Journal
INTERNATIONAL JOURNAL OF FATIGUE
Volume 50, Issue -, Pages 47-56Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.ijfatigue.2012.04.006
Keywords
Fatigue tests; Al alloys; Negative R-ratio; Crack growth; Quantitative fractography
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Effect of varying negative R-ratio on the fatigue striation patterns was examined for Al-based V95-T4 (analogue of 7057T6) and D16T (analogue of 2024T3) alloys. Three different sequences of cyclic loads and of the varying maximum and minimum stress levels were applied in air atmosphere to the test alloy panels 10 x 160 x 460 mm in size. The tests were conducted at room temperature with the loading frequencies in the range of 0.5-1.5 Hz. Fractographically, the magnitudes of striation spacing were found increasing for increasingly negative R-ratios. To estimate the effects of negative R-ratio on the crack growth rate correction-function surfaces were constructed for the stress-intensity factor K-J. The fractographic analysis suggests that the unloading portions of cycling trajectory are only responsible for the fatigue striation effects. Such a mechanism appears dominating in the positive as in the negative ranges of R-ratio. (C) 2012 Elsevier Ltd. All rights reserved.
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