Joining of Polymer-Metal Hybrid Structures by Sergio T. Amancio Filho Lucian-Attila Blaga & Lucian-Attila Blaga

Author:Sergio T. Amancio Filho,Lucian-Attila Blaga & Lucian-Attila Blaga
Language: eng
Format: epub
ISBN: 9781119466772
Publisher: John Wiley & Sons, Inc.
Published: 2017-12-12T00:00:00+00:00

6.7 Fasteners

“Fastener” can be described as a specific type of mechanical hardware for mechanically joining parts. As an example, we can list rivets, bolts, screws, pins, studs, nuts, collars, washers, nut plates as general fasteners. There are some special fasteners within these groups, which are the pin/collar system series, lockbolt series, rivets (solid and blind rivets), blind bolts, which bring together the characteristics of bolts and blind rivets, among others.

Because of its small size, the importance of mechanical hardware is usually underestimated, despite its relevancy to the safety and efficiency of the aircraft operation.

Mechanical fastening is a process that involves the technology of joining elements by the use of fasteners, and its financial feasibility increases when it reaches an automated process. The automation of fastener installation, specifically drilling and riveting, makes the process highly competitive when compared to the other processes such as welding. Moreover, no other technology is very efficient when quick disassembling (nondestructive) is necessary, for repairs, for instance.

Fasteners can be described and selected according to several and complementary criteria. It is important to collect and establish details as much as possible about the joint requirements, so a proper fastener specification can be obtained for such applications. “Proper fastener selection and application is the first step toward building reliable hardware; therefore, a standard approved parts list consisting of a limited number of types and styles will result in optimum performance, reliability, maintainability, and economy” [25]. As it was discussed in material the selection section of this chapter for joined parts, the same can be applied for fastener selection. Important aspects must be concomitantly considered, including fastener material, load nature and level, corrosion aspects and then protective finishing, work temperature, mechanical properties, lightning, more specifically fatigue aspects, torque application, work vibration, weight, accessibility, installation, and so on.

Although an intrinsic issue, it is important to mention that the proper dimensional specification of the joint will lead to a proper selection and specification of the fastener. Thickness and hole tolerances may be evaluated in order to guarantee the proper fastener specification. Interface sealing and torque application (clamp force) must be taken into account when specifying the joint fasteners.

One first classification of fasteners is based on the nature of the application, regarding the continuity or permanency of the fastener installation, that is, for permanent or temporary joints. For permanent joints, fasteners can be installed once, and so for their removal, a mechanical process, such as drilling, must be applied, causing their destruction. On the other hand, for temporary joints, we can use removable fasteners, which can be removed and, in some cases, reinstalled.

Accessibility is another very important criterion to be considered. Where the hole can be accessed from both sides, “head” and “tip,” solid rivets or bolts could be installed. When there is only one-side access, called blind access, blind rivets or blind bolts may be chosen; or if there is a need for creating two-side access, doors can be specified, adequate for the design and structure requirements, such as inspection doors on aircraft wings.

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