On the non-destructive detection of fatigue damage in industrial aluminium alloys by positron annihilation |
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Authors: | Uwe Holzwarth Petra Schaaff |
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Affiliation: | (1) Institute for Health and Consumer Protection, European Commission, Joint Research Centre, Via E. Fermi 1 (T.P. 500), Ispra, VA, 21020, Italy;(2) Present address: Società Italiana Brevetti, Via Carduzzi 8, Milano, 20123, Italy |
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Abstract: | The average positron lifetime has been determined non-destructively and in-situ during fully symmetric push-pull fatigue experiments
in the bulk material of the aluminium alloys 2024 T3 and 7075 T6 using a servo-hydraulic fatigue testing system equipped with
a mobile positron beam produced by a 72Se/72As generator (initial activity of ≈ 0.9 MBq; average positron penetration depth ≥1 mm). Contrary to earlier investigations
on stainless steel using the same experimental approach, no variation of the average positron lifetime could be observed during
fatigue and neither early nor late stages of fatigue damage could be revealed. It is concluded that fatigue induced changes
of the defect spectra in technologically relevant aluminium alloys are masked for the present method by saturation trapping
in precipitates. A sufficiently high increase of the dislocation density and the creation of vacancy clusters must be confined
to the vicinity of propagating fatigue cracks or the fatal fatigue crack. Therefore the zone with sufficient detectable fatigue
damage has not enough statistical weight to modify the average positron lifetime of the aluminium alloy bulk material. |
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