Cord-rubber Composites Research Articles

Fatigue Behavior of Cord-Rubber Composite Materials under Different Loading Conditions.

Cord-rubber composites are subjected to a wide range of loads in various applications. However, their fatigue behavior remains relatively under-researched. To address this gap, a set of representative specimens was developed, and a validated numerical model was employed to assess fatigue-relevant parameters. In this study, we present the results from two series of tests with different strain ratios (R values). One series was subjected to a pure pulsating tensile strain (R ~0), while the second series experienced an increased mean strain with an R ratio between 0.2 and 0.3. A direct comparison of the two series demonstrated that a higher strain ratio results in a longer service life. This is reflected in an increase in the slope (k) from 13 to 23, as well as an increase in the ultimate fiber strain from 8% to 11% at Nd = 50,000 load cycles for a survival probability of 50%. Both series indicate a comparable scatter in the test results. This comparative analysis shows that the strain ratio significantly impacts the fatigue behavior of cord-rubber composite materials based on cyclic tests under different loading conditions. The findings of this study demonstrate the necessity of considering different load situations when evaluating or designing components.

Failure behaviors of cord-rubber composite materials under mixed mode I/II loading: Experimental and numerical simulation

Cord-rubber composites are widely used in automation with their flexibility and high strength. Interlaminar delamination damage is one of the main failure modes of this component during service. Therefore, we investigated the interlaminar delamination behavior of cord-rubber composites under different loading modes. Herein, an analytical method was proposed for determining the mode I and mode II fracture toughness of cord-rubber composites through T-peel and 0-degree peel tests. The interlaminar delamination mechanism of mixed mode I/II for cord-rubber composites was investigated using the cohesive zone model (CZM). Based on the analytical method, the interlaminar delamination failure behavior under mixed mode I/II loading conditions is accurately prediction, and the error is below 14 %. Meanwhile, cohesive failure within the cord fabric layer occurs first, followed by interfacial failure at the interface between the cord fabric and rubber layers.

QUASI-STATIC BENDING FATIGUE OF CARBON CORD–RUBBER COMPOSITES USED IN TIMING BELTS

ABSTRACT Cord–rubber composites such as timing belts are subjected to coupled tension and bending under typical service conditions. Due to their increased modulus, carbon cords are replacing traditional glass cords as reinforcing materials in timing belt products. The bending fatigue behavior of carbon cord–reinforced hydrogenated butadiene rubber (CC-HNBR) composites is of increasing interest for both understanding their failure mechanism and supporting the development of new industrial products. In this work, a simple experimental setup that replicated in a simplified way the real-pulley situation encountered in a timing belt operation was developed to investigate the effects of applied tension, bending curvature, frequency, and R ratio on the bending fatigue life of CC-HNBR composites. Furthermore, a numerical investigation of the stress distribution within the CC-HNBR composite, under both uniaxial tension and coupled tension and bending loading, was carried out using finite element analysis. Cord-dominated fracture was observed close to the point at which the specimen just left the pulley using a thermal imaging camera at high stress levels. This location is due to the combined effects of bending and maximum tension at this site. There was a reduction in the bending fatigue life as a result of a higher level of bending strain introduced by a smaller-diameter pulley. Frequency had negligible effects on the bending fatigue life within testing regimens probably resulting from the rubber generating only limited heat buildup even at the highest test frequencies. Higher R ratios led to a longer bending fatigue life, potentially due to the strain-induced crystallization of the HNBR matrix at the tip of any generated cracks. This study provides a basic investigation into the bending fatigue behavior of CC-HNBR composites under coupled tension and bending loading conditions, shedding some light on the failure characteristics of CC-HNBR composites under the interaction of bending and tension deformations.

Revealing the microstructures and seepage characteristics in the uncured rubber-cord composites using micro-computed tomography and lattice Boltzmann approach

