Symbols

Symbol	Name	Unit	Definition
d	Root diameter	mm	By default, d is identical to mean diameter (dmean); dmax, and dmin refer to the maximum and minimum diameters measured along a root.
E r	Root modulus of elasticity	MPa	Resistance to being deformed elastically; defined as the quasi-linear part (elastic zone) of the slope when tensile stress and strain are plotted. Root material is heterogeneous; therefore Er is an ‘equivalent’ elasticity characterizing the root structure.
$f(m)$	Load applied to a tested root	N	$f$ varies with the data measurement step (m).
F	Load for failure in tension	N	F is equal to the maximum of $f(m)$ in this study.
L 0	Initial gauge length	mm	Vertical distance between the two clamps prior to a mechanical test.
m	Step of measurement	–	A step of measurements when applying a load during a mechanical test.
m max	Maximum step of measurements	–	Maximum step of measurements when applying a load during a mechanical test.
T r	Root tensile strength	MPa	Ultimate stress at root failure divided by root cross-sectional area, Tr = F/(πd2/4).
$\epsilon (m)$	Strain	%	Relative extended length of a root during a mechanical test; $\epsilon$ varies with the data measurement step (m).
ε r	Root tensile strain	%	Relative extended length at root failure due to tension.
$\Delta l(m)$	Root extension	mm	Root extension during a mechanical test (in mm); $\Delta l$ varies with the data measurement step (m).
$\sigma (m)$	Stress	MPa	Stress a root undergoes during a mechanical test (in MPa); $\sigma$ varies with the data measurement step (m), $\sigma =$f/(πd2/4).
$\dot{\sigma }(m)$	The first derivation of stress	–	The first derivative of $\sigma (m)$ along $\epsilon (m)$.