The correlation model of acoustic emission in fine diamond turning

The process of cutting of an aluminum alloy has been monitored by the acoustic emission method. Single-crystal natural and synthetic diamond tools have been used in the investigation. The comparative analysis has demonstrated that the correlation model of acoustic emission, which was put forward by Pan and Dornfeld, is valid for the conditions of fine diamond turning of aluminum alloys.     

基于改进CRITIC法的TBM刀具声发射信号研究

针对地下施工中TBM(Tunnel Boring Machine)刀具磨损更换频繁且缺乏有效方法对其状态进行评估问题,将声发射技术用于TBM刀具检测,以TBM模态掘进试验台为对象,采集不同磨损程度的滚刀声发射信号研究声发射单特征参量及多特征参量对滚刀磨损状态趋势评估影响,提出基于改进CRITIC声发射多特征融合刀具状态评估新方法。滚刀磨损量测试表明,改进CRITIC声发射多特征融合后所得评估值对刀具磨损信息更敏感,能有效评估及预测刀具磨损状态,可为TBM刀具现场检修、保养提供指导。     

Investigation of the influence of a waveguide on changes in the parameters of acoustic emission signals

We investigate the influence of waveguides used in acoustic emission tests of materials in corrosive environments on changes in the parameters of acoustic emission (AE) signals. A method of boundary interpolation is suggested for determining the natural frequencies of the waveguides. This method enables one to perform calculations for cylindrical waveguides of various lengths and diameters. We present analytic relations used to select a waveguide with the required geometric parameters in agreement with the resonance bandwidth of an AE transducer. This selection reduces the losses of AE signals in passing through the waveguide. Experimental investigations of the attenuation of AE signals in the waveguide are also carried out.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 2, pp. 64–71, March–April, 1994.     

The study of the influence of wear of a cutting tool of cBN-based composite material on the tool fracture probability in the finish turning of hardened steels

The authors have experimentally clarified the influence of the tool wear on the tool fracture probability in the finish turning of hardened steels of various hardness values using a tool with a round cutting insert of cBN/Si₃N₄ composite. The maximum stresses and fracture probability have been determined for the tool face and flank. Recommendations regarding the use of cBN/Si₃N₄-inserted cutting tools are provided.     

The study of the influence of wear of the cutting tool with an insert of cBN-based composite material on the tool vibrations in finish turning of hardened steels

It has been found out that wear of a cutting tool with an insert of cBN-based composite material has an effect on the tool vibrations in finish turning of hardened steels with various hardness values. The influence of the tool vibrations on the machined surface roughness has been studied.     

Experimental and analytical characterization of acoustic emission signals

The identification of crack growth signals is extremely important in order to effectively use acoustic emission techniques to detect, locate, and determine the significance of an internal flaw. The results of an analytical methodology, incorporating a source model that is an actual crack propagation and arrest event, are presented in this paper to predict a time dependent acoustic emission signal. The integral equation method is used to calculate the dynamic Mode I stress caused by a crack propagating with a prescribed velocity, after which the displacements at any point are calculated. These time dependent displacements are the analytical form of the acoustic emission waveforms. An experimental procedure, which uses a laser interferometer to measure velocities normal to the specimen's surface, is used to investigate acoustic emission waveforms in a compact tension specimen. The experimental results are used to verify the analytical model.     

An investigation of the effects of material anisotropy and heterogeneity on pulsed, laser-generated acoustic signals

Point-source and line-source models for the laser ultrasonic source in materials exhibiting transverse isotropy are applied to the specific problem of laser generation and ultrasonic propagation in unidirectional, polymer matrix composite materials. Comparing experiment and theory, it is shown that these composite materials exhibit homogeneous behavior, at the frequencies investigated, for ultrasonic wave propagation perpendicular to the fiber direction. For ultrasonic propagation in the fiber direction, ultrasonic dispersion, resulting from the inhomogeneous nature of the composite, affects the laser ultrasonic signal.     

