Nondestructive testing and crack evaluation of ferromagnetic material by using the linearly integrated hall sensor array

Magnetic flux leakage testing (MFLT), which measures the distribution of a magnetic field on a magnetized specimen by using a magnetic sensor such as a Hall sensor, is an effective nondestructive testing (NDT) method for detecting surface cracks on magnetized ferromagnetic materials. A scan-type magnetic camera, based on the principle of MFLT, uses an inclined Hall sensor array on a printed circuit board (PCB) to detect small cracks at high speed. However, the wave forms appear in a direction perpendicular to the scan because the sensors are bonded at different gradients and heights on the PCB despite careful soldering. In this paper, we propose linearly integrated Hall sensors (LIHaS) on a wafer to minimize these waves and to improve the probability of crack detection. A billet specimen is used to determine the effectiveness of the LIHaS in multiple crack detection. This paper was recommended for publication in revised form by Associate Editor Joo Ho Choi Prof. Jinyi Lee was born in Korea in 1968. He received the bachelor degree in mechanical design from Chonbuk University, Jeonju, Korea, in 1992. Also he received the master and Ph.D degree in mechanical and aeronautics & space engineering from Tohoku university, Sendai, Japan, in 1995 and 1998, respectively. He was a Researcher from 1998 to 2000 with the Tohoku university, Iwate university, Iwate Techno-Foundation and Saitama university, Japan. From 2000 to 2003, he worked for Lacomm Co., Ltd. and Gloria Techniques, Korea, as a researcher. In 2003, he was a lecturer with the Chosun university, Gwangju, Korea. Since 2005, he has been an Assistance Professor, Chosun university. His research interests are in application of magneto-optical film, laser and CCD line scan sensor, and development of magnetic camera. He is the author or coauthor of fifteen patents and over 50 scientific papers. Jiseong Hwang was born in Republic of Korea in 1979. He received the B.S and M.S degree in control and instrumentation engineering in 2005 and 2006, respectively, from the Chosun University, Gwangju, korea, where he is currently working toward the Ph.D. degree. His research interests are NDT and Evaluation, Magnetic camera. Jongwoo Jun was born in Korea in 1974. He received the bachelor degree in electronics engineering from Inje University, Kimhae, Korea, in 1999. He received the master degree in electronics engineering from Changwon University, Changwon, Korea, in 2005. Also he is currently working toward the Ph.D. degree in information & communication engineering from Chosun University, Gwangju, Korea. He worked for Lacomm Co., Ltd. and Gloria Techniques from 1999 to 2005, Korea, as a researcher. His research interests are development of magnetic camera, NDT and evaluation. Dr. Seho Choi was born in Korea in 1964. He received bachelor degree in the department of electrical and electronic engineering from Kyungpook National University, Daegu, Korea, in 1987. And he received master degree in the department of elec trical and electronic engineering from Korea Advanced Institute of Science and Technology in 1989. He received Ph.D. degree in the department of electrical and electronic engineering from the University of Sheffield in the U.K. in 2001. He had been worked for Agency for Defense Development as a Researcher from 1989 to 1992, Korea. Since 1993, he has been worked for POSCO Research Lab. as a principal researcher. His main research activities are developing Surface Defect Inspection System for hot and cold rolled steel strip, hot wire rod, and hot slab. He is also interested in developing Internal Defect Detection System for steel products by using Ultra-sonic and magnetic camera techniques. His major is image processing to detect tiny defect in high background noise image. He published many scientific papers as the author or coauthor.     

基于AFM的纳米梁杨氏模量和残余应力测量

针对同一工艺流程下相同杨氏模量和残余应力的双端固支梁阵列,建立了简化的杨氏模量和残余拉应力的弯曲测试模型,并将应力刚化理论应用到几何非线性有限元分析中用于上述模型的理论误差评价.提出将拉曼频移测试与原子力显微镜(AFM)弯曲测试相结合的实验方案,首先利用拉曼频移判断结构中的应力拉压性质,随后利用AFM测量梁阵列的弹性系数,最终利用MATLAB求解超定方程组的方法解得梁阵列的杨氏模量和残余应力,测试结果证明了该实验方案的可行性.     

