木材高温干燥过程中的弹性应变

本文对美洲黑杨锯材高温干燥过程中的弹性应变进行了研究。结果表明：高温干燥使得木材表层产生较大的塑化变定,并对干燥后期木材内层的正常收缩造成障碍。心层的拉伸应力与木材内裂有关,当心层拉伸应力超过木材横纹拉伸极限强度时,木材产生内裂。因此,在用高温干燥工艺快速干燥杨木类软阔叶树材时,在干燥后期应注意由于干燥应力转向而引起的干燥缺陷。     

针叶树材纵向气体渗透的三维流阻网络

气体在木材中的渗透是通过木材内的孔隙通道进行 ,而木材内的孔隙结构非常复杂 ,在纵向、径向、弦向的连接特性均不相同。以往关于针叶树材气体渗透的模型或理论 ,只考虑针叶树材内气体渗透通道在 1个或 2个方向上的连接。本文根据针叶树材管胞流阻和管胞在纵向、径向、弦向的连接特性 ,建立了一个描述针叶树材纵向气体渗透性的三维流阻网络 ,并运用重正化变换求解出流阻网络的流阻 ,计算了针叶树材气体纵向渗透系数。所得马尾松木材气体纵向渗透系数计算值与其测量结果进行比较 ,两者十分吻合 ,表明本文关于针叶树材气体纵向渗透三维流阻网络理论的科学性     

杨树,河柳速生材干燥技术的研究

为解决我国木材资源的不足，近年来对森林资源的利用正在迅速地向速生短轮伐期木材及间伐小径材等方面开拓。由于对速生材的材性及加工技术研究起步较晚，以往在利用上仅限于人造板及造纸原料。木材干燥是合理利用木材的基础，是保证木制品质量的关键，也是速生材能否取代传统商品材的一个重要技术因素，对速生材的利用将起积极的推动作用。我省速生树种中杨树、河柳占很大比例，杨树中黑杨、青杨居多，此外还普遍分布着泡桐、水杉等树种。由于多数速生材心边材含水率差异大，成材快速干燥时易产生翘曲、皱缩等缺陷，从而影响了它们的直接加…     

木材导热系数的研究

本文运用非平衡态热力学线性理论分析了含水率在纤维饱和点以下木材的传热,结果表明木材中的水蒸汽和束缚水参与了传热,木材导热系数由传导导热系数与因水蒸汽和束缚水扩散产生的两个等效导热系数组成。推广Siau关于木材细胞的导热理论,依据水分吸附和扩散的原理,导出了木材弦向和径向导热系数计算公式,与已发表的36种气干材弦向实验值和23种气干材径向实验值符合较好。分析木材径向传热的方法也适用于木材纵向传热。     

纤维微米切削理论与微米木纤维形成机理研究

分析了木材在传统切削中由于尺寸效应存在所产生的缺陷,提出微米木纤维加工理论,在微米量级的水平下重新解释木材的切削加工过程与切削方式.并从端向、横向和纵向分别对切削过程进行分析,进而从微观理论上解释木纤维微米级切削时刀具刃口圆弧半径、切削厚度的确定以及刀尖圆弧半径和微米加工厚度的选择.     

胶合成材（续二）

胶合成材（续二）李黎９原料选配设备胶合成材生产工艺是用机械加工的方法，去除木材中固有的各种缺陷，将木材原料纵向接长后胶合拼宽、并层积至需要的厚度，是一种无缺陷规格材的加工工艺。因此，快捷、高效地去除木材原料中的缺陷，最大限度地减少木材的损失、提高木材...     

针叶树木材细胞力学及纵向弹性模量的计算--试件纵向弹性模量的预测

依据针叶树木材管胞和射线细胞的结构模型。使用计算机抽样模拟解剖结构参数。以及使用针叶树木材纵向弹性模量计算公式和方法,计算人工林杉木,马尾松幼龄材和成熟材试件纵向弹性模量,计算结果与常温条件下气干试件测定结果十分符合。在试件晚材率和管胞解剖结构参数改变的条件下。计算预测了人工林杉木,马尾松幼龄材和成熟材纵向弹性模量的变化。结果表明：试件纵向弹性模量随晚材率,管胞长度,管胞壁厚度的增加而增加,而试件纵向弹性模量随管胞直径增加而减小。本文提出的纵向弹性模量计算的预测方法,对于运用现代生物技术控制和改变针叶树木材的材质,材性有实际意义。     

树木生长应力与木材利用

在采伐树木时常常听到由锯口处传出的噼噼啪啪的爆裂声,若观察伐倒原木的端面可发现木材裂隙,严重者木材沿纵向产生辟裂。在制材或木材加工中也常见板、方材出现开裂、翅曲现现。究其原因主要是由于树木自身的生长应力(内含应力)在采伐、加工过程中失去应力平衡而突然释放所致。树木的生长应力大(对木材而言可称为术材的残余应力),影响木材的使用价值和降低木材的利用率。这是因为:发生端裂的     

