High strain rate induced initial chip formation of certain metals during micromachining processes

Abstract

As microtechnology and nanotechnology become increasingly important to the needs of society, the need to create devices in engineering materials becomes more apparent. High speed milling has been shown to provide a great deal of promise in creating microstructures and in nanotexturing surfaces in engineering materials. Cutting tool rotation is expected to reach 1 000 000 revolutions per minute (rev min^?1) compared with conventional cutting speeds of around 30 000 rev min^?1. Rotating the tool this quickly reduces cutting forces, which produces a higher quality of cut so that post- processing is not required. Clearly, strain rates imparted to the workpiece at these speeds are very high and this influences initial chip formation and chip removal mechanisms. High strain rates imparted cause distinct chip formations in engineering materials to occur which are similarly observed in other materials, most notably biological materials such as cancellous bone. Certain soft metals such as aluminium do not machine very well because the material adheres to the cutting tool. However, high strain rates tend to overcome these limitations. This paper examines high strain rate initial chip formation in metals, compares these results to other materials, and shows that an initial chip curl model can be applied to describe high strain rate machining phenomena at the microscale.     

19—A STUDY OF NEEDLED FABRICS. PART VI: THE MEASUREMENT OF PUNCHING FORCE DURING NEEDLING

An account is given of an investigation in which a small needle board was fitted to the compression cage of an Instron Tensile Tester and used to measure the forces developed during the penetration of a web by needles. The punching speeds were much lower than those in a needling machine. The effects of web weight, type of fibre, fibre length and fineness, density, a reinforcing base fabric, and punching speed were studied.     

无线传感器网络实时传输协议的研究与实现

无线传感器网络能够协作地实时监测、感知和采集网络分布区域内的各种环境或监测对象的信息,并对他们进行处理,然后传送到用户。在该过程中,数据的实时传输协议对应用的成功起着至关重要的作用。基于TinyOS1.1.11平台对SPEED协议进行了实现,解决了反向压力和拥塞后的恢复问题,并对其进行了测试,最后提出了能更好地满足实时无线传感器网络应用的一些思路。     

Iterative Path Tracking of an Omni-Directional Mobile Robot

We propose a path-tracking algorithm that is developed using an iterative learning control (ILC) technique and use the algorithm to control an omni-directional mobile robot. The proposed algorithm can be categorized as an open–closed PD-type ILC; it generates robot velocity commands by a PD-type ILC update rule using both previous and current information. When applied to the omni-directional mobile robot, it can decrease position errors and track the desired trajectory. Under the general problem setting that includes a mobile robot, we show that the proposed algorithm guarantees that the system states, outputs and control inputs converge to within small error bounds around the desired ones even under state disturbances, measurement noises and initial state errors. By using simulation and experimental tests, we demonstrate that the proposed algorithm converges fast to the desired path, and results in small root-mean-square (r.m.s.) position error under various surface conditions. The proposed algorithm shows better path-tracking performance than the conventional PID algorithm and achieves faster convergence and lower r.m.s. error than the existing two ILC algorithms.     

Substrate temperature effect on the photophysical and microstructural properties of fluorine-doped tin oxide nanoparticles

Transparent conducting oxide of fluorine-doped tin oxide (FTO) thin films was deposited from chemical solutions of tin chloride and ammonium fluoride using streaming process for electroless and electrochemical deposition (SPEED) at substrate temperature 450, 500, and 530 ℃ respectively. The effect of substrate temperatures on the microstructural properties such as crystallite size, dislocation density, micro strain, volume of the unit cell, volume of the nanoparticles, number of the unit cell, bond length and the lattice constants were examined using XRD technique. Only reflections from (110) and (200) planes of tetragonal SnO₂ crystal structure were obvious. The peaks are relatively weak indicating that the deposited materials constitute grains in the nano dimension. Hall measurements, which were done using van der Pauw technique, showed that the FTO films are n-type semiconductors. The most favorable electrical values were achieved for the film grown at 530 ℃ with low resistivity of 7.64×10^-4Ω·cm and Hall mobility of -9.92 cm²/(V·s).     

