Abstract: A new micromechanical method, the weighted residual self-consistent method (WRSCM) is developed to study the effective thermal conductivity of two-phase composites with different particle geometries in the presence of a thermal barrier resistance at the interface between constituents. The imperfect interface involves the continuity of the normal flux but allow for a finite temperature differences across the interface. Within the framework of self-consistent scheme, the effective thermal conductivity of two-phase composite is obtained using numerical iterative method on the basis of a surface integral of temperature over the imperfect interfaces. Numerical results show that for the given composite system, due to the existence of an interfacial thermal resistance, the particle geometries have significant impact on the effective thermal conductivity of composites.
Abstract: NiFe2O4, ZnFe2O4 and Ni0.64Zn0.36Fe2O4 were prepared by a chemical co-precipitation method. The positive ferrite ZnFe2O4 usually exhibits antiferromagnetism. The magnetization of Ni0.64Zn0.36Fe2O4 is much larger than that of NiFe2O4, which can be explained by doping with nonmagnetic cations or cations with weak magnetization in an inverse spinal ferrite if these cations occupy A sites, the magnetic moment of Fe3+ ions at the B sites would be oriented in the same direction. Experimental values found for the molecular magnetic moments of NiFe2O4 and Ni0.64Zn0.36Fe2O4 were lower than their theoretic values because surface structure defects resulted in a magnetic spin glass structure.
Abstract: Contact problem, which exists widely in mechanical engineering, civil engineering, manufacturing engineering, etc., is an extremely complicated nonlinear problem. It is usually solved by the finite element method. Unlike with the traditional finite element method, it is necessary to set up contact elements for the contact analysis. In the different types of contact elements, the Goodman joint elements, which cover the surface of contacted bodies with zero thickness, are widely used. However, there are some debates on the characteristics of the attached elements of the Goodman joint elements. For that this paper studies the type, matching, and meshing of the attached elements. The results from this paper would be helpful for the finite element contact analysis.
Abstract: The thermal behaviour of polymer dispersed liquid crystals (PDLC), blends of poly(ethylene-co-methylacrylic acid) (PEMA) with 4-(n-hydroxypropoylxy)-4'-cyanobiphenyl (H3CB) prepared by solvent-induced phase separation (SIPS) method, has been characterized using differential scanning calorimetry (DSC) and polarized light microscopy (POM). Study shows that the concentration of the mixture of PEMA/ H3CB must be least 30%, which will exhibit nematic to isotropic transition phase during heating or cooling. Above 30 wt % 3CB the mixtures exhibited nematic phase, and this was detected as a splitting of the nematic-isotropic peak in the DSC thermograms. The clearing temperature of the PEMA/H3CB mixtures was higher than that of pure H3CB’s, the average increasing being 14°C, which is the evident that the polymer matrix could stable the nematic phase. This behaviour is in contrast with other reports about polymer-dispersed liquid crystals. In addition, thermal decomposition was also studied by thermogravimetry in nitrogen environments. A double-stage decomposition process was found in nitrogen atmosphere, and this was mainly due to H3CB for the first step and the PEMA decomposition for the second step.
Abstract: Polyphosphric acid (PPA) modified asphalt binders were produced in the laboratory using one base asphalt and four levels of PPA contents (0.6%, 1.0%, 1.5% and 2.0% by weight of base asphalt). Penetration test, softening point test, rotation viscosity test, creep test with bending beam rheometer (BBR) and four components test were carried out to study the performance of PPA modified asphalt binders and possible modification mechanism. The results indicate that the high-temperature performance of PPA modified asphalt binders are obviously improved and temperature susceptibility are decreased, but the low-temperature performance slightly decline compared with base asphalt. The PPA content has a very significant effect on softening point whereas it has no significant influence on low-temperature performance according to variance analysis (ANOVA). Finally, four components test reveals that the primary modification mechanism of PPA is the change of chemical composition of asphalt binder.
