Method of arresting crack growth for application at a narrow working space

Abstract

The many fracture accidents in engineering applications are related to fatigue crack initiation and growth. Therefore, the inspection of fatigue crack initiation and the arrest of crack growth are very important for the safe operation of a machine and the maintenance of a structure. Non destructive inspection has been developed in order to prevent a fracture accident resulting from the cracks or defects. When a crack initiates in machine equipment, continuous observation of the crack is carried out and the crack growth is arrested by some method. To arrest the crack growth, stop-holes are drilled at the crack tips in a case of initiation of a small number of cracks. Drilling the stop-hole is an effective method to prevent crack growth because it reduces stress concentration at the crack tip. Application of residual stress around the stop-holes and making a plastic hardening zone around the crack tips are effective to arrest crack growth. Applying a patch for repairing cracked parts is more effective than drilling stop-holes. In practical cases, patches are applied to repair cracked parts in airplane bodies, bridges, etc. However those methods cannot be used in some cases, because of the conditions of working space, for example. In this paper, an example of the application of a crack arrester at a car facility is introduced. Then, the effectiveness of the crack arrester is discussed. When many cracks are initiated and working space is very small, the crack arrester is a good tool for repairing the cracked parts. It is necessary to develop a method for stopping crack growth in order to replace cracked equipment, because new equipment should be designed carefully for preventing crack initiation again.

Keywords

• fatigue
• crack growth
• stop-hole
• crack arrester
• stress concentration
• residual stress