  In this study, we explore the mechanics of a bigon and a bigon ring from a
combination of experiments and numerical simulations. A bigon is a simple
elastic network consisting of two initially straight strips that are deformed
to intersect with each other through a fixed intersection angle at each end. A
bigon ring is a novel multistable structure composed of a series of bigons
arranged to form a loop. We find that a bigon ring usually contains several
families of stable states and one of them is a multiply-covered loop, which is
similar to the folding behavior of a bandsaw blade. To model bigons and bigon
rings, we propose a numerical framework combining several existing techniques
to study mechanics of elastic networks consisting of thin strips. Each strip is
modeled as a Kirchhoff rod, and the entire strip network is formulated as a
two-point boundary value problem (BVP) that can be solved by a general-purpose
BVP solver. Together with numerical continuation, we apply the numerical
framework to study static equilibria and bifurcations of the bigons and bigon
rings. Both numerical and experimental results show that the intersection angle
and the aspect ratio of the strip's cross section contribute to the bistability
of a bigon and the multistability of a bigon ring; the latter also depends on
the number of bigon cells in the ring. The numerical results further reveal
interesting connections among various stable states in a bigon ring. Our
numerical framework can be applied to general elastic rod networks that may
contain flexible joints, naturally curved strips of different lengths, etc. The
folding and multistable behaviors of a bigon ring may inspire the design of
novel deployable and morphable structures
