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Journal Article

Grommet Hole Reinforcement and Lightning Strike Protection in Composite Structural Assembly

Aircraft design and assembly challenges include provision of hole protection from lightning strike in fastened joints, especially in the vicinity of fuel tanks or electrical services. Installation of interference fit fasteners helps minimize the effect of lightning strike and also enhances the durability and load transfer ability of the joint. However, these are known to cause laminate damage during installation which can degrade the fastener system performance. Use of a pre-installed expanded grommet into the hole prior to installing interference fit fasteners has been shown to greatly enhance the effectiveness of the joint as well as the conductivity of electrical current into the structure to minimize arcing or plasma discharge at the fastener in the event of lightning strike.
Technical Paper

Automated Installation of an Expanded Light-Weight Rivetless Nut Plate Assembly

Installation of removable access panels and sub-assemblies frequently requires installation of anchor nut plates in the support structure. Several nut plate methods are used including conventional riveted nut plates, gang channels, or bonded or glued-on nut plates. None of these current methods lend themselves to automated assembly. Fatigue Technology Inc. (FTI) has designed and adapted its ForceTec® rivetless nut plate into an innovative light weight aluminum ForceTec “Lite” product that is fully assembled with a self locking nut element encapsulated in a sealed dome or shell. This paper will present a new method of installing an expanded rivetless nut plate using a unique segmented mandrel that expands the completely assembled nut plate into a pre-drilled hole.
Technical Paper

A Superior Method of Installing Aircraft Fittings and Hardware

Typical aerospace hardware and fittings; especially those that penetrate bulkheads, are usually large and heavily flanged, requiring a thick or large diameter pad-up around the penetration hole. The assembly is often complex with multiple holes to accept satellite fasteners to attach the fitting to the structure. This process adds weight to the structure, limits design flexibility, is labor intensive and often time consuming to install. This paper introduces an innovative method of installing aerospace fittings and hardware using proven cold expansion technology. This advanced bulkhead fitting system provides a fast and robust installation process that reduces both cost and assembly complexity compared to traditional methods, while providing a lighter weight installation, increased structural design options and improved fatigue life.
Technical Paper

Manufacturing Savings and Increased Productivity Using the ForceMate® Bushing Installation System

Reduced manufacturing costs and flow time, along with increased structural fatigue life and reduced in-service maintenance problems can be realized with the Fatigue Technology Inc. (FTI) ForceMate® (FmCx™) system of installing high-interference bushings into aircraft structures. Bell Helicopter reported [1] a projected $24 million cost savings with the use of ForceMate. This paper will describe the ForceMate system in detail as well as an alternative bushing installation method, BushLoc, and the manufacturing benefits realized with their use. The ForceMate bushing installation system installs bushings with a consistently high level of interference in a fraction of the time of traditional methods, such as shrink and press fit. It is a safer method, reduces hardware variability and provides a higher integrity bushing installation with significant structural fatigue life improvement.
Technical Paper

Incorporating Hole Cold Expansion to Meet Durability and Damage Tolerance Airworthiness Objectives

Aircraft structural integrity requirements now embrace damage tolerance requirements as the basis for design and continued safe operation. The challenge facing industry is how to economically achieve these requirements in both new and, to a greater extent, the growing volume of aging aircraft. Compensating for damage tolerance analysis could lead to overweight structures. Not allowing for residual cracks in repairs could compromise the long term structural integrity, induce on-going inspection penalties and possibly result in unnecessary major structural replacement or repair. Hole cold expansion is a proven method for retarding the growth of cracks originating in holes. This paper discusses the technology and the effectiveness of the induced residual compressive stresses in reducing the stress intensity factor and permitting the use of smaller initial flaw sizes to meet damage tolerance requirements.
Technical Paper

Advanced Design Fatigue Resistant Rivetless Nut Plate System

This paper discusses an advanced design rivetless nut plate system which overcomes the inherent problems associated with typical riveted and rivetless nut plate configuration used in blind assembly of aerospace structures. The ForceTec™ (FtCx™) rivetless nut plate system presented utilizes hole cold expansion technology to radially expand a nut retainer into the fastener hole. Torque and push-out resistance are achieved by the resultant high interference fit of the retainer. Residual compressive stresses induced in the metal surrounding the hole during cold expansion and the reduction in applied cyclic stress range, caused by the high interference fitted retainer, significantly improve resistance to fatigue cracking. This system significantly reduces the high stress concentration associated with other methods and has demonstrated superior nut plate qualities with fast, consistent and reliable installation.
Technical Paper

Production and Repair of Fastened Joints Incorporating Cold Expansion

Fastened joints are an integral part of aircraft design. Due to their complexity and function, they are also the primary source of structural fatigue problems. The incorporation of residual compressive stresses around a fastener hole greatly enhances the fatigue resistance and integrity of a fastened joint. This paper describes the split-sleeve cold expansion method to create residual compressive stresses which extend the fatigue life of holes in both new structure and field repairs. Data from test programs highlight process benefits and crack retardation effects for various specimen configurations. Other process features such as cold expansion to size are explained, along with the status of process automation.