In recent years, China's aerospace industry has flourished, achieving rem)arkable achievements that have drawn global attention. With the development of the aerospace industry, the demand for aviation fasteners has correspondingly increased. Fasteners used in aerospace are required to meet high-quality standards due to their use in high-temperature, high-pressure, and high-strength environments. Globally, aerospace fastener manufacturers are mainly concentrated in Europe, the United States, and other countries and regions. Below, I will elaborate on aviation fasteners to help everyone understand the important role of fasteners in the aerospace industry.
Fasteners are a type of mechanical component that secures two or more parts together, with extremely wide applications and are known as the "grains of industry." Aerospace fasteners specifically refer to those used in aerospace, made from specific materials, with special properties or purposes, and are capable of meeting the unique technical requirements of the aerospace industry.
Aerospace fasteners are typically used in aircraft, satellites, rockets, and other aerospace vehicles. They are a typical type of high-end fastener and an essential basic component in aerospace vehicles, with much higher performance requirements than fasteners in other fields. Aviation fasteners can be categorized into many types based on different classification standards, each category containing many different specifications and types to meet the diverse needs of different materials and structures.
Common classifications of aviation fasteners include:
① Divided into removable fasteners and permanent fasteners based on removability, with removable fasteners including bolts, screws, and nuts; permanent fasteners include high-lock nuts, common rivets, etc.;
② Classified by product type, into bolt (screw) types, nut types, single-sided fasteners, special fasteners, etc.;
③ Classified by material used, 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 Classified by differences in assembly operation requirements, into single-sided connection fasteners and double-sided connection fasteners;
⑤ Classified by the nature of the working load, into tensile and shear types.
Special classifications of aviation fasteners:
Aviation fasteners are commonly classified by product type. Next, I will introduce rivet fasteners, bolt fasteners, nut fasteners, single-sided fasteners, and special fasteners in detail:
（1）Rivet fasteners: For aerospace applications, quality assurance and lightweight are the most important selection factors. Rivet fasteners are one of the most widely used fasteners on aircraft, with materials including aluminum alloys, stainless steel, heat-resistant alloys, titanium alloys, etc. Currently, most rivets are primarily used for connecting thinner structures of aluminum alloy and titanium alloy composites, with diameters generally below Φ4mm. To meet the high-life requirements of aircraft structures, most are assembled using automatic riveting machines and flexible assembly systems. With the continuous increase in rivet material strength, load-bearing rivets for important parts have also been developed, such as bimetallic rivets and high-shear rivets, with strengths comparable to that of shear-type titanium alloy high-lock bolts.
（2）Bolt fasteners: The most commonly used fasteners in larger load-bearing parts of aircraft are bolt fasteners, including ordinary bolts, high-lock bolts, tapered bolts, etc. High-lock bolts are a type of threaded fastener that can be used on one side and are widely used in the aviation industry. For aircraft design, weight reduction is an important indicator. The use of high-specific-strength materials can replace larger fasteners with lower specific strength. Therefore, a large number of TC4 titanium alloy fasteners with a tensile strength of 1100MP are used in the aircraft body structure. In addition to specific strength, other properties such as fatigue resistance, corrosion resistance, rigidity, brittleness, compatibility, and heat resistance must also be considered in the design.
（3）Nut fasteners: Nut fasteners are used in conjunction with bolts and come in various structural forms to suit different applications, including hex nuts, twelve-point nuts, spline nuts, clip nuts, barrel nuts, high-lock nuts, etc. Most nuts feature a self-locking structure. Clip nuts include those with ears, without ears, floating, and grouped floating types, with sealed and unsealed forms. The earless clip nut can improve structural life; hex nuts are widely used on aircraft; twelve-point nuts are used extensively on engines and high-strength bolts; high-lock nuts are used in large quantities in conjunction with high-lock bolts, including shear-type and tensile-type high-lock nuts, with structures such as ordinary high-lock nuts, self-aligning high-lock nuts, sealed high-lock nuts, and upset high-lock nuts.
（4）Single-sided fasteners: The fasteners used in non-open parts of aircraft mainly have two structural forms: one is for removable parts such as access panels and cabin covers, and the other is for permanent structures. Among them, the threaded insert is divided into clearance type, interference type, and main load-bearing structural type. The large base titanium alloy single-sided threaded insert is designed specifically for the assembly of composite material structures. The interference single-sided threaded insert fastening system can improve sealing and anti-fatigue properties, while the high-strength insert fastening system can be used for main load-bearing structures.
(5) Special fasteners: These include ring groove nails and their fastening systems, quick-release lock fasteners, and composite material fasteners. The ring groove nail and its fastening system are permanent fasteners that are riveted on one side and installed on both sides, widely used in Boeing and Airbus aircraft. They can be classified into clearance type and interference type based on the mating form, and into pull rivet type and upset rivet type based on the installation form. Most currently used systems employ titanium alloy ring groove nails with a load distribution for uniform loading. Quick-release lock fasteners are mainly used for connections at openings and hatch areas, offering various structural forms for rapid assembly and disassembly, with high reliability requirements, needing to meet the standard of up to 1500 reliable disassemblies. Composite material fasteners are made of composite materials and include rivets, bolts, screws, and nuts. They are ideal for solving issues related to weight, strength, corrosion, lightning strike, and radar image, and their strength can reach the shear strength of high-strength aluminum rivets, currently only suitable for secondary load-bearing structures of aircraft.
Currently, the number of aerospace fastener manufacturers in China is still relatively small. In the future, manufacturers with aerospace fastener production technology will have more competitive advantages. Enterprises can increase their efforts in independent research and development to break through existing technical and financial barriers.
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