An Experimental Investigation of Wave Propagation in Fractured Brittle Material

Citation

Patel, Bibhuti Bhusan (1998) An Experimental Investigation of Wave Propagation in Fractured Brittle Material. Engineer's thesis, California Institute of Technology. doi:10.7907/w1t3-1f55. https://resolver.caltech.edu/CaltechETD:etd-09232004-112403

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. An experimental method for visualizing and analyzing the propagation of plate stress waves in a brittle plate is developed. A procedure has been developed to cast Break-Away glass (a low molecular weight polystyrene material) plate specimens in an open mold. The specimens are loaded with short duration (200 [...]s) stress pulses on one edge by an electromagnetic stress wave generator. The propagating stress waves generate out-of-plane deformations on the specimen surface, which are observed using Twyman-Green interferometry. The fringe patterns created by the propagating stress waves are captured using a high speed camera - pulsing laser combination at 4[...]s intervals. A generalized "Fringe Analysis Procedure" is developed to subtract the reference interferogram from the subsequent interferograms. The "Fringe Analysis Procedure" employs a fringe edge detection algorithm to obtain the sharp edge lines of the fringes in an interferogram. A digitizer is used to extract points on these edge lines and assign them fringe numbers. The "griddata" option in the commercial software "Matlab" is utilized to interpolate the deformation field on to the nodes of a uniform grid. The field values at these nodes in the reference image are then subtracted from corresponding values in the subsequent images to obtain the actual deformation patterns generated by the propagating stress waves. The "Fringe Analysis Procedure" has eliminated the subjective element introduced by human judgment in manual fringe tracing procedures. The developed experimental method and the image analysis technique is used to investigate the propagation of stress waves in Break-Away glass plate specimens.

Thesis Files