  In this work, we show that collisions of one type of nonlinear wave can lead
to generation of a different kind of nonlinear wave. Specifically, we
demonstrate the formation of topological solitons (or transition waves) via
collisions of elastic vector solitons, another type of nonlinear wave, in a
multi-stable mechanical system with coupling between translational and
rotational degrees of freedom. We experimentally observe the nucleation of a
phase transformation arising from colliding waves, and we numerically
investigate head-on and overtaking collisions of solitary waves with vectorial
properties (i.e., elastic vector solitons). Unlike KdV-type solitons, which
maintain their shape despite collisions, our system shows that collisions of
two vector solitons can cause nucleation of a new phase via annihilation of the
vector soltions, triggering the propagation of transition waves. The
propagation of these depends both on the amount of energy carried by the vector
solitons and on their respective rotational directions. The observation of the
initiation of transition waves with collisions of vector solitons in
multistable mechanical systems serves as an example of new fundamental
nonlinear wave interactions, and could also prove useful in applications
involving reconfigurable structures.
