Use of Aerospace Fasteners in Mechanical and Structural Applications

Short Communication

Ann J Materials Sci Eng. 2014;1(4): 5.

Use of Aerospace Fasteners in Mechanical and Structural Applications

Melhem GN1,2*, Bandyopadhyay S1 and Sorrell CC1

1School of Materials Science and Engineering, University of New South Wales, Australia

2Perfect Engineering Pty. Ltd, Australia

*Corresponding author: Melhem GN, School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia

Received: September 16, 2014; Accepted: November 15, 2014; Published: November 20, 2014


The intention of the present short review is to introduce to the non-specialist reader the feasibility of the use of alternative materials not generally considered by engineers working in mechanical and structural applications. That is, the use of specialised aerospace rivets in the more general area of construction is considered. To this end, the text briefly overviews the different types of fasteners used in the construction industry and their common mechanisms of failure. The most common types of fasteners used for conventional mechanical and structural applications are all-steel rivets and pop rivets consisting of aluminium shank and mandrel of a higher strength alloy. In contrast, the aerospace industry makes universal use of pop rivets consisting of high-strength aluminium alloys, the design and installation of which are illustrated. These more specialised rivets are suitable for implementation because the aluminium alloys used exhibit superior mechanical properties and corrosion resistance compared to those of other rivets. For comparison, the mechanical properties of the aluminium alloys used in both conventional and aerospace rivets are surveyed in tabular form.

Since environmental failure by galvanic corrosion owing to exposure to seaspray is very common, the factors that affect galvanic corrosion are discussed. A relatively comprehensive graphic survey of the galvanic series for corrosion of metals and alloys in seawater, drawn from a variety of sources, is provided. While this provides a well known ranking of the susceptibility to corrosion, this version of the series is uncommon in that it illustrates the series generically for alloys and it differentiates the metals and alloys into four ranges of corrosion resistance rather than as a continuous series. More specifically, since the susceptibility to corrosion of chemically similar alloys can be subtly shaded and hence difficult to rank, the galvanic series for corrosion in seawater of an extended range of aluminium alloys also is provided. Finally, an example of the successful 10-year performance of aluminium alloy aerospace rivets for the rectification of the failure of a major rooftop structure, which failed rapidly owing to steel shank-aluminium alloy workpiece corrosion from seaspray, is briefly mentioned.


In the construction industry, which regularly involves mechanical and structural applications, metallic materials are utilised heavily. One major area of application is mechanical fasteners or connections, which include rivets, bolts/nuts, lock bolts, and pins [1,2]. More broadly, fasteners are categorised generally as follows:

Threaded fasteners

Bolt/nut systems are designed with threads, which allow this fastener to be removed without damage to the system.


Rivets are permanent fasteners that constrain the joint with a head (factory-head) and an expanded tail (shop-head or buck-tail) on the opposite end of the shank.

Blind fasteners

Blind fasteners are those that are installed and can be accessed on one side of the joint only, such as pop rivets.

Pin fasteners

Pin fasteners typically are of a single elongated piece (solid or tubular), although they may include a malleable collar.

Special-purpose fasteners

Specialised fasteners often are designed for quick removal and replacement and may include studs, latches, slotted springs, and retaining rings.

Fasteners for composites

In the joining of composites, specialised design considerations often are required for joints subject to high stresses, tight tolerance requirements, thermal expansion mismatch, galvanic corrosion, and/ or leakage.


Failure of fastening systems usually is from static loading (overload in tension, bending, shear, or torsion), dynamic fatigue (from cyclic loading or repeated impact), or corrosion (galvanic, chemical, or stress) [1]. Typical locations of failure of the most common mechanical fasteners are directly beneath the head(s) of rivets, at the thread-shank transition (in bolts), at the first inner thread (in nuts), and at microstructural imperfections. Alternatively, failure of the plates or sheets being joined regularly is by dynamic fatigue [3].

Although it usually is straightforward to design for static and dynamic loads in mechanical and structural systems, the potential effects of corrosion are more difficult to predict. This is partly because they depend on factors that are intrinsic to the product, such as the chemical composition and the microstructure, which is dependent on the processing. It also is because they depend on factors that are extrinsic to the product, particularly the environmental conditions to which it is exposed. Consequently, these effects often can be overlooked when specifying materials for such applications.

Most conventional threaded fasteners are fabricated from various grades of alloy steel, which may have protective coatings, such as zinc, tin, cadmium, or aluminium [1]. In contrast, pop rivets are constructed from alloys in all-steel, all-aluminium, and aluminium shank/steel mandrel configurations. In most construction applications, the joined plates and sheets also consist of alloys of steel and aluminium. Therefore, the potential for galvanic corrosion resulting from the opposition of dissimilar metals is clear [4].

The principles of galvanic corrosion are well known [5-8]. Since many mechanical and structural applications are exposed to rainwater, condensed humidity, seawater, and seaspray, the metals used in these systems are subject to anodic corrosion by electrochemical reactions during which at least one of the metals is altered from the metallic to the non-metallic state. In terms of galvanic corrosion, there are five general issues of consideration:

Galvanic series

In galvanic reactions, dissimilar metals act as cathode and anode while the water acts as electrolyte. This configuration is sufficient to establish an electrical circuit involving a potential (voltage) difference between the electrodes and associated current (amperage) flow. The electromotive force (EMF) series [5], which ranks the potential for corrosion between pure bimetallic couples in water in terms of electrochemical cell voltages, is well known. Another, perhaps more practical, variant is the galvanic series, which provides the same ranking for commercial metals and alloys in seawater, which is a more conductive electrolyte than water. This is shown in Figure 1. These data, which are drawn from a range of sources, can be used to determine the probable location of corrosion (i.e., oxidation). For example, if structural steel members (i.e., mild steel) are fastened with a zinc-plated bolt and nut, their relative vertical locations in Figure 1 indicate that the former acts as the cathode (higher in Figure 1 → decelerated corrosion) and the latter acts as the anode (lower in Figure 1 → accelerated corrosion). The greater the separation of the two in Figure 1, the more severe the corrosion. Since electrons are conducted to the anode and cause reaction, then the zinc-plated bolt and nut will corrode (where the contact surface areas of both electrodes are identical) and hence form zinc oxide (ZnO).