Dynamic Viscoelasticity of Polyester/Rubber Composites under Cyclic Loading

This paper focuses on the influence of dynamic viscoelasticity and surface temperature on the fatigue mechanism and fatigue lifetime of polyester/rubber composites. Rubber composites show significant viscoelasticity during fatigue process. The variations of dynamic elastic modulus, mechanical loss angle, loss energy per cycle exhibit different trend in fatigue initial stage and final stage. Due to high viscoelasticity high heat generation occurs under cyclic loading, which leads to a high surface temperature. It is found that the variation of specimen surface temperature depends strongly on cycling frequency and stress amplitude. SEM (scanning electron microscopy) observation and static residual stiffness studies reveal that the surface temperature affects fracture morphology and fatigue lifetime of rubber composites strongly because of heat aging.

Blast performance of layered charges enveloped by aluminum powder/rubber composites in confined spaces

A layered charge composed of the JH-2 explosive enveloped by a thick-walled cylindrical casing(active aluminum/rubber and inert lithium fluoride/rubber composites) was designed and explosion experiments were conducted in a 1.3 m3tank and a 113 m3bunker.The blast parameters,including the quasistatic pressure(ΔpQS),special impulse(I),and peak overpressure(Δpmax),and images of the explosion process were recorded,and the influence of the Al content(30% and 50%) and Al particle size(1,10,and 50 μm) on the energy release of aluminum/rubber composites were investigated.The results revealed that the use of an active layer increased the peak overpressure generated by the primary blast wave,as well as the quasistatic pressure and special impulse related to fuel burning within tens of milliseconds after detonation.When the Al content was increased from 30% to 50%,the increases of ΔpQS and I were not obvious,and Δpmaxeven decreased,possibly because of decreased combustion efficiency and greater absorption of the blast wave energy for layers with 50% Al.Compared with the pure JH-2charge,the charge with 1 μm Al particles produced the highest Δpmax,indicating that better transient blast performance was generated by smaller Al particles.However,the charge with 10 μm Al particles showed the largest ΔpQSand I,suggesting that a stronger destructive effect occurred over a longer duration for charges that contained moderate 10 μm Al.

Enhancing thermal conductivity of silicone rubber composites by insitu constructing SiC networks:A finite-element study based on first principles calculation

Polymer composites as thermal interface materials have been widely used in modern electronic equipment.In this work,we report a novel method to prepare highly through-plane thermally conductive silicone rubber(SR)composites with vertically aligned silicon carbide fibers(VA-SiCFs)entangled by SiC nanowires(SiCNWs)networks.First,a series of carbon fibers(CFs)skeletons were fabricated in sequence of coating poor thermally conductive polyacrylonitrile-based CFs with polydopamine,icetemplated assembly,and freeze-drying processes.Furthermore,VA-SiCFs networks,i.e.,long-range continuous SiCFs-SiCNWs networks,based on the prepared CFs skeletons,were in-situ obtained via template-assisted chemical vapor deposition method.The thermal conductivity enhancement mechanism of VA-SiCFs networks on its SR composites was also intensively studied by finite element simulation,based on the first principles investigation of SiC,and Foygel’s theory.The in-situ grown VA-SiCFs networks possess high intrinsic thermal conductivity without the thermal interface between fillers,acting as the high-efficiency through-plane long-range continuous thermal conduction path,in which the SiCNWs were the in-plane“thermal spreader”.The VA-SiCFs/SR composites reached a high through-plane thermal conductivity,2.13 W/(m·K),at the filler loading of 15 vol.%,which is 868.2%,and 249.2%higher than that of pure SR sample,and random-CFs@polydopamine(PDA)/SR composites at the same content,respectively.The VA-SiCFs/SR composites also exhibited good electrical insulation performance and excellent dimensional stability,which guaranteed the stable interfacial heat transfer of high-power density electronic devices.

Comparison of nonlinear modeling methods for the composite rubber clamp

The cubic stiffness force model(CSFM)and Bouc-Wen model(BWM)are introduced and compared innovatively.The unknown coefficients of the nonlinear models are identified by the genetic algorithm combined with experiments.By fitting the identified nonlinear coefficients under different excitation amplitudes,the nonlinear vibration responses of the system are predicted.The results show that the accuracy of the BWM is higher than that of the CSFM,especially in the non-resonant region.However,the optimization time of the BWM is longer than that of the CSFM.

Mechanical Test and Meso-Model Numerical Study of Composite Rubber Concrete under Salt-Freezing Cycle

A composite rubber concrete(CRC)was designed by combining waste tire rubber particles with particle sizes of 3~5 mm,1~3 mm and 20 mesh.Taking the rubber content of different particle sizes as the influencing factors,the range and variance analysis of the mechanical and impermeability properties of CRC was carried out by orthogonal test.Through analysis,it is concluded that the optimal proportion of 3~5 mm,1~3 mm,and 20 mesh particle size composite rubber is 1:2.5:5.5 kinds of CRC and 3 kinds of ordinary single-mixed rubber concrete(RC)with a total content of 10%~20%were designed under this ratio,and the salt-freezing cycle test was carried out with a concentration of 5%Na 2 SO4 solution.The physical and mechanical damage laws during 120 salt-freezing cycles are obtained,and the corresponding damage prediction model is established according to the experimental data.The results show that:on the one hand,the composite rubber in CRC produces a more uniform“graded”structure,forms a retractable particle group,and reduces the loss of mechanical properties of CRC.On the other hand,colloidal particles with different particle sizes are used as air entraining agent to improve the pore structure of concrete and introduce evenly dispersed bubbles,which fundamentally improves the durability of concrete.Under the experimental conditions,the CRC performance is the best when the overall content of composite rubber is 15%.

