受拉面节子对杉木幼龄材抗弯性能的影响OA北大核心CSTPCD
The effect of knots in tension face on bending properties of Cunninghamia lanceolate juvenile wood
为厘清节子特征与分布位置对木材抗弯性能的影响,并探究其在树干轴向高度的变化规律,采用三点弯曲法分别检测人工林杉木幼龄材无节、有节试件的弹性模量(MOE)和静曲强度(MOR),统计分析节径比、节面积和节距与试件抗弯性能的关系,记录试件面内应变分布,观测试件破坏区域形貌,最终解释节子对木材抗弯性能的影响.研究表明:树干轴向高度增加易使节子尺寸变大;节子对试件MOE影响规律不明显,节子显著降低试件MOR;节径比和节面积与MOR负相关,节距和MOE与MOR正相关,节距和MOE对MOR有极显著影响.节径比、节面积、节距及MOE与MOR的线性拟合决定系数是0.580,当破坏发生在节子处时,以上4个因素与MOR的线性拟合决定系数是0.658;当破坏发生在非节子处时,MOE与MOR的线性拟合决定系数是0.856,节径比、节面积和节距对MOR影响小.无节试件的破坏主要表现为木材纤维撕裂和弧形裂纹,剪切应变沿木材纵向有效扩张;有节试件结构失效发生在节子处时,主要表现为节子断裂或木材沿节子轮廓破坏,节子处易出现剪切应变集中.当破坏发生在节子处,节子特征和MOE能较有效评估MOR;当破坏发生在非节子处时,采用MOE能有效评估MOR.
This work was aimed at revealing the effect of knots'features and distribution locations on wood bending strength and investigating the variation of this effect on tree growth direction.In this study,the specimens made from Cunninghamia lanceolate juvenile wood were obtained from three different heights of tree stems and divided into two groups,including specimens with and without knots.The locations of knots at the bottom of the specimens were examined.The modulus of rupture(MOR)and modulus of elasticity(MOE)of the specimens were measured using the three-point bending test.After the bending test,the images of the failure regions were collected.Knot information,including knot to specimen thickness ratio,knot area and knot to loading distance was recorded.The influence of knot features on MOR and MOE was statistically analyzed.The results showed that the size of knots increased as the increase in height of tree stem.MOR of the specimens with knots decreased as the increase in height of tree stem.The influence of knots on MOE of the specimens was trivial and knots significantly decreased MOR of the specimens.The knot to specimen thickness ratio and knot area negatively related to MOR,and knot to loading distance and MOE posi-tively related to MOR.Knot to loading distance had extremely significant influence on MOR and MOE.The knot to specimen thickness ratio,knot area,knot to loading distance and MOE can explain MOR with R2=0.580.Knot to specimen thickness ratio,knot area,knot to loading distance and MOE can explain MOR with R2=0.658 when the specimens are failure only at knots.The linear relationship between MOE and MOR of the specimens with knots was R2=0.580.Knot to specimen thickness ratio,knot area,knot to loading distance and MOE can explain MOR with R2=0.851 when the specimens with knots are not failure at knots.Because there is a strong linear relationship between MOE and MOR(R2=0.856),the influence of knot to specimen thickness ratio,knot area,knot to loading distance on MOR was slight when the specimens with knots were not failure at knots.The structural failure of specimens with-out knots was tearing of fibers.Shear strain can effectively transfer along fiber direction of wood without knots.The structural failure of specimens was sharp fractures or rupture around knots.Shear strain accumulation was prone to occur in knots when the specimens fail at knots.The effect of knots of bending properties of Cunninghamia lanceolate juvenile wood was statistically analyzed.The key knot parameters affecting bending properties of the specimens were found.
孙辉波;李万兆;张勰;何功秀;石江涛
南京林业大学材料科学与工程学院,南京 210037湖南省林业科学研究院,长沙 410004中南林业科技大学林学院,长沙 410004
林学
杉木幼龄材节子节径比节面积节距静曲强度弹性模量
Cunninghamia lanceolate juvenile woodknotknot to specimen thickness ratioknot areaknot to loading distancemodulus of rupturemodulus of elasticity
《林业工程学报》 2024 (004)
34-39 / 6
国家重点研发计划(2021YFD2201302-2);江苏高校"青蓝工程"资助(2022).
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