Effect of growth-interrupted method on quality of AlGaAs/GaAs multiple quantum wells prepared by MBE

AlGaAs/GaAs multi-quantum well （MQW） was prepared by molecular beam epitaxy（MBE） with growth-interrupted heterointerface （GIH） method and continuous growth （CG） method, respectively. The microstructures Of the MQWs were characterized by double-crystal X-ray rocking curve （DCRC） and atomic force microscopy （AFM）, and the photoluminescence （PL） properties of the MQWs were also studied. The MQWs grown with GIH method show that higher order satellite peaks of Pendelloesung fiinges are observed in DCRC, the roughness of surface is much reduced in AFM, and the full width at half maximum （FWHM） of exciton line is much narrower in PL. The results indicate that the GIH method reduces the monolayer growth step density at the heterointerface due to the migration of surface atomsfor a few minutes grower interruption, and substantially improves the quality of AlGaAs/GaAs MQWs.     

A study on the influence of friction evolution on thickness changes in sheet metal forming

In this paper previous study on the influence of frictional contact effects on velocity field [2], is extended to the case of blank thickness variation with respect to some parameters characterising the friction evolution law. The algorithm presented can be used in sheet metal forming for the thickness distribution optimisation.     

An experimental study of the tribological behaviour of the brass/steel pair

This paper presents a study of the behaviour of the brass/steel pair in the presence of friction and wear. A plan of experiments, based on the techniques of Taguchi, was performed on a pin-on-disc machine. The objective was to establish a correlation between load, sliding velocity and temperature in contact with the wear and coefficient of friction. These correlations were obtained by multiple linear regression. Finally, confirmation tests were performed to make a comparison between the foreseen results from the mentioned correlations and the experimental results.     

An experimental study on the formability of intermetallic nickel aluminide

In this paper, the formability of ductile intermetallic Ni₃Al and limiting strains at room temperature are presented. Uniaxial tensile tests are carried out to identify uniform elongation, work hardening behavior, and fracture character. Forming limit diagrams are determined and the effect of biaxial deformation on limiting strains and failure modes are shown. The bulk formability is investigated by cold upset testing on continuous cast and extruded bars. Forming limit diagrams, both for bars and sheets, do not show a significant effect of thermomechanical processing and sheet thickness at the range of 0.30-0.46 mm. These observations are in agreement with common ductile metals where larger deformations are obtained in biaxial modes. Microcrack initiation at grain boundaries is shown to contribute to lower limiting strains in the plane strain region during sheet metal stretching and compression of intermetallic nickel aluminide.     

FEM study on the influence of air gap and specimen thickness on the detectability of flaw in the yoke method

The yoke method is usually used as a magnetic testing method of welds. In this paper, we study the influences of the air gap between the magnetic pole and the specimen surface on the average magnetic flux density passing through the specimen, and the specimen thickness on the leakage magnetic flux density from a flaw using finite element method (FEM). When the air gap increases the average magnetic flux density at the center of the specimen length decreases. We can estimate the intensity of the magnetic field on the specimen surface by extrapolating the magnetic flux density in space to that at lift-off being zero. Moreover, the maximum leakage magnetic flux density from a flaw decreases with increase in the specimen thickness even if the average magnetic flux density passing through the specimen is the same.     

An experimental study of spherical indentation on piezoelectric materials

The response of lead zirconate titanate and barium titanate piezoelectric ceramics to spherical microindentation was investigated. Force vs penetration depth curves obtained from instrumented indentation reveal that the indentation stiffness depends on the material condition (i.e. poled vs unpoled) and the type of indentor (i.e. electrically conducting vs insulating). Good agreement was found between the experimental results and predictions of an analytical model of Giannakopoulos and Suresh (1999) for the spherical indentation of a transversely isotropic piezoelectric material. A parametric analysis was conducted to identify key material properties that influence the indentation response. An error analysis was performed so as to assess the influence of the variabilities in constituent properties on the scatter in the measured indentation stiffness. This indentation method has been shown to offer a new methodology for characterizing some properties of piezoelectric materials. Advantages and limitations of such a technique are discussed.     

