Advanced Materials Research Vols. 152-153

Abstract: A type of quasi-isotropic carbon/epoxy composites was prepared. In order to study the dynamic mechanical properties of composites, the compressive specimens were investigated in the normal direction, as well as in the in-plane direction at different strain rates by Hopkinson pressure bar (SHPB) technique. The macro- and micro-fracture morphology of the damaged specimens was obtained utilizing the scanning electron microscope (SEM). The experimental results showed that the dynamic stress-strain behaviour can be significantly affected by the strain rates. As the strain rates increased, the maximum strength and maximum modulus increased, the ultimate strain reduced. The compressive strength and the ultimate strain in the in-plane direction are obviously lower than that in the normal direction. The main way of the dynamic compressive failures in the normal direction is shear failure due to the brittle fracture of the fibre. Interfacial crack and delamination can be produced in the in-plane direction.

Abstract: In this article, the effects of different content and compound ratio of low-grade fly ash and limestone powder on the strength, water requirement and adaptability with admixture of green complex binder were studied, and the influence of particle size distribution and particle morphology on its performance was analyzed. The results indicated that the strength decreased obviously with the increase of mineral content. There was an optimum ratio of fly ash and limestone powder (6:4) at a certain mineral content. Water requirement decreased, and the saturated content of admixture points became small with the increasing of limestone powder. The effects of content on the strength were much more than that of particle size distribution for composite cement with high volume of mineral admixtures.

Abstract: The combined admixture of limestone powder and substandard fly ash for the preparation of C40 machine-made sand concrete were studied. The results show that the C40 machine-made sand concrete prepared with the combined admixture of limestone powder and substandard fly ash has very good workability, with a 60min slump loss of less than 15mm. The combined admixture of limestone powder and substandard fly ash has very good filling effect and crystal nucleus effect, which makes hardened cement paste structure and interface structure more compact. The chloride ion permeability coefficient of machine-made sand concrete at 28d are less than 182×10-14m2/s, showing that the C40 machine-made sand concrete has good resistance to chloride ion permeation. It can be seen from SEM and energy spectrum technique that the structure of machine-made sand concrete is compact, and the C-S-H gel in the concrete has low calcium-silicate ratio.

Abstract: Meso topography is used to examine the damage degree of lead-free Sn-Zn solder. Real-time meso topography is observed using scanning electronic microscope(SEM), which is assembled in a loading machine. The solder’s deformation and fracture is simulated using a damage accumulation process. The observed meso-structure evolutionary processes of the solder material is then analyzed according to the macro-meso combined mechanism. Some image processing technique are used. A new model of fracture mechanism and degree of damage is proposed.. that We show that the proposed meso structure evolution equations can accurately model the degree of material damage.

Abstract: A new kind of die steel, WD1 used for warm work dies, was developed. The behavior of carbide dissolution and precipitation in WD1 steel during heat treatment was investigated by using optical microscopy, X-ray diffractometer and transmission electron microscopy. The results show that there are three types of carbide, namely MC, M6C and M7C3 carbide, in the annealed WD1 steel; and M6C and M7C3 carbides are dissolved totally during heating for quenching; then MC, M2C, M6C and M7C3 carbides are precipitated during tempering. The secondary hardening peak is reached after tempering at 520°Cfor two hours. This hardening is mainly caused by the precipitation of Mo2C carbide.

Abstract: Nanometer barium-strontium titanate based coated aluminum oxide (ABST) was prepared by the sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectrophotometry (FTIR). Its application in speciation of Cr(III) and Cr(VI) from water were studied. The results showed that the nanometer barium-strontium titanate was immobilized on aluminum oxide firmly, becoming a new adsorbent. Two forms of chromium showed different exchange capacities at different pH values, viz. Cr (III) selectively retained at pH 10–13, whereas Cr (VI) retained at pH 1. Hence complete separation of the two forms of chromium is possible. Retained species were eluted with 5mL of 1 mol•L−1 HCl and 1 mol•L−1 NaOH. The Cr(III) and Cr(VI) concentration was measured by atomic absorption spectroscopy. The adsorbent had a promising prospect in the separation of Cr(III) and Cr(VI) in environment water.

Abstract: Comparing with conventional expressway embankment filled with clay only, the sand embankment tipped by intensely-weathered rock (IWR) can effectively reduce the consumption of cultivated land resource caused by the construction of expressway engineering. So it is significant to research the constructions of sand embankment tipped by IWR if local sand resources are enough. Combined with the construction of Qing-Lin freeway, in China, the slope stability of the embankment filled with sand and tipped by IWR outside was analyzed in the paper, and the analysis was conducted by the strength reduction method. The effects of the changes of compaction, water content, ratio of slope, height of the embankment and different IWR-width on the safety factor of the slope stability were investigated. The results indicate that, when the height of embankment is constant, the ratio of slope is the most important factor which influences the stability of side slope, and the IWR-width does not have a decisive effect on the safety factor on subsoil condition and it can be determined according to the convenience of site construction.

Abstract: A 2D FE model of cracked aluminum plates repaired with adhesively bonded composite patches was established in this paper, and then the model was validated by comparing the calculated SIF and fatigue life of repaired structure with existing results. The result shows that the model is accurate enough to be used to analyze the mechanical property of cracked aluminum plates repaired with adhesively bonded composite patches.

Abstract: The ZnO nanoparticles were synthesized by Nucleation-Crystallization Separation and co-precipitation. The structures and formed phase temperature of the samples were researched by X-ray diffraction (XRD) and DSC -TGA. Gas sensing properties of the samples were measured by a stationary state gas distribution method under static state. The results show that the ZnO prepared from Nucleation-Crystallization Separation has a higher response to 50 ppm ethanol and gasoline than ZnO prepared from co-precipitation. The sensitivity of ZnO prepared from Nucleation-Crystallization Separation to 50 ppm ethanol and gasoline are 34 and 68, which is better than the sensitivity of ZnO prepared from co-precipitation (17 and 28). The good sensing property may be due to the independence of nucleation and crystallization steps, which helps the more uniformity and thermal stability and the larger space utilization of ZnO particles.