Sigmabending

Sigmabending is a term used in materials science and biomechanics to describe a non-linear bending behavior in which the curvature or deflection of a slender element varies along its length in a sigmoidal, or logistic, pattern. The concept emphasizes that bending is not uniform along the member, but concentrates in a mid-region that undergoes rapid curvature change, with the ends approaching a plateau set by boundary conditions.

In practice, sigmabending arises from combinations of non-linear stiffness, heterogeneous material properties, viscoelastic damping, and complex boundary conditions. It has been observed in soft polymers, hydrogels, and biological tissues under load, and is of interest in the design of flexible structures and soft robotics where localized bending is desirable.

Modeling and measurement: Researchers characterize sigmabending by fitting curvature along the length to a sigmoid function, k(s) = k_min + (k_max - k_min) / (1 + exp(-a (s - s0))). The fit yields inflection point s0 and slope a, which quantify the location and sharpness of bending transition. Experimental methods include digital image correlation, laser profilometry, and strain gauge arrays; simulations often use non-linear finite element models.

Applications include guiding the design of compliant mechanisms, soft actuators, wearables, and bio-inspired robotics; the concept also aids in interpreting tissue responses in biomechanics and in optimizing load paths to minimize damage.

See also: sigmoid function, bending, non-linear elasticity, soft robotics.