在环境扫描电子显微镜样品舱内低真空模式下,对鱼鳞云杉木材小试样进行垂直于纹理方向的原位拉伸试验,实时监测TR系统裂纹扩展的全过程。在生长轮层次上,TR裂纹以台阶式生长方式穿过早晚材;在细胞层次上,TR裂纹以劈裂模式在胞间层或接近胞间层处分离细胞。用数字散斑相关方法计算试件在破坏之前的位移场和应变场,定量地展示载荷传递的详细信息,证实具有非均质的木材的微、细结构对其力学性能的影响。结果表明:将环境扫描电子显微镜下的力学试验与数字散斑相关分析相结合的研究方法,可从本质上揭示木材的细、微观力学损伤机制。
In situ tensile tests of spruce( Picea jezoensis var. microsperma )sample perpendicular to the grain were carried out on LV mode in an environmental scanning electron microscope(ESEM)chamber. The whole process of crack propagation for TR system was observed in real-time. At the growth ring level, the TR cracks advanced through the alternating early- and latewood layers with a stepwise manner. At the cellular level, the TR cracks advanced in a peeling mode by separating cell walls close to or at the middle lamella. Displacement and strain fields for a load level were obtained from digital speckle correlation method(DSCM)before the specimen was damaged. The mechanism of load transfer was revealed in details. The influence of heterogeneous microstructure of wood on its mechanical properties was testified. The results in this study indicate that the research method of mechanical test carried out with ESEM in combination with DSCM can reveal in nature the mechanism of wood microscopic damage.