Hole Cold Expansion the Fatigue Mitigation Game Changer of the Past 50 Years

Abstract

Over the past 50 years, mitigating cracks from holes has been a major focus of aerospace research, design, and stress engineers. Technology and design philosophies were developed to focus on predicting and increasing fatigue life of metal aircraft structure. One of the innovations to have the biggest impact to slow or arrest crack growth was to induce beneficial residual stresses around a hole. The zone of residual compressive stresses shields the hole from the effects of cyclic loads. The split sleeve cold expansion method was pioneered in the early 1970s by Boeing and Fatigue Technology. The split sleeve cold expansion process has become the bench mark method in mitigating fatigue cracks and enhancing durability and damage tolerance of aerospace metal structures. This paper will review the history of cold expansion methods and the evolution of this technology to the controlled and widely accepted methods used by industry today.