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Positron annihilation lifetime measurements of mechanically fatigued polystyrene samples

: Erichsen, J.; Nagel, C.; Günther-Schade, K.; Renner, M.; Altstadt, V.; Faupel, F.


Journal of polymer science. B, polymer physics 46 (2008), Nr.18, S.1991-1995
ISSN: 0887-6266
ISSN: 1099-0488
ISSN: 0098-1273
Fraunhofer IFAM ()

Early stages of cyclic fatigue-loaded polystyrene (PS) specimens were investigated by positron annihilation lifetime spectroscopy (PALS) at a maximum stress amplitude of 15 MPa. PALS yields information about the average unoccupied hole volume. A linear increase in the ortho-positronium (o-Ps) lifetime was observed in a range from 0 to 50,000 cycles. This increase occurs homogeneously distributed at different positions along a sample of 170 mm. The average unoccupied void volume increases by 1.2%. On the other hand, the o-Ps intensity shows no systematic change upon cycling. The results suggest a homogeneous and linear increase in free volume prior to craze formation.