THE GROWTH OF SHORT CRACKS UNDER CYCLIC LOADING

Abstract

Considered small (short) crack in a solid body. In certain cases, there is a difference in the mechanical behavior of solid bodies in the presence of short or long cracks in the same place details. Discusses some of the effects arising from cyclic loading during the initial  growth of short cracks, and transforming it into a long. The urgency  of the problem of small cracks are fairly obvious, but it is not clear  what the crack is considered small. It is possible to give several  definitions of small cracks. For example, it is convenient to refer to  the small cracks are those that meet the lower resolution limit of the flaw detection equipment. However, the resulting absolute sizes are not associated with the process of the mechanical behavior of body  with crack. Better the crack length comparable with the characteristic width of the specimen (parts) or diameter of the  plastic zone at the tip of the crack. Under cyclic loading the behavior of cracks in the area of concentration also has its own  characteristics, which are expressed in the initial acceleration of the  crack, and then, with increasing length, her speed drops. Among the considered types of short cracks can be identified cracks that entirely fit in the areas of high stresses around notches. Such cracks are called mechanically short. The length of such cracks is  comparable with the crack length, determining a threshold stress  intensity factors in the experiments to determine the characteristics  of cyclic crack resistance. As can be seen from the calculations, the mechanically short crack grows rapidly at first, but as the field of  concentration, reaches a minimum and then increases again, leaving a region of concentration. Further, the crack goes into the category of long, following the classic formula of Paris.