The internal microstructure distribution of cord-rubber-air during the processing of uncured rubber-cord composites (URCs) determines the finished product's performance. For the first time, we used computed tomography (CT) and the lattice Boltzmann method (LBM) to establish a geometrical representation model of the real microscopic pore-fracture structures of URCs and investigate the seepage law of fluid in porous URCs, where the reinforced rubber formula was originally designed to reduce CT artifacts of cord. The results showed that the average porosity and pore radius of the original cord (0.2711 and 15.53 μm, respectively) were considerably larger than those of the URCs (0.0509 and 4.46 μm, respectively); the pore number of the cord was the largest when the pore radius was 5–10 μm, accounting for 29.36% of the total number; however, the pore number accounted for 31.36% of the total number of the URCs when the pore radius was 2–3 μm. Moreover, the characteristics of the pore/throat surface area and pore volume/throat length exhibited perfect consistent patterns with those of the pore radius. Furthermore, the fluid flow velocity increased in both cord and URCs as the displacement differential pressure increased, but decreased dramatically as the fluid kinematic viscosity increased. The critical values of displacement differential pressure and kinematic viscosity were different in the cord and URCs samples, presenting 11.1209 Pa/1.3696 × 10−3 m2/s and 14.2984 Pa/2.8869 × 10−4 m2/s, respectively. This phenomenon should be attributed that when the uncured rubber was injected into the original cord sample, its porosity decreased, its pore radius decreased, the number of micro-scale pores increased, and flow resistance became larger, resulting in a higher critical value of displacement differential pressure and a lower critical value of kinematic viscosity.

Multilayer structural analysis and application of overlap structure for cord–rubber composite

AbstractAs an advanced composite material with a flexible structure, cord–rubber composite has the advantages of high strength, high modulus, and lightweight, widely used in aerospace and other fields. Compared with our previous work, we focus on the effects of three kinds of overlap structures (positive–positive, positive–invert, concave–convex) on the mechanical properties of cord–rubber composites through uniaxial tensile tests and finite element simulation. When the interlaced distance is 5 mm, the concave–convex overlap structure reaches the maximum tensile strength (74.79 MPa). With the increased interlaced distance, the failure form of the cord rubber composite gradually transfers from the overlap end to the interface slip and fixture end. The maximum Von Mises stress distribution of cord–rubber composite flexible support tends to be uniform through rational design by the mechanical characteristics of the three kinds of overlap structures.

EXPERIMENTAL STUDY OF THE RHEONOMIC PROPERTIES OF BREAKER RUBBER AND RUBBER-CORD COMPOSITE UNDER QUASI-STATIC LOADING

Samples of filled breaker rubber and rubber-cord composite were tested for quasi-static cycling loadings with constant strain rates. The dependence of the rubber mix stress-strain diagram on the strain rate was revealed even for low strain rates. A difference was observed between stress-strain diagrams for the first loading and for subsequent ones. The second and subsequent diagrams are close to each other. This effect is referred to in the literature as the Mullins effect. Eight experiments were conducted with different loading programs to determine the manifestation of this effect for breaker rubber. The stress-strain curves depend differently on the strain rate for the first and subsequent loadings. The dependence on strain rate can be described as using the generalized Maxwell model for the first loading, but not for subsequent ones. Moreover, a similar study was done for a bi-ply rubber-cord sample with a 45° cord angle. The same conclusion regarding the Maxwell model applicability was also proven. Finally, numerical simulation of the bi-ply rubber-cord composite was carried out to determine the dimensions of the edge effect zones and, thereby, to estimate the allowable dimensions of the sample. Two types of boundary effects were revealed. Their dimensions were calculated for the 45° rubber-cord sample with various lengths. It was shown that short samples can also be used, if the longitudinal strain is properly recalculated.

Study on Thermo-oxidative Aging Mechanism of Air Spring Rubber Cord Composites

To study the thermo-oxidative aging mechanism of air spring rubber cord composites, observe the changes in surface micro-morphology, study the thermo-oxidative aging mechanism of air spring rubber cord composites, observe the changes in surface micro-morphology, infrared spectrum, quality, hardness, and mechanical properties during the process of thermo-oxidative aging, and analyze the aging mechanism. The results show that the micro-morphological changes of the rubber surface of the rubber cord composites go through two stages: at 0-72 h, the rubber surface The results show that the micro-morphological changes of the rubber surface of the rubber cord composites go through two stages: at 0-72 h, the rubber surface develops from no cracks to a large number of cracks; at 96-336 h, the rubber surface changes from a cracked state. The size of the crack on the rubber surface affects the rate of change of IRHD hardness. The larger the crack, the greater the hardness growth rate, otherwise the opposite. In the aging process, the rubber is in a state of dynamic development. The increase of cross-linking density causes changes in microscopic The increase of cross-linking density causes changes in microscopic morphology and accessible volume, which affects the IRHD hardness. The aging mechanism is more complicated. Material failure is dominated by the failure of the rubber matrix.