国产油松、马尾松原木品质应力波法试验及其缺陷研究

为了探讨振动法测量木材动态弹性模量时应力波波速的差异性,本实验选取含有不同节子及内部孔洞的国产油松、马尾松原木为试验材料,采用纵向敲击法测量原木试材的动态弹性模量。建立原木缺陷的数学模型,模拟计算和分析表明,木材节子及孔洞对应力波波速及弹性模量均有影响,而且降低了木材品质。     

针叶树材径向和弦向气体渗透的三维流阻网络

将针叶树材气体渗透的三维流阻网络理论进行了扩充 ,提出了气体径向和弦向渗透次级流阻网络的二维等效流阻网络及二维等效流阻网络流阻基元的确定和等效流阻的求解方法 ,将三维流阻网络从关于针叶树材气体纵向渗透性研究 ,扩展到针叶树材气体径向和弦向渗透性研究。提出了针叶树材径向和弦向气体渗透三维流阻网络理论 ,计算了马尾松试件径向和弦向渗透系数 ,并与测量值进行比较 ,结果表明两值相符合。将本文的针叶树材径向和弦向气体渗透三维流阻网络理论与此前关于针叶树材纵向气体渗透的三维流阻网络工作相结合 ,可以使用三维流阻网络计算针叶树材纵向、径向、弦向的气体渗透系数 ,其在木材干燥、改性、防腐有应用价值     

木材干燥应力应变超微观模型的构筑

木材干燥应力应变研究不论在理论上探索还是用于指导生产实践,都具有重大的意义。然而木材干燥应力与应变的关系是非常复杂的,因为木材属于既有弹性又有塑性的材料———弹塑性材料。应变的大小受很多因素的影响,包括材料自身的因素,例如密度、管胞或纤维胞壁的微纤丝的角度以及恒定或变化的环境因素(如大气的温度、相对湿度)等。还有依从于时间的因素(申宗圻,1990)。正是由于木材本身的特殊结构及其在干燥过程中各参数变化的复杂性,建立一个精确性较高和适用性较广的干燥应力应变数学模型很困难。若不靠数学物理方法,单纯的试验很难重现实…     

南方阔叶树材干燥初期应变特点的研究

在不同温度和平衡含水率条件下研究南方阔叶树材干燥初期应变特点。试验结果表明，干燥初期表层呈现伸张弹性应变和塑性应变，内层为压缩应变。伸张弹性应变的最大值是产生表裂的主要原因，塑性应变而引起的表层固定变形是产生内裂的原因。     

Probabilistic evaluation of the final moisture content of kiln-dried lumber using the bootstrap method

This paper presents a probabilistic method of evaluating the final moisture content (MC) of lumber obtained at the end of the kiln-drying process. The final MC data of three different drying tests conducted in past studies were analyzed using the bootstrap method. Target MC was tentatively set below 20 % in the analysis. Two characteristic parameters representing the final MC were estimated with bootstrap confidence intervals. These parameters were the standard deviation (SD) and the percentage of the population that met the MC requirement of less than 20 % (P ₂₀). The histograms of the final MC and the subsequent goodness-of-fit tests revealed that the final MC data of two drying tests did not follow any classical probability distributions, including Normal, Log-Normal, Weibull, and Gamma distributions, thus indicating the need for nonparametric statistics. The uncertainty of the final MC could be evaluated with the estimated SD and P ₂₀. After deriving the relationships between P ₂₀ and the corresponding probability that P ₂₀ is not achieved, we demonstrated how such relationships could provide a kiln operator with information to facilitate better decision-making in optimizing a drying schedule.     

Mathematical modeling to predict drying deformation and stress due to the differential shrinkage within a tree disk

Although many mathematical models for wood drying have been developed to predict the drying behavior of lumber, there were limited results on drying models dealing with tree disks. This study attempted to try to develop mathematical models to predict the drying stresses and crack formation in a tree disk assumed as a cylindrically orthotropic material with radial variations of properties. The results showed that the drying stress changes nonlinearly with decreasing moisture content (MC) due to mechano-sorptive effects. The higher the orthotropic properties of tree disks are, the larger the drying stress occurs. The developed mathematical model showed that the pattern of cracks such as V-crack or heart check significantly depended on the MC distribution along the radial direction. The model also indicated that a dominant factor controlling the drying behavior of tree disk was the differences in MC between heartwood and sapwood within a tree disk of a given species without any chemical or mechanical treatments. Received 8 September 2000 The authors wish to thank Prof. H.S. Jung, Seoul National University, Korea, for his valuable advice. This work was supported by the grant of Post-Doc. Program, Chonbuk National University in Korea (2000).     

