白桦单根的抗拉力学特性研究

Mechanical Characteristics of Tensile Strength for Betula platyphylla Single Root

为研究根系力学特性,对华北地区白桦(Betula platyphylla)进行单根拉伸,系统分析白桦根系材料的力学特性。结果表明:在同一标距、同一拉伸速率下,抗拉强度与直径存在着负相关关系,且表现为幂函数关系,极限延伸率与直径呈负相关关系,最大抗拉力与直径存在正相关关系;同一拉伸速率下,标距较小的单根有较小的弹性模量和较大的平均抗拉力、平均抗拉强度及平均极限延伸率;以400 mm/min和10 mm/min不同速率拉伸根系,根系在400 mm/min下大多为脆性断裂,易拉断破坏,拉伸速率的变化对抗拉强度和最大抗拉力的影响不显著。对白桦根系的应力应变曲线分析表明,根系直径较小时,随应变增加应力呈线性增大,表现出较好的线弹性关系,直径增大后,应力应变曲线递增缓慢,没有明显的线性区间。根据白桦应力应变曲线的特征,建立并拟合得出了白桦单根本构关系的经验模型,检验表明模型的拟合结果与试验数据基本吻合。

In order to study the mechanical characteristics of root system, the single root of Betula platyphylla, growing in North China Region, was stretched to systemically analyze the mechanical characteristics of Betula platyphylla root system. The results showed that under the same root length and test speed, the tensile strength was negatively correlated with the root diameter, which showed as a power function relation; the limit elongation was negatively correlated with the root diameter, while a positive correlation was found between tensile resistance and root diameter. With the same test speed, single root with smaller root length had smaller elastic modulus and larger average tensile resistance, average tensile strength and average limit elongation. When two different rates of extension, 400 mtrdmin and 10 mm/min, were used in the experiments, root system was mostly brittle fracture with 400 mm/min, it can be easily tensile failure, but the changes of rates of extension had non significant influence on tensile strength and maximum tensile resistance. The analysis of stress-strain curves for Betula platyphylla root system revealed that when root diameter was small, the stress linearly increased with increasing strain, which showed a good linear elastic relationship; when root diameter increased, the progressive increase of stress-strain curves was slow, and there was no obvious linear interval. According to the characteristics of stress-strain curves of Betula platyphylla, an experience model to fit the constitutive relationship of Betula platyphylla single root was established. The testing results indicated that the modeled curves were well closed to the experimental curves.