Measurement of residual stress in thick section composite laminates using the deep-hole method

The deep-hole method is a method of measuring residual stress in large metallic components. In this paper, an extension to the deep-hole method is described to allow the residual stresses in thick section composite laminated plates to be evaluated. The method involves first drilling a small hole through the laminate perpendicular to the surface. The material around the hole is then machined away, resulting in a change in diameter of the hole due to the release of residual stress. This change in diameter is measured and used to calculate the residual stress. The calculation requires the evaluation of coefficients that depend on the properties of the composite. In this work, the finite element method is used to evaluate these coefficients. Using this method, the residual stresses in a 22 mm thick carbon/epoxy composite plate are measured and reported.     

基于GMR传感器的小体积二维电子罗盘设计

针对二维电子罗盘存在的体积、精度较难平衡等问题,对二维电子罗盘展开了研究。通过对硬件与算法的优化设计,提出了一种较为实用的解决方案。硬件上采用新型的二维GMR传感器感测磁场,使用C8051F350单片机自带的Δ-ΣA/D模块进行了信号调理,有效减少了信号调理器件,使用了针对GMR传感器优化的算法,在无干扰下可保证其具有较好的辨向精度,在有外部干扰的环境中,通过旋转校准,依然可以保证较高的精度。同时,将校准数据IAP到单片机Flash中,即使系统掉电也可以保证数据不丢失。经国防科技工业弱磁一级计量站的测试,其测试结果表明,该设备在无干扰情况下精度可达±2°,在强干扰下精度依然较高,具有较强的工程实用价值。     

工程陶瓷磨削表面残余应力测试

作为特殊的硬脆工程材料,陶瓷零件的断裂强度和韧性对表面应力状态异常敏感,测试其表面应力有重要意义。 阐述X射线法的测试原理和方法,建立微挠度法的测试模型,介绍压痕裂纹法、剥层法、云纹法的测试原理。比较各种方 法,提出探求一种更精确、更经济、更实用的测量方法是非常迫切的课题。     

Liftoff insensitive thickness measurement of aluminum plates using harmonic eddy current excitation and a GMR sensor

This paper describes the implementation of a device that measures the thickness of metallic plates. A pancake coil for magnetic field sinusoidal excitation is used and detection is performed with a bridge giant magneto-resistor sensor. The paper uses the theory of the linear transformer to explain the liftoff effect with a special attention to the point of interception phenomenon. The transformer model shows that to attain the interception points with instantaneous measured voltages independent of the liftoff gap the excitation coil must be driven with imposed current. This effect was explored to show that a simultaneous process of thickness and conductivity measurement is feasible.     

Improvement of crack inspection possibility using gradient directional magnetization and linearly integrated hall sensors

A method for improving crack detection using scan-type magnetic flux leakage testing is proposed herein. Usually, the crack detection ability decreases when the crack length direction is parallel to the magnetization direction. We propose a gradient directional magnetization method that improves the probability of detection regardless of the direction of the sensor array, which is parallel to the magnetizer??s poles and perpendicular to the length of the crack. The effectiveness of the gradient directional magnetization method was verified using finite element method simulation and experimental tests.     

Optical tomography sensor configuration using two orthogonal and two rectilinear projection arrays

This paper represents the configuration of an optical tomography sensor by using infrared emitters and phototransistors. The projection geometry of the sensor is based on the combination of two orthogonal and two rectilinear projection arrays. A fixture is designed for holding all emitter–receiver pairs in parallel. Selection of the phototransistor is explained so that the tomography sensor developed is free of noise caused by the surrounding environment. This paper describes all points to be considered when designing an optical tomography sensor. The results show that the developed system has the capability to detect the concentration profile of the flow.     

Dynamic contact stress analysis using a compliant sensor array

A flexible sensor array has been developed for the measurement of contact stress distribution between flexible bodies. The array incorporates 960 contact geometry modulation resistive (CGMR) transducers to provide a spatial resolution of 10 mm × 10 mm. The high flexibility of the array and its special structure enable it to comply with the very large displacements of the interface between the human body and a flexible cushion. In addition, a method and instrument have been developed to measure, digitize and record dynamic contact stress distributions with a sampling rate of up to 300 frames per second (960 sensors/frame). Measurements performed using this system under static and dynamic conditions are consistent with those performed through the contact pressure display (CPD) method. The new method has been used by the authers and their associates to obtain basic data required for the new field of cushioning mechanics.     

