Abstract: Deterioration of fly ash concrete (FAC), high performance concrete (HPC), and high performance hybrid fibers reinforced expansive concrete (HPHFREC) subjected to combined action of flexural load and 5% magnesium sulfate solution is investigated. The change of dynamic modulus of elasticity (DME) was monitored and recorded as to observe the corrosion of concrete specimens in magnesium sulfate environment. Results show that in the initial exposure stage, the relative dynamic modulus of elasticity (RDME) of concretes increase steadily as a result of the reinforced effect of flexural load and nucleation of attack products, consequently the microstructure is compacted and the strength of the concretes is enhanced in some extent. As for the later corrosion proceed, the interior cracks occurred and the flexural load accelerated the degradation of concrete. HPC demonstrated good corrosion resistance when it was exposed to only magnesium sulfate solution, and HPHFREC showed the best stress corrosion resistance when it was subjected to combined action of magnesium sulfate solution and flexural load.
Abstract: Al-12Si alloys containing1%, 2% and 3% lithium were prepared. The alloys were melted by a vacuum induction furnace. The microstructure was observed by optical microscopy, tensile test was performed at a rate of 1mm•s-1. Hardness was determined by a Vicker’s hardness machine. Adding 1%Li to the of Al-12Si alloy, the alloy is modified and its structure is eutectic. When Li content is 2% or 3%, the structure is hyper-eutectic, and proeutectic Si-phases are present. The Al-12Si-1Li alloy has a tensile strength of 190MPa and an elongation of 1%. With the increment of lithium, the strength and elongation of Al-12Si containing Li alloys gradually decreases, because of the presence of proeutectic Si-phases. The alloys exhibits hardening behaviors when ageing at 200°C, and the hardness decreases to a value with the prolongation of the ageing time.
Abstract: La1-xSrxCr1-yMnyO3-δ(LSCM) has unique advantages over the traditional anodes for it’s stability and high catalytic activity being an anode of solid oxide fuel cell(SOFC). Doped cerium material and Co element are used to improve the conductivity both in oxidative and reductive conditions. La0.7Sr0.3Cr0.5Mn0.5-xCoxO3-δ-Ce0.8Ca0.2O2(LSCMCo-CDC) composite anode materials are synthesized in one-step by glycine nitrate process(GNP). X-ray diffraction patterns(XRD), scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDS) are used to characterize the powders. The conductivity of LSCMCo-CDC increases with increasing the quantity of Co when the temperature is above 750°C, and the maximum values are 10.5 Scm-1 and 0.7 Scm-1 of LSCMCo0.15-CDC at 800°C in air and H2 atmosphere, respectively. It’s conductivity in intermediate temperature have been promoted obviously comparing to that of LSCM-CDC and LSCMCo. Good chemical compatibility between LSCMCo-CDC and La0.9Sr0.1Ga0.8Mg0.2O3-δ(LSGM) is confirmed by XRD results.
Abstract: Since composite sandwich structures are susceptible to low-velocity impact damage, a thorough characterization of the loading and damage process during impact is important. In the present paper, the low-velocity impact response of carbon fiber composites lattice structures are investigated by experimental and numerical methods. Impact tests on composite plates are performed using an instrumented drop-weight machine (Instron 9250HV) and a new damage mode is observed. A three-dimensional finite element model is built by ABAQUS/Explicit and user subroutine (VUMAT) to predict the peak loading and simulate the complicated damage problem. It can be found that numerical predictions coincide well with experimental results.
Abstract: A serious of spherical Co-MCM-41s with different cobalt content was synthesized and characterized by XRD, SEM, N2 isotherms and ICP techniques. The influences of synthesis conditions on the structure were also studied. The use of ascorbic acid as reductant had significant influence on the morphology and the catalytic activity of Co-MCM-41. The prepared samples exhibited higher catalytic activity in the direct hydroxylation of benzene by H2O2 than those with common morphology.
Abstract: The present paper deals with the interactions between a main crack and a surrounding layer of crazing patterns. Analysis of the stress field distribution as well as the energy induced during these interactions is based on damage criteria through the resolution of some differential equations conditions and the use of a numerical approach. The effect of amplification and shielding on the resulting stress field is shown through a study of mode I. It is proven, herein, that crazes closer to the main crack dominate the resulting interaction effect and reflect an anti-shielding of the damage while a reduction constitutes a material toughness.
