Analysis technique for interaction of rectangular open-ended waveguides with surface cracks of arbitrary shape in metals

The use of microwave technique has proved to be a viable means for crack detection and sizing surface cracks in metals. In this technique, the surface of the specimen is interrogated with a radiating open-ended waveguide probe and a crack is assumed to be a simple short-circuited rectangular waveguide, causing peturbations in the probe reflection coefficient. Since the growth of fatigue in metals is a stochastic process, the cracks do not have a constant predetermined shape. We describe a new formulation to model the problem of an open-ended waveguide probe radiating into a conducting metal with a surface-breaking crack of arbitrary shape. In this formulation, the crack is first modeled by an appropriate number of short rectangular waveguides. The generalized scattering matrix technique is then used to calculate the scattering matrix of the new segmented waveguide structure. The probe reflection coefficient of the dominant mode, TE₁₀, is finally calculated for various positions of the crack in order to predict the probe output signal. To demonstrate the accuracy of the model, we consider two special cases of a long and an elliptical-shape cracks. The comparison of our results with those available in the literature substantiates the model introduced in this paper. To further validate the model, we present results associated with a fatigue crack of complex geometry which are compared with those obtained using a finite element code.     

Thin-skin analysis technique for interaction of arbitrary-shape inducer field with long cracks in ferromagnetic metals

In using the AC field measurement (ACFM) technique for non-destructive evaluation (NDE) of metals, a current-carrying wire structure is used to induce eddy current within a thin layer of the metal and a magnetic field sensor to measure the field perturbations in the vicinity of the metal. The sensitivity of ACFM crack detection and sizing relies on an appropriate design of the wire structure geometry together with a dully placement of the sensor. This paper presents an analytical modeling technique for evaluating the electromagnetic field interaction of an ACFM probe with a long uniform crack in a ferromagnetic metallic slab. The probe in the proposed model can have an arbitrary-shape wire inducer with no restrictions on its relative sensor position. The technique is accurate and very efficient computationally. It first uses the two-dimensional Fourier transform to obtain the field distribution at the metal surface. The Laplacian field distribution above the metal is then determined by satisfying the so-obtained boundary condition at air–metal interface. To demonstrate the accuracy of the model, we consider the special case of a rhombic wire inducer. The comparison of our results with those obtained using the conventional algorithm in the literature validates the accuracy of the model introduced in this paper. To show the generality of the model, we also present theoretical and experimental results associated with a solenoid inducer with a three-dimensional geometry for which no analytical solution is available in the literature. The theoretical prediction of crack signal supported by experimental results is used to develop a model-based method for inverting crack signal into crack depth.     

小规格高强度热轧H型钢孔型优化

为解决H210 mm×134 mm×6 mm×10 mm规格A572(Gr65)高强度热轧H型钢翼缘端部“龟裂”问题,借助有限元模拟软件,对其成因进行了分析。结果表明,A572(Gr65)钢高温塑性较差,当其粗轧段压下量较大且轧槽深度较浅时,粗轧中间坯腿长不足,后续道次长腿困难,导致第6、第11、第14道次孔型未充满,轧件腿端未被加工,从而出现翼缘端部“龟裂”缺陷。为此,对孔型系统进行了优化,成品翼缘端部“龟裂”缺陷得以消除。     

Using a wavelet network for reconstruction of fatigue crack depth profile from AC field measurement signals

This paper presents a wavelet-network-based technique for reconstructing the crack depth profile of a fatigue crack in a metal from the output signal of an alternating current field measurement (ACFM) probe. The main feature of this technique is that it requires only the ACFM probe output signals along the crack opening. The database for training the network is established by developing a random crack-depth generator, using a fast pseudo-analytic ACFM probe output simulator. The validity of the proposed technique is demonstrated by comparing the actual and reconstructed depth profiles of several simulated and machine-made cracks with no predetermined geometries.     

