Generalized thermoelastic waves in functionally graded plates without energy dissipation

In this paper, a dynamic solution of the propagating thermoelastic waves in functionally graded material (FGM) plate subjected to stress-free, isothermal boundary conditions is presented in the context of the Green–Naghdi (GN) generalized thermoelastic theory. The FGM plate is composed of two orthotropic materials. The materials properties are assumed to vary in the direction of the thickness according to a known variation law. The coupled wave equation and heat conduction equation are solved by the Legendre orthogonal polynomial series expansion approach. The convergency of the method is discussed through a numerical example. The dispersion curves of the inhomogeneous thermoelastic plate and the corresponding pure elastic plate are compared to show the characteristics of thermal modes and the influence of the thermoelasticity on elastic modes. The displacement, temperature and stress distributions of elastic modes and thermal modes are shown to discuss their differences. A plate with a different gradient variation is calculated to illustrate the influence of the gradient field on the wave characteristics.     

Micro-electroforming under periodic vacuum-degassing and temperature-gradient conditions

Pinhole defects in deposits are one of the problems which have not yet been solved fundamentally when micro-electroforming of nickel into high-aspect-ratio (HAR) micro-moulds. To reduce the voids of micro-electroformed parts, a new micro-electroforming technique carried out under periodic vacuum-degassing and temperature-difference conditions was introduced in this paper. The effect of vertical temperature gradient between the bath electrolyte (low temperature) and the electrodeposition surfaces (high temperature) on the existing natural convection motion within the HAR micro-trenches was analyzed numerically, and the mechanism of vacuum degassing was also introduced. To investigate the feasibility of the exploited technique, a series of experiments were performed using special equipment developed by the authors, followed by an evaluation of the surface morphology of nickel micro-electroforms. Experimental results showed that, when comparing with the conventional electroforming practices, a significant reduction in pinhole defects of the samples electroformed by the novel process was obtained. The combined electrodeposition conditions with periodic vacuum degassing (20 kPa) and vertical temperature gradient (25 °C/65 °C) between the bath electrolyte and the electrodeposition surfaces help to reduce the formation of gas bubbles as well as to speed up the elimination of the dissolved gas during the micro-electroforming of nickel.     

Experimental study of hydrogen/air premixed flame propagation in a closed channel with inhibitions for safety consideration

An experimental study of hydrogen/air premixed flame propagation in a closed rectangular channel with the inhibitions (N₂ or CO₂) was conducted to investigate the inhibiting effect of N₂ and CO₂ on the flame properties during its propagation. Both Schlieren system and the pressure sensor were used to capture the evolution of flame shape and pressure changes in the channel. It was found that both N₂ and CO₂ have considerable inhibiting effect on hydrogen/air premixed flames. Compared with N₂, CO₂ has more prominent inhibition, which has been interpreted from thermal and kinetic standpoints. In all the flames, the classic tulip shape was observed. With different inhibitor concentration, the flame demonstrated three types of deformation after the classic tulip inversion. A simple theoretical analysis has also been conducted to indicate that the pressure wave generated upon the first flame-wall contact can affect the flame deformation depending on its meeting moment with the flame front. Most importantly, the meeting moment is always behind the start of tulip inversion, which suggests the non-dominant role of pressure wave on this featured phenomenon.     

钛合金超声扭振铣削强度优化设计仿真

钛合金具有比强度大、热传导率低等特点,对其进行强度优化设计仿真,可以提高其切削加工性能。运用Abaqus软件建立了二维超声扭振铣削模型,并采用John-cook分离准则、任意的拉格朗日-欧拉(ArbitraryLagrange-Euler,ALE)网格划分方法和施加相应边界等条件,根据刀-屑的周期分离原理,确立了接触率与角速度、振动频率和超声振幅之间的关系。此外,采用单因素法依次改变角速度、频率和振幅,以此进行强度优化设计仿真。结果表明,切削力和温度均随角速度的增加而增加;振幅的增大使得切削力有所降低,而温度却有所上升;频率的变化对两者影响不大。并得出结论:给定参数范围内,影响切削力的权重依次为振幅、角速度和频率;影响温度的权重依次为角速度、振幅和频率。     

Wear fault diagnosis of an emulsion pump crank bearing

The total load on a crank bearing was calculated by performing a load analysis of the crank connecting rod mechanism.The Reynolds equation for hydrodynamic lubrication of the crank bearing was established at the Reynolds boundary condition and was then solved using the Holland method. From this the regular track of the bearing axis was obtained. As the crank bearing gradually wears the eccentricity ratio corresponding to the minimum oil film thickness increases gradually. The oil-bound film eventually breaks down, which allows friction and collision between the metal surfaces of the crank pin and the bearing. The rigid impact leads to excitation of high frequency vibrations at the natural frequencies of the connecting rod. The experiments show that the wear condition of the crank bearing can be identified correctly through the vibration signature at the natural frequencies of the connecting rod. The degree of wear can be predicted accurately through the energy content of the high frequency bands.     

