodium hydroxide (TN12) compared to untreated crumb rubber. The density value of the mortar cube mixed with treated crumb rubber decreased when the percentage of replacement for treated crumb rubber increased. In the application of roof tiles, lower density values provide an advantage for workability during installation. For water absorption, the treated crumb rubber contributes to a lower percentage of water absorption (acceptable until 6% for SF and 9% for NaOH) compared to the control sample as untreated crumb rubber. Therefore, a mixture of mortar with treated crumb rubber, especially NaOH solution, is better than the untreated crumb rubber specimen.

A method to obtain probabilistic fatigue lives under varying strain peaks for rubber components with small samples

AbstractUniaxial tension fatigue experiments are conducted on filled natural rubber (NR) specimens. According to the test data, typical probabilistic distributions under constant strain peak are investigated. Accordingly, a small sample probabilistic fatigue life curve fitting method is proposed, where a Weibull distribution is utilized for the tested rubber. A power‐Weibull statistical model with nonconstant scatter and the conventional group method for complete data are also employed to evaluate the proposed method. It turns out that the slope and intercept relative errors from the small sample fitting method are below 7.86% and 0.943%, respectively, of the complete data methods. It indicates that the proposed method can obtain high‐precision probabilistic fatigue life curves in the case of small samples, which has a certain significance for the efficient test and reliability of rubber fatigue in engineering applications.

The tire–road contact: A mechanical mixing seen as a shear-induced diffusive process

In this paper, the mechanical mixing of road minerals and tire tread rubber is studied experimentally and numerically. A rubber specimen on an experimental set-up is used. SEM observations show that particles on the surface are composed of an intimate mixture of rubber compounds and minerals. A longitudinal section is also observed, showing that the minerals have migrated into the surface. This phenomenon can be seen as a diffusive process driven by shear. To understand the underlying mechanisms, a numerical model is proposed using soft bodies to represent the rubber top layer. A layer of minerals is then sheared onto this surface. The minerals migrate progressively into the rubber, forming a mixed layer of rubber and minerals. The results show also that the mixing mainly depends on the shear rate in the layer containing the minerals. Due to a reinforcing effect of the minerals, velocity is increasingly accommodated in the layer without minerals. As a result, the shear rate in the mixed layer decreases, and therefore the mineral migration. This coupled mechanism explains why the mixing process stops before reaching a homogenized state in the entire domain. To support this analysis, a diffusion coefficient is derived as a function of the shear rate in the mixed layer.

A unified pseudo-elastic model of continuous and discontinuous softening in the finite deformation of isotropic soft solids

Building on a recently devised approach of hyperelasticity with intrinsic softening, a new framework for capturing both continuous and discontinuous softening in the finite deformation of isotropic incompressible elastomers is considered here. The continuous and discontinuous softening effects of interest pertain to the loading and unloading paths, respectively, and the model is developed within the theory of pseudo-elasticity. The performance of the model in capturing these effects is then compared with the deformation behaviour of a variety of elastomers, including a range of hydrogels from truly independent double-network (t-DN) to tough and nanocomposite hydrogels, dielectric elastomers and carbon-black filled rubber specimens, under uniaxial and multiaxial deformations. The model is demonstrated to show a favourable simulation and prediction of the extant experimental data. The application of the model is then extended to capturing the softening behaviour under rate-dependent loading, based on a prior work by the authors incorporating the rate effects directly into the pseudo-hyperelastic model, by assuming that the model parameters evolve with the deformation rate. The capability of the model to capture the rate-dependent effects accurately will be shown by considering the rate-dependent behaviour of two hydrogel specimens. Given the simplicity of the functional form of the model, akin to a standard pseudo-elastic model, the low(er) number of model parameters, the ability to capturing the softening behaviour in the deformation of a wide range of elastomeric materials, and the easy extension for incorporating additional features such as the rate-effects, the proposed model provides another step towards the unification of various complex deformation features into a single modelling framework, for a more universal application to the finite deformation of soft solids.

Effects of the etching process on the surface, friction and wear characteristics of silicone rubber coated with micro-sized ceramic particles.

This study investigates the friction and wear characteristics of silicone rubber used in hydraulic systems, focusing on surface properties achieved through coating strategies. Silicone rubber specimens with varying surface characteristics, prepared by coating with micro-sized ceramic particles and employing etching processes, were examined. Surface morphology, roughness, water droplet contact angles, and friction and wear characteristics were evaluated. The silicone rubber was coated with ceramic particles (average size: 16 μm) and subsequently etched for different durations (1, 5, 10, 30, and 60 minutes). The results revealed that longer etching times led to increased surface roughness, while shorter etching times resulted in improved wear characteristics. The friction coefficient demonstrated a discernible reduction with escalating etching durations, with Etching-60M showing approximately 50% lower friction coefficient compared to Etching-1M. Wear rates ranged from 2.47 × 10-7 to 1.43 × 10-6 mm3 N-1 mm-1, indicating an increasing trend with longer etching times. Distinct wear mechanisms were observed between non-etched and etched specimens, with the latter exhibiting more pronounced wear tracks. Finite element analysis highlighted variations in stress behavior during contact sliding, indicating that surface modifications significantly impact wear resistance. While longer etching times improved friction characteristics, shorter etching times yielded superior wear characteristics. Further research is recommended to explore optimal etching conditions considering various variables.

