Baseline-free fatigue crack detection based on spectral correlation and nonlinear wave modulation

Liu, Peipei,Sohn, Hoon,Yang, Suyoung,Lim, Hyung Jin Institute of Physics Publishing 2016 Smart materials & structures Vol.25 No.12

<P>By generating ultrasonic waves at two different frequencies onto a cracked structure, modulations due to crack-induced nonlinearity can be observed in the corresponding ultrasonic response. This nonlinear wave modulation phenomenon has been widely studied and proven capable of detecting a fatigue crack at a very early stage. However, under field conditions, other exogenous vibrations exist and the modulation components can be buried under ambient noises, making it difficult to extract the modulation components simply by using a spectral density function. In this study, the nonlinear modulation components in the ultrasonic response were extracted using a spectral correlation function (the double Fourier transform) with respect to time and time lag of a signal’s autocorrelation. Using spectral correlation, noise or interference, which is spectrally overlapped with the nonlinear modulation components in the ultrasonic response, can be effectively removed or reduced. Only the nonlinear modulation components are accentuated at specific coordinates of the spectral correlation plot. A damage feature is defined by comparing the spectral correlation value between nonlinear modulation components with other spectral correlation values among randomly selected frequencies. Then, by analyzing the statistical characteristics of the multiple damage feature values obtained from different input frequency combinations, fatigue cracks can be detected without relying on baseline data obtained from the pristine condition of the target structure. In the end, an experimental test was conducted on aluminum plates with a real fatigue crack and the test signals were contaminated by simulated noises with varying signal-to-noise ratios. The results validated the proposed technique.</P>

Damage detection using sideband peak count in spectral correlation domain

Liu, Peipei,Sohn, Hoon Elsevier 2017 Journal of Sound and Vibration Vol.411 No.-

<P><B>Abstract</B></P> <P>Nonlinear ultrasonic techniques have been proven to be more sensitive to the presence of an early-stage damage than linear techniques. Among various nonlinear techniques, laser nonlinear wave modulation spectroscopy (LNWMS) utilizes a pulse laser to exert a broadband input and a damage on the target structure exhibits nonlinear wave modulation among various input frequency components. A sideband peak count (SPC) technique in the spectral frequency domain was proposed to estimate the damage-induced nonlinearity. In this study, the SPC operation is conducted in the spectral correlation domain so that noise has less influence on damage detection performance and a higher sensitivity to damage can be achieved. In addition, through spatial comparison of SPC over an inspection area, damage can be detected without relying on the baseline data obtained from a pristine condition. The performance of the proposed technique is validated using a numerical simulation performed on an aluminum plate with a simulated crack, and experiments performed on an aluminum plate with a fatigue crack and a carbon fiber reinforced polymer plate with delamination.</P>

Development of a “stick-and-detect” wireless sensor node for fatigue crack detection

Liu, Peipei,Lim, Hyung Jin,Yang, Suyoung,Sohn, Hoon,Lee, Cheul Hee,Yi, Yung,Kim, Daewoo,Jung, Jinhwan,Bae, In-hwan SAGE Publications 2017 Structural health monitoring Vol.16 No.2

Crack localization by laser-induced narrowband ultrasound and nonlinear ultrasonic modulation

Peipei Liu,Jinho Jang,Hoon Sohn 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.25 No.3

The laser ultrasonic technique is gaining popularity for nondestructive evaluation (NDE) applications because it is a noncontact and couplant-free method and can inspect a target from a remote distance. For the conventional laser ultrasonic techniques, a pulsed laser is often used to generate broadband ultrasonic waves in a target structure. However, for crack detection using nonlinear ultrasonic modulation, it is necessary to generate narrowband ultrasonic waves. In this study, a pulsed laser is shaped into dual-line arrays using a spatial mask and used to simultaneously excite narrowband ultrasonic waves in the target structure at two distinct frequencies. Nonlinear ultrasonic modulation will occur between the two input frequencies when they encounter a fatigue crack existing in the target structure. Then, a nonlinear damage index (DI) is defined as a function of the magnitude of the modulation components and computed over the target structure by taking advantage of laser scanning. Finally, the fatigue crack is detected and localized by visualizing the nonlinear DI over the target structure. Numerical simulations and experimental tests are performed to examine the possibility of generating narrowband ultrasonic waves using the spatial mask. The performance of the proposed fatigue crack localization technique is validated by conducting an experiment with aluminum plates containing real fatigue cracks.

