Damage visualization using laser-generated residual guided waves with optimization of laser scanning path

2022 ◽  
Vol 166 ◽  
pp. 108463
Author(s):  
Hongyuan Wang ◽  
Chao Zhang ◽  
Hongli Ji ◽  
Jinhao Qiu
Keyword(s):  
Laser Scanning ◽  
Guided Waves ◽  
Scanning Path ◽  
Damage Visualization

scholarly journals Laser ultrasonic imaging of wavefield spatial gradients for damage detection

2020 ◽  
pp. 147592172095133
Author(s):  
Zihan Wu ◽  
See Yenn Chong ◽  
Michael D Todd
Keyword(s):  
Laser Scanning ◽  
Ultrasonic Imaging ◽  
Image Processing Technique ◽  
Spatial Gradient ◽  
Spatial Covariance ◽  
Laser Ultrasonic ◽  
Spatial Gradients ◽  
Orientation Map ◽  
Scanning Area ◽  
Damage Visualization

This article describes a new damage visualization method to investigate and analyze propagating guided Lamb waves using analyses of wavefield spatial gradients. A laser ultrasonic interrogation system was used to create full-field ultrasonic data measurements for ultrasonic wavefield imaging. The laser scanning process was performed based on both a raster scan and a circle scan. From the high-resolution wavefield data, a spatial gradient–based image processing technique was developed using gradient vectors to extract features sensitive to defects. Local impedance changes at the damaged area would result in a local distortion of the waveform which was captured and quantified by the variation of the gradient vectors in the scanning area as time evolves. Such variation was accumulated over time with a statistical threshold filter to generate a gradient-orientation map for damage visualization. The proposed algorithm was capable of producing distinctive damage patterns when tested experimentally on a 3-mm aluminum plate with multiple simultaneous simulated defects. Compared to conventional techniques like local wavenumber estimation, the generation of the accumulated orientation map involves no filtering process in the frequency or wavenumber domain, at the expense of more accurate shaping of the defect. A spatial covariance analysis was adopted to locate damage from the results as well as to evaluate the correlation between different kinds of defects. Combining the proposed approach with conventional laser ultrasonic imaging techniques enables a fast and robust damage identification and characterization process which requires lower computational burden and practical operation.

Analysis and Prediction of Edge Effects in Laser Bending

2000 ◽  
Vol 123 (1) ◽  
pp. 53-61 ◽  
Author(s):  
Jiangcheng Bao ◽  
Y. Lawrence Yao
Keyword(s):  
Residual Stress ◽  
Edge Effects ◽  
Laser Scanning ◽  
Laser Forming ◽  
Stress Distributions ◽  
Rate Dependency ◽  
Laser Bending ◽  
Numerical Investigations ◽  
Wide Range ◽  
Scanning Path

Laser forming of sheet metal offers the advantages of requiring no hard tooling and thus reduced cost and increased flexibility. It also enables forming of some materials and shapes that are not possible now. In single-axis laser bending of plates, the bending edge is found to be somewhat curved and the bending angle varies along the laser-scanning path. These phenomena are termed edge effects, which adversely affect the accuracy of the bending and result in undue residual stress. Numerical investigations are carried out to study the process transiency and the mechanism of the edge effects. Temperature dependency of material properties and strain-rate dependency of flow stress are considered in the numerical simulation to improve prediction accuracy. Numerical results are validated in experiments. Patterns of edge effects and resultant residual stress distributions are examined under a wide range of conditions. A more complete explanation for the mechanism of the edge effects is given.

scholarly journals A flash-based thermal simulation of scanning paths in LPBF additive manufacturing

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Kamel Ettaieb ◽  
Sylvain Lavernhe ◽  
Christophe Tournier
Keyword(s):  
High Performance ◽  
Laser Scanning ◽  
Thermal Field ◽  
Computational Cost ◽  
Three Dimensional ◽  
Three Dimensional Model ◽  
Content Type ◽  
Proposed Model ◽  
Scanning Path

Purpose This paper aims to propose an analytical thermal three-dimensional model that allows an efficient evaluation of the thermal effect of the laser-scanning path. During manufacturing by laser powder bed fusion (LPBF), the laser-scanning path influences the thermo-mechanical behavior of parts. Therefore, it is necessary to validate the path generation considering the thermal behavior induced by this process to improve the quality of parts. Design/methodology/approach The proposed model, based on the effect of successive thermal flashes along the scanning path, is calibrated and validated by comparison with thermal results obtained by FEM software and experimental measurements. A numerical investigation is performed to compare different scanning path strategies on the Ti6Al4V material with different stimulation parameters. Findings The simulation results confirm the effectiveness of the approach to simulate the thermal field to validate the scanning strategy. It suggests a change in the scale of simulation thanks to high-performance computing resources. Originality/value The flash-based approach is designed to ensure the quality of the simulated thermal field while minimizing the computational cost.

