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This paper presents an analysis of the hybrid reinforcement of polyoxymethylene composites. Basalt fibers and monocrystalline silicon carbide fibers were used as reinforcement. Basic tests of mechanical properties were carried out, such as the static tensile and flexural test. The tests were repeated under external factors, such as the influence of water aging and a wide range of exploitation temperatures. The materials were also subjected to tribological tests, that is, determination of the friction coefficient and the specific wear rate. Strength tests revealed an increase in the stiffness of the material as well as a reduction the friction coefficient and abrasive wear. The addition of monocrystalline fibers significantly limited water absorption, stabilized the strength properties in the water environment as well as provided better material's resistance to dynamic impact. KEYWORDS basalt fiber, composites, polyoxymethylene, silicon carbide whisker, 1 | INTRODUCTION Polymeric materials, that is, plastics, appeared as a result of research work carried out at the beginning of the 20th century, and in the mid 20s the [...]

A novel silicon carbide (SiC)-strengthened magnetorheological elastomers (MREs) was developed to enhance its viscoelastic performance. The influences of the size and weight content of the SiC particles on the viscoelastic performance of the MREs were systematically studied. The shear storage modulus, damping property, and magnetorheological effects were analyzed to evaluate their dynamic properties. Under optimum condition, the initial storage modulus (Go) of the MRE-0.06-SiC-3 (SiC weight content 3.2 wt%, mean diameter 0.06 pm) is about 2.16 times larger than the MRE-0.06-SiC-0 (nondoped MRE), whereas the magnetorheological effect was almost kept constant. In addition, the damping properties of the as-prepared MREs which were obtained from the intrinsic damping, the magnetomechanical hysteresis, and the interface damping were also analyzed. These results provided a meaningful method for developing MREs with controllable storage modulus and damping capacity. POLYM. ENG. SCI., 53:2615-2623, 2013. © 2013 Society of Plastics Engineers, INTRODUCTION Magnetorheological (MR) materials have attracted a wide variety of attention because of their controllable and reversible mechanical properties under applying the external magnetic field (1-4). Magnetorheological elastomer (MRE), which [...]

This paper reports the mechanical properties and fracture behavior of silicon carbide (3C-SiC) thin films grown on silicon substrates. Using bulge testing combined with a refined load-deflection model of long rectangular membranes, which takes into account the bending stiffness and prestress of the membrane material, the Young's modulus, prestress, and fracture strength for the 3C-SiC thin films with thicknesses of 0.40 and 1.42 [micro]m were extracted. The stress distribution in the membranes under a load was calculated analytically. The prestresses for the two films were 322 [+ or -] 47 and 201 [+ or -] 34 MPa, respectively. The thinner 3C-SiC film with a strong (111) orientation has a plane-gstrain moduli of 415 [+ or -] 61 GPa, whereas the thicker film with a mixture of both (111) and (110) orientations exhibited a plane-strain moduli of 329 [+ or -] 49 GPa. The corresponding fracture strengths for the two kinds of SiC films were 6.49 [+ or -] 0.88 and 3.16 [+ or -] 0.38 GPa, respectively. The reference stresses were computed by integrating the local stress of the membrane at the fracture over edge, surface, and volume of the specimens and were fitted with Weibull distribution function. For the 0.40-[micro]m-thick membranes, the surface integration has a better agreement between the data and the model, implying that the surface flaws are the dominant fracture origin. For the 1.42-[micro]m-thick membranes, the surface integration presented only a slightly better fitting quality than the other two, and therefore, it is difficult to rule out unambiguously the effects of the volume and edge flaws. [2007-0191] Index Terms--Bulge test, fracture property, microelectromechanical systems (MEMS), silicon carbide (SIC) thin films, Weibull distribution function.