铝合金焊缝裂纹的阵列涡流检测仿真研究

为了分析阵列涡流传感器扫查不同位置表面横向裂纹时的线圈输出信号特征,以及焊缝受热区金属材质变化对线圈输出信号的影响,建立铝合金焊缝裂纹的阵列涡流检测的三维有限元模型。结果表明:当裂纹长度分别为1.6、3.0、4.5mm时,裂纹长度与线圈感应电动势的波峰幅值呈单调递增关系,探头扫查侧面裂纹时的线圈感应信号总是大于正上方裂纹;焊接所引起的5A06铝合金材料电导率减小会使线圈的感应电动势幅值增大,且当裂纹长度分别为1.6、3.0、4.5 mm时,裂纹长度越大,电导率减小在裂纹检测时对线圈输出信号的影响越小。     

锚固法兰结构设计与有限元分析

锚固法兰是大口径、高内压、远程输气（油）管道系统中的关键部件,其工况复杂。针对某规格锚固法兰的结构设计,结合生产实践,运用有限元方法进行分析计算,解决了设计难题,满足了工程要求。     

基于涡流阵列的裂纹检测仿真分析

分析了涡流阵列检测技术的基本原理。利用有限元方法建立了一种涡流阵列传感器的仿真模型,研究了裂纹检测时的输出信号特征,并考察了工作频率对输出特性的影响。研究表明,裂纹的出现会导致感应线圈输出信号的幅值和相位发生变化,随着激励信号频率的增加,涡流阵列传感器输出信号的差异变大,在3MHz左右时达到最大,然后减小。试验为该传感器的进一步研究及应用提供了参考。     

On the suitability of induction coils for crack detection and sizing in metals by the surface magnetic field measurement technique

The surface magnetic field measurement (SMFM) technique has proved to be an accurate means for crack detection and sizing cracks in ferrous metals. The technique involves the use of two U-shaped current-carrying wires of sufficiently high frequency while measuring the discontinuity in the resultant magnetic field at the crack edge with an appropriate magnetic field sensor. In this work, we describe a mathematical algorithm to obtain the crack signal from the output of an induction coil used in a SMFM probe. We also discuss the measurement errors due to the coil size and shape. To reduce the measurement errors, we present an algorithm in which the crack signal is recovered by appropriate deconvolution of the coil output signal and its spatial transfer function. The algorithm is then used to recover crack signals for various coil shapes and sizes. The study of the results demonstrates the effectiveness of the algorithm in the case of large coils.     

基于神经网络方法的应力腐蚀裂纹定量重构

应力腐蚀裂纹(SCC)主要沿着晶界进展,具有类似于树枝分叉的复杂微观结构,其无损定量检测难度较大。基于应力腐蚀裂纹的简化模型和神经网络,提出了一种SCC定量重构方案。主要思路包括将SCC等效为导电率不为零的半椭圆裂纹,采用涡流饼式探头检测信号作为重构源信号,利用FEM-BEM混合法程序计算教师信号,针对所选神经网络提出相应的裂纹参数化方法。最后利用提出的重构方法对模拟SCC进行了定量重构试验。结果表明,所提出的基于主成分分析和神经网络的方法可用于应力腐蚀裂纹的定量重构。     

Analytical solution for interaction of an arbitrary frequency curved rectangular inducer with a transverse ring shaped groove surrounding a long conductive cylinder

Field distributions around a transverse flaw surrounding a conductive cylinder which is excited by a three-dimensional inducer at arbitrary frequency are presented analytically. The solution is obtained by developing a two-dimensional Fourier series model and using Bessel functions in the third dimension. The metal is assumed as a lossy material and all possible field components in the conductor are expanded. After applying the mode-matching technique, a linear system of AX=B is solved to obtain the unknown coefficients. The accuracy of the proposed modeling technique is confirmed by comparing our results with those obtained by CST finite integration code.     