High friction of rubber caused by negative fluid pressure under glycerol lubrication

The friction coefficient, tread block deformation, and fluid pressure of rubber specimens at the contact interface between them and a glass plate under glycerol lubrication with different end-face corner radii of the tread blocks were experimentally measured. The friction coefficient increased as the end-face corner radius decreased. The tread blocks were deformed due to friction, and a negative fluid pressure formed at the contact interface. The friction coefficient was positively correlated with the resultant normal force of the normal load and the fluid force. Therefore, controlling the fluid pressure by changing tread blocks’ end-face corner radius will enhance their friction under lubrication.

Insights on the J‐integral expression of pure shear carbon black filled natural rubber specimen and predicting the crack growth rate using finite element method

AbstractThe J‐integral approach manifests itself in an efficient way to determine the crack growth and failure mechanism of tread and sidewall compounds used in tyres. Therefore, for a pure shear (PS) specimen of carbon black filled natural rubber, the J‐integral formula was vivisected, and the material parameters were defined using the concepts of solid mechanics considering the planar stress conditions. Theoretical calculations, experimental observations, and finite element analysis were executed to calculate the J value for different strain percentages. Different hyperelastic material models were used to understand the hyperelastic behavior of the test compound, but Yeoh model was found to be the best fit with the least error against the experimental test data. The frequency sweep dynamic mechanical analyzer test was done to observe the viscoelastic response of the material. It was observed that the J value decreased with decreasing contour radius and had exhibited stark difference with the global tearing energy values, indicating the effects of stress softening and the dependence of J value on the elastic characteristics of the material. Further, the J value attained from finite element methods for a random strain 22% was used to predict the crack growth rate of the pre‐notched PS specimen.Highlights J‐integral formula for pure shear specimen using solid mechanics approach. J value comparison of theoretical, experimental, and finite element methods. Dependence of J value on the elastic characteristics of the material. Different hyperelastic models compared and Yeoh model chosen for analysis. Prediction of crack growth rate at a random strain percentage.

Combination of active sensing method and data-driven approach for rubber aging detection

Rubber bearings are key components of base-isolated structures, and the monitoring of their damage states is an important task. Aging is a primary concern affecting the service life and isolation effect of rubber bearings. Therefore, this study combined an active sensing method and a data-driven approach to detect rubber aging. A shear stiffness, accelerated aging, and active sensing experiments were conducted on a scaled rubber specimen. As the aging level increased, the shear stiffness of the specimens gradually increased from 116.69 to 127.82 N/mm, but this change was not linear. Due to variations in the degree of aging, discrepancies may arise in the time and frequency domain characteristics of detection signals. However, establishing an empirical relationship between the degree of aging and the features of detection signals were highly challenging. A deep-learning-based data-driven method was used to predict the aging level and shear stiffness using detection signals. The deep learning model successfully detected the aging level, and the prediction accuracy on the validation and test sets reached 99.98%. For the deep learning model for aging level prediction, the optimal input vector length is 4096, the recommended number of layers is 3–5, and the recommended number of cells in each layer is 256–2048. Moreover, the deep learning model also detected the shear stiffness of the rubber specimen. The mean absolute error was 0.27 N/mm on the validation set and 0.28 N/mm on the test set. For the deep learning model for shear stiffness prediction, the optimal input vector length is 4096, and the optimal structure is seven layers with 2048 cells in each layer.

Tensile Characteristics of Rubber Material of Firefighting Supplies According to Test Piece Shape

Currently, rubber materials are widely utilized in firefighting supplies. They are utilized as rubber packing, such as air respirators, rubber bands, such as pipe windows, and rubber packing, such as fire extinguishers. EPDM initially utilized the rubber packing material, but because of aging and curing, it is difficult to maintain air tightness in the cracked gap; therefore, it has been replaced with NBR and utilized until now. In addition, among the material's physical properties, tensile properties are required, and the form usually adopted as a tensile test specimen is generally an aging form. However, rubber utilized in firefighting supplies employs rubber packing or rubber ring products. Currently, tensile tests are conducted by manufacturing a sample as a dumbbell from a separately manufactured sample without conducting a tensile test with a rubber ring-type specimen. Furthermore, questions often arise about the tensile properties of rubber rings. Therefore, this study tested the tensile properties with a ring-shaped specimen. In KS M ISO 37, it is generally known that an annular-type test piece is desirable for tensile strength measurement. An annular-type test piece has a lower value than an annular-type test piece, and an annular test piece with an elongation rate is almost the same value as an annular-type test piece. Therefore, the test was conducted to find the difference between the test piece as a dumbbell and the actual ring-shaped specimen. As a result of the tensile test, the tensile strength was found to be lower in the range of 11.8-15.5% in the ring-shaped test piece than in the age-shaped test piece, and the elongation rate was lower in the range of 4.1-40.1% than in the age-shaped test piece. This is thought to be because the stress of the stretched high-ring-shaped specimen is not equal to the cross-sectional area of the specimen. However, the tensile property value of the rubber material was satisfied with both types of test pieces with the reference value required for approval.

