Development of Direct Visualization and Recording System for Photographing the Propagation of plastic Zones and Cracks in Structural Members

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1. A firect visualization and recording system for phorographing the developemtn of Luders lined was developed by applying laser beam in the Shilieren method.2. Though it takes time to finish the surface of the specimen, this system has the following excelent featured;1) It is a direct vesualization method which does nto use any chemicals, strain paint, strain gauges etc.2) The method is independent of the environmental conditions like the temperature, humidity and the skillfulness of the experimentor and then has stable reproduciafility.3) The method does not need any computational procedures.4) It is capable of recording the dynamic change of the loaded specimen unfer the testing machine.3. Since the luders lines occur discontinuously, the test results (the hard copy picutred for the Luders lines distribution) are not coincide with the distribution of the yielded zones obtained from the numerical analysis which is beaed on the continum mechanics. But, if it is assumed that the area surrounded by the envelope to the tips of luders lines is the plastic zone in the test, it corresponds well to the plastic zone obtained from the finite element analysis.4. The strain measurements by wire strain gauges show that the area inside of the Luders lines is the yielded zone and the strain inside the Luders lines is about 70% of the strain for the initiations of strain-hardening, <epsilon>_<st>, at the initiation and increase to <epsilon>_<st> after finishing all the posible dislocations.5. It was not succesful to find the effective method for visualizing and recording crack in a concrete. But, a mathematical expression to evaluate the critical stess intersity factor K_<ic> was developed and it is shown that crack propagation can be analyzed fairly well by the boundary element method by utilizing the acoustic emission techique for the evaluation of the Kic values.