Fatigue Crack Localization Using Laser Nonlinear Wave Modulation Spectroscopy (LNWMS)

Peipei Liu,Hoon Sohn,Tribikram Kundu 한국비파괴검사학회 2014 한국비파괴검사학회지 Vol.34 No.6

Nonlinear features of ultrasonic waves are more sensitive to the presence of a fatigue crack than their linear counterparts are. For this reason, the use of nonlinear ultrasonic techniques to detect a fatigue crack at its early stage has been widely investigated. Of the different proposed techniques, laser nonlinear wave modulation spectroscopy (LNWMS) is unique because a pulse laser is used to exert a single broadband input and a noncontact measurement can be performed. Broadband excitation causes a nonlinear source to exhibit modulation at multiple spectral peaks owing to interactions among various input frequency components. A feature called maximum sideband peak count difference (MSPCD), which is extracted from the spectral plot, measures the degree of crackinduced material nonlinearity. First, the ratios of spectral peaks whose amplitudes are above a moving threshold to the total number of peaks are computed for spectral signals obtained from the pristine and the current state of a target structure. Then, the difference of these ratios are computed as a function of the moving threshold. Finally, the MSPCD is defined as the maximum difference between these ratios. The basic premise is that the MSPCD will increase as the nonlinearity of the material increases. This technique has been used successfully for localizing fatigue cracks in metallic plates.

Fatigue Crack Localization Using Laser Nonlinear Wave Modulation Spectroscopy (LNWMS)

Liu, Peipei,Sohn, Hoon,Kundu, Tribikram The Korean Society for Nondestructive Testing 2014 한국비파괴검사학회지 Vol.34 No.6

Nonlinear features of ultrasonic waves are more sensitive to the presence of a fatigue crack than their linear counterparts are. For this reason, the use of nonlinear ultrasonic techniques to detect a fatigue crack at its early stage has been widely investigated. Of the different proposed techniques, laser nonlinear wave modulation spectroscopy (LNWMS) is unique because a pulse laser is used to exert a single broadband input and a noncontact measurement can be performed. Broadband excitation causes a nonlinear source to exhibit modulation at multiple spectral peaks owing to interactions among various input frequency components. A feature called maximum sideband peak count difference (MSPCD), which is extracted from the spectral plot, measures the degree of crack-induced material nonlinearity. First, the ratios of spectral peaks whose amplitudes are above a moving threshold to the total number of peaks are computed for spectral signals obtained from the pristine and the current state of a target structure. Then, the difference of these ratios are computed as a function of the moving threshold. Finally, the MSPCD is defined as the maximum difference between these ratios. The basic premise is that the MSPCD will increase as the nonlinearity of the material increases. This technique has been used successfully for localizing fatigue cracks in metallic plates.

Fatigue crack localization using noncontact laser ultrasonics and state space attractors

Liu, Peipei,Sohn, Hoon,Yang, Suyoung,Kundu, Tribikram Acoustical Society of America 2015 Journal of the Acoustical Society of America Vol.138 No.2

<P>A fatigue crack and its precursor often serves as a source of nonlinear mechanism for ultrasonic waves, and the resulting nonlinear features are often much more sensitive to the fatigue crack than their linear counterparts. Among various nonlinear ultrasonic techniques, the proposed laser nonlinear wave modulation spectroscopy (LNWMS) is unique in that (1) it utilizes a pulse laser to exert a single broadband input instead of conventional two distinctive sinusoidal waves, and (2) a complete noncontact measurement can be realized based on LNWMS. Under a broadband excitation, a nonlinear source exhibits modulations due to interactions among various input frequency components. These modulations are often weak and can be hardly directly detected. In this paper, a damage feature called Bhattacharyya distance is extracted from the ultrasonic time signal corresponding to a pulse laser input and used to quantify the degree of damage-induced nonlinearity and localize the crack. This feature is a measure of a statistical distance used to detect the geometrical changes between state space attractors reconstructed before and after damage formation. It has been successfully used for localizing fatigue cracks in metallic plates.</P>

Detection of genome-wide structural variations in the Shanghai Holstein cattle population using next-generation sequencing

Dengying Liu,Zhenliang Chen,Zhe Zhang,Hao Sun,Peipei Ma,Kai Zhu,Guanglei Liu,Qishan Wang,Yuchun Pan 아세아·태평양축산학회 2019 Animal Bioscience Vol.32 No.3

