Complex Deformation in Soft Cylindrical Structures via Programmable Sequential Instabilities.

Area of Science:

• Soft robotics
• Materials science
• Mechanical engineering

Background:

• Hyperelastic cylindrical shells exhibit significant deformation under pressure, making them suitable for programmable inflatable structures.
• The initial buckling behavior of these shells under vacuum is understood, but the post-buckling regime remains less explored.

Purpose of the Study:

• To investigate the post-buckling behavior of hyperelastic cylindrical shells under negative pressure.
• To identify design parameters that control post-buckling deformation modes.
• To harness instability-driven deformations for creating programmable soft machines.

Main Methods:

• Experimental analysis of hyperelastic cylindrical shells under varying negative pressure.
• Systematic variation of shell geometry (e.g., homogeneous shells) and thickness distribution.
• Observation and characterization of post-buckling deformation modes, including coupled twisting-contraction and bending.

Main Results:

• A specific region in the design space was identified exhibiting a coupled twisting-contraction post-buckling deformation mode.
• The proportion of twist versus contraction can be precisely controlled by adjusting the geometry of homogeneous shells.
• Bending as a post-buckling mode can be induced by circumferentially varying shell thickness.

Conclusions:

• The post-buckling regime of hyperelastic cylindrical shells offers rich, recoverable deformation modes.
• Programmable control over twisting-contraction and bending deformations is achievable through geometric and thickness design.
• These instability-driven, recoverable deformations can be utilized to develop soft machines with programmable movements from a single actuation input.