Application of TTSP to wood- development of a vertical shift factor

The applicability of the time-temperature superposition principle (TTSP) to wood has been investigated aiming at the prediction of long-term mechanical properties of wood by both horizontally and vertically shifting of short-term stress relaxation data obtained by experiments. The expression of TTSP considering the vertical shift factor (b(T)) for wood is proposed the first time. The results showed that: (1) TTSP applied to poplar and the master curve that was obtained from 1 h of tests at 283.2, 303.2, 320.2, 343.2, and 363.2 K in a relative humidity (RH) of 60% could predict the stress relaxation behavior for approximately 42 years at 283.2 K and 60% RH. (2) There was a linear correlation between lga(T) and T-1, lg a(T) = 6590.40 T-1-23.64 (R-2 = 0.994), which followed the Arrhenius equation well, while the apparent activation energy was 34.6 kcal mole(-1). (3) The b(T) had a linear relationship with temperature, and the relation was lgb(T) = 0.0013T-0.37 (R-2 = 0.999). (4) The long-term relaxation curve of the long-term verification test had high goodness of fit with the master curve. The results can be interpreted that the TTSP expression considering the b(T) proposed in this paper is rational.