Cuixiang Pei

Cracks measurement using fiber-phased array laser ultrasound generation

A phased array laser ultrasound generation system by using fiber optic delivery and a custom-designed focusing objective lens has been developed for crack inspection. The enhancement of crack tip diffraction by using phased array laser ultrasound is simulated with finite element method and validated by experiment. A non-contact and non-destructive measurement of inner-surface cracks by time-of-flight diffraction method using fiber-phased array laser ultrasound generation and electromagnetic acoustic transducer detection has been studied.

Method improvement of EMAT signals simulation and its applications in TBC inspection

In this paper, a code of finite element method is developed for numerical simulation of electromagnetic acoustic testing (EMAT) signals. In order to improve the simulation efficiency of ultrasonic field, a new explicit integration alg orithm of time domain is introduced in the simulation code. As an extending application of EMAT to the quality control of Thermal Barrier Coating (TBC), the feasibility of an EMAT transducer, which is proposed for detecting delaminating defect in TBC, is investigated by using the new code.

A study of internal defect testing with the laser-EMAT ultrasonic method

This paper studies the ultrasonic detection and evaluation of internal volume defects in metals using laser generation and electromagnetic acoustic transducer (EMAT) detection. A finite element model is developed to simulate the interaction of laser-generated ultrasonic waves with the defect in the material. Not only have the directly scattered shear waves been observed, but also the mode-converted creeping waves on the defect surface. A noncontact laser-EMAT ultrasonic testing experimental system was successfully applied to validate the observed phenomena in the simulation results. The defect can not only be detected and located by the directly scattered shear waves, but can also be quickly evaluated with a new method based on quantitative time-of-flight analysis of the directly scattered waves and the mode-converted waves on the defect surface.

On-site nondestructive inspection by upgraded portable 950 keV/3.95 MeV X-band linac x-ray sources

We have developed and upgraded portable 950 keV/3.95 MeV X-band (9.3 GHz) linac x-ray sources for on-site nondestructive testing (NDT) for social and industrial infrastructures. We integrated the hardware devices as well as software systems. For the hardware, we established all designed parameters including x-ray intensities of 0.05/2 Gy min−1 at 1 m for 950 keV/3.95 MeV systems, respectively. Concerning the software, we adopted the wavelet analysis for enhanced image contrast and partial angle computed tomography (CT) for a small region of interest. The wavelet analysis is effective to reduce scattered low energy x-ray noise in addition to using physical filters and collimators. The partial CT is inevitable to reconstruct an inner reinforced iron tube in concrete. We successfully performed on-site inspection three times, namely of a nitrogen acid distillation tower, a reinforced concrete pier and a large sample cut from a bridge. We obtained the x-ray images of the inner tube, determined the sizes of reinforced iron parts and evaluated the mechanical tolerance. Moreover, we are developing a new x-ray camera specified for MeV x-rays used for NDT of heavy objects. Then, our system will become a self-consisting and specialized high energy x-ray on-site inspection system. We are going to promote an application to NDT of social and industrial infrastructures in Japan and around the world.

Numerical simulation of phased-array laser ultrasound and its application for defect inspection

Inthispaper, anumerical code isdeveloped for theanalysis of phased-array laserultrasound. Thesignal enhancement of ultrasonic waves induced by a multi-beam laser source in phased array is simulated by using finite element method (FEM). The use of phased-array laser ultrasound for crack inspection with shadow method is investigated by simulation method.

Image enhancement for on-site X-ray nondestructive inspection of reinforced concrete structures.

The use of portable and high-energy X-ray system can provide a very promising approach for on-site nondestructive inspection of inner steel reinforcement of concrete structures. However, the noise properties and contrast of the radiographic images for thick concrete structures do often not meet the demands. To enhance the images, we present a simple and effective method for noise reduction based on a combined curvelet-wavelet transform and local contrast enhancement based on neighborhood operation. To investigate the performance of this method for our X-ray system, we have performed several experiments with using simulated and experimental data. With comparing to other traditional methods, it shows that the proposed image enhancement method has a better performance and can significantly improve the inspection performance for reinforced concrete structures.

Design of ultrafast laser-driven microactuator based on photoacoustic mechanism.

In this work, an ultrafast laser-driven microactuator based on the photoacoustic mechanism was proposed with large amplitude and high response frequency. The microactuator was fabricated by LIGA technology. The displacement of the microactuator could be up to 11 μm at resonance state when the repeat frequency was around 14 kHz using a nanosecond pulse laser. Theoretical model was set up and the calculated results agree reasonably well with the experimental data. The microactuator based on the photoacoustic mechanism provides a more efficient actuation method.

Measurement of residual stress with laser-EMAT ultrasonic method

In this work, a non-contact ultrasonic method based on laser generation and EMAT (electromagnetic acoustic trans- ducer) detection is proposed for residual stress measurement. A numerical method based on finite element model is established to simulate the laser-generated ultrasound in pre-stressed media to determine the capability and sensitivity of this method. Fi- nally, the laser-EMAT ultrasonic method isstudied to measure the residual stress in bearing balls to assess the fatigue level of the bearings.

A New Method for Plastic Strain Measurement with Rayleigh Wave Polarization

In this work, a new non-contact and coupling-free ultrasound method with measuring Rayleigh wave polarization (RWP) by electromagnetic acoustic transducers (EMATs) is applied for plastic strain measurement, which can provide a very promising alternative and reference-free ultrasonic testing technique with high spatial resolution. Two specially designed EMAT receivers are developed to measure the polarization of Rayleigh wave generated by an enhanced meander-line-coil EMAT. The change in RWP due to the plastic strain has been successfully measured. And the measurement results indicate that the plastic strain at the specimen surface can be evaluated with good accuracy by measuring the relative change in RWP with the proposed EMAT-based method.

Influence of shielding plates on dynamical response of HL-2M vacuum vessel due to electromagnetic force during a plasma disruption

Purpose In this paper, numerical modelling and dynamical response analysis were performed for the HL-2M vacuum vessel (VV) and shielding plates (SPs) during a plasma disruption by using an updated ANSYS parametric design language (APDL) code developed by the authors. The purpose of this paper is to investigate the influence of the SPs on the dynamical response of VV owing to a transient electromagnetic (EM) force and to optimize the design of SPs in view of the minimization of the structural dynamic response. Design/methodology/approach The Lagrangian approach, i.e. the moving coordinate scheme developed by the authors, was updated to tackle the EM-mechanical coupling effect in the dynamic response analysis of the VV-SPs system due to the transient EM force during plasma disruptions. To optimize the structural design of HL-2M SPs, the influence of the key parameters of SPs, i.e., the side length, thickness and material properties, was clarified on the basis of the numerical results and an optimized design of SPs was obtained. Findings The updated APDL code of the Lagrangian approach is efficient for the transient dynamical response analysis of the VV-SPs system owing to the EM force. The SP of a smaller side length, larger thickness tungsten material better mitigates the dynamical response of the VV-SPs system. Originality/value The Lagrangian approach was updated for the EM–mechanical coupling dynamical response analysis of the VV-SPs system, and the influence of the SP parameters on the dynamical response of the VV-SPs system of HL-2M Tokamak was clarified.