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Volume Changes in Filled Rubber Under Uniaxial Cyclic Loading
Elina KAZINA,Olesja STARKOVA,Andrey ANISKEVICH
Materials Science , 2011, DOI: 10.5755/j01.ms.17.3.592
Abstract: Styrene-butadiene rubber, neat and filled with different silica content was investigated under uniaxial cyclic loading under a constant crosshead speed, with increasing deformation amplitude in subsequent loading cycles. Rubber was investigated in order to evaluate the reversibility of structure rearrangements, occurring in rubber when subjected to cyclic loading. Volume uniformly increases with growing strain and shows hysteresis at unloading. After complete unloading, no residual strain changes are observed. These data are in good conformity with the data of density measurements, which were made on specimens before and after the tests. By correlating data, obtained from volume changes and kinetics of hysteresis losses there were made assumptions on deformation mechanisms at different elongations. Deformational mechanisms, responsible for volume changes in rubber are reversible. Volume changes in specimen occur due to voids formation caused by filler microstructure breakage, rubber chains disentanglement, spaces between rubber macromolecular chains shrinkage, and chain slippage under higher elongations. Voids formation and deformation of rubber macromolecular chain reaches equilibrium state after certain elongation. http://dx.doi.org/10.5755/j01.ms.17.3.592
Mechanical properties and environmental stress cracking resistance of rubber toughened polyester/kenaf composite
eXPRESS Polymer Letters , 2010, DOI: 10.3144/expresspolymlett.2010.10
Abstract: In this study rubber-toughened polyester-kenaf fibre composites were prepared by adding various percentages of kenaf fibre in unsaturated polyester resin and subsequently cross linked using a mixture of organic peroxide methyl ethyl ketone and cobalt octanoate. Three percent (3%) of liquid natural rubber (LNR) were added as a toughening agent. The mechanical properties of the composites were evaluated by impact and flexural testing. Environmental stress cracking resistance (ESCR) of polyester-kenaf composite in acid and base medium was also studied. It was found that the addition of LNR increased impact strength by about 66% and flexural strength by 70%. Measurement of ESCR shows that the composite has the fastest diffusion rate in acid medium, followed by that in base medium and then without medium. Bonding mechanisms were assessed by scanning electron microscope and FTIR analysis.
A tube concept in rubber viscoelasticity  [PDF]
Aleksey D. Drozdov
Physics , 2001,
Abstract: A constitutive model is derived for the time-dependent response of particle-reinforced elastomers at finite strains. An amorphous rubbery polymer is treated as a network of long chains linked by permanent junctions (chemical crosslinks, entanglements and filler particles). A strand between two neighboring junctions is thought of as a sequence of mers whose motion is restricted to some tube by surrounding macromolecules. Unlike the conventional approach that presumes the cross-section of the tube to be constant, we postulate that its radius strongly depends on the longitudinal coordinate. This implies that a strand may be modeled as a sequence of segments whose thermal motion is totally frozen by the environment (bottle-neck points of the tube) bridged by threads of mers which go through all possible configurations during the characteristic time of a test. Thermal fluctuations affect the tube's radius, which results in freezing and activation of regions with high molecular mobility (RHMs). The viscoelastic response of an elastomer is associated with thermally activated changes in the number of RHMs in strands. Stress-strain relations for a rubbery polymer at finite strains and kinetic equations for the concentrations of RHMs are developed by using the laws of thermodynamics. At small strains these relations are reduced to the conventional integral constitutive equation in linear viscoelasticity with a novel scaling law for relaxation times. The governing equation is determined by 5 adjustable parameters which are found by fitting experimental data in tensile dynamic tests on a carbon black filled natural rubber vulcanizate.
Damage initiation mechanism in rubber sheet composites during the static loading  [PDF]
R. Luong,N. Isac,E. Bayraktar
Archives of Materials Science and Engineering , 2007,
Abstract: Purpose: Mechanical behaviour and damage initiation mechanisms in thin rubber sheet composites were investigated under static solicitation at room temperature. Two types of rubber are used in this study; Natural rubber, NR vulcanised and reinforced by carbon black and Synthetic rubber (styrene-butadiene-rubber, SBR).Design/methodology/approach: A comprehensive study has been carried out in order to identify a threshold criterion for the damage mechanism to explain a tearing criterion for the concept of tearing energy of the elastomers and also to give a detail for the damage mechanism depending on the loading conditions. A typical type of specimen geometry of thin sheet rubber composite materials was studied under static tensile tests conducted on the smooth and notched specimens with variable depths. In this way, the effects of the plane stress on the damage mechanism are characterized depending on the rubber materials.Findings: Damage mechanisms during tensile test have been described for both of rubber types and the criteria which characterize the tearing resistance, characteristic energy for tearing (T) was explained. Damage in the specimens were evaluated just at the beginning of the tearing by means of the observations in the scanning electron microscopy (SEM).Practical implications: A tearing criterion was suggested in the case of simple tension conditions by assuming large strain. In the next step of this study, a finite element analysis (FEA) will be applied under the same conditions of this part in order to obtain the agreement between experimental and FEA results.Originality/value: This study propses a threshold criterion for the damage just at the beginning of the tearing for thin sheet rubber composites and gives a detail discussion for explaining the damage mechanisms by SEM results. This type of study gives many facilities for the sake of simplicity in industrial application.
