Phase aberration correction in ultrasonic phased array non-destructive testing systems

Phase aberration correction for medical ultrasound systems has attracted a great deal of attention. Since phased array techniques are now widely employed for industrial non-destructive testing （NDT） applications in various fields, the problem of phase aberrations in the process of NDT testing is considered. The technique of cross-covariance for phase aberration correction is presented. The performance of the technique for phase aberration correction is tested by means of echo signals obtained in practical non-destructive testing experiment. The results show that the technique has the better accuracy of phase correction.

Compressive Strength of Basic Magnesium Sulfate Cement Coral Aggregate Concrete(MCAC)on Non-Destructive Testing

Basic magnesium sulfate cement coral aggregate concrete(MCAC)is a new type of concrete consisting of basic magnesium sulfate cement,coarse coral aggregate,coral reef sand and seawater.The rebound hammer(RH),the ultrasonic pulse velocity(UPV)and the compressive strength(fcu)tests of 14 sets of cube specimens of the MCAC after 28 d of aging were conducted.The impact of the content and length of sisal fiber on the relationship between the fcu-RH and the fcu-UPV was determined.A mathematical model was established to predict the strength of the MCAC using the UPV,RH,and comprehensive UPV/RH methods and to obtain the curves of test strength.The applicability of the test strength curves of ordinary portland concrete(OPC),light-weight aggregate concrete(LAC),and coral aggregate concrete(CAC)to MCAC was assessed.The results showed that the test strength curves of OPC,LAC and CAC were inappropriate to determine the strength of MCAC using non-destructive method.The relative standard error of the curves of test strength of the RH method and the comprehensive method met the specifications,whereas that of the UPV method did not.

Determining rock crack stress thresholds using ultrasonic through-transmission measurements

The crack initiation stress threshold is widely used in excavation industries as rock spalling strength when designing deep underground structures to avoid unwanted brittle failures.While various strain-based methods have been developed for the estimation of this critical design parameter,such methods are destructive and often requires subjective interpretations of the stress–strain curves,particularly in rocks with pre-existing microcracks or high porosity.This study explore the applicability of non-destructive ultrasonic through-transmission methods for determining rock damage levels by assessing the changes in transmitted signal characteristics during loading.The change in velocity,amplitude,dominant frequency,and root-mean-square voltage are investigated with four different rock types including marble,sandstone,granite,and basalt under various stress levels.Results suggest the rate of signal variations can be reliably used to estimate crack closure and crack initiation stress levels across the tested rocks before failure.Comparison of the results between the conventional techniques and the new proposed methods based on ultrasonic monitoring are further discussed.

Laser ultrasonic testing for near-surface defects inspection of 316L stainless steel fabricated by laser powder bed fusion

The laser powder bed fusion(L-PBF)method of additive manufacturing(AM)is increasingly used in various industrial manufacturing fields due to its high material utilization and design freedom of parts.However,the parts produced by L-PBF usually contain such defects as crack and porosity because of the technological characteristics of L-PBF,which affect the quality of the product.Laser ultrasonic testing(LUT)is a potential technology for on-line testing of the L-PBF process.It is a non-contact and non-destructive approach based on signals from abundant waveforms with a wide frequency-band.In this study,a method of LUT for on-line inspection of L-PBF process was proposed,and a system of LUT was established approaching the actual environment of on-line detection to evaluate the method applicability for defects detection of L-PBF parts.The detection results of near-surface defects in L-PBF 316L stainless steel parts show that the crack-type defects with a sub-millimeter level within 0.5 mm depth can be identified,and accordingly,the positions and dimensions information can be acquired.The results were verified by X-ray computed tomography,which indicates that the present method exhibits great potential for on-line inspection of AM processes.

