Abstract: The objectives of this paper are to find the compressive strength and ultrasonic pulse velocity (UPV) of recycled concrete with various percentages of natural fine aggregate replaced by Recycled brick fine aggregate (RBFA) as well as the residual strength and residual UPV of recycled concrete subjected to elevated temperatures. Experiment results showed that the compressive strength and UPV decreased as amount of RBFA in concrete increased, the long-term performance of compressive strength and UPV development increased as the RBFA content increased. The residual strength of recycled concrete increased slightly after heating to 300°C and the residual UPV of recycled concrete decreased gradually as the exposed temperature increased beyond 300°C. In the range of 580 -800°C, recycled concrete lost most of its original compressive strength and UPV. After subjected to the temperature of 800°C, compared to plain concrete, recycled concrete with 100% RBFA had a greater discount rate of compressive strength and UPV of the order of 5-15% and 6-10%. Regression analysis results revealed that the residual strength and residual UPV of recycled concrete had a high relevance after elevated temperatures exposure.
Abstract: This paper investigated the volume fraction effect of micro-sized SiC on the tribological behavior of SiCp reinforced AZ91D Mg-based metal-matrix composites (MMCs). The Mg MMCs were prepared by the melt-stirring technique for wear tests. The hardness and coefficient of friction of Mg MMCs increase as increasing volume fraction of SiC particle in MMCs. The SiCp/AZ91D MMCs exhibit superior wear resistance under lower and moderate sliding condition. However, the effects of the SiC particle reinforcements on wear resistance are not as conclusive under severe sliding condition (50N-1500 rpm for all vol.% of MMCs, 50N-1000rpm for 3 vol. % MMCs), since the matrix of MMCs were softened at elevated temperature under such severe condition. However, the incorporation of SiC particles could enhance the wear resistance of AZ91D matrix alloy for most of the sliding conditions.
Abstract: The low-melting CaCl2-NaCl-Al2O3 materials were used as the electrolyte of the low temperature aluminium electrolysis. The electrical conductivity and density of the materials were measured by the Continuously Varying Cell Constant Technique, ac-techniques, and Archimedes method. The materials were composed of 71wt.%~87wt.%CaCl2 (corresponding NaCl), NaCl and Al2O3(without and saturated). The measurement temperature ranges were 550°C~800°C. The results showed that Additive Al2O3 decreased the electrical conductivity of the materials, and resulted in the increase of the activation energy of conductance. The function relationship between the electrical conductivity and temperature was linear, and conformed to the Arrhenius equation. Increasing the CaCl2 content decreased the electrical conductivity of the materials, but the density was increased. With the increase of the CaCl2, the decrease scope of the electrical conductivity was small and the increase trend of the density was slow down. The decisive factor of the electrical conductivity of the materials was temperature.
Abstract: . (Al2O3)p/Al composites were in situ synthesized from Al-CeO2 system. The reinforcement phases, morphologies of particles and interfaces between particles and matrix were characterized by XRD, SEM, EDX, TEM and SAED. The in situ generated Al2O3 particles have various irregular shapes and disperse uniformly in matrix. The sizes of Al2O3 particles are normally less than 200nm. The interfaces between particles and matrix are clean. Moreover, there are large numbers of high density dislocations and the generated extensive micro-nano subgrains around Al2O3 particles. These novel characterizations contribute to the significant improvement of composites properties.
Abstract: Dual-phase lamellar precipitates can be easily occurred in the austenitic steel valve in heat treatment and use. They affect seriously the performance of the valve at high-temperature, which is one important reason leading to valve failure. The morphology and precipitation location of lamellar precipitates of the 5Cr21Mn9Ni4N (21-4N) exhaust valve were investigated by scanning electron microscopy, and the influencing factors and precipitating mechanisms were analyzed. Experimental results show that, the lamellar precipitation is very sensitive to using or aging temperature, the higher temperature the more precipitates. The lamellar precipitation consists of continuous and discontinuous precipitation. The latter mainly appeared at the locations with larger deformation. Slip bands and deformation twins at high-temperature deformation and grain boundaries are important locations for precipitation.
Abstract: The evolutional laws of rock under uniaxial stress are studied based on damage mechanics, rock rheology mechanics and chaos theory. Firstly, the damage rheological evolution equations are set up on the base of damage mechanics under the isotropic and orthogonal anisotropy conditions. The chaotic characters are tested in the process of evolution and the chaotic effect is analyzed. The root reason of rock damaged is made clear. The creep curve of Kelvin model considering damage is illustrated by FLAC3D, and the deformation process is explained by chaos theory. It will be help to understand the mechanics property of rheology of damaged rock and predict development phases. It is also much value in solving various practical problems of geotechnical engineering and acquainting other materials’ rheology evolution..
Abstract: Kaiser effect was noticed while submitting marble samples to Brazilian tests. An automatic data acquisition system was applied by means of analog to digital conversion, upon recording analog signals of stress, strain and acoustic emission (AE) emitted from Portuguese marble specimens under diametrical loadings in different loading cycles. Results confirm that the Kaiser effect was pronounced and was easy to be detected under Brazilian tests with a felicity ratio varied from 0.92 to 1.09. This means it is possible to measure the pre-existing stresses in rocks under complex states of stress by means of other tests besides uniaxial compression. Results also show that cumulative AE events vs. stress curve is more suitable for Kaiser effect recognition than cumulative AE energy vs. stress curve as every event has different scales of energy.
Abstract: A new method based on a solution graft technique was used to prepare poly (vinylidene fluoride) grafted polystyrene sulfonated acid (PVDF-g-PSSA) proton exchange membrane. Polystyrene is grafted into PVDF modified by plain sodium silicate (Na4SiO4). There is a linear relationship between the degree of grafting and the content of Na4SiO4. Fourier transform infrared spectroscopy is used to characterize changes of the membrane's microstructures after grafting and sulfonation. The morphology of the membrane's microstructures after grafting and sulfonation is studied by scanning electrolytic microscope (SEM). The effect of plain sodium silicate (Na4SiO4) concentration and relative humidity on the conductivity of the electrolyte was investigated by the impedance at room temperature. The results show that the styrene has been grafted into PVDF. The conductivity of PVDF-g-PSSA electrolyte doped 10% plain sodium silicate (Na4SiO4) is 0.016 S/cm at room temperature. The conductivity of the electrolyte changes slightly at a relative humidity range of 20%-70%. The weightlessness of PVDF-g-PSSA electrolyte heated to 40°C was less than 2%, which indicated that water capacity was good.
Abstract: The surface morphologies of micro-arc oxidation coatings and chemical oxidation coating formed on AZ91D alloy were observed by scanning electron microscopy. The fatigue properties of both specimens with micro-arc oxidation coatings and chemical oxidation coating after the pre-corroded treatments in neutral salt spray test were investigated comparatively. The result shows that pre-corrosion treatment decreases the fatigue life, but the pre-corroded fatigue life of specimens with chemical oxidation is lower than that with micro-arc oxidation. The thickness of micro-arc oxidation coatings has no obvious influence on the pre-corroded fatigue life of AZ91D alloy.