  We investigate and experimentally observe the existence of topologically
protected interface modes in a one-dimensional mechanical lattice, and we
report on the effect of nonlinearities on topological protection. The lattice
consists of a one-dimensional array of spinners with nearest neighbor coupling
resulting from magnetic interactions. The distance between the spinners is
spatially modulated to obtain a diatomic configuration, and to produce a
non-trivial interface by breaking spatial inversion symmetry. For small
amplitudes of motion, the interactions are approximately linear, and the system
supports topologically protected interface modes at frequencies inside the bulk
bandgaps of the lattice. Nonlinearities induced by increasing amplitude of
motion cause the interface modes to shift outside the bandgaps and merge with
the bulk bands. The resulting edge-to-bulk transition causes the extinction of
the topologically protected interface mode and extends it to the entire length
of the chain. Such transition is predicted by analytical calculations and
verified by experimental observations. The paper thus investigates the
existence of topologically protected interface modes obtained through broken
spatial inversion symmetry, and documents their lack of robustness in the
presence of nonlinearities.
