4种常见乔木单根拉伸的应力应变曲线分析

Analysis of Stress-Strain Curves for Four Common Arbor Root Systems

选取华北地区河北省北沟林场4种常见乔木油松、白桦、落叶松、蒙古栎进行拉伸试验,分析了直径、根长和拉伸速率对其应力应变曲线的影响。试验结果表明,乔木单根的应力应变曲线整体都为单峰曲线,没有出现明显的径缩现象,4种乔木的应力应变曲线都表现出弹塑性材料特征。相同加载条件,同一直径径级水平下,白桦和蒙古栎的抗拉力学性能比较接近,均具有较大的弹性模量、抗拉强度和较小的极限延伸率;油松和落叶松的力学性能接近,具有较小的弹性模量及抗拉强度和较大的极限延伸率。随着直径的增加,乔木根的弹性模量、极限延伸率和抗拉强度均降低。随着根长的增加,落叶松的弹性模量表现为下降的趋势,而其余3种乔木的弹性模量均表现出上升的趋势。极限延伸率、抗拉强度均与根长成负相关。速率的增加使得根系更容易被拉断破坏,白桦和落叶松的弹性模量、抗拉强度均与拉伸速率成负相关,极限延伸率与拉伸速率成正相关。

In order to investigate the influences of root diameter,root length and tensile rate on stress—strain curve,four common arbor root systems,i.e.,Pinus tabulaeformis,Betula platyphylla,Quercus mongolica and Larix gmelinii,were selected to perform tensile experiments.Results show that the overall stress—strain curve of every single arbor root system is the single-peak curve and does not have the apparent size-shrink phenomenon.Stress—strain curves for the four trees present elastoplastic material characteristics.Under the same loading condition and with the same diameter size,Betula platyphylla performs the tensile mechanical properties close to Quercus mongolica,both of which have larger elastic modulus and tensile strength and smaller elongation;Pinus tabulaeformis and Larix gmelinii have similar mechanical properties,with smaller elastic modulus and tensile strength and larger elongation.With the increase in root length,elastic modulus of Larix gmelinii manifests a downward trend,whereas elastic moduli of the other three trees manifest an increasing trend.Both of the ultimate elongation and tensile strength are negatively correlated with the root length.For Betula platyphylla and Larix gmelinii,the increase in tensile rate makes roots to be failure more easily;elastic modulus and tensile strength are negatively correlated with tensile rate;and ultimate elongation is positively correlated with and the tensile rate.