Three shapes of silicon carbide tensile specimens were tested--curved with a low stress-concentration factor and straight with a circular hole or an elliptical hole. The nominal thickness was 125 [micro]m with a net section that is 100-[micro]m wide; the overall length of these microspecimens was 3.1 mm. They were fabricated by an improved version of deep reactive ion etching, which produced specimens with smooth sidewalls and cross sections having a slightly trapezoidal shape that was exaggerated inside the holes. The novel test setup used a vertical load train extending into a resistance furnace. The specimens had wedge-shaped ends which fit into ceramic grips. The fixed grip was mounted on a ceramic post, and the movable grip was connected to a load cell and actuator outside the furnace with a ceramic-encased nichrome wire. The same arrangement was used for tests at 24[degrees]C and at 1000[degrees]C. The strengths of the curved specimens for two batches of material (made with slightly different processes) were 0.66 [+ or -] 0.12 and 0.45 [+ or -] 0.20 GPa, respectively, at 24[degrees]C with identical values at 1000[degrees]C. The fracture strengths of the circular-hole and elliptical-hole specimens (computed from the stress-concentration factors and measured loads at failure) were approximately 1.2 GPa with slight decreases at the higher temperature. Fractographic examinations showed failures initiating on the surface--primarily at corners. Weibull predictions of fracture strengths for the hole specimens based on the properties of the curved specimens were reasonably effective for the circular holes but not for the elliptical holes. [2007-0057] Index Terms--Ceramics, material testing, silicon carbide (SIC), temperature.

The main scattering mechanisms limiting mobility in SiC MOSFETs were examined with the help of Hall-effect mechanisms of n-channel MOS devices. Findings reveal that surface-roughness scattering and Coulomb scattering were the main scattering mechanisms limiting electron mobility found in SiC MOSFETs at room temperature.

The strain relief and dislocation motion in III-nitride films that are grown on step-free 4H-SiC mesas are studied. The results show that the nucleation of threading dislocations in the absence of interfacial steps is an extremely difficult process, which proves that the strain relief for such III-nitride films is not dominated by the greater excess stress driving dislocation tilt.

A model, which is developed for heterogeneous materials that undergo dynamically driven phase transformations in its constituents, is extended to comprise the evolution of damage. The complex interplay between loading states, viscoplasticity, damage, and solid-solid phase transformations is analyzed at both the micromechanics and macromechanics levels

A model that allows composites containing constituents that undergo phase transitions when they are dynamically loaded is developed. The effect of local microstructure on the macroscopic stress-strain and thermodynamic response of the SiC-Ti composite is investigated for different orientations of loads relative to the fiber axes.

The mechanical properties of the SiCp/Al and AA6061 degraded by neutral 3.5% NaCl solution at room temperature (23 degree Celsius) and high temperature (100 degree Celsius) are investigated. Fracture surface and surface of the samples before and after immersion corrosion test are examined by an optical and scanning electron microscopes.

Scanning tunneling microscopy (STM) was used to study adsorption of molecular oxygen on 6H-SiC (0001)-3*3 surface. The interaction of atomic O beam with the 3*3 surface results in the formation of silicon oxide nanoclusters.

The phase stability of two MAX phases, [V.sub.3]Si[C.sub.2] and [V.sub.2]SiC is investigated, by means of first-principles total-energy calculation within the generalized-gradient approximation and the projector-augmented wave method. It is suggested that the two MAX compounds should be possible to synthesize as stable (or metastable) phases.

Byline: A.R. DeArellano-Lopez, A. Dominguez-Rodriguez, K.C. Goretta, J.L. Routbort High-temperature constant load and constant strain rate compressive tests have been performed on Al.SUB.2O.SUB.3 reinforced with different concentrations of SIC whiskers. The samples were obtained from three sources, but contained whiskers from the same source. The temperature range was from 1300 to 1500[degrees]C and experiments were conducted in air and argon. Strain rates varied from 3x10.SUP.−8 to 5x10.SUP.−5 s.SUP.−1 with stresses between 3 and 500 MPa. Stress exponents were found to vary between 1 and 5 and depended on microstructure, whisker concentration and stress, indicating a change in the mechanism controlling plastic deformation. Change from diffusional creep to a damage accumulation mechanism was supported by TEM observations on samples as-received and deformed both in the n=l regime and in the n=5 regime. Degradation of Sic whiskers occurred when testing in air.

A molecular dynamics (MDs) simulation and micromechanics bridging method are used for examining the thermoelastic properties of SiC/epoxy nanocomposites. A micromechanics-based scale bridging method is described that has handled both the elastic and residual fields of the nanocomposites with the help of the effective interface concept and sequential information transfer.

The dominant recombination processes controlling the carrier lifetime in n-type 4H-SiC epitaxial layers grown with low concentrations of the [Z.sub.1/2] defect are examined by analyzing the variation in the carrier lifetime with temperature. The studies have shown that further enhancement of the total lifetime under the high injection conditions of a device structure has required very thick epilayers, effectively passivated surface and interface recombination and a further reduction in the remaining [Z.sub.1/2] concentrations.

