Abstract:

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.

Key words: in situ tensile tests, crack propagation, damage mode, displacement fields, strain fields