Studies on Mechanism of Creep of Wood under Changing Moisture Content Conditions and Methods for Reducing its Creep

1.研究了木材在不同含水率条件下弯曲蠕变的应力相关性和蠕变过程中产生的声发射。在含水率变化与蠕变应变之间的指数回归方程中，在回潮条件下，指数的拟合值随着应力水平的增加而增大，而在失水条件下，指数的拟合值略大于1，与应力水平无关。在蠕变应变与施加的应力成正比的应力水平之外，通常会产生高能电子能谱。在风干和回湿条件下，在50%的应力水平以上产生AEs，而在高含水率和失水条件下，它们在35%的应力水平以上产生。当标本破裂时，立即或在标本破裂前短时间内产生大量的血管紧张素转换酶。我们研究了在不同含水率条件下，乙酰化处理对层压板弯曲蠕变的降低效果。在回潮和失水条件下，在压缩侧和拉伸侧层中含有乙酰化层板的层合板的蠕变小于仅由未经处理的层板组成的层合板的蠕变。在回潮和失水条件下，拉伸侧层中含有乙酰化层板的层合板的蠕变最大，而在压缩侧层中含有乙酰化层板的层合板在失水条件下的蠕变最小，在回潮条件下的蠕变略高于未处理层板的层合板。这种现象可以用乙酰化和未经处理的椎板之间收缩和膨胀的差异以及它们之间的压缩和拉伸蠕变的差异来解释。

1. We investigated the stress dependence of bending creep of wood under changing moisture content conditions and the acoustic emission(AE)generated during its creep process. In the exponential regression equation between the change in moisture content and the creep strain, the fitted values of exponent increased with increasing stress level under moisture-regain condition, whereas they are somewhat more than 1 and independent of stress level under moisture-loss condition. AEs generally were generated beyond the stress level within which creep strain was proportional to the applied stress. Under air-dry and moisture-regain conditions, AEs were generated above a stress level of 50 while under high moisture content and moisture-loss conditions, they were done above a stress level of 35 %. When creeprupture occurred, many AEs were generated immediately or for a short time before specimen was-ruptured.2. We investigated the reducing effect of acetylating treatment on the bending creep of laminated wood under changing moisture content conditions in connection with the layers composed of acetylated laminae. The creep of laminated wood with acetylated laminae in compression side and tension side layers was smaller than that of laminated wood composed only of untreated laminae under moisture-regain and moisture-loss conditions. The laminated wood with the acetylated lamina in tension side layer showed the largest creep under moisture-regain and moisture-loss conditions, whereas the laminated wood with the acetylated lamina in compression side layer had the smallest creep under moisture-loss condition, and had a little more creep than the laminated wood only with untreated laminae under moisture-regain condition. This phenomenon can be explained in terms of both the warps due to the differences in shrinkage and swelling between the acetylated and the untreated laminae and the differences in compressive and tensile creeps between them.