Development of Statistical evaluation method for fatigue crack profagation under random loading

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1) Exzmination of performance of developed statistical fatigue test machine;We finally completed a statistical fatigue test machine by which we can execute a test for 5 specimens simultaneously. Basic performance of the testing machine was examined. Response of gain and phase difference is shown to be flat between 020Hz and it is shown that frequency response prosperity is sat isfactory. Drift of mean load after long time usage is shown to be very small. Therefore, it is confirmed that there is no problem in executing fatigue test. In addition, multi-task real time system was developed on a personal computer to control this testing machine and to execute data processing efficiently.2) Execution of preliminary experiment for the statistical fatigue testing machine;Accuracy of automated crack length measuring by compliance method and the effects of random loading on fatigue crack propagation were examined preliminarily. It was confirmed that measuring accuracy of crack length was as good as one by visual observation and the relation between the statistical factor in random loading and the fatigue crack propagation characteristics were obtained. By using developed testing system, fatigue crack propagation data were obtained. 3) Application to reliability analysis;In addition to acquire fatigue crack propagation data, a reliability analysis has been done. Effects of scattering in fatigue crack propagation and initial shape of surface crack on final failure probability was analysed by Monte carlo simulation.4) Re-examining of usual data;Usually,data of fatigue crack propagation were collected on the basis of deterministic theory. However, those data are not sufficient to understand the probabilistic characteristics of crack propagation. Therefore,we tried to separate a scattering factor in data processing from the one in materials strength itselt and considered a contribution of each scattering factor to total scattering level.