Asymmetric bending boundary layer: The λ-test

In this paper, the MecaWet group investigates the mechanics of two asymmetric ribbons bound at one end and pulled apart at the other ends. They characterize the elastic junction near the bonding and conceptualize it as a bending boundary layer. While the size of this junction decreases with the pulling force, they observe the surprising existence of the binding angle as a macroscopic signature of the bending stiffnesses.

The results thus challenge the standard assumption of neglecting bending stiffness of thin shells at large tensile loading. In addition, the rotational response of the structure exhibits a nonlinear and universal behavior regardless of the ratio of asymmetry. Leveraging the independence of the binding angle to the pulling force, they finally introduce the λ-test—a visual measurement technique to characterize membranes through simple mechanical coupling.

Nathan Vani, Alejandro Ibarra, José Bico, Étienne Reyssat, and Benoît Roman. "Asymmetric bending boundary layer: The λ-test." Proceedings of the National Academy of Sciences 122, no. 11 (2025): e2426748122. DOI: https://doi.org/10.1073/pnas.2426748122