Study On Creep Behavior Of Chinese Fir Inculding The Moisture Content And Stress Effect

In this paper, the test material is the 15-year-old planted Chinese fir(Cunninghamia lanceolata(Lamb.)Hook). Mainly to study the Chinese fir's properties of bending and creep in different conditions of moisture content, and properties of creep in different conditions of stress level, then establish an appropriate model for creep. We can reach the conclusion after analyzing the experimental test result:1 Moisture content of Chinese fir samples had a conspicuous affect to the bending properties. The largest bending load, maximum strain, maximum stress and flexural modulus of elasticity of Chinese fir with the increase when moisture content decreased within the fiber saturation point,and the value of the maximum load and maximum stress of the moisture content within the fiber saturation point were 75% when the moisture content of 0%.2 Chinese fir related strongly with the creep stress level and moisture content of samples. In different stress levels conditions, the creep of the elastic deformation, viscoelastic deformation and viscous deformation with the increase in stress level increases, and creep law of different stress levels are also different. Creep under the low stress tend to be a limit, but under the high stress tend to damage, creep deformation and stress level are not a linear relationship. In different moisture conditions, the sample of the total creep deformation, viscous creep and viscoelastic creep ,within the fiber saturation point are increase when the moisture content increase, the elastic deformation of the moisture content in 12% and 6% were larger than the moisture content in 0% and 20%.3 The R2 between the cruves simulated by six components model with the parameters sovling by origin and the test cruve are above 0.99. Use the model to predict long-term creep, it was found that the forecast is too linear and the curve deformation predicted is far more than the actual value, so introduced an exponential index parameterλto t which on the part of the the expression in the model of viscous deformation, can solve the problem well.