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 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.

Automatic Measurement of Concrete Deformation Field under Uniaxial Compression Based on DSCM

2011 ◽  
Vol 320 ◽  
pp. 58-63 ◽  
Author(s):  
Wei Weng ◽  
Rui Dong Peng ◽  
Hong Bin Liu ◽  
Wei Jia Ma ◽  
Sheng Hua Zhang
Keyword(s):  
Uniaxial Compression ◽  
Experimental Studies ◽  
Correlation Method ◽  
Ccd Camera ◽  
Compression Process ◽  
Full Field ◽  
Digital Speckle Correlation Method ◽  
Speckle Correlation ◽  
Digital Speckle ◽  
Digital Speckle Correlation

As a kind of optical approach to measure full field deformation with the properties of non-contact, Digital Speckle Correlation Method (DSCM) has been adopted widely with the development of computer technology. The deformation of concrete under external loads is usually uneven and thus it should be characterized by full filed measurement so as to obtain accurate results. It should be effective for engineering to monitor the deformation of concrete by using digital speckle correlation method, and such monitoring is helpful to study the law of uneven deformation of concrete and discover its damage characteristics. The images of the surface of concrete specimens at the different stress were captured and recorded with a high-resolution CCD camera during uniaxial compression process. An own software was developed to analyze these images by DSCM. The nature texture of the specimen surface were searched and matched in different images, therefore the displacement field and the strain field of the surface of concrete specimens were calculated out. Experimental studies have shown that digital speckle correlation method can be well used to calculate the accurate deformation of concrete just through a direct photograph of concrete surface under different loads.

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.

Study on Displacement Measurement for Induced Strain Field Based on Digital Speckle Pattern Interferometry Method

2013 ◽  
Vol 273 ◽  
pp. 510-514
Author(s):  
Jing Liu ◽  
Hui Zhang ◽  
Jun Li ◽  
Da Chuan Chen ◽  
Yan Kun Tang
Keyword(s):  
Strain Field ◽  
High Speed ◽  
Speckle Pattern ◽  
Measuring Method ◽  
Full Field ◽  
Digital Speckle Pattern Interferometry ◽  
Level Measurement ◽  
On Line ◽  
Interferometry Method ◽  
Digital Speckle

Digital Speckle Pattern Interferometry ( DSPI for short ) method has become one of the most practical worthy techniques for speckle measuring methods with the high-speed development of optic-electronical technique, image processing technology and electronic computer technology. There is a lot of advantages about it, such as uncomplicated operation, non-contacting, advanced automatic level, measurement on-line and extensive using. In this thesis, the displacement variation of the induced strain field for driving by piezoelectric ceramics can be measured by using this method. Thus we can come to a conclusion that digital speckle pattern interferometry is a new measuring method for extracting small-signal. It also provides a powerfully theoretical and experimental platform for study of automated, full-field, high-precision and nondestructive measurement.

scholarly journals Experimental Measurement of Mode Shapes and Frequencies for Vibration of Plates by Optical Interferometry Method

2000 ◽  
Vol 123 (2) ◽  
pp. 276-280 ◽  
Author(s):  
Chi-Hung Huang ◽  
Chien-Ching Ma
Keyword(s):  
Video Recording ◽  
Field Configuration ◽  
Mode Shapes ◽  
Resonant Frequencies ◽  
Full Field ◽  
Out Of Plane ◽  
Vibrating Plates ◽  
Optical Reconstruction ◽  
Fringe Patterns ◽  
Plane Displacement

Most of the published literature for vibration mode shapes of plates is concerned with analytical and numerical results. There are only very few experimental results available for the full field configuration of mode shapes for vibrating plates. In this study, an optical system called the AF-ESPI method with the out-of-plane displacement measurement is employed to investigate experimentally the vibration behavior of square isotropic plates with different boundary conditions. The edges of the plates may either be clamped or free. As compared with the film recording and optical reconstruction procedures used for holographic interferometry, the interferometric fringes of AF-ESPI are produced instantly by a video recording system. Based on the fact that clear fringe patterns will appear only at resonant frequencies, both resonant frequencies and corresponding mode shapes can be obtained experimentally at the same time by the proposed AF-ESPI method. Excellent quality of the interferometric fringe patterns for the mode shapes is demonstrated.

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