Studies On Thermo-mechanical Properties Of Shape Memory Polymer Based3D Braided Composites

As a type of newly arisen intelligent materials, thermal-responsive shape memory polymer(SMP)can recover its original (or temporary) shape upon exposure to external stimuli. However, neat SMP isbadly restricted for application due to its shortages, including low stiffness and strength, smallrecovery stress, serious creep and relaxation. Three-dimensionally(3D) braided fiber reinforced SMPcan overcome these weaknesses as well as combine virtues of3D braided composites like littledelamination and good designable characteristics, which leads to better mechanical properties.Exisiting constitutive models of SMP were proposed in simple load conditions, which can not bedirectly used in complex loading or structures conditions. Thus, a reasonable constitutive function wasderived and the thermo-mechanics of SMP, along with the deformation mechanism of its composites,were researched with Finite Element Method(FEM). The details include the following:(1). The three-cell structure of3D braided composites was introduced. Parameterized modeling ofperiodic interior cells of3D braided composites was implemented using APDL language ofANSYS software, which saves a lot of time in modeling and periodic meshing. Then, theperiodic boundary conditions suitable for finite element analysis were specified in themesoscopic mechanical model of3D braided composites;(2). Two different FEMs of modeling (user-defined material subroutine of ABAQUS and Pronyseries fitting method) and simulation of thermo-mechanical performance of SMP were pursued,and the thermo-mechanical and shape memory properties of SMP were analyzed, along withtheir dependence on the external loads, including strain load and loading rate, cooling andheating rate;(3). A viscoelastic constitutive relationship under nonconstant temperature states was put forward forSMP based3D braided composites. Then the finite element simulation results of stress-strainrelationships and shape memory properties were obtained, as well as their dependence onexternal loads and braiding parameters, including braiding angle and fiber volume fraction.