Search Results

In a fastening system when there is a small misalignment of the holes, the holes are enlarged to align the axes and a next size fastener is used to fit the joint. But when the misalignment is large then the enlargement need to be proportionally large. In this case a bushing is press fit onto the hole to handle the fastening. If we press fit a bushing, it generates residual stresses in the panel. These residual stresses reduce the damage life of the components on which the bushings were press fit. In the aircraft engine nacelle components the damage life is very critical in various failure conditions such as fan blade out condition, wind milling and bird strike. It increases the flight time in these events. Here four different case studies were considered to study the damage life of the aircraft components made of Aluminum or composite material.

The fastener analysis for an airframe panels under random cyclic loading conditions were analyzed with various elaborate solutions. But here a simple technique is proposed to analyze the problem. The fastener system in any structure could develop crack at the edges of the hole or at the fastener head rim location and propagate further between bolts. The sub- layer crack and micro cracks are hard to locate visually. Here a solution method is presented to detect the crack for various types of fastener conditions such as the fully contacted fastening, partial contact and no-contact condition. This is one of the useful tools to check the health of the fastening systems. Part I of this paper shows the necessity for a fix that arise in the initial misfit conditions. They also show the fastening efficiency for all the different condition. Here we would like to address the detection of a crack in any of the above fastening conditions.

The fastener analysis for an airframe panels under random cyclic loading conditions were analyzed with various elaborate solutions. But here a simple technique is proposed to analyze the problem and prove the necessity for a design solution. It is shown that the misfit in the fastener system reduces the load capacity of the joint due to the lack of contact or reduced contact. This reduced contact also produces various stress concentration at the contact zones. In the cyclic loading environment this reduced load capacity and increased stress concentration produces elastic plastic deformation around the contact locations and at the same time a crack develops and propagates beyond the fastener system. This creates a load leak transparent to the fastener system. Thus the misfit fastener systems have a higher probability of aging than the fit fasteners. With the proof in hand various design patterns were proposed to improve the fatigue characters under varying types of loading conditions.