Simultaneous Measurement Of 3-D Displacement Components Caused By Crack Growth Using Circular Gratings Moire Fringes And Graphical Analysis
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Date
2012-05
Authors
Yen, Kin Sam
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Cracking is well-known to be a major cause of failures in concrete structures.
By monitoring the growth of cracks, early remedial measure can be taken to save the
structure from failure. To sense all the three crack modes namely, opening mode,
sliding mode and tearing mode, a method that is able to measure the 3-D
displacement components simultaneously with a single setting is needed. The moiré
pattern formed by overlapping two circular gratings with slightly different pitches is
proposed as a measurement tool because the moiré pattern is repeatable and unique
for a relative in-plane (2-D) displacement between the two gratings. The wave
properties, i.e. the amplitude and phase shift extracted from the transformed moiré
fringe in the polar plane directly corresponds to the eccentricity magnitude and
direction of the two gratings. Thus, graphical analysis method is developed to extract
the 2-D displacement information from the circular gratings moiré pattern. In the
presence of a gap between the two grating planes, different moiré patterns can be
observed from the normal and off-normal viewing directions with the grating plane.
The absolute difference of the 2-D displacement represented by the two moiré
patterns captured from different viewing directions is related to the out-of-plane
displacement between the two gratings. Based on the developed graphical analysis
method, an out-of-plane displacement measurement method is established for the
simultaneous 3-D displacement components determination.
Description
Keywords
Simultaneous measurement of 3-D displacement components , caused by crack growth using circular gratings moire fringes