Simulation as a Support for Ultrasonic Testing

Ultrasonic testing is a very important non-destructive method for testing components for safety of nuclear power plants and other security and delicate parts in other industries. Nowadays, thanks to the development of computer technology, it is possible to simulate processes which occur during ultrasonic testing. That is why numerical simulations are becoming an integral part of non-destructive testing. Simulations are used to determine parameters of ultrasonic examination, especially parameters of probes and scan plan and also in the analysis of results. They are used in such cases, when it is necessary to verify applicability of probes and methods. This verification could be provided on the weld and test block which are not manufactured. It could be also provided on defects, which are not manufactured in test block, but their presence is possible in given weld joint. Simulations are very useful for verifying the propagation of ultrasonic signal in given area (e.g. weld area). If movement of probe is limited, possibility of whole volume scan should be verified.

Study of ultrasonic phased array inspection imaging technology for NDT

A research about the ultrasonic phased array imaging principle from A-scan signal to B-scan image for non-destructive testing （NDT） was conducted in this paper, the ultrasonic phased array inspection imaging system used in industrial field was developed and the experiment was performed on the steel testing block by the system with 64 elements, 5 MHz phased array transducer. Experimental results show that the flaws could be accurately detected and the flaws size could be estimated from the B-scan images, and the B-scan images could clearly show the location of the flaws, but the quality of B-scan images needs to be enhanced by digital signal processing and controlling dynamic focusing for improving the image resolution.

The Boiler Tube Wall Thickness Quantitative Evaluation Fusing the Magnetic and Ultrasonic Technique

Wall thickness is always a key index for boiler tube inspection in power plant,in order to improve the inspection efficiency and accuracy,a new method fusing the magnetic and ultrasonic technique was proposed.The magnetic technique was used to do full inspection and locate the flaws,and the ultrasonic was employed to implement further quantitative inspection accu- rately.After comparing the precision of the polynomial,exponential and logarithmic function,the polynomial model was selected to fit the relations between the wall thickness and the peak value of magnetic signals,and the data measured by ultrasonic thickness meter was used to calibrate the model parameters online,the defect depth can be sized quickly.The experimental results demon- grate that the model used in this system has better accuracy than the statistics relation model clearly,and it is also suitable for defect evaluation real-time.Moreover,it is unnecessary to have much more experimental data for the curve fitting technology,so it has better practicability than the other methods.

An ultrasonic multi-wave focusing and imaging method for linear phased arrays

To overcome the inherent limits of traditional single wave imaging for nondestructive testing,the multi-wave focusing and imaging method is thoroughly studied.This method makes the compressional waves and shear waves focused in both emission and reception processes,which strengthens the focusing energy and improves the signal-to-noise ratio of received signals.A numerical model is developed to study the characteristics of a multi-wave focusing field.It is shown that the element width approaching 0.8 wavelengths of shear waves can keep a balance between the radiation energy of two waves,which can achieve a desirable multi-wave focusing performance.And an experiment using different imaging methods for a linear phased array is performed.It can be concluded that due to the combination of the propagation and reflection characteristics of two waves,the multi-wave focusing and imaging method can significantly improve the imaging distinguishability of defects and expand the available sweeping range to a sector of-650 to 65°.

Research on Ultrasonic NDT System for Complex Surface Parts

Aimed at inner quality controlling for complex surface parts, an ultrasonic testing system for complex surface parts has been developed using ultrasonic NDT(Non-destructive Testing)which has features of strong penetration, well direction, high sensitivity, low cost, and harmless to people and material. The technologies of the computer, NC (Numerical control), precision mechanism, signal analysis and processing were integrated in the testing system. The system includes a PC, system software, ultrasonic data acquisition card, stepper motor drive card and five-axis precision mechanical device, etc. The software was developed using WIN98-based VC++. According to CAD data of the parts and interpolation methods, the scanning programs can be programmed. The five-axis scanning system is driven by the CNC(computer numerical control) system to control the attitude of ultrasonic probes. The system’s automatic scanning for complex surface parts, real-time acquiring ultrasonic data and automatic identifying flaw signal have been realized. This system can be used not only for testing complex surface parts, but for testing random curve parts. With fast testing speed, high sensitivity, high testing precision and high reliability, the system has a wide adaptability.

