Yoshihiko Hagiwara

PREDICTIONS OF ANISOTROPY AFFECTED FATIGUE CRACK PROPAGATION PATHS IN PURE ALUMINUM SHEETS

The anisotropy affected fatigue cracks that propagate on the rolling direction as mixed mode I-II cracks in CCT-specimens of pure aluminum sheets were predicted using Finite Element Method. The crack growth paths were estimated based on the value of mode I, II, total stress intensity factor range, and the ratio of mode II and mode I energy release rate of the crack. The predictions of crack propagation paths in no-hole specimens and 6-type holed specimens with 0, 30, 45 and 60 degrees of rolling direction towards loading direction were performed and the results were coincided with experimental results.

Measurement for Actual Stress Distribution by Using X-Ray Diffraction during Rotary Bending Fatigue Test

The purpose of this investigation is to detect a damage from actual stress distribution in the surface of specimen by using X-ray diffraction technique during fatigue test. An apparatus to measure the actual stress distribution along specimen circumference was fabricated by use of a cantilever type rotary bending fatigue machine and a stress analyzer based on single exposure technique with two position sensitive proportional counters. The authors developed a method for collecting separately the diffraction profile at each position along the circumference. Actual stress distributions at the maximum tensile applied stress were dynamically measured. As a result, the shape of the distribution was keeping stable with the increase in the number of stress cycles until crack initiation. When the crack length reached greater in size than the width of irradiation area, the actual stresses at the crack position were suddenly decreased down to 0MPa, and the distribution showed a V-shape. These results show that the method adopted in this study is available for detecting both the position and the period of crack initiation.