Ultrasonic and structural characterization of anisotropic austenitic stainless steel welds: Towards a higher reliability in ultrasonic non-destructive testing

The non-destructive testing of austenitic stainless steel welds of the primary coolant piping system is a significant problem for the nuclear industry. Ultrasonic techniques would be very helpful to detect, locate and size potential defects. Unfortunately, austenitic welds are coarse-grained, heterogeneous and anisotropic. This leads to aberration and scattering of the ultrasonic waves. In this paper, we present several experimental results of ultrasonic testing of two austenitic welds exhibiting high anisotropy. In order to explain the observed display of wave propagation phenomena such as beam deviation, we use finite element modeling. The modeling is associated with a complete characterization of the inspected welds. Two essential characteristics of the welds are determined: the average elastic constants of the weld and the grain orientations. The capability of the model is illustrated in different testing configurations. This work associating structural characterization and modeling shows that a better understanding of the phenomena of ultrasonic propagation should allow the interpretation and reliability of the industrial inspections of heterogeneous anisotropic welds to be improved.     

Numerical modeling and simulation for ultrasonic inspection of anisotropic austenitic welds using the mass-spring lattice model

This paper deals with two-dimensional numerical modeling and simulation of ultrasonic nondestructive testing of austenitic welds, which are assumed to be homogeneous and transversely isotropic. The numerical computer model used in this work is the rectangular mass-spring lattice model (RMSLM). The model’s capability has first been investigated for accurately simulating ultrasonic waves in the austenitic weld medium. Compatible numerical models for transmitting probes ‘tailored’ for the austenitic weld have also been developed so that incident waves can be sent precisely in desired directions. A two-dimensional numerical simulator, consisting of the probe models and the RMSLM, has been applied to realistic, typical ultrasonic testing problems of austenitic welds, and effective test setups for them have been found. This demonstrates the capability and usefulness of the simulator.     

Characterization of ultrasonic Rayleigh surface waves in asphaltic concrete

This research examines the application of ultrasonic Rayleigh surface waves to the non-destructive evaluation (NDE) of asphaltic concrete in the frequency range 40–100 kHz. Two ultrasonic parameters, the phase velocity and amplitude attenuation, are considered to be sensitive to local compositional and structural variations and are measured. A wedge technique is used to generate Rayleigh surface waves in an asphaltic concrete beam with uniformly distributed aggregate, and this technique is shown to be effective in launching Rayleigh waves in this highly viscoelastic (absorptive) and heterogeneous medium. Three different ultrasonic detection setups using contact and non-contact transducers as receivers are examined and their results are compared. The experimental results show that the wedge generation technique along with an air-coupled receiving transducer with a finite-size aperture is the most reliable for characterizing Rayleigh waves in asphaltic concrete. It is also experimentally demonstrated that the proposed setup may be used to detect aggregate segregation in asphaltic concrete.     

A comparative study of two non-destructive testing methods to assess near-surface mechanical damage in concrete structures

Concrete specimens displaying surface-breaking cracks are tested using two non-destructive testing techniques: the measurement of electrical resistivity and the transmission of ultrasonic surface waves. The capacity of each method to detect, localize and characterize the induced crack pattern—i.e. its width and depth—is investigated. The specimens are made of concrete with three different mixes. A major crack is induced in the middle of the specimen using a three point bending setup. As the bending strength is increased, three different loading levels are obtained. Both methods were able to correctly localize the main crack and follow its evolution. However, due to the complex crack pattern, the crack depth could not be estimated. Nevertheless, the ultrasonic technique was able to detect a change of state of the material before cracks became visible. As the crack intensity increases, variations of ultrasonic parameters in the apparently undamaged area surrounding the main crack were observed, thus highlighting the sensitivity of ultrasonic waves to distributed damage. The obtained results have also thrown bases for further research to couple resistivity and ultrasonic non-destructive methods.     