An experimental study on the corrosion amount using a statistical analysis

A non-destructive estimation of the corrosion amount in the existing RC structure is highly desired and therefore this paper presents a proof-of-concept experimental demonstration of such a method, which is based on the eddy heat imaging (EHI) technique. Its basic principle is to convey a corrosion signal to the surface of RC structures by eddy heating. To develop the EHI method, the first key step is to address the question of whether the rate of change in surface temperature is strongly associated with the corrosion amount. In order to make the problem tractable, special equipment was designed, from which 81 observations were obtained for data analysis. After the statistical analysis of the observational data and preliminary application on an in-service bridge, the results show that the EHI method is a promising approach to the quantitative measurement of the corrosion amount of RC structures.     

试验因素对波纹度影响的分析

汽车板冲压成形表面波纹度对零件涂装后的鲜映性有着重要的影响,而鲜映性直接反映汽车外观质量.为明确波纹度影响因素,测量准确可靠的试验数据,基于gom在线应变测量系统,通过BUP1000板材综合成形试验机对典型汽车外板进行马克杯冲压,分析了冲压后不同变形量、试样表面检测方向及试样冲压速度等因素对试样表面波纹度的影响.研究结...     

An experimental and theoretical investigation of the influence of stress state on cavitation during hot working

The effect of stress triaxiality on cavity growth during necking in the hot tension test was investigated and quantified. Experimentally, Ti–6Al–4V specimens deformed over a range of temperatures and strain rates developed necks of different sharpness and thus of varying levels of the ratio of hydrostatic to effective stress. The magnitude of these stresses was calculated using the classical work of Bridgman. Metallographic examination revealed that the average cavity size, cavity population, and cavity volume fraction were higher in the central region of each specimen as compared to that in the edge region. An analytical model was developed to separate the effects of cavity nucleation and coalescence from the apparent cavity growth rate and thus to determine the individual cavity growth rate at the two locations. The ratio of the cavity growth rate at the center of the specimen to that of the edge was correlated to the stress state (i.e., ratio of mean to effective stress) and compared to predictions derived from the work of Rice and Tracey and of Pilling and Ridley. These comparisons demonstrated that model predictions based on the Pilling-and-Ridley work provided good agreement with observations at low levels of hydrostatic stress, while the Rice-and-Tracey approach was better at higher levels. In addition, it was established that the analysis could be applied over a wider range of processing and material parameters than that originally assumed by Pilling and Ridley and Rice and Tracey.     

An experimental study on forming characteristics of pre-coated sheet metals

To analyze the forming and friction characteristics of pre-coated metals (PCMs) that are widely used in household appliances, rectangular deep drawing and friction tests were performed. There were four types of die materials (STD11(TiCN), STD11(TD), STD11, AMPCO) used in the deep drawing tests, and the results show that STD11 and AMPCO are better than others in respect to forming load and surface roughness. The friction mechanism, the thickness of materials and the effect of the roller’s diameter on the friction coefficient and surface roughness were examined in the friction test. The PCMs used in the tests had low friction coefficients (μ=0.15–0.20) in non-lubricated condition due to the coating film acting as lubrication. The friction coefficient decreased as the radius of the roller increased and the surface of product became better as the thickness of the material decreased.     

An experimental setup for the study of gas-solid reequilibration phenomena

The effect of Y additions on the oxidation mechanism of NiAl at 1270 K has been investigated. Mass transport in the alumina scale was examined with¹⁸O tracers. Proton activation analysis (¹⁸O(p, )¹⁵N) and SIMS were used to measure the¹⁸O distribution in the scale. On pure NiAl and low-doped (0.07% Y) NiAl mainly outward scale growth was observed. Addition of 0.5% Y induces oxide formation at both interfaces of the scale. Larger quantities of Y added to the alloy (>0.5%) do not dissolve completely in the NiAl, but form Y-rich segregates. Internal oxidation of these intergranular segregates was observed. The relation between the modification of the scale-growth mechanism and the improved adherence of the scale to the alloy due to the addition of Y is discussed.     