Development of a welding residual stress predictor using a function-replacing hybrid system

Welding is a reliable and efficient metal-joining process widely used in industries. Residual stresses are inherent and detrimental in welded structures. Researchers have developed many direct measuring techniques for welding residual stress. Intelligent techniques have been developed to predict residual stresses to meet the demands of advanced manufacturing planning. The existing tools are limited in application and need attention. This research paper details the development and use of a function-replacing hybrid for predicting the residual stress in butt-welding.     

Nondestructive testing and characterization of residual stress field using an ultrasonic method

To address the difficulty in testing and calibrating the stress gradient in the depth direction of mechanical components, a new technology of nondestructive testing and characterization of the residual stress gradient field by ultrasonic method is proposed based on acoustoelasticity theory. By carrying out theoretical analysis, the sensitivity coefficients of different types of ultrasonic are obtained by taking the low carbon steel(12%C) as a research object. By fixing the interval distance between sending and receiving transducers, the mathematical expressions of the change of stress and the variation of time are established. To design one sending-one receiving and oblique incidence ultrasonic detection probes, according to Snell law, the critically refracted longitudinal wave (LCR wave) is excited at a certain depth of the fixed distance of the tested components. Then, the relationship between the depth of LCR wave detection and the center frequency of the probe in Q235 steel is obtained through experimental study. To detect the stress gradient in the depth direction, a stress gradient LCR wave detection model is established, through which the stress gradient formula is derived by the relationship between center frequency and detecting depth. A C-shaped stress specimen of Q235 steel is designedto conduct stress loading tests, and the stress is measured with the five group probes at different center frequencies. The accuracy of ultrasonic testing is verified by X-ray stress analyzer. The stress value of each specific depth is calculated using the stress gradient formula. Accordingly, the ultrasonic characterization of residual stress field is realized. Characterization results show that the stress gradient distribution is consistent with the simulation in ANSYS. The new technology can be widely applied in the detection of the residual stress gradient field caused by mechanical processing, such as welding and shot peening.     

Vibration control of a cable-stayed bridge using electromagnetic induction based sensor integrated MR dampers

This paper presents a novel electromagnetic induction (EMI) system integrated in magnetorheological (MR) dampers: The added EMI system converts reciprocal motions of MR damper into electiral energy (electromotive force or emf) according to the Faraday’s law of electromagnetic induction. Maximum energy dissipation algorithm (MEDA) is employed to regulate the MR dampers because it strives to simplify a complex design process by employing the Lyapunov’s direct approach. The emf signal, produced from the EMI, provides the necessary measurement information (i.e., realtive velocity across the damper) for the MEDA controller. Thus, the EMI acts as a sensor in the proposed MR-EMI system. In order to evaluate the performance and robustness of the MR-EMI sensor system with the MEDA control, this study performed an extensive simulation study using the first generation benchmark cable-stayed bridge. Moreover, it compared the performance and the robustness of proposed system with those of Clipped-Optimal Control (COC) and Sliding Mode Control (SMC), which were previously studied for the benchmark cable-stayed bridge. The results show that the MR-EMI system reduced the vibrations of the bridge structure more than those of COC and SMC and show more robust performance than that of SMC. These results suggest that EMIs can be used cost-effective sensing devices for MR damper control systems without compromising the performance of them.     

Study on residual stress in viscoelastic thin film using curvature measurement method

Using LSM (laser scanning method), the radius of curvature due to thermal deformation in polyimide film coated on Si substrate is measured. Since the polyimide film shows viscoelastic behavior, i.e., the modulus and deformation of the film vary with time and temperature, we estimate the relaxation modulus and the residual stresses of the polyimide film by measuring the radius of curvature and subsequently by performing viscoelastic analysis. The residual stresses relax by an amount of 10% at 100°C and 20% at 150°C for two hours.     

Readout of micromechanical cantilever sensor arrays by Fabry-Perot interferometry

The increasing use of micromechanical cantilevers in sensing applications causes a need for reliable readout techniques of micromechanical cantilever sensor (MCS) bending. Current optical beam deflection techniques suffer from drawbacks such as artifacts due to changes in the refraction index upon exchange of media. Here, an adaptation of the Fabry-Perot interferometer is presented that allows simultaneous determination of MCS bending and changes in the refraction index of media. Calibration of the instrument with liquids of known refraction index provides an avenue to direct measurement of bending with nanometer precision. Versatile construction of flow cells in combination with alignment features for substrate chips allows simultaneous measurement of two MCS situated either on the same, or on two different support chips. The performance of the instrument is demonstrate in several sensing applications, including adsorption experiments of alkanethioles on MCS gold surfaces, and measurement of humidity changes in air.     