Objective: The Shanghai Holstein cattle breed is susceptible to severe mastitis and other diseases due to the hot weather and long-term humidity in Shanghai, which is the main distribution centre for providing Holstein semen to various farms throughout China. Our objective was to determine the genetic mechanisms influencing economically important traits, especially diseases that have huge impact on the yield and quality of milk as well as reproduction. Methods: In our study, we detected the structural variations of 1,092 Shanghai Holstein cows by using next-generation sequencing. We used the DELLY software to identify deletions and insertions, cn.MOPS to identify copy-number variants (CNVs). Furthermore, we annotated these structural variations using different bioinformatics tools, such as gene ontology, cattle quantitative trait locus (QTL) database and ingenuity pathway analysis (IPA). Results: The average number of high-quality reads was 3,046,279. After filtering, a total of 16,831 deletions, 12,735 insertions and 490 CNVs were identified. The annotation results showed that these mapped genes were significantly enriched for specific biological functions, such as disease and reproduction. In addition, the enrichment results based on the cattle QTL database showed that the number of variants related to milk and reproduction was higher than the number of variants related to other traits. IPA core analysis found that the structural variations were related to reproduction, lipid metabolism, and inflammation. According to the functional analysis, structural variations were important factors affecting the variation of different traits in Shanghai Holstein cattle. Our results provide meaningful information about structural variations, which may be useful in future assessments of the associations between variations and important phenotypes in Shanghai Holstein cattle. Conclusion: Structural variations identified in this study were extremely different from those of previous studies. Many structural variations were found to be associated with mastitis and reproductive system diseases; these results are in accordance with the characteristics of the environment that Shanghai Holstein cattle experience.

Acoustic Radiation and Dynamic Study of a Steel Beam Damped with Viscoelastic Material

Quanmin Liu,Xiaozhen Li,Peipei Xu,Linya Liu,Yun-Lai Zhou 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.7

Steel structures subject to dynamic loads are prior to generate excessive vibration and noise. Viscoelastic treatment is an effective measure to mitigate the vibration and noise from thin-walled structures in a broad frequency range. H-shaped steel beams are widely used in civil engineering. So an experiment system is established and a series of impact hammer tests are conducted to assess the modal parameters, dynamic response and acoustic behaviour of an H-shaped steel beam coated with various viscoelastic treatments. Firstly, the spectra of the velocity response and acoustic radiation of the bare beam are analysed based on the tested data. Secondly, the resonance frequencies and modal loss factors of the beam with various viscoelastic treatments derived from the frequency response function are compared. Finally, the effect of the layout and thickness of viscoelastic patches on the mitigation of vibration and noise is discussed experimentally. It is shown that the modal loss factor of the first mode increases from 0.012 to 0.191 when the web is treated with 5 mm thick constrained layer damping (CLD). The viscoelastic patches on the web of the H-shaped beam are more effective to control the vibration and noise of the beam than the patches on the flanges. The viscoelastic treatment has distinct effect on the reduction of structural vibration and noise owing to the different dominant frequencies of vibration and noise as well as the frequency-dependent radiation efficiency. The normal velocity level of the H-shaped beam with an 8 mmthick web can be reduced by more than 10 dB and the sound pressure level around the beam about 8 dB when the web is partially covered with the constrained layer damping composed of 2.0 mm thick damping layer and 3.0 mm thick constraining layer.

Construction of TiO2 hollow nanosphere/g-C3N4 composites with superior visible-light photocatalytic activity and mechanism insight

Yinhua Jiang,Fan Liu,Yan Liu,Yuanzhi Hong,Peipei Liu,Liang Ni 한국공업화학회 2016 Journal of Industrial and Engineering Chemistry Vol.41 No.-

An interlayer structure hybrid photocatalyst of TiO2 hollow sphere/g-C3N4 (TOCN) has been successfullyconstructed via a facile impregnation process. The photocatalytic activity was evaluated by degradingRhodamine B under visible irradiation. TOCN-2 with 33 wt.% g-C3N4 had much higher photocatalyticefficiency (98.09%) than pure g-C3N4 (18.62%) and TiO2 hollow sphere (16.37%). Significantly, TOCN-2 showed much superior photocatalytic performance than TiO2 nanoparticle/g-C3N4 composite (53.16%),indicating the hollow morphology of TiO2 also played a crucial role for RhB degradation. In TOCN system,both the morphology effect of TiO2 and the synergistic effects between TiO2 and g-C3N4 resulted insignificantly enhancing photocatalytic performance.