Fuzai Lv

Bio: Fuzai Lv is an academic researcher from Zhejiang University. The author has contributed to research in topics: Guided wave testing & Hysteresis. The author has an hindex of 6, co-authored 18 publications receiving 100 citations.

Helical comb magnetostrictive patch transducers for inspecting spiral welded pipes using flexural guided waves

Abstract: A wavefront analysis indicates that a flexural wave propagates at a helix angle with respect to the pipe axis. The expression for calculation of the helix angle for each flexural mode is given, and the helix angle dispersion curves for flexural modes are calculated. According to the new understanding of flexural guided waves, a helical comb magnetostrictive patch transducer (HCMPT) is proposed for selectively exciting a single predominant flexural torsional guided wave in a pipe and inspecting spiral welded pipes using flexural waves. A HCMPT contains a pre-magnetized magnetostrictive patch that is helically coupled with the outer surface of a pipe, and a novel compound comb coil that is wrapped around the helical magnetostrictive patch. The proposed wideband HCMPT possesses the direction control ability. A verification experiment indicates that flexural torsional mode T(3,1) at center frequency f=64kHz is effectively actuated by a HCMPT with 13-degree helix angle. Flexural torsional modes T(N,1) with circumferential order N equals 1-5 are selected to inspect a seamless steel pipe, artificial defects are effectively detected by the proposed HCMPT. A 20-degree HCMPT is adopted to inspect a spiral welded pipe, an artificial notch with cross section loss CSL=2.7% is effectively detected by using flexural waves.

Ultrasonic guided wave-based switch rail monitoring using independent component analysis

Abstract: Switch rails are indispensable components of high speed railway systems, which have stringent nondestructive testing requirements owing to the severe operating conditions. In this article, an ultrasonic guided wave method is proposed for defect detection and localization using independent component analysis (ICA). The temperature effect is included in the data matrix by a random selection of the signals measured at different temperatures. A damage index named the average standard Euclidian distance (ASED) is used to evaluate the deviations of the test signals from the baseline signals in the feature space consisting of the independent components for the defect detection. Once the defect existence is found, defect localization is conducted by another ICA-based decomposition of a new data matrix with additional test signals for the same defect. Independent components whose coefficient vectors show a high correlation with the standard step change vector are chosen to construct the ICA-based residual signal. Then the time instance and location of the defect is determined by observing the first very high peak occurring in the residual signals. A detectability index for defect location (DIDL) is proposed. Experimental validations are performed for the defects on the foot and web of a switch rail. The results of the ASED curves clearly indicate the existence of artificial defects, and the ICA-based residual signals show the location of the defects. The proposed method is found to be superior to conventional methods such as simple baseline subtraction and optimal baseline subtraction regarding the DIDL.

Scattering of torsional flexural guided waves from circular holes and crack-like defects in hollow cylinders

Abstract: A study on the scattering of torsional flexural guided waves from circular holes and crack-like defects in hollow cylinders is carried out through finite element simulation and laboratory experiment. Two types of defects: circular holes and crack-like defects with varying orientation angles are studied. Results show that the reflection coefficients for flexural modes with different helix angles of propagation detecting a crack-like defect vary greatly, while for a circular hole the reflection coefficients for different flexural modes are similar. It is observed that there exists a specific flexural mode that shows the maximum reflection coefficient for a crack-like defect. The scattering properties can be utilized to classify defects as circular hole and crack-like, the range of the orientation angle of a crack-like defect can also be predicted. The detection sensitivity for oblique crack-like defects is significantly improved by using flexural modes that propagate at a helix angle with respect to the pipe axis. A flexural mode sweeping technique is proposed for classifying and characterizing defects in hollow cylinders. The proposed classification and characterization method is validated by laboratory experiments. Pipeline inspection using flexural guided waves can be supplemental to current inspection using only axisymmetric waves in order to improve the probability of an accurate and reliable inspection process.

Multi-feature integration and machine learning for guided wave structural health monitoring: Application to switch rail foot:

Abstract: Switch rails are weak but essential components of high-speed railway systems that have urgent nondestructive testing requirements owing to aging and the associated potential for fatigue damage accu...

