Flexural motion in laser evaporative heated cantilever workpiece: Three-dimensional analysis

Laser evaporative heating of metallic surfaces generates a recoil pressure at liquid–vapor interface. Since the magnitude of recoil pressure is considerably high, despite the small evaporative area, the pressure force generated normal to the workpiece surface is considerably high. Consequently, pressure force initiates a flexural motion of the workpiece subjected to a laser evaporative heating. In the present study, flexural motion of a steel plate, with a cantilever arrangement, due to laser evaporative heating is considered. Stress field in the workpiece is also taken into account. Three-dimensional motion of the workpiece is modeled and governing equations of motion and stress field are solved numerically using the finite element method. It is found that surface displacement in the order of 20 m is predicted and the maximum equivalent stress in the order of 700 kPa is obtained. Additional copper element in the workpiece alters the temporal variation of stress levels.     

阶梯型弯曲振动聚能器的设计

在考虑转动惯性及剪切形变的影响下,研究出了一种简单并近似有效的阶梯型弯曲振动聚能器的设计方法,能很好地满足工程上的需要,并以纯弯曲理论对其放大倍数进行了分析,实验表明实测的弯曲聚能器谐振频率与理论符合很好。     

Flexural vibration band gaps in thin plates with two-dimensional binary locally resonant structures

The complete flexural vibration band gaps are studied in the thin plates with two-dimensional binary locally resonant structures, i.e. the composite plate consisting of soft rubber cylindrical inclusions periodically placed in a host material. Numerical simulations show that the low-frequency gaps of flexural wave exist in the thin plates. The width of the first gap decreases monotonically as the matrix density increases. The frequency response of the finite periodic thin plates is simulated by the finite element method, which provides attenuations of over 20dB in the frequency range of the band gaps. The findings will be significant in the application of phononic crystals.     

纤维布抗弯加固梁跨中剥离应力的近似计算

首先综述了纤维复合材料(FRP)抗弯加固梁中防剥离破坏的各种措施，分析了跨中混凝土保护层的剥离破坏机理，提出一个近似计算跨中保护层剥离应力上限的方法，可供防剥离设计参考。     

轴向受压螺旋杆的动态稳定性与振动

基于Kirchhoff理论讨论端部受轴向压力作用的圆截面弹性螺旋杆的动态稳定性问题。以杆中心线的Frenet坐标系为参考系,建立用欧拉角描述的弹性杆动力学方程。杆的螺旋线平衡状态由方程的特解确定。基于静力学分析的结论,在动力学范畴内继续讨论轴向受压螺旋杆平衡状态的稳定性。在一次近似意义下证明了螺旋杆在空间域内的欧拉稳定性条件为时域内的Lyapunov稳定性条件。从而进一步认识Lyapunov和欧拉两种不同稳定性概念之间的相互关系。导出轴向受压螺旋杆弯扭耦合振动固有频率的近似解析表达式。     

螺纹联接的耐久性及防松措施

重点分析了交变载荷作用下 ,螺纹联接的耐久性及其影响因素。增加预紧力和降低螺栓刚度是提高耐久性的有效措施。比较了常用的几种螺纹防松措施的防松性能及其适用场合     

BE-SONOS flash memory along with metal gate and high-k dielectrics in tunnel barrier and its impact on charge retention dynamics

We investigate the effect of a high-k dielectric in the tunnel layer to improve the erase speed-retention trade-off. Here, the proposed stack in the tunnel layer is AlLaO₃/HfAlO/SiO₂. These proposed materials possess low valence band offset with high permittivity to improve both the erase speed and retention time in barrier engineered silicon-oxide-nitride-oxide-silicon(BE-SONOS). In the proposed structure HfAlO and AlLaO₃ replace Si₃N₄ and the top SiO₂ layer in a conventional oxide/nitride/oxide(ONO) tunnel stack. Due to the lower conduction band offset(CBO) and high permittivity of the proposed material in the tunnel layer, it offers better program/erase(P/E) speed and retention time. In this work the gate length is also scaled down from 220 to 55 nm to observe the effect of high-k materials while scaling, for the same equivalent oxide thickness(EOT). We found that the scaling down of the gate length has a negligible impact on the memory window of the devices. Hence, various investigated tunnel oxide stacks possess a good memory window with a charge retained up to 87.4%(at room temperature) after a period of ten years. We also examine the use of a metal gate instead of a polysilicon gate, which shows improved P/E speed and retention time.     

Physico-chemical,thermal, and flexural characterization of Cocos nucifera fibers

Currently there is a growing interest in reinforcing polymers using natural fibers for a wide variety of applications because of their desirable properties such as biodegradability, low density, low cost, and abundant availability. In this study, the raw lignocellulosic fibers of Cocos nucifera palm were extracted, and characterization studies such as Fourier transform-infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis were conducted and reported. Composite samples were prepared using polyester resin, and the effect of fiber loading on flexural strength is reported. Surface morphology of the fractured samples was examined using a scanning electron microscope.     

Fire behaviour of hybrid filament-wound single and adhesively bonded composites tubes under static pressure

The present work aims to experimentally investigate the fire behaviour of water-filled E glass reinforced thermoset resin hybrid filament-wound composites tubes under static pressure. Heretofore, fire endurance tests have been conducted on single and adhesively bonded tubes manufactured by CTRA Company. Furthermore, internal pressure tests until failure have been performed on the burnt single and burnt joined tubes in order to quantify their abilities to contain the fluid after being exposed to heat flux. A comparison between the pressure behaviour of exposed to fire (burnt) and non-exposed tubes (single and joined) was also inspected. The identification of the fire-induced damage mechanisms of the tubes was performed through optical microscopy, Scanning Electron Microscopy (SEM) and X-ray tomographic observations. Finally, the thermal analysis was carried-out on burnt specimens in order to better understand the multiphysical phenomenon taking place during the fire endurance tests. The experimental results have revealed that the combustion process of both single and joined tubes was described in four steps namely tube heating, resin degradation, ignition and flame decay. Moreover, it was found that no leakage was witnessed on the tubes (single and joined) outer surfaces during the fire endurance tests. The comparison between the pressure behaviour of the burnt single tube and the burnt joined one has proved that the single tube is much resistant under internal pressure loading than the burnt joined tube. Finally, the fire-induced damage included matrix cracking and delamination between the tube plies which was noticed from microscopic observations.     

Physical background of the endurance limit in poly(ether ether ketone)

In this study, it is demonstrated that the apparent endurance (fatigue) limit for plasticity-controlled failure in poly(ether ether ketone) is related to an evolution of the yield stress. The increase of the yield stress has two separate causes: (a) stress- and temperature-accelerated physical aging of the amorphous phase and (b) strain hardening as a result of texture development. Yield stress evolution is monitored using thermomechanical treatments during which the material is exposed to temperature and load. The combined contributions of both temperature and applied stress to yield stress evolution (below T _g) can be effectively modeled using an effective time approach employing an Arrhenius temperature-activation as well as Eyring stress activation. Combination of the yield stress evolution with a previously developed model for plasticity-controlled failure allows prediction of time-to-failure under both static and cyclic load, quantitatively capturing the observed apparent endurance limit.