Amorphous ribbon domain refinement by scribing

Domain control has been applied to amorphous metal ribbon by mechanical and laser scribing. Mechanically scribed lines were made using a number 88 tungsten carbide scriber with minimum applied pressure. The scribing interval was varied from 0.6 to 10 mm. Laser scribing was performed by using a well-focusedQ-switch YAG laser. The laser power level and scribing interval were varied to obtain optimal magnetics properties. Core loss reductions of 20-25 percent were measured for mechanically and laser scribed Metglas 2605S-2 ribbon. A mechanism of domain refinement is suggested.     

Simulation of skew domain wall bowing in SiFe laminations with asymmetric roll orientation

Cyclic motion of 180° domain walls spanning perfect monocrystalline laminations with first-order positive cubic anisotropy (like 3% SiFe) has been simulated using a finite segment technique. Only drive field, eddy field, and surface tension forces on the domain wall were considered. Calculations were made for various crystal orientations over the range between     

Micromagnetics of closed-edge laminations

Previous work has shown that lamination of the film core in a recording head eliminates noisy closure domains but introduces potentially noisy curling-edge walls. As a possible means of avoiding the edge walls, attention is given to minimization of the energy of an infinite strip composed of two laminations connected along their edges. Under the conditions that the spacer thickness is ≳0.2×(magnetic-sublayer thickness) and that the energy is less than that of the closure-domain state, it is predicted that: fully stray-field-free flux closure with now walls occurs if the sum of anisotropy and exchange-stiffness energies within magnetic connections is negative; if this energy sum is positive, then part of the flux leaks through the spacer, forming edge walls whose angle is <90° (polarization switching of these walls contributes to hysteresis); and if two would-be edge walls are so thick as to impinge on each other, then the actual ground state is one of saturation along the hard axis. An advantage of closed edges is the need for thicker and therefore fewer sublayers; a disadvantage of thicker sublayers is greater eddy currents     

Observation of residual stress and defects in silicon induced by scribing

Residual stresses induced by three scribing methods, diamond point scriber, laser scriber and diamond blade saw, are studied quantitatively by infra-red photoelasticity. It is clear that diamond blade saw scribing is most desirable, for residual stress induced by it is several times smaller than the stress caused by the other methods. The stress gradient differs between the laser scribed sample and the others, probably because of the difference in stress generation mechanism. Removing the damaged layer by etching reduces residual stress. The three scribing methods are also studied by the observation of defects after annealing and the results are compared with those determined by photoelastic measurement.     

Embrittlement of electrical steel laminations by nitrogen pick-up during heat treatment

Heat treated electrical steel laminations have shown evidence of low ductility behavior, characterized by a small number of bends till fracture, on repeated bending tests. The laminations were produced using a new grade of electrical steel with much lower aluminum content than usual. The problem happens when the oxygen potential (measured by the dew point of the atmosphere) of the heat treatment atmosphere is abnormally high. Furthermore, ductility can be restored by a low-oxygen potential heat treatment. Although the heat treatment resulted in a loss of ductility, the magnetic properties were not deteriorated. The low ductility samples always show intergranular fracture, whereas the un-treated laminations fracture by cleavage. The low ductility is associated with the formation of silicon–manganese nitride precipitates formed at grain boundaries, although they are not the cause of the low ductility. Ductility could be restored by a low dew point heat treatment but the inclusions remained in the grain boundaries. The low ductility and its recovery must be ascribed to the presence of nitrogen atoms segregated to the grain boundaries when the heat treatment atmosphere has a high oxygen potential. The lack of aluminum in the composition of the steel hinders the scavenging effect of this element on nitrogen atoms in solution in the steel.     

Measurement of rotating flux in silicon iron laminations

A method of calculating the magnitude and direction of the instantaneous flux density in a thin lamination of magnetic material is described. The technique was demonstrated by measuring the rotating flux in samples of mild steel, grain-oriented silicon iron, and at a point in the T-joint of a three-phase, three-limbed transformer core. The flux in the mild steel sample was found to rotate at a constant angular velocity and to be constant in magnitude. In the silicon iron sample, and at a point in the T-joint, the flux density varied both in angular velocity and magnitude. A large 150 Hz component of rotational flux was found to cause high localized power loss in the T-joint. The power loss was measured using the "initial rate of rise of temperature method" and was compared with the predicted rotational hysteresis loss.     

