Development of a Non-collinear Nonlinear Ultrasonic-Based Technique for the Assessment of Crack Tip Deformation

Non-collinear nonlinear ultrasonic (NCNLU) wave mixing technique has been established to study the localized plastic deformation at the crack tip during fatigue. A pair of ultrasonic shear wave was mixed non-collinearly to obtain a longitudinal wave of frequency equal to the sum of the two shear wave frequencies under a resonant condition. Experiments were carried out on notched 9Cr-1Mo 3-point bend specimen during high-cycle fatigue. The variation of the NCNLU parameter with the stress accumulation at the crack tip during the fatigue crack initiation and propagation and mapping of the deformation zone around the crack tip are described in this paper.     

基于合成孔径聚焦的超声TOFD检测技术及图像增强

为了精确定位开口裂纹的端部在铝合金厚板对接焊缝中的位置,对其超声衍射时差法(TOFD,time off flight diffraction)的 B 扫描图像进行了处理.为了提高图像的横向分辨率,引入了合成孔径聚焦技术(SAFT, synthetic aperture focusing technique).根据缺陷端部和换能器之间的几何关系,建立了图像SAFT处理的数学模型,实现了B扫描图像的SAFT重建.为了提高图像的纵向分辨率,先将原始图像进行了线性化处理,从而提出了一种新的超声TOFD法B扫描图像处理技术L-SAFT(linearization-SAFT).结果表明,该技术有效地提高了图像的分辨率.利用该技术能快速、准确地捕捉裂纹端部在试件中的横向和深度位置,实现缺陷的精确定位与定量.     

Measurement of axial stress using mode-converted ultrasound

A new ultrasonic technique for stress measurement using mode conversion is proposed and applied to the estimation of axial stresses in high-tension bolts. The effect of axial stresses on acoustic wave velocities in axisymmetric cylindrical solids is analyzed, and a linear acousto-elastic equation is formulated. Theoretical ray analysis is performed to compute time of flight (TOF) of mode-converted waves in cylindrical solids. To evaluate the validity of the proposed method, mode-converted longitudinal and shear waves in carbon-steel bolts are generated and captured to measure the TOF of the waves. Simultaneous velocity measurement of two differently polarized acoustic waves are made with enough resolution to estimate axial stresses with values less than 10% of the yield stress of the bolt material. It is observed from experimental results that the TOF ratio of longitudinal and shear waves is linearly proportional to the axial stress in bolts within 5% error, as expected from theory.     

一种基于超声TOFD法的近表面缺陷检测模式

针对常规超声TOFD法存在近表面检测盲区的问题,提出一种纵波三次反射的TOFDW检测模式.分析了TOFDW模式的声传播特性,并阐明了该模式的检测原理.通过人工缺陷检测,研究了该模式检测信号和图像特征及检测灵敏度和精度.对实际焊缝进行了检测,并通过破坏性试验对无损检测结果进行了验证.结果表明,TOFDW模式能够识别常规模...     

基于自适应滤波的超声杂波抑制方法

在超声衍射时差(time of flight diffraction,TOFD)法检测获取的回波中,作为固定存在的侧向直通波信号会导致近表面缺陷信号不易于识别. 针对这一问题,提出一种基于自适应滤波技术的杂波信号抑制方法. 该方法通过迭代滤波器自身参数,调节参考信号以满足待处理回波中杂波的时基抖动变化要求,并予以去除,从而分离出与其混叠的近表面缺陷信号. 阐明了基于自适应滤波技术的杂波信号抑制原理,并利用所提方法对计算机仿真信号及人工缺陷检测回波进行了杂波抑制处理. 结果表明,所提方法可有效滤除超声TOFD法检测回波中具有时基抖动特性的杂波信号,并提取近表面缺陷信号.     

超声相控阵技术的发展及应用

扼要介绍超声相控阵技术的发展历史、原理及特点。着重介绍其最新研究动态及其在核工业无损检测与评价中的典型应用。指出将相控阵技术同其它诸如纵波一发一收（TRL）、声时衍射（TOFD）技术、数字信号处理（DSP）及成像等技术结合起来，将有助于充分发挥其特点，提高其检测能力，促进无损检测与评价的发展及应用。     

Reliability assessment of manual ultrasonic time of flight diffraction (TOFD) inspection for complex geometry components

Experimental probability of detection (POD) and probability of sizing (POS) curves are developed for the detection and sizing of surface-breaking cracks in components having complex geometry. A manual ultrasonic time of flight diffraction (TOFD) inspection system has been used to develop these POD and POS curves. Initially, it was assumed and subsequently verified that signal responses have a normal distribution. The effects of probe angle and probe center-to-center spacing on both POD and POS were observed. Unlike the PODs previously reported for conventional ultrasonic amplitude based flaw sizing techniques, the PODs associated with TOFD in the range of defect sizes considered here, exhibit a decreasing trend for a fixed set of experimental parameters. It is important to emphasize that the curves obtained in this work are specific to the geometry, specimen dimensions, set of notches and the specific probes used in the experiment. However, when using a manual TOFD inspection system, these curves can be useful for planning the risk-based inspection of components having complex geometry (such as a steam turbine rotor shaft).     

