The practical need for short fatigue crack growth rate models

Abstract

Accurate fatigue crack growth rate models in the short crack regime are essential to the design and sustainment of modern aerospace structures. In this paper we briefly recap the short crack problem space and offer a case study demonstrating the practical significance of these models in the service life prediction for combat aircraft primary structure under a complex manoeuvre plus buffet loads spectrum. The necessity of accurate fatigue crack growth rate predictions in the short crack regime is demonstrated for this practical application using two models assessed against coupon fatigue test results representative of a critical aircraft structural location. A fractography based fatigue crack growth rate model relying on direct, quantitative fractography measurements in the short crack regime, is shown to offer better predictions of both total crack growth life and crack growth rates at a range of crack depths than long crack-based models.