Optimal laminations of thin underwater composite cylindrical vessels

This paper deals with the optimal design of deep submarine exploration housings and autonomous underwater vehicles. The structures under investigation are thin-walled laminated composite unstiffened vessels. Structural buckling failure due to the high external hydrostatic pressure is the dominant risk factor at exploitation conditions. The search of fiber orientations of the composite cylinders that maximize the stability limits is investigated. A genetic algorithm procedure coupled with an analytical model of shell buckling has been developed to determine numerically optimized stacking sequences. Characteristic lamination patterns have been obtained. FEM analyses have confirmed the corresponding significant increases of buckling pressures with respect to initial design solutions. Experiments on thin glass/epoxy and carbon/epoxy cylinders have been performed. The measured buckling pressures appear to be in good agreement with numerical results and demonstrate the gains due to the optimized laminations.     

Wavenumber domain analysis of two-dimensional SAW images captured by phase-sensitive laser probe system

This paper is aimed at demonstrating how the wavenumber domain analysis of two-dimensional (2-D) images captured by phase-sensitive laser probe systems is applied in the characterization of RF SAW devices. Effectiveness is demonstrated through the selective characterization of spurious resonance modes and scattered, nonguided modes appearing in SAW resonators.     

Magnetic domain structure of isotropic MnAlC permanent magnet alloys

Observations of the magnetic domain structure were made on an isotropic MnAlC alloy (of the following composition: 73.0 wt% manganese, 26.4 wt% aluminium and 0.6 wt% carbon) homogenized at 1373 K for 1 h, quenched in water and tempered in the temperature range from 723 to 923 K. Observation of the magnetic domain structure was carried out by the Bitter powder pattern technique. It was found that the magnetic properties of the MnAlC alloy are closely related to the type of magnetic domain structure.     

激光选区熔化成形高强铝合金晶粒细化抑制裂纹研究现状EI北大核心CSCD

高强铝合金(2×××,7×××等)因具有比强度高、加工性好等优点而被航空航天、汽车等领域广泛应用。随着大推重比飞行器设计及汽车轻量化技术的发展,轻质结构材料的需求日益增加,同时零部件也面临着“薄壁化、中空化、复合化”的发展趋势,高强铝合金的传统加工方法越来越难以满足要求。近年来,激光选区熔化成形(selective laser melting,SLM)作为一种常见的金属增材制造技术(additive manufacturing,AM)在复杂零部件成形领域受到关注,有望成为进一步拓宽高强铝合金应用领域的新兴技术。然而,SLM成形高强铝合金因易产生周期性热裂纹和粗大柱状晶不良组织等问题而发展缓慢,晶粒细化是克服增材制造高强铝合金这一固有热裂问题的关键所在。本文综述了近年来SLM成形高强铝合金显微组织和力学性能调控等方面的研究进展,归纳了不同体系合金的力学性能,重点阐述了抑制SLM成形高强铝合金中热裂纹形成的主要策略,包括SLM工艺参数优化以及通过微合金化或添加纳米颗粒细化晶粒等方法。指出当前研究存在的主要问题是合金成分的改变对材料综合性能以及热处理制度的影响规律尚不清晰等,并展望了未来的发展趋势,如SLM成形新型高强铝合金成分设计与综合性能评价、利用后处理工艺等手段进一步提升合金综合性能以及专用晶粒细化剂的设计与细化机制探究等。     

Effects of stresses on magnetic properties of silicon-iron laminations

The magnetic properties of grain-oriented 3 1/4% silicon-iron, as used in laminated transformer cores, are extremely sensitive to mechanical stresses. Power loss and magnetostriction (the cause of core vibration and noise) are most affected by compressive stresses. The theoretical effects of different types of stress on the domain structures of silicon-iron are correlated with measurements made on single laminations and transformer cores. The ways in which stresses can arise in cores and possible methods of avoiding or eliminating them in practice, are discussed.     

轮胎激光散斑干涉相位图多方向频域滤波方法

为解决激光数字剪切散斑干涉技术应用于轮胎缺陷检测中轮胎缺陷相位条纹图噪声对包裹相位图解包和轮胎缺陷尺寸测量产生严重影响问题,通过对散斑干涉相位图的形成与条纹特征分析,研究一种根据不同方向的条纹密度来设置不同截止频率的多方向频域低通滤波方法。该方法只需进行一次滤波就能有效滤除噪声,还能更好地保留图像的边缘信息。实验结果表明:在两组滤波实验中,与中值滤波方法相比,多方向频域低通滤波的边缘保持指数分别是其4.257倍、2.869倍;与正余弦滤波方法相比,多方向频域低通滤波方法的残差点数分别是正余弦滤波方法的16.456%、36.555%,体现出较好的滤波特性。     

Crystal structure refinement of YAlO3, a promising laser material

Yttrium orthoaluminate, YAlO₃, has a perovskite-like orthorhombic crystal structure ($\text{a}\text{= 5.330(2)}\text{A}\text{?}$, $\text{b}\text{= 7.375(2)}\text{A}\text{?}$, $\text{c}\text{= 5.180(2)}\text{A}\text{?}$; space group Pnma-D¹⁶_2h). The structure has been refined from 880 independent X-ray reflections to R = 0.075. The oxygen coordination around Al³⁺ remains nearly cubic whereas the YO₁₂ - and YAl₈-polyhedra are rather distorted.     

