Bimodular rubber buckles early in bending

TL;DR

This study demonstrates that modeling rubber as bimodular, being stiffer in compression than tension, explains earlier buckling during bending, aligning theory with experimental observations.

Contribution

It introduces a bimodular rubber model within incremental buckling theory, revealing earlier buckling predictions consistent with experiments, unlike previous models.

Findings

Bimodular modeling predicts earlier buckling in rubber under bending.

Finite Element Analysis struggles to accurately simulate rubber bending instability.

Experimental results align with bimodular theory predictions.

Abstract

A block of rubber eventually buckles under severe flexure, and several axial wrinkles appear on the inner curved face of the bent block. Experimental measurements reveal that the buckling occurs earlier ---at lower compressive strains--- than expected from theoretical predictions. This paper shows that if rubber is modeled as being bimodular, and specifically, as being stiffer in compression than in tension, then flexure bifurcation happens indeed at lower levels of compressive strain than predicted by previous investigations (these included taking into account finite size effects, compressibility effects, and strain-stiffening effects.) Here the effect of bimodularity is investigated within the theory of incremental buckling, and bifurcation equations, numerical methods, dispersion curves, and field variations are presented and discussed. It is also seen that Finite Element Analysis software seems to be unable to encompass in a realistic manner the phenomenon of bending instability for rubber blocks.