Ultrasonic imaging of concrete members using an array system

The use of an ultrasonic array system is described, which can be used combined with 3D reconstruction calculations. In this way ultrasonic reflection and backscatter from the inside of concrete members can be imaged and interpreted. The application of the system is demonstrated for two examples: measuring the concrete cover of utility pipes in a tunnel and the examination of transversal ducts in a bridge plate.     

Effect of the presence and size of a real macro-crack on diffuse ultrasound in concrete

In civil engineering structures, the first layer of concrete plays a role in terms of water-tightness, and contributes to the protection of metal frames from corrosion by external chemical agents (water, CO₂, chlorine etc.). In concrete, a crack is comprised of an external part with a surface opening, and a completely or partially closed part below the surface. The aim of this paper is to identify the contribution of a real macro-crack on the diffuse ultrasound parameters. The methods ability to characterize the open part of the crack is confirmed. The results reveal the influence of the closed part of the crack, with regions in partial contacts, on the diffusion parameters.     

铝板结构主动Lamb波扫查合成损伤成像方法

单激励主动Lamb波板结构损伤时间反转成像方法仅对面向激励器的损伤侧敏感,在实施过程中会存在伪损伤点问题,影响对损伤的正确评估。研究提出扫查合成损伤成像方法,首先通过扫查的方法轮流选择压电元件进行激励,从多个角度实现对损伤的照射,再将扫查得到的信号进行合成成像,实现对损伤的监测。在铝板结构上的试验结果表明,该方法可有效消除监测结果的方向敏感性和伪损伤点,提高损伤成像监测结果的准确性和稳定性。     

合成孔径聚焦技术在TOFD检测中的应用

为了准确定位和测量在低合金厚板对接焊缝中的缺陷,对超声衍射时差法的D扫描图像进行了处理。为了提高图像的横向分辨率,准确识别缺陷的位置和尺寸,引入了D扫描图像的合成孔径聚焦算法(SAFT-D)。根据缺陷端部和换能器之间的几何关系,建立了D扫描图像SAFT-D处理的数学模型,实现了D扫描图像的SAFT重建。试验结果表明,SAFT-D算法有效地提高了图像的分辨率,增强了缺陷识别的能力,能够准确地定位和定量工件中的缺陷。     

Ultrasonic sparse-TFM imaging for a two-layer medium using genetic algorithm optimization and effective aperture correction

This paper introduces a sparse total focus method (TFM) as a viable solution to the trade -off between the imaging precision and computational efficiency. A corrected two-layer TFM algorithm is first established; then the element layout in the sparse arrays is optimized by the genetic algorithm to improve the spatial resolution and contrast resolution. Using the effective aperture theory, the weighting functions of the optimized sparse array elements are investigated, and the corrected sparse-TFM algorithm is developed. Experiments are conducted on the side-drilled holes in a wedged specimen. Results indicate that the proposed sparse-TFM can greatly increase the computational efficiency while maintaining a relatively low error.     

A Bayesian approach for sparse flaw detection from noisy signals for ultrasonic NDT

Ultrasonic pulse-echo methods for flaw detection have been widely employed as an effective strategy for nondestructive evaluation, and flaw detection plays an important role due to its ability to detect localized damage in structures. In practice, flaw damage typically occurs in a few areas in the material, resulting in only a few echoes that exist in a received signal, which motivates us to detect flaws using sparse representation methods. In this study, the noisy signal is modelled by a linear combination of modulated Gaussian pulses, which form an over-complete dictionary. The over-complete dictionary is designed such that the sparseness of the representation is expected. A robust sparse Bayesian learning framework is employed with the goal of enforcing model sparseness and reducing the source of ill-conditioning in the inversion problem for flaw detection. Useful information, including the range of frequency and bandwidth parameters of the flaw echoes, is also estimated. Based on this information, we propose a post-processing scheme for structure noise elimination and flaw detection. The capability of the proposed method is quantitatively evaluated by simulation studies and is further validated by the experimental data.     

A new sensing skin for qualitative damage detection in concrete elements: Rapid difference imaging with electrical resistance tomography

In this paper we investigate whether a thin layer of electrically conductive materials that is painted to the surface of concrete elements can be used as sensing skin to detect and locate cracking and damage in the concrete substrate. Cracking of the concrete results in the rupture of the sensing skin, thus locally increasing its electrical resistivity. We monitor the local change in the electrical resistivity of the sensing skin using electrical resistance tomography. In this work, we utilize difference imaging scheme. Experiments on polymeric substrates as well as on concrete substrates are performed. The results indicate that the developed sensing skin can be successfully used to detect and locate cracking and damage on concrete and potentially other nonconductive substrates.     