The study of wear of cutting tools of cBN-based composite material and the influence of tool wear on cutting forces in turning hardened steels

The paper presents some findings of the investigation of finish turning of KhVG hardened steel using a cutting tool with an insert made of a cubic boron nitride based composite (cBN-Si₃N₄ system). The behavior of tool wear throughout the machining time as well as the influence of the tool wear on cutting force components and resulting cutting force have been clarified.     

Influence of tool material and tool wear on tool temperature in hard turning reconstructed via inverse problem solution

In this work the cutting tool temperature distribution that develops during turning of hardened cold-work tool steel is modeled on the basis of experimental data. The data obtained from a series of thermocouples, placed on a PCBN insert, into an anvil, and into a toolholder, were used as the input for the model. An inverse problem was solved, where the heat fluxes were computed. The temperature distribution was modeled for the case of new tools, as well as for the case of its development in the course of a tool wear. The reconstructed temperature distributions were in good agreement with the measured data. The heat flux through rake face was found to be reducing with the decrease of thermal conductivity of the tool material.     

An experimental study of fluidized-bed coating: influence of operating conditions on growth rate and mechanism

This study investigates the influence of fluidizing gas velocity, atomizing air, and liquid flow rates, liquid concentration, initial bed mass, and particle size on the mechanism of growth of sand particles in a batch fluidized-bed coater. An aqueous solution of NaCl was used as the coating liquid and sprayed in the bed by means of a pneumatic atomizer. The results showed that for a given particle size, the fluidizing air velocity was the most important factor affecting the coating kinetics and stability. The dominant mechanism was the onion-ring layering, especially at excess gas velocities higher than 0.27 m/s. For a fixed value of the mass ratio of solute introduced in the bed to the initial particle mass, binder concentration, liquid flow rate, and the initial bed weight had no effect on the growth mechanism. The deposition quality was found to be affected by the droplet size. A decrease of droplet size resulting from increasing the atomizing air flow rate permitted homogenous coating of the solid surface.     

光导热塑全息特性实验研究

本言语对光导热塑全息记录材料的某些特性进行了探讨，提出了一种简便实用的光学测试方法，给出了实验结果，并对实验中有关问题进行了讨论。     

Identification of signals in the context of acoustic emission in concrete

The study presented in this paper is placed in the context of the frequency analysis of acoustic emission in concrete. The purpose is to study the ability to identify an acoustic emission event by deducing its spectrum from a detected signal. The identification is carried out progressively so as to separate the various functions involved in the acoustic emission process, and to approach the usual conditions of acoustic emission processing during fracture tests of concrete specimens. Impulses of different forms are generated on the surface of concrete test specimens, and the signals detected are analyzed. The identification of signals takes into account the frequency response of the transducers and the wave attenuation as function of the frequency.     

An acoustic emission study of plastic deformation in polycrystalline aluminium

Acoustic emission experiments were performed on polycrystalline and single crystal 99.99% aluminium while undergoing tensile deformation. It was found that acoustic emission counts as a function of grain size showed a maximum value at a particular grain size. Furthermore, the slip area associated with this particular grain size corresponded to the threshold level of detectability of single dislocation slip events. The rate of decline in acoustic emission activity as grain size is increased beyond the peak value suggests that grain boundary associated dislocation sources are giving rise to the bulk of the detected acoustic emissions.     