Fourier transform technique with refinement in the frequency domain for the synthesis of optical thin films

An optical thin-film synthesis technique combining a Fourier transform approach with the refinement of design parameters in the Fourier space is proposed. The theory and numerical examples are described.     

Mismatching refinement with domain decomposition for the analysis of steady‐state metal forming process

The finite element analysis of three‐dimensional metal forming processes is generally subject to large computational burden due to its non‐linearity. For economic computation, the mismatching refinement, an efficient domain decomposition method with different mesh density for each subdomain, is developed in the present study. A modified velocity alternating scheme for the interface treatment is proposed in order to obtain good convergence and accuracy in the mismatching refinement. As a numerical example, the analysis of the axisymmetric extrusion processes is carried out. The results are discussed for the various velocity update schemes and for the variation of the length of overlapped region. The three‐dimensional extrusion processes for a rectangular section and an E‐section are analysed in order to verify the effectiveness of the proposed method. Comparing the results with those of the conventional method of full region analysis, the accuracy and the computational efficiency of the proposed method are then discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

Magnetic and optical properties of amorphous NdFeCo thin films by pulsed laser deposition technique

Rare earth and transition metal doped (NdFeCo) thin films were fabricated on Si (100) substrate by pulsed laser deposition technique keeping the substrate at constant temperature of 300 °C. A KrF Excimer laser (248 nm, 20 ns) was used as an energy source for the deposition. Thin films were deposited without and under the influence of transverse magnetic field applied across the plume. The applied magnetic field was varied from 3 to 6 kOe. The deposited films were characterized by XRD, FESEM, VSM and SE (Spectroscopic Ellipsometry). The deposited films were amorphous in nature. All the films regardless of the applied magnetic field exhibit perpendicular magnetic anisotropy. The thickness of the thin films was found to increase monotonically from 166 to 266 nm with the increase in the applied external magnetic field. The saturation magnetization has a maximum value of 1682 emu/cc for the film deposited under 4.5 kOe magnetic field. The value of optical band gap energy for the same film is found to have a maximum value of 3.1 eV. The values of both the saturation magnetization and the band gap energy were decreased with the increase in the applied magnetic field.     

纳滤在L-鸟氨酸后提取中的应用研究

研究了采用纳滤技术代替活性碳对L-鸟氨酸发酵液进行脱色的可行性.从6种有机膜中选择了截留分子量为500的纳滤膜,并考察了料液pH、温度、压力、离子强度对L-鸟氨酸膜透过性能的影响.结果表明膜透过最优条件为:料液温度t=45℃、pH=9.0、操作压力p=2.0 MPa,在此条件下渗滤透过液的透光率T430 nm=96%,L-鸟氨酸收率达到95.8%.此方法在技术上是完全可行的.     

一种时域解调激光干涉仪调制信号的方法

针对某低频水平振动校准设备的激光干涉仪,利用NI公司的多功能采集卡,采集激光干涉仪的调制信号及与其同相位的电容式位移传感器的输出信号.根据激光干涉仪调制原理,提出一种时域解调调制信号的方法.根据调制信号条纹的时域特性和它被限幅的实际特点,利用labview软件实现了信号的解调,并将电容位移传感器信号作为参考信号,还原解调后信号的相位,从而得到振动台高精度的振动波形.实验证明,此方法对连续振动信号的解调效果良好,具有较好的重复性和稳定性,精度可达到激光干涉仪发射激光波长的四分之一.     

On the scribing and subsequent fracturing of silicon semiconductor wafers

The integrated circuits deposited on silicon wafers are often separated by scribing with a diamond tool followed by bending to produce fracture. Using a commercial scribing tool we find permanent deformation and three types of crack. The median crack which propagates downwards is the objective of the scribing process. Lateral cracks which form, apparently following plastic deformation, may lead to chipping on either side of the scribing tool. These cracks and also the chevron cracks which form on the surface are very similar to cracks observed in scratching glass. However, in silicon, because of its anisotropy, the chevron cracks may be a serious problem since they can guide the median crack out of the scribing direction onto a preferred cleavage plane. This aspect leads to a brief discussion of the crystallography of silicon and recommendations for scribing configurations which should minimize undesired fracture. Finally, it is shown that the established methods of linear elastic fracture mechanics may be used to predict the maximum radius of curvature required to fracture a wafer containing a prescribed series of median cracks.