混合モード条件下の疲労き裂におけるき裂開口とすべり変形挙動（画像相関法による変位計測とFEM解析に基づいて）

摘要

実際の構造物中の欠陥から発生したき裂は，必ずしrnもき裂の直交方向（き裂開口方向）からのみ負荷を受rnけるわけではなく，き裂の開口方向（モードⅠ）と相対rnすべり方向（モードⅡ）を含む混合モード条件下にあrnる場合が多い．%Under mixed-mode conditions, the crack opening displacement and the sliding displacement seem to be suppressed by the crack surface contact behavior in the relative sliding between the upper and the lower sides of the crack. Especially, the crack surfaces of the fatigue crack with a compres-sive residual stress tend to contact each other owing to the crack closure. Therefore, it is important to evaluate the effect of the crack opening and the sliding suppress behavior quantitatively. In this study, forces that suppress the crack opening and sliding were calculated along the crack using FEM analysis. Nodes of crack edges in a FEM model, simulating the length and slanted angle of the crack in the examined specimen, were fixed to be equal to the displacement mesured by using the image correlation method. The resulting reaction forces evaluated on the nodes in the FEM model are equivalent to the crack opening and sliding suppress forces. However the fluctuation of the evaluated force is too large to estimate the effect of the crack opening and the sliding suppress behavior. Accordingly, the method to decrease the fluctuation is proposed by selecting the displacement fixed node, which seems to be the crack opening and the sliding suppressed point. As a result, the fluctuation of the evaluated force decreased and the crack sliding suppress force seems to be caused by the crack surface contact. On the other hand, the crack opening suppress force was equivalent to the residual stress measured by the X-ray.