A holistic integrated dynamic design and modelling approach applied to the development of ultraprecision micro-milling machines

Ultraprecision machines with small footprints or micro-machines are highly desirable for micro-manufacturing high-precision micro-mechanical components. However, the development of the machines is still at the nascent stage by working on an individual machine basis and hence lacks generic scientific approach and design guidelines. Using computer models to predict the dynamic performance of ultraprecision machine tools can help manufacturers substantially reduce the lead time and cost of developing new machines. Furthermore, the machine dynamic performance depends not only upon the mechanical structure and components but also the control system and electronic drives. This paper proposed a holistic integrated dynamic design and modelling approach, which supports analysis and optimization of the overall machine dynamic performance at the early design stage. Based on the proposed approach the modelling and simulation process on a novel 5-axis bench-top ultraprecision micro-milling machine tool – UltraMill – is presented. The modelling and simulation cover the dynamics of the machine structure, moving components, control system and the machining process, and are used to predict the overall machine performance of two typical configurations. Preliminary machining trials have been carried out and provided the evidence of the approach being helpful to assure the machine performing right at the first setup.     

A simple model for the oxidation of carbon-containing composites

The isothermal oxidation mechanism of the carbon-containing composites has been investigated based on the experimental data reported in the literature. The results showed that the oxidation kinetics was affected not only by temperature and time but also by carbon content and the sample shape. For the oxidation kinetics, a series of quantitative kinetic models have been developed based on the controlling step. In this model, the effects of carbon content, sample size and temperature on the reaction fraction have been especially discussed. Incorporation of the experimental data into the new model indicates that a good agreement has been reached.     

柱胞夹芯复合材料动态特性的模态研究

薄壁半椭球壳是一种新型的柱胞单元,具有轻质、跨度高、承载能力强等优点。设计了一种以薄壁球壳周期排列作为复合材料芯层的柱胞夹芯复合材料,利用将ANSYS有限元模态分析与模态实验相结合的方法研究其模态特性,发现两者结果吻合较好。利用被验证的模型研究了薄壁球壳的赤道半径(r_1)、极半径(r_2)、赤道半径/极半径(r_1/r_2)及壁厚对柱胞夹芯复合材料模态频率的影响规律。研究发现:柱胞夹芯复合材料的模态频率随着球壳单元赤道半径或极半径的增大而增大,随着壁厚的增大而逐渐减小。球壳弹性模量增大到一定值以后,壁厚对频率的影响程度减弱。当r_1/r_2小于1时,模态频率呈增大趋势,当r_1/r_2大于1时,模态频率随比值的增大而逐渐减小,即芯层球壳越接近圆形,柱胞夹芯复合材料的固有频率越大。     

Morphological and dynamic mechanical studies on polybibenzoate-polypyrrole composites

Polypyrrole composites electropolymerized on polybibenzoate samples were studied by scanning electron microscopy and dynamic mechanical analysis. The micrographs of the composites show their porous structure. The dynamic mechanical measurements reveal the three relaxations of the host polybibenzoate and the glass transition of the polypyrrole.     

A novel approach to fixture layout optimization on maximizing dynamic machinability

In the aerospace industry, the reasonable layout of fixture can efficiently suppresses machining vibration of thin-walled aerospace structure during machining. Based on the analysis of typical structural components encountered in the aerospace industry, a general frame-structure workpiece with fixture constraints can be equivalent as Mindlin plates with simultaneous elastic edges and internal supports. On basis of the equivalent models, the powerful pb-2 Ritz method defined by the product of a two-dimensional polynomial and basic functions can be introduced to be taken as trial functions. Substituting displacement functions into energy functional and minimizing total energy by differentiation leads to eigenfrequency equations of the workpiece–fixture system. Consequently, a novel nonlinear programming problem based on the frequency sensitivity can be built to optimize the layout of fixture supports to maximize the fundamental nature frequency of the workpiece–fixture system. The feasibility of the proposed approach is validated by a machining case.     

