Method to Assess the Effects of a Flaw with Residual Stress for Rotorcraft Metallic Structures

Accounting for effects of damage on the fatigue strength of metallic principal structural elements (PSE) is a requirement for fatigue tolerance evaluation of transport category rotorcraft. Parallel to the current structural test approach for showing regulatory compliance, an analysis method is sought. However, developing and executing an analytical compliance methodology has many challenges. One example is the stress state at the root of a flaw, and how that stress state interferes with the residual stress induced by specific processes such as shot peening. This paper presents an analysis method to determine the stress state at the root of a flaw with the presence of residual stresses. The method can quantify the effect of the residual stress on various flaw shapes and sizes, to avoid overly conservative assumptions in certification analysis.