干燥应力下木材细胞壁形变响应机制及开裂模型构建

The generation of drying cracking is due to drying stress, which severely restricts wood efficient utilization. In general, the research of drying stress focuses on macroscopic aspects. If the drying cracking is explained in essence, it is absolutely necessary to study drying stress in microscopic scale to establish the response relationships between drying stress and cell wall deformation. This project regards Eucalyptus plantation wood as raw material, focuses on wood drying stress, the mechanical properties and geometrical deformation of wood cell wall under different moisture content and temperature during conventional drying. The influence rules of moisture content and temperature on the above parameters are analyzed and the influence mechanism of moisture content and temperature on the mechanical properties of wood cell wall is clarified. The relationships between drying stress and geometric deformation of wood cell wall is determined by means of moisture content. On that basis, the prediction model to drying cracking in wood surface is established according to the interrelationships between the two by finite element theory. This project aims to reveal the response mechanism of wood cell wall under drying stress, explain the causes of drying cracking from microscopic view, thereby achieve the simulation and prediction for drying cracking. The research results will provide theoretical and technical support for reducing drying cracking and exploring the inhibition mechanism.

木材干燥应力是导致干燥开裂的主要原因，严重制约着木材的高效利用。传统应力研究主要集中于宏观方面，若从本质上解释干燥开裂问题，则必须将应力研究深入至微观尺度，建立干燥应力与细胞壁形变间的响应关系。本项目以桉树人工林木材为研究对象，重点研究常规干燥过程中，不同含水率、温度条件下木材的干燥应力、细胞壁力学性能、细胞壁几何形变，分析含水率、温度变化对以上各参数的影响规律，阐明含水率、温度变化对木材细胞壁力学性能的作用机理；以含水率为媒介，确立整个干燥周期内干燥应力与木材细胞壁几何形变间的响应关系；并在此基础上，利用有限元理论建立基于二者相互关系的干燥表裂预测模型。研究成果旨在揭示干燥应力作用下木材细胞壁的响应机制，从微观角度解释干燥开裂产生的原因，实现干燥表裂的模拟预测，为有效减少木材干燥开裂问题和探寻开裂抑制机理提供理论依据和技术支持。

木材干燥应力是导致干燥开裂的主要原因，严重制约着木材的高效利用。将干燥应力研究深入至微观尺度，建立干燥应力与细胞壁形变间的响应关系是解释干燥开裂问题的关键。本项目以窿缘桉木材为研究对象，采用超景深电子显微镜研究了不同含水率条件下木材细胞壁几何形变、干缩性能；采用非接触全场应变测量系统和电化学方法对常规干燥过程中干燥应力进行了在线检测，确立了整个干燥周期内干燥应力与木材细胞壁几何形变间的响应关系；并利用拓展有限元法建立了木材横截圆盘干燥开裂预测模型。研究结果显示：木材细胞壁的整体干缩与含水率呈线性关系，含水率对细胞壁弦、径向干缩差异影响不大，纤维饱和点以下其数值基本保持在1.5左右。木材宏观干缩应变随含水率的降低而增大，材性部位和纹理方向对其影响显著。木材宏观干缩略小于细胞尺度的干缩，而弦、径向干缩差异却与之相反；宏观干缩并不是细胞干缩的简单累积，它还受细胞类型和排列方式等因素的影响。有限元模拟结果与试验结果具有较好地一致性，模拟结果显示裂纹尖端呈现明显的应力集中，而裂纹经过区域应力值明显较小，说明裂纹形成过程也是应力的释放过程。上述研究结果揭示了干燥应力作用下木材细胞壁的响应机制，从微观角度解释干燥开裂产生的原因，实现干燥表裂的模拟预测，为有效减少木材干燥开裂问题和探寻开裂抑制机理提供了理论依据和技术支持。项目执行期间，共发表了第一标注高水平学术论文5篇，其中SCI收录3篇，EI收录2篇，申请国家发明专利2项。