Stability analysis of radial inflation of incompressible compositerubber tubes

The inflation mechanism is examined for a composite cylindrical tube composed of two incompressible rubber materials, and the inner surface of the tube is subjected to a suddenly applied radial pressure. The mathematical model of the problem is formulated, and the corresponding governing equation is reduced to a second-order ordinary differential equation by means of the incompressible condition of the material, the boundary conditions, and the continuity conditions of the radial displacement and the radial stress of the cylindrical tube. Moreover, the first integral of the equation is obtained. The qualitative analyses of static inflation and dynamic inflation of the tube are presented. Particularly, the effects of material parameters, structure parameters, and the radial pressure on radial inflation and nonlinearly periodic oscillation of the tube are discussed by combining numerical examples.

SYNTHESIS OF NATURAL RUBBER-g-MALEIC ANHYDRIDE AND ITS USE AS A COMPATIBILIZER IN NATURAL RUBBER/SHORT NYLON FIBER COMPOSITES

Natural rubber grafted maleic anhydride （NR-g-MAH） was synthesized by mixing maleic anhydride （MAH） and natural rubber （NR） in solid state in a torque rheometer using dicurnyl peroxide （DCP） as initiator. Then the self-prepared NR-g-MAH was used as a compatibilizer in the natural rubber/short nylon fiber composites. Both the fimctionalization of NR with MAH and the reaction between the modified rubber and the nylon fiber were confirmed by Fourier transform infrared spectroscopy （FTIR）. Composites with different nylon short fiber loadings （0, 5, 10, 15 and 20 phr） were compounded on a two-roll mill, and the effects of the NR-g-MAH on the tensile and thermal properties, fiber-rubber interaction, as well as the morphology of the natural rubber/short nylon fiber composites were investigated. At equal fiber loading, the NR-g-MAH compatibilized NR/short nylon fiber composites showed improved tensile properties, especially the tensile modulus at 100% strain which was about 1.5 times that of the corresponding un-compatibilized ones. The equilibrium swelling tests proved that the incorporation of NR-g-MAH increased the interaction between the nylon fibers and the NR matrix. The crosslink density measured with NMR techniques showed that the NR-g-MAH compatiblized composites had lower total crosslink density. The glass transition temperatures of the compatibilized composites were about 1 K higher than that of the corresponding un-compabilized ones. Morphology analysis of the NR/short nylon fiber composites confirmed NR-g-MAH improved interfacial bonding between the NR matrix and the nylon fibers. All these results signified that the NR-g-MAH could act as a good compatilizer of NR/short nylon fiber composites and had a potential for wide use considering its easy to be prepared and compounded with the composites.

Rubber sheet strewn with TiO_2 particles: Photocatalytic activity and recyclability

A new method for the preparation of rubber sheet strewn with titanium dioxide particles （TiO2-strewn sheet） is presented. This simple and low cost method is based on the use of TiO2 powder （Degussa P25） being strewn onto the sheet made from rubber latex （60% HA） through a steel sieve. The characteristic of the TiO2-strewn sheet was studied by using scanning electron microscopy/energy dispersive X-ray spectrometer （SEM/EDS） and X-ray diffractometer （XRD） techniques. The photocatalytic activity of TiO2-strewn rubber sheet was evaluated using Indigo Carmine （IC） dye as a model for organic dye pollutant in water. The results showed that the TiO2-strewn sheet could degrade IC dye solution under UV light irradiation. The effects of pH, initial concentration, and the intensity of UV light on the photodegradation were also investigated. Kinetics of the photocatalytic degradation was of the first-order reaction. The used TiO2-strewn sheet can be recovered and reused. The recycling uses did not require any cleaning between successive uses and no decline in the photodegradation efficiency was observed compared with freshly prepared TiO2-strewn sheet.

A strong and reversible adhesive fibrillar surface based on an advanced composite with high strength and strong adhesion

A material-structure integrated design method is proposed in this paper,with which micropillar and microwedge arrayed surfaces are fabricated based on a novel nanoparticlereinforced silicone rubber composite(NRSRC)with high mechanical strength and strong surface adhesion.It is found that the micropillar-arrayed surface and the microwedgearrayed surface show a normal adhesive strength of 50.9 kPa and a shear adhesive strength of 137.3 kPa,respectively,which are much higher than those of previously reported adhesive surfaces made by pure soft polymers.Furthermore,the micro-wedgearrayed surface shows not only strong and stable adhe-sion on rough and smooth substrates but also an obvious anisotropy in the adhesion property.The latter consequently leads to an easy control of the attachment/detachment switch,which is evidenced by a mechanical gripper with a microwedged surface.Therefore,firmly picking up and easily releasing a heavy glass plate can be realized.All these results demonstrate the apparent advantages of the present compo-sitebased fibrillar surfaces in achieving reliable and reversible adhesion and should have promising applications for manufac-turing advanced adhesive devices,such as mechanical fixtures,portable climbing equipment and space robots.