We should prefer ductility for the criterion to estimate the safety of structures in the case where the applied net stress is beyond the yield stress. Fracture behaviors of the structural element with crack approaching stress concentrator like open hole, might be affected by interaction between crack and concentrator and by plate thickness. In the present report, the interaction effects as well as the thickness effects on relation of COD vs. elongation, on critical COD and on fracture strains are investigated. Experiments have been carried out using steel plates with crack approaching circular hole under uniform tension. Main results obtained are as follows : (1) The relationships between COD and ε _y , elongation averaged in net section, are not affected very much by either F _Ia values or plate thicknesses. Here, F _Ia = K _Ia /σ√π c , K _Ia is stress intensity factor at the crack tip approaching hole. (2) The critical COD value increases with increasing F _Ia value and with decreasing plate thickness, and this thickness effect is more remarkable in the case where F _Ia is large. (3) The fracture strains (ε _y ) _f as well as the fracture overall strains of the plates with large F _I a values are larger than those of the plates with only a crack, if plate widths are sufficiently large. And the fracture strains increase with decreasing plate thickness.