Abstract: [Objective] In order to clarify the softening and flattening mechanisms of oaks in different cutting directions, bending creep behavior of different oak boards(longitudinal plain-sawed lumber, longitudinal quarter-sawed lumber, transverse plain-sawed lumber and transverse quarter-sawed lumber) were investigated by dynamic mechanical analysis(DMA).[Method] DMA creep curves of oak samples were analyzed and fitting by Burger model and general Kelvin model to evaluate the creep performance of different oak samples.[Result] The results showed that both Burger model and general Kelvin model could describe creep characteristic of oak well, R² of Burger model is larger than 0.90 and R² of general Kelvin model is larger than 0.99. Under the same moisture content, the elastic module(E₀) and bulk viscosity(η_n), which were calculated by general Kelvin model, decreased with temperature increasing from 70 to 90℃. The retarded time(τ'), which were calculated by Burger model, increased when the temperature increased from 70 to 90℃. According to η_n, it was the following order:longitudinal plain-sawed lumber > longitudinal quarter-sawed lumber > transverse quarter-sawed lumber > transverse plain-sawed lumber.[Conclusion] It was suggested that the higher the temperature, the much easier for the oak board flattening. Transverse warp of oak board was easier to flat than that of longitudinal warp. Longitudinal warp of plain-sawed lumber was harder to flat than quarter-sawed lumber. However, comparing to quarter-sawed lumber, restoration of transverse warp for plain-sawed lumber was easier.

Key words: oak, orthotropic, Burger model, viscoelasticity