摘要
【目的】研究木材剪切断口的断裂特征、断裂方向和分形曲线特征，计算剪切断口的分形维数；测量木材抗剪强度，利用线性回归探讨木材横向、纵向抗剪强度与分形维数的关系。【方法】以生长在黑龙江的杉松、银白杨、樟子松、白桦和紫椴为试验树种，根据纤维板生产和《造纸木片》（ GB/T 7909—1999）对木片原料的尺寸要求，按照《木材物理力学试材锯解及试样截取方法》（ GB/T 1929—2009），制作5种树种的剪切试验试件。通过剪切试验，采集木材断口形貌特征，获得断口分形曲线，测量木材断裂时所需的力。【结果】横向剪切试件时，无论试件是否软化，都沿剪切方向呈曲线断裂，断裂面高低不平；未软化的针叶材以弯曲较大的曲线断裂，阔叶材以弯曲不大、稍平直的曲线断裂，断裂表面相对平滑一点；软化后的针叶材以弯曲不大的曲线断裂，阔叶材以弯曲稍大的曲线断裂，个别伴有撕裂痕迹。软化后纵向剪切试件时，试件沿剪切方向呈直线断裂；针叶材、阔叶材的断裂特征差异不明显。横向剪切试件断口分形曲线呈细小的锯齿状或“Z字状”，软化后试件剪切断口分形曲线比未软化的略显复杂；软化后试件纵向剪切断口的分形曲线没有软化前、后横向剪切断口的分形曲线复杂。5种试验试件剪切断口的分形维数在2.047～2.133之间。软化后试件横向抗剪强度最低，纵向抗剪强度大于未软化试件横向剪切强度。【结论】各树种试件软化后的纵向抗剪强度与其断口分形维数之间存在着正相关关系，但相关性并不显著；横向抗剪强度与断口分形维数之间线性正相关。软化后试件横向抗剪强度最低，此情况下剪切木材最易断裂，因此建议在研磨解离木片时，应使原料软化，沿着横向剪切，这样消耗能量较小。
Objective]The purpose of this study was to investigate the characteristics of wood shear fracture,fracture orientation and shear fracture fractal curves,and calculate the fractal dimension of the shear fracture;The shear strength of the test timbers were measured,using linear regression analysis,the relationship of transverse/longitudinal shear strength of test timbers and fractal dimension were also discussed. [Method]Five tree species distributed in Heilongjiang Province,those are： Abies holophylla, Populus alba, Pinus sylvestris var. mongolica, Betula platyphylla and Tilia amurensis were selected as testing materials. Shear strength testing specimens were produced according to the sizes requirements of raw wooden material during the production of fiberboard and GB/T 7909—1999 paper chips and the sawing-testing methods of GB/T 1929—2009 physical and mechanical wood samples. Fracture morphology of wood, fracture fractal curves were gathered and the forces required to break test timbers were measured by shearing fracture of the testing specimens on mechanical testing bench. [Result]When specimens were sheared in the transverse directions： A varying fracture surface was exhibited regardless of the specimen softened or not. Unsoften-softwoods were fractured with bigger curves,hardwood specimens were fractured with flatter curves and the fracture surface were more smooth; Soften-softwood were fractured with small curves while hardwood were fractured with largish curves with avulsion in some samples. When specimens were sheared in the longitudinal direction in softened conditions： they were fractured in rectilinear line in shear directions; No obvious differences in fracture characteristics between softwood and hardwood were found. The fractal curve of transverse sheering fractures were showed the shape of serration or zigzag,fractal curves of soften-specimens were more complicated than that of the unsoftened. The longitudinal shear fractal curves of soften-samples were less complicated than that of the transverse shear fractal curves,regardless of softened or not. The fractal dimensions on the shear fracture of the testing samples for five wood species were 2 . 047 -2 . 133 . The transverse shear strength of soften-samples was the lowest while the longitudinal shear strength of soften-samples was still enormously stronger than that of unsoften-samples.[Conclusion]The transverse shearing soften-samples were generally shown curved fracture while linear fractures emerge along fiber direction. When soften-samples were sheared in longitudinal direction, linear fracture was presented with flatter curves or fractured in a near-gradient straight line. The fractal curves of transverse and longitudinal fracture in softened situation were more complicated with the shape of serration or zigzag. The fracture structure had irregular self-similarity and it was more complicated for the soften-samples compared to the unsoften-samples. The longitudinal fractal curves of soften-samples were simpler than that of transverse fracture,no matter softened or not. No significant correlation was found between longitudinal shear strength of soften-samples and fracture fractal dimension. While it revealed a linear correlation between the transverse shear strength and the fractal dimensions. Transverse shear strength was the lowest for soften-samples. It was suggested to soften the timber before grinding dissociation chips with transverse shearing in order to minimize energy consumption.
出处
《林业科学》
EI
CAS
CSCD
北大核心
2015年第6期127-134,共8页
Scientia Silvae Sinicae
基金
黑龙江省自然科学基金面上项目(C201334)
关键词
木材
抗剪强度
分形维数
断口特征
timber
shearing strength
fractal dimension
fracture features
