Analysis of extrudate swell behaviour of rubber compounds using laser scan detector

Summary Classical extrudate swell measurements such as the gravimetric or the shrinkage techniques, are difficult, complex and time consuming methods. Using laser scan detector, new instruments have been recently developed which allow the extrudate swell behaviour of rubber compounds to be analysed in a quick and reliable manner.This paper discusses the requirements for suitable analysis of the extrudate swell of rubber compounds. Due to the specific elastic response of rubbers, these requirements differ from those for thermoplastics. Recent results obtained using typical industrial formulations, such as natural rubber/polybutadiene blends, are presented and their practical significance is discussed.Paper presented at the VIIIth International Congress on Rheology, Naples, Sept. 1–5, 1980.With 3 figures     

The behaviour of field-responsive fluids during shear start-up

The application of an external field (magnetic or electric) to suspensions of particles in a carrier liquid often causes a dramatic increase in the flow resistance. The transient stress response of these systems during the start-up of shear flow was studied as a function of the shear rate, using a system of carbonyl iron particles dispersed in paraffinic spindle oil under magnetic flux densities up to 0.57 T. It was found that initially the stress increased in proportion to the applied strain, reaching a plateau value at a characteristic strain of 0.2. Similar strain dependence of the transient stress behaviour was observed for shear rates spanning the range 0.01 s^–1 to 10 s^–1, suggesting that strain-governed deformation and rupture of the particle aggregates in the fluid was the main contribution to the response. In addition, the steady state flow curves of these fluids were obtained over the shear rate range 0.1 to 100 s^–1.     

High-rate decremental-strain-rate test

A modified torsional split-Hopkinson bar is intoduced and used to study material response associated with a sudden reduction of stain rate during high-rate plastic deformation. In tests on 1100-0 aluminum iniial deformation at a strain rate of approximately 2400 s⁻¹ is reduced by a factor of 15 after 200 μs of high-rate deformation. After the reduction, the deformation continues at the low rate for additional 550 μs. The change in the strain rate is obtained by using a stepped input bar. The results for 1100-0 aluminum show a decrease in the flow stress following the reduction in the strain rate. A short delay exists between the beginning of the strain-rate reduction and the response of the stress. The magnitude of the drop in the stress agrees with the difference in flow stress expected in constant-strain-rate tests in the corresponding high- and low-strain rates. Following the stress reduction. The stress remains essentially constant with no hardening during the subsequent deformation at the low rate.     

Finite element simulation of deformation behaviour of cellular rubber components

This paper presents a new prospect of investigating the mechanical behaviour of cellular rubber using a porous hyperelastic material model within the framework of homogenisation method to consider pore volume fraction. There are number of hyperelastic material models to describe the behaviour of homogeneous elastomer, but very few to characterise the complex properties of cellular rubber. The analysis of dependence of material behaviour on pore density using the new material model is supported with experiments to characterise the actual material behaviour. The finite element simulations are then followed by compression load tests to validate the material model.     

Experimental estimation of wall slip for filled rubber compounds

The phenomenon of wall slip during flow of rubber compounds through capillaries is investigated for a typical styrene-butadiene elastomer with carbon black. It was found that at low temperature (110°C) the dependencies of slip velocity V _c on shear stress are described by the power law but, additionally, V _c depends on radius of a channel. At high temperatures there is a critical shear stress below which sliding is absent. Sliding appears only at higher shear stresses where, again, V _c depends on shear stress and the radius of a channel.     

Rheological behaviour of mixtures of rubber and crumb from scrap pneumatic tyres

Summary In continuation of earlier studies the flow behaviour of mixtures of rubber (SBR, EPDM) and crumb from scrap tyre treads was estimated at 120°C with the aid of a high-pressure capillary rheometer. The influence of the capillary dimension on the flow curves was studied. With narrow and short capillaries the flow behaviour proved to be independent of the filler concentration. At low shear rates a discrimination of the flow characteristics according to the filler loading was observed only with capillaries above a certain width and length. At high shear rates with such a capillary an inversion of the rating of the flow curves was found.

