Comparison of fracture morphologies of ring shake surface and shear surface in Dahurian larch.

To understand the mechanism of ring shakes in Dahurian larch (Larix gmelinii), the ring shake surface on the tangential section was observed and compared with the shear surface of green and air-dry wood. Macroscopically, the ring shakes occurred in the heartwood between the 20th and 40th growth ring. The ring shake surface exhibited an even and clean structure without the fluff. The shear surface of the green wood showed a larger amount of fluff compared to that of air-dry wood. In microscopy, ring shake failure occurred at the end of the latewood and/or the beginning of earlywood or within the earlywood zone. The ring shake surface was covered with a resinous substance, and the wood cells were observed after removing the resinous substance with ethanol. The tracheid walls in the ring shake and shear surface of green wood primarily exhibited intercell failure and rarely intrawall and transwall failures. In air-dry wood, the tracheid walls in the shear surface mostly exhibited intrawall and transwall failures. In the ring shake surface, there was hardly any failure in the epithelial and ray cells, thereby showing a distinct difference compared to the shear surface of the green and air-dry woods. [ABSTRACT FROM AUTHOR]