Ultrasonic surface wave propagation and interaction with surface defects on rail track head

Electromagnetic acoustic transducers (EMATs) are non-contact ultrasonic transducers capable of generating wide band ultrasonic surface waves on metallic samples. A lab-based laser-EMAT system has been developed to observe the ultrasonic surface wave propagation and interaction with surface breaking defects on the sample rail head surface. A wide band EMAT generating surface waves with a frequency content between approximately 50 and 500 kHz is used to propagate ultrasonic waves on the surface of a rail head down the length of the sample. A stabilised Michelson interferometer is used to measure the out-of-plane displacement of the surface wave. A complete picture of the ultrasonic surface wave on the sample surface over time is reconstructed using this technique, with exceptionally high spatial and temporal resolution. Despite the curvature of the rail head, the ultrasonic surface wave propagating down the rail is found to have similar properties to Rayleigh waves by direct comparison to those observed on flat samples using the same technique.     

超声检测过程的数值模拟

简要评述超声检测过程的数值模拟,探讨超声波声场的模拟、超声波和缺陷的相互作用、换能器－缺陷检测系统、超声波在材料和构件中的传播路径、探头设计和超声检测可靠性等。     

TLB型复杂焊接结构超声SH导波成像检测

通过光弹试验分析超声水平剪切(shear horizontal,SH)导波具有优异传播性能,构建了超声导波成像检测系统,基于合成孔径聚焦对超声SH导波用于TLB型式复杂焊接结构成像检测进行了重点研究.结果表明,基于合成孔径聚焦的超声SH导波成像用于TLB型式复杂焊接结构构件检测是可行的,检测图像能够表征板材中区域特征,对焊缝有较好的定位功能,但在焊缝之后会形成长约100 mm的固有散射盲区.文中为进一步提高TLB型式复杂焊接结构超声导波成像检测应用水平提供了基础.     

Using nonlinear ultrasound to track microstructural changes due to thermal aging in modified 9%Cr ferritic martensitic steel

This research investigates second harmonic generation in Rayleigh surface waves propagating in 9%Cr ferritic martensitic steel. Previous experimental results show that nonlinear ultrasound is sensitive to certain microstructural changes in materials such as those due to thermal embrittlement and precipitation hardening. This research measures the ultrasonic nonlinearity parameter as an indicator of microstructural changes due to thermal aging in 9%Cr ferritic martensitic steel specimens. The specimens are isothermally aged for different holding periods to induce progressive changes in the microstructure and to obtain different levels of thermal damage. As thermal aging progresses, the existing dislocations are annihilated in the beginning and precipitates are formed; these microstructural evolutions lead to large changes in the measured nonlinearity parameter, β. Nonlinear ultrasonic experiments are conducted for each specimen using a wedge transducer for generation and an air-coupled transducer for detection of Rayleigh surface waves. The amplitudes of the first and second order harmonics are measured as a function of propagation distance, and these amplitudes are used to obtain the relative nonlinearity parameter at different aging stages. A possible scenario for the microstructural evolution during thermal aging is proposed based on the results from the nonlinear ultrasonic measurements, scanning electron microscopy (SEM), and Rockwell HRC hardness. These results indicate a clear trend that the measured nonlinearity parameter is sensitive to variations in dislocation and precipitate density, and thus can be useful in tracking microstructural changes in this material during thermal aging.     

用于无损检测的电磁超声换能器研究进展

电磁超声换能器(EMAT)是一种通过电磁耦合方法产生和接收超声波的换能器。由于EMAT具有非接触性、无需耦合剂等优点,受到广大无损检测与评估工作者的广泛关注。从物理原理出发,介绍了EMAT过程数学建模、装置设计以及工程应用等方面的研究现状,并对其发展趋势作出了展望。     

Effects of ultrasonic treatment on microstructure and tensile strength of AZ91 magnesium alloy

In this study, the effects of ultrasonic treatment on microstructural features and tensile strength of AZ91 magnesium alloy were investigated. AZ91 melts were subjected to ultrasonic waves of different power levels for 5 min using an ultrasonic device with frequency of about 20 kHz and maximum power of 600 W and cast in sand moulds. The results showed that ultrasonic treatment of the melt prior to casting had a significant effect on the size and sphericity of α-Mg dendrites as well as on the size, continuity, sphericity and distribution of intermetallic particles formed during cooling and solidification of the alloy. Increasing the applied ultrasonic power resulted in smaller, more rounded and better distributed grains and particles. The microstructural effects were mainly attributed to the cavitation and streaming phenomena which took place during ultrasonic treatment in the melt. Tensile strength of the alloy was significantly improved by ultrasonic treatment of the melt. Discontinuity and refinement of Mg₁₇Al₁₂ particles in the ultrasonically treated samples is thought to be the main reason for this improvement. The paper also examines different possible mechanisms responsible for microstructural modification of different phases under ultrasonic treatment conditions.     

