Comparison of the time-moisture and time-temperature equivalences in the creep properties of Chinese fir

The present study investigated how the applications of the time-moisture superposition principle (TMSP) under a moisture content (MC) range of 0-14.2% and the time-temperature superposition principle (TTSP) under a temperature range of 30-150 degrees C would affect to Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) creep behaviors across grain orientations via a dynamic mechanical analysis instrument. The results showed that both TMSP and TTSP could describe the evolution of creep in the radial and tangential directions. Master curves constructed by TMSP and TTSP overlapped at a reference condition (30 degrees C, 0% MC), regardless of the grain orientation. In addition, an equivalent relation between the effects of moisture and temperature on the creep behavior was assumed based on TMSP and TTSP. Under the tested temperature, the effect of the per unit MC was equivalent to that at ca. 33 and 44 degrees C for the radial and tangential specimens, respectively. These findings elucidate the effects of moisture and temperature on the rheological properties of wood cell walls and are helpful for better utilizing wood in civil engineering applications.