With the development of the aerospace industry, the demand for aviation fasteners has also increased accordingly. Due to the fact that fasteners used in aerospace are employed in high-temperature, high-pressure and high-intensity environments, their quality requirements are particularly high.
Currently, the major manufacturers of aerospace fasteners are mainly concentrated in countries and regions such as Europe and the United States worldwide.
Now let’s elaborate on aviation fasteners to help you understand the crucial link in aerospace – fasteners.
Fasteners are a type of mechanical parts that firmly connect two or more components. They are widely used and are known as the “rice of industry”. Aerospace fasteners specifically refer to fasteners used in aerospace, processed from specific materials, with special properties or functions, and capable of meeting the special technical requirements of aerospace.
Aerospace fasteners are generally used in aircraft, satellites, rockets and other aerospace vehicles. They are a typical type of high-end fasteners and an essential basic component in aerospace vehicles. Their performance requirements are much higher than those of fasteners in other fields.
According to different classification standards, aerospace fasteners can be divided into many categories. Each major category also includes many different specifications and types to meet the diverse needs of different materials and structures.
Common classifications of aviation fasteners:
① Fasteners can be classified into detachable fasteners and permanent fasteners based on whether they are detachable. Detachable fasteners include bolts, screws and nuts, while permanent fasteners include high-lock nuts and common rivets, etc.
② According to product types, fasteners can be classified into bolt (screw) type, nut type, single-sided fastener type, special fastener type, etc.
③ Based on the materials used for fasteners, they can be classified into carbon structural steel fasteners, alloy structural steel fasteners, stainless steel fasteners, high-temperature alloy fasteners, aluminum alloy fasteners, titanium alloy fasteners, titanium-niobium alloy fasteners and non-metallic fasteners, etc.
④ According to the differences in assembly operation requirements, fasteners can be classified into single-sided connection fasteners and double-sided connection fasteners.
⑤ According to the differences in the nature of working loads, fasteners can be classified into tensile type and shear type.
Special Classification of Aerospace Fasteners:
Aircraft fasteners are generally classified by product type. The following is a detailed introduction to rivet fasteners, bolt fasteners, nut fasteners, single-sided fasteners and special fasteners:
(1) Rivet-type fasteners: For fasteners used in aerospace, quality assurance and lightness are the most important selection factors. Rivet-type fasteners are one of the most widely used fasteners on aircraft. Their materials include aluminum alloys, stainless steel, heat-resistant alloys, titanium alloys, etc. Currently, most rivets are mainly used for connecting relatively thin structures of aluminum alloy and titanium alloy composite materials, with diameters generally below Φ4mm.
To meet the high-lifespan requirements of aircraft structures, most are assembled using automatic riveting machines and flexible assembly systems. With the continuous improvement of rivet material strength, load-bearing rivets for important parts have also been developed, such as bimetallic rivets and high-shear rivets, whose strengths can reach that of shear-resistant titanium alloy high-lock bolts.
(2) Bolt-type fasteners: The most commonly used fasteners in the parts of an aircraft that bear significant loads are bolt-type fasteners, which mainly include common bolts, high-lock bolts, and conical bolts. High-lock bolts are a type of threaded fastener that can be used on a single side and are widely used in the aviation industry.
For aircraft design, weight reduction is an important indicator. Using high specific strength materials can replace large-sized fasteners with lower specific strength. Therefore, 1100MPa TC4 titanium alloy fasteners are widely used in the aircraft structure. In addition to specific strength, other properties such as fatigue resistance, corrosion resistance, rigidity, brittleness, compatibility, and heat resistance also need to be considered in the design.
(3) Nut-type fasteners: Nut-type fasteners are used in conjunction with bolts and come in various structural forms to meet the requirements of different applications, including hex nuts, dodecagon nuts, spline nuts, flange nuts, bucket nuts, high-lock nuts, etc. Most nuts adopt self-locking structural forms. Flange nuts include flanged flange nuts, unflanged flange nuts, floating flange nuts and grouped floating flange nuts, etc., and have two sealing forms: sealed and unsealed.
Among them, unflanged flange nuts can improve the service life of the structure. Hex nuts are widely used in aircraft. Dodecagon nuts are widely used in engines and high-strength bolts. High-lock nuts are used in conjunction with high-lock bolts and are widely used, including shear-resistant high-lock nuts and tensile-resistant high-lock nuts, with structures such as common high-lock nuts, self-aligning high-lock nuts, sealed high-lock nuts and upset high-lock nuts.
(4) Single-sided fasteners: There are mainly two structural forms of fasteners used in non-exposed areas of aircraft. One is the plate nuts/bolts and quick-release fasteners used in detachable parts such as covers and cabin doors. The other is the single-sided blind rivets widely adopted in permanent connections. Among them, blind rivets can be mainly divided into two categories: one is the pull-type blind rivets, which can be further classified into single-sided rivets and single-sided bolts; the other is the threaded blind rivets, which can be further classified into clearance type, interference type and main load-bearing structure type.
Among them, the large flange titanium alloy single-sided threaded blind rivets are specially designed for the assembly of composite material structures. The interference single-sided threaded blind rivet fastening system can improve sealing and fatigue resistance performance, and the high-strength blind rivet fastening system can be used in main load-bearing structures.
(5) Special fasteners: including blind rivets and blind rivet fastening systems, quick-release lock fasteners and composite material fasteners. Blind rivets and blind rivet fastening systems are a type of permanent fasteners that can be installed on both sides but riveted on one side. They are widely used in Boeing and Airbus aircraft. According to the fit type, they can be classified into clearance type and interference type. According to the installation type, they can be divided into pull riveting type and upset riveting type.
At present, most of the fastening systems adopt titanium alloy ring slot bolts with uniform loading, such as titanium alloy ring slot bolts and ring slot bolt fastening systems. Quick-release lock type fasteners are mainly used for the connection of access panels and hatches, and have various structural forms. They can achieve rapid installation and removal functions and have high reliability requirements, needing to meet the index requirement of reliable disassembly up to 1500 times.
Composite material fasteners are fasteners made of composite materials, including rivets, bolts, screws and nuts, etc. They are ideal fasteners for addressing issues such as weight, strength, corrosion, lightning strikes and radar images. Currently, their maximum strength can reach the shear strength of high-strength aluminum rivets, and they can only be used in secondary load-bearing structures of aircraft.
In the future, manufacturers with aerospace fastener production technology will have a greater competitive edge. Enterprises can increase their efforts in independent research and development to break through the existing technological and financial barriers.
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