FATIGUE LIFE OF LUGS UNDER SERVICE LOADING - TEST RESULTS AND PREDICTIONS.

Aircraft pin-lug joints with and without interference fit were tested under maneuver loading programs with random loading sequence. The effect of design load, lug material and interference fit on the spectrum fatigue life was investigated. The interference fit of 0. 3% had a strong beneficial effect on the fatigue life for all loading programs, even when local tensile stress peaks exceeded the material yield stress. Test results were compared with predictions based on Miner's Rule, the relative Miner Rule and a notch analysis method. Miner's Rule mostly resulted in rather conservative estimates. Use of the Relative Miner Rule for comparing different aircraft spectrum test results obtained in different laboratories on lug specimens with similar shape, size and stress concentration factor resulted in reasonable agreement between actual lives and predicted values.