An innovative experimental study of corner radius effect on cutting forces

The cutting forces are often modelled using edge discretisation methodology. In finish turning, due to the smaller corner radii, the use of a local cutting force model identified from orthogonal cutting tests poses a significant challenge. In this paper, the local effect of the corner radius r_? on the forces is investigated using a new experimental configuration: corner cutting tests involving the tool nose. The results are compared with inverse identifications based on cylindrical turning tests and elementary cutting tests on tubes. The results obtained from these methods consistently show the significant influence of the corner radius r_? on the cutting forces.     

铝合金多楔带轮旋压成形数值分析与试验研究

针对汽车发电机离合器使用的P6PL118型多楔带轮,提出了一种镦粗成形与旋压成形相结合的新工艺。基于Deform软件,研究了镦粗与旋压成形过程中摩擦因子、尾顶压下量与旋轮进给量对金属流动的影响,并研究了旋压成形中成形载荷及成形结束时的应变分布情况。在旋压机上进行试验,结果表明,得到的多楔带轮满足尺寸要求,晶粒更加细化。齿顶和齿底处加工流线清晰,沿齿形外廓线分布。旋压成形后工件顶部硬度提高最为明显,其次是工件中部,工件底部硬度提高最少。旋压件与毛坯态相比,维氏硬度平均提高25.9%,并具有更好的齿面硬度与耐磨性。     

An experimental study on grinding of silicon carbide reinforced aluminium alloys

This paper presents the results of an experimental research on the grinding of metal matrix composites. The aim of the investigation is to enhance the knowledge about the machinability of some aluminium alloys reinforced with SiC of different shape (powder or whiskers) and content. Investigations on chip morphology, ground surfaces and trend of forces acquired during the grinding process were carried out. The results show that the presence of the reinforcement enhances the machinability in terms of both surface roughness and lower tendency to clog the grinding wheel, when compared to a non-reinforced Al alloy. Particle-reinforced composites exhibit a linear relationship between the roughness of the ground surface and the average hardness of the material. Whisker-reinforced composites show higher roughness values than particulate composites. Data of grinding forces obtained under different machining conditions are reported which permit the evaluation of the specific cutting energy.     

焙烧参数对预焙阳极特性影响的实验研究

搭建了实验平台,采用实验的方法研究了升温速率和终焙温度对预焙阳极体积密度、气孔率、电阻率和挥发分析出率等参数的影响。结果表明,气孔率、电阻率和挥发分析出率都随升温速率的增大而增大,在升温速率较小时,体积密度随升温速率的增大快速减小,当升温速率超过80℃/h后,再增大升温速率,体积密度变化不大。体积密度、气孔率和挥发物析出率都随终焙温度的升高而升高,而电阻率则随终焙温度的升高而降低。     

An experimental and numerical study on laser percussion drilling of thick-section alumina

A major challenge in laser percussion drilling of thick-section ceramics is to obtain a low taper and low spatter deposition hole leading to high quality post-processing. In order to achieve the fine hole drilling, it is important to understand the mechanism of laser percussion drilling. In this paper, an experimental and numerical study on laser percussion drilling was carried out. A two-dimension (2D) axisymmetric finite element (FE) model for simulation of temperature field and proceeding of hole formation during percussion drilling was developed. The FE model was validated by the corresponding experiment. Furthermore, a theoretical model for evaluation of temperature at melt front and velocity of melt ejection was presented in order to further validate the FE model and study the spatter deposition. The effects of laser peak power, pulse duty cycle and pulse repetition rate on hole diameter and spatter deposition were investigated by the developed models and experiments, in which the simulated results were in good agreement with the experiments. The study indicated that the size and temperature of the melt front significantly affected the hole diameter formation and spatter deposition during laser percussion drilling. The characteristic of melt front was mainly determined by the employed laser peak power, pulse repetition rate and pulse duty cycle. Based on the experimental and numerical study, the process parameters were optimised and a drilled-hole with low taper and low spatter deposition was obtained using a 3.5 kW CO₂ laser. A microstructural and element compositional study was also performed in this work, by which the characteristics of microstructure and element composition in HAZ around laser drilled hole were revealed.     