Numerical analysis of welding residual stress using heat source models for the multi-pass weldment

Numerical prediction of welding-induced residual stresses using the finite element method has been a common practice in the development or refinement of welded product designs. Various researchers have studied several thermal models associated with the welding process. Among these thermal models, ramp heat input and double-ellipsoid moving source have been investigated. These heat-source models predict the temperature fields and history with or without accuracy. However, these models can predict the thermal characteristics of the welding process that influence the formation of the inherent plastic strains, which ultimately determines the final state of residual stresses in the weldment. The magnitude and distribution of residual stresses are compared. Although the two models predict similar magnitude of the longitudinal stress, the double-ellipsoid moving source model predicts wider tensile stress zones than the other one. And, both the ramp heating and moving source models predict the stress results in reasonable agreement with the experimental data.     

Measurement and calculation of surge-arrester residual voltages

This paper presents accurate measurement of residual voltages of surge arresters (SA) by two designed charge meters (D-dot probes) as well as simulation validation in the high-conduction regime. Simultaneous impulse voltage measurements were conducted by using two D-dot probes, two uncompensated commercial mixed resistive–capacitive (RC) probes and an uncompensated damped capacitive voltage divider (CD). Residual voltage measured by two commercial mixed RC probes and the CD showed longer rise time, an initial inductive overshoot superimposed on the waveform and a significant decay even before the current peak instant, contrary to those measured by the two D-dot probes. Theoretical investigations are also introduced for the inductive coupling in the CD loop and analysis of the test circuit. Quantification of measurement errors has shown the superiority of D-dot probe over the other devices used. Finally, good agreement was found between the measured current and voltage waveforms for 33-kV SA and those computed from the test circuit analysis.     

陶瓷微板热隔离气体传感器阵列热干扰分析

热干扰特性是影响微热板气体传感器阵列热结构设计的重要因素之一。为探讨微热板阵列传感器单元之间的热力学特性关系,设计并制备了具有独立式加热功能的热隔离结构4单元微热板气体阵列,传感器阵列单元由Al N陶瓷衬底、Pt膜电极组成,为提高加热效率,阵列单元中间加热区采用激光微加工刻蚀热隔离通孔设计,与边缘形成微梁连接结构。利用有限元法对传感器阵列结构进行了热干扰仿真分析,验证了热隔离结构设计的合理性。给出了4种热干扰测试模式,并进行了热干扰特性测试分析,给出了4单元之间的热干扰规律曲线,得出传感器单元功耗300m W时最大干扰温度达169.6℃,最小热干扰温度84.7℃。热隔离通孔设计可有效降低传感器单元热传导损耗,热干扰分析对微热板传感器阵列的热结构设计具有重要意义。     

三维柔性阵列触觉传感器结构设计

为减少类皮肤三维柔性触觉阵列传感器设计的复杂度,本文比较了基于导电橡胶的几种传感器结构设计方法,提出了采用整体式框架结构,节点行之间独立的非线性传感器结构.此设计不仅有利于传感器结构的加工实现,而且大大地降低了解耦算法的复杂度.仿真结果表明基于该结构的传感器可以实现大规模三维柔性触觉的信息测量以及传感器规模的扩展.     

Redistribution of residual stress in plasma-sprayed coatings

A mathematical model is proposed for the residual-stress redistribution in plasma-sprayed coatings on melting.     

A residual stress analysis program using a Matlab GUI on an autofrettaged compound cylinder

A program for the residual stress analysis of an autofrettaged compound cylinder is designed using a Matlab graphical user interface (GUI) and program design technique. The high-pressure vessels are autofrettaged in order to increase their operating pressure and fatigue life. An autofrettage process causes plastic expansion of the inner section of the cylinder, adding residual compressive stress to the bore after relaxation. Such a compound cylinder is produced via a shrink-fit procedure that incorporates a monobloc tube that has previously undergone autofrettage. This paper presents a simple and visual tool to calculate the residual stress and describe the distribution of residual stress for both the elastic-perfectly plastic model and the strain-hardening model.