Damage tolerance assessment of aircraft attachment lugs

Abstract A comprehensive development of damage tolerance design criteria and analysis methods for aircraft attachment lugs is presented. A concise summary is presented of analysis methods and their correlation with test results from 236 fatigue crack growth and 16 residual strength tests of attachment lugs covering a wide variety of design variables. Logic is presented for the selection of an initial flaw size criterion, based upon a survey of cracking data, assessment of NDI capabilities and consideration of manufacturing quality for aircraft attachment lugs. Data are presented showing the damage tolerance of double element (redundant) lugs with a single initial flaw, but other data are discussed showing a high likelihood of multiple fatigue cracking in lugs. Logic is then presented for initial flaw size criteria for multi-load-path attachment lugs which give appropriate credit for redundancy without ignoring the possibility of multiple cracking.