Development of tension and compression creep models for wood using the time-temperature superposition principle

This paper describes the development of long-term creep models for wood intension and compression using the time-temperature superposition principle (TTSP). Short-term accelerated creep tests were conducted in both tension and compression in a controlled environment. The tested specimens include southern pine (Pinus spp.), Douglas-fir (Pseudotsuga menziesii), and yellow-poplar (Liriodendron tulipifera). Test temperatures ranged from 20? to 80?C. The moisture contents (MCs) for testing tension parallel to the grain were 6, 9, and 12 percent for Douglas-fir and southern pine, and 6 and 9 percent for yellow-poplar. The MCs for testing in compression parallel to the grain were 9 and 12 percent for Douglas-fir and southern pine, and 6, 9, and 12 percent for yellow-poplar. The strain was measured using bonded strain gauges. The individual compliance curve for each temperature was plotted against the log-time axis to obtain a master curve. The temperature shift-factor relationship was then plotted. A nonlinear regression analysis was used to estimate the model parameters. The results show that the TTSP was successfully applied to all three species tested at the MCs just stated in both tension and compression. Success of the TTSP was supported by smooth-fitting master curves, conformance to the Arrhenius equation, and the activation energies falling within published results.

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