Influence of Prior Deformation on The Sensitisation of AISI Type 304 Stainless Steel and Applicability of EPR Technique

Abstract

The influence of prior plastic deformation on the degree of sensitisation (DOS) of AISI 304 stainless steel has been studied for various levels of cold work ranging from 0 to 25% using the ASTM standard A262 practices A and E, and the electrochemical potentiokinetic reactivation (EPR) technique. Peak current density and reactivation charge density were determined from single loop EPR experiments and the ratio of the peak current during reactivation to that during activation was determined from double loop EPR experiments. The feasibility of using these techniques for determining the DOS in cold worked samples was examined. The reproducibility of the EPR results is rather poor. There appears to be no well defined systematic trend between the degree of cold work and the DOS as estimated from the EPR parameters. EPR parameters were found to be dependent on the temperature of aging and the degree of prior cold work. Threshold values above which a sample can be treated as sensitised cannot therefore be determined from EPR tests without being confirmed independently by conventional ASTM standard methods.     

A multi-link system control strategy based on biological reaching movement

In the multi-link arm control process, the problems of trajectory planning and trajectory realization have been recognized as being of key importance. We developed a technique by which to realize a reaching movement control of the multi-link arm system, which was inspired by experimental results for reaching movements of macaques or human beings. The proposed method can treat the effect of the dynamics of the multi-link system and the trajectory planning of the end-effector, which has a bell-shaped speed profile, as well as the difficulties of redundancies of multi-link systems. Two-link arm reaching movement experiments revealed the same features, as demonstrated by the results of biological experiments on humans and macaques. In addition, the results obtained using a two-dimensional four-link model in a standing-up movement control experiment agreed well with 'standing-up from a chair' movement of human beings. Since the proposed method has a simple structure and its implementation process is simple, the proposed method will be effective for use in a multi-link system control strategy.     

Classic contributions: cryogenic treatment Effects of cryogenic treatments on mechanical properties and wear behaviour of high-speed steel M2

Abstract

In this contribution, originally published in 2000, the levels of hardness, impact toughness and wear resistance of M2 high-speed steel after conventional heat treatment are compared with those imparted by additional subzero and deep cryogenic processing.     

Classic contributions: cryogenic treatment Influence of deep cryogenic treatment on microstructure,mechanical properties and dimensional changes of vacuum heat-treated high-speed steel

Abstract

In this contribution, originally published in 2002, it is shown that the microstructure of AISI M2 high-speed steel can be modified substantially by a vacuum heat treatment combined with a deep cryogenic treatment to optimise the ratio between hardness and fracture toughness. This ratio is affected significantly by the volume fractions of retained austenite and undissolved eutectic carbides, as well as by the mean distance between these carbides. Values calculated using a newly developed semiempirical equation prove that, for given vacuum heat treatment conditions, the volume fraction of retained austenite and the hardness have a significant effect on the fracture toughness. Analysis of vacuum heat-treated modified 'Navy C' ring specimens confirms that the dimensional changes can be controlled. The main factors that influence the dimensional changes are the volume fraction of retained austenite and the steel's hardness.     

Effect of Co60 gamma ray irradiation for carbon fibre on interfacial properties in epoxy resin composites

Abstract

In order to improve the interfacial adhesion between carbon fibre and resin matrix in composite materials, it is necessary to treat the surface of the carbon fibre. In this paper, γ-ray irradiation technique was used to modify polyacrylonitrile based carbon fibre. Laser Raman spectrum and X-ray photoelectron spectroscopy were used to investigate and analyse the structure and chemical composition near the surface of the carbon fibre. The influence of irradiation parameters on the interlaminar shear strength (ILSS) of carbon fibre reinforced epoxy composite materials and the bundle tension strength of carbon fibre was studied. The interfacial adhesion behaviour of composites was characterised using torsional braid analysis. The results show that after irradiation the ILSS of the composite was increased by 20%, while the glass transition peak of the specimen, determined from torsional braid analysis, shifts towards a higher temperature compared with an unirradiated specimen. The value of the glass transition temperature T _g is increased from 416.8 to 424.3 K. After irradiation there was no apparent change in the bundle tensile strength of carbon fibre. Investigations indicate that after irradiation the decrease of microcrystal size, the increase of surface free energy of carbon fibre surface and the active chemical function group formed from unsaturated carbon atoms improve the interface adhesion between the carbon fibre and the matrix in the composites.