内部および表面の鋳造欠陥を起点とするアルミニウム合金ダイカストの超長寿命疲労特性

概要

論文の詳細を見る
By the ultrasonic fatigue test for Al-Si-Cu die-casting, the influence of internal or surface defects on super-long life properties was investigated. The results were as follows: (1) When surface defects were the crack starting points, the S-N curve leveled off around 10^7 cycles. On the other hand when the defects were internal defects, the S-N curve showed continued degradation as N_f increase. (2) When the crack starting point was an internal defect, ODA (Optically Dark Area) was observed around the crack initiation point after 10^8 cycles. However, ODA was not observed when the compulsory fatigue was applied for no-break sample that was tested over 10^<10> cycles of N_f. This suggests that the incidence of fatigue crack from the defect point or its progress were not recognized. (3) By using the following formula, which compares the relationship between ΔK_<CD> ∝(√<area>)^<1/3> and ΔK_<th> ∝(√<area>)^<1/3> based on the √<area> parameter model, it is possible to explain the breaking or nonbreaking phenomenon caused by the casting defect in the super-long life area (over 10^7 cycles).
2006-11-25