  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.
