Numerical Simulation With FEM On Swelling And Large Deformation Behavior Of Anisotropic Hydrogel

Hydrogel is a typical kind of soft material,with the rise of 4D printing technology and the rapid development of intelligent soft robot in recent years,hydrogel has been widely used in bionic engineering and medical devices due to its good biocompatibility,environmental sensitivity and swelling deformation.The swelling and deformation process of hydrogel involves the diffusion of liquid in porous elastomers and the interaction of many physical and chemical fields,such as light,temperature,electric field and magnetic field.The mechanical analysis and numerical simulation of this process can simplify the complexity of the problem and provide an important basis for better design of hydrogel devices.In addition,because most of the biological tissues in nature are anisotropic materials,the current numerical simulation methods for anisotropic hydrogel are still relatively inadequate.As a result,the development of finite element numerical simulation method for the analysis of swelling and large deformation behavior of anisotropic hydrogel has important guiding significance for the design of soft material functional devices and bionic configurations.Under this research background,this paper mainly carries out the following research contents:Firstly,the equilibrium equation in the swelling process of isotropic hydrogel is deduced based on the second law of thermodynamics.The user subroutine UHYPER in ABAQUS is developed,which can describe the properties of isotropic hydrogel.The free swelling behavior of hydrogel and the 4D printed soft matter functional devices are simulated.In the framework of continuum mechanics,the chemical potential which can simulate the swelling behavior of hydrogel is introduced into the strain energy density function.According to this strain energy function,the ABAQUS user subroutine UHYPER is compiled.The correctness of the program is verified by comparing the numerical and analytical solutions in the process of free swelling of hydrogel.The effect of material parameters on swelling is also studied.It is found that the larger the degree of crosslinking or interaction coefficient,the stronger the inhibition of swelling behavior.In addition,based on the three basic deformation modes of 4D printing,several petal models and origami configurations are constructed,showing the applicability of the algorithm in the field of soft matter devices.Secondly,the user subroutine UANISOHYPER is developed based on the strain energy function of fiber reinforced anisotropic hydrogel.The free swelling behavior of anisotropic hydrogel and related engineering devices are numerically simulated.A constitutive model for describing fiber-reinforced anisotropic hydrogel is selected,and the relationship between stress and strain invariants is deduced.The user subroutine UANISOHYPER is compiled according to this free energy function.An example of free swelling is constructed to verify the accuracy of the program.The effect of modulus of fibers on swelling elongation is studied.It is found that modulus of fibers inhibit the swelling in the direction of fibers,but promote the swelling in other directions reversely.In addition,a hydrogel double-layer plate is constructed.It is found that the bending or torsion of the structure always proceed in the direction of fiber distribution.Based on this,an improved design of 4D printing petal torsion model is made,which simplifies the process flow and achieves better imitation result than the original model.The finite element model of anisotropic soft robot finger is also established,and the effect of different modulus of fibers on its bending is studied,which proves the reverse promotion of modulus of fibers again.Thirdly,a platform based on ISIGHT software for structural optimization design of soft matter functional devices is established.The packaging device during drug transport,anisotropic twisted petal configuration and 4D printed Calla petal configuration are optimized by using this platform.The optimization results can meet the design requirements well.In the optimization process,it can automatically update the model parameters,divide the structure mesh and output the results of analysis,which greatly saves the material and time cost of the design.In addition,the influence of initial simplex on optimization convergence is studied for downhill simplex method.It is found that the smaller the initial simplex is,the smaller the search radius is at the beginning of iteration and the shorter the time required to achieve convergence is.Comparing the optimization results of simplex method and Hooke-Jeeves algorithm in the optimization design of Calla configuration,it is found that the simplex method converges faster and calculates more accurately than Hooke-Jeeves algorithm in this case.The optimization platform provides a convenient and efficient design method for intelligent soft matter devices and 4D printing configuration.