Investigation On Mechanical Behavior Of Shape Memory Polymers And Their Origami Structures

As a type of stimulus-responsive intelligent polymer materials,shape memory polymer(SMP)can undergo shape changes by responding to external stimuli.SMP has many advantages such as large deformation,low preparation cost,fast response speed,adjustable response temperature,and various excitation methods,so it has become one of the currently popular functional materials.4D printing technology,as an additive manufacturing technology for intelligent materials,provides new opportunities for the further development and application of SMP.Origami is a traditional folk art.It has been widely used in many engineering fields such as deployable structures and mechanical metamaterials due to its small space occupation,diverse deformation methods,excellent mechanical characteristics,and wide design space.This thesis combined origami structures,SMP smart materials and 4D printed technologies to design and prepare several deployable smart structures,and in-depth studies of their mechanical properties.The specific contents are as follows.(1)Mechanical properties test and parameter fitting were performed for two kinds of SMP materials(RGD8530 and Vero White Plus).Uniaxial tensile experiments,Dynamic mechanical analysis(DMA)tests,and shape memory tests were used to test and characterize the static mechanical properties,dynamic mechanical properties and shape memory properties of the SMP materials.The mechanical properties and physical parameters of the materials were obtained.Then,the SMP material parameter equation was established.(2)A cylindrical SMP origami metamaterial was designed and its mechanical properties was studied.The twisted crease of Kresling origami pattern was embedded into the internal structure of the cylindrical plate while soft SMP materials and rigid plastic are used to construct origami metastructure,so that the origami metastructure has super compressibility,torsional-contraction coupling effect(TCE),mechanical bistability of folding and unfolding,and self-transformation characteristics of thermal response.The finite element method was used to study the folding and deployment performance and TCE of the origami metamaterial.Besides,the origami metamaterial was extended from a single level(subunit)to a multilevel structures.The effects of structural parameters and temperature on their folding and unfolding behavior are also discussed.(3)Inspired by origami structure,intelligent circular origami metastructures with characteristics of super large folding ratio,mechanical bi-stable state and selfdeployment were designed,and then formed by multi-material printing technology of additive manufacturing.The behavior of folding and deployment and shape memory characteristics of the origami metastructures were explored through experiments and finite element simulations,and the feasibility of the structure was verified.In addition,the metastructures can be extended to large scale and multi-level pattern.