Holographic Inspection of Plates Containing Areas of Localized Thickness Variation

1994 ◽  
Vol 116 (2) ◽  
pp. 162-167 ◽  
Author(s):  
H. M. Shang ◽  
M. Lwin ◽  
T. E. Tay
Keyword(s):  
Visual Detection ◽  
Accurate Estimation ◽  
Thickness Variation ◽  
Uniform Pressure ◽  
Circular Plates ◽  
Double Exposure ◽  
Simple Method ◽  
Exposure Holography ◽  
Fringe Patterns

Circular plates, under unknown clamping conditions and containing simulated defects in the form of circular localized thinning or thickening, are inspected by double-exposure holography. With an incremental uniform pressure applied between exposures, eccentric defects are readily revealed from the distinct irregular fringe patterns. In the case of central circular defects, however, the absence of distinct irregular fringe patterns does not enable easy visual detection of the defects. The simple method of analysis described in this paper, based on the fact that the displacement in a defective plate differs from that in a defect-free plate, allows easy deduction of central and eccentric defects from the fringe patterns. Furthermore, this method enables identification of the type of defect (localized thinning or thickening), the extent of thickness variation, as well as an accurate estimation of the location and size of the defect.

Holographic Evaluation of Edge Delamination in Bars Bonded to a Rigid Support With Foam-Adhesive

1996 ◽  
Vol 118 (3) ◽  
pp. 330-334 ◽  
Author(s):  
S. Qin ◽  
H. M. Shang ◽  
C. L. Giam ◽  
C. E. Tee
Keyword(s):  
Theoretical Analysis ◽  
Rapid Detection ◽  
Iterative Procedure ◽  
Point Load ◽  
Nonlinear Relationship ◽  
Rigid Support ◽  
Double Exposure ◽  
Simple Method ◽  
Exposure Holography ◽  
Edge Delamination

When a bar having one end bonded to a rigid support with foam-adhesive is loaded, the high peeling stresses at the bonded edge foster edge delamination along the interface of bonding. Upon inspection by double exposure holography, with an incremental point load applied at the free end of the bar between exposures, the indistinct fringe perturbation and the unknown resilience of the foam-adhesive (quantified by its foundation modulus) impede unambiguous evaluation of the condition of adhesion. This paper describes a simple method for rapid detection and assessment of artificially created edge delamination in such bar structures. The theoretical analysis elucidates the suitability of modelling the bar as partially clamped, and having an equivalent slope at its support related to the foundation modulus. Two dimensionless parameters are defined, which have between them a linear relationship for a nondelaminated bonding but a nonlinear relationship for a delaminated one. Finally, a simple iterative procedure is described for estimating the delaminated length without having to predetermine the elasticity of the support.

Estimation of Size and Depth of Debonds in Laminates From Holographic Interferometry

1992 ◽  
Vol 114 (2) ◽  
pp. 127-131 ◽  
Author(s):  
H. M. Shang ◽  
E. M. Lim ◽  
K. B. Lim
Keyword(s):  
Rigid Body ◽  
Holographic Interferometry ◽  
Rigid Body Motion ◽  
Body Motion ◽  
Accurate Assessment ◽  
Plate Model ◽  
Double Exposure ◽  
Testing Technique ◽  
Simple Method ◽  
Exposure Holography

Double-exposure holography has been shown to be a useful nondestructive testing technique for the detection of debonds in laminates when subjected to vacuum stressing. The size of a debond is estimated from the boundary containing anomalous fringes and subsequently, its depth is estimated from these fringes using a thin-plate model. Rigid-body motion is frequently present during testing, causing ambiguity in the identification of the shape of the debond and hence difficulty in the estimation of its size and depth. In this paper, a simple method is presented which isolates the effects of rigid-body motion so that accurate assessment of the detected debonds can be achieved. Also, the use of a circle to outline the ambiguous boundary is found suitable for square debonds.