Effect of Cyclic Compression Loading On Crushing Response of Polymer Based Composites Sandwich Panels  [PDF]
M Sripathy,K V Sharma,M Krishna
International Journal of Soft Computing & Engineering , 2013,
Abstract: The objective of work was focused to investigatemicrostructure of polyurethane foam and cyclic crushingstrength of its sandwich structure which made of sisal / coir /bamboo / glass fabrics as reinforcement with polyester resin toform composites skin. The tested sandwich panels wereconstructed four type of FRP faceplates made of sisal / coir /bamboo / glass fiber reinforcements impregnated in polyesterresin in four different material combinations. Each specimensubjected ten cyclic compression loading upto 40% maximumstrain. The results indicate that the foams initially harden afterthe first cycle and then soften in subsequent cyclic loading. Thehysteresis loops tend to shrink and approach asymptotically to asteady state before failure both the foam and the skin. Theconsidered damage is in a form of through-width zone of crushedfoam core accompanied by a residual crushing in the foam. It isshown that such damage causes a significant reduction ofcompressive strength. Glass/polyester and bamboo/polyester skinbased sandwich structures have superior compressive strength.Coir /polyester based sandwich structure shows next toglass/polyester sandwich structures.
Effect of Particle Size and Concentration of Flyash on Properties of Polyester Thermoplastic Elastomer Composites  [PDF]
M.S. Sreekanth, V.A. Bambole, S.T. Mhaske, P.A. Mahanwar
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2009, DOI: 10.4236/jmmce.2009.83021
Abstract: The performance of filled polymers is generally determined on the basis of the interface attraction of filler and polymers. Particulate filled polymer composites are becoming attractive because of their wide applications and low cost. In this study the effects of flyash with three varying particle size and filler concentrations (viz. 5 to 40 weight %) on the mechanical, thermal, electrical, rheological and morphological properties of polyester thermoplastic elastomer (Hytrel?) was investigated. Composites of polyester thermoplastic elastomer with varying concentrations of flyash were prepared by twin screw extrusion. Mechanical properties such as flexural strength and modulus increases with filler loading, where as tensile strength is found to be decrease with increase in flyash loading. Dielectric strength of composites also increases with flyash loading. Morphological studies revealed that there is good dispersion of filler in the polymer matrix. Thermal properties were found to be improved with flyash addition. Further, it was observed that the mechanical (flexural), thermal as well as electrical properties of composites improved with decrease in particle size of filler.
Finite viscoelasticity of filled rubbers: the effects of pre-loading and thermal recovery  [PDF]
Aleksey D. Drozdov,Al Dorfmann
Physics , 2001, DOI: 10.1007/s001610100073
Abstract: Constitutive equations are derived for the viscoelastic behavior of filled elastomers at isothermal loading with finite strains. A particle-reinforced rubber is thought of as a composite where regions with low concentrations of junctions between chains are randomly distributed in the bulk material. The onset of these inclusions is associated with the inhomogeneity in spatial distribution of a cross-linker during the mixing process. With reference to the theory of transient networks, the time-dependent response of an elastomer is modelled as thermally activated processes of breakage and reformation of chains in domains with low concentrations of junctions, whereas junctions in the bulk medium are treated as permanent. Stress-strain relations are developed by using the laws of thermodynamics. Adjustable parameters in the constitutive equations are found by fitting experimental data in tensile relaxation tests for several grades of unfilled and carbon black filled natural rubber. It is demonstrated that (i) the average relaxation time noticeably grows with the elongation ratio, which is explained by mechanically-induced crystallization of strands, and (ii) the relaxation spectrum of a filled elastomer is not affected by mechanical pre-loading and thermal recovery at elevated temperatures.
