A fracture-mechanics approach to predicting the fatigue life of adhesively-bonded repairs

摘要

In 2009 the FAA introduced a slow-growth approach for certifying composite and adhesively-bonded structures. In the case of adhesively-bonded repairs this approach requires that the growth of any disbond is slow, stable and predictable under cyclic-fatigue loads. The present paper addresses the challenge of developing a methodology, based upon fracture-mechanics, which is capable of enabling this approach to be implemented. We have examined the growth of disbonds from small natural-ly-occurring material discontinuities in adhesively-bonded structures which are typical of aerospace bonded-repairs. It is shown that the disbond growth histories can be accurately modelled using a form of the Hartman and Schijve equation to describe the measured fatigue properties of the adhesive, coupled with a finite-element analysis of the bonded repair. It is also shown that the scatter in the disbond growth histories can be captured by allowing for small changes in the fracture-mechanics threshold term. These findings suggest that the Hartman-Schijve crack-growth equation has the potential to address the 'slow growth' approach to certifying adhesively-bonded structures and bonded repairs outlined in the US FAA Airworthiness Advisory Circular No: 20-107B.