Ultrasonic C-scan inspection of brazed joint in thin panel honeycomb structure

The non-destructive testing of brazed joint in honeycomb structure with thin panel （ thickness ： 0. 2 mm） was studied by ultrasonic C-scan method. Samples with different types of artificial defect were designed; the characteristic signal and the main parameters of the test were determined by the pre-experiment, and then parameters were optimized by orthogonal design, finally the optimum process was verified by a single panel sample. The multiple reflection echoes were chosen as the characteristic signal. The optimal C-scan results were achieved when the 20 MHz focus probe was used, and the pass band range for received signal were selected as 8 - 17. 5 MHz. The defects such as incomplete penetration and core damage can be detected with ultrasonic C-scan, and the detection accuracy can reach to 1 ram.

Application of the digital matched-filter technique to ultrasonic non-destructive testing

Acoustic-pulse compression is obtained in systems with different timebandwidth products by applying the digital matched-filter technique to ultrasonic non-destructive testing. The signal is linearly frequency -modulated (LFM) pulse and the digitized electrical-excitation signal itself is used as a digital matched filter. Experimental results are in good agreement with theory. Suppressions of side lobes achieve -41.9 dB and -41.5 dB for the Hamming and Gaussian weighted signals respectively. It shows that the application of the digital matched-filter technique improves the performances of a ultrasonic testing system explicitly.

Simulation of Ultrasonic Propagation in Transformers within Thermal Fields and Intelligent Methodology for Hot-spot Temperature Recognition

Hot-spot temperature of transformer windings is a crucial indicator of internal defects.However,current methods for measuring the hot-spot temperature of transformers do not apply to those already in operation and suffer from data lag.This study introduces a novel inversion method that combines ultrasonic sensing technology,multiphysics simulation,and the K-nearest neighbors algorithm.Leveraging the penetrative ability and temperature sensitivity of ultrasonic sensing,a detailed physical field simulation model was established.This study extensively investigates the characteristics of ultrasonic wave signals inside transformers.The investigation includes different temperature fields,ranging from 40℃ to 110℃ at 10℃ intervals,and various ultrasonic wave emitter conditions.By extracting the key features of the acoustic signals,such as the peak time,propagation time,and peak amplitude,an accurate inversion of the winding hot-spot temperature is successfully achieved.The results demonstrate that this method achieves a high accuracy rate(98.57%)in inverting the internal winding hot-spot temperatures of transformers,offering an efficient and reliable new approach for measuring winding hot-spot temperatures.

基于EWT-FastICA的水下超声回波信号降噪方法研究

针对水下超声无损检测易受噪声信号干扰导致缺陷检测精度低的问题,提出基于经验小波变换(EWT)结合快速独立分量分析(FastICA)的水下超声回波信号降噪方法。首先,应用EWT算法对超声回波信号进行分解,得到不同尺度的模态分量(IMF);其次,通过模糊熵(FuzzyEn)算法计算各模态分量模糊熵值,筛选出所需要的模态分量;最后,进行FastICA运算,将筛选出的IMF重构,最终实现超声回波信号与噪声信号的盲源分离,得到纯净的超声回波信号。仿真与实例实验表明,EWT-FastICA结合的降噪方法在超声回波信号降噪处理中,改善了传统经验模态分解出现的模态混叠、端点效应,以及过包络、欠包络等现象,并且降噪处理过程更加快速、准确,可应用于类似的水下超声检测信号降噪处理。

Successes and challenges in non-destructive testing of aircraft composite structures

Composite materials are increasingly used in the aerospace industry.To fully realise the weight saving potential along with superior mechanical properties that composites offer in safety critical applications,reliable Non-Destructive Testing(NDT)methods are required to prevent catastrophic failures.This paper will review the state of the art in the field and point to highlight the success and challenges that different NDT methods are faced to evaluate the integrity of critical aerospace composites.The focus will be on advanced certificated NDT methods for damage detection and characterization in composite laminates for use in the aircraft primary and secondary structures.

