| As emerging hot-spot research fields,soft actuators and soft robotics have attracted more and more attention in recent years.The innovative design of soft actuators and soft robotics is inseparable from the mechanical optimization design of soft-material structures.In this thesis,the pre-strained soft-material structures are taken as the research object,including both the pre-compressed soft-material beam structures and the pre-stretched soft-material rectangular membrane structures.By means of analytical derivation,numerical simulation and experimental verification,the load-displacement curves of structures are systematically solved in combination with detailed parametric analysis and optimized structural design,which provides the required load-displacement curves for the subsequent innovative structural design of soft actuators.The specific research contents and main achievements of this thesis are listed as follows:（1）For the three kinds of soft materials commonly used in the laboratory,the appropriate constitutive model is carefully selected,and all the model parameters are determined by combining theory and experiments,which provides the necessary material basis for the follow-up study of this thesis.Firstly,both the uniaxial tensile test of standard soft-material samples and the bulging test of circular soft membranes are carried out for the three kinds of soft materials(i.e.Dragon SkinTM 10 silicone rubber,Ecoflex00-20 silicone rubber and VHB-4910 acrylic foam)under laboratory conditions,and the relevant test data are obtained.Then,the third-order Ogden hyperelastic constitutive model is adopted to describe the mechanical behavior of soft materials.By introducing reasonable deformation assumptions and geometrical approximations,the explicit analytical expressions are derived for both the force-displacement curve in the uniaxial tensile test model and the pressure-volume curve in the circular-membrane bulging test model.Finally,by comprehensively considering the two kinds of experimental data and analytical expressions for the uniaxial tensile test model and the circular-membrane bulging test model,all the parameters of Ogden model are obtained by using the least square method,and the good fitting result between theory and experiments also verifies the correctness and validity of both the proposed deformation assumptions and the analytical solutions of pressure-volume curves in the circular-membrane bulging test model to a certain extent.（2）The soft-material beam structures are designed,and the required load-displacement curves with specific symmetry are obtained through parametric analysis and optimization,which provides a useful guidance for the structural design of soft actuators.Firstly,a catapult-shaped bistable beam structure with pre-compression and made of soft material is designed.With the help of the Ogden constitutive model,the finite element simulation and the parametric analysis are carried out by using ABAQUS software.The effects of the structural size,the degree of pre-compression and boundary conditions on the load-displacement curve of softmaterial beam structures are investigated in detail,and the useful conclusions are summarized.Then,under the guidance of the obtained conclusions,through the optimization design of soft-material beam structures,the required“sinusoidal”load-displacement curve and a pair of load-displacement curves with mirror symmetry are obtained,respectively.Finally,the pre-compressed soft-material beam structures are fabricated under laboratory conditions.Through the displacement-controlled loading test on the electronic universal testing machine,the required experimental load-displacement curves are obtained,which preliminarily verifies the correctness and validity of the design of the pre-compressed soft-material beam structures.（3）As a counterpart of the pre-compressed soft-material beam structures,the bulging model of the pre-stretched rectangular membrane structures under uniform pressure is studied analytically,which provides a helpful guidance for the structural design of soft actuators.Firstly,a reasonable assumption associated with the bulge deformation,i.e.the so-called circular-arc approximation,is proposed.Based on this assumption,explicit analytical expressions of the pressure-height curve and the pressure-area curve are derived.Meanwhile,the quantitative relations between the initial slope of the pressure-height curve（and the pressure-area curve）and the pre-stretch rate as well as the material parameters are also given.Then,the validity of the proposed circular-arc assumption and the correctness of the analytical expression of the pressure-height curve are fully verified by the finite element simulations.Finally,based on the analytical expression of the pressure-height curve,the detailed parametric analysis is carried out and the useful conclusions are summarized.The research work of this thesis would be of certain theoretical significance and reference value for the structural design and optimization of soft actuators. |
