TREE MECHANICS AND WOOD MECHANICS - RELATING HYGROTHERMAL RECOVERY OFGREEN WOOD TO THE MATURATION PROCESS

Growth stress can be approached from the point of view of the mechanic al standing of trees as well as that of the loading history applied to the material before tree felling. Stress originates in wood maturatio n causing both rigidification and expansion to the cell-wall material. Locked-in strains are partially released by cutting specimens from th e tree, and, more completely, by boiling them in a green state, so as to exceed to softening point of lignin. It has been supposed that the rheological conditions during such hygrothermal recovery might be simi lar to those existing during maturation, when lignification of the sec ondary cell wall occurred. A rheological model of wood in the process of formation is proposed to support this hypothesis and derive informa tion on the average maturation rigidity.