北流白话单字调声学实验研究

北流白话与博白白话、玉林白话的差别是相当大的,为填补北流白话研究的空白,丰富方言学和声学语音学研究的内容,特利用实验语音学的方法,借助实验手段对北流六麻白话单字调的情况进行研究分析,并根据声学实验数据和五度标调法确定该方言九个调类的调值,发现该方言的调型和调类也与北流市区的白话不同,从声学特征的角度对此逐一进行较为细致深入的阐述说明。与北流市区白话和广州话相比,该方言的声调呈现出“过渡”特征,即向广州话靠拢,这可以从地理位置上得到合理的解释。     

An experimental study on the influence of particles on grain boundary migration

The pinning effect of particles on grain boundary migration was studied in a Fe–20 mass% Cr alloy deoxidised with Ti and Zr. The different nitrogen contents (65, 248 and 490 ppm) were used to vary the number of precipitated inclusions. The specimens from equiaxed zones of metal samples with different particle densities were examined by in situ observations during a 60-min holding time at 1200 and 1400 °C in a Confocal Scanning Laser Microscope. The change of particles pinning effect on the grain growth was described by an average grain size, [`(D)]_textA bar{D}_{text{A}} , and the ratio between the perimeter and area of grains, P _GB/A _G. It was found that the pinning effect of particles (mostly complex Ti–Zr oxynitrides) on grain growth decreased with a decreased nitrogen content in the metal. Furthermore, the effect of particles decreased with an increased temperature of treatment, due to the reduction of the number of particles on the grain boundaries.     

Optimal machining conditions with costs of quality and tool maintenance for turning

Although there is a voluminous literature on machine tool economics, the cost of machining quality has received little attention. In this paper, we develop a timedynamic economic model for single-pass turning. The model incorporates considerations on the stochastic nature of tool-life and such tool maintenance activities as tool replacement and tool regrinding. We model the quality cost of tool-cutting in terms of deviation from target roughness and deviation from target dimension. The cost of deviation is either the Taguchi type under continuous assumption or in terms of the cost to the entire workpiece under discrete assumption. The connection between quality cost and tool maintenance cost is explicitly addressed. Essentially, quality cost as well as machining cost is a function of two sets of decisions: machining conditions as defined by the choice of cutting speed and feed rate (depth of cut is a constant in single-pass operations), and the condition of the cutting tool as defined by the tool retirement and regrinding policy. The cost of tool failure is also incorporated.     

基于RDT和WT方法识别超高层建筑的模态参数

摘要：超高层建筑风致振动相关的动态参数尤其是阻尼比数据资料的缺乏会增加设计阶段动态参数准确选取的难度。因而,现役超高层建筑动态响应的实测与参数识别对这些动态数据资料的补充和设计准确性的校验是十分必要的。本文将基于强风作用下超高层建筑—上海金茂大厦动态响应的现场实测,使用Morlet小波变换并且结合随机减量技术(RDT)识别上海金茂大厦的固有频率和阻尼比。数值结果表明,上海金茂大厦固有频率的识别非常精确,但发现阻尼比的识别随着阶数的升高其标准差有增大的趋势。     

The impact of surface integrity by hard turning versus grinding on rolling contact fatigue – Part I: Comparison of fatigue life and acoustic emission signals

Hard turning and grinding are finishing processes for the manufacture of precision components, such as bearings, gears and cams. However, the effects of distinct surface integrity by hard turning versus grinding on rolling contact life are poorly understood. Four representative surface types were prepared: as-turned, as-ground, turned and polished and ground and polished. Surface integrity was characterized by surface topography, microstructure and micro/nanohardness. Fatigue tests were performed with an acoustic emission sensor and the signal processing software. The surface topographies show that skewness of the as-ground surface is much more negative than the as-tuned one while other surface parameters are equivalent. The turned surface has a thicker strain hardened zone and a thinner thermal affected zone than those of the ground one. The ground surface has higher micro- and nanohardness on surface and in the subsurface than the turned one. The amplitude of acoustic emission signal is the most stable and sensitive signal to fatigue failure. The turned surface may have a longer life (> 84%) than the ground one with equivalent surface finish. The fatigue lives of the bearing assembly are nearly identical for the turned surface versus the polished surface and the turned polished surface versus the ground and polished surface. In addition, polishing may not necessarily improve fatigue life of the machined surface, but increase bearing assembly life as much as 40%.