Determinacao de parametros da mecanica de fratura a partir de imagens fotoelasticas usando processamento digital

The stress intensity factor is one of the Linear Elastic Fracture Mechanics parameters used for assuring safety of structures against crack propagation. Photoelasticity is an experimental stress analysis technique that can be used for determining this factor based on geometrical parameters from isochromatic fringes at crack tip in biréfringent models. Regions where light extinction occurs are the key points, in case of images with a same color hue. Digital Image Processing gray levels algorithms can be used for obtaining these points. Thinning operations are typical examples of such algorithms. Its applications produces medial central lines, generating one pixel width fringe loops having the origin at crack tip. The radius connecting crack tip to points on these fringe loops and related angles are basic values used for computing the stress intensity factor. A computer-based system, named FOTOEL, for digital image processing of gray isochromatic images, with resource for computing the stress intensity factor for the opening mode, Ki, is developed in this thesis. Two-parameters methods of Irwin and Schroedl & Smith, and the overdeterministic method of Dally are the numerical procedures implemented in FOTOEL. The system has been developed in WindowsTM, using C language for compatible IBM-PCTM microcomputers. An overview of the fundamentals of Photoelasticity, Linear Elastic Fracture Mechanics, Digital Image Processing and Numerical Methods used for calculating Ki from photoelastic technique is done. Synthetic isochromatic generated by computer and experimental isochromatics are processed by FOTOEL. Results are compatible with prescribed values, in case of synthetic images, and with results found in the technical literature in case of experimentally generated images. DETERMINATION OF FRACTURE MECHANICS PARAMETERS FROM PHOTOELASTIC IMAGES USING DIGITAL PROCESSING WELLINGTON ANTONIO SOARES

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