Electronic Speckle Pattern Interferometry (ESPI) NDE of cracks in pressure vessels with FEA modelling

Master Thesis


Permanent link to this Item
Journal Title
Link to Journal
Journal ISSN
Volume Title

University of Cape Town

This dissertation describes the results of an attempt to simulate the Electronic Speckle Pattern Interferometric fringe patterns observed around a crack or combination of cracks in a pressure vessel by finite element methods. Electronic Speckle Pattern Interferometry (ESPI) is a coherent optical measurement technique that produces a contour map of the surface displacement of an object when it is stressed. The sensitivity of the techniques is of the order of half the Wavelength of light. The objective of the study was to determine a procedure for the modelling of interferometric fringes by finite elements. The finite element model may then be used to study the effects of crack geometry on fringe patterns and produce a library of reference fringe patterns for comparison with experimental fringe patterns found for unknown flaws. The approach to the problem was to simulate the fringe patterns for a crack free cylinder and compare these with these observed experimentally. The FE model modulus of elasticity was than to be calibrated to minimise uncertainty in the exact value of the elastic modulus. Once the model was calibrated, various cracks and combinations of cracks were introduced into both the physical cylinders and the FE model and fringe patterns obtained were compared. The experimental results for the cracks and combinations of cracks were compared with the finite element predictions at a range of loads.

Includes bibliographical references.