In situ visualization of hardwood microcracks occurring during drying

Microcracks produced in an Acacia hybrid (Acacia mangium × Acacia auriculiformis) and Melia azedarach during drying were visualized in situ using confocal laser scanning microscopy (CLSM); the morphological differences were compared. In the Acacia hybrid, numerous microcracks were found between the wood fiber and ray parenchyma, which propagated toward both the pith and bark. The microcracks closed with further drying, but persisted until the last stage of drying. In Melia azedarach, however, few microcracks formed between the wood fiber and ray parenchyma in the latewood region; they also propagated toward both the pith and bark. Because the microcracks subsequently closed, some could not be detected by CLSM. These morphological characteristics resulted from differences in the wood structure and we conclude that the interface zone between the wood fiber and ray parenchyma is one type of weak point on the transverse surface that is susceptible to checking.