Abstract: Limestone powder is a readily available and inexpensive material. As an admixture, limestone powder partially replacing fly ash or slag which gets serious to supply today has great significance in the aspects of solving raw materials of concrete, reducing project cost and environment protection. Effects of complex adding of ultra-fine limestone powder and fly ash on the workability and strength of concrete are studied in this paper. Experimental results show that: The fluidity of fresh concrete increases with the ratio of ultra-fine LP to fly ash increasing. The slump loss decreases with the ratio of ultra-fine LP to fly ash increasing. When the ratio of LP to fly ash increases from 5:5 to 9:1, the W/B decreases slightly and the slump of concrete almost is in the region of 210-230mm, the compressive strength of concrete remain basically unchanged. The concrete can produce lots of air bubble when the ratio of ultra-fine LP to fly ash exceeds 8:2 .When the proportion of admixtures of ultra LP and fly ash exceeds 50%, the 28 days compressive strength decreases obviously.
Abstract: The fracture splitting method is being increasingly used for manufacturing connecting rods that are made of the powder forging material, high-carbon steel, etc., which are comparatively easy to fracture, in order to improve the accuracy and productivity. In this paper, a microalloyed high carbon steel used for fracture splitting connecting rod is developed by the process “EAF-EBT-LF-CC-CR”. The steel microstructure, nonmetallic inclusions, precipitated phases, mechanical property and fracture surfaces are investigated by microscope, SEM and TEM. The results show that the steel is constituted of pearlite and a small mount of ferrite, the nonmetallic inclusions in the steel include MnS, Al-rich (taken to be Al2O3) and Al-Ca-rich (taken to be CaO-Al2O3) particles. The precipitations mainly are VC, VN, (Mn, Cu)S, etc. these precipitations are beneficial to fine the pearlite group, short lamellar spacing of pearlite and improve the strengthening of the microalloyed high carbon steel. The tensile tests indicate that the microalloyed high carbon steel has high yield strength, ultimate tensile strength (UTS), but low elongation and contraction of area. It is required for heavier loads, higher performance of automobile engine and less distortion on fracture splitting. The fracture surface of connecting rod shows distinct brittle fracture character and it is beneficial to improve fracture splitting performance.
Abstract: Nano Metal/C (Metal=Fe, Co) composite materials, in which nano iron and cobalt particles were uniformly distributed in carbon matrix, was prepared by pyrolysis of M-exchanged cation exchange resin(M-PAA). X-ray diffraction (XRD), Transmission Electron Microscope (TEM) results showed the particle size and morphology of nano iron and cobalt in M/C could be controlled by pyrolytic temperature. The particle size of Co and Fe in M/C obtained at 500 was respectively 15-40 nm and 10-35 nm. DTA was employed to test the thermal decomposition of ammonium perchlorate (AP) in the M/C and AP mixture. Results indicated the decomposition temperature at high-temperature decomposition of AP was lowered with the addition of amount of M/C-500, and the high temperature decomposition peaks of AP respectively lowered as much as 145.2°Cand 68.3°C with adding amount of 5% of Co/C and Fe/C obtained at 500 . The high and low temperature decomposition peaks of AP overlapped with addition of Co/C.
Abstract: This paper researched the fabrication of perovskite (CaTiO3) synroc by self-propagating high temperature synthesis (SHS) and the characterization of the products. This synthesis process is simpler, the fabricated synroc can immobilize waste loading up to wt( 35%) SrO with satisfied physical properties (density>4.2 g•cm-3, open porosity<0.2%). The microstructure analyses by XRD and SEM/EDS show that the major phase is perovskite which well agrees with the design. It proves that SHS offer a suitable Sr-waste synroc which is favorable for geological disposal.
Abstract: The cold roll B-added Ti-IF steel is annealed for different times at 810 oC. The microstructure development is studied by Optical Microscope（OM） and the concentration of boron and phosphorus segregation at grain boundary is measured by Auger electron spectroscopy（AES）. The result shows that the grain of the cold- rolled sample is elongated along the rolling direction and the elongated grains become into equi-axis shape after annealing 60 to 180sec. Boron and phosphorus segregated at gain boundaries. But boron’s concentration at grain boundary is higher than that of phosphorus and increase from 5at.% or so to about 10at% after annealing 150sec, Then boron’s concentration decrease slowly to 8at.% at 240sec. While phosphorus’s concentration increase to the max of 2.5at.% or so at 120sec, then its concentration decrease to 1at.% or so after annealing 240sec.