Heat Affected Zone Induced by Laser Forming

Volume 1 ◽  
2004 ◽  
Author(s):  
L. Casamichele ◽  
A. Gisario ◽  
V. Tagliaferri
Keyword(s):  
Mechanical Properties ◽  
Heat Affected Zone ◽  
Laser Scanning ◽  
Standard Condition ◽  
Laser Forming ◽  
Hole Drilling ◽  
Flexible Tool ◽  
Indentation Tests ◽  
Testing Complex ◽  
Scanning Path

Laser forming induces mechanical and structural modifications around the Laser Scanning Path. Various conventional methods are currently available to estimate properties of materials like X-ray and neutron diffraction, strain/curvature measurement, hole drilling, layer removal, chemical etching, etc. but their use is severely restricted due to measurement accuracy, applicability to different materials and geometrical configurations. An application of an experimental method to estimate mechanical properties associated with laser forming of metallic sheets is proposed. This method is based on an instrumented indentation technique which offers a more flexible tool to measure mechanical properties of Heat Affected Zone. The main advantage of this technique consists of testing complex geometric forms with a cheap system able to be used for on-line implementation. The experimental validation of the method was performed calibrating the procedure by using several indentation tests in standard condition. A full map of mechanical properties was subsequently traced employing systematic investigations focused on specimens zone closer to the laser heated scanning path.

Guided Waves for Aircraft Panel Monitoring

2013 ◽  
Vol 558 ◽  
pp. 107-115 ◽  
Author(s):  
Pawel Malinowski ◽  
Tomasz Wandowski ◽  
Wieslaw Ostachowicz
Keyword(s):  
Signal Processing ◽  
Wave Propagation ◽  
Laser Scanning ◽  
Guided Waves ◽  
Guided Wave ◽  
Contactless Measurement ◽  
Measurement Technology ◽  
Additional Mass ◽  
Guided Wave Propagation ◽  
Panel Surface

The reported research concerns experimental investigation toward the monitoring of an aircraft panel. Guided wave propagation phenomena were used to obtain information about the state of the monitored structure. A curved aluminium panel with rivets was investigated. Piezoelectric transducer was used to excite guided waves in chosen structural element. The generated signal was amplified before applying it to the transducer in order to ensure measurable amplitude of excited guided waves. Measurement of the wave field was realized using laser scanning vibrometer that registered the velocity responses at a points belonging to a defined mesh. This contactless measurement technique allowed to investigate phenomena related to wave propagation in the aircraft panel. In the first stage, due to high complexity of the element, baseline measurements were taken. Next, a discontinuity (additional mass) was introduced on the panel surface and the measurements were repeated. Signal processing methods for features extraction from signals were proposed. These features were applied in order to detect and localize the presence anomalies in the investigated panel. The signal processing was conducted in MATLAB with the procedures developed by the authors. The used measurement technology (vibrometer) allowed to register whole wavefield of the propagating guided waves. This allowed to visualize the interaction of the waves with rivets. After introducing the discontinuity on the panel surface wave interaction with it was investigated. Two positions of the additional mass were considered. One just before the riveted stiffener and second after the stiffener. Because of this the influence of the stiffener on the damage detection abilities could be investigated. It can be concluded that the guided wave can be used for monitoring of such complex structures. The vibrometer measurements allowed learn about the guided wave propagation phenomena and perform successful damage localization.

scholarly journals Structural Health Monitoring (SHM) Methods in Machine Design and Operation

2014 ◽  
Vol 61 (4) ◽  
pp. 653-677 ◽  
Author(s):  
Marek Barski ◽  
Piotr Kedziora ◽  
Aleksander Muc ◽  
Paweł Romanowicz
Keyword(s):  
Structural Health Monitoring ◽  
Health Monitoring ◽  
Laser Scanning ◽  
Guided Waves ◽  
Numerical Models ◽  
Theoretical Models ◽  
Spectral Element ◽  
Machine Design ◽  
Destructive Testing ◽  
Structural Health

Abstract The present paper is devoted to the discussion and review of the non-destructive testing methods mainly based on vibration and wave propagation. In the first part, the experimental methods of actuating and analyzing the signal (vibration) are discussed. The piezoelectric elements, fiber optic sensors and Laser Scanning Doppler Vibrometer (SLDV) method are described. Effective detecting of the flaws needs very accurate theoretical models. Thus, the numerical methods, e.g. finite element, spectral element method and numerical models of the flaws in isotropic and composite materials are presented. Moreover, the detection of the damage in structures, which are subjected to cyclic or static loads, is based on the analyzing of the change in natural frequency of the whole structure, the change of internal impedance of the material and the change in guided waves propagating through the investigated structure. All these cases are characterized in detail. At the end of this paper, several applications of the structural health monitoring systems in machine design and operation are presented.

Contour Scanning Method With Inner Supports for Micro-Shell Structural Strengthening Strategy Based on Two-Photon Polymerization Technology

2019 ◽  
Author(s):  
Yu-Wen Tseng ◽  
Chao-Yaug Liao ◽  
Chin-Huang Tseng ◽  
Po-Kai Chen
Keyword(s):  
Laser Scanning ◽  
Structural Strength ◽  
Scanning Method ◽  
Planning Strategy ◽  
Two Photon ◽  
Scanning Path ◽  
Scanning Path Planning ◽  
Structure Collapse ◽  
Fabrication Time ◽  
Two Photon Polymerization

Abstract The traditional two-photon polymerization manufacturing technology encounters two difficulties in fabricating submillimeter/micron-scale structures: excessively long fabrication time and weak structural strength, causing collapse of the structure. To solve these problems, this research first develops a new laser scanning path planning strategy, namely, the contour scanning method with inner supports. The concept is to reduce the fabrication time by manufacturing only submillimeter/micron structural shells as well as to generate the support structure below the horizontal area of the shell to enhance the structural strength. In this study, a method for generating a laser scanning path is presented, and a simple micro-cuboid and a micro-calcaneus with complex shape are fabricated to verify the proposed method. The method can effectively reduce the fabrication time and prevent submillimeter/micron structure collapse.

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