An experimental study on the effect of thinning band on the sheet formability in negative incremental forming

In negative incremental forming, a characteristic thinning band occurs on the parts when wall angles approach the maximum obtainable [D. Young, J. Jeswiet, Wall thickness variations in single point incremental forming, Proceedings of the Institute of Mechanical Engineers, Part B, Journal of Engineering Manufacture 218 (2004) 1453–1459]. The effect of this ultra-thin band on the fracture occurrence of part was studied in the current investigation. It was found that the occurrence of a thinning band on the test specimen of a formability test does not mean an effect on the test result. A reduction in the formability due to the occurrence of the thinning band occurs only if the specimen fractures in the flange area. In order to evaluate the real forming limit of a sheet metal, a condition regarding the occurrence of part fracture is proposed.     

An experimental study of the fracture properties of oil pipeline girth welds

The application of fracture mechanics to the "Fitness For Purpose" assessment of the fracture properties of pipeline girth welds is generally essential for the safe operation of oil pipeline systems. Based on the analysis of the fracture toughness requirements of the oil pipeline girth weld, a systematic study has been conducted on the fracture behavior of the API 5L X65 steel pipelin egirth weld made by two welding materials. The critical COD values of the pipe line girth weld under the different temperatures are tested. In the paper other influential factors on fracture behavior are also discussed, such as the welding materials, the welding positions (flat welding, vertical welding, overhead welding), the welded joint area (weld, heat-affected zone, fusion line and base metal) and the experiment temperature. The result shows that the welding material, the welded joint area and the experiment temperature have considerable influence on the fracture behavior of pipeline girth welds. It is also concluded that t he effect of the welding position is related to the welding process. The study provides a scientific basis for the welding of oil pipelines.     

气动脉宽调制位置伺服系统分段控制器的研究

本文介绍了一种分段控制方法,并在ＰＷＭ高速开关阀控气缸位置伺服系统中根据该方法设计了一种分段模糊控制器和一种分段ＰＩＤ控制器,实现了脉冲宽度调制高速开关阀控气缸位置伺服系统的精确控制。研究表明,系统获得了较好的定位和跟踪精度,这表明对于ＰＷＭ高速开关阀控气缸位置伺服系统,采用分段控制方案是可行的。     

The influence of thickness and rolling ratio on the inclusion behavior in plate steels

The effect of various advanced steelmaking techniques on the resulting nonmetallic inclusions and mechanical properties of plate steels has been investigated in previous publications. In this work, two additional variables are examined, the plate thickness and rolling ratio, and their influence on the previously reported results is presented. Conventional practice, calcium-treated, and electroslag-remelted aluminum-killed A516 carbon steels are investigated in plate thickness from 2–15 in. (51–381 mm) and with rolling ratios from 1:1 to 10:1. A total of 11 production plates are evaluated. The primary emphasis is made in comparing the conventional to the calcium-treated steels. The inclusion structure of each of the steels is reported via photomicrographs of inclusions in the three principal metallographic cross sections relative to the rolling direction. In addition, quantitative image analysis is used to quantify the inclusion structures in each of these cross sections. The Charpy-V-notch and dynamic tear upper shelf energies and tensile percent reduction of area are used to compare the properties of the investigated steels. Correlations between the inclusion sizes and the toughness and ductility properties are determined and compared to previous A533B results. The calcium-treated steels were found to be superior to the conventional practice steels in all thicknesses and for all rolling ratios.