表面波天线与压电陶瓷换能器在超声导波信号接收中的效果比较

在一定条件下,超声导波检测试验中的压电陶瓷片可以作为一种表面波天线生成电磁波。将表面波天线技术应用于结构的超声导波检测,并将表面波天线接收信号与压电陶瓷片接收信号进行对比,两者完全吻合,表明表面波天线可以有效接收到超声导波检测信号。同时,对表面波天线位置对接收信号的影响进行了试验研究,发现天线处于不同位置时,接收信号在时间轴上完全吻合,且当其与试件距离不变时,接收信号无明显变化,符合表面波的传播特性。     

Optimization of ultrasonic measurement of remelted zone thickness using backscattered waves

The present work is concerned with non-destructive evaluation of the thickness of the remelted zone formed on aluminum alloy castings by using ultrasonic backscattered waves. Remelted zones with different thicknesses were formed on the surface of an Al–Cu–Si alloy casting plate, and backscattered waves were measured at various positions on the plate by immersion method with different distances of the water path to obtain an optimum focal depth in the specimen. When the ultrasonic wave was focused on the boundary between the remelted zone and the matrix, the amplitude ratio of the backscattered wave from the matrix to that from the remelted zone reached a maximum. The longitudinal wave velocity and the density were measured with test pieces containing remelted zones to obtain acoustic impedances of the remelted zone and the matrix. The reflectivity at the boundary calculated from the acoustic impedances was less than 1.5% (−37 dB).     

薄壁十字交叉激光焊结构缺陷超声Lamb波检测

为了有效识别薄壁十字激光焊结构中未焊透缺陷,开展了超声Lamb波法检测研究. 采用有限元分析方法模拟了A0和S0模态Lamb波在薄壁中与缺陷的作用结果,对缺陷尺寸与回波反射系数的关系进行了预测. 在此基础上,进行仿真结合试验,确定了不同模态Lamb波的入射点、激励角度,探讨了A0和S0模态Lamb波用于识别1.9 mm厚薄板十字激光焊接结构未焊透缺陷的可行性,并获得了超声Lamb波反射系数与缺陷尺寸的关系. 结果表明,仿真研究和试验实测结果的趋势具有较好的一致性. 采用超声Lamb波检测时,A0模态波能够有效检测十字焊接结构中的未焊透缺陷,且可一定程度上表征缺陷的尺寸;而S0模态波对结构中的未焊透缺陷不易于识别.     

Ultrasonic inspection of long steel pipes using Lamb waves

An ultrasonic inspection technique using Lamb waves was evaluated to detect and determine the exact location of flaws present in long steel pipes. Since multiple modes of Lamb waves are generated due to their dispersive characteristics in the inspected pipes, the selection of a specific Lamb wave mode is very important for inspection of flaws. Experimental studies of flaw detectability with the use of each Lamb wave mode, namely, the A₀ S₀, A₁, and S₁ modes and their ultrasonic attenuation characteristics were conducted. The experimental results showed that the A₀ mode is the most effective for detection and exact determination of the location flaws. A lucite wedge containing a water column that generates the A₀ Lamb wave mode was developed and used in the present inspection study. It was found that the ultrasonic beam divergence after wrapping around the inspected pipe once interferes with exact determination of the location of flaws and that the maximum reflection signals are obtained when the transducer is offset axially from the straight line with the position of the flaw. The present study showed feasibilities of ultrasonic inspection with the use of Lamb waves for detection of flaws in insulated or inaccessible steel pipes.     

Acoustoelastic effect in concrete material under uni-axial compressive loading

This study deals with the general matter of non-destructive evaluation of pre-stressed structures in civil engineering. Usually such structures are composed of concrete and are steel reinforced. Proposed idea is the evaluation of mechanical stress state of a concrete body (instead of steel cables) via ultrasonic non-destructive evaluation (NDE), by using the link between ultrasonic velocities and mechanical stresses provided by the acoustoelasticity theory. Velocities of the ultrasonic waves (longitudinal and transversal with different polarizations) are observed during propagation through a concrete body submitted to uni-axial loading (compressive testing). Obvious variations in velocity are found depending on the mechanical stress state (e.g. Δc=92 m/s at σ=16 MPa for longitudinal waves). Thus acoustoelastic behavior of concrete is demonstrated. Further analyses provide acoustoelastic coefficients of concrete about ten times higher than the common ones of steel. The feasibility of stress evaluation using ultrasounds in concrete structures is proved under laboratory conditions.     