Thermally induced structural changes of resorcinol formaldehyde latex adhesive used in cord-rubber composites

In this study, the accelerated thermal exposure of resorcinol formaldehyde latex (RFL) adhesive used in cord rubber composites was investigated. In particular, the structural changes of the RFL with and without curatives (sulfur, zinc oxide, accelerator and stearic acid) during thermal treatment at 100 °C were identified by a multiscale approach using dynamic mechanical analysis (DMA), atomic force microscopy (AFM), and solid-state nuclear magnetic resonance (ssNMR). The RFL samples with curatives show an approximately four-fold increase in the overall elastic modulus at room temperature during thermal treatment of up to 10 days. At the same time, DMA results indicated an increase of Tg of the latex phase from −39 °C to −3 °C. However, for the RFL samples without curatives, there was no change in the Tg of the latex phase. At the nanoscale, AFM mappings on samples with curatives have also confirmed an increase in the nanoscale modulus in the latex phase (50 ± 10 MPa to 140 ± 20 MPa) and in the RF resin phase (330 ± 100 MPa to 620 ± 200 MPa) for the same thermal treatment duration. Finally, solid-state NMR analysis showed a decrease in the intensity of the vinyl groups (noted at 115 ppm and 145 ppm) in the latex phase indicating the possibility of further sulfur cross-linking during the 10 days of thermal treatment for samples containing curatives. Our studies have highlighted the prominent role of the curatives in the RFL adhesive, as well as its initial structure and evolution during thermal treatment. Accordingly, the RFL structure was drastically modified by the accelerated thermal exposure.

A simple anisotropic visco-hyperelastic constitutive model for cord-rubber composites

In this study, we developed an anisotropic visco-hyperelastic constitutive model for cord-rubber composites, in which the unit-volume strain energy function could be decomposed into four parts to facilitate and simplify the identification of material parameters. The computation accuracy of the model was significantly improved by introducing viscous potential energy. A simple approach for fitting the parameters with the uniaxial tension and bias-tension experimental data was developed. The developed model was also validated by comparing the numerical results with the bias-tension experimental data under different strain rates, and very good agreement was obtained.

Mechanical properties and failure mechanism of overlap structure for cord-rubber composite

Overlap structure plays a vital role in mechanical properties of cord-rubber composite, which directly affects safety performances of rubber products. However, the mechanical properties and failure mechanism of the overlap structure of the cord-rubber composite are still not clear. In this work, the experiment and simulation results for the mechanical properties are compared, and a cohesion zone model is introduced to analysis the failure mechanism of the overlap structure for the cord-rubber composite. The results show that the errors of both real cord model and rebar layer model simulated the limit load of the overlap structure are about 5%. And an interlaminar damage evolution plays a key role in the strength of the overlap structure. Simultaneously, this work can provide a theoretical basis for the design of the cord-rubber composite.

ВОЗМОЖНОСТИ ОПТИМАЛЬНОГО ПРОЕКТИРОВАНИЯ АВТОМОБИЛЬНОЙ ШИНЫ ПО КРИТЕРИЮ ПРОСТРАНСТВЕННОЙ РАВНОПРОЧНОСТИ

A procedure is proposed for calculating the internal profile and optimal distribution of materials for a pneumatic car tire in a mold configuration. To adequately describe the elastic-dissipative properties of tire rubbers and rubber-cord composites, nonlinear elastic deformation Mooney–Rivlin model and viscoelastic Prony model as well as experimental data of static and dynamic tests are considered. An algorithm for finite element analysis of the stress-strain state of a passenger car tire is described in the MSC.Marc software package, and results of numerical solution of applied problems are presented on the tire landing on the rim and its loading with working pressure, as well as on the contact interaction of a passenger car tire with the road surface at maximum operating load at rest and during stationary rolling at a speed of 90 km/h. It was found that the contact loading of the tire when interacting with the road surface does not lead to a significant difference in the deformed state in the zone opposite diametrically to the contact zone from that for a tire mounted on a rim and loaded with excess operating pressure. In this case, the nature of the distribution of strains in the radial section near the contact zone of the tire with the road surface is the same under conditions of compression and stationary rolling. Areas of concentration of equivalent stresses and strains in the bead zone of the tire and in the zone of the edges of the breaker are revealed. For a quick comparison of competing tire designs, it is recommended to calculate the average values of the total strain energy density per wheel revolution. The developed calculation methods make it possible to predict the performance characteristics of automobile tires at the design stage and are tested in the manufacturing of these products.

