Xiongbing Li

Significance of accurate diffraction corrections for the second harmonic wave in determining the acoustic nonlinearity parameter

The accurate measurement of acoustic nonlinearity parameter β for fluids or solids generally requires making corrections for diffraction effects due to finite size geometry of transmitter and receiver. These effects are well known in linear acoustics, while those for second harmonic waves have not been well addressed and therefore not properly considered in previous studies. In this work, we explicitly define the attenuation and diffraction corrections using the multi-Gaussian beam (MGB) equations which were developed from the quasilinear solutions of the KZK equation. The effects of making these corrections are examined through the simulation of β determination in water. Diffraction corrections are found to have more significant effects than attenuation corrections, and the β values of water can be estimated experimentally with less than 5% errors when the exact second harmonic diffraction corrections are used together with the negligible attenuation correction effects on the basis of linear frequency de...

Simultaneous evaluation of acoustic nonlinearity parameter and attenuation coefficients using the finite amplitude method

A novel method to determine acoustic parameters involved in measuring the nonlinearity parameter of fluids or solids is proposed. The approach is based on the measurement of fundamental and second harmonic pressures with a calibrated receiver, and on a nonlinear least squares data-fitting to multi-Gaussian beam (MGB) equations which explicitly define the attenuation and diffraction effects in the quasilinear regime. Results obtained in water validate the proposed method. The choice of suitable source pressure is discussed with regard to the quasilinear approximation involved. The attenuation coefficients are also acquired in nonlinear regime and their relations are discussed.

Novel path generation algorithm for high-speed pocket milling

A novel tool path generation algorithm is presented for high-speed pocket milling. A spiral fashion polyline is obtained by linear interpolation which is offset from the pocket boundary. The control points are then inserted into the polyline under exponential regularisation. Finally, the smooth tool path is generated via B-spline curve fitting. The tool path generated through this method can be directly used by the machine controller with a NURBS interpolation function, which avoids the time-consuming computation of dividing them into many short line segments. Compared with conventional methods of direction-parallel and contour-parallel path generation, the tool paths obtained by this algorithm have less cutting force fluctuation because they are Cncontinuous, smooth and have no direction jump. The engineering applications proved that the presented method can not only save machining time over the conventional algorithm, but also can avoid solving time-consuming scalar elliptic partial differential equations which are needed by existing spiral tool path generation method.

Assessment of Acoustic Nonlinearity Parameters Using an Optimized Data-Fitting Method with Multi-Gaussian Beam Model-Based Diffraction Corrections

ABSTRACT This article presents a novel approach to determine the nonlinearity parameter using an optimized data fitting method. Based on the quasilinear theory of the Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation, the fundamental and second harmonic pressure fields are expressed using multi-Gaussian beam (MGB) models which separate attenuation and diffraction effects from the plane wave solutions. The developed diffraction corrections are used with a curve-fitting method to extract the nonlinearity parameter together with other acoustic parameters including the attenuation coefficients at the fundamental and second harmonic frequencies. The source nonlinearity is also considered in the fitting process. The proposed scheme is validated through experiments in water and shows that a reliable nonlinearity parameter can be acquired within the range of suitable input power that satisfies the quasilinear approximation involved.

Automatic ultrasonic inspection of flaws in a propeller-blade

Ultrasonic technique is very promising for non destructive inspection. In this paper, a method is presented on automatic ultrasonic inspection of defects in a propeller-blade without computer aided design (CAD) models. The 3D surface data are obtained by ultrasonic measurement, and then the inspection path is planned after the CAD model has been reconstructed. A C-scan image is obtained in real-time ultrasonic automatic inspection. Thereafter, defective area and sound area are separated through binarisation of the C-scan image, and an auxiliary table is used to segment defects in order that defects are disconnected to each other. Then, an algorithm based on edge element is proposed, simplifying the process of extracting edge. Finally, application of these procedures for inspecting a propeller-blade is demonstrated.

A self-reciprocity calibration method for broadband focused transducers

A procedure is developed for self-calibration of broadband, spherically focused ultrasonic transducers based on reciprocity. The input and received signals are measured in a pulse-echo configuration. These signals are used in conjunction with a multi-Gaussian beam model to obtain the electromechanical transfer function of the transducer. This calibration procedure is advantageous because it reduces the experimental configuration to a single transducer and a reflector. Experimental results indicate that the transfer function is insensitive to on-axis reflector placement. This result supports the feasibility of integrating the calibration procedure into actual testing in some situations.

