  Topological defects are a ubiquitous phenomenon in diverse physical systems.
In nematic liquid crystals (LCs), they are dynamic, physicochemically distinct,
sensitive to stimuli, and are thereby promising for a range of applications.
However, our current understanding of the mechanics and dynamics of defects in
nematic LCs remain limited and are often overwhelmed by the intricate details
of the specific systems. Here, we unify singular and nonsingular line defects
as superelastic rods and combine theory, simulation, and experiment to
quantitatively measure their effective elastic moduli, including line tension,
torsional rigidity, and twist--stretch coefficient. Interestingly, we found
that line defects exhibit a negative twist--stretch coupling, meaning that
twisted line defects tend to unwind under stretching, which is reminiscent of
DNA molecules. A patterned nematic cell experiment further confirmed the above
findings. Taken together, we have established an effective elasticity theory
for nematic defects, paving the way towards understanding and engineering their
deformation and transformation in driven and active nematic materials.
