Mixed-Mode Stress Intensity Factor Determination of Riveted Lap Joints Used in Aircraft Fuselage Structures

Abstract

In the present work, mixed-mode stress intensity factor (SIF) of multiple cracks in a riveted lap joint has been determined, with and without the presence of stringer under two different (uniaxial and biaxial) loading conditions. Geometry correction factor (Y) has been determined with consideration of mode II and mode III fractures, and the effect of stringer on SIF of intermediate as well as edge cracks was investigated. Diametrically opposite surface cracks with various crack depth ratios (a/t) were considered for a typical longitudinal splice joint. At the crack middle region [(S/S 0) = 0], SIF of cracks estimated under uniaxial loading condition reduces gradually with crack depth ratio due to frictional contact, whereas in the case of biaxial loading, higher SIF was observed at lower crack depths [(a/t) = 2]. The presence of stringer reduces the SIF of multiple cracks as it decreases the secondary bending moment caused by the eccentric loading. Compression of crack surfaces is observed at regions closer to crack middle [(S/S 0) = −0.33] due to the presence of stringer, and mode I fracture was observed to be dominant at the crack surface region [(S/S 0) = ± 1]. Influence of mode II fracture is higher at the crack middle region due to crack interaction in unstiffened plates, whereas the effect reduces with the presence of stringer. A three-parameter relationship has been developed to estimate the SIF of multiple cracks in a riveted lap joint. The residual life of the riveted joints can be determined from the calculated mixed-mode SIF.