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A round-robin analysis was conducted which evaluated and compared different methods currently in practice for predicting crack growth under random loading. This report describes the prediction method used by the Fracture Mechanics Engineering Section (FMES) at NASA-Langley Research Center. It also presents the ratios of the predicted lives to the test lives for eleven of the thirteen specimens tested.
For the eleven predictions made, the ratios of the predicted lives to the test lives ranged from 2.13 to 0.82. Considering that the normal scatter in fatigue-crack-growth rates may range from a factor of two to four under identical loading conditions, these ratios are quite good.
The analysis procedure used by FMES was relatively simple. The loading history for each specimen was analyzed to determine the root-mean-square maximum and minimum stresses. The predictions were then made by assuming the tests had been conducted under constant amplitude loading at the root-mean-square maximum and minimum stress levels. Only a relatively simple computer program and a desk-top computer were required to make these predictions.
random loads, fatigue-crack propagation, 2219-T851 aluminum alloy, fracture toughness, numerical integration
Head, Fracture Mechanics Engineering Section, MDB, RFED, NASA-Langley Research Center, Hampton, Va.