基于临界折射纵波无损评价激光熔覆层应力

基于临界折射纵波声弹性理论对激光熔覆层应力的评价方法进行研究.结果表明,激光熔覆层各向异性组织及层间界面是导致其临界折射纵波信号信噪比低、波形畸变程度大的主要因素,弹性极限内随应力的增大,临界折射纵波信号间时间差基本呈线性规律增大,当应力达到658 MPa时,再随应力的增大,时间差呈跳跃趋势变化,激光熔覆层各向异性组织引起的熔覆层不均匀塑性变形是导致上述结果的主要因素,且随应力的增大该影响程度亦逐渐增大.应力验证结果最大相对误差为4.5%,因而认为采用临界折射纵波法可实现激光熔覆层应力的无损评价.     

Ultrasonic velocity measurements for characterizing the annealing behaviour of cold worked austenitic stainless steel

Precise measurements of shear wave velocities have been made in 20% cold worked and annealed samples of alloy D9 (Ti-modified austenitic stainless steel) to characterize the microstructural changes during annealing. The variation in wave velocity with annealing time exhibited a three stage behaviour. In the first stage, a slight increase in the velocity during recovery regime has been observed. This is followed by a significant increase in the velocity in the recrystallization regime (second stage) and reaching saturation on completion of recrystallization (third stage). Microstructural observations using optical metallography confirmed these three stages. The maximum variation in velocity is observed only when the polarization or the propagation direction of the shear wave is alingned with the cold working direction. Variation in shear wave velocity during annealing process, in general, is just opposite to that of the variation in longitudinal wave velocity. A number of velocity measurements were made by changing the propagation and polarization directions of the shear waves with respect to the cold working direction. Based on these measurements, a suitable velocity ratio parameter is suggested for determining the degree of recrystallization during annealing of cold worked alloy D9.     

超声衍射传播时间法与射线照相法对缺陷检出能力的比较

介绍国外焊缝用超声衍射传播时间法(TOFD)与射线照相法在缺陷检出能力和定量精度方面的比较,最后得出,锅炉、压力容器焊缝(板厚>12.7mm)可用超声TOFD法取代RT检测的结论。     

2D finite element modeling of the non-collinear mixing method for detection and characterization of closed cracks

The non-collinear mixing technique is applied for detection and characterization of closed cracks. The method is based on the nonlinear interaction of two shear waves generated with an oblique incidence, which leads to the scattering of a longitudinal wave. A Finite Element model is used to demonstrate its application to a closed crack. Contact acoustic nonlinearity is modeled using unilateral contact law with Coulomb׳s friction. The method is shown to be effective and promising when applied to a closed crack. Scattering of the longitudinal wave also enables us to image the crack, giving its position and size.     

基于超声杂波抑制的缺陷检测

超声TOFD(time of flight diffraction,衍射时差)法检测的D扫描图像中,作为背景杂波的侧向波与近表面缺陷波会发生混叠,致使近表面缺陷不易于检测. 针对这一问题,提出一种基于杂波抑制的缺陷检测方法. 该方法通过图像能量分布统计,确定背景杂波分量并予以去除,从而分离出与其混叠的缺陷信号,实现近表面缺陷的检测. 建立了的超声TOFD法检测信号的数学模型,阐明了基于图像能量分布的杂波抑制原理. 制作了人工缺陷试块及实际焊缝试块,并对其检测获取的图像进行了杂波抑制处理. 结果表明,提出的方法可有效去除图像中的非缺陷目标、提取近表面缺陷波,从而提高系统的有效检测范围.     

一种基于WMM的超声信号噪声抑制新方法

超声衍射时差（time of flight diffraction,TOFD）法存在接收的缺陷衍射信号能量低、易于被噪声干扰的问题.为了解决这一问题,根据TOFD法检测过程中两相邻测点回波中缺陷信号具强相关性、噪声信号具随机性的特点,在传统小波模极大值（waveletmodular maximum,WMM）方法的基础上...     

Material microstructure effects on ultrasonic waves under simple shear and pure shear

In this paper, the longitudinal and transverse wave velocities propagating into aluminum alloy A6061 under simple shear and pure shear were studied experimentally. Compared with the same velocity change tendencies of transverse wave under simple shear and pure shear, longitudinal wave velocity showed different change tendencies under both shear states, regardless of the same shear strain states in two cases. Furthermore, the measured longitudinal wave velocity changes under pure shear state were apparently categorized into two types according to different material surface states, i.e., simply decreasing change tendency at polished surface state, and chaotic change tendencies at unpolished material surface state. Consequently, the finite element analysis was carried out to investigate the deformation-induced microstructure effects on ultrasonic waves under plastic deformation. The analyzed results indicate that the transverse wave velocity changes depend on textures mainly, whereas the longitudinal wave velocity shows a sensitive response to the point defects.     

