Authors: NIKLAS KARL J
Publish Date: 1997/09/01
Volume: 80, Issue: 3, Pages: 275-287
Abstract
The aim of this paper was to examine the mechanical behaviour of hollow internodes with transverse nodal septa subjected to bending and twisting and to determine the extent to which this behaviour agreed with predictions made by the theory of elastic stability treating thin walled tubes or ‘shells’ This theory determined the experimental protocol used in this study because it required the empirical determination of two important material properties of stem tissues ie the Youngs elastic modulus E and the critical shear stress τ and required the use of a dimensionless grouping of variables as a descriptor of internodal shape ie l2 /2 tR where l is internodal length t is wall thickness and R is external radius All of these variables were measured for a total of 92 internodes removed from the stems of field grown plants from a total of six species followed by correlation analyses to determine whether the ability of internodes to resist twisting relative to bending summarized by the quotient τ /E correlated with the shape descriptor l2 /2 tR Analyses of the data indicated that 1 the extent to which nodal septa influenced internodal bending stiffness declined as internodal length increased relative to wall thickness or external radius and 2 the ability to resist torsion relative to the ability to resist bending declined as internodal length increased relative to wall thickness or external radius Both of these trends agreed well with the theory of elastic stability Also as theory predicts the mechanical behaviour of internodes was correlated better with the shape descriptor l2 /2 tR than with any measure of absolute internodal size eg l or t Thus internodal shape in part defined by the spacing of nodal septa which influences l largely dictates the mechanical behaviour of stems subjected to twisting or bending
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