Belalpour Dastjerdi Parinaz, Landis Eric N
Civil & Environmental Engineering, University of Maine, 5711 Boardman Hall, Orono, ME 04469, USA.
Materials (Basel). 2021 Oct 2;14(19):5755. doi: 10.3390/ma14195755.
In this study, the fracture mechanics of eastern spruce were characterized in relation to end-grain orientation. Compact tension-type specimens with small pre-formed cracks were prepared such that grain angle varied relative to the load axis. Specimens were loaded under crack mouth opening displacement (CMOD) control as to maintain stable crack growth. Specimen fracture was characterized using both -curve and bulk fracture energy approaches. The results showed that under a RT grain orientation, as well as grain deviations up to about 40∘, cracks will follow a path of least resistance in an earlywood region. As the grain angle exceeds 40∘, the crack will initially move macroscopically in the direction of maximum strain energy release rate, which extends in the direction of the pre-crack, but locally meanders through earlywood and latewood regions before settling once again in an earlywood region. At 45∘, however, the macroscopic crack takes a turn and follows a straight radial path. The results further show that RT fracture is macroscopically stable, while TR fracture is unstable. None of the end-grain fracture orientations showed rising -curve behavior, suggesting that there is not a traditional fracture process zone in this orientation.
在本研究中，对东部云杉的断裂力学特性与端木纹方向的关系进行了表征。制备了带有小预制裂纹的紧凑拉伸型试样，使木纹角度相对于载荷轴发生变化。试样在裂纹开口位移（CMOD）控制下加载，以保持裂纹稳定扩展。使用J -曲线和体断裂能方法对试样断裂进行了表征。结果表明，在径向木纹取向以及木纹偏差高达约40°的情况下，裂纹将在早材区域沿着阻力最小的路径扩展。当木纹角度超过40°时，裂纹最初将在宏观上沿最大应变能释放率的方向移动，该方向沿预制裂纹方向延伸，但在局部会蜿蜒穿过早材和晚材区域，然后再次在早材区域稳定下来。然而，在45°时，宏观裂纹会转向并沿直线径向路径扩展。结果还表明，径向断裂在宏观上是稳定的，而切向断裂是不稳定的。没有一种端木纹断裂取向表现出上升的J -曲线行为，这表明在该取向不存在传统的断裂过程区。
