Applied Mechanics and Materials Vols. 138-139

Abstract: We report the tensile behavior of corroded steel plates with huge corrosion pit. The behavior of corroded steel plates is not easy to predict because of its surface roughness. We therefore conducted tensile tests first to understand the behavior experimentally using the corroded steel plates taken from plate girder bridge. Before the testing, a 3D laser prove system was employed to measure the surface irregularity. In addition, finite element model was developed here to predict the behavior numerically. The model was validated by the tensile test results so that the finite element model can be reliably used for the parametric study. It is found from the parametric study that the location of huge corrosion pit affects the tensile strength, at most 15%.

Abstract: Titanium oxide (Ti-O) films have been widely used in the fields of electron, photology and medicine due to its distinctive optical, electrical and chemical properties. In this paper, Ti-O films were synthesized by micro-arc oxidation firstly, and then surface was modified by NaOH alkali solution under different treatment time. The wettabilities of as-prepared films were investigated by contact angle measurements using four common liquids. nanoindentation was adopted to obtain the films’ nanohardness and modulus. The results show that Ti-O films tend towards hydrophilia and its surface energy increased after alkali treatment, but no obvious effects to nanohardness and modulus of Ti-O films. Surface roughness of Ti-O films increases after alkali treatment firstly, but decreased with continuing to increasing the times of alkali treatment.

Abstract: Two interstitial-free steel grades, one based on combined niobium and titanium additions and the other based on titanium only addition, were investigated. Annealing experiments were used to study the effect of niobium on the mechanical property. And tensile-shear fatigue tests were used to study the effect of niobium on the fatigue property of spot welding. The experimental results show that niobium addition not only can significantly improve the mechanical properties of the basic materials by way of grain refinement, but also has beneficial effects to the fatigue strength of spot welding.

Abstract: In this paper, tensile fatigue properties of 316L stainless steel thin sheets with a thickness of 0.1 mm are studied. The tests are implemented by using micro mechanical fatigue testing sysytem (MMT-250N) at room temperature under tension-tension cyclic loading. The S-N curve of the thin sheets descends continuously at low cycle region. Cyclic σ-N curve and ε-N curve are obtained according to the classical macroscopical fatigue theory. The results agree well with the experimental fatigue data, showing that the traditional fatigue research methods are also suitable for description of MEMS fatigue in a certain extent. The effect factor of frequency was considered in this study and the results show that the fatiuge life and the fatigue strength are increased as loading frequency increasing.

Abstract: Utilizing CFD, the influences of skirt board structure on high speed maglev train's aerodynamic resistance and the stability under crosswind are studied. Studies have been conducted on the aerodynamic of skirt boards which located on different positions. Simulation analyses are finished with maglev train running at speed of 350km/h for both with and without crosswind. Study results show that, some skirt boards are likely to be pulled apart, further, lower the safety limit speed.

Abstract: The joining of dissimilar metals, T2 copper and Q235 mild steel was carried out by friction stir welding. The material flow of different shapes of the probe and different forms of welding joints were studied, the material flow behavior on different locations from the probe was also analyzed. The experimental results showed that the screw thread in probe is the main factor in driving material flow along the thickness direction of the weld during FSW of copper and steel, the flow morphology of the weld is significantly different with vary forms of welding joints, and the material flow on different locations from the probe are quite different from each other. Instantaneous cavity will form at the upper of the weld with the use of left screw thread probe during FSW, and if not promptly and adequate padding, it is prone to appear hole-type defects.

Abstract: A nanosecond pulsed plasma discharge is used to ignite a propane-jet flame. The nonequilibrium plasma is produced by repetitive pulses of 30 kV peak voltage, 70 ns pulse width and 2 kHz repetition rate. The experimental results shows that the use of a repetitively nanosecond pulsed discharge resulted in significant increase in flame stability.

Abstract: Friction stir welding (FSW) was applied to TA15 titanium alloy plates. Welds were produced by employing rotational speed of 375rpm and a travel speed of 23.5mm/min.The microstructure and mechanical properties of friction stir welded joints were investigated. Flow pattern of the materials also were analysed. The stir zone (SZ) was characterized by α-phase and β-phase, but the size of the grain in the middle of the SZ was much finer than that of the upper. The interface between the base metal (BM) and SZ is associated with the flow state of the plastic materials. Results of transverse tensile test indicated that all the joints exhibited lower tensile strength than the BM, and the maximum tensile strength of the as-welded joint is about 97.6% of the average strength of the BM.

Abstract: Based on coupling structural-acoustic modal model, using piezoelectric materials and loudspeaker/microphones as actuator/sensors, the analytical simulations are presented for the actively controlled the sound transmission through double plate structure. Firstly, the results show the potential for using PVDF sensors to improve sound transmission loss. Secondly, the effects of parameters of actuator/sensor and double plate structure on control performances are discussed. And some useful conclusions are obtained, for example, if volume velocity sensor is applied to radiating plate, transmission loss will improve significantly, no matter what type actuators (i.e. loudspeakers or PZT actuators on either plate) are used; symmetrical rectangular PVDF sensors should be applied on radiating plate; using loudspeaker/microphone configuration should be avoided for the same thickness double plate structure; the increased thickness of cavity leads to the better control performance.

Abstract: When the effects of dielectrophoresis (DEP) is applied in the detector design, it can be used to detect and locate multi targets.In this paper, the DEP force of neutral objects in the non-uniform electric field is firstly derived.According to analyze the force of insulators in the non-uniform electric field,we can conclude that the mechanical expression of matching detection is DEP force.Then the parameters of DEP force are analyzed and simulated, and it is of great significance to design detector and choose parameters for detector.Finally, through the analysis of the principle of matching detection, the article gives the technology implementation approach of this principle.The results show that this detection method can be used to detect the targets which has the same dielectric material with the detected objects, and it has a strong anti-interference ability.