垂直圆管内掺氢甲烷燃烧不稳定性研究

为了研究垂直圆管内掺氢甲烷燃烧的不稳定性,自行搭建了上端为开口下端为闭口的透明圆形燃烧管道（半径r=\mathrm{30}\mathrm{m}\mathrm{m},管长L=\mathrm{600}\mathrm{m}\mathrm{m}）,火焰在开口端被点燃,向闭口端传播,在化学当量比条件下,通过改变氢气体积分数进行实验。结果表明,当氢气体积分数\gamma \ge50%后,火焰在传播过程中出现了数量众多的小尺寸胞状结构,并逐渐演变为平滑的弯曲火焰锋面结构,而在50%的工况中没有出现此现象;对初级不稳定性振荡以及次级不稳定性振荡出现的原因进行了分析,火焰表面积的快速变化是形成初级不稳定性振荡的主要原因,燃烧过程中产生的有限振幅的声学振荡是次级不稳定性振荡产生的原因;对不同工况反应过程组分流量的敏感性分析可以得出,链式反应R1（H+O₂\stackrel{}{̿}O+OH）为促进燃烧反应速率的主导链式反应;火焰传播过程中的最大压力出现在次级不稳定性振荡阶段,由于开口声压损失以及开口预混未燃气体损失,最大压力的数值随氢气体积分数的增加而减小。     

Prediction of ash flow temperature based on liquid phase mass fraction by FactSage

To investigate the relationship between flow temperature (FT) and the temperature that corresponds to different liquid phase mass fractions, the FTs of 10 coal ashes and 45 synthetic ashes were tested by an ash-fusion-temperature analyzer. The linear correlation between the FT and the temperature that corresponded to a 90% liquid phase (T₉₀) calculated by FactSage was: FT = 245.837 + 0.765T₉₀, and its correlation coefficients was 0.91. This model may be more accurate for low Si/Al coal. The differences between measured and predicted FT based on the model were in the measuring error range.     

Experimental study of explosion dynamics of syngas flames in the narrow channel

This article introduced the experimental study of the propagation of a syngas premixed flame in a narrow channel. The structural evolution, flame front position and velocity characteristics of lean and rich premixed flames were investigated at different hydrogen volume fractions as the flame was ignited at the open end of the pipe and propagated to the closed end. The comparative study of the syngas fuel characteristics, flame oscillation frequency and overpressure oscillation frequency prove that the syngas explosion flame oscillation in the narrow passage has a strong coupling relationship with overpressure and fuel heat release rate. The results was shown that the flame structure was strongly influenced by the hydrogen volume fraction of the syngas and the fuel concentration. The distorted tulip flame only appears in lean mixture. At 30% of hydrogen volume fraction, the flame exhibits intense and unstable propagation, manifested as the reciprocating and alternating movement of the flame front. As the volume fraction of hydrogen increased, the velocity of flame propagation and the frequency of oscillation increased. When the hydrogen volume fraction γ ≥ 0.4 at the equivalence ratio of Φ = 0.8, the pressure oscillation amplitude gradually increases and reaching the peak after 200–320 ms. Significantly, when γ = 0.3, the pressure peak increases abnormally. This work can provide support for the safe use of syngas in industry by experimental study of various explosion parameters in the narrow channel.     

GCr15轴套纵扭超声磨削表面形貌预测及试验研究

目的 构建纵扭超声磨削(LTUG)表面形貌预测模型,分析工艺条件和参数对表面粗糙度Ra值的影响,揭示GCr15轴套LTUG内圆表面形成机理。方法 基于弹性变形对LTUG单颗磨粒运动轨迹的影响,根据切削厚度概率密度函数和相邻磨粒轨迹重叠效应,建立了多磨粒超声振动作用下的最大未变形切削厚度模型,利用表面残余材料高度公式建立了GCr15轴套内圆磨削形貌预测模型,以LTUG和普通磨削(OG)方式对GCr15轴套内圆进行试验,采用正交试验验证表面形貌模型的准确性,观察并分析LTUG和OG作用后的GCr15轴套内圆表面形貌,最后利用所建立的表面形貌模型,研究磨削参数和超声振幅对表面Ra值的影响。结果 结果表明,基于所建立的表面形貌模型计算而得的表面Ra值与试验结果间的误差在13.2%以内,与OG相比,LTUG作用下的表面沟槽磨痕更均匀;LTUG作用下的表面轮廓呈现规律的周期性波动,且随振幅的增大,表面轮廓顶峰之间的间距逐渐增大;LTUG作用下的表面Ra值均低于OG,表面Ra值的降低幅度最大达到20%,随振动幅值的增大,表面Ra值逐渐减小,当振幅增大到一定程度时,表面Ra值呈现增大趋势。结论 建立的LTUG形貌预测模型具有良好的准确性,在合适的工艺参数下,LTUG可明显降低表面Ra值,与OG相比,在相同时间内,LTUG作用下的磨粒运动轨迹长度更长,且LTUG区域的弹性变形对磨粒运动轨迹和最大未变形切削厚度均有不同程度的影响。     

曲面金属表面粒子掩膜电沉积微坑阵列研究

目的在曲面金属表面制作微结构阵列。方法提出一种采用界面转移法在曲面金属零件表面制作胶体粒子掩膜,并在胶体粒子间隙中电沉积金属制作微坑阵列的工艺。采用扫描电子显微镜和接触角测量仪,对沉积层的表面形貌和润湿性能进行检测。结果采用界面转移法可以在金属零件表面形成均匀排列的单层胶体粒子掩膜,在0.3 A/dm~2的电流密度下电沉积20 min去除粒子掩膜后,在曲面金属零件表面得到均匀排列的微坑阵列,单个微坑尺寸约为3.4μm。在0.3 A/dm~2的电流密度下电沉积10～50 min,微坑的尺寸随电沉积时间的增大而增大,疏水性随微坑尺寸的增大而先增大后减小,微坑尺寸为5μm左右时,沉积层的疏水性最好,其圆柱面接触角约为120°。结论采用界面转移方法制作胶体粒子掩膜并结合电沉积工艺,可以在曲面金属表面制作均匀的微坑阵列。带有微坑阵列的沉积层为疏水表面,通过调节电沉积电流密度和沉积时间可获得疏水性最好的微坑结构阵列。