engleski

Experimental Determination of SIF for 3D Cracks

In the past few years the increasing number of analytical and numerical methods, together with development of computer technology, were introduced in mechanical engineering. However, experimental verification of numerically obtained results is often necessary. Direct application of photoelasticity for SIF measurement is based on different approach than usual photoelastic measurements. The photoelastic effects in a vicinity of a crack tip is always shadowed by the influence of a plastic deformation, crack modeling errors, optical deformations caused by caustic effect, or the fact that this zone is too small for accurate measurements. This is especially the case in three dimensional fracture models were stress freezing method is used. Methods for determining SIF from full field fringe patterns which are based on the near-field equation for the stresses are not adequate. The objective of this work was to develop a method for determining fracture parameters with full field photoelastic fringe pattern analysis in order to increase the accuracy of SIF measurements. The basis of the method is to use the fringe equation in a form of series with unknown coefficients (KI, KII, etc.). A statistical regression method (nonlinear data fit) is used to determine this coefficient from optical measurements. A sample experimental result of a cracked shaft subjected to bending is presented in the end of this work. Methods for manufacturing models, loading, stress freezing, determining fringe values and data processing are described.

Fracture Mechanics; Photoelasticity; Stress intencity factors; Experimental Fracture Mechanics

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