Showing papers by "Harbin Institute of Technology published in 1990"

Tool wear and failure monitoring techniques for turning—A review

Abstract: Although a wide variety of tool failure sensing techniques have been developed over the years, few of them have been used in industries successfully. This paper provides a review of the numerous techniques and methods of monitoring tool wear particularly in turning operations. By and large, these techniques appear to be “single-minded” in that they are capable of detecting and diagnosing tool wear and failure relating to particular classes of faults. A universal approach which can detect the very many failure modes in tool condition monitoring has still not been devised.

Decomposition and dissolution kinetics ofδ' precipitation in Al-Li binary alloys

Abstract: Aside from its technological importance, the Al-Li alloy system also exhibits interesting phase transformations involving both equilibrium and metastable states. Recent theoretical studies have shown that a supersaturated solid solution could take different transformation paths when it is quenched into theα +γ′ field. Suggestions were made that a rapidly quenched solution phase should first undergo a congruent ordering transformation before it decomposes into a two-phase mixture by either a secondary spinodal decomposition or the classical nucleation and growth process. Moreover, a metastable miscibility gap was predicted at lower temperatures. The objective of this research is to study the transformation paths and dynamics in Al-Li binary alloys of three compositions (5.2, 7.0, and 12.0 at. pct Li). This investigation emphasizes thein situ small-angle X-ray scattering (SAXS) observations on specimens subjected to various aging conditions. Special attention is paid to the early stages of the transformation in an attempt to characterize the various possible modes of phase separation on one hand and to study the dynamics of the precipitation process on the other. The following results are obtained: the congruent ordering precedes decomposition at low temperatures; the metastableγ′ solvus curve is reconfirmed; but the predicted metastable miscibility gap is not found. Guinier radii measurements of the particles showed Ostwald ripening is quickly reached upon heating to the aging temperatures. Slowing down behavior is seen at aging temperatures close to the solvus boundary. Activation energies for Li diffusion were obtained using the modified Lifshitz, Slyozov, and Wagner (MLSW) model. A test of dynamical scaling behavior is carried out for the Al-12.0 at. pct Li alloy.

Variable-structure control approach of decentralised model-reference adaptive systems

Abstract: In the paper, the problem of decentralised model-reference adaptive control, for linear time-varying large-scale systems, is investigated by using a variable-structure control approach. The global reaching condition of the sliding mode of a composite system is derived and a new scheme of decentralised control is proposed. This scheme can guarantee the stability of a sliding manifold of the composite system. Furthermore, a modified scheme is given which makes the weighted sum of the sliding manifold motions converge to the prospective speed. Finally, a numeral example is calculated.

Modelling the three‐dimensional fluid flow and heat transfer in a moving weld pool

Abstract: A three‐dimensional model for the fluid convection and heat flow in arc welding is proposed. It extends the previous two‐dimensional model by accounting also for the fluid flow and heat transfer in a travelling rather than a stationary mode. The model can be applied to analyse the heat‐ and fluid‐flow phenomena in welding processes. It is found that the fluid velocity in the pool front is higher than that in the pool rear. The fluid velocity field and the temperature distributions are directly proportional to the welding amperage and inversely to the welding speed. The comparison of the calculated and measured results show that the model is much more accurate than Rosenthal's theory and the pure conduction numerical method. Theoretical predictions based on the model are found to be in good agreement with experimental measurements.

Performance of real time associative memory using a photorefractive crystal and liquid crystal electrooptic switches

Abstract: We present a real time holographic associative memory implemented with photorefractive KNSBN:Co crystal as the memory element and a liquid crystal electrooptic switch array as the reflective thresholding device. Our experiment stores and recalls two images and shows that the system has real time multiple-image storage and recall functions. An associative memory with a dynamic threshold level to decide the closest match of an incomplete input is proposed.

Motion compensation for ISAR and noise effect

Abstract: A method of motion compensation for inverse synthetic aperture radar (ISAR) is proposed. The techniques of interpolation, cross correlation, and estimation are used together. Essential to the method is the fact that avoiding cross-range image aliasing due to Doppler ambiguities requires range profiles to be generated at an adequate rate. The effect of noise on motion compensation is studied by means of simulation. The quality of the reconstructed image is used to evaluate the method. >

Wechselwirkungen zwischen WIG-Schweißlichtbogen und fokussiertem Laserstrahl

Abstract: Die Gemeinsamkeit zwischen dem Lichtbogen- und dem Laserstrahl-schweisen liegt in der Bildung eines Plasmas oberhalb des Einwirkortes /1/. Daher richteten sich die den Untersuchungen zugrundeliegenden Fragestellungen auf die Beeinflusbarkeit des Schweislichtbogens durch einen fokussierten Laserstrahl und auf die mogliche technische Bedeutung eines solchermasen kombinierten Schweisverfahrens /2,3/.

Thermally stimulated current studies on polyimide film

Abstract: We have experimentally observed that there are two peaks in the TSC-spectra of Du Pont polyimide film. The low temperature peak which appears in the 50°-70°C temperature range is possibly ascribed to the dipole depolarization of unimidized polyamic acid in the film, whereas the high temperature peak which exists in the 160°- 180°C temperature range is clearly due to the depolarization of the space charge of ions, according to our experimental results. The ions are principally generated through the ionization of unimidized polyamic acid and are bound into a Frohlich two-potential well.

Microdiffraction study of β-SiC whiskers in an SiCW-6061Al composite

Abstract: The crystal structure of β-SiC whiskers in an SiC W -6061Al composite was studied by microdiffraction. The results show that there are two kinds of whiskers which have hexagonal and trigonal shapes in transverse section. It was found that the trigonal whisker is a single crystal which has the f.c.c. structure and grows along the direction [1 1 1] fcc . The hexagonal whisker consists of thin crystal layers which have f.c.c. and h.c.p. ( a = 3.082 A , c = 5.032 A ) structures respectively and stack along the growth direction [1 1 1] fcc // [0 0 0 1] hcp with ( 2 1 1 ) fcc // (1 0 1 0) hcp . A twin relationship was found to exist between the thin f.c.c. crystal layers, the twin plane being (1 1 1) fcc . The side faces for both the hexagonal and trigonal whiskers are {1 1 2} fcc . On the basis of the above results, the reason why the whiskers have different shapes is discussed.

A new method of motion compensation for ISAR

Abstract: A detailed consideration of the accuracy requirement for the compensation for the inverse synthetic aperture radar is presented. A new scheme of the motion compensation is submitted, in which the overall target, not any particular target scatter, is tracked to do the motion compensation. Some experimental results are given. The results indicate that this scheme of motion compensation is effective and feasible. >

An application of topological method to analysing the three-dimensional flow in cascades (II)—Topological analysis on the vector field patterns of skin-frictions and section streamlines

Abstract: With an application of topological analysis, in this paper the skin-friction line patterns on compressor and turbine cascade surfaces are depicted and the streamline patterns of the secondary flow fields in the cross-section of a curved pipe and a turbine cascade are drawn under given conditions. In addition the structures of vortices within three-dimensional viscous flow fields in cascades are analysed.

The inspection of solder joints on printed circuit boards by phase-shift holographic interferometry

Abstract: The principle of inspecting solder joints on printed circuit boards (PCBs) by phase-shift holographic interferometry is described. By using this technique, defective solder joints can be easily distinguished from good ones without analysing complicated holographic interferograms. Experiment shows that most defects in solder joints, such as breaks and voids, can be detected successfully.