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우수창(S.C. Woo),김문생(M.S. Kim),신형섭(H.S. Shin) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.3
Brittle materials are very weak for impact because of typical characteristics which happen to be easily fractured with low fracture toughness and crack sensitivity. When brittle materials are subjected to impact due to small spheres, high contact pressure is occurred to impact surface and then local damage on specimen is developed, since there are little plastic deformations due to contact pressure compared to metals. This local damage is a dangerous factor which gives rise to final fracture of structures. In this research, the crack propagation process of soda lime glass by impact of small sphere is explained and the effects of the constraint conditions of impact spheres and materials for the material damage were studied by using soda-lime glass, that is the effects for the materials and sizes of impact ball and thickness of specimen. Especially, this research has focused on the damage behavior of ring crack, cone crack and several kinds of cracks.
高溫下 304 스테인리스鋼의 複數表面龜裂의 成長學動에 관한 實驗的 硏究
서창민(C. M. Suh),신형섭(H. S. Shin),황남성(N. S. Hwang),정대윤(D. Y. Jung) 한국해양공학회 1995 韓國海洋工學會誌 Vol.9 No.1
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.<br/> 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.<br/> The results are as follows;<br/> When multi-surface-cracks are lying on the surface of material, the major surface crack has greater influence on the the fatigue life than the subcracks.<br/> The aspect ratio of multi-surface-cracks is lower than that of single crack because of the interaction and coalescence of surface cracks.<br/> Crack growth shape turns to semiellipse from the semicircle notch. After coalescence, the surface crack length increases rapidly, and it leads to fracture.<br/> Further, the slope transition of Paris law was found in the da/dN-ΔK₁ plots.