scholarly journals Experimental determination and finite element analysis of coefficients of the multi-parameter Williams series expansion in the vicinity of the crack tip in linear elastic materials. Part I

2020 ◽  
pp. 237-249
Author(s):  
L. V Stepanova
Keyword(s):  
Series Expansion ◽  
Digital Image ◽  
Power Series Expansion ◽  
Crack Tip ◽  
Higher Order ◽  
Accurate Estimation ◽  
Principal Stresses ◽  
Isochromatic Fringe ◽  
Higher Order Terms ◽  
Fringe Patterns

This study aims at obtaining coefficients of the multi-parameter Williams series expansion for the stress field in the vicinity of the central crack in the rectangular plate and in the semi-circular notched disk under bending by the use of the digital photoelasticity method. The higher-order terms in the Williams asymptotic expansion are retained. It allows us to give a more accurate estimation of the near-crack-tip stress, strain and displacement fields and extend the domain of validity for the Williams power series expansion. The program is specially developed for the interpretation and processing of experimental data from the phototelasticity experiments. By means of the developed tool, the fringe patterns that contain the whole field stress information in terms of the difference in principal stresses (isochromatics) are captured as a digital image, which is processed for quantitative evaluations. The developed tool allows us to find points that belong to isochromatic fringes with the minimal light intensity. The digital image processing with the aid of the developed tool is performed. The points determined with the adopted tool are used further for the calculations of the stress intensity factor, T-stresses and coefficients of higher-order terms in the Williams series expansion. The iterative procedure of the over-deterministic method is utilized to find the higher order terms of the Williams series expansion. The procedure is based on the consistent correction of the coefficients of the Williams series expansion. The first fifteen coefficients are obtained. The experimentally obtained coefficients are used for the reconstruction of the isochromatic fringe pattern in the vicinity of the crack tip. The comparison of the theoretically reconstructed and experimental isochromatic fringe patterns shows that the coefficients of the Williams series expansion have a good match.

Automatic analysis of knee ligaments using double exposure holography

1991 ◽  
Vol 24 (6) ◽  
pp. 489
Author(s):  
Huang Zhi ◽  
Torsten Wredmark ◽  
Ulrik Willers ◽  
Ingegerd Dirtoft ◽  
Rolf B Johansson
Keyword(s):  
Automatic Analysis ◽  
Double Exposure ◽  
Knee Ligaments ◽  
Exposure Holography

An Approximate Analysis of Circular Plates With Variable Thickness

1982 ◽  
Vol 104 (3) ◽  
pp. 533-535
Author(s):  
A. K. Naghdi
Keyword(s):  
Variable Thickness ◽  
Simple Technique ◽  
Bending Moment ◽  
The Other ◽  
Uniform Pressure ◽  
Approximate Analysis ◽  
Circular Plates ◽  
Numerical Examples ◽  
Classic Theory ◽  
Rotationally Symmetric

Based on classic theory of beams and certain modifications, a simple technique is derived in order to obtain an approximate value of the maximum bending moment in a rotationally symmetric circular plate with a variable thickness. It is assumed that one of the two concentric boundaries of the plate is clamped, and the other is free. Numerical examples for both cases of constant and variable thickness plates subject to uniform pressure or rim line loading are presented.

Virtual Ground Fence: A Simple Method for Protection against High Frequency Simultaneous Switching Noise

2012 ◽  
Vol 2012 (1) ◽  
pp. 001081-001084 ◽  
Author(s):  
Jesse Bowman ◽  
A. Ege Engin
Keyword(s):  
Power Distribution ◽  
Distribution System ◽  
Power Efficiency ◽  
Printed Circuit Board ◽  
Supply Voltage ◽  
Circuit Board ◽  
Voltage Source ◽  
Accurate Estimation ◽  
Simple Method ◽  
Power Distribution System

