Studies on bending, folding and buckling of soft materials

The complex configurations of soft materials are vital for many biological systems because they allow them quickly response to environmental stimuli and therefore achieve some necessary living functions. Such stimulus-sensitive properties are ascribed to the large deformation resulted from the bending, folding and buckling and have attracted the scientists to explore their essences in a variety of scenarios relating to mechanical force, temperature, humidity, pH value, electricity, magnetism to van der Waals force. Up to date, some exciting achievements have been made and successfully applied to soft robot, sensor, nano-reactor and artificial organ. However, there are still many challenging problems to be well addressed in future.<br><br>This research aims to investigate the bending, folding and buckling of soft materials via theoretical analysis, numerical simulation and experimental validation. The retractile behaviours of a spherical shell perforated by sophisticated apertures, attributed to the buckling-induced large deformation are studied. The buckling patterns observed in experiments are reproduced in computational modeling by imposing velocity-controlled loads and eigenmode affine geometric imperfection. It is found that the buckling behaviours are topologically sensitive with respect to the shape of dimple and the buckliball featured with rounded-square apertures has the maximal volume retraction ratio. Afterwards, a kirigami approach is used to fold a patterned planar sheet into a buckliball under a certain thermal stimulus. By minimizing the potential strain energy, we obtain a critical temperature, below which this bilayer sheet exhibits identical principal curvatures everywhere in the self-folding procedure and above which the buckling occurs. The applicability of the theoretical analysis to the self-folding of sheets with a diversity of patterns is verified by the finite element method. Finally, the opening and closure of pine cones is revealed, which is attributed to the self-bending of its scales. It undergoes three states of humidity-driven deformation in terms of Föppl–von Kármán plate theory. Both numerical simulation and experimental data support the theoretical analysis and indicate the longitudinal principal curvature and transverse principal curvature bifurcate at a critical humid value which relies on the thickness and shape of scales.<br><br>The findings in this dissertation are significant not only for understanding the principle of natural structures with stimuli-responsive properties, but also for offering a novel way to design and fabricate functional shape-morphing structures for a variety of applications.