Radiused lead-in for interference fit fasteners

Abstract

The invention provides a radiused lead-in for interference fit fasteners. An assembly comprises first and second structural elements having aligned holes, a fastener that occupies at least respectiveportions of the holes without a surrounding sleeve, and a mating part that is coupled to the fastener. The fastener comprises: a head; a circular cylindrical shank extending from the head; a mating portion comprising external projections; and a transition portion disposed between the shank and the mating portion. The transition portion comprises a first radiused lead-in section that meets the shank at a shank / lead-in intersection and a second radiused lead-in section that meets the first radiused lead-in section. The first radiused lead-in section curves gradually in a first axial direction toward the mating portion and has a first profile that is a circular arc having a first radius, while the second radiused lead-in section curves abruptly in the first axial direction and has a second profile that is a circular arc having a second radius which is much smaller than the first radius. The maximum diameter of the mating portion is smaller than the minimum diameter of the second radiusedlead-in section.

Description

technical field [0001] This disclosure generally relates to the use of fasteners to secure two or more structures or workpieces (at least one of which is made of a composite material such as fiber-reinforced plastic) in such a way that the fasteners They sit in corresponding holes in the layers for a high interference fit. Specifically, the disclosure relates to interference fit fastener assemblies that include a bolt or pin and mating parts (eg, nuts or collars) but do not include a sleeve surrounding the fastener. Background technique [0002] A common practice for fastening layers of material together is to sandwich the layers, drill holes, and then insert some type of fastener into the holes, thereby securing the layers together. These fasteners are typically inserted with a net or clearance fit into receiving holes in the layers. For many applications, this is sufficient. However, when the assembled structure is subjected to cyclic loading, loosening of the fit of th...

AI Technical Summary

Problems solved by technology

The use of a socket bolt system has the following disadvantages: (a) the parts require a complex installation method; (b) the parts require careful handling to prevent damage; and (c) the system requires extensive measurements during the process (resulting in longer assembly times). long)

Using loose fit fasteners with cap seals has the following disadvantages: (a) the system allows joint deflection to increase over time, affecting fatigue strength; and (b) the amount of time involved in applying the seal cap increases assembly time

Additionally, existing interference fit solutions used in metal aircraft structures may not be optimal for reducing installation force loads when installing fasteners

High installation force loads can cause composite cracking or excessive delamination

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