scholarly journals Flaw Detection and Characterization Using Shearography

1997 ◽  
Author(s):  
Siew-Lok Toh ◽  
Fook-Siong Chau
Keyword(s):  
High Speed ◽  
Flaw Detection ◽  
Electronic Version ◽  
Interferometric Method ◽  
Full Field ◽  
Computer Image Processing ◽  
Before And After ◽  
Fringe Patterns ◽  
Laser Interferometric ◽  
High Pass

Shearography is a laser interferometric method developed originally for full field observation of surface strains of components. Since flaws usually induce strain concentrations around them, shearography can be employed to detect the flaws. Conventional shearography involves exposing high resolution films before and after the components are loaded. The exposed films are developed and then viewed via a high-pass filtering optical setup. Though the images obtained are good, this method is time-consuming. With the advent of high-speed computers, associated sophisticated imaging hardware and software, the Digital Speckle Shearing Interferometry (DSSI) method which employs a CCD (charged-coupled device) camera and computer image processing to produce the interferometric fringe patterns has been developed. In contrast with the conventional shearography, the electronic version does not require any film and is faster. The techniques are used to detect and characterise (a) flaws simulating delaminations in composites and (b) thinning in pipes.

scholarly journals Using Shearography to Find the Flaws

1999 ◽  
Vol 121 (02) ◽  
pp. 62-63
Author(s):  
Siew-Lok Toh ◽  
Fook-Siong Chau
Keyword(s):  
Ccd Camera ◽  
Warning Signs ◽  
Composite Panel ◽  
Interferometric Method ◽  
Full Field ◽  
Digital Version ◽  
Computer Image Processing ◽  
Fourier Filtering ◽  
Digital Speckle ◽  
Fringe Patterns

This article highlights warning signs that a composite panel may be delaminating or thinning, but engineers have a powerful nondestructive testing tool in shearography. This is a laser interferometric method developed originally for full-field observation of surface strains of components. Flaws usually induce strain concentrations around them, and shearography can be employed to detect those flaws. A relatively new variation, digital speckle-shearing interferometry (DSSI), uses a charged-coupled device (CCD) camera and computer image processing to capture and process the interferometric fringe patterns. The digital version is faster than conventional shearography, and does not require any film or Fourier filtering. The main advantages of digital speckle shearing interferometer are the ease and speed with which fringe patterns can be obtained.

scholarly journals High-Speed Holographic Shape and Full-Field Displacement Measurements of the Tympanic Membrane in Normal and Experimentally Simulated Pathological Ears

2019 ◽  
Vol 9 (14) ◽  
pp. 2809 ◽  
Author(s):  
Haimi Tang ◽  
Payam Razavi ◽  
Koohyar Pooladvand ◽  
Pavel Psota ◽  
Nima Maftoon ◽  
...  
Keyword(s):  
Tympanic Membrane ◽  
Middle Ear ◽  
High Speed ◽  
Sound Pressure ◽  
Motion Pattern ◽  
Motion Patterns ◽  
Full Field ◽  
Field Displacement ◽  
Frequency Domains ◽  
Before And After

To improve the understanding of the middle-ear hearing mechanism and assist in the diagnosis of middle-ear diseases, we are developing a high-speed digital holographic (HDH) system to measure the shape and acoustically-induced transient displacements of the tympanic membrane (TM). In this paper, we performed measurements on cadaveric human ears with simulated common middle-ear pathologies. The frequency response function (FRF) of the normalized displacement by the stimulus (sound pressure) at each measured pixel point of the entire TM surface was calculated and the complex modal indicator function (CMIF) of the middle-ear system based on FRFs of the entire TM surface motions was used to differentiate different middle-ear pathologies. We also observed changes in the TM shape and the surface motion pattern before and after various middle-ear manipulations. The observations of distinguishable TM shapes and motion patterns in both time and frequency domains between normal and experimentally simulated pathological ears support the development of a quantitative clinical holography-based apparatus for diagnosing middle-ear pathologies.

Static and Dynamic Deformation Measurements of Micro Beams by the Technique of Digital Image Correlation

2006 ◽  
Vol 326-328 ◽  
pp. 211-214 ◽  
Author(s):  
Xiao Yuan He ◽  
Wei Sun ◽  
Xiang Zheng ◽  
Meng Nie
Keyword(s):  
Dynamic Characteristics ◽  
High Speed ◽  
Dynamic Deformation ◽  
Full Range ◽  
Frame Rate ◽  
Image Correlation ◽  
Static Tests ◽  
Full Field ◽  
Fringe Patterns ◽  
Vibration Parameters

It is critical to measure the static and dynamic deformation of the micro beam over their full range of voltage and frequency inputs, which are key parameters for predicting device behavior. In this study, full-field technique by correlation of projected fringe patterns is selected to determine static deformation, while dynamic parameters can be obtained by DIC with high-speed CMOS camera, whose maximal frame rate is 32k f/s. The static tests of micro beams are carried out by applying electric field forces under different dc voltage, while the dynamic tests are excited by harmonic excitations. Using the DIC method, the whole field in-plane or out-of-plane displacements of the micro beams are obtained, and hence the dynamic characteristics by post-processing of vibration analysis. Experimental results including the bending deformation and vibration parameters are reported and compared with finite element method. This study verifies the feasibility of this technique to measure both static and dynamic characteristics of MEMS components.

