Validation of Expanded ForceMate Bushings in 2050-T84 Aluminum Lithium Lugs

Aluminum Lithium (Al-Li) alloys were originally developed in the 1950’s in an effort to increase strength and corrosion resistance while decreasing density when compared to the materials commonly used in the aerospace industry.  While early development efforts achieved these objectives, the anisotropic nature of Al-Li alloys compounded the complexity of design.  The unique properties of these alloys limited the use of many industry standard design practices, including high interference fit (HIF) bushings. 

The continuous development of Al-Li alloys has lead to new alloys that more closely matched to the design requirements of the OEM’s including lower weight, improved mechanical performance and increased toughness due to a reduction in the degree of anisotropy.  In the case of 2050-T84, an analysis of the elongation properties supported the use of HIF bushings, to include the ForceMate system.

ForceMate bushings are installed into critical high performance joints by radially expanding the initial clearance fit bushing.  An expansion mandrel is pulled through the bushing, yielding it into the material.  This results in a high interference fit with a significantly reduced risk damage to the interface between the bushing and the parent material.  

In conjunction with an OEM, Fatigue Technology conducted a validation test program using 2050-T84 lugs into which ForceMate bushings were installed to optimize the installation and ensure no damage to the Al-Li. 

This paper will review the ForceMate installation method used and discuss the test program and results that were attained.  The ForceMate bushings were successfully installed with no incipient damage.  Retention force results exceed the requirements by almost 3X and the fatigue life improvement was 15X that of the baseline transition fit bushings.  We will also discuss the observations and cautions related to high interference fit expanded bushings in Al-Li alloys; particularly in different material grain directions.