微流体速度流型影响因素数值模拟分析

微流体速度流型对微流控芯片分离分析和混合反应效果都有重要影响。本文采用数值分析的方法研究在压力驱动和电渗驱动方式下管道大小与形状、弯曲管道以及表面粗糙度对微流体速度流型的影响。模拟结果表明管道的形状和大小对微流体的动量传递有很大的影响,进而影响微流体的速度流型。电渗驱动下弯道引起的弯道内外径速度差可以通过改变弯道形状和电渗强度的方法进行改善。对摩擦力的模拟中发现小管径密集粗糙颗粒的情况下得到的流型是最好的。模拟结果对微流控芯片的设计加工具有一定的指导意义。     

Improvements in the prediction and characterization of the thermoelastic response of glass-fibre reinforced composite products

Significant improvements in the prediction of the thermoelastic constant of SMC (sheet moulding compound) have been made as a result of the use of the iso-stress version of the Young's modulus of the polyester—limestone matrix (i.e. the “series” rule of mixtures version) in place of the iso-strain version (i.e. the “parallel” rule of mixtures version). The thermoelastic constants of GMT (glass-mat-reinforced thermoplastic) and RTM (resin-transfer-moulded material) can also be accurately predicted. The property variations in large moulded GMT panels, with nominal glass contents of 20% and 40%, have been studied using the SPATE equipment and a thermoelastic technique has been developed, based on the simple disc specimen subjected to two opposed in-plane compressive forces, for the determination of the principal material directions in these panels.     

On the thermal expansion effects in the transverse direction of laminated composite plates by means of a global-local higher-order model

In this paper, a new efficient global-local higher-order model is proposed for the thermoelastic analysis of laminated composite and sandwich plates. The proposed model takes into account explicitly the contribution of thermal expansion in the transverse displacement component. To satisfy the transverse displacement continuity along the thickness direction, the continuity condition of transverse displacement at interfaces, which is not satisfied in many other schemes, has been a priori enforced. This model fully satisfies the free surface conditions and the geometric and stress continuity conditions at interfaces. As the number of variables of the proposed model is independent of the number of layers of laminates, compared to the 1,2-3 theory proposed by Li and Liu (1997) [20], the present model offers some significant improvements, and is able to predict accurately thermoelastic response of laminated plates under uniform temperature without a corresponding increase in the number of unknowns. The governing equations of equilibrium are derived by means of the principle of virtual displacements involving the thermal strain field. Applying Navier's technique, analytical solutions in terms of a double trigonometric series for simply supported laminated plates are presented. Results of benchmark examples are compared with the three-dimensional thermoelastic solutions as well as other published works. Numerical results show that the proposed model is more rigorous and can better predict the thermoelastic response in comparison with the 1,2-3 theory and other two-dimensional models.     

Effects of information loss in texture details due to the PIFS encoding on load and friction in hydrodynamic bearings

Textured surfaces can significantly improve the performance of hydrodynamic bearings. However, there is no generally accepted method for their accurate and automated 3D characterization. A promising solution to this problem is partition iterated function system (PIFS) model, which encapsulates information about 3D topography of textured surfaces. However, some loss in surface details can occur. Therefore, before PIFS could be used, effects of this information loss on load and friction need to be investigated. In this study, this issue was addressed using a textured hydrodynamic pad bearing. The results obtained showed that PIFS models might become useful in characterization of textured surfaces.     

A solution to the stacking sequence of a composite laminate plate with constant thickness using simulated annealing algorithms

Due to its high reliability, composite material is commonly used in industry. Moreover, the stacking sequence is very crucial to the strength of the composite material. However, the arrangement of this sequence is very time-consuming. Actually, since stacking sequences are usually NP complete, simulated annealing (SA) algorithms were borrowed to deal with the stacking sequence problems in this study. The edging stress of a composite plate with constant thickness, which was obtained using an analytical method, was used as the objective function in the SA algorithms. Three examples of constant thickness and symmetrical composite laminate plates were used to examine the performance of the proposed algorithms. The results of computational tests presented are very promising.     

神经网络对磨损自补偿摩擦副磨合过程的预测

利用ＢＰ人工神经网络建立了磨损自补偿状态下的摩擦副磨合特性预测的仿真计算模型。用Ｌ－Ｍ规则进行神经网络学习训练可使网络收敛快,误差小。网络输出结果与实验结果比较有极好的吻合性。该神经网络可用于青铜－４５＾＃钢摩擦副表面粗糙度对磨合特性影响的准确预测,亦可为工程设计人员在摩擦学设计是提供有效的计算工具。     

Investigating the Effect of Surface Finish on Mixed EHL in Rolling and Rolling-Sliding Contacts

Surface finish may significantly affect the lubrication performance of a tribological interface through the influence of topography on micro/nanoscale fluid flows around localized contacts at surface asperities. This paper aims to study the mixed lubrication performance of a group of engineered surfaces, including turned, isotropically finished, ground, and dimpled surfaces, under different operation conditions by means of a deterministic mixed elastohydrodynamic lubrication (EHL) model. The honed surface was used to mate with other surfaces. The results indicate that a longitudinal contact ellipse favors longitudinally oriented mating surface roughness and that a transverse contact ellipse, as well as a line contact, prefers a transversely orientated mating surface roughness for lubrication enhancement.     

玻璃钢材料在便携式安检设备中的应用及展望

论文综合评述了玻璃钢材料的性能特点,采用玻璃钢材料代替传统金属材料,采用传统的手糊成型工艺方法制作了线扫描平板便携式安检设备的机箱。实际应用表明,玻璃钢材料质量更轻、强度更高,使用寿命更长,可设计性更强,加工工艺性较好,能完全满足便携式安检设备的性能需要,采用该材料后设备体积减少约20%、质量减少约50%,提高了产品的市场竞争力。     

Complementary TEM characterization of a squeeze-cast metal-matrix composite by dissolution of the sample in butanol

Transmission electron microscopy observations of ion-beam thinned samples and samples extracted using a butanol dissolution technique gave information regarding the interface microstructure which could not be obtained from the ion-beam thinned samples, and that therefore both these sample preparation routes should be considered when observing aluminium metal-matrix composites in the transmission electron microscope.     

螺旋铣孔工艺参数对CFRP分层的影响研究

选取螺旋铣孔过程中切削速度、轴向进给以及偏心量为对分层产生主要影响的工艺参数。为得到建模所需数据,切削实验采用三因素三水平全因素实验设计,并使用螺旋铣孔工艺专用涂层刀具。基于实验数据,通过多元非线性回归-响应曲面法,建立分层缺陷和螺旋铣孔工艺参数之间的数学模型,并用MATLAB画出响应曲面图,最后通过曲面图直观地分析了三种参数对分层的影响,指出两个导致分层的主要因素。