基于木材多尺度微观结构的热-重-力学性能响应机制

The mechanical properties of wood play an important role for its processing and utilization, and thermal treatment of wood has a significant influence on its mechanical properties while improve its dimensional stability. However, the formation theory of wood mechanical properties and the effects of heat on that remain unclear. This project will establish an 3D structural model of wood cell wall and wood unit based on the interpretation of wood multi-scale microstructure using high resolution in-situ imaging and analysis technology. A relation model between wood microstructure and macro-mechanical property will be built based on Mori-Tanaka theory, aiming to reveal the formation mechanism of wood mechanical properties. Besides, a heat-mass response model of wood chemical components is expected to be built based on the Arrhenius equation, illustrating how heat influences the content and distribution of wood chemical components. Moreover, the effects of heat on wood microstructure as well as content and distribution of chemical components will be illustrated, and the previous wood microstructure and macro-mechanical property relation model will be modified to be suitable for thermal treated wood. Finally, a comprehensive wood heat-mass-mechanical property prediction model will be achieved by coupling heat-mass response model and modified wood microstructure and macro-mechanical property relation model, and the comprehensive model will be experimentally verified. The comprehensive model built in this project is based on the common features of all wood species, so it is generally useful for both softwood and hardwood, and can theoretically explain formation mechanism of wood mechanical properties and the effect of heat on that.

木材的力学性能是其加工和利用的重要特性，热处理在提高木材尺寸稳定性的同时对力学性能也具有较大的影响，但木材力学性能的生成理论及热对其的作用机制还没有完全探明。本项目使用高分辨率原位成像和分析技术，从多尺度对木材微观结构进行解译，建立木材细胞壁和木材基本单元的三维结构模型；基于Mori-Tanaka理论建立木材微观构成与宏观力学性能的构效关系模型，揭示木材力学性能的生成机制；基于Arrhenius方程构建木材化学成分的热-重响应模型，阐明热对木材化学成分含量及分布的影响机制；通过解析热处理对木材微观构成的影响，修正力学性能构效关系模型以适用于热处理后的木材。将木材热-重响应模型和热处理前后的木材力学性能构效关系模型进行耦合，构建综合的木材热-重-力学性能预测模型并进行实验验证。本项目基于木材所有树种共有特征构建的力学性能预测模型具有普遍适用性，从理论上解释木材的力学性能生成及热影响机制。

本项目围绕木材弹性力学性能生成机制及温度对其作用机制两个关键问题展开研究。使用SilviScan等原位成像和分析技术解译了杉木的多尺度结构，获得了管胞/木纤维形态、细胞壁厚度、微纤丝角、动态弹性模量等关键参数，构建了无瑕疵桦木和杉木多尺度结构模型；基于Arrhenius方程和独立平行反应模型建立了木材及其单个化学成分定量热分解量预测模型，揭示了热对木材及其化学成分质量损失的作用机理；从纳米、微米、毫米三个尺度分析总结了热处理对木材结构单元及力学性能的影响，并建立了热处理质量损失与木材弹性力学性能的关系模型，阐明了木材质量损失对木材弹性力学性能的作用机理； 根据纤维增强理论、经典层合板理论、Malek-Gibson分析模型、Mori-Tanaka理论，采用六步法，逐尺度建立了细胞壁单层、细胞壁、早晚材和无瑕疵木材的弹性力学性能分析模型，模型预测结果比较准确，揭示了无瑕疵木材弹性力学性能生成机制；最后，对上述模型进行耦合，建立了“木材多尺度热-重-弹性力学性能分析模型”，并编写了软件实现可视化操作和应用。本项目研究成果可应用于从理论上解释木材组成、结构和热对木材弹性力学性能的影响，为预测木材及木制品的弹性力学性能提供了理论和工具，同时为计算和模拟木材及其制品在结构中的破坏提供了理论基础。