Several studies are conducted to explain the impact of the forward current stress on the low frequency noise exhibited by the different 4H-SiC p-n junctions. The stress is shown to lead to the onset of the burst noise in these junctions.

The high-resolution x-ray diffraction technique is employed to study the various strain and crystal defects observed in the thin AlN/GaN structures grown on (0001) SiC. The different growth rates of the metalorganic chemical vapor deposition are shown to be the main determinant of the differences observed in the strain levels and defect populations of the two heterostuctures.

Byline: Yi-Qiang He, Bin Qiao, Jian-Ming Yang, Na Wang, Zhen-Hua Chen, Liang Hao Processes of rolling after extruding and rolling after hot-pressing of multi-layer spray deposited Al-8.5Fe-1.3V-1.7Si/SiCP, and the effect of the two different processes on the microstructure and mechanical properties of the composite were investigated. The microstructure of the composite prepared by different processes was observed by OM, SEM and TEM. The results showed that more uniform microstructure and more excellent mechanical properties of the composites were obtained by rolling after hot-pressing than rolling after extruding. The excellent mechanical properties can be attributed to avoiding of SiC particles lamination which is familiar to the composite as-extruded by hot-pressing, stable microstructure, and good bonding between SiC particles and the matrix.

A newly developed model for anisotropic ceramic crystals undergoing potentially large deformations that could occur under significant pressures or high temperatures and study silicon carbide (SiC) with a focus on [alpha]-SiC. The results revealed that electric current generated in shock-loaded [alpha]-SiC crystals of certain orientations could affect the dislocation mobility and hence the yield strength at high pressure.

A multiscale modeling of the degradation of the thermal conductivity of polycrystalline silicon carbide due to the thermal (Kapitza) resistances of grain boundaries is described. The available experimental values of the thermal conductivity of polycrystalline SiC has shown that the present Kapitza resistances cannot be directly used for predicting the thermal conductivity of polycrystalline silicon carbide.

Atomic-scale simulations of tensile testing are performed on a series of silicon carbide (SiC) with varying chemical disorder in order to examine the changes in mechanical properties due to the accumulation of irradiation damage. The variations of the mechanical properties as a function of chemical disorder are correlated with the crossover from homogenous elastic deformation to localized plastic flow percolating through the system.

The formation of subwavelength periodic strained layers associated with nanovoids in the cross section of femtosecond laser-irradiated lines written inside 4H-SiC single crystals is described. The conventional and high-voltage transmission electron microscopies are carried out for microstructural analyses and the cross section of the irradiated lines have four to six groups of fine periodic structures.

The effects of Si doping on the evolution of stress in [Al.sub.x][Ga.sub.1-x]N:Si thin films grown on 6H-SiC by metal organic chemical vapor deposition are examined by using in situ water curvature measurements. The model describing tensile stress generated by dislocation effective climb is modified for accounting for the dislocation reduction and has produced an improved fit to the experimental stress-thickness data.

X-ray diffraction analysis and numerical simulation were used to understand structural properties of each (100), (110), and (111) Si substrate orientation for the heteroepitaxially grown 3C-SiC films. The observations from atomic force microscopy analysis and radius of curvature measurements showed that the 3C-SiC surface morphology and average residual stress depended strongly on the silicon substrate orientation.

The structural, mechanical and dimensional evolutions of silicon carbide (SiC) induced by heavy-ion irradiations are analyzed by using Rutherford backscattering spectrometry and channeling (RBS/C), nanoindentation and surface profilometry measurements. The studies have shown that the modifications of the macroscopic properties are because of the amorphization of the material.

Thermal conductivity and mechanical effects of silicon carbide nanoparticles uniformly dispersed in water are examined. The enhancements in thermal conductivities for the nanofluids with varying nanoparticles loadings are maintained at test temperatures and the results of thermal conductivity are rationalized based on the theories of heat transfer in fluids.

A three-dimensional numerical finite element modeling method is used for comparing interfacial residual thermal stress distribution in AlN single crystals grown by using different substrates such as silicon carbide, boron nitride, tungsten, tantalum carbide, and niobium carbide. The AlN film has curved upward or in a concave shape when SiC, BN and W substrates are used as the stress concentration at the edges of the AlN film is tensile at the interface and has caused detachment of the film from the substrate.

