engleski

Risk Minimization in the Designing Procedure

The great number of numerical and experimental techniques in fracture mechanics, such as the linerisation of stress concentration factors or multi-parameter methods of fringe analysis in photoelasticity, are employed for determining the stress intensity factors (SIF) of the cracks in deformed structures. The optical method of caustics is originally applied to mechanically isotropic materials, where the proces of evaluation of SIFs is reduced to the epicycloidal dark spot measuring. The reflection method of caustics is presented here as a new developed for the application to nontransparent mechanically anisotropic materials such as fibe reinforced composites. The size of the dark spot depends upon the load intensity, while its shape depends extremely upon the mehhanical properties of the material and the position of cracktip. The optical effect needs to be digitized and analyzed by the automatic image analyzer that enables the filtering of the image, necessary for dark zone boundary recognition and extraction of the foggy blurred zones. This makes possible to use the classical diametar measuring technique or advanced multi-point over-deterministic data reduction method. The evaluation process includes variations of SIFs and simulations of caustics for all possible situations and comparison of the simulated caustic area with characteristics points discarded from experimental image. The problem of detecting the border of the dark spot is solved by new developed differential method, shifting the real image into the gradient image and collecting the points located at the position of the maximum light intensity gradient. All computer programs are adapted to use these techniques as automatic and standard procedure, effectively increasing the possibilities of image analysis of experimental caustics.

fracture mechanics; experimental methods; stress intensity factors; stress concentration factors; method of caustics

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