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Optical Engineering

Dynamic stress analysis by high-resolution reflection moiré photography
Author(s): Martin B. Whitworth; Jonathan Mark Huntley
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Paper Abstract

A high-resolution moiré photography system is described in which a reflection phase grating attached to a specimen is imaged onto a reference grating to form moiré fringes. A tuned camera lens has been used to resolve grating frequencies of 150 lines mm-1, giving a sensitivity of 6.7 μm fringe-1 and to improve fringe contrast. The fringes are formed in real time and have been recorded with a high-speed image converter camera at framing rates of up to 106 frames s-1 with a field of view of up to 35 mm diameter. Sequences of fringe patterns have been analyzed by a 2-D Fourier transform method to obtain the dynamic displacement field with submicrometer accuracy. A field lens has been used to collimate the light incident on the specimen, and it is demonstrated that this makes the system insensitive to out-of-plane specimen motion, avoiding fictitious strains. An example is presented of the application of the technique to the measurement of the mode I stress intensity factor in a cracked polymethyl methacrylate (PMMA) plate under stress pulse loading.

Paper Details

Date Published: 1 March 1994
PDF: 8 pages
Opt. Eng. 33(3) doi: 10.1117/12.157660
Published in: Optical Engineering Volume 33, Issue 3
Show Author Affiliations
Martin B. Whitworth, Univ. of Cambridge (United Kingdom)
Jonathan Mark Huntley, Univ. of Cambridge (United Kingdom)

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