Stress relaxation behavior of wood in the plastic region under indoor conditions

The stress relaxation behavior of wood in the plastic region was measured by clamping wood specimens with bolts for up to 5years under indoor environmental conditions. An initial stress was applied by displacement control, whereby a steel plate or a washer was embedded in the radial direction of the wood. The difference in the stress ratio was small in the plastic region due to the difference in the initial stress level, and the higher the initial stress, the higher the stress that was maintained. By contrast, the clamp force virtually disappeared in the elastic region. The estimated stress ratio after 50years was 15% in the elastic region and approximately 20-40% in the plastic region. Due to the influence of humidity fluctuation, it was difficult to maintain stress in the elastic region, but it seems to be possible to maintain the stress for a long time using partial plastic embedment with sufficient extra end distance.