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Wednesday, June 27, 2007 - 9:30 AM
ASC1.3

Innovative Bushed Joint Technology for Durability and Metallic/Composite Structural Assembly

L. Reid, Fatigue Technology,, Seattle, WA

Modular aircraft demand high-speed assembly and low cost manufacturing.  Joining of major subassemblies requires close tolerance alignment and minimal/no machining during final assembly of joint components.  Lug and clevis arrangements facilitate component/assembly, removal and repair in service and are typically bushed to provide a sacrificial wear surface and a means of allowing final machining for alignment.  In composite structures they also provide a bearing surface to protect the composite laminate.  

High interference expanded ForceMate bushings are rapidly/consistently installed and overcome problems associated with traditional thermal or freeze fit bushings.  Installation is accomplished by pulling an expansion mandrel through the initially clearance fit bushing.  Besides the high interference fit, the expansion induces a beneficial residual compressive stress around the bushing, which greatly enhances the fatigue life, durability and damage tolerance of the bushing installation.  In critical lug attachments such as engine pylons and landing gear ForceMate bushings have eliminated or greatly extended the inspection intervals. 

Installation in highly loaded fatigue critical joints such as wing attachment, recent innovations in metal, composites and composite/metal aircraft assembly joints provide the following:

a.                   Elimination of potential fatigue damaging burrs

b.                   Off-center ream allowance

c.                   Multiple bushing installations without disassembly of the lug or joint

d.                   Protection of holes in composite structure

e.                   Close tolerance assembly of metal to composite structure such as floor beam to frame attachment

f.                    A double-flanged nested bushing arrangement

g.                   Facilitate installation of pre lubricated lined bushings

h.                   Installation of spherical bearings into bushed lugs 
This paper will describe the ForceMate method and benefits, present fatigue life and durability data, as well as qualification testing providing enhancement in push-out, torque resistance, and vibration.  Discussion of innovative applications on aircraft assemblies as well as in-service cost savings will be provided.


Summary: To facilitate modular assembly of aircraft and enhance durability of lugs and clevises, joints are typically bushed to provide a sacrifical wear surface, a machinable alignment, or to facilitate removal and reassembly. High interference fit expanded ForceMate bushings provide a fast and convenient installation method that enhances fatigue life, durability and damage tolerance of the joint. It facilitates rapid assembly and correction for misalignment as well as installation of double flanged bushings, non-concentric bushings and lubricated liners. They provide protection for holes in composite structures and facilitate close tolerance assembly of metal to composite structure. This paper describes the ForceMate method, structural enhancements, and manufacturing assembly time savings and cost benefits.