ABSTRACT
Anisotropy in strength is due in part to the cellular nature of timber and in part to the structure and orientation of the microfibrils in the wall layers. Correlation coefficients of 0.902 and 0.907 have been established between hardness and compression strength perpendicular to the grain of timber at 12% moisture content and timber in the green state, respectively. However, in certain modes of stressing, fracture does not occur and failure must be defined in some arbitrary way such as the maximum stress that the sample will endure or, in exceptional circumstances such as compression strength perpendicular to the grain, the stress at the limit of proportionality. Testing standards still permit the derivation of structural stresses from small clear test pieces, but it is better to use structural-size test pieces as the effects of strength limiting characteristics are easier to quantify with such pieces.