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Zusammenfassung In Fortsetzung früherer Arbeiten wurde das Fließverhalten von Mischungen aus Kautschuk (SBR, EPDM) und Gummimehl von Altreifenlaufflächen mit Hilfe eines Hochdruckkapillarviskosimeters bei 120°C ermittelt, wobei der Einfluß der Kapillardimensionen auf die Fließkurve untersucht wurde. Bei der Verwendung von engen und kurzen Kapillaren erwies sich das Fließverhalten als unabhängig von der Füllstoffkonzentration. Im Bereich niedriger Schergefälle wurde eine Abstufung der Fließkurven nach dem Füllstoffgehalt nur mit Kapillaren von ausreichender Länge und ausreichendem Durchmesser gefunden; mit einer solchen Kapillare wurden im Bereich hoher Schergefälle Anzeichen für eine Inversion der Fließkurven beobachtet.

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With 10 figures     

Effect of curatives and antidegradants on flow properties of uncured rubber compounds

Summary Using new processability testing techniques, the effects of curatives and antidegradants on flow properties of uncured rubber compounds have been studied. Results obtained show that a change of the cure system or the antidegradant type can affect the viscosity curve and the extrudate swell behaviour of NR and SBR compounds.CBS N-cyclohexyl-2-benzothiazole sulphenamide - DTDM 4,4-Dithiodimorpholine - TMTD Tetramethylthiuram disulphide - 6PPD N-Phenyl-N(1,3-dimethylbutyl)-p-phenylenediamine - TMQ 1,2-Dihydro-2,2,4-trimethylquinoline, polymerized - PBN Phenyl--naphthylamine - phr part per hundred rubber Paper presented at the VIIIth International Congress on Rheology, Naples, Sept. 1–5, 1980.With 7 figures and 2 tables     

Rheological model optimization using advanced evolutionary computation for the analysis of the influence of recycled rubber on rubber blend dynamical behaviour

Rheological models of tested rubber blend samples, with different ratios of smut/recycled material, were developed, analyzed and discussed according to experimental data. The experimental measurements show the dynamical behavior of these samples after a short-term axial load. The rheological model of samples was assumed as a viscoelastic Voigt-Maxwell and hyperelastic Mooney-Rivlin model. Real coded genetic algorithms were implemented for optimal model parameters identification in order to minimize the difference between the real sample behavior and dynamical model output. Numerical results obtained for analyzed mixture were compared with the original sample to verify the presented method. In purpose of predicting the dynamical characteristics for desirable rubber blends, an interrelation was formed based on the concentration of recycled material in sample blends and dynamical model parameters dependence.     

Tire-ice model development for the simulation of rubber compounds effect on tire performance

The material properties of the rubber compounds, which are highly dependent on temperature, have a vital role in the tire behavior. A comprehensive study on the effect of the rubber properties on tire performance, for different temperatures, as well as different road conditions is required to adequately predict the performance of tires on ice.In this study, a theoretical model has been developed for the tire-ice interaction. The temperature changes obtained from the model are used to calculate the height of the water film created by the heat generated due to the friction force. Next, the viscous friction coefficient at the contact patch is obtained. By using the thermal balance equation at the contact patch, the dry friction is obtained. Knowing the friction coefficients for the dry and wet regions, the equivalent friction coefficient is calculated. The model has been validated using experimental results for three similar tires with different rubber compounds properties. The model developed can be used to predict the temperature changes at the contact patch, the tire friction force, the areas of wet and dry regions, the height of the water film for different ice temperatures, different normal load, etc.     

High-rate deformation and fracture of fiber reinforced concrete

This paper presents the results of dynamic compression and splitting-tensile tests of cardiff fiber reinforced concrete (CARDIFRC) composite using the Kolsky technique and its modification. The strength and deformation characteristics of fiber-reinforced concrete were determined experimentally at high strain rates. The mechanical characteristics were found to depend on the strain rate and stress rate. A uniform interpretation of the rate effects of fracture of the tested fiber-reinforced concrete is given on the basis of a structural-temporal approach. It is shown that the time dependences of both the compressive and tensile strengths of fiber reinforced concrete are well calculated using the incubation time criterion.     

