Incorporating Hole Cold Expansion to Meet Durability and Damage Tolerance Airworthiness Objectives

Aircraft structural integrity requirements now embrace damage tolerance requirements as the basis for design and continued safe operation. The challenge facing industry is how to economically achieve these requirements in both new and, to a greater extent, the growing volume of aging aircraft. Compensating for damage tolerance analysis could lead to overweight structures. Not allowing for residual cracks in repairs could compromise the long term structural integrity, induce on-going inspection penalties and possibly result in unnecessary major structural replacement or repair. Hole cold expansion is a proven method for retarding the growth of cracks originating in holes. This paper discusses the technology and the effectiveness of the induced residual compressive stresses in reducing the stress intensity factor and permitting the use of smaller initial flaw sizes to meet damage tolerance requirements. Some ideas are presented on how practical results and applications can be used to incorporate these benefits in analysis to extend fatigue life and provide terminating repair action in repairs.