Studies on Dispersion of Insoluble Sulfur in Passenger Car Radial Belt Skim Compound

Good dispersion of compounding ingredients in a rubber formulation is crucial for mechanical performance. After mixing, certain materials like sulfur, recycled materials, and zinc oxide can remain undispersed within the rubber matrix, which can lead to critical flaws and influence performance. Improper dispersion is one of the reasons for poor physico mechanical properties. The influence of temperature, mixing time and storage time of different grades of insoluble sulfur collected from one source are studied along with the standard sample of different sources. To better understand the reason for poor sulfur dispersion and high blooming, all the chemical and physical properties are analysed. The topological structures are evaluated using the thermomechanical techniques. The reason for poor dispersion and premature failure of the rubber specimen has been studied by SEM-EDS. The degradation of insoluble sulfur to soluble sulfur can be negligible during the melt mixing if the mixing is done in a controlled way. The final mixing temperature shall be maintained at 90 °C to 95 °C to restrict the insoluble to soluble sulfur conversion. This paper highlights the methodology of the development of oil-coated sulfur in rubber composites and provides insight into the dispersion of polymeric sulfur in natural rubber-based tyre carcass compounds.

Performance Characteristics of Silicone Rubber for Use in Acidic Environments.

Silicone rubber insulators are widely used in power grids because of their excellent performance, but aging has been an inevitable problem of silicone rubber, especially in extreme conditions, such as acidic conditions. In order to clarify the performance changes in silicone rubber in an acidic environment, this paper uses the developed acid-resistant silicone rubber sheet and common silicone rubber samples as the research objects, and conducts an aging comparison test on them in a natural acidic environment. The electrical properties, physical properties, and chemical properties of the two types of silicone rubber specimens with different aging times are analyzed to obtain the performance characteristics of silicone rubber under a natural acidic environment. The research results show that the dry flash voltage and pollution flashover voltage of the acid-resistant silicone rubber after one year of aging are greater than those of the common type; the water repellency of both types of silicone rubber remains in good condition. The silicone rubber produced by our team according to the self-developed acid-resistant silicone rubber formula has indeed played a role in delaying aging in an acidic environment compared with the common-type silicone rubber.

Estimation of non-linear mechanical properties of rubber using Split Hopkinson pressure bar

The material non-linearity is a very important phenomenon in the behavior of the materials subjected to high strain rate loading. Rubber is a material which has high damping properties due to which it is more vulnerable in applications that involve absorption of vibration and shock; generally, these damping materials are subjected to high strain rate loading while absorbing the load. In the present work, various types of rubbers are subjected to very high-velocity impact due to which a very high strain rate loading is applied on the rubber specimens through the usage of Split Hopkinson Pressure Bar apparatus. The behavior of the rubber specimens at this high-velocity impact loading is studied through the variation of stress, strains, and strain rate with time. A comparison is drawn between various rubbers and the best rubber for the impact applied, is evolved and the same is presented in the work.

Experimental Investigation of Nano Al2O3 Filled Silicone Rubber Specimen Used in Outdoor Insulation

Experimental Investigation of Nano Al2O3 Filled Silicone Rubber Specimen Used in Outdoor Insulation

An analytical solution to predict temperatures of dumbbell-shaped rubber specimens under cyclic deformation

Abstract The objective of this study is to propose an analytical solution that can predict temperatures of dumbbell-shaped rubber specimens under cyclic deformation. To achieve this, first, a new mathematical equation was developed based on a modified Mooney-Rivlin (MR) strain energy function, the pseudo-elasticity theory, and the inverse analysis method. This equation was used to determine the internal heat generation rates of rubber compounds. With heat generation rates, the governing equation of heat conduction and the mathematical expression of boundary conditions were further generated to describe the heat transfer in rubber compounds. Based on these equations, a novel analytical solution was developed—the RTDS solution (a solution to predict Rubber Temperatures in Dumbbell-shaped Specimens). This RTDS solution was used to predict rubber temperatures in dumbbell-shaped specimens under cyclic deformation. The results showed that the RTDS solution took 11.9 seconds to derive the rubber temperature results with an average mean absolute percent error (MAPE) of 9.2% compared with lab recordings. The RTDS solution identified a logarithmic increase in rubber temperatures at rising strain levels, and it also identified an increase in rubber temperatures with the rising strain rates. Moreover, the RTDS solution characterized an inverse proportional relationship between the rubber temperature increments and the ambient temperatures.