Sherby—Dorn plots

Fig. 10 Sherby-Dorn plots of creep rate versus strain showing the different creep phases a U PVC pipes for constant hoop stresses of 37 to 42 MPa at a temperature of 20 °C (60 K below Tg) (using data of Castiglione et al. [42]) b Highly oriented UHMWPE fibres at room temperature (using data of Berger et al. [43])...

Concerning the above-mentioned critical quantities the authors have in fact established (i) that irrespective of stress level damage is apparently initiated at a critical creep strain ec of 3 to 3.5% (ii) that a notable deviation of creep data from the potential law starts just at this strain level and (iii) that although the strain rate dev/df is a function of stress, the minimum in the Sherby-Dorn plot also occurs (for the tubular specimens) at ec. The postulated changes in sample morphology at about the time when the strain values started to deviate from Findley s equation, were in fact seen by these and other authors [42,52], who detected in U PVC deformed micro-cavities later... 

Recent work has shown that the creep and recovery behaviour of ultra high modulus polypropylenes is very similar to that of LPE. Again the Sherby-Dorn plots form a good entry to the detailed examination of the creep response. Plateau creep behaviour similar to that of LPE has been observed, and the high stress process correlates well with the a-relaxation process in terms of its activation energy. 

The falling strain rate sections of the Sherby Dorn plots are associated with the extension of the springs to reach constant extension at the plateau regions. The "critical stress" is merely seen as indicating a fall to a strain rate level which is less than the sensitivity of the measuring equipment, and below this stress, removal of the load permits almost total recovery through flow in the dashpot... 

Fig.17. Sherby-Dorn plots of creep strain rate vs creep strain for drawTi polypropylene at 30 C, at indicated stress levels.

Figure 11.14 Sherby-Dorn plots of creep of ultrahigh modulus polyethylene at different temperatures. (Reproduced from Wilding M.A. and Ward I.M. (1981) Routes to improved creep behaviour in drawn linear polyethylene. Plast. Rubber Proc. Appl., 1, 167. Copyright...

Figure 3.22 Sherby-Dorn plots of creep for ultra high-modulus PE at different temperatures [29]...

Presentation of creep data Sherby—Dorn plots... 

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