レーザ干渉変位計による微小疲労き裂の開閉口挙動に関する研究

抄録

An interferometric strain/displacement gage system was developed to measure the crack closure behavior of small fatigue cracks nucleated in smooth specimens by fatigue. Interference takes place between laser beams reflected by two Vickers indentations. Linear image sensors were used to detect the movement of interferometric fringes due to strain. The resolution in displacement of our system was ± 1nm for the gage length of 100μm. The system was first applied to a through-thickness fatigue crack at the center of a low-carbon steel plate. The profile of crack opening displacement agreed with the prediction based on the Dugdale model. The crack opening point of small surface cracks in fatigue specimens of aluminum alloy 2024-T3 was determined from the record of load versus displacement. Surface cracks smaller than about 100μm in length mostly showed faster growth rates than those given by the da/dN versus ΔK_eff relation for long cracks.