Enhancement of Adhesion between EPDM and Polyester Fabric by Using Natural Rubber Modified by Maleic Anhydride  [PDF]
A. A. El-Wakil
International Journal of Polymer Science , 2011, DOI: 10.1155/2011/591948
Abstract: This study presents a new method for improving adhesion between ethylene propylene diene monomer (EPDM) rubber and polyester fabric. In this work, natural rubber was modified by maleic anhydride in order to improve the adhesion force between ethylene propylene diene monomer rubber and polyester fabric. The effect of thermal aging and ionizing radiation on the stability of the rubber mix as well as on the peel strength of the rubber-coated fabric was investigated. It was observed that the natural rubber modified by maleic anhydride improved the peel strength of the EPDM rubber-coated polyester fabric. 1. Introduction Modification of the surface by introducing polar groups such as peroxide functionalities has been a main route to improve adhesion of polyolefins, and the synthesis of block copolymers consisting of a polyolefin-like part and a polar part is another alternative approach to improve the adhesion of polyolefins. The idea of these two methods is to utilize the interaction between the polar groups and the target material to improve adhesion. Based on the same idea, the surface adhesion of substrates can be improved effectively by surface graft copolymerization since the surface graft chains could be designed to have considerable polarity [1, 2]. The modification of rubber is one alternative method to prepare a product that has some improved properties than that of the unmodified rubber. One of the most important rubbers is natural rubber (NR) because of its attractive range of properties which allows it to compete with synthetic rubbers. The NR backbone, cis-1,4-polyisoprene, facilitates certain types of chemical modification to yield a wide range of modified NR. The mechanical properties of the adhesive interface layer are critical in the design and application of adhesive structural components in general engineering applications [3]. Ethylene propylene diene monomer (EPDM) rubber is one of the fastest growing synthetic rubbers on the market today. It can be widely used in many fields due to its saturated hydrocarbon backbone with the presence of double bonds in side chains [4–10]. Several workers have reported that the rubber to polyester fabric adhesion was poor due to reduction in the number of hydrogen bonds or due to a lack of reactive hydrogen in the polyester molecules as well as its hydrophobic nature. For this reason, several attempts were made to improve the ethylene propylene diene monomer (EPDM) rubber/polyester adhesion by the selection of suitable additives in the rubber mix. The adhesion promoter used consists of hexamethylene
Modelling of damage initiation mechanism in rubber sheet composites under the static loading  [PDF]
T. Da Silva Botelho,N. Isac,E. Bayraktar
Journal of Achievements in Materials and Manufacturing Engineering , 2007,
Abstract: Purpose: Modelling – Finite Element Analysis (FEA) of the damage initiation mechanisms in thin rubber sheet composites were carried out under static solicitation at room temperature. Natural rubber vulcanised and reinforced by carbon, NR is used in this study.Design/methodology/approach: Experimental results were compared with that of the Finite Element Analysis (FEA). Damage mechanism has been described with a threshold criterion to identify the tearing resistance, characteristic energy for tearing (T) and damage in the specimens was evaluated just at the beginning of the tearing by assuming large strain. Typical specimen geometry of thin sheet rubber composite materials was considered under static tensile tests conducted on the smooth and notched specimens with variable depths.Findings: This stage of this research, a finite element analysis (FEA) has been applied under the same conditions of this part in order to obtain the agreement between experimental and FEA results. The numerical modelling is a representation of a previous experimental study. The specimen is stretched more than once its initial size, so that large strains occur. A hyper elastic Mooney-Rivlin law and a Griffith criterion are chosen.Practical implications: A tearing criterion was suggested in the case of simple tension conditions by assuming large strain. In the next step of this study, a finite element analysis (FEA) will be applied under the same conditions of this part in order to obtain the agreement between experimental and FEA results.Originality/value: This study proposes a threshold criterion for the damage just at the beginning of the tearing for thin sheet rubber composites and gives a detail discussion for explaining the damage mechanisms. Comparison of FEA results with those of experimental studies gives many facilities for the sake of simplicity in industrial application.
Specific energy absorption capacity of glass-polyester composite tubes under static compressive loading  [PDF]
M. Stamenovi?,S. Puti?,M. Zrili?,Lj. Milovi?
Metalurgija , 2011,
Abstract: The experimental determination of energy of glass-polyester composite tubes static fracture is done. The tubes are of defined structure and known processes of fabrication. The aim was to determine the possibility of their usage as damping elements during impact. Two types of tubular samples with different diameters were tested until fracture under static (low speed) compressive loading. The applied forces and sample lengths were measured until complete destruction of samples. From the diagrams received directly from testing devices, certain energy values explained in the paper were determined.
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