In-Situ observation on microfracture behavior ahead of the crack tip in 63Sn37Pb solder alloy

in-situ transmission electron microscopy (TEM) tensile tests on as-cast and aged 63Sn37Pb solder alloys were conducted, and the fracture behavior in nanometer scale ahead of the crack tip was inspected and discussed. Results show that the fracture was completed by connecting the discontinuous cracks or voids. Dislocation behavior was concentrated along the grain boundaries for as-cast samples, and displayed mainly as dislocation climb. The crack was intergranular dominated under the lower strain rate. While remarkable mutual dislocation emission was detected in the aged solder. Transgranular cracks were dominant in the fractured area, and they propagated by linking up with the nanometer scale cracks ahead of the crack tips under the effective promotion of the inverse dislocation emission. At the same time, the partial interphase or intergranular cracks in the thinned area were also found. Under this condition, a new critical stress intensity factor K _c ^′ to define the mutual dislocation emission was proposed.     

Magnetic Field Analysis of Disk Coreless Permanent Magnet Synchronous Motor Based on Thickness Variation Halbach Array

Being a new permanent magnets(PMs) arrangement, the Halbach array could approve the magnetic flux density effectively, through weakening the magnetic flux density in one side of the PMs array, meanwhile strengthening the magnetic flux density in the other side. In the disk coreless PM synchronous motor (PMSM), the magnetic flux density is required to be sine wave and the peak value should be as high as possible. The paper deals with the application of the 90° Halbach array in the disk coreless PMSM, adopting NdFeB PMs. For the thickness of PMs influences the magnetic flux density in the air gap, the thickness variation technology is adopted. Through altering the adjacent PMs thickness, nine different PMs thickness combination is analyzed by FEM methods. And the conclusion is that when the thickness of tangential magnetization PMs is great than that of the radial magnetization PMs, the magnetic flux density wave is closer to sine wave than when the thickness of the tangential magnetization PMs is smaller than that of the radial magnetization PMs. Furthermore, when the thickness of the tangential magnetization PMs is great than that of the radial magnetization PMs, keeping the thickness of the tangential magnetization PMs being 0.006 m and the thickness of the radial magnetization PMs variation from 0.0048 m to 0.006 m, the magnetic flux density in the air gap will become closer to sine wave gradually, and then it becomes nonsinusoidal again. And when the thickness of radial magnetization PMs is 0.0054 m and 0.0055 m, the waves of magnetic flux density in the air gap are better than others.     

Use of the time constant to detect corrosion speed in reinforced concrete structures

The relatively simple to measure ‘time constant’ is presented as an index for characterizing the level of corrosion experienced by steel in concrete. This communication, largely in the form of a technical note, explicitly illustrates that the time constant determined from electrochemical testing has significant merit for monitoring corrosion of steel in concrete, and appears to be insensitive to the area of electrode being probed. In this work, the time constant, κ, is determined following a galvanostatic excitation signal, revealing a good correlation between the value of κ and corrosion status across specimens of widely varying geometry. Although this notion has been suggested in the past, this work presents both a survey and consolidated review to indicate the utility of the parameter as an index to corrosion rate on-site.     

A foam engulfment model for lost foam casting of aluminum

In lost foam casting of aluminum, pressure equilibrium between the liquid metal and the decomposing foam can produce a variety of different shapes for the metal flow front, ranging from convex to concave. In extreme cases, the flow front can become so strongly concave that small pieces of the foam pattern begin to break off inside the concave hollow of the flow front and become enveloped by the advancing liquid metal. When this happens, the entire mechanism of foam decomposition changes from steady ablation to a more chaotic motion in which the metal seems to “chew” its way through the pattern, creating large bubbles of vaporizing polymer liquid in its wake. These bubbles usually lead to undesirable anomalies in the final casting. In most cases, the nonlinear equations that govern the shape of the flow front depend on a single nondimensional number, which relates the onset of the engulfing motion to specific material, geometric, and process parameters. Numerical solutions to these equations are obtained for several special cases. These solutions help to explain a number of experimental observations that until now have been poorly understood.     

An anti-windup strategy for active vibration isolation systems

An anti-windup augmentation technique for active vibration isolation systems is considered in this paper and shown to lead to high-performance vibration isolation through simulations and experiments. First, the anti-windup construction is described and desirable properties of the augmented closed-loop system are illustrated. Then, the anti-windup technique is tested on a simulation example and finally shown to perform excellently on a commercial vibration isolation device: Newport Corporation's Elite 3^TM active vibration isolation system which has been patented and is now commercialized with this architecture. Both simulation and experimental results confirm the effectiveness of the anti-windup scheme.     

Delphi开发环境下的实时数据采集程序设计

本文介绍了利用Delphi开发平台开发数据采集程序的两种方法，并结合某测深仪给出了一个编程的例子.     

Sensor fault tolerant control using sliding mode observers

Previous work has considered the use of sliding mode observers for fault detection and isolation (FDI) in uncertain linear systems whereby the unknown faults are reconstructed by appropriate processing of the so-called equivalent output error injection. The paper builds on this work and considers such a scheme within the broader context of fault tolerant control. Specifically, by correcting the faulty measurement by an estimate of the fault obtained from the sliding mode FDI scheme, good closed-loop performance is still maintained. An example of such a scheme, which has been implemented in real-time on a laboratory dc motor rig, is described.