Volume fraction

About: Volume fraction is a research topic. Over the lifetime, 16312 publications have been published within this topic receiving 374181 citations.

Newtonian Viscosity of Amorphous Silicon Carbonitride at High Temperature

Abstract: The creep viscosity of chemical-precursor-derived silicon carbonitride (SiCN), which is known to remain predominantly amorphous at temperatures below 1400°C, was measured in the temperature range 1090-1280°C. Experiments were done in uniaxial compression at constant loads in pure nitrogen atmosphere. The creep behavior exhibited three stages. In stage I the strain rate decreased rapidly with time and deformation was accompanied by densification. In stage II the samples exhibited a steady-state creep rate. In stage III, which commenced after long-term deformation, creep gradually declined to rates that were below the sensitivity of our apparatus. The relative density of the specimens during stage II and stage III remained constant at ≅2.3 g/cm3. The shear viscosity in stage II was nearly Newtonian and was measured to be 1.3 × 1013-5.0 1013 Pa·s at 1280°C, which is approximately 103 times the value for fused silica. The creep-hardened as well as uncrept specimens contained silicon nitride crystallites. The volume fraction of these crystals was variable but always less than 5%. Such a small volume fraction of crystals does not explain the dramatic creep-hardening behavior in stage III, even if it is assumed that the crystals formed during creep deformation in stage II.

Uncertainty quantification for multiscale modeling of polymer nanocomposites with correlated parameters

Abstract: We propose a stochastic multiscale method to quantify the correlated key-input parameters influencing the mechanical properties of polymer nanocomposites (PNCs). The variations of parameters at nano-, micro-, meso- and macro-scales are connected by a hierarchical multiscale approach. The first-order and total-effect sensitivity indices are determined first. The input parameters include the single-walled carbon nanotube (SWNT) length, the SWNT waviness, the agglomeration and volume fraction of SWNTs. Stochastic methods consistently predict that the key parameters for the Young’s modulus of the composite are the volume fraction followed by the averaged longitudinal modulus of equivalent fiber (EF), the SWNT length, and the averaged transverse modulus of the EF, respectively. The averaged longitudinal modulus of the EF is estimated to be the most important parameter with respect to the Poisson’s ratio followed by the volume fraction, the SWNT length, and the averaged transverse modulus of the EF, respectively. On the other hand, the agglomeration parameters have insignificant effect on both Young’s modulus and Poisson’s ratio compared to other parameters. The sensitivity analysis (SA) also reveals the correlation between the input parameters and its effect on the mechanical properties.

Surface nanocrystallization induced by shot peening and its effect on corrosion resistance of 1Cr18Ni9Ti stainless steel

Abstract: The nanocrystalline microstructure in the surface of 1Cr18Ni9Ti stainless steel induced by high-energy shot peening has been characterized by means of X-ray diffractometry and transmission electron microscopy. The effects of shot peening on corrosion resistance of the steel have been investigated by polarization curves and pit corrosion tests, and the surface morphologies of the corrosion samples have been characterized by scanning electron microscopy. The results show that shot peening can cause surface nanocrystallization; that is, a nanocrystalline microstructure with an average grain size of ∼ 18 nm forms in the surface layer of the sample, and furthermore, can induce α-martensite of about 15% in volume fraction. With increasing depth from the shot-peened surface, the grain size increases, but the volume fraction of the α-martensite decreases. The surface nanocrystallization can improve the potentiodynamic polarization behavior of 1Cr18Ni9Ti stainless steel in 3.5% NaCl solution. Comparing to the as-received coarse crystalline counterpart, the passive film on the surface of the shot-peened sample is easier to form and more stable. Shot-peening-induced surface nanocrystallization can markedly enhance the corrosion resistance of 1Cr18Ni9Ti stainless steel in the chlorine–ion-contained solution.

Effect of composition on coupled electric, magnetic, and dielectric properties of two phase particulate magnetoelectric composite

Abstract: The particulate composite materials of ferrite-ferroelectric ceramics viz. nickel-cobalt-copper ferrite (i.e., Ni0.94Co0.01Cu0.05Fe2O4) and barium titanate were synthesized by the double sintering ceramic technique. The presence of constituent phases in the composites was confirmed by x-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The electrical properties such as dc resistivity and thermo-emf were measured as a function of temperature and volume fraction of constituent phases. The ac conductivity was calculated from dielectric data in the frequency range from 100Hzto1MHz. It is concluded that the conduction in the present composites is due to small polarons. The relative dielectric constant measured as a function of applied frequency varies with the variation in the dc resistivity and molar fraction of constituent phases. It shows dispersion in the lower frequency range. The hysteresis behavior was studied to understand the magnetic properties su...