Research of the properties of rubber-cord composites in the presence of new adhesion promoters

Studies of experimental adhesion modifiers based on a mixture of fatty acids from the production of light vegetable oils. The properties of rubber compounds and their vulcanizates obtained using experimental adhesion promoters KK with cobalt content from 7.5 to 16.5% are investigated. The plastic-elastic and vulcanization properties of the properties of breaker rubber compounds based on polyisoprene, the physical and mechanical properties of breaker rubbers and the bond strength in the “rubber-brass-plated steel cord system” were studied. When testing belt rubbers containing experienced adhesion promoters or an imported analog of Manobond 680C, the following features were revealed. The plasticity of the prototypes was in the range of 0.2-0.4. This indicates satisfactory processing properties. The Mooney viscosity of the prototypes was lower than that of the production sample. The use of experienced adhesion promoters instead of the analogue (Manobond 680C) increases the resistance to scorching. On the basis of the analysis of elastic-strength properties, it was found that in terms of the conditional tensile strength, the prototypes were inferior to the serial ones. However, rubbers containing the KK-12, KK-13.5, KK-15 promoters met the control standards. The tensile elongation at break of the experimental rubbers is higher than that of the serial sample. This may indicate the formation of a more uniform cure network in the presence of the test products. When testing rubber-metal-hard composites, it was noted that, under normal conditions, the experienced adhesion promoters have advantages over Manobond 680C. However, at elevated temperatures, under conditions of salt and steam-air aging, they are slightly inferior to Manobond 680C. It has been established that the experimental adhesion promoters provide the required set of technical properties of belt rubbers with a CO2 + content of 12–16.5% wt. Thus, it is possible to recommend the adhesion promoters KK 12, KK-13.5, KK 15 for practical use in the composition of belt rubber compounds. This will allow replacing a foreign-made product and reducing the cost of production.

An Anisotropic Hyperelastic Constitutive Model with Bending Stiffness Interaction for Cord-Rubber Composites: Comparison of Simulation Results with Experimental Data

Based on the invariant theory of continuum mechanics by Spencer, the strain energy depends on deformation, fiber direction, and the gradients of the fiber direction in the deformed configuration. The resulting extended theory is very complicated and brings a nonsymmetric stress and couple stress. By introducing the gradient of fiber vector in the current configuration, the strain energy function can be decomposed into volumetric, isochoric, anisotropic, and bending deformation energy. Due to the particularity of bending deformation, the reinforced material has tensile deformation and compression deformation. The bending stiffness should be taken into consideration, and it is further verified by the bending simulation.

IN SITU MEASUREMENT OF TIRE PLY STEER BASED ON AN INTELLIGENT TIRE SYSTEM

ABSTRACT Ply steer is an inherent property of a belted tire, manifesting as the nonzero side force at a slip angle of zero, and it is thus an important design factor relevant to a vehicle's straight running, safety, and comfort. Although ply steer is a rolling contact phenomenon, there is a lack of approaches for direct measurement and modeling of tire ply steer force in motion. Thus, we developed an in situ measurement method for tire ply steer based on a recently proposed accelerometer-based intelligent tire system. This new measurement method is significant for three main reasons: it facilitates understanding of the inherent mechanism of ply steer for radial tires, it improves the intelligent tire's accuracy based on the accelerometer, and it provides an in situ measurement approach for tire ply steer. An accelerometer-based intelligent tire was developed to obtain acceleration measurements at different conditions in which the lateral behavior is of particular interest. Two unusual phenomena that have never been reported are observed: (1) lateral accelerations demonstrate asymmetrical behavior with respect to positive/negative slip angles and (2) lateral accelerations at zero slip angle still exist. It is hypothesized that the underlying reason for these two unusual phenomena is the ply steer–dependent kinematics, which can conversely be used to measure tire ply steer in situ. To this end, the mixed Lagrange–Euler approach for rolling contact kinematics is used to formulate tire lateral acceleration, which links both rigid motion and elastic displacement. It is clearly found that the lateral acceleration is proportional to the square of the rotating velocity and the second-order gradient of displacement. Based on this kinematic model, the features of lateral acceleration can be easily explained by tire ply steer, which manifests as the sinusoidal lateral deformation modes due to the coupling of the bending-twist deformation of the cord–rubber composites of the tire belt. The proposed hypothesis has been verified by finite element method simulations, and the experimental results prove that tire ply steer leads to the observed unusual lateral acceleration pattern. Thus, the quantitative value of ply steer could be measured in situ by integrating the obtained lateral acceleration and thus the apparent elastic slip angle, even under zero external wheel slip angle. In this manner, the intelligent tire system provides a direct measurement approach for tire ply in motion. In addition, the accuracy of the intelligent tire's algorithm might be improved by suitable modeling of the asymmetrical acceleration with respect to left/right slip based on the proposed hypothesis of ply steer–dependent kinematics.