离心铸造复合轧辊超声波探伤缺陷判定与质量改进措施

利用超声波探伤技术能够检测出离心铸造复合材料轧辊工作层与芯层冶金结合质量好坏，确定芯部有否缩松。阐述轧辊结合层超声探伤常见的典型回波形式和它们的形成原因，以及回波形式与结合层质量的关系。根据轧辊轴芯超声波穿透检查的不同结果，对轴芯区的质量分别作出技术判定，并介绍改进质量的相应措施。     

超声无损检测中的导波技术

介绍超声无损检测中的导波技术,给出该技术中一些特征的表现形式,如相速度,群速度与频散,并对无损检测中常见的ＳＨ模式导波,细棒中的导波以及兰姆波作了简要的作用。     

超声波作用下医用钛合金(Ti-6Al-4V)植入物的电解抛光

在电解抛光钛合金(Ti-6Al-4V)植入物的过程中引入功率超声波.分析了功率超声波对电解抛光过程的作用及对抛光效果的影响.通过合理利用功率超声波的能量特性,发挥其对传质过程的强化作用、空化效应,并与电化学抛光的特点相结合,对钛合金植入物进行抛光处理.结果表明,引入功率超声波,不但可以大幅度改善钛合金植入物的表面粗糙度,而且还可以增加其表面氧化膜中Ti的氧化物含量,进一步提高钛合金植入物的生物相容性和耐腐蚀性.     

Characterization of stress corrosion cracking in carbon steel using nonlinear Rayleigh surface waves

This research uses nonlinear Rayleigh surface waves to characterize stress corrosion cracking (SCC) damage in carbon steel. Cold rolled carbon steel is widely used for buried fuel pipelines; the environment surrounding these pipelines creates a mildly corrosive environment, which, in combination with an applied stress, can cause SCC. To ensure the safe operation of these structures, it is crucial that damage due to SCC be detected before their structural integrity is reduced by large cracks. In the early stages of SCC, microstructural changes such as dislocation formation and microcrack initiation occur, which have shown to considerably increase the acoustic nonlinearity of a material. These microstructural changes distort and generate higher harmonics in an initially monochromatic ultrasonic wave. This research considers four different levels of SCC induced in four separate 1018 steel specimens, a material which has a similar susceptibility to SCC as steel used for buried fuel pipelines. Then nonlinear ultrasonic measurements are performed before and after the SCC damage is induced. Nonlinear Rayleigh surface waves are utilized to detect the SCC damage that is concentrated near the material surface. The amplitudes of the fundamental and second harmonic waves are measured with contact wedge transducers at varying propagation distances to obtain the acoustic nonlinearity of the specimens as a function of SCC damage. The results show an increase in the measured acoustic nonlinearity in the early stages of SCC, indicating the feasibility of using this nonlinear ultrasonic method to detect the initiation of SCC in carbon steels.     

3D simulations and experiments of guided wave propagation in adhesively bonded multi-layered structures

Understanding guided wave propagation in multi-layered plates and interaction with discontinuities can be difficult, as well as the interpretation of the ultrasonic signals. Propagation of guided waves can be studied analytically solving the equations of motion with the proper boundary conditions; nevertheless analytical models can be difficult to solve for complex multi-layered structures or having inner discontinuities. The problem can be efficiently studied using numerical techniques. Simulation of guided wave propagation in multi-layered structures, for ultrasonic waves in the MHz range, is solved here with the finite element analysis based on an explicit integration rule to solve the equations of motion in a dynamic analysis. Simulation allows a better understanding of propagation and interference phenomena by creating a window of observation in the multi-layered plate. Numerical results determined for a three-layer Al plate, without or with discontinuities, matched very well with experiments, providing an efficient tool to visualize and extract significant information in the transmitted waves and to optimize wave mode and configuration for a rigorous ultrasonic inspection.