Time reversal and microwave techniques for solving inverse problem in Non-Destructive Evaluation

Non-Destructive Evaluation (NDE) methods are used to inspect materials without damaging their usefulness. The key problem in NDE is the inverse problem which involves reconstructing materials’ physical profiles, like inner discontinuity etc., using information in the measured NDE signal. Inverse problem solutions in NDE can be classified as model-based and system-based approach. In model-based approach, an accurate forward model is used in an iterative framework. This approach provides a resultant materials' physical profile that minimizes the error between the measured signal and a simulated signal. However, this approach requires repeated calculations of a numerical model in each iteration, making it computationally demanding. This paper presents a model-based method that also provides a direct approach to inversion using principles of time reversal. Time reversal focusing is based on the fact that when a wave solution is reversed in time and back-propagated the wave comes to focus at the source. Using a computational model, this paper applies principles of time reversal to microwave NDE data to solve the inverse problem of defect detection in dielectric materials. A two-dimensional finite difference time domain (FDTD) model, for simulating the propagation of forward and time reversed wave fields, is developed. A dielectric sample with artificial defects, illuminated by a Gaussian modulated pulse, is used in the simulations. The microwave measurements are recorded, time reversed and propagated using the FDTD model to highlight the scatterer/defect. Maxima in the energy image indicate locations of defects. Simulation results demonstrate the feasibility of the technique to detect defects in dielectric materials. The FDTD model is validated using experimental data.     

面向产品设计的铝合金件翻边成形

以某车身铝合金内板件为研究对象,利用有限元模拟软件ABAQUS建立了翻边及回弹过程的有限元模型。通过优化上弯曲半径R1、下弯曲半径R2、翻边角度α等3个产品特征参数和润滑条件μ、模具间隙T等两个工艺参数,来减小回弹值和降低弯裂风险。结合正交试验和灰色关联的方法将多目标问题转化为单目标问题,得到较优的设计参数指导产品设计,并进行试验验证。结果表明,影响综合目标的主次顺序为:模具间隙翻边角度上弯曲半径下弯曲半径摩擦系数,得到优化后的组合参数为R1=5 mm,R2=9 mm,a=75°,μ=0.1,T=t,采用优化后的参数设计零件,得到的实际零件的回弹在公差范围内且无弯裂缺陷。     

基于ANSYS仿真分析的管材涡流检测频率优化研究

针对传统的涡流检测激励频率确定方法存在与实际情况不符和难以得到最佳检测频率的问题,基于大型通用有限元软件ANSYS建立了外径19 mm、壁厚2 mm的1Cr18Ni9Ti不锈钢管材涡流检测内插式探头和穿过式探头的仿真模型,根据差动探头的特性,通过计算距人工缺陷不同距离时检测线圈电流的实部IREAL、虚部IIMAG和线圈的阻抗差ΔZ,进而得到缺陷仿真信号,通过比较不同频率下缺陷信号的幅值和相位,确定穿过式探头的最佳检测频率为50 kHz。     

小规格高强度热轧H型钢孔型优化

为解决H210 mm×134 mm×6 mm×10 mm规格A572(Gr65)高强度热轧H型钢翼缘端部“龟裂”问题，借助有限元模拟软件，对其成因进行了分析。结果表明，A572(Gr65)钢高温塑性较差，当其粗轧段压下量较大且轧槽深度较浅时，粗轧中间坯腿长不足，后续道次长腿困难，导致第6、第11、第14道次孔型未充满，轧件腿端未被加工，从而出现翼缘端部“龟裂”缺陷。为此，对孔型系统进行了优化，成品翼缘端部“龟裂”缺陷得以消除。     

Identification of friction coefficients and hardening parameters using optimization methods coupled with a 3D finite element code

This work deals with the identification of parameters for constitutive models by inverse modeling. This is a topic which has been of increasing interest among researcher within the sheet metal forming community. A method for analytical sensitivity analysis is presented and a non-linear least square technique is used to solve the inverse problem, i.e. minimize the least-square error between a experimental and a model data-set. The constitutive relations are modelled using exponential hardening, isotropic yield conditions and coulomb friction. The experimental data was sampled from a deep drawing operation, and the model data was produced by a corresponding finite element model.     

