The Study On The Mechanical Biomimetics And The Geometric Nonlinearity Effects Based On Typical Organism

The capability of Natural organism to undergo large deformations without the need of external confinement leads to different types of mechanical instabilities that often break spatial symmetries, generate small or multi-scale structure. If we could learn from the morphology and the function of the organism, control the mechanism and design bodies with controllable distribution of residual stresses, it would be possible to harness these mechanical instabilities, turning them into a powerful design and shaping mechanism. Based on the surface of the seashell helical structure, we combine the differential geometry, variational principle and the continuous elastic mechanical theory, and then predict the morphology of spiral mono-stability and multi-stability by using this model. Also based on triggering the snapping of the Venus flytrap, we propose a coupled mechanical bistable mechanism that explains the rapid closure of the Venus flytrap in a comprehensive manner, consistent with a series of experimental observations. Elasticity theory is also employed a mechanical bistable mechanism to interpret the rapid closure of the Venus flytrap and predict the morphological transition from experiments.The helical shapes in natural and engineered systems often exhibit nearly uniform radius and pitch, helical shell structures with changing radius and pitch, such as seashells and some plant tendrils, add to the variety of this family of aesthetic beauty. Here we develop a comprehensive theoretical framework for tunable helical morphologies, and report the first biomimetic seashell-like structure resulting from mechanics of geometric frustration. Here, the local energy minimization cannot be realized because of the geometric incompatibility, and hence the whole system deforms into a shape with a global energy minimum whereby the energy in each segment may not necessarily be locally optimized. Our work predicts the chiral transformation both from theory and experiments. We perform finite element simulations to model the large deformation of thin structures in three dimensions and illustrate the mechanical self-assembly principle in spontaneous helical structures. Large shell or plate deformation with geometric nonlinearity is treated through a novel, analytically tractable theoretical framework which combines continuum elasticity, differential geometry and stationarity principles. Two key dimensionless parameters (η= W(?)>>1, α= f2/f1<0) are shown to govern structural bistability. Here we show that the mechanical anisotropy pertinent to helical deformation, together with geometric nonlinearity associated with multi-stability, can lead to a selection principle of the geometric shape and multi-stability in spontaneous helical ribbons. Simple table-top experiments were also performed to illustrate the working principle. Our theoretical analysis also predicts the lifting of ground state degeneracy due to edge effects. Our work is also related to the spontaneous curling, twisting, and strained multilayer structures where both geometric nonlinearity and mechanical anisotropy play important roles on the geometric shape.Plants are not known for fast motions. Yet some plants, such as the Venus flytrap can move in a fraction of a second to catch insects for nutrients, even though they do not have nerves or muscles. The rapid motion of the Venus flytrap has intrigued scientists for centuries. Darwin did a first systematic study on the trap closure mechanism, and considered the plant as "one of the most wonderful in the world". Thereafter, several physical mechanisms have been proposed, such as the rapid loss of turgor pressure, an irreversible acid-induced wall loosening mechanism, and the snap-through model by mechanical instability, but with no unanimous agreement among researchers. Tissue cluture and rapid propagation techniques are used to nurture the Venus flytrap. Also microstructure of the leaves is observed by using low magnification microscope and confocal microscopy. We propose a coupled mechanical bistable mechanism that explains the rapid closure of the Venus flytrap in a comprehensive manner, consistent with a series of experimental observations. The mechanics and geometry in the Venus flytrap’s inactive traps are investigated through experiments, theoretical modeling and numerical analysis. Our experiments demonstrated the quasi-bistable behaviors in traps that no longer function as normal (i.e., no capability to be triggered to closure). A minimal model is proposed based on mechanical instability to explain this type of behaviors which have preserved some features of the active traps. Inspired by these findings, we also performed table-top experiments that exhibit multi-shape transition. Based on the principles learnt from the Venus flytrap, we are also able to manufacture a preliminary "flytrap robot". By studying the mechanics of the Venus flytrap, it is promising to design smart bio-mimetic materials and devices with snapping mechanisms as sensors, actuators, artificial muscles and biomedical devices (e.g., drug delivery systems).