Extended Data Fig. 7: FEA results showing the contribution of in-rod twisting and global torsion.
From: Large recoverable elastic energy in chiral metamaterials via twist buckling
FEA simulations are performed using the same chiral model under different boundary conditions. R = 7, r = 1.5, h0 = 30 mm; α0 = 5°. (a) Compressive-twisting buckling: rotation θ is free for a specified compression ε. This is the boundary condition used in the main text to generate compressive chiral buckling. (b) Purely twisting condition without external compression: θ is specified, with free ε. Results from this condition indicate the contribution from in-rod twisting. In this case, all energy is contributed by global torsion because the global compressive force is zero for freely compressive boundary. Comparing U1rod in (a) and (b), we obtain the energy ratio of in-rod twisting is ηtwist = 1.6/4 = 40% at θ = 120°, matching the analytical result in Fig. 2d. (c) Results for step simulation used to separate global torsion and global compression. From n to n + 1 step (εn+1 = εn, θn+1 = θn + ∆θ); from n + 1 to n + 2 step (εn+2 = εn+1 + ∆ε, θn+2 = θn+1). Separating the total energy accumulated by global compression or torsion steps shows that the contribution from global compression can reach 95 ~ 100%. This is correct because the freely rotatable boundary condition under specified compression induces zero global torque, and thus the work done by global torque is zero. The nonlinear micropolar model in the Supplementary Note 4 indicates that all energy is contributed by chirality, as “chirality” is defined as the coupled axial force (global compression force) generated by global torsion in the micropolar model.