MATLAB在落叶松结构用集成材胶合工艺技术研究中的初步应用

对MATLAB在落叶松结构用集成材胶合工艺技术研究中的应用进行了初步尝试。应用MATLAB软件。通过对数据统计主成分进行分析,得到7项指标在整体效果中占有的比重,进而证明了极差分析、方差分析中根据干态剪切强度、湿态剪切强度、干态剪切木破率和湿态剪切木破率的情况来选取最佳工艺参教是可行的。     

Local water vapor diffusion coefficient when drying Norway spruce sapwood

In this article, a one-dimensional and a two-dimensional approach to the evaluation of local diffusion coefficients for Norway spruce sapwood from measured moisture content (MC) values are presented. A studied wood sample was dried from the initial green condition to about 15% mean MC, but here only the diffusive part of the drying process between approximately 25% and 15% mean MC was treated. Measured local MC values were based on nondestructive X-ray computed tomography data. Finite element calculations were performed with two alternative diffusion coefficients to test the appropriateness of the diffusion coefficients that were evaluated from the measured MC values. The evaluated diffusion coefficients show interesting dependence on MC and distance from the evaporation surface. The advantage of using the methods presented is that the diffusion coefficient is calculated on a local level without having to define a function for the diffusion coefficient’s dependency on other parameters.     

Kiln drying behavior of lumber from ten fast-growth plantation species in Costa Rica

Abstract

Plantation wood from tropical climate has been introduced rapidly in the national market; however, there is lack of knowledge about the process. The main objective of this study was to investigate the kiln drying behavior of 10 plantation-grown wood species from natural forest in Costa Rica using the recommended drying schedule. Initial moisture content (MCi), final moisture content (MCf), drying rate, drying time, and drying defects were evaluated. The drying schedule applied produced the following results: (1) high MCi (over 110%) in four species and lower values in two species. (2) The largest drying time was found in species with high MCi, and the shortest drying time in species with lower MCi. (3) Significant variations of target MCf were found in some species, despite equalization and conditioning. (4) Exponential relationship MC=a*?^?t*b was used to establish a moisture content (MC) decrease model, which is not a good indicator of drying time for fives species. (5) High incidence of drying defects was found in Alnus acuminata and Vochysia guatemalensis. According to the above results, it is necessary to test other drying schedule oriented to improve lumber quality and to decrease variability of MC in wood from plantation trees.     

The Effect of Bark Condition,Delivery Time and Climate-adapted Wet Storage on the Moisture Content of Picea abies (L.) Karst. Pulpwood

The wet-base moisture content (MC) in outer sapwood of Norway spruce (Picea abies (L.) Karst.) pulpwood in different wood management programmes from the forest to the mill was studied from the point of view of three objectives: (1) the importance of rapid raw material delivery, (2) the effect of bark condition as a result of harvesting during the late dormant season and the growing season, and (3) the possibilities for retaining the pulpwood MC using climate-adapted wet storage. The reduction in MC after felling was significant in the pulpwood stored without wet storage. When not wet-stored, pulpwood with a high degree of bark damage dried out more rapidly than wood with a low degree of bark loss. In pulpwood, wet-stored in accordance with climate-adaptation, the MC remained or increased during storage. The shorter the drying time before wet storage, i.e., faster delivery to the mill, the more significant the increase in MC. The increase in MC during wet storage was more significant in pulpwood with a low degree of bark damage. Climate-adapted wet storage reduced the variation of the MC. When conducted with fresh pulpwood, i.e., drying time shorter than 4 weeks (low bark loss) or 2 weeks (high bark loss), a more homogeneous MC distribution was gained.     

Effect of steam pretreatment on wood moisture content and characteristics of vacuum drying

The effects of high temperature steam pretreatment on the change in wood moisture content (MC) and characteristics of vacuum drying were investigated in this study. Poplar and manchurian walnut woods were pretreated with high temperature steam at 100°C and 140°C, prior to vacuum drying. A comparison of the characteristics of vacuum drying between steam pretreated wood and untreated wood was carried out. The results show that during steam pretreatment, the MC of wood decreased within a few hours. The reduction of MC varied with the temperature; the higher the temperature, the faster the MC dropped. During the vacuum drying stage, the rates of drying of pretreated samples were higher than those of untreated samples when MC was below the fiber saturation point. Furthermore, the total drying time of samples treated at a steam temperature of 140°C was lower than that of untreated samples. Therefore, a vacuum procedure after steam pretreatment can effectively shorten the drying time when drying wood.     

桦木,柞木小径材刨切薄板热压干燥的研究

对桦木、柞木两树种小径材刨切薄板（２１３ｍｍ×７０ｍｍ×４ｍｍ）热压干燥工艺的研究,着重探讨了：（１）热压干燥对桦木、柞木小径材刨切薄板翘曲度的影响;（２）热压干燥工艺参数及其交互作用与板片终含水率及厚度压缩率的关系,建立多元线性回归方程;（３）通过电镜分析,确定桦木、柞木小径材刨切薄板的优化干燥工艺条件。