Damping properties of silicone rubber/polyacrylate sequential interpenetrating networks

Silicone rubber/polyacrylate sequential interpenetrating polymer networks（IPNs） were prepared by silicone rubber sheet dipped into the solution composed of different acrylate monomers and benzoyl peroxides（BPOs） for different time at room temperature and then acrylate polymerized at 80 ℃ for 2 h. The molecular structure and damping properties of sequential IPNs were studied by means of FT-IR and dynamic mechanical analysis（DMA）, respectively. The FT-IR spectrum shows that polyacrylate distributes unevenly along the thickness direction of IPNs, i.e. the concentration of polyacrylate decreases from the midst to the surface of the IPNs. The DMA shows that cold crystallization of silicone in the temperature range from -47 ℃ to -30 ℃ is reduced and loss factor of IPNs is improved after interpenetrating with polyacrylate. This suggestes that IPNs can be used as damping materials.     

Compressive deformation of semi-solid SiC_p/ZA27 composites

1　INTRODUCTIONTheapplicationofcastingSiCp/ZA2 7compositesisgreatlylimitedduetotheinhomogeneousdistribu tionofSiCpandtheporosityexistedinthematrix[1] .However,semi solidformingtechnology (SSF )e mergedintherecentyearscannotonlydecreaseore liminatetheporosityandenhancethecompactnessofthematrix ,butalsoimprovetheuniformdistributionofthereinforcementthroughtheredistributionofthereinforcementfromitsuniquecharacteristicsofmouldfilling[2 ] .Inaddition ,SSFisanearnet shapeform ingtechnology …     

Electrochemical behaviour of polypyrrole/sulfated poly(β-hydroxyether) composites

The electrochemical behaviour of polypyrrole (PPy) doped with a sulfated poly(β-hydroxyether) (S-PHE) has been examined. PPy/S-PHE films are mechanically strong and electroactive in propylene carbonate solution, but electroinactive in aqueous solution. It was demonstrated that PPy/S-PHE could be made electroactive in aqueous media by first performing cyclic voltammetry in propylene carbonate/water mixtures. Contact angle measurements indicated that this pre-treatment procedure results in a significant increase in wettability of PPy/S-PHE films. The ability of pre-treated PPy/S-PHE films to sense other electroactive species in aqueous solution was also demonstrated.     

Synthesis of polypyrrole–SBS composites and the particle size effect on the electrorheological properties of their suspensions

The electrorheological (ER) behavior of polypyrrole (PPy)–SBS composite suspensions was investigated. The PPy–SBS composites were prepared to improve mechanical and electrical properties, and thereby enhance the ER response of their suspensions. Various PPy–SBS composites were synthesized by emulsion polymerization controlling the amount of SBS. The ER response initially decreased and then increased with increasing amount of SBS. The dielectric constant and conductivity of the PPy–SBS composite particles and the dielectric constant of the PPy–SBS composite suspensions were not consistent with the ER behavior, but the particle size did. A power-law dependence, τ = 0.207βd²E^3/2, shows a good fit to the ER behavior of PPy–SBS composite suspensions with various amounts of SBS. The dependence of E^1.5 is consistent with the conduction model and the dependence of d² is consistent with the polarization model, but the dependence of β is not consistent with the either model. A surfactant, Brij^®30, was added to the PPy–SBS composite suspension to reduce the non-linear conduction and thereby enhance the ER response. It was observed that the ER response was enhanced by adding the surfactant.     

Dielectric characteristics and nonlinear properties of ZnO–polypyrrole composites

The nonlinear properties and frequency characteristics of ZnO–polypyrrole composites were investigated at 200 Hz–5 MHz frequency interval with different zinc oxide contents. Samples were prepared using hot press method at 130 °C. Results show an optimum point for breakdown voltage at ZnO content of 70%. Breakdown voltage decreases from 590 to 380 V and after that tends to increase from 450 to 740 V due to the absence of polypyrrole at grain boundaries. No matter how breakdown voltage behaves, nonlinear coefficient increases from 4.2 to 9 by increasing ZnO content because of the increase in acceptor-like states at grain boundaries by increasing ZnO content. The electrical parameters such as dielectric constant, dielectric loss and series resistance of samples show a strong dependence on frequency especially below 1 kHz. These parameters fall off by increasing frequency up to 1 kHz, which is related to charge transportation through the Schottky barrier at grain boundaries. The high dielectric constant of samples below 1kHz is related to the Maxwell–Wagner polarization at grain boundaries. The presence of different anomalies at different frequency intervals is related to interfacial polarization because of different structures of grains and intergranular layer with a huge difference in conductivity.     

