Papers by Author: Li Lin

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Authors: Y. Zhao, Zhen Yue Ma, Li Lin, X.M. Li, M.K. Lei
Abstract: This paper provides a nondestructive method for determination of the density, thickness and velocity of homogeneous coating from an inversion of experimental ultrasonic reflection coefficient amplitude spectrum (URCAS). The detailed analyses of the inverse algorithm and sensitivity of URCAS to the density, thickness and velocity are presented, and the sensitivity is identified as a basis for selecting the experimental data used in inversion. An example of the method and experimental measurement for comparison was given for an epoxy coating with the thickness of 0.277 mm. The relative errors between the inversion and reference value of the density, thickness and velocity were found to be 0.5 %, 3.97 %, and 0.97 %, respectively.
Authors: Ji Cheng Li, Di Wu, Li Lin, Xi Meng Li
Abstract: In this paper, the exact solutions of PZT coupled electric impedance and structure mechanical impedance were derived with the investigation of the dynamic interaction between the PZT and the host structure. In the frequency range of 0.1-120 kHz, numerical simulation of the PZT coupled electric impedance was performed using MATLAB code. Experimental investigations were conducted with a PZT excitation and electric impedance measurement system developed by our laboratory in the frequency ranges of 30-55 kHz and 80-100 kHz. The profile and resonant frequencies of predicted and measured impedance frequency spectra were in close agreement and the largest deviation is 0.402%.
Authors: Manabu Iwai, Tetsutaro Uematsu, Li Lin, Anurag Sharma, Kiyoshi Suzuki
Authors: Y. Zhao, Zhen Yue Ma, Li Lin, X.M. Li, M.K. Lei
Abstract: Ultrasonic testing porosity of TBC (thermal barrier coating) has been investigated by numerical simulation based on the implementation of FDTD (Finite Difference Time Domain) method for the RPM (random pores model). Numerical simulations of measuring ultrasonic longitudinal and transverse velocities were carried out for the plasma sprayed ZrO2 coatings with porosities ranging from 0.5 % to 4 %. The results show both longitudinal and transverse velocity decrease with the increase of porosity, which is similar to the experimental results in the reference (J. Thermal Spray Technol 12 (2003) 530-535). The investigation proves that the combination of the RPM and FDTD method is available for simulating ultrasonic testing of TBC porosity.
Authors: Li Lin, Xiang Zhang, Jun Chen, Xi Meng Li
Abstract: Ultrasonic attenuation coefficient is firstly calculated utilizing the finite difference time domain method based on a novel 2-D RVM for carbon fiber reinforced plastic (CFRP) composite materials. The results show that the void morphology has detrimental effect on ultrasonic attenuation. Even at the fixed porosity, ultrasonic attenuation coefficient fluctuates due to the randomness of void morphology in CFRP composite materials. This work significantly helps to understand ultrasonic scattering mechanism of voids and formulation of CFRP composite material properties.
Authors: Hai Yan Qiao, Ji Cheng Li, Li Lin, Xi Meng Li
Abstract: The PZT-based electro-mechanical (E/M) method was utilized to measure the impedance of a 1-D steel beam with cracks introducing and developing. Quantitatively assessment of cracks was made by using damage metrics Root Mean Square Deviation (RMSD) and Covariance (Cov). Changes in the coupled impedance of PZT and the beam (500mm×20mm×6mm) were investigated during the appearance and extension of cracks. With the depth of crack dc increasing from 0.6mm to 1.8mm, the peaks of impedance spectrum shifted to lower frequency in the frequency range of 182 kHz-370 kHz and the amplitude showed a decreasing tendency. Moreover, the initial crack brought more significant changes in impedance than that from the developing of cracks. The relationships between dc and RMSD/Cov were investigated. It was proved that RMSD and Cov were efficient in quantitatively presenting the extension of cracks on the 1-D beam.
Authors: Jun Chen, J. Xing, Li Lin, Sheng Zhi Hao, M.K. Lei
Abstract: Surface treatment of hard nitride film with high-intensity pulsed ion beam (HIPIB) was investigated in the present research. On considering the high energy density and short pulse duration of HIPIB source, a one-dimension physical model was built according to the structure feature of film-base sample. It was found that the irradiation of HIPIB lead to a very fast thermal recycle of heating rate 1011K/s and cooling rate up to 1010K/s. The highest temperature located at the surface of film irradiated. When using the HIPIB parameters of accelerating voltage 350kV, pulse duration 70ns and current density 60A/cm2, the surface layer of film would be melt with depth of about 0.35mm, that was verified by the experimental result along with the grain refinement effect due to the fast solidification process.
Authors: Y. Zhao, Li Lin, X.M. Li, M.K. Lei
Abstract: Ultrasonic phase spectrum of reflection coefficient has been used to nondestructively characterize the density, porosity, and microcracks of plasma sprayed Cr2O3 coatings irradiated by high-intensity pulsed ion beam (HIPIB). The ultrasonic measurement was investigated using immersion focusing pulse echo method with a 25 MHz transducer and the phase spectrum of reflection coefficient has been experimentally obtained. The relationship among velocity, density, attenuation coefficient and the phase spectrum was analyzed based on an acoustic transmission model in a multi-layered structure. The velocity relates to the harmonic frequency of the phase spectrum, and the density and attenuation coefficient play roles on the amplitude of the maximum and the shape of the spectrum. The effects of the three parameters (velocity, density and attenuation coefficient) on the amplitude of the maximum of the phase are similar. Some critical value exists which change the relationship between the individual parameter and the maximum of the phase spectrum. When one of the three parameters exceeds the corresponded critical value, the amplitude of the maximum decreases in the form of exp( ) n y = A Bx . For the as-sprayed and irradiated coatings with the thickness of 50 0m, the velocity calculated from the phase spectrum is 2522 and 2772 m/s, harmonic frequency corresponding to 12.61 and 13.86 MHz, respectively. These ultrasonic determinations demonstrated that the coating becomes more densified after irradiation by HIPIB, in agreement with SEM observations. Ultrasonic phase spectrum itself is a good indicator to reveal differences between density and microstructures of coating prepared with various conditions as well as to follow their evolution after HIPIB irradiation.
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