The experimental results for wurtzite epitaxial GaN layers grown on sapphire and SiC substrates with different values of the residual strain is presented. The results obtained provide insight into the high dislocation density which enhanced the spin relaxation rate through the Elliott-Yafet mechanism and the influence of the valence-band structure on the hole-spin relaxation.

Molecular dynamics simulations with Tersoff potentials are used for studying the response of single crystalline SiC nanotubes under tensile, compressive, torsional, combined tension-torsional and combined compressed-torsional strains. The results have shown that the nanotubes deform through bond-stretching and breaking and have displayed brittle properties under uniaxial tensile strain, except for the thinnest nanotube at high temperatures, which has failed in a ductile manner.

The density functional theory is used to explore the correlation between hardness and shear mode cracking and study the controlling parameters of hardness in brittle materials. The results showed that both the unstable stacking energies and the surface energies have a monotonic relationship with the hardness in Ge, Si, 3C-SiC, cBN, and diamond.

The development of a fundamental energy-based mechanics method for the study of intrinsic surface effects of nanowires is reported. The method could be used to derive the excess force, energy, and elastic constants of surface and edges of [111] [beta]-SiC nanowires at freestanding and uniaxial deformation states.

A comparative electron spin resonance is used for studying (100)Si/Si[O.sub.2] entities, which are grown by thermal oxidation of biaxial tensile strained (100)Si (sSi) layers. The reduction of detrimental-interface defects is one of the reasons for the mobility enhancement in sSi/Si[O.sub.2] based metal-oxide-semiconductor structures over standard Si/Si[O.sub.2] ones.

Dry oxidations are used for characterizing the pressure dependence of the growth kinetics of Si[O.sub.2] along three orientations of the 4H-SiC polytype. The studies have shown that the density of interface states on the (0001) Si-face is not reduced by faster oxide growth rates within the monitored energy window.

The white x-ray section topography with a long sample-to-film distance is used for the direct determination of the Burgers vector senses and magnitudes of elementary dislocations in a high-quality silicon carbide single crystal. The studies have shown very weak but extraordinarily long-range elastic interactions between elementary screw dislocations, which have governed dislocation-propagation behavior and the distribution of dislocations.

Studies of basal plane dislocations (BPDs) defect morphology provides insight into the presence of shear stresses in SiC homoepitaxy of typical power device structures.

The effects of sulfur contamination on a Pt-gate silicon carbide based field-effect gas sensor are examined under ultrahigh vacuum conditions. Oxygen is shown to be effective at removing the sulfur and the rate of sulfur oxidation is suppressed at high sulfur coverages, but not as strongly as on low-index single-crystal surfaces.

The various effects of the differences in the polytypes and stability energies of the silicon carbide (SiC) nanoclusters on their energy gaps are explained. The analysis reveals that an identical-size energy-gap dependence can be achieved for very small clusters.

The correlation between atomic structure and the load-displacement (P-h) curve of nanoindentation of amorphous a-SiC is demonstrated by using molecular dynamics simulations. The nanoindentation damage is observed to be less localized in a-SiC compared to 3C-SiC.

An effective interatomic interaction potential is proposed for molecular dynamics simulations of SiC and it is used for studying the structural, elastic and dynamical properties of crystalline (3C), amorphous and liquid states of SiC. The elastic constants are predicted as a function of density for the crystalline and amorphous phases.

The effect of crystallographic orientation and ion fluence on the shape of damage distributions induced by 500 keV [N.sup.+] implantation into 6H-SiC is examined. The damage buildup mechanism is interpreted with the direct-impact, defect-stimulated amorphization model in order to explain the damage formation and the composition of structural disorder versus the ion fluence and the implantation tilt angle.

The growth mechanism of bamboo-shaped SiC nanotubes (SiCNTs) and elliptically hollow SiC nanospheres in addition to the normal SiCNTs under hydrothermal conditions are described. The formation of the various forms of SiCNTs like other nanotubular structures has showed intrinsic structural versatilities.

The shock response of a silicon carbide is investigated using the methods of plate impact, and monitored using manganin stress gauges mounted to be responsive to lateral stress. A two-step stress response is observed, indicating the presence of delayed failure at the impact face.