Chun Guang Xu

Metal Surface Fatigue Detection Using Nonlinear Ultrasonic

Based on theory of ultrasonic nondestructive testing on surface fatigue damage of metal components, the wave law of ultrasonic nonlinearity caused by fatigue is studied. When there are lattice defects in metal material, second-order nonlinear coefficient β changes during ultrasonic propagation. According to the point, the system of nonlinear ultrasonic testing is build. The change trends of harmonic amplitudes and ultrasonic coefficients are measured during fatigue bending testing of materials such as 45 steel, 2024 aluminum alloy and 304 stainless steel. The results shows: in elastic phase, the ratios of harmonic and fundamental waves monotonically increase with fatigue life, and in plastic phase, deformations appear and micro-cracks expand into macro-cracks in materials, the ratios firstly decrease and then increase with fatigue life. However the quadratic sums of nonlinear coefficient are approximately linear with the fatigue life. Therefore, when the relationship between the quadratic sums and fatigue life is known, it can be used to characterize fatigue state of metal materials.

The Relationship between Minimum Zone Sphere and Minimum Circumscribed Sphere and Maximum Inscribed Sphere

Among the four methods (minimum zone sphere, minimum circumscribed sphere, maximum inscribed sphere, and least square sphere), only the minimum zone sphere complies with ANSI and ISO standards and has the minimum sphericity error value. Evaluation of sphericity error is formulated as a non-differentiable unconstrained optimization problem and hard to handle. The minimum circumscribed sphere and the maximum inscribed sphere are all easily solved by iterative comparisons, so the relationship between the minimum zone sphere and the minimum circumscribed sphere, the maximum inscribed sphere is proposed to solve efficiently the minimum zone problem. The relationship is implemented and validated with the data available in the literature.

Ultrasound Imaging Using Spatial Domain Phase Information

The aim of this paper is to determine the efficacy of the ring-shaped array used for imaging the objects inside the array. Hyperbola algorithm and ellipse algorithm which are conventionally used in the field of guided wave for locating the defects are developed and combined here to extract the image. Meanwhile, much more phase information is added in this process. Fan-shaped ultrasound radiation is generated separately by the 45 rectangular ultrasonic transducers which are circular embedded in the wall of a container. The time of flight data and the attenuation data are obtained and stored in the A-scan wave of each receiving transducer, subsequently, they are applied for reconstructing the image of all tested objects. The validity of the combined measuring method with phase information is demonstrated by imaging the distributed polyurethane objects.

Detection Resolution Analysis of Scanning Acoustic Microscopy Used in Electronic Packaging

Scanning Acoustic Microscopy (SAM) has been a powerful non-destructive testing tool used in electronic packaging and material characterization. With the development of 3D electronic packaging, internal dimensions of electronic packaging are getting more and more smaller, and the detection accuracy of existing non-destructive testing technology is far behind the requirements of manufacturing technology. In this study, a set of practical SAM system was developed independently by our Lab. And its detection resolution was analyzed using high frequency focused transducers with center frequency ranging from 20 MHz to 100MHz. The experimental results show that the lateral resolution of the ultrasonic transducer with 100MHz central frequency can reach about 40 microns, which is consistent with calculated resolution. Comparing with Sparrow criteria, Rayleigh criteria is more coherent with the experimental results.

Modelling and Measurements of Ultrasonic Fields in Composites

Widely use of composite structures such as fiber-reinforced composites advances the demand for reliable and effective techniques of ultrasonic nondestructive testing. The model to calculate acoustic field around anisotropic materials is introduced, including propagation and penetration model of Gaussian beams in front of and behind the composites. Simulation and experiments on transmitted acoustic field of composites with different thickness were conducted. Some characteristics of ultrasonic filed around composite materials, such as focal distance and beam spread have been researched theoretically and experimentally. The accuracy of the proposed model is verified by the comparison of the model-based predictions with the experimental results. The achievement will be useful for detecting the defects inside of composites nondestructively.

Research on Making Constant Valve Block of Residual Compressive Stress Based on Ultrasonic Testing

We proposed a new method of measuring the residual stress for the component based on the acoustoelastic theory and focused on a new technology of making constant value block of residual stress by shot peening in order to solve problems of residual stress testing by ultrasound. Monitored the residual stress value of block by self-developed ultrasonic residual stress measurement system. The results indicate that the value of the test block changes not much, so it can provides a new way to improve the ultrasonic testing of residual stress.

Defect Detection of the Segmental Spherical Shell Based on Ultrasonic Transducer Array

It is of great significance to monitor and quantify the defects in the thin segmental spherical shell components. In the paper the guided wave’s inspiring method has been obtained from the wave-mode conversion based on the theory of the guided wave propagating in the thin spherical shell. Using the wavelet to process the testing signal, and the ellipse localization imaging algorithm, the defect’s localization and orientation can be detected accurately. Experimental results show the defect’s direction and location can be detected effectively and clearly.

The Curved Plate Flaw's Location and Direction Detecting Based on the Transducer Array

The curved structural plate components have been widely used in petroleum, natural gas, chemical industry, and other industries fields, monitoring and detecting the curved structural plate components flaw has a great significance for improving the components integrity, reliability and lifespan in service. Based on the elastic wave fundamental theory, elastic wave equations, and phase velocity dispersion characteristic curves in curved plate component, the article gives the phase velocity practical detecting method. By using the comsol finite element software, the author proposed a wave propagating forward modeling analytical method, which gives a guidance to study the relationship between the wave and the flaw. By adopting the ellipse algorithm, the article proposed a positioning and imaging method which was used to locate the flaws position and distinguish the flaws direction. Based on the theoretical and technical analysis above, a number of experiments has been done, and the results shows that the detecting and imaging method can locate and image the flaws position and its geometrical morphology precisely for the curved plates flaw detecting.

Application of Silicon Carbide Diode in Ultrasound High Voltage Pulse Protection Circuit

SiC diode (Silicon Carbide Diode) is a newly commercial available Schottky barrier diode with zero reverse-recovery-time, which is a perfect candidate for fabricating high voltage pulse protection circuit in ultrasonic transceiver system. With SiC diode’s high performance, the circuit can deliver 400 volts or higher voltage protection level, which is not an easy job for other kind of diodes. In this article, the theory of diode-bridge protection circuit is briefly discussed, and a SiC diode-bridge protection circuit was fabricated, and some experiments has been done to verify the feasibility of using SiC diodes in diode-bridge protection circuit.

Detection Resolution of Acoustic Microscopy in Micro-Scale

Scanning acoustic microscopy (SAM) is a powerful non-destructive testing tool used in the field of electronic package, micro-and nanomaterial and medication. The capability to distinct how minimum of defect is very important to detect the flaw in electronic packages. The detection resolution of SAM depends on the frequency of ultrasonic focus transducers. In this paper, the Multi-Gaussian Beam model to simulate the sound field of the focused transducers is discussed. Mainly the frequency domain imaging algorithm and 2D-Deconvolution method for better image quality and high resolution is analyzed. Finally, the calibration experiments for the detection resolution of 100MHZ transducer is carried out. In addition, the micro flaws with different dimensions are observed at different defocusing location. It is concluded that the detection resolution decreases with the deviating from focus plane, so the flaws should be sensitive on the focus area by precisely controlling the vertical position for better detection resolution.