TREE FORMS AND INTERNAL-STRESSES .2. STRESSES AROUND THE BASE OF A BRANCH

The surface stress in a branch induced by an external load and its Young's modulus were measured in a standing tree in an investigation of the rationality of tree form with the result of the finite-element method (FEM) analysis which had been reported previously. The following conclusions were made: (1) In a real tree branch, two factors are important to prevent stress concentration. One is the roundness around the base of the branch, and the other is the small Young's modulus there. In the case of a branch which does not have a roundness, Young's modulus generally was small, especially at the base of the branch where there was severe stress concentration. These facts support the result of a FEM analysis that the roundness and the small Young's modulus around the base of a branch are useful in the reduction of a stress concentration there. (2) The complicated flow of grain around the base of a branch makes for isotropy there. This enables the branch to respond flexibly to force not only in one direction but in all directions.