| In the manufacturing process of wood products, the wood needs to be pressured in many cases, such as wood chips to soften flattening process, rolling process, hot pressing of plywood and wood flooring. Those are process of pressure applied in wood under different conditions. But wood is an anisotropic and porosity material. It will produce deformation in the compressed process. Poplar is the used materials of the wood-based panel production, but the experimental data of transverse compression is limited at different temperatures. Therefore, this paper addresses the study of mechanical behavior in Poplar at different temperatures along the radial compression under large deformation. Stress-Strain relationship of poplar is established in transverse compression, and the process of cross-pressure deformation characteristics of the poplar cells is observed.Time-temperature equivalence test is a better way that using short-term experimental data predict the long -term mechanical properties of materials. However, there are no many reports about this method used to wood materials. The main problem is that wood is a heat flow composite material containing the fiber, lignin, and half fibers with multiple changes in the region of polymer blend, which is a material of non-simple thermal flow. How to apply the Time - Temperature Superposition Principle to predict the long-term mechanical properties of wood has been the concern of scientists and become a difficult problem of the wood science field. There is no paper reporting the analytical formula or calculation basis about following laws of shift factors. Therefore, this paper addresses the study of the applicability of Time–Temperature Superposition Principle in polar at different temperatures through the three-point bending method. The long-term mechanical properties of wood had been obtained through the horizontal shift and vertical shift of short-term experimental data. The formula of Time–Temperature Superposition Principle in wood was firstly proposed considering the vertical shift factor.The results show that:1. Under pressure from poplar wood in the radial, the entire process of transverse compression can be divided into three stages: linear elastic stage, the weak linear hardening after yielding stage and the power hardening stage. It is difficult to determine compression dense point, so using a linear equation to describe its elastic phase, and a 3 times polynomial description of the compression stress-strain relationship of its post-yield deformation is more convenient.2. Strainε= 3.2% is the end point of elastic stage in the stress - strain curve. Strain (ε= 16%) is the point of wood rays starting buckling. Strain (ε= 22%) is the point of vessel molecular cells beginning to crush. Strain (ε= 40%) is the point of the specimen beginning to compaction. Strain (ε= 65%) is can be regarded as the compaction point that cell lumen have been completely filled. Along the curve after the compaction point is the compaction stage, the stress - strain relations reflect the relationship of a material change in physical distance within the molecule linearly with the applied stress.3. The Time–Temperature Superposition Principle is successfully applied to the polar and the relaxation property is predicted. For example, the master curve for polar tested extrapolated to approximately 9.5 years mechanical properties from 1h of testing under 10℃,30℃,50℃,70℃,90℃and RH=60%.4. The test had a linear horizontal-shift-factor temperature relationship and satisfied the Arrhenius formulation, the relation was y = 4723.7x-17.976 (R~2 = 0.9848). The apparent activation energyΔE is 21.6 kcal /mole.5. The vertical shift factor bT had a linear relationship with temperature, the relation is y = 0.0045x-0.368 (R~2 = 0.9435). It is Show that the expression of wood - temperature superposition principle considering the vertical shift factor basis this study is reasonable. 6. It is a good result of fitting master curve with long test modulus curve for 1138h under the temperature of 10℃and the relative humidity of 60%.
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