树盘干缩异向性引起应变的测算及分析

Investigation of tangential strain caused by shrinkage anisotropy using image analytical method

研究探讨了干燥过程中树盘受抑制干缩应变、自由干缩应变、弹性应变、黏弹性蠕变应变以及机械吸附蠕变的图像解析测算法;运用该方法测算了白桦树盘常规缓慢干燥(含水率分布均匀)过程中干缩异向性引起的弦向各应变,分析了干燥过程中不同含水率阶段的应力状态及应力与各应变的关系。结果表明:应变的图像解析测算法可满足精度要求;树盘干燥至fiber saturation point(FSP)以下,弦向首先受拉伸应力作用,随着干燥的进行,拉伸应力转变为压缩应力;应力方向与各应变对应关系不同,与黏弹性蠕变应变无明显对应关系,与机械吸附蠕变基本对应。

This study investigated the image analytical method which was used to measure the tangential strains, including practical shrinkage strain, free shrinkage strain, elastic strain, viscoelastic creep strain, and mechano-sorptive （MS） creep, which caused by shrinkage anisotro-py during slow conventional drying of wood disks. Also we analyzed the stress in different moisture content （MC） and the relations between stress and strain. The results showed that the image analytical method could meet the requirements in accurate level;below the fiber satura-tion point （FSP）, the wood disks were initially subject to tangential tensile stress;with the de-creasing MC, the tensile stress turned into compressive stress. The relations between stress and strain were complex. It had no obviously corresponding connections with the viscoelastic creep strain, and it was almost corresponding with the MS creep.