声波散射在焊接板结构超声导波合成孔径阵列成像中的作用

为揭示声波散射在焊接板结构超声导波合成孔径阵列成像中的作用机制,将散射回波矩阵和散射渡越时间矩阵用于分析描述超声水平剪切（shear horizontal,SH）导波声波散射,探讨了焊缝散射和边界散射在导波成像中的作用关系.结果表明,散射矩阵是揭示声波散射在超声导波阵列成像作用机制的有效工具,散射回波矩阵与散射渡越时间矩阵具有相同的散射矩阵因子,导波图像出现与散射矩阵因子成倍数关系的“条带”伪像,图像椭圆簇轨迹特征复杂化,图像背景噪声增强,图像信噪比减小.研究工作可为深入开展焊接板结构超声导波非直线阵列成像算法研究提供基础.     

Extended synthetic aperture focusing technique for ultrasonic imaging of concrete

Quantitative nondestructive characterization of defects and inclusions in portland cement concrete structures are realized in this paper via extended reconstructions for linear array ultrasound systems. This is accomplished through generalization of traditional Kirchhoff-based synthetic aperture focusing technique migration to mitigate the effects of limited aperture and handle multiple scans as a single virtual array with increased effective aperture. Pearson’s correlation is utilized to account for uncertainty in relative position of individual measurement and mitigate the need for robotic precision when placing adjacent scans. The robustness of the method is demonstrated on artificially generated data as well as in-situ measurements for assessment of internal portland cement concrete characteristics such as inclusions and cracks.     

钢管水浸超声检测中45°横波折射角的调整方法

ASTM E213《金属管材超声波检验的标准操作方法》规定,为了扫查到整个钢管壁厚,必须保证超声波探头要能够在管材或者管壁中产生一个波束中心近似45°的横波。为解决水浸自动超声设备的检测方法问题,需要对横波折射角度进行精准控制。介绍了水声程调节法、外伤二次声程调节法两种技术,达到了精确调整声束在钢管中的横波折射角度的目的。     

A new non-contacting non-destructive testing method for defect detection in concrete

A new non-destructive testing (NDT) method for defect detection in concrete structures is presented. The method is based on the dynamic response of flawed concrete structures subjected to impact loading. Conversely to similar NDT techniques, such as the impact-echo method, the present method uses non-contacting devices for both impact generation (a shock tube producing shock waves) and response monitoring (laser vibrometers measuring concrete surface velocity). Experimental and numerical (finite element) studies have been carried out for concrete specimens containing artificial defects (penny-shaped cracks parallel to the free surface) with varying length and depth. According to the experimental and numerical results, it appears that the present method enables an effective detection of defects, particularly in the range of shallow defects.     

High-speed non-contact defect imaging for a plate-like structure

Images of defects in a plate-like structure can be obtained from amplitude distributions measured using the scanning laser source technique. This paper discusses high-speed non-contact imaging for defects in a plate. Fundamental experiments conducted using a contact piezoelectric transducer as a receiving device revealed the effect of the generated wave shape and measurement speed on the defect images. Generating tone-burst waves consisting of multiple frequency components and averaging the images obtained in multiple frequency bands (frequency image averaging, FIA) gave clearer defect images in which noisy effects due to low signal-to-noise ratio and spurious images due to multiple reflections in high-speed imaging were reduced. Moreover, FIA was shown to be effective for high-speed non-contact imaging using a laser Doppler vibrometer.     

Automatic flaw detection in NDE signals using a panel of neural networks

The magnetic flux leakage (MFL) method is widely used for the assessment of the condition of off-shore cables, gas pipes and aerial tramway cables. At Empa, a measuring device was developed to use the physical effect of MFL for large diameter steel cables as used in civil engineering structures.It is considered that the automatization of the flaw detection task would offer great advantages, both from an economic point of view as well as in terms of reliability. In this work the application of a feature extraction model based on an analytical approximation of the MFL intensity is presented. Parameters that are closely related to the size and position of a defect are used as fitting variables in the solution of the inverse problem that links the recorded MFL intensity to the flaw that generates it.Using these significant parameters a committee of neural networks is trained in order to obtain a robust flaw detection algorithm.     