飞机发动机叶片榫槽爬波原位检测

文章尝试利用爬波特性解决飞机叶片榫槽原位检测难题。分析了飞机叶片榫槽原位爬波检测的原理,介绍了仪器、探头的选用原则,设计了模拟叶片试块,确定了检测灵敏度,并对原位检测方法作了说明。通过对检测结果的分析表明,采用小尺寸高频双晶爬波探头可以有效地对发动机叶片榫槽裂纹进行原位检测,而且检测方便快捷,灵敏度高,信号容易辨别,从而为爬波检测技术开辟了新的应用领域。     

STUDIES ON INTENSE STRAIN REGION AT CRACK TIP BY USING RECRYSTALLIZATION TECHNIQUE

本文用再结晶法测定了中心裂纹拉伸试件裂纹尖端强应变区的塑性应变分布,求得了强应变区参数与J积分及裂纹尖端张开位移COD的定量关系,并用三维弹塑性有限元法进行了计算。实验和计算结果表明,用再结晶法研究三维弹塑性裂纹问题是一种很有效的方法。     

Propagation of transient ultrasound in thick annular waveguides: modeling, experiments, and application

A wave mode expansion solution is formulated for transient excitation of circumferential waves in a thick annulus. The excitation is a distributed traction source on the outer surface modeling a piezoelectric transducer with an angular wedge. The solution provides valuable information on the modal content of the detected signals and the radial dependence of the ultrasonic field within the waveguide. The predicted waveforms are compared with experimental results obtained with several transducers, for various transducer wedge angles, and for various positions of the receiver on the outer surface. The trends predicted by the model are confirmed by the experiment and lead to the selection of good operating parameters (frequency, wedge angle and type, and source–receiver position) for the detection of cracks present on the inner surface of the waveguide. The time-windowed, band-limited wavelet transform of the signal is found to be an effective means to localize the cracks. The technique is successfully tested on a partially annular component of the pitch shaft of the H-46 helicopter.     

Mesoscale modeling of amorphous metals by shear transformation zone dynamics

A new mesoscale modeling technique for the thermo-mechanical behavior of metallic glasses is proposed. The modeling framework considers the shear transformation zone (STZ) as the fundamental unit of deformation, and coarse-grains an amorphous collection of atoms into an ensemble of STZs on a mesh. By employing finite element analysis and a kinetic Monte Carlo algorithm, the modeling technique is capable of simulating glass processing and deformation on time and length scales greater than those usually attainable by atomistic modeling. A thorough explanation of the framework is presented, along with a specific two-dimensional implementation for a model metallic glass. The model is shown to capture the basic behaviors of metallic glasses, including high-temperature homogeneous flow following the expected constitutive law, and low-temperature strain localization into shear bands. Details of the effects of processing and thermal history on the glass structure and properties are also discussed.     

强度匹配对钢结构梁柱节点断裂行为的影响

通过三维弹塑性有限元分析，采用裂纹张开位移CTOD作为断裂韧度参量，研究了梁柱节点梁翼缘焊缝强度匹配对其断裂韧度要求的影响，从而为梁柱节点的设计以及焊接材料的选择提供一定的依据。计算结果表明，梁翼缘焊缝高匹配焊缝的节点，柱翼缘发生屈服的范围较大：采用高匹配能够显著降低对其断裂韧度的要求；而低匹配焊缝区域的塑性区较大，Von Mises等效应力也较大，有利于裂纹的张开。因此，对于钢结构梁柱节点，梁翼缘和柱翼缘连接处采用高匹配焊缝能够显著降低其发生脆性断裂的可能性。有限元计算结果和试验结果相比较可以看出，钢框架梁柱节点采用Q235B钢其抗震性能较差。