The failure of fiber-reinforced ceramic-matrix composites under dynamic loading

High-strain-rate compressive failure mechanisms in fiber-reinforced ceramic-matrix composite materials have been characterized. These are contrasted with composite damage development at low strain rates and with the dynamic failure of monolithic ceramics. It is possible to derive significant strain-rate strengthening benefits if a major fraction of the fiber reinforcement is aligned with the load axis. This effect considerably exceeds the inertial microfracture strengthening observed in monolithic ceramics and nonaligned composites. Its basis is shown to be the transspecimen propagation time period for heterogeneously-nucleated, high- strain kink bands. For high-strain-rate tensile loading conditions, it is found that behavior is not correctly described by the current matrix fracture/fiber pullout models. This is a consequence of the rapid and extreme frictional heating produced at the fiber-matrix interface by sliding velocities on the order of 100 m/s. At rapid loading rates, the near-interface matrix appears to virtually melt, and the frictional interface shear resistance is reduced to the point that the fibers debond throughout the specimen, and pull out without failing. This suggests that for sufficiently rapid loading, the stress to fail the composite will approach that merely to create the initial matrix crack (i.e., a stress level well below the ultimate strength normally attainable under quasistatic conditions).     

Quasi-static and dynamic compression behaviors of metallic glass matrix composites

Compressive tests were conducted on metallic glass matrix composites at a series loading rates. It was found that mechanical properties of the composite, e.g. yielding stress and plasticity, have a week dependence on strain rates of 4.0 × 10⁻⁴ s⁻¹–4.0 × 10⁻¹ s⁻¹. Four composites were tested at a constant strain rate of 2.3 × 10 s⁻¹ to uncover the dynamic deformation behaviors. Compared with the quasi-static case, the yielding strength increased under dynamic loading rate, but the plasticity decreased significantly. On the other hand, the dynamic compressive has closely relation with the dendrite size and volume fraction. The decreasing of the dendrite size and volume fraction leaded to the dynamic yielding strength increased but the plasticity decreased. For a same composite, e.g. T1 alloy, the yielding strengths increased slightly but fracture strain decreased with increasing of dynamic strain rates.     

Study of cyanoethylated alfa fiber reinforced composites by dynamic mechanical analysis

Cyanoethylation of long alfa fibers was studied, and these chemically modified fibers were used to manufacture alfa-polyester composites. The dynamic mechanical thermal properties of an unsaturated polyester resin (cured) and of composites of unmodified and chemically modified alfa-polyester were studied using a dynamic mechanical analyzer over a wide temperature range. The data suggest that in spite of the fragility of the cyanoethylated alfa fibers compared to the unmodified ones, both unmodified and modified alfa-polyester composites manifest the same order of mechanical properties: T_g, tan δ and E′ values are very near in the two cases. Fragility of fibers is compensated by the better interfacial bond between the fibers and the matrix. The scanning electron micrographs of the fracture surface of the samples reveal the improved bonding at the interface between the cyanoethylated fiber and the polyester resin. The article is published in the original.     

TiC颗粒增强钛基复合材料的静动态力学性能

利用伺服式疲劳实验机和杆一杆型冲击拉伸实验机对TiC颗粒增强钛基复合材料TP650和基体钛合金的静动态力学性能进行研究,得到不同应变率下复合材料的应力一应变曲线.结果表明,复合材料和基体材料的屈服应力均随应变率的增加而提高,属于应变率敏感材料;TP650的破坏形式以颗粒附近基体的撕裂以及颗粒与基体合金的脱粘为主,几乎没有发生颗粒破碎现象.假设复合材料的微观结构为非均质单胞在空间的周期性重复排列,利用有限元软件对钛基复合材料的静动态力学性能进行数值模拟研究,计算结果与实验结果吻合良好.进一步通过数值模拟预测了颗粒形状和颗粒体积分数的变化对TiC颗粒增强钛基复合材料静动态力学性能的影响.     

High-speed contouring using a novel dynamic interpolation mechanism

The authors examine the development of algorithms to minimise position error during high-speed contouring operations. The approach taken is to dynamically modify the interpolation process at each loop closing based upon an examination of the current actual and desired state of all axes. The decision rules arising from the analysis are implemented within an existing open architecture control system which allows both the rapid communication of state and actioning of decisions. Experiments demonstrating the effectiveness of the approach are presented.     

New standardized procedure for the measurement of the static and dynamic properties of forming machines

The geometrical accuracy and the surface quality of sheet metal parts as well as the tool wear are influenced by process parameters and by static and dynamic interactions between the press and the tool. Therefore the qualitative characterization of the machine behavior is of high importance for both press manufacturers and press operators. Within research project (Behrens et al. in Entwicklung und Erweiterung standardisierter Messverfahren zur statischen und dynamischen Pressenvermessung. Final Report of the AiF Research Project 13742 N, 2005), a procedure for the measurement of the static machine behavior has been developed, which for the first time allows the standardized measurement of the ram deflection and the bolster plate deflection along with previously standardized characteristic values. The determination of the procedure as measurement directions and the automated evaluation of the measurements ensure not only reproducible results but also easy comparison of two machines. Additionally a new procedure for the measurement of the dynamic press behavior has been standardized which allows the comparison of the static and the dynamic characteristic values. The project [1] was funded under number AiF 13742 N by the Arbeitsgemeinschaft industrieller Forschungsvereinigungen “Otto von Guericke” e.V. with budget funds from the German Federal Ministry of Economics.     