Receiver calibration and the nonlinearity parameter measurement of thick solid samples with diffraction and attenuation corrections

&NA; This paper presents analytical and experimental techniques for accurate determination of the nonlinearity parameter (&bgr;) in thick solid samples. When piezoelectric transducers are used for &bgr; measurements, the receiver calibration is required to determine the transfer function from which the absolute displacement can be calculated. The measured fundamental and second harmonic displacement amplitudes should be modified to account for beam diffraction and material absorption. All these issues are addressed in this study and the proposed technique is validated through the &bgr; measurements of thick solid samples. A simplified self‐reciprocity calibration procedure for a broadband receiver is described. The diffraction and attenuation corrections for the fundamental and second harmonics are explicitly derived. Aluminum alloy samples in five different thicknesses (4, 6, 8, 10, 12 cm) are prepared and &bgr; measurements are made using the finite amplitude, through‐transmission method. The effects of diffraction and attenuation corrections on &bgr; measurements are systematically investigated. When diffraction and attenuation corrections are all properly made, the variation of &bgr; between different thickness samples is found to be less than 3.2%. HighlightsProcedure for determining the absolute nonlinearity parameter of solids is clearly described.Attenuation and diffraction corrections for the 2nd harmonic wave are explicitly provided.Simplified calibration method for receiver transfer function is newly introduced.Attenuation coefficient of the 2nd harmonic wave in the quasilinear regime is determined.

A more general model equation of nonlinear Rayleigh waves and their quasilinear solutions

A more general two-dimensional wave motion equation with consideration of attenuation and nonlinearity is proposed to describe propagating nonlinear Rayleigh waves of finite amplitude. Based on the quasilinear theory, the numerical solutions for the sound beams of fundamental and second harmonic waves are constructed with Green’s function method. Compared with solutions from the parabolic approximate equation, results from the general equation have more accuracy in both the near distance of the propagation direction and the far distance of the transverse direction, as quasiplane waves are used and non-paraxial Green’s functions are obtained. It is more effective to obtain the nonlinear Rayleigh sound beam distributions accurately with the proposed general equation and solutions. Brief consideration is given to the measurement of nonlinear parameter using nonlinear Rayleigh waves.

Statistics associated with the scattering of ultrasound from microstructure

HIGHLIGHTSThe statistical behavior of ultrasonic scattering in polycrystals is investigated.Maximum scattering amplitudes can be theoretically predicted.Bounds and confidence levels on scattering amplitudes are derived.The extreme value statistics theory is applied to ultrasound scattering.The statistics are relevant for any finite number of waveforms N. ABSTRACT The spatial statistics of an ensemble of waveforms containing ultrasonic scattering from microstructure are investigated. The standard deviation of the waveforms is of primary interest, because it is related to the maximum scattering amplitudes in the extreme value statistics theory. Further statistical measures are employed to define theoretical confidence bounds, which bound the experimentally calculated maximum amplitude when a finite number of waveforms are included in the ensemble. These statistical measures are applied in conjunction with a previously developed ultrasonic backscatter model. It is validated through ultrasonic scattering measurements performed on a stainless‐steel pipe sample. These considerations are important for forward models related to the probability of detection (POD) of defects and inverse models used for characterization of polycrystalline microstructures.

Measurement of Rayleigh Wave Beams Using Angle Beam Wedge Transducers as the Transmitter and Receiver with Consideration of Beam Spreading

A theoretical model, along with experimental verification, is developed to describe the generation, propagation and reception of a Rayleigh wave using angle beam wedge transducers. The Rayleigh wave generation process using an angle beam wedge transducer is analyzed, and the actual Rayleigh wave sound source distributions are evaluated numerically. Based on the reciprocity theorem and considering the actual sound source, the Rayleigh wave beams are modeled using an area integral method. The leaky Rayleigh wave theory is introduced to investigate the reception of the Rayleigh wave using the angle beam wedge transducers, and the effects of the wave spreading in the wedge and transducer size are considered in the reception process. The effects of attenuations of the Rayleigh wave and leaky Rayleigh wave are discussed, and the received wave results with different sizes of receivers are compared. The experiments are conducted using two angle beam wedge transducers to measure the Rayleigh wave, and the measurement results are compared with the predictions using different theoretical models. It is shown that the proposed model which considers the wave spreading in both the sample and wedges can be used to interpret the measurements reasonably.