Micromechanical modelling of deformation and failure in Ti–6Al–4V/SiC composites

The tensile behaviour and the associated fracture micromechanisms were determined in a Ti–6Al–4V alloy uniaxially reinforced with 35 vol. % Sigma 1140+SiC monofilaments. Damage in the form of fiber fracture was localized in a given section of the composite, and the critical micromechanical parameters which control the composite behavior (namely the matrix elasto-plastic response, the fiber elastic modulus and strength, the interfacial sliding resistance, and the residual stresses originated by the thermal expansion mismatch between matrix and fibers) were determined using various experimental and analytical techniques. They were used as input data to simulate the composite deformation and fracture. The composite stress–strain curve was determined by the self-consistent method. The failure locus was determined by computing the probability of nucleating clusters containing one, two, three or more broken fibers. The analysis was based on the stress concentration introduced by one fiber failure in its neighbours, which was determined from the finite element analyses of a representative volume of the composite containing one fiber break, and included the effects of matrix plasticity, residual stresses, and interfacial sliding. This result was extended to analyze the stress concentration around a cluster of broken fibers by a superposition technique. The average composite strength and the extent of damage were accurately predicted by the model when failure was dictated by the nucleation of a cluster containing two neighbour broken fibers. These results demonstrate the potential of the new model to assess the strength and ductility of fiber-reinforced composites which fail under local load sharing conditions by the unstable propagation of a cluster of broken fibers.     

Effect of plastic deformation on microstructure and hardness of AlSi/A1 gradient composites

The effects of plastic deformation on the evolution of microstructure and micro-hardness were studied on plates made from a cylindrical ingot of AISi/AI aluminum composite. This ingot was produced by double-stream-pouring continuous casting（DSPCC）. The results show that the three layers, i.e. the external pure aluminum, internal AI-Si alloy and the transition gradient layer, are maintained after compression as well as rolling processing. With the decrease in thickness of the gradient composite plate, the fluctuation of micro-hardness in transition layer in the direction normal to the applied force is significantly reduced. A simplified lamination model was used to evaluate qualitatively the micro-hardness distribution in the direction parallel to the applied force. However, the model is invalid in the explanation of the fluctuation of the micro-hardness in the direction normal to the applied force. The micro-hardness distribution variation in this direction is mainly attributed to the deformation of a（Al） matrix incorporated the dissolution and spheroidization of eutectic silicon phase.     

Shape memory effect in Mn-V-C austenitic steels involving deformation reorientation of ɛ-martensite

The shape memory effect with a reversible deformation of 1.6–1.7% in the metastable steels like 20G20S2F with the ?-martensitic original structure is obtained as a result of the shear repeated twinning of ?-martensite during cold deformation and the subsequent ? → γ transformation during heating.     

Neutron diffraction study of the deformation behavior of beryllium–aluminum composites

Neutron diffraction measurements of the mean phase elastic strains during loading were performed on two different beryllium–aluminum composites. The first was Be–47.5Al–2.5Ag produced from hot isostatically pressed powder fabricated by rapid solidification using a centrifugal atomization process; the second was a commercially available Be–38Al extruded powder product. Under rapid solidification, Be–Al undergoes liquid phase separation, resulting in a three-dimensional interpenetrating morphology in which both phases are continuous. Elastic strains in the individual phases were measured as a function of tensile and compressive load at the Los Alamos Neutron Scattering Center using a pulsed neutron source. The deformation behavior was unusual due to the unique composite microstructure and elastic properties of beryllium. Notably, the aluminum developed compressive elastic strains in the direction perpendicular to the compressive loading axis. These strains were compared with predictions from finite element analyses to clarify the stress state in each phase during deformation.     

The ω-phase formation in titanium upon deformation under pressure

The ω-phase formation in titanium of the VT1-00 grade upon deformation under pressure has been investigated by X-ray diffraction analysis and diffraction electron microscopy. The deformation was effected by two methods: shear under a pressure of 6 GPa in Bridgman anvils and high-strain-rate equal-channel angular pressing at a pressure of about 2 GPa. Upon deformation under a pressure of 6 GPa, the ω phase is formed as grains that are isolated or clustered into groups. Upon deformation at a pressure of 2 GPa, this phase arises in the form of nanosized particles that are orientationally related to the α phase. After deformation by shear under pressure using one revolution of the anvils, new grains of the α phase up to 2–3 μm in size have been detected. The grains are nearly free of dislocations and have wavy boundaries. The origin of these grains is tracealle the reverse ω → α phase transformation that takes place upon pressure release and occurs via the “normal” rather than martensitic mechanism, at the expense of migration of the inter-phase boundaries. Upon heating, the reverse ω → α transformation at 100°C does not yet begin, whereas at 220°C the transformation proceeds almost completely. A temperature distribution in the titanium sample upon shear under pressure at a rate of 0.3 rpm has been calculated; according to this distribution, the maximum temperature rise is 12 K.     

