Internal Structure and Its Fractography of Structural Particleboard

通过对结构刨花板的变形和断裂行为的研究，主要结果如下：(1)定向刨花板的内部结构为对接节点小距离穿插的结构，层间胶层的剪切作用降低了定向刨花板的强度。在三层刨花板和定向刨花板的每一次疲劳中，三层刨花板和定向刨花板的疲劳均可采用三参数威布尔函数作为寿命分布模型，并且循环蠕变速率与疲劳寿命转变Nc之间的关系可以用一个单一的近似公式来表示，即内部结构变形的临界点。从最外表面到内部的间歇性剪切断裂和各种微裂纹都会自行扩展，从而促进循环松弛。另一方面，在三层刨花板中，稳定阶段的循环松弛是直线发展的，这是由于初始阶段各种裂纹的扩展所致。(4)三层刨花板疲劳过程中的最小滞回与寿命密切相关，因此可以推测断口条件。在定向纤维板疲劳过程中，能量损失率增大。

From the investigation on the deformational and fractural behaviors of structural particleboard, the main results were summarized as follows;(1) The shearing action at some glue layers between strands reduces the the strength of oriented strandboard, having the internal structure in which the butt joints are interspersed at small distance. Furthermore, the deformational recovery action of the strands deformed fixedly in various curves or collapses reduces the strength of oriented strandboard in which the lapped joints are interspersed at small distance.(2) In each fatigue of three-layer particleboard and oriented strandboard, a 3-parameter Weibull function can be adopted for the model of life distribution, and besides, a single approximate formula can be applicable for the relationship between the rate of cyclic creep and the fatigue life transition N_c, i.e., the critical point of deformation of internal structure.(3) In the oriented strandboard, both the intermittent shearing fracture from the outmost surface to the interior and various micro-cracks propagates themselves thereby promoting the cyclic relaxation. On the other hand, in the three-layer particleboard the cyclic relaxation during the stable stage is rectilinearly developed, resulting from the propagation of various cracks during the initial stage.(4) The minimum hysterisis during the fatigue of three-layer particleboard is closely relative to the life, so that the fractographic condition can be presumed. The ratio of energy loss increases during the fatigue of oriented strandboard.