Modified relative arrival time technique for sizing inclined cracks

In this paper, a modified relative time technique is proposed for estimating the length and the orientation of inclined cracks using ultrasonic B-scan signals. The proposed technique utilizes the relative position of the tip diffraction echo to the corner reflection echo in an ultrasonic B-scan image to estimate the crack length and the crack inclination angle. Both finite element simulated signals and experimental signals, which are obtained from a specimen with a 3 mm crack with different inclination angles, are used to evaluate the estimation error of the proposed technique. The results show that the proposed technique overcomes the shortcoming of the conventional relative arrival time technique in sizing inclined cracks.     

钢轨踏面裂纹的表面波B扫描成像检测

用超声表面波来检测钢轨踏面裂纹,设计和加工了具有不同深度的裂纹试样。采用频率为0．5MHz的表面波探头对裂纹试样进行B扫描成像检测。为克服钢轨中传播的多模式表面波导致检测图像分辨率低的缺点,采用对A扫描信号移位叠加的方法对图像进行了处理。此方法不仅能对表面裂纹进行较精确的定位,也能定性区分表面裂纹的深度。     

Determination of concrete rebars characteristics by enhanced post-processing of GPR scan raw data

A method for the estimation of rebar radius by post-processing the raw data acquired by the ground penetrating radar as a B-scan radargram is proposed. Considering the hyperbola trace and the diffracted amplitudes an inverse problem consisting of two steps was stated. Using at first hyperbola fitting, the wave velocity and the coordinates of the hyperbola apex are identified. Then the rebar radius is retrieved as solution of a further optimization problem for which the cost function measures the misfit between the actual value of the maximum diffracted amplitudes and their theoretical predictions. The procedure was implemented in Matlab and tested in realistic situations. The obtained results showed improved accuracy.     

基于形状插值的B超图像三维表面重建

B超图像由于受其成像机理的限制,其成像质量较差,无法采用与CT(计算机断层扫描)、MRI(磁共振成像)类似的三维重建方法。针对B超图像的缺点,采用基于形状的插值方法将其转换为等分辨率体数据。此外,对插值算法进行了适当改进,使重建的速度和效果得到明显改善。最后,分别采用移动立方体(marching cubes)算法、连接轮廓线、光线投射(ray casting)算法对B超图像进行三维重建。结果表明,移动立方体算法在重建的真实性和快速性方面都得到了更满意的效果。     

基于同步挤压小波和脉冲压缩的钢轨踏面裂纹电磁超声表面波检测方法研究

钢轨踏面上的疲劳裂纹严重影响着列车行车安全。 针对如何快速有效地检测出踏面斜裂纹的问题,本文提出了一种快 速检测钢轨踏面裂纹的方法。 首先分别建立了含高斯白噪声、正弦信号加高斯白噪声干扰的数学模型,分析了编码脉冲压缩、 同步挤压小波变换和先同步挤压小波变换后脉冲压缩共 3 种信号处理方法的噪音抑制效果。 其次,为了验证上述方法对噪音 的抑制能力,使用激励频率为 1 MHz 的表面波电磁超声换能器对含裂纹的钢轨踏面进行检测。 最后,以检测得到裂纹的超声 回波为研究对象,比较了希尔伯特黄方法处理单一频率脉冲对应的超声回波信号和先同步挤压后脉冲压缩方法对应的降噪能 力和超声成像效果。 实验结果表明:本文所提方法可以获得钢轨踏面裂纹的位置信息及其数量。 希尔伯特黄变换在处理无同 步平均的原始超声回波时,由于回波信噪比低,经验模态分解(EMD)失效。 在以巴克码为激励信号且无同步平均采集的条件 下,先进行同步挤压小波变换后脉冲压缩处理,得到的超声回波信噪比相较于只采用相位编码脉冲压缩提高了 6. 82 dB,相比于 只做同步挤压小波变换提高了 11. 02 dB,能明显提升检测速度和 B 扫图像分辨率。     

Denoising ultrasonic pulse-echo signal using two-dimensional analytic wavelet thresholding

When an ultrasonic angle-beam pulse-echo setup is used, two kinds of noise are present in the received signal: (1) wedge noise, and (2) random noise. In this study, we propose a method for removing both random and wedge noises using a two-dimensional stationary wavelet transform (2D SWT). To improve the performance of the 2D SWT, we employ analytic wavelet thresholding. This requires calculating the analytic signal for a 2D signal and extracting the envelope of the signal, but no regular generalization of analytic signals to multi dimensions is available. We prove that under some certain conditions, the envelope of the ultrasonic B-scan can be extracted exactly by introducing a reference vector. The performance of the proposed denoising method is assessed using simulated and experimental data. The experimental results show that our proposed denoising method is able to reveal the echoes from a surface breaking crack as small as 0.1 mm.     

承压设备超声相控阵检测应用实例

例举了对氢气缓冲罐插入式接管与蒸汽管道两个承压设备的超声相控阵检测实例。通过翔实的数据与直观的视图,凸显了该项技术对于常规无损检测技术的优势。     

快速和高精度透视测量玻璃纤维/树脂复合材料构件内部的离面位移

提出一种光学干涉谱域相位对照B扫描,透视测量透明或半透明玻璃纤维/树脂复合材料内部离面位移的方法。针对玻璃纤维增强树脂基复合材料,设计了一种由树脂层模仿树脂基体、气隙层模仿裂缝气隙、玻璃层模仿玻璃纤维构成的树脂-玻璃复合构件,然后以此复合构件作为标定和量化系统的标准件进行实验研究。通过对平滑或散斑表面树脂-玻璃复合构件分别进行加载前后干涉光谱的两次拍摄,完成构件内部切面的离面位移测量,测量速度快。该系统的视场范围为3.5 mm、轮廓测量分辨率为±26.6 μm、离面位移测量精度为±0.1 μm、测量深度为2.66 mm。该方法在玻璃纤维增强树脂基复合材料力学性能测量和无损检测领域应用前景良好。     

基于分形的肝脏B超图像的识别方法

本文首先引入离散分形布朗随机场模型,得到肝脏B超图像的分形维数与变差函数之间的关系。分形维数可以通过计算图像的变差函数并用最小二乘线性回归法来得到,它被选为图像的特征值,做为分类依据。实验表明,正常肝脏与癌变肝脏的B超图像表现出不同的灰度值空间变化特征。采用不同的滞后距离方向对最终的图像分类结果有一定的
影响,使用四个方向的平均值的分类精度最高。