피로 (疲勞) 크랙 전파기의 연구

다국어 초록 (Multilingual Abstract)

Study of the fatigue crack propagation rate was started by Head, and later Frost and Dugdale studied it. Irwin clarified the crack propagation behavior by using the concept of stress intensity factor and fatigue crack propagation. In this paper, fatigue crack propagation behavior which was occurred from "0" hole notch of spring steel bar and mild steel bar under repeated rotary bending stress was regulated by using the concept of stress intensity factor. And fracture toughness K_c, threshold intensity Kth and transition point of fatigue crack propagation, and so on were discussed. The results obtained are as follows; 1) The applicable range of the Paris`s 4 power law relationship to the propagation period is the tensile mode and shearing mode. 2) Transition point exists in the range 2 × 10^-6∼ 5 × 10^-5㎏/㎜^3/2 of crack propagation rate and it is dependent upon the stress state. 3) The value of m is inversely proportional to the K_c and Kth but K_c is the more influential factor. 4) Threshold intensity K_th and fracture toughness K_c is directly proportional to the stress level and it depends upon the stress condition.