Near field inversion method to measure the material properties of a layer

This study develops an in situ methodology that uses ultrasonic waves to measure the material properties of a layer. These material properties include the longitudinal and shear wave speeds, as well as the thickness of the layer. The unknown properties are determined by comparing measured experimental data with values obtained from a theoretical model. Emphasis is placed on the effectiveness of measuring both the in-plane, and the out-of-plane surface displacement components with a laser Doppler vibrometer. An inversion scheme compares (in the frequency domain) the experimentally measured data with data predicted using the theoretical model, and an error-function quantifies the difference between these values. Finally, a downhill-simplex algorithm is used to minimize this error-function and thus determine an optimum set of material properties.     

激光超声技术及其应用

综述了激光超声技术的基本特点,介绍了激光超声产生机理及检测方法。概述了激光超声技术在工业无损检测技术中的应用。得出激光超声技术作为一种新兴技术,具有非接触、远距离、高时空分辨力等特点,将在工业无损检测中具有十分广泛的应用价值。     

A novel technique for visualizing ultrasonic waves in general solid media by pulsed laser scan

This study proposes a novel technique to visualize ultrasonic waves propagated in a general solid medium. A specimen was scanned by a pulsed laser for generation of ultrasound, and the propagated waves were received by a fixed transducer. This technique then provided a snapshot of traveling waves based on the reversibility for the wave propagation, which is confirmed in this paper. We experimentally and numerically investigated and visualized the wave propagation in a steel plate with a slit. Furthermore, we demonstrated inspection of an elbow pipe with an artificial defect, as an application of the proposed technique to a structural component. Non-contact laser scanning for ultrasound excitation enabled us to inspect a wide area of an arbitrarily shaped object. The distinguishing advantages of this technique were determined to be well-suited to the quick and easy wide-range inspection of real structures.     

河床模型地形的无接触快速测量技术

针对河床模型地形测量的需要，介绍了两种无接触快速地形测量技术，即利用超声波实现水下地形无接触快速扫描测量和利用激光与CCD光学成像原理实现水上地形的无接触快速测量，并介绍了测量系统的组成、工作原理及有关主要技术问题的解决方法。     

Development of Barkhausen noise calibration blocks for reliable grinding burn detection

Artificial thermal damage to gear steel material was produced using two heating methods: induction heating and laser irradiation. In the present work, the aim was to obtain in-depth knowledge about the possibilities of producing controlled thermal damage to calibration samples for the Barkhausen noise (BN) method used in gear grinding burn detection and to detect this damage with the BN method. Laser irradiation was found to be a suitable method for controlled production of thermal damage. The results show that both the laser input power and laser traverse rate must be optimized to avoid the rehardening or magnetic saturation of the samples. A framework for the optimal laser parameters was constructed for the steel material studied here.     

Non-destructive and non-contacting stress–strain characterization of aerospace metallic alloys using photo-thermo-mechanical radiometry

A photo-thermo-mechanical non-destructive inspection methodology was developed theoretically and experimentally for non-contact, non-destructive evaluation of mechanical stress–strain relations in metallic materials. A one-dimensional thermal-wave model modified to include mechanical stress explicitly was used to fit experimental data from both frequency scan and stress scan tests and determine the thermal effusivity and diffusivity of an aerospace-industry-relevant aluminum 6061 alloy. Within the elastic regime the thermal conductivity values measured from both photothermal radiometry (PTR) amplitude and phase showed very good agreement, thereby establishing the self-consistency of the new photo-thermo-mechanical radiometry (PTMR) method. Furthermore, a linear conductivity–stress dependence was found, thus establishing the dominant role this property plays in the ability of PTMR to monitor mechanical changes in the aluminum alloy. It was demonstrated that PTMR can be used as a non-contact “strain gauge” within and far beyond the operational strain range of commercial strain gauges, up to the fracture point.     

激光位移传感器在圆柱度误差检测中的应用研究

为了提高圆柱度测量的效率和准确性,针对目前手工检测效率低等缺点,提出一种以三维激光位移传感器的测量原理为依据的光电非接触圆柱度测量方法。与传统方法相比,该方法首先搭建了以回转主轴和伺服执行机构为主的测量控制系统平台;其次,利用机械装置的相对运动,通过传感器采样测量物体各测量截面的信息,实现圆柱度误差测量。     

Optimized laser processing of calibration blocks for grinding burn detection with Barkhausen noise

Calibration samples for the Barkhausen noise (BN) method were produced with laser processing. A planet gear wheel used for production quality control was subjected to laser irradiation to verify the BN sensor output. Different samples were found to respond similarly to the laser processing although the laser parameters needed to be adjusted for different surface qualities separately. The surface optimization for laser processing was studied with different surface qualities of samples. The ground surface was compared with a sandblasted and vibratory ground surface. The ground and sandblasted surfaces were both amenable to the laser processing whereas the vibratory grinding process created inhomogeneous surfaces for laser beam absorption. Laser processing was found to produce uniform changes in the residual stress values in two perpendicular measuring directions. The root mean square value of the BN voltage signal exhibited linear correlations with the values of the residual stress and surface hardness.     

无损检测仪器设备内部校准的有效性

为确保无损检测数据准确和结果可靠,应以量值溯源为基础,对无损检测仪器设备实施内部校准时,应保证内部校准的有效性。     

不锈钢增材制造件的激光超声表面波声速研究

利用激光超声技术对增材制造件进行无损检测具有重要的理论和应用价值.因此,针对不同激光功率下制备的316L不锈钢增材制造样品进行试验.利用激光超声在样品不同成型方向上测试,对表面波声速进行了表征.结果表明:不同激光功率下制备的316L不锈钢增材制造件的成型质量与表面波传播速度有着密切的关系,而且同一增材制造件在不同成型方...     

Determination of paper stiffness and anisotropy from recorded bending waves in paper subjected to tensile forces

Experiments and theory for bending wave propagation of paper sheets in tension are presented. An all-electronic pulsed TV holography technique is used to record the bending wave field initiated by a laser pulse. A theory for bending wave propagation in tensile-loaded paper is developed. The bending waves are influenced by mechanical properties such as density, thickness, bending stiffness, anisotropy and also by tensile forces in the paper. The paper stiffnesses are determined by matching the measured deformation field with the calculated theoretical field. The results show that the bending wave pattern is strongly influenced by the tensile force. For a non-destructive on-line measurement of, e.g. stiffnesses and anisotropy in the paper machine the tensile force must be considered.     

Application of neural networks to laser ultrasonic NDE of bonded structures

The purpose of this study is to develop artificial neural networks for the nondestructive evaluation of a bounded structure using laser generated surface waves. The radial basis model is employed and the inputs of the networks are the sampled dispersion curves while the output is the thickness of the bonding layer or unbond ratio. Numerical simulated dispersion curves with noises were used to train and test the neural networks. The dispersion curves of laser ultrasonic experiments acquired by spectral analysis method were also utilized to test the systems. For comparison, simplex inverse method was also introduced. The results demonstrate that neural networks are well suited for on-line evaluation of bonding thickness and unbond ratio of a bonded layered structure.     

Diagnosis of austenitic steel valves with the magneto-optical method

Samples selected from damaged austenitic steel valves of diesel engines have been examined using the magneto-optical (MO) method. The method uses a magnetic excitation normal to the material surface and enables the assessment of two conditions of the originally non-magnetic austenitic steel, namely an integral one, when the coercivity H_c is measured, and a local one that concentrates on the detection and assessment of individual defects. The results have shown that the operational load increases H_c of these materials and a defect of the fatigue crack type has been detected in the position of the valve failure.