Advanced Materials Research Vols. 415-417

Abstract: This study investigates the effect of moisture content on the residual bending strength after bending fatigue of T300/914 composite laminates immersed in water for 7 days and 14 days. Displacement-controlled three-point bending fatigue tests were conducted on specimens. After 40,000 cycles the fatigue test was stopped and the residual properties were measured on the tested specimens. Reduction in material strength was found to depend on the level of moisture content. Experimental results reveal that the moisture content in the laminates increased with immersion time. Compared to the unaged specimens, the residual bending strength after bending fatigue decreased by 6.67% and 37.04%, respectively. The residual bending strength and strength retention decreased with increased immersion time.

Abstract: The failure reasons of the valve shell from automobile redirector were investigated by metallography, fractography and mechanical property test. The result showed that continuous Si-phase with dentritic shape due to the improper solution-aged process and excessive Fe element remained due to the ineffective modification treatment were the main reasons of components’ brittle fracture.

Abstract: This paper deals with nonlinear dynamic analysis of a cantilever FGM rectangular plate with piezoelectric layers subjected to the transversal excitation in thermo-electro-mechanical environment. The material properties of plate and piezoelectric layers are assumed to be temperature-dependent. The governing equations of the functionally graded plate are based on the Reddy’s third-order shear deformation plate theory that includes thermo-piezoelectric effects and Hamilton’s principle. The governing nonlinear partial differential equations are transformed into ordinary nonlinear differential equations using the Galerkin method and the nonlinear and linear frequencies obtained using the Runge–Kutta method. The effects played by control voltage and system initial conditions on the nonlinear vibration of the plate are studied.

Abstract: By using a new type of single-beam normalized photo-acoustic spectroscopy that with weak signal detection and non-invasive testing, the photo-acoustic spectroscopy of semiconductor SiO₂ nano-crystals was measured，the measured spectra of semiconductor SiO₂ nano-crystals absorption coefficient was 0.20, and powders band gap is 3.4eV. The TEM image shows that the semiconductor SiO₂ nano-crystals are round lump structure, while the grain size of the semiconductor SiO₂ nano-crystals is about 70x200 nm, and the average particle size after the reunion is 100x300 nm. Compared with their micron crystal, the optical and electrical properties of semiconductor nano-crystals and nano-particle size are closely related. By changing the size of semiconductor nano-crystals, the mix could achieve the goal of changing the optical and electrical properties. Because of the semiconductor SiO₂ nano-crystals‘ special properties of optics and electronics and photo-semiconductor nano-materials, they are widely used in many areas of modern science and technology.

Abstract: Flash point is one of the major physical and chemical properties used to determine the fire and explosion hazards of liquids; therefore, the prediction of flash point is an important safety consideration. However, the study on flash point and the correlation between flash point and pressure has been inadequate, and needs further investigation. So in this paper, the experimental method is adopted to study the correlation between the closed flash point temperature of RP-5 Aviation Kerosene and low pressure environment. In the experiments, use the BS-1 closed bomb apparatus to measure the oil samples and use the hypobaric chamber to change the environment pressure from 50kPa to 101.3kPa. Through the experiment data, it indicates that the atmospheric pressure is much lower than the normal atmosphere, there is a quadratic function relation between the reciprocal Aviation Kerosene's flash points and logarithm of environment pressure, therefore the relationship between the reciprocal Aviation Kerosene’s flash points and altitude is reciprocal. Compared the experiment results with theoretical results, it finds that the experiment result is closed to reality. The experiment results will provide the scientific data for the safety of aircraft tank, and benefit the fire protection, such as inflammable liquid production, transport, storage et al in oil pipeline management.

Abstract: Loosening of screw of the abutment on a dental implant can result in a failure for the prosthesis. The purpose of this study is to understand the change at the joint between the implant and abutment after being subjected to a repeated force. The investigated parameters include loss of torque and shift of abutment against implant. The specimen for this study is IM12 of Metal Industries Research & Development Centre (MIRDC). Implant is embedded in cylindrical resin. Abutment is then tightened on it with a torque of 35 N-cm. A mushroom-shaped crown is placed on top of the abutment. To simulate occlusal loading, an MTS machine is used with a 300N load at 1 Hz for 50,000 cycles. When 10,000 and 25,000 cycles are reached, specimens are checked for any rotation. Finally loss of torque is measured. No shifts of angle and no significant loss of torque are observed in 5 tested specimens.