Stack imaging of spectral amplitudes based on impact-echo for flaw detection

The impact-echo method recently has drawn a remarkable amount of attention for nondestructive evaluation of defects in concrete structures. Extracting resonance frequencies responsible for the locations of reflectors, the depth and the presence of defects are estimated. So far, however, the technique has some limitations for practical applications. This is because there exist unresolved problems in the application of the impact-echo to concrete structures in service. Consequently, the method is studied theoretically on the basis of the elastodynamics and the signal analysis. In order to circumvent the difficulty to identify peak frequencies in the conventional procedure, a new procedure to evaluate defects in concrete is investigated, applying an imaging procedure. Thus, stack imaging of spectral amplitudes based on the impact-echo is developed. This procedure is applied to a prestressed concrete beam to classify a grouted duct and an ungrouted duct. The location and the presence of the ungrouted duct can be visually identified.     

用超声波探伤法检测硬质合金顶锤质量的可行性研究

本文介绍了超声波探伤的原理和硬质合金顶锤的质量检验,分析了超声波探伤的方法,在硬质合金顶锤探伤中采用直探头、直接接触从顶锤尾部进行探伤的方法,确定了探伤仪合理的工作参数,对硬质合金顶锤探伤结果进行了分析,建立了与合成压机及工艺相适应的探伤标准。证明了利用超声波探伤的方法检测硬质合金顶锤的内在质量的可行性,对于金刚石生产厂家控制顶锤的质量、降低硬质合金顶锤消耗具有积极意义,生产实践证明,与利用超声波探伤检测之前相比,顶锤消耗降低了2kg／万克拉左右。     

一种X射线数字成像检测缺陷尺寸的测量方法

提出了一种X射线数字成像检测缺陷尺寸的测量方法。借鉴半波高法,以半波高法下的尺寸测量误差为基准,对不同缝隙尺寸试样在相同的检测条件下进行X射线数字成像检测,计算该检测条件下的总不清晰度,总结出缺陷尺寸与总不清晰度比值同波高比例的关系,并通过试验进行了验证。结果表明,该方法简单、实用性强,可为实现缺陷尺寸的准确测量提供技术支持。     

内螺纹钢管的漏磁检测方法与缺陷识别

轧制无缝钢管时芯棒与管体之间以相对进动的方式高速旋转 ,易在钢管内壁形成内螺纹。内螺纹槽超深的钢管不符合相关质量标准 ,但生产厂却难以检测出内螺纹超深的钢管。用漏磁高速检测技术结合计算机智能识别软件构成的检测方法和系统 ,可探测和识别这些内螺纹 ,能标记超深螺纹位置和持续范围。将检测信息反馈到轧制工艺中 ,可明显提高合格钢管产量。检测结果符合相关标准 YB40 83和 GB/ T1 2 60 6要求     

重轨探伤不合的原因分析及改进研究

针对重轨探伤不合的问题,以U71Mn探伤不合试样为研究对象,通过宏观检验、光学显微镜、扫描电镜等手段进行分析研究。结果表明,探伤不合的主要原因是轨腰存在孔洞、微小裂纹以及MnS夹杂物、氮化物夹杂等缺陷。经过对冶炼、连铸及铸坯冷却方式、轧钢工艺加以改进,提高了铸坯内部质量及重轨探伤合格率。     

A far-field airborne radar NDT technique for detecting debonding in GFRP–retrofitted concrete structures

A far-field airborne radar (FAR) nondestructive testing (NDT) technique integrating inverse synthetic aperture radar (ISAR) measurements and a backprojection algorithm for the condition assessment of glass fiber reinforced polymer (GFRP)–wrapped concrete structures is proposed. The method is directed toward the detection of near-surface defects and delaminations located in the vicinity of GFRP–concrete interface. Normal and oblique incidence measurement schemes were adopted and studied for their effectiveness in detecting near-surface anomalies. This technique is also applied to the detection of rebars in reinforced concrete cylinders. Laboratory measurements in the frequency range 8–12 GHz were made on artificially damaged GFRP–concrete cylinders for validating the concept of this technique. Spatial resolutions (range and cross-range) are improved by integrating radar measurements at different azimuth angles and in different frequencies, and implementing the developed progressive image focusing scheme. The feasibility of the proposed FAR NDT technique for distant inspection is validated through these studies.