When integrating sensitive RF analog devices with complex VLSI digital components, simultaneously switching drivers cause supply voltage fluctuations which can propagate both horizontally and vertically between the power/ground planes. The same voltage source on a printed circuit board can be shared to increase power efficiency and reduce space used. In order to accomplish this, on board filtering is needed to isolate the noise between these two types of devices for proper operation. Hence, accurate estimation and improvement of the performance of power/ground planes is critical in a mixed-signal system. We present a new method to minimize the noise transfer at high frequencies to the power distribution system, called the Virtual Ground Fence. At its basic level, the Virtual Ground Fence consists of quarter-wave transmission-line stubs that act as short circuits between power and ground planes at their design frequency. We will present various configurations of Virtual Ground Fence for different coupling scenarios.

scholarly journals INVESTIGATION OF THE DYNAMIC BEHAVIOUR OF NON-UNIFORM THICKNESS CIRCULAR PLATES RESTING ON WINKLER AND PASTERNAK FOUNDATIONS

2020 ◽  
Vol 60 (2) ◽  
pp. 127-144
Author(s):  
Saheed Salawu ◽  
Gbeminiyi Sobamowo ◽  
Obanishola Sadiq
Keyword(s):  
Natural Frequency ◽  
Circular Plate ◽  
Analytical Solutions ◽  
Dynamic Behaviour ◽  
Circumferential Stress ◽  
Thickness Variation ◽  
Circular Plates ◽  
Uniform Thickness ◽  
Weighted Residuals ◽  
Elastic Foundations

The study of the dynamic behaviour of non-uniform thickness circular plate resting on elastic foundations is very imperative in designing structural systems. This present research investigates the free vibration analysis of varying density and non-uniform thickness isotropic circular plates resting on Winkler and Pasternak foundations. The governing differential equation is analysed using the Galerkin method of weighted residuals. Linear and nonlinear case is considered, the surface radial and circumferential stresses are also determined. Thereafter, the accuracy and consistency of the analytical solutions obtained are ascertained by comparing the existing results available in pieces of literature and confirmed to be in a good harmony. Also, it is observed that very accurate results can be obtained with few computations. Issues relating to the singularity of circular plate governing equations are handled with ease. The analytical solutions obtained are used to determine the influence of elastic foundations, homogeneity and thickness variation on the dynamic behaviour of the circular plate, the effect of vibration on a free surface of the foundation as well as the influence of radial and circumferential stress on mode shapes of the circular plate considered. From the results, it is observed that a maximum of 8.1% percentage difference is obtained with the solutions obtained from other analytical methods. Furthermore, increasing the elastic foundation parameter increases the natural frequency. Extrema modal displacement occurs due to radial and circumferential stress. Natural frequency increases as the thickness of the circular plate increases, Conversely, a decrease in natural frequency is observed as the density varies. It is envisioned that; the present study will contribute to the existing knowledge of the classical theory of vibration.

Transient interference gratings and holograms in dyed plastic

1984 ◽  
Vol 62 (7) ◽  
pp. 669-673
Author(s):  
Sergio Calixto ◽  
R. A. Lessard
Keyword(s):  
Real Time ◽  
Diffraction Efficiency ◽  
Laser Light ◽  
Thick Layer ◽  
Double Exposure ◽  
Naked Eye ◽  
Sufficient Intensity ◽  
Exposure Holography ◽  
Reading Beam ◽  
Made In

Transient diffraction gratings were holographically made in dyed plastic by absorbing laser light. Mean energy values of 40 mJ/cm2 absorbed in a 3-mm thick layer were needed to make gratings that lasted about 10 s. The writing beams and a reading one of different wavelength were simultaneously made to fall on the plastic: the reading beam was diffracted by the grating, which produced transient diffracted beams of sufficient intensity to be seen by the naked eye or to be stored permanently by conventional photographic methods. Curves showing diffraction efficiency versus exposure with grating frequency as a parameter are presented. Applications to real-time single and double exposure holography are also discussed.

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