Covercrete with hybrid functions – A novel approach to durable reinforced concrete structures

Due to the corrosion of steel in reinforced concrete structures, the concrete with low water–cement ratio (w/c), high cement content, and large cover thickness is conventionally used for prolonging the passivation period of steel. Obviously, this conventional approach to durable concrete structures is at the sacrifice of more CO₂ emission and natural resources through consuming higher amount of cement and more constituent materials, which is against sustainability. By placing an economically affordable conductive mesh made of carbon fiber or conductive polymer fiber in the near surface zone of concrete acting as anode we can build up a cathodic prevention system with intermittent low current density supplied by, e.g., the solar cells. In such a way, the aggressive negative ions such as Cl^?, , and can be stopped near the cathodic (steel) zone. Thus the reinforcement steel is prevented from corrosion even in the concrete with relatively high w/c and small cover thickness. This conductive mesh functions not only as electrode, but also as surface reinforcement to prevent concrete surface from cracking. Therefore, this new type of covercrete has hybrid functions. This paper presents the theoretical analysis of feasibility of this approach and discusses the potential durability problems and possible solutions to the potential problems.     

新型纳米铜/石蜡复合材料的制备及其热性能

采用高能球磨法制备了纳米铜/石蜡温敏复合材料。通过傅立叶变换红外光谱仪(FTIR)、X射线衍射仪(XRD)和高分辨透射电镜(TEM)等对复合材料进行了成分、物相和微观形貌的分析研究,并测试了材料热膨胀性和热敏性。结果表明,复合材料主要由铜、石蜡及少量氧化亚铜组成。石蜡在铜粒表面包覆均匀,形成类似核-壳结构。铜粉和石蜡的质量比对复合材料热膨胀性和热敏性影响明显。     

A novel way to produce bulk SiCp reinforced aluminum metal matrix composites by friction stir processing

Friction stir processing (FSP) has been developed to produce upper surface modification of metallic materials in recent studies. The feasibility to make bulk dispersal SiCp reinforced Al metal matrix composites (MMCs) were studied successfully in this paper. The distribution of well-dispersed SiCp got a range of 5 mm × 2 mm on the cross-section of joints. Excellent bonding between SiCp and base metal can be obtained by this process. The percentage of SiCp over 1.5% was found in the bulk reinforced region not only confined to 100 μm magnitude under the upper surface. The microhardness of MMCs can reach steady 10% higher than the one of the base metal (about HV88) at the depth of 1.0 mm under surface.     

A simple, novel method for the preparation of metallophthalocyanines

New metallophthalocyanines (Me---Pc) in the crystalline form were synthesized by the direct reaction between the 1,2-dicyanobenzene and filings of the metallic elements or intermetallic alloys. The reaction took place at about 480 K in vacuum over a few days. Some remarks on the reaction mechanism of the Me---Pc formation are made. It is assumed that under the experimental conditions used the 1,2-dicyanobenzene liquid undergoes a catalytic tetramerization. The catalytic atom of the metal is simultaneously coordinated by the forming tetramer.     

一种新型动态电弧电子模拟负载的研究

提出了一种新型的电子模拟负栽，并通过理论分析和大量的实验研究证明了采用这种电子模拟自载模拟动态电弧的实时变化是可行的。     

Surface characterization of novel alumina-based composites for energy efficient sliding systems

Friction, wear, and lubrication have direct influence on performance, reliability, and service life of devices that contain moving components. These are universal in applications of energy conversion, power generation, energy harvesting in the broader fields such as agriculture, transportation, drug delivery, and bioengineering. The useful life of these systems and their energy efficiency can be improved by improving the surface properties (performances) of sliding systems. Further, the applications of sliding systems are limited in extreme environments such as high temperature and space application etc. due to their limited surface properties. Therefore, development of a new class of materials with superior surface properties will improve the energy efficiency, sustainability, and applicability. This paper focuses on development of self-lubricating materials with superior surface properties for reduced friction and wear applications.