Corrosion Pillowing in Aircraft Fuselage Lap Joints
JOURNAL OF AIRCRAFT Vol. 44, No. 3, May–June 2007
Corrosion Pillowing in Aircraft Fuselage Lap Joints
Nicholas C. Bellinger,∗ Jerzy P. Komorowski,† and Ronald W. Gould‡ National Research Council Canada, Institute for Aerospace Research, Ottawa, Ontario K1A 0R6, Canada
DOI: 10.2514/1.18589 This paper presents the results of studies that have been carried out at the National Research Council Canada on the effect that corrosion pillowing has on the structural integrity of fuselage lap joints. Modeling of corrosion pillowing using finite element techniques showed that the stress near the rivet holes increased to the material (Al 2024T3) yield strength when the corrosion present was above 6% thickness loss. In addition, the analysis showed that pillowing resulted in a stress gradient through the skin thickness, which suggested that semi-elliptical cracks with high aspect ratios could form. During teardowns of service-exposed lap joints, these types of cracks were found at numerous holes and a closer examination of the fracture surfaces revealed the presence of fatigue striations. Therefore, a new source of multisite damage, other than fatigue, was identified.
I. Introduction
N THE 1980s, it became apparent that commercial transports would remain in service well beyond their original design life, which raised concerns that corrosion combined with fatigue could lead to catastrophic failures of fuselage lap joints. Although there are multiple lap joint designs present in a single fuselage, for older aircraft the majority of them consist of an outer and inner skin fabricated from aluminum 2024-T3 joined together with multiple rows of countersunk rivets (Fig. 1), as well as an adhesive layer. During the operation of an aircraft, the adhesive layer can deteriorate and disbond allowing moisture to migrate between the skins. This moisture can, in turn, breakdown the material protective system resulting in the formation of crevice corrosion. As the corrosion forms, the
Corrosion Pillowing in Aircraft Fuselage Lap Joints
Nicholas C. Bellinger,∗ Jerzy P. Komorowski,† and Ronald W. Gould‡ National Research Council Canada, Institute for Aerospace Research, Ottawa, Ontario K1A 0R6, Canada
DOI: 10.2514/1.18589 This paper presents the results of studies that have been carried out at the National Research Council Canada on the effect that corrosion pillowing has on the structural integrity of fuselage lap joints. Modeling of corrosion pillowing using finite element techniques showed that the stress near the rivet holes increased to the material (Al 2024T3) yield strength when the corrosion present was above 6% thickness loss. In addition, the analysis showed that pillowing resulted in a stress gradient through the skin thickness, which suggested that semi-elliptical cracks with high aspect ratios could form. During teardowns of service-exposed lap joints, these types of cracks were found at numerous holes and a closer examination of the fracture surfaces revealed the presence of fatigue striations. Therefore, a new source of multisite damage, other than fatigue, was identified.
I. Introduction
N THE 1980s, it became apparent that commercial transports would remain in service well beyond their original design life, which raised concerns that corrosion combined with fatigue could lead to catastrophic failures of fuselage lap joints. Although there are multiple lap joint designs present in a single fuselage, for older aircraft the majority of them consist of an outer and inner skin fabricated from aluminum 2024-T3 joined together with multiple rows of countersunk rivets (Fig. 1), as well as an adhesive layer. During the operation of an aircraft, the adhesive layer can deteriorate and disbond allowing moisture to migrate between the skins. This moisture can, in turn, breakdown the material protective system resulting in the formation of crevice corrosion. As the corrosion forms, the