可水声定位的水下弹载测试系统设计

为了获取水下弹体发射全过程的多通道飞行姿态数据,并且针对水下弹体发射入水后难以搜寻的问题,设计了一种可水声定位的水下弹载测试系统。采用STM32F103C8T6作为主控芯片,控制系统多通道数据采集、存储与超声波脉冲信号的发出。设计了功率放大电路和阻抗匹配电路,提高了系统工作效率。经过测试,加载在换能器上的激励电压峰-峰值达134 V,可驱动换能器发出超声波。实验结果表明,采集系统可以连续高精度地采集弹体全过程飞行数据,在水下3.8 m可探测到目标,达到实际使用要求。

电容式微机械超声换能器的声学封装方法

针对水下超声检测的迫切应用需求,提出了一种电容式微机械超声换能器(CMUT)水密封装方法,选用聚氨酯(PU)和聚二甲基硅氧烷(PDMS)完成了CMUT封装。对封装后的CMUT主要性能参数进行测试和对比得出,PU和PDMS封装后的CMUT中心工作频率分别约为1.75和2.05 MHz,3 dB相对带宽比分别达到了97.14%和92.68%,展示出优异的宽频带特性。PU封装的CMUT最大发射电压响应和接收灵敏度较PDMS封装的CMUT分别高出0.14和1.21 dB,且其输出声压能力在1~20 cm范围内高于PDMS封装的CMUT。该研究结果验证了两种材料封装的CMUT都能够满足水下超声检测应用要求,为CMUT水密封装方法优化提供了理论和实验依据。

Applications of Non-destructive Tests for Diagnosis of Heritage Buildings:Case Studies from Singapore and Malaysia

Non-destructive tests have been increasingly used in historic buildings not only for pre-restoration investigation but also as useful tools to evaluate the effectiveness of eventual interventions.These tests can complement and supplement destructive tests like laboratory analysis of extracted samples as long as a sound sampling plan has been put in place to commensurate with the pattern and extent of dilapidation and materials distribution.Common methods employed in projects in Singapore and Malaysia include the infrared thermography,ground penetrating radar,microwave moisture tomography and ultrasonic pulse echo tomography.The paper discusses about a selection of case studies,demonstrating the application of various techniques for the identification of hidden details,defects and deterioration,and moisture detection.

中国现代声学与马大猷

声学的历史是非常古老的,但是现代声学却是从19世纪末20世纪初开始的。中国现代声学的发展则要稍晚一些。本文将中国现代声学的发展历程分为四个阶段:草创时期、奠基时期、发展时期、创新时期。简述了马大猷在中国现代声学发展中所做出的主要贡献和他的学术成就。可以看到,马大猷作为中国现代声学的奠基人,他也是简正波理论的奠基人之一,在中国现代声学发展中起了重要作用。本文还对马大猷的学术思想和社会贡献作了初步探讨。

水下模型地形超声成像分析与实时测量

针对水利工程试验中水下模型地形的测量问题,分析比较了高频超声回波信号与阵列超声成像信号特征,并提出了一种超声成像测量方法。该方法直接利用高频超声成像仪获取水下模型地形的实时图像,通过分析提取图像中的地形成像亮带线,从而实现水下模型地形的快速无接触实时测量。结果表明基于高频超声成像的测量方法能够有效地规避水中悬浮粒子对水下模型地形测量的干扰,能够实现地形的实时测量,测量误差在3个像素宽(1.8 mm)以内。该方法自适应性强,速度快,分辨率高,为水下模型地形的动态分析与实时测量提供了一种有效途径,并已运用到实际工程中。

水下无损检测技术的研究现状和发展趋势

文章介绍了水下构件的损伤形式和水下无损检测的技术手段,根据实践经验指出了目前存在的问题,并分析了今后的发展方向。