Dynamic Holographic-Electronic Speckle-Pattern Interferometry

1993 ◽  
Vol 60 (4) ◽  
pp. 866-874 ◽  
Author(s):  
M. A. Ahmadshahi ◽  
Sridhar Krishnaswamy ◽  
S. Nemat-Nasser
Keyword(s):  
High Speed ◽  
Speckle Pattern ◽  
Processing System ◽  
Ccd Camera ◽  
Electronic Speckle Pattern Interferometry ◽  
Relative Deformation ◽  
Full Field ◽  
Speckle Patterns ◽  
Fringe Patterns ◽  
Laser Light Source

The development of a nondestructive, full-field, quantitative optical technique, and its feasibility to study dynamic deformations of opaque and diffusively reflecting solids under transient loads, are discussed. The technique involves recording a sequence of dynamically changing two-beam speckle interference patterns (also called holographic speckle patterns) of a rapidly deforming body which is doubly illuminated by a laser light source. The time sequence of speckle patterns is recorded by means of a high-speed camera on an ultra-sensitive 35-mm film. The developed negatives are then digitized by a CCD camera into an image processing system. An initial speckle pattern corresponding to the undeformed state of the object is taken as the reference, and subsequent speckle patterns are digitally subtracted (reconstructed) from it to produce time- varying fringe patterns corresponding to the relative deformation of the test object. In order to gain confidence that the technique can be used to record truly transient deformation, it is tested here on a vibrating plate at resonance, thereby obtaining the evolution of the fringe pattern during 1/2 cycle of deformation corresponding to 160 μs.

scholarly journals Full-Field Operational Modal Analysis of an Aircraft Composite Panel from the Dynamic Response in Multi-Impact Test

Sensors ◽  
2021 ◽  
Vol 21 (5) ◽  
pp. 1602
Author(s):  
Ángel Molina-Viedma ◽  
Elías López-Alba ◽  
Luis Felipe-Sesé ◽  
Francisco Díaz
Keyword(s):  
Modal Analysis ◽  
Energy Absorption ◽  
High Speed ◽  
Operational Modal Analysis ◽  
Modal Identification ◽  
Image Correlation ◽  
Composite Panel ◽  
Impact Excitation ◽  
Full Field ◽  
The Impact

Experimental characterization and validation of skin components in aircraft entails multiple evaluations (structural, aerodynamic, acoustic, etc.) and expensive campaigns. They require different rigs and equipment to perform the necessary tests. Two of the main dynamic characterizations include the energy absorption under impact forcing and the identification of modal parameters through the vibration response under any broadband excitation, which also includes impacts. This work exploits the response of a stiffened aircraft composite panel submitted to a multi-impact excitation, which is intended for impact and energy absorption analysis. Based on the high stiffness of composite materials, the study worked under the assumption that the global response to the multi-impact excitation is linear with small strains, neglecting the nonlinear behavior produced by local damage generation. Then, modal identification could be performed. The vibration after the impact was measured by high-speed 3D digital image correlation and employed for full-field operational modal analysis. Multiple modes were characterized in a wide spectrum, exploiting the advantages of the full-field noninvasive techniques. These results described a consistent modal behavior of the panel along with good indicators of mode separation given by the auto modal assurance criterion (Auto-MAC). Hence, it illustrates the possibility of performing these dynamic characterizations in a single test, offering additional information while reducing time and investment during the validation of these structures.

Laser interferometric method for determination of elastoplastic strain field

2003 ◽  
Author(s):  
Shibin Wang ◽  
Jingwei Tong ◽  
Mario Cottron ◽  
Linan Li ◽  
Zhiyong Wang
Keyword(s):  
Strain Field ◽  
Elastoplastic Strain ◽  
Interferometric Method ◽  
Laser Interferometric

3D Profile Variety Measurement of Pectoral Fin in Fish Fast Start

2011 ◽  
Vol 83 ◽  
pp. 280-284
Author(s):  
Ming Jiang ◽  
Shu Zhang ◽  
Xiao Yuan He
Keyword(s):  
Fourier Transform ◽  
High Speed ◽  
Kinetic Characteristic ◽  
Three Dimensional ◽  
Pectoral Fin ◽  
Fourier Transform Profilometry ◽  
Fast Start ◽  
Fringe Patterns ◽  
3D Information ◽  
3D Profile

Fast-starts are brief, sudden accelerations used by fish during predator-prey encounters. In this paper, a three-dimensional (3D) test and analysis method is critical to understand the function of the pectoral fin during maneuvers. An experiment method based on Fourier Transform Profilometry for 3D pectoral fin profile variety during fish maneuvers is proposed. This method was used in a carp fast-start during prey. Projecting the moiré fringes onto a carp pectoral fin it will produce the deformed fringe patterns contain 3D information. A high speed camera captures these time-sequence images. By Fourier transform, filter, inverse Fourier transform and unwrap these phase maps in 3D phase space, the complex pectoral fin profile variety were really reconstructed. The present study provides a new method to quantify the analysis of kinetic characteristic of the pectoral fin during maneuvers.

scholarly journals Experimental study of the dynamic behaviour of High Performance Concrete (HPC) under tensile loading

2018 ◽  
Vol 183 ◽  
pp. 02043 ◽  
Author(s):  
Bratislav Lukić ◽  
Dominique Saletti ◽  
Pascal Forquin
Keyword(s):  
High Speed ◽  
High Performance ◽  
High Performance Concrete ◽  
Imaging System ◽  
Spall Strength ◽  
High Speed Imaging ◽  
Dynamic Tensile Strength ◽  
Full Field ◽  
Local Point ◽  
Measurement Results

This paper presents the measurement results of the dynamic tensile strength of a High Performance Concrete (HPC) obtained using full-field identification method. An ultra-high speed imaging system and the virtual fields method were used to obtain this information. Furthermore the measurement results were compared with the local point-wise measurement to validate the data pressing. The obtained spall strength was found to be consistently 20% lower than the one obtained when the Novikov formula is used.

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