The heterogeneous nature of corn stalks, with hard,
fibrous skins and softer spongy pith inside, indicates that
fibrous skin consumes the predominant energy when
they are cut as shown in Fig. 18. Shearing was proved to
be the energy efficient method for cutting fibrous lignocellulosic
materials. According to the reports, ultimate
shear stresses were approximately one-fourth of the
ultimate tensile stresses for winter wheat[21], one-fifth
for switchgrass[22], and one-third for alfalfa stems[23].
When traditional saw blade passed through corn stalk,
the corn stalk outer skin broke into thin fiber bundles as
shown in Fig. 17a. Then those fibers were individually
hooked by the saw tooth and drew to the parallel orientation
that deviated from the stalk, finally broken primarily
by tensile stresses. Whereas, when corn stalk was
cut by bionic saw blade, due to the special outer margin
curves, the saw blade passed through the stalk smoothly
as shown in Fig. 17b, and outer skin fibers did not scatter
as dispersedly as cutting by traditional saw blade. In
other words, those fibers did not deviate from the stalk
cylindrical surface easily, and they were finally nipped
off mainly by shear stresses. It has been concluded that
shear failure is expected to be more energy efficiency
than tensile failure for fibrous materials cutting. This
would be the reason that bionic saw blade consumes less
cutting energy than traditional saw blade. This phenomenon
indicates that the bionic saw blade has potential
extension to cut other biomass materials with fibrous
lignocellulose and may hold promise for improved energy
efficiencies.