| Silicone rubber foams have been widely used in various engineering fields.However,The foams prepared by the traditional methods have the high non-uniformity in cell size,shape and connectivity.As a result,it is hard to design and fine-tune the mechanical behavior with stochastic properties.Therefore,it has become an important topic for scholars to study the possibility of designing and forecasting the mechanical behavior of silicon rubber porous material at the micro-structure level.Recently,silicone rubber foam with ordered open-cell structure could be printed layer by layer using a direct ink writing(DIW)printing platform.However,the research work of 3D printing of the silicone foams with woodpile structure and the related mechanical behavior are both in the initial stage,which seriously restricts their application and development in the future engineering field.In this thesis,we analyzed the important parameters in the process of additive manufacturing of the silicone foams with woodpile structure.In the meanwhile,theoretical,experimental and numerical simulation studies were carried out on the corresponding compression mechanical behavior,compression-shear coupling mechanical behavior and stress relaxation behavior.The main content of this thesis is outlined as follows:1.Additive manufacturing of the silicone foams with woodpile structure were analyzed.This part introduces DIW 3D printing platform suitable for silicone rubber printing paste and the shear thinning characteristics of silicone rubber printing ink.Besides,base on these control parameters in the process of additive manufacturing of the 3D printed foams,the motion state of the printing ink in the feeding section,the conveying section with a screw and the printing needle section were studied respectively.Then,the calculation model of the extrusion volume flow rate was established.Considering the printing platform movement speed,we developed the prediction model for the filament diameter and compared it with the corresponding experimental results.2.Several micro-structure design programs of the woodpile structure were proposed.The simple tetragonal(ST)structure shows the axial compression deformation mechanism and the face center tetragonal(FCT)structure shows the bending deformation mechanism.With the hybrid idea,we design a hybrid(HYB)structure with axial compression-bending coupling deformation mechanism.In addition,this part compares the theoretical models,which be developed for the relative density and elastic modulus of the above-mentioned structures,with the corresponding experimental and numerical simulation results.3.The super-clastic behavior of the 3D printed foams was further discussed.Considering the effects of matrix materials and micro-porous structure parameters,we focused on research elastic buckling effect of ST structure under compression load,and established the critical conditions for the elastic buckling platform of ST structures.In addition,the ST-2 structure with a wider stress platform than random foams was designed and fabricated,which shows a two-stage elastic buckling platform effect.4.This chapter studied on the shear mechanical behavior of the printed foams under different compression strains.Based on the theoretical analysis,we find the the mechanism of negative shear mechanical behavior of ST structures.In addition,the influence of friction coefficient on the shear-slip behavior and the corresponding slip criterion of the 3D printed silicone foams with woodpile structure were researched.5.The stress relaxation behavior of the 3D printed foams was tested and compared with the random foams.Based on the three-parameters linear solid model,we studied the stress relaxation of FCT structure.With the generalized Maxwell model,and 3D printed foams with woodpile structure,considering the air spillover effect,were characterized.In addition to,this part predicted the long-term stress relaxation behavior of 3D printed foams with FCT structure and random foams with a direct extrapolation method. |
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