Excitation of axisymmetric and non-axisymmetric guided waves in elastic hollow cylinders by magnetostrictive transducers

Abstract: Ultrasonic guided waves have been successfully applied in nondestructive evaluation (NDE) and structural health monitoring (SHM) of pressure vessels and pipelines due to their advantages, such as long detection range and high inspection efficiency. Compared with other ultrasonic guided wave actuators, magnetostrictive transducers are more cost-effective, involve simpler fabrication process, and have higher possible transduction efficiency. The normal mode expansion (NME) method is adopted to analyze the forced response and perturbation analysis of elastic hollow cylinders with respect to magnetostrictive loadings, including partial loading, axial array loading, and circular array loading. The phase velocity and frequency spectra of axisymmetric/non-axisymmetric guided waves excited by magnetostrictive transducers are analyzed. The theoretically predicted trends are verified by finite element numerical simulations and experiments.

Inspection and monitoring systems subsea pipelines: A review paper:

Abstract: One of the largest movers of the world economy is the oil and gas industry. The industry generates billions of barrels of oil to match more than half the world’s energy demands. Production of energ...

The use of active materials for machining processes : A review

Abstract: This paper provides a review of active materials in the context of applications to manufacturing machining processes. The important concepts and background of active materials are briefly introduced. After which, the applications of these materials are discussed as applied to relevant themes in machining processes. A brief overview of research work on experimental and theoretical studies on various process monitoring and control is considered, and several research papers on these topics are cited. This paper concludes with a discussion of future research areas and a suggests path forward.

Structural Health Monitoring (SHM) and Determination of Surface Defects in Large Metallic Structures using Ultrasonic Guided Waves.

Abstract: Ultrasonic guided wave (UGW) is one of the most commonly used technologies for non-destructive evaluation (NDE) and structural health monitoring (SHM) of structural components. Because of its excellent long-range diagnostic capability, this method is effective in detecting cracks, material loss, and fatigue-based defects in isotropic and anisotropic structures. The shape and orientation of structural defects are critical parameters during the investigation of crack propagation, assessment of damage severity, and prediction of remaining useful life (RUL) of structures. These parameters become even more important in cases where the crack intensity is associated with the safety of men, environment, and material, such as ship’s hull, aero-structures, rail tracks and subsea pipelines. This paper reviews the research literature on UGWs and their application in defect diagnosis and health monitoring of metallic structures. It has been observed that no significant research work has been convened to identify the shape and orientation of defects in plate-like structures. We also propose an experimental research work assisted by numerical simulations to investigate the response of UGWs upon interaction with cracks in different shapes and orientations. A framework for an empirical model may be considered to determine these structural flaws.

Review of Current Guided Wave Ultrasonic Testing (GWUT) Limitations and Future Directions.

Abstract: Damage is an inevitable occurrence in metallic structures and when unchecked could result in a catastrophic breakdown of structural assets. Non-destructive evaluation (NDE) is adopted in industries for assessment and health inspection of structural assets. Prominent among the NDE techniques is guided wave ultrasonic testing (GWUT). This method is cost-effective and possesses an enormous capability for long-range inspection of corroded structures, detection of sundries of crack and other metallic damage structures at low frequency and energy attenuation. However, the parametric features of the GWUT are affected by structural and environmental operating conditions and result in masking damage signal. Most studies focused on identifying individual damage under varying conditions while combined damage phenomena can coexist in structure and hasten its deterioration. Hence, it is an impending task to study the effect of combined damage on a structure under varying conditions and correlate it with GWUT parametric features. In this respect, this work reviewed the literature on UGWs, damage inspection, severity, temperature influence on the guided wave and parametric characteristics of the inspecting wave. The review is limited to the piezoelectric transduction unit. It was keenly observed that no significant work had been done to correlate the parametric feature of GWUT with combined damage effect under varying conditions. It is therefore proposed to investigate this impending task.

A non-isothermal phase field study of the shape memory effect and pseudoelasticity of polycrystalline shape memory alloys

Abstract: In this paper, a non-isothermal phase field (PF) model is proposed to investigate the shape memory effect (SME) and pseudoelasticity (PE) of polycrystalline shape memory alloys (SMAs) with consideration of the latent heat effect. The latent heat release and absorption accompanying the phase transformation processes are explicitly considered by coupling the phase field evolution with latent heat conduction. A modified Gibbs free energy function is proposed to accommodate the continuously varying temperature. It is shown that the SME and PE of polycrystalline SMAs under different ambient temperatures can be well characterized with the proposed PF model within a unified framework. The PF simulation results are in accordance with the previously reported experimental results. The influences of various factors such as the ambient temperature, grain size, crystal orientation, and latent heat effect on the phase transformation process and mechanical responses as well as the temperature evolution of SMAs are systematically discussed by conducting PF simulations. Some important implications for the devise of elastocaloric cooling devices are provided.