Silver–polypyrrole composites: Facile preparation and application in surface-enhanced Raman spectroscopy

A facile method to prepare silver–polypyrrole composite (Ag–PPy) by a modified silver mirror reaction is reported. PPy films pretreated by Al(NO₃)₃ solution were immersed into the silver ammonia with glucose. Silver ammonia ions were reduced to two-dimensional staggered silver nanosheets which immobilized on the surface of polypyrrole. The silver nanosheets with different morphologies and sizes can serve as active-substrates for surface-enhanced Raman spectroscopy (SERS). Using 4-mercaptopyridine (4-Mpy) as probe molecules, the as-prepared composites exhibited excellent surface-enhanced Raman scattering.     

Synthesis of novel hexagonal micro-sheet polypyrrole and micro-sheet polypyrrole with grooves in the presence of α-cyclodextrin/Acid Red G inclusion compounds

Novel hexagonal micro-sheet polypyrrole (PPy) was synthesized via the self-assembly method in the aqueous solution containing α-cyclodextrin (α-CD)/5-acetamido-4-hydroxyl-3-(phenyliazenyl) naphthalene-2,7-disulfonic acid (Acid Red G) inclusion compounds (α-CD/ARG ICs) and ferrous cations. And micro-sheet polypyrrole with grooves was obtained by dipping the micro-sheet PPy into alkaline solution for 12 h. The existence of α-CD/ARG ICs in aqueous solution was testified by UV–vis spectra. Scanning electron microscopy (SEM) images revealed that the micro-sheet PPy was over 10 μm in average length, 0.6–10 μm in broadbrim and 100–200 nm in thickness. The conductivities of the micro-sheet PPy were in the range from 2.78 to 12.50 S cm^?1 and the conductivities of the micro-sheet PPy with grooves were in the range from 3.70 to 7.69 S cm^?1. Cyclic voltammograms (CVs) were measured to examine the electrochemical behaviors of the prepared PPy, and the oxidation peak of micro-sheet PPy was increased to 1.34 V which was higher than those of other PPy samples. The experimental conditions were also optimized, and the optimization of experimental conditions was the quantities of pyrrole monomers, α-cyclodextrin and Acid Red G were 20, 4 and 4 mmol, respectively, and the perfect micro-sheet PPy was synthesized at 5 °C and no-stirring for over 12 h. It was found that the complex aggregations of α-CD/ARG ICs and ferrous cations might have the function as a “template” during the polymerization of pyrrole monomers, but this “template” was broken off from the prepared micro-sheet PPy in the alkaline condition.     

Hot deformation behavior and microstructure evolution of TiC–Al_2O_3/Al composites

Hot compression behavior of TiC–Al2O3/Al composites was studied using the Gleeble-1500 system at a temperature range of 300–550 °C and at strain rate range of 0.01–10.00 s-1. The associated structural changes were studied by TEM observations. The results show that stress level decreases with deformation temperature increasing and strain rate decreasing, which can be represented by a Zener–Hollomon parameter in an exponent-type equation with hot deformation activation energy Q of 172.56 kJ·mol-1.Dynamic recovery occurs easily when strain rates are less than 10.00 s-1. Dynamic recrystallization can occur at strain rate of 10.00 s-1.     

Synthesis of micromulti-prisms polypyrrole boxes in the presence of α-cyclodextrin

Polypyrrole (PPy) boxes with micromulti-prisms have been synthesized in aqueous solution via a self-assembled method using α-cyclodextrin (α-CD) as a dopant and FeCl₃ as an oxidant. The morphology and the micro-structure of the as-synthesized PPy boxes were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), and Fourier-transform infrared (FTIR) spectrum. The formation mechanism of the PPy boxes structure was also discussed. And the congregated structure of dissociative pyrrole monomers with the inclusion complexes (between α-CD and pyrrole monomer) was proposed to play a significant role in forming the multi-prisms sectional PPy-CD boxes.     

TiC/AZ91D composites fabricated by in situ reactive infiltration process and its tensile deformation

1 Introduction Relative to aluminum matrix composites, magnesium-matrix composites are receiving interests increasingly in recent years due to their low densities and high specific properties. They are potentially attractive for the applications in aeros…     

Mechanism of localized severe plastic deformation and damage fracture in fine-blanking using mixed displacement and pressure FEM

1 Introduction Strain localization always appears in the form of plastic shear band during the large plastic deformation of metallic material. For most of metal forming processes, the appearance of plastic shear band will cause non-homogeneous deformation…     

Control of deflection deformation of plate-shape castings in solidification

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