Abstract: In the present work, rapidly solidified hypereutectic Al-Si-Cu-Mg alloys strips was prepared by single roller melt-spinning method. The microstructures, phase and morphology characteristics of the resultant strips were characterized by means of SEM, TEM and XRD technique. The results show that the grains are refined after rapid solidification processing, and the micro-nanocrystals are formed. Compared with equilibrium solidification, the microstructures are changed obviously. The nucleation and growth of primary silicon are suppressed and primary silicon can not deposited, meanwhile, α-Al phase is nucleated which prior to eutectic. Therefore, the microstructures become into the metastable state. The microstructures of the strips are composed of primary micro-nanostructure α phase and feather-needles-like (α+Si) eutectic which set in the α phase. The mechanism of the formation for microstructures of melt-spinning Al–Si alloy have also been discussed.
Abstract: In order to understand the effects of deoxidizer such as aluminium, titanium and magnesium on the impact toughness of heat affected zone (HAZ), three low carbon steels deoxidized by Ti-Al, Mg and Ti-Mg were obtained. After smelting, forging, rolling and welding simulation, the effects of Al, Ti and Mg addition on the impact toughness of HAZ in low carbon steel were studied. The inclusion characteristics (size, morphology and chemistry) of samples before welding and the fracture pattern of the specimens after the Charpy-type test were respectively analyzed using optical microscope and scanning electron microscopy (SEM). The following results were found. The density of inclusion in Ti-Mg deoxidized steel is bigger than Ti-Al deoxidized steel. The average diameter is decreased for the former than the latter. The addition of Ti-Mg can enhance the impact toughness of the HAZ after welding simulation. The maximal value of the impact toughness is 66.5J/cm2. The complex particles of MgO-TiOx-SiO2-MnS are most benefit to enhance impact toughness. The improvement of HAZ is attributable to the role of particle pinning and the formation of intergranular ferrite.
Abstract: OBJECTIVE: As a kind of nanometer natural material, bacterial cellulose (BC) has been widely used in the field of food processing, paper making, pharmaceutical science, etc. In recent years, it is found that there is a good application potentiality of BC used in the medical science, especially in the field of regeneration medicine. There are some reports about BC being used in tissue engineering. It is of great necessity to investigate its tissue compatibility. In this research, the cell compatibility of BC was studied by using the method of cell-culturing combined with rat adipose- derived stem cells (ADSCs) as the seed cells. MATERIAL and METHODS: BC membranes were prepared by Key Laboratory of Industrial Microbiology, Ministry of Education, Tianjin University of Science and Technology. The average pore size and porosity of it were 0.8-3.5μm and 93％, respectively. The ADSCs were isolated from the fat pad located in pars inguinalis of 3-weeks Wistar rats by using type II collagenase and then cultured using DMED medium contained 10% new-born calf serum. The status of cell growth was observed everyday. The cell growth curve was determined by MTT method and stem cell phenotype was identified by flow cytometry. Cells in exponential phase of growth were planted on the surface of BC membrane which had been sterilized beforehand by steam at 121°C for 20 min at cell density of 3.0×105cells/mL. The cell-BC compound was cultured by using DMED medium contained 10% new-born calf serum. The growth status and the biological characterization of ADSCs cultured on the BC were determined at different culture time. RESULTS: Most ADSCs primary cultured in vitro showed fusiform shape when they were cultured for 72 hours. The amount of the cells increased along with the culture time and confluenced at 7 days. The exponential phase of growth of primary cultured ADSCs in vitro appeared when they were cultured for 3 to 9 days. The result of flow cytometry showed that ADSCs could express the stem cell symbol. The portait section of cell-BC compound were made after 10 days cultured in vitro. It was shown that ADSCs compact grew on the surface of BC. CONCLUSION: It is indicated that ADSCs grew on the BC membrane still retain the biological activity of stem cell and BC has good biocompatibility. It might be further studied for BC as tissue engineering scaffold.
Abstract: The cross-linked polystyrene prepolymer was synthesized with divinylbenzene (DVB) as crosslinker via free-radical crosslinking copolymerization (FCC) and used as the matrix materials for E-glass fiber reinforced composites. The surface modification was performed by treatment of E-glass fiber with γ-methacryloylpropyl trimethoxysilane (MPS) solution. Fourier transform infrared spectroscopy (FTIR) was used to identify the functional groups on the surface modified glass fibers. Dynamic mechanical thermal analysis (DMTA) of these composites revealed that the dynamic storage modulus (E′) was gradually enhanced with the increasing content of DVB (0~3.0 wt %) whereas the damping parameter (tanδ) peaks are lower and broader, indicating better load bearing capacity. Moreover, the Tg was shifted to higher temperature corresponding to the increasing of crosslinking density. Morphology of fracture surfaces for these composites showed different fiber-matrix interfacial adhesion which was mainly attributed to the variation of crosslinking network structure in the interface.