22nd Congress of International Council of the Aeronautical Sciences, Harrogate, UK, 28 August - 1st September, 2000
Paper ICAS 2000-4.5.R1

PREDICTING FATIGUE LIFE IMPROVEMENT IN COLD EXPANDED FASTENER JOINTS

X. Zhang (1), Z. Wang (2), J. Gaerke (3)
(1) College of Aeronautics, Cranfield University, UK; (2) Beijing Aeronautical Technology Research Centre, PRC; (3) Directorate of Technical Airworthiness, National Defence Headquarters, Canada

Keywords: cold expansion, life prediction, fastener joints, precycling, spectrum loading

This work investigates the effectiveness of applying the cold expansion process to a fatigue-aged fastener joint. Experimental tests were conducted using low load transfer joint specimens made of 2024-T351 aluminium plate. Cold expansion was applied at 0, 25, 50, and 75 percent of the baseline fatigue life. The improvements in fatigue life were substantial, the factors ranging from 1.7 to 3.6, depending on the degree of fatigue ageing prior to cold expansion. A strategy for predicting fatigue life improvement is proposed. The analysis is based on the damage tolerance methodology and consists of two parts: (a) determination of the residual stresses induced by cold expansion using a closed-form solution, and (b) calculation of crack growth life under flight load spectrum using fracture mechanics theory. The predicted crack growth life was validated by test. The results of this investigation indicate that: (a) fatigue life can be improved significantly by cold expansion process applied at 25-50% of the baseline life; (b) it is possible to predict the life improvement using a crack growth approach combined with baseline test data.

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