An Experimental Study on the Growth Behavior of Multi-Surface-Cracks in Type 304 Stainless Steel at Elevated Temperature

J. Ocean Eng. Technol. 1995;9(1):63-72.

고온하 304 스테인리스철의 표면규열의 성장거동에 관한 실험적 연구

서창민,신형섭,황남성,정대윤

경북대학교 기계공학부,안동대학교 공대 기계공학과,영남전문대학 기계과,영남전문대학 기계과

Keywords: elevated-temperature fatigue, multi-surface crack, crack growth behavior, aspect ratio, coalescence

핵심용어: 고온피로, 복수 표현균열, 균열성장거동, 균열형상비, 합체

Abstract

The crack which is discovered in various structures and machine elements is multi-cracks. Multi-cracks may cause serious problems because they grow individually, and coalesce into one and it leads to fracture. Fatigue tests have been carried out to study the growth and coalescence behavior of multi-surface-cracks initiated at the semicircular surface notch in type 304 stainless steel at elevated temperature. The results are as follows; When multi-surface-cracks are lying on the surface of material, the major surface crack has greater influence on the fatigue life than the subcracks. The aspect ratio of multi-surface-cracks is lower than that of single crack because of the interaction and coalescence of surface cracks. Crack growth shape turns to semiellipse from the semicircle notch. After coalescence, the surface crack length increases rapidly, and it leads to fracture. Further, the slope transition of Paris law was found in the da/dN-$Delta$K$_1$ plots.