Stress Intensity Factor of Cracks in Bolted Joints Based on Three-dimensional Finite Element Analysis

One of the major strength problems for bolted joint of aircraft is the onset and growth of cracks due to fatigue loading. But at present, the analysis of stress intensity factor (SIF) for bolted joint with crack are mainly based on two-dimensional finite element model. For that, three-dimensional (3D) finite element model of a bolted joint with cracks has been developed using the non-linear finite element code MSC Marc. Issues in modeling non-linear touching, and the friction between the joint parts, and the pre-stress force of bolt are all taken into account. SIF solutions along the thickness of bolted joint are obtained for different damage models. The results show that K I is dominant, and K II and K III have small contributions although the crack model beside hole is complex. SIF reaches maximum at the faying surface and minimum at the outside surface for all crack length. For a given crack length, SIF of a symmetric crack is always higher than the one of an asymmetric crack. SIF at the faying surfacing for countersunk is higher than that for straight hole for same crack length. But the trend of SIF at the outside surface is opposite. In other words, the type of fastener hole has a great influence on SIF of bolted joint.