Strain-coupling effects in start-up experiments

A strain-coupling integral constitutive equation is used to analyze a start-up shear flow experiment. The theory is used to examine the effect of strain-coupling on the strain at the maximum in the shear stress-time curve. The analysis shows that there is a significant dependence of this strain on the shear rate even when a factorable strain-coupling model is used.     

光纤陀螺低温快速启动技术

光纤陀螺的启动时间与超辐射发光二极管(SLD)的输出性能密切相关。论文建立了SLD的ArcTan模型,并利用该模型分析光功率的温度敏感度和驱动电流敏感度。结果显示低温启动时,改变驱动电流可更快实现光功率稳定(与变温控制相比)。以此为指导设计了新型驱动电路,实现光功率自动控制,有效缩短光纤陀螺低温启动时间。论文描述了SLD的新型数学模型,设计出SLD的新型驱动电路。以低温(的40℃)启动时间较长(～8.5s)的陀螺仪表为应用对象,改进驱动电路后,该仪表可在2.5s内完成启动。     

The mechanical behaviour of rubber under hydrostatic compression and the effect on the results of finite element analyses

Using finite element tools for the dimensioning of rubber components is state of the art. When conducting finite element simulations, a split of the strain energy function, which results in stresses, into a deviatoric and a volumetric part is made. The mechanical behaviour of reinforced natural rubber under hydrostatic pressure is determined to prove the validity of this assumption. Furthermore, a nearly incompressible material behaviour is assumed in simulations of rubber, which may cause an insufficient outcome quality especially for rubber components that are exposed to hydrostatic pressure like highly confined bushings. In this paper, a method is presented to determine the compressibility, or its reciprocal the bulk modulus of rubber. The effect of the bulk modulus of a natural rubber on the simulation results of a bearing is pointed out. The obtained results are compared to test data to show the significance of the value of the bulk modulus for achieving a satisfactory outcome quality. Therefore, reliable information about the in-use behaviour of rubber components is obtained to reduce the costs and the effort in the dimensioning process.     

High-rate Characterization of 304L Stainless Steel at Elevated Temperatures for Recrystallization Investigation

An integrated experimental technique was developed for high-rate mechanical characterization of 304L stainless steel at elevated temperatures by using a modified split Hopkinson pressure bar (SHPB). A sandwich structure consisting of two platens and the specimen in between was heated before mechanical loading while the bars were maintained at room temperature to eliminate the temperature gradient effect on the wave propagation in the bars. Upon contacting the cold bars, temperature gradients form in the platens, leaving the temperature in specimen constant and uniform. Pulse shaping techniques were employed to maintain constant strain-rate deformation and dynamic stress equilibrium in the specimen. Dynamic compressive stress-strain curves at elevated temperatures for the 304L stainless steel were obtained. To relate recrystallization to impact loading, a momentum trapping system was employed to apply a single loading on the specimen during one dynamic experiment. We also controlled the quenching time to study its effect on recrystallization.     

Rupture of rubber

Summary The theory of the tearing of rubber has been further confirmed by experiments on three test pieces of widely different shapes, for each of which the tearing energy can be calculated. This rupture concept has been used to interpret measurements of out growth under conditions of both static and dynamic loading.

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Zusammenfassung Die Theorie des Reißens von Gummi wird durch Versuche an drei Proben von wesentlich verschiedener Gestalt, für die jeweils eine Reiß-Energie berechnet werden kann, weiter erhärtet. Diese Vorstellung über den Bruchvorgang wird dazu verwendet, Meßergebnisse bezüglich des Einschnittwachstums (Rißvergrößerung) sowohl bei statischer als auch bei dynamischer Versuchsführung zu interpretieren.

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Presented at a meeting on Flow, Fatigue, and Failure held in Leeds on January 8th and 9th, 1959, by the British Society of Rheology.