The Viscoelastic Behavior Of Birch Plasticized By Moisture

This study was aimed at investigating the creep behavior, stress relaxation behavior, and dynamic viscoelasticity of birch plasticized by moisture and temperature, deepening theoretical study of wood viscoelasticity, and providing a scientific basis for its application. Creep and stress relaxation behavior were both examined at six constant MCs(0%, 6%, 12%, 18%, 24%, >30%) and 11 temperatures ranging from 5℃ to 105 ℃. Experiments were conducted using Dynamic Mechanical Analyzer with its Relative Humidity Control(Q800). Burgers model and Findley power law were used to fit the measured creep data. Zener and logarithmic models were used to fit the measured stress relaxation data. Time–temperature superposition(TTS) was attempted for long-term creep and stress relaxation prediction. It was shown that:1.The total compliance, instantaneous compliance, and creep compliance of specimens at all MCs specimens increased at higher temperatures, but samples with higher MCs were affected more pronounced, nearly an order of magnitude greater. Creep compliance of all samples increased dramatically at certain temperatures.2.The total compliance, instantaneous compliance, and creep compliance were affected greatly by the MC of specimens and increased significantly with the increase in MC. The initial relaxation and final relaxation decreased with the increase in MC. The effect of temperature was greater with the increasing MC.3.At higher temperature and MC, a complex interaction of temperature and MC on the total compliance, instantaneous compliance, creep compliance and relaxation modulus was found.4.At certain temperature and MC, 30-min creep compliance was higher than the corresponding instantaneous compliance.5.Both Burgers model and Findley power law fitted the 30-min creep curves of samples well. Findley power law fitted better compared to Burgers model. Both Zener and logarithmic models fitted the 30-min creep curves of samples well. Logarithmic model fitted better compared to Zener model.6.The TTS principle could be used to obtain the long-term creep and stress relaxation responses of birch from short-term creep curves.7.The storage modulus decreased with the increase in temperature and MC. Greater reduction was found at higher temperature and MC. The loss factor decreased with the decrease in MC.