Applied Mechanics and Materials Vols. 152-154

Abstract: The three key oxide molar ratios of geopolymer concrete: n(SiO2)/n(Al2O3), n(Na2O)/n(Al2O3) and n(H2O)/n(Na2O) were studied in this paper to determine their effects on reinforced geopolymer concrete by testing the corrosion weightless rates of reinforcing steel bar and carbonation depth. It was found that both of them were decreased first but increased at a certain point with increasing n(SiO2)/n(Al2O3); they showed a downtrend with the increase of n(Na2O)/n(Al2O3). Increasing n(H2O)/n(Na2O) caused an increase in both of them while a small decline was observed in carbonation depth when n(H2O)/n(Na2O)＜28.With the the same amount of cementitious material, resistance to corrosion of steel bar of geopolymer concrete was better than that of common concrete.

Abstract: This paper aims at to study the damping ratio and nonlinear stiffness property of rubber isolator effect on vibration response under different excitation level and temperature. By the means of experiment, the curves of amplitude-frequency of rubber isolator were obtained. Based on the experimental results, the damping ratio was ascertained by the method of half power point. A single freedom mechanics model that describes the isolated system was built, and the equation of frequency response deduced and solved by harmonic balance method. Furthermore, the effects of nonlinear factor of stiffness effect on vibration response were analyzed. The precision of the approximation that solved by harmonic balance method was validated using Runge-Kutta method. It is indicated that the equation of frequency-response can be used to describe the property of frequency-response of rubber isolator.

Abstract: In order to study the environmental effect on fatigue properties of die-cast magnesium alloys, several fatigue tests were performed for AM50HP and AZ91HP in ambient air, vacuum, engine oil, deionized water and 3.5% NaCl solution. It is found that the S-N curves are steeper in corrosive environment and AM50HP shows a higher sensitivity to the action of 3.5% NaCl solution than AZ91HP. Both alloys do not have endurance limits in 3.5% NaCl solution, whereas endurance limits could be detected in ambient air, which are about 90MPa and 100MPa for AZ91HP and AM50HP respectively. It is also found that FCP rate is substantially increased in corrosion media: the presence of oxygen causes the production of oxide film on the fresh surfaces made during the cyclic loading and the oxide film would restrict the deformation of the matrix beneath the hard film and promote hydrogen embrittlement in the wet condition.

Abstract: A novel smart coating sensor, consisted of driving layer, sensing layer and protective layer, has been successfully developed, and it was utilized to detect crack initiation and growth in fatigue tests. The results show that the smart coating sensor can detect cracks above 300μm, corresponding to the increment of the sensing layer’s resistance at the level of 0.05Ω. Subsequently, the development of SCS is of importance significance in the substitution of an existed inspection that requires substantial disassembly and surface preparation, and, thus, can find numerous applications in difficult-to-access locations on commercial and military aircrafts.

Abstract: A model for compressible Air Cushion Vehicles (ACV) is presented. In this model the compressible Bernoulli's equation and the Newton's second law of motion are used to predict the dynamic behavior of the heave response of the ACV in both time and frequency domains. The mass flow rate inside the air cushion of this model is assumed to be constant. The self excited response and the cushion pressure of the ACV is calculated to understand the behavior of the system in order to assist in the design stage of such systems. It is shown in this study that the mass flow rate and the length of the vehicle's skirt are the most significant parameters which control the steady state behavior of the self excited oscillations of the ACV. An equation to predict the transient time of the oscillatory response or the settling time in terms of the system parameters of the ACV is developed. Based on the developed equations, the optimum parameters of the ACV that lead to minimum settling time are obtained.

Abstract: The instability of the bipolar plate for welding fuel cell was analyzed taking the bipolar plate as thin plate. The minimum compressive stress is calculated based on thin plate instability theory caused by longitudinal compressive stress. The simplified thermal stress distribution function is determined using the analytical solution of the plane heat conduction equation. The maximum compressive stress is determined through the analysis of the longitudinal stress distribution of the cross section passing through the solder point during heating and cooling process. The results are used to obtain the pre-tensile stress controlling the instability of the bipolar plate for welding fuel cell, and the minimum pre-tensile stress is the difference between the maximum compressive stress and the minimum compressive stress as the thin plate loses instability.

Abstract: Polyethersulfone (PES) hollow fiber membranes have been widely used in many fields, such as ultrafiltration, microfiltration, reverse osmosis, liquid/liquid or liquid/solid separation, gas separation, hemodialysis, and so on. In this paper, the sheet PES hollow fiber membranes were prepared. The morphology and performance of membranes can be controlled. By studying the influence of the compositions and conditions on the morphology and performance of PES hollow fiber membrane, the relationship of morphology and performance of the membrane is acquired. The additives were used such as glycerol, BuOH and PEG. In addition, immerse phase inversion was used as membranes preparation method. The morphology of the membrane was controlled by changing kinds of additive, concentration of additive and so on. It was found that the membrane morphologies were changed by additive obviously. Porosity , pure water flux, scanning electron microscopy(SEM) were used to characterize the morphology and performance of the membranes.

Abstract: Dynamic impact loading/energy-absorbed response curves of controlled T800/5228A laminates and corresponding “Ex-situ” toughened T800/5228E laminates were contrastively studied. It was concluded that both Hertzian failure loading and the maximum loading were improved by interlaminar toughening, based on the enhancement of Mode II crack strength. T800/5228E laminates presented less damage area than T800/5228A laminates under equivalent impact energy, but consumed more total energy, and further study show that serious external damage on the surface of T800/5228E lamiantes may be responsible for the more impacted energy consumed .

Abstract: Continuous cooling transformation (CCT) diagram of steel 22MnB5 was studied using dilatometer method. The influence of the hot forming process parameters, such as the heating temperature and holding time on the mechanical properties and microstructure of stamped parts was analyzed by tensile tests and the metallographic observation on the parts with various processing parameters. The microstructural evolution obtained from the dilatometer samples reveals that the cooling rates not smaller than 20K/s induced fully martensitic microstructure. As the cooling rate decreasing, more ferrite and pearlite or more bainitic microstructure forms. Tensile tests results show an excellent tensile strength and ductility combination of 22MnB5. The tensile strength and yield strength reach 1500MPa and 1200MPa respectively, with total elongation of around 10%.

Abstract: SiC macroscopic spheres have been synthesized by a microwave heating and carbothermal reduction method with commercial carbon spheres as template and fly ash as silica source. The morphology and structure of SiC hollow spheres were characterized using X-ray diffraction, N2 adsorption isotherms, scanning electron microscope and energy-dispersive. The results show that the SiC hollow spheres have retained the similar size with the original carbon sphere template. The shell of SiC hollow sphere is composed of curving SiC wires, and the shell thickness can be modulated by the ratio between C and SiO2. The formation of curving SiC wires attribute to the VLS mode, the Fe catalyst is indispensable reason of it.