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依赖性以及蠕变过程中产生的声发射。在含水率变化与蠕变应变的指数回归方程中，在回潮条件下，指数的拟合值随着应力水平的增加而增加，而在失湿条件下，指数的拟合值略大于1，且与应力水平无关。ae通常在蠕变应变与外加应力成正比的应力水平之外产生。在风干和回潮条件下，应力水平在50%以上产生ae，在高含水率和失水条件下，应力水平在35%以上产生ae。当蠕变发生时，许多ae在试样破裂时立即产生或在试样破裂前短时间内产生。研究了不同含水率条件下乙酰化处理对复合木材弯曲蠕变的降低作用，并与乙酰化层组成的层数有关。在复湿和失湿条件下，压缩侧层和拉伸侧层乙酰化层合木材的蠕变小于未处理层合木材的蠕变。拉伸侧层乙酰化层合材在回湿和失湿条件下的蠕变最大，而压缩侧层乙酰化层合材在失湿条件下的蠕变最小，在回湿条件下的蠕变略大于未处理层合材。这一现象可以用两种方式来解释：乙酰化层与未处理层在收缩和膨胀方面的差异所导致的翘曲，以及它们之间在压缩和拉伸蠕变方面的差异。

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.