Degradation behavior of moduli in extruded pure magnesium during low- to giga-scale cyclic tension fatigue

The mechanical properties of extruded pure magnesium during cyclic tension fatigue in the low- to giga-scale regime at room temperature have been investigated using ultrasonic reflection methods with longitudinal and shear waves. The acoustic velocities and calculated Young’s and shear moduli decreased by a large percentage with an increase in the number of cycles in all cycle modes due to growth of grain boundary voids. The eventual degradation of the properties was largest during giga-cycle fatigue, in which the moduli decreased by ～9%. The elastic behavior depended on the drive stress and the number of cycles rather than on fatigue time. Longitudinal and shear wave propagation characteristics and investigations of a grain boundary before and after fatigue using electron backscatter diffraction based on field-emission scanning electron microscopy and focused ion beam transmission electron microscopy revealed that the largest boundary void gap width was less than several nanometers (almost closed). The Poisson’s ratio and bulk modulus were affected notably by the void gap, in which the threshold corresponds to the longitudinal wave amplitude. Other damage phase data were determined using scanning electron microscopy, Vickers hardness, and surface roughness tests under progressive fatigue; these results also indicated slight grain boundary degradation.     

Pulsed electromagnetic methods for defect detection and characterisation

The magnetic flux leakage (MFL) method has very good defect detection and location capabilities, but defect sizing capabilities, especially for sub-surface defect characterisation, are limited. The pulsed magnetic flux leakage (PMFL) technique has recently been introduced and shown to have great potential for automated defect sizing for surface-breaking defects using time-frequency signal processing techniques, but sizing of sub-surface defects has proved problematic. In this paper, pulsed magnetic reluctance (PMR), a new electromagnetic (EM) non-destructive evaluation (NDE) technique, is introduced and incorporated into a dual PMFL/PMR probe for the characterisation of surface and sub-surface defects in ferromagnetic materials. Experimental results from a comparison study of the two techniques using variety of defects analysed using time-frequency analysis show that the techniques offer complementary information, with PMFL providing defect location data and data for the characterisation of surface defects and PMR offering sub-surface defect characterisation capabilities. The work concludes that integration of these inspection techniques in the new pulsed EM probe can provide enhanced defect characterisation capabilities for flux leakage-based inspection systems using relatively simple time-frequency signal processing techniques.     

精密管棒材数字成像无损探伤和测量系统

精密管材和棒材广泛用于核能和航空航天等领域,其细微缺陷探伤和尺寸精密测量极为重要。为此研制了精密管棒材数字成像无损探伤和测量系统。该系统由超声纵、横向缺陷探伤、超声尺寸测量、涡流探伤等子系统组成,实现了管材内壁、外壁纵横向缺陷超声探伤,棒材内部缺陷超声纵波探伤,棒材纵向缺陷超声横波探伤;棒材周向、径向缺陷超声横波探伤;管材壁厚超声测量,管材、棒材直径超声测量,管材、棒材椭圆度超声测量;管材、棒材缺陷涡流穿过式探伤及异物(渗碳等)检测,管材、棒材材料背景噪声穿过式涡流检测,管材、棒材旋转点式涡流探伤。各检测子系统均依据轴向编码器和周向编码器进行缺陷检测和尺寸测量的时基线记录显示、B扫显示和C扫成像显示,实现了高灵敏度、高分辨力、高可靠性的管材和棒材无损检测。     

基于超声TOFD法直通波幅度分布的近表面缺陷检测

针对超声衍射时差法（TOFD）的近表面检测盲区问题,提出一种基于直通波幅度分布分析的近表面缺陷检测方法。在近表面缺陷检测信号的直通波部分选取多个关键点,揭示了各关键点幅度分布与近表面缺陷深度的关系,获得了用于近表面缺陷检测的幅度分布特征值。试验结果表明,该方法能准确检测出埋深1．0mm的人工缺陷,有效地提高了对近表面缺陷的识别能力。     

AZ31镁合金板材纵波轧制形变规律及边部损伤分析

纵波轧制+平辊轧制(LFR)是一种减轻镁合金轧制边裂的新型轧制工艺,通过一道次纵波轧制+二道次平轧,可有效减少镁合金板材边裂。为了进一步明晰LFR变形规律,本文通过对比AZ31镁合金板材纵波轧制+平轧(LFR)及平轧+平轧(FFR)热-力耦合有限元虚拟轧制对比和物理实验,分析了纵波轧制变形区金属变形规律及其对板材边部损伤的影响。结果表明：纵波轧制形成了异形搓轧区,板材各部位受到较大的三向剪切作用;急速金属流动产生的塑性变形热避免了板材边部温降,有利于提升塑性;剪切及温度影响促使LFR板材形成混晶组织,降低了波谷部位损伤,进而有效抑制了镁合金板材边裂的产生及发展。     

基于电磁超声斜入射SV波的厚壁管道裂纹检测系统

为对厚壁管道缺陷进行有效检测,将电磁超声检测技术与数字信号处理器(DSP)技术相结合,开发了基于电磁超声的厚壁管道裂纹检测系统。通过DSP控制检测系统在厚壁管道中激发电磁超声斜入射SV波,经过DSP将裂纹回波信号处理后显示于上位机。试验结果表明,系统能够在壁厚为35mm的管道中检测出深度2mm的裂纹缺陷。