Abstract: In this paper, on the base of considering building base isolation system stiffness distribution characteristics, the iterative perturbation methods for isolation structure dynamic calculation with non-classical damping are established systematically by using the upper and lower structure stiffness ratio as perturbation parameters. Theoretical derivation and examples show that the method can clearly realize effective separation between the super structure and isolation layer damping ratio and coupling among all variables. The calculation process is simple, stable and fast convergence. The calculated results are also accurate. At the same time, this paper also compares the method proposed in this paper with the classical damping method and analyses the influence of basic damping and the super structure damping on isolation structure dynamic response.

Abstract: The enthalpy relaxation rate (r_h) is defined by enthalpy change in unit time to describe non-isothermal crystallization behavior of iPP from its melt. Dates of r_h are transformed from those of heat flow rate which are collected by means of DSC directly. The curve by plotting with r_h to time indicates that the process of non-isothermal crystallization can be separated into two stages by the time point of inflection at r_h curve. The two stages are called stage Ⅰand stage Ⅱ. The curve of r_h is differentiated and the curve of A_h produced. There are two time inflection point in curve of A_h. Combined different trends of r_h and A_h during the whole process, the non-isothermal crystallization are further separated into four sub-stages, which are called stage Ⅰ₁, stage Ⅰ₂, stage Ⅱ₁ and stage Ⅱ₂. The critical values of time and relative crystallization degree which divide the process of non-isothermal crystallization of iPP are present. It provides one new method to uncover the details of non-isothermal crystallization process.

Abstract: The plastic requirements of earth inhabitant are enormous and have environment impacts of such consumption. An average person consumes many tons of those materials which ultimately disposed as wastes. Therefore, the trend of environmental awareness increases the demanding of biodegradable plastic. Presently, the biodegradability test has been reported in various kinds of standards. However, the biodegradation in aerobic condition under controlled composting system is the main focus of this research. As we have known that microorganisms in compost are the key player of biodegradation which differ from country to country. Therefore, our own compost was fermented from rice straw together with cow dropping and urea for 60 days. It was found that the properties of compost were acceptable the requirements of ISO 14855-2. Such that the compost was utilized for testing the biodegradation of cellulose and polylactic acid powder which operated by Microbial Oxidative Degradation Analyzer (MODA). The compost was designed to control the humidity, aeration ratio and temperature at 58oC. It was discovered that the percentage of biodegradability of cellulose and polylactic acid powder were 80 and 98, respectively after 60 days testing. Thus, from this report, we have confirmed that our compost attain the criterion of standard requirement.

Abstract: Weldox960 steel is widely used in mechanical structure of military equipments as anti-wear parts. The tribological behavior and mechanisms of weldox960 steel were investigated under dry sliding friction conditions. The results show that friction coefficient of the steel increases from 0.268 to 0.365 with the increase of load. When the loads are smaller than 8N, the wear rates of the steel are in the range of 0.57~0.67×10^-3 mm³/m, and the wear mechanism is multi-plastic deformation wear. If the loads are bigger than 10N, the wear rates increase to the range of 1.29~1.43×10^-3 mm³/m, and the wear mechanisms change into delamination of the work-hardening layer and abrasive wear. The friction coefficients keep in a steady state of about 0.31 when the sliding speeds change from 0.05m/s to 0.2m/s. At the low speeds of 0.05m/s and 0.1 m/s, the wear rates are in the range of 1~1.3×10^-3 mm³/m and the wear mechanisms are multi-deformation wear and abrasive wear. When the sliding speed increases to a critical value of 0.15m/s, the wear rates increase to 6.2×10^-3 mm³/m and the wear mechanisms change into fatigue delamination of the work-hardening layer and multi-plastic deformation wear as well as oxidation wear.