Study Of Instability And Fracture Behavior Of Soft Solid

With the abilities of large deformation,recoverability,energy storage,the instability of soft solids can be widely utilized in the areas like flexible electrons,soft robots,energy harvesting and biomedical science etc.There are a variety of instability phenomena which can be observed on the surface or interior of soft solids accomplished by fracture phenomenon.The interior cavitation instability and surface instability delamination are the common and important subjects of the instability of solid solids.We mainly study the cavitation instability and surface instability induced delamination of soft solids with consideration of environmental coupling,fracture and interfacial delamination.This research can give a reference for the design of soft structure and devices using instability.We first establish the numerical calculation method of cavitation instability in gels.The gel is a typical representative of soft solid which not only contains the multifield coupling deformation,but also can recover the classical soft solids under certain circumstance.By the large deformation theory of gels and the variational principle,the numerical calculation theory and realization method for multi-field coupling deformation in gels have been established using the UHYPER subroutine of ABAQUS.We propose the volume control method and the corresponding numerical realization scheme for cavitation instability problem.This method has been verified by the comparison with theoretical prediction for the cavity expansion in a symmetrically deformed spherical gel.This method is capable of calculating the cavitation instability problem with consideration of complex geometry,boundary condition,materials and different loading methods which can easily consider the surface tension effects.We investigate cavitation to fracture transition in soft solids.We established a fracture mechanics analytical model with sphere-ring defects.Based on the numerical method for cavitation instability,we study the transitional behavior from cavitation to fracture in soft solids and improve the energy release rate formula of single edge notch tensile problem for large deformation.The relation between crack propagation and energy release rate has been calculated under pressure control and volume control loading condition respectively which reveals the transition behavior from cavitation to fracture inside soft solids.We analyze the influence of inhomogeneity on the instability behavior in soft solids.Due to the difference between materials near cavity and materials at an infinite distance,we introduce a spherical shell wrapping the cavity and establish an idealized spherical shell model considering the material inhomogeneity.We derive a cavity expansion formula under the influence of material inhomogeneity near cavity surface.As a special case for cavity expansion inside inhomogeneous soft solids,we investigate the cavitation instability behavior near the interface of two soft solids using the numerical method and compare them with the results from idealized spherical shell model.The influence of the two parameters,i.e.shear modulus ratio and shell thickness,on the critical condition and the instability mechanism has been revealed.We analyze the environmental coupling “cavitation catapult” instability behavior of a sporangium-like structure.The analysis model using polymer gel to simulate the environment-mechanics coupling of the plant cell has been proposed.By using the incompressible fluid element to control the cavity volume,we analyze the cavitation instability phenomena of a partially constrained polymer cell and reveal that the sudden dramatic expansion of the cavity corresponds to the transition of the overall free energy minimum of the system.We obtain the relation between environmental humidity and the curvature of the annular wall along with relation between environmental humidity and free energy of the system.The mechanical mechanism of dispersing spores at an extraordinarily high acceleration for a sporangium-like structure has been revealed.At the end,we investigate the surface instability induced delamination of a film/substrate system and the microfluid control device based on this method.A cavity microchannel can be locally triggered by instability induced delamination near the surface of a film/substrate system under compressive stress.Based on the theoretical and numerical analysis,the relation between local instability induced delamination and overall surface wrinkle along with the post instability behavior and delamination extension have been investigated.We propose a method to control and manipulate micro-fluid using surface delamination induced cavity microchannel for the microfluidic control device.The validation of this method has been confirmed by a principle experiment.The method of calculating the flow in the microchannel using Lattice Boltzmann method has been established and the relation between the microfluid rate and compressive strain has been calculated.The main research results will provide insights into the cavitation instability and surface instability induced delamination which gives reference to the calculation method and theoretical basis for the design and analysis of soft structure base on instability.