Fatigue of carbon cord-rubber composites: Effect of frequency, [formula omitted] ratio and life prediction using constant life models

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.

Constitutive model research for rubber-cord composites used in rubber track

In order to characterize the mechanical behaviors of rubber track with large deformation, nonlinearity and anisotropy in different operational conditions, a constitutive model for rubber-cord composites with interaction between rubber and cord is developed. The total strain energy is decomposed into three parts, representing the strain energy from rubber, cord, and interaction between rubber and cord. Based on the particle swarm optimization and Newton iteration method, an optimization algorithm for model parameters fitting is proposed. With the obtained parameters, the mechanical behaviors of rubber-cord composites are predicted by the developed model, and the prediction results have a good agreement with test data. The proposed model is validated by comparing finite element simulation results with uniaxial tension data of rubber-cord composites. The maximum error is about 10.86 %. Moreover, the influences of cord off-axis angle on the mechanical properties of rubber-cord composite are analyzed. The proposed model can be used for finite element analysis, and lays the foundation for finite element simulation of rubber tracks.

Strain analysis of cord-rubber composites using DIC

This contribution deals with the experimental investigation of cord-rubber composites with polyamide cord reinforcement. A loading procedure including internal pressure, compression and torsion was applied to the specimens. For deformation analyses at the surface of the specimens, 3D Digital Image Correlation was applied. Tangential strain values were determined by means of a special evaluation procedure using B-spline approximation of the DIC point data. The results show large strain differences between cord and elastomer sections. Based on the obtained experimental data, validation of numerical simulations of the cord-rubber composites can be performed in further investigations.

Experimental Investigation of Viscoelastic Characteristics of Rubber-Cord Composites Considering the Process of Their Self-Heating

The dissipative characteristics of rubber-cord composites under the action of cyclic load considering the features of their self-heating have been experimentally investigated. Full-scale uniaxial tension experiments are performed on the plane specimens along the reinforcement fibers of the unidirectional rubber-cord composites. In compliance with the test results, stress–strain curves for the specimens are determined, which form the hysteresis loops under cyclic loading. The tensile testing of the specimens is performed under long-term cyclic loading using the experimental setup INSTRON ElectroPuls E3000 Test System. The process of significant self-heating of the specimens under their long-term cyclic deformation has been experimentally established and studied. Using the non-contact methods, the variation in the specimen temperature in time is measured. The mechanisms of their non-stationary heating are obtained, as well as the dependences of the stabilization temperature of the thermal state on the loading conditions. It has been determined that the area of hysteresis loops, which is formed when specimens undergo deformation in the temperature-stabilized state, depends nonlinearly on the amplitude of strains. The qualitative and quantitative dependences of the loss modulus, as well as the dissipation coefficients and relaxation times on the loading frequency, strain amplitude and temperature due to the material self-heating, are determined. The approximation dependences of the loss modulus of the composite on the loading frequency and self-heating temperature are constructed on the basis of the generalized three-parameter linear (Zener) model and the exponential temperature-dependent initial elastic modulus.

Development of a novel fatigue test method for cord-rubber composites

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.

On the lifetime prediction of rolling lobe air springs

Abstract In this paper, the fatigue life of rolling lobe air springs made from cord-rubber composites is investigated with particular focus on the crack nucleation approach. Commonly used test specimens like the simple tension test specimen or the dumbbell specimen fail in the fatigue analysis of rolling lobe air springs because the fatigue characteristic of the cord-rubber interface is represented insufficiently. Therefore a new cord-rubber specimen is developed. The fatigue characteristic of the new specimen is discussed and Wohler curves for two different predictors based on Cauchy stress and configurational stress are determined. Using FEA with a two-scale model of the air spring, the cycles-to-failure with respect to piston diameter and different inner pressures are determined and compared to test results taken from the literature. The results from the literature were derived at elevated temperature. Therefore, the Arrhenius approach is used to take into account different temperatures. In addition the crack growth approach using the cracking energy density is applied. The results show an improvement in the prediction of rolling lobe air springs fatigue life with respect to the crack initiation plane orientation and the cycles-to-failure using the new specimen. Compared to the crack nucleation approach, the crack growth approach seems to slightly overpredict the fatigue lives.