低温活立木树干内冰晶形成扩展规律及其对应力波波速的影响

Sub-zero temperature can cause the phase of part of water in standing trees from liquid water to solid ice, and further change the inner structure of the trunk. However, the mechanism of ice crystal formation and propagation in trunk is unknown, which is the key to carry out the researches on frozen cracks in stems, brittle fracture of wood, and quality assesment of standing trees at cold temperature. Meanwhile, we found that stress wave velocity increases as tmperature decreases, which has an abrupt jump near 0 C temperature. This may be relevent to ice content, but it is not clear how the ice content changes in standing trees. Thus, the laws of stress wave propagation in standing trees at cold temperature are still confused, which hinders the development of stress wave technique for evaluating the quality of standing trees at cold temperature. In order to reveal the mechanism of ice crystal formation and propagation in standing trees and explain the effect of sub-zero temperature on the propagation velocity of stress wave, this project will mainly focus on the following three aspects: (1) the response of ice formation and content in the trunk of standing trees to environment temperature; (2) the response of the macroscopic and microscopic structures of trunk to the formation and propagation of ice; and (3) the effect of ice formation on the stress wave velocity in trunk. The research results will provide a scientific basis for evaluating the quality of standing trees at cold temperature. It can also offer a reference to study tree cold hardiness, tree physiology, frost crack in stem and brittle fracture of wood at cold temperature.

低温（冰点以下温度）导致活立木树干内的部分水发生相变，形成冰晶，改变其内部构造，但冰晶形成扩展规律不详。揭示树干内冰晶形成扩展规律是开展树干冻裂机制、木材低温脆断和低温活立木检测研究的关键。同时，我们发现活立木中应力波波速随温度降低会升高，在冰点上下有"跳跃"，推断这与冰含量有关，但活立木内冰含量变化规律尚不清楚，导致应力波传播规律难以把握，这阻碍了低温活立木应力波无损检测技术的发展。本项目将以此为切入点，以揭示低温活立木树干内冰晶形成与扩展规律，阐释其对应力波波速的深层次影响机理为目标，从活立木树干内冰晶形成及含量对环境温度的响应、树干内宏微观构造对冰晶形成与扩展的响应、树干内冰晶形成对应力波波速的影响等三方面，开展低温活立木树干内冰晶形成扩展规律及其对应力波波速的影响研究。项目可望为低温活立木质量判定、树干冻裂机制、木材低温脆断、树木抗冻、低温树木生理学等研究提供科学依据。

低温（冰点以下温度）导致活立木树干内的部分水发生相变，形成冰晶，改变其内部构造。揭示树干内冰晶形成扩展规律是开展树干冻裂机制、木材低温脆断和低温活立木检测研究的关键。本项目开展了活立木树干内冰晶形成及含量对环境温度的响应、树干内宏微观构造对冰晶形成与扩展的响应、树干内冰晶形成对应力波波速的影响等三方面研究。通过项目研究，系统监测了环境温度、湿度、地表温度、树干内部温度、树干内部含水率和冰含量等基础数据，分析了它们之间的内在联系，构建了相关关系模型;从宏观和微观两个尺度，利用电阻断层成像、CT扫描和低温电镜观测等手段，观察并分析了冰晶在低温活立木横截面以及细胞结构中的形成与扩展过程;深入探讨了低温活立木内部温度、含水率、冰含量与应力波波速之间的关系，构建了相关关系模型;实现了揭示低温下活立木树干内冰晶形成及扩展规律，阐释其对应力波波速的深层次影响机理的研究目标。项目研究结果可望为低温活立木质量判定、树干冻裂机制、木材低温脆断、树木抗冻、低温树木生理学等研究提供科学依据。