Three dimensional constitutive equation for shape memory polymers and its applications
형상 기억 고분자의 3차원 구성 방정식과 그 응용

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dc.description학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2014. 8. 유웅렬.-
dc.description.abstractThis thesis proposes new three-dimensional constitutive equation for shape memory polymer(SMP) and its possibilities for various applicatins. Differently from existing models, the new model is three dimensionally described, applicable to the problems with three dimensional geometry, able to deal with large deformation, usable for the composites which are combination of SMP and other materials and adoptable for the multiphysics situations.

The proposed model considers SMP as a parallel connection of rubbery and glassy phase and assumes non-mechanical strain exists in glassy phase to realize shape memory effect. These features are an idea obtained from the molecular structures of SMP and their behavior. The non-mechanical strain as a key element are calculated from principal stretches and principal directions of total deformation.

To validate the model, or to compare it to experiments, this thesis proposes the method of getting material parameters experimentally which are needed to the constitutive equation. And it also presents the comparisons experimental and three dimensional modeling results, which includes punching test as a multiaxial problem.

This thesis applies the new model to shell structure which exists in three-dimensional space. Because existing shell structural theories are applicable to only linear elasticity or pure inelasticity and not applicable to complex SMP constitutive equation, this thesis describes SMP constitutive equation for shell structure by using the method of midplane, the typical method for shell element. Then, the comparisons of the shell and experimental or three dimensional results are presented for the validation.

Theoretical studies on magneto-responsive SMP composites are dealt in this thesis because very few researches about this topic exist. A representative volume element (RVE) is set. SMP as a matrix and iron partices as reinforcements are input in this geometry. Then, mechanical behavior of this composites are investigated under various magnetic fields. These progresses will helpful to the prediction of the relation between the magneto-responsive SMP composites and magnetic field because experimental with real magnetic field is very difficult.

And the proposed model are tried to be applied to various physical situations to see the practicality and potential of the model.
dc.description.tableofcontentsAbstract i
List of figures viii
List of tables xv
1. Literature review 1
1.1. Thermo-responsive SMPs 1
1.1.1 Principle 1
1.1.2 Review of experiments 5 Molecular structures of selected SMP materials 5 SMP test 7
1.1.3 Review of constitutive models 8 Early models 8 One dimensional multi-phase models 10 Phenomenological models 11 Other models to account for SM effects 13 3D Finite element modeling for SMP 14 Summary of limitations of existing models 15
1.2. Other SMPs 16
1.2.1 Light activated SMPs 16
1.2.2 Electro-activated SMP composites 17
1.2.3 Magneto-responsive SMP composites 17
1.3. Applications 19
1.3.1 Medical applications 19
1.3.2 Structural applications 20
1.3.3 Applications with composites 20
1.4. Research objectives 21
2. 3D constitutive model of shape memory polymer 23
2.1. 3D constitutive equation of shape memory polymers 23
2.1.1 Phenomenological two-phase model 23
2.1.2 Mechanical models for the glassy and rubbery phases 28
2.1.3 Non-mechanical strain 30 Schematic explanation of non-mechanical strain 30 Three dimensional form of non-mechanical strain 33
2.1.4 Summary of the constitutive equation 36
2.2. Experimental 39
2.2.1 Material preparations 39
2.2.2 Relaxation and isothermal uniaxial tests 39
2.2.3 Thermo-mechanical shape memory tests 40
2.2.4 A punching test 40
2.3. Results and discussion 41
2.3.1 Determination of material parameters 41
2.3.2 Validation examples 44 Uniaxial tensile behavior of SMPs 44 Punching simulation 52
2.3.3 Creep test under periodic temperature input (Two-way shape memory) 58
2.4. Summary 62
3. Constitutive equation for shell modeling 63
3.1. Shell constitutive equation of SMP 66
3.1.1 Common formulae for shell analysis 66
3.1.2 Application to linear elasticity [128] 69
3.1.3 Application to SMP constitutive equation 71
3.2. Results and discussion 74
3.2.1 Uniaxial tensile behavior of SMP shell 74
3.2.2 Punching simulation with SMP shell 79
3.2.3 Folding simulation with SMP shell 84
3.3. Summary 90
4. Composites for magneto-responsive SMP 91
4.1. Two approaches: RVE and Continuum constitutive equation 91
4.2. Modeling procedure 92
4.2.1 Representative volume element and periodic boundary conditions 92
4.2.2 Governing equations 96
4.2.3 Geometry and boundary conditions 97
4.3. Simulation procedures 98
4.3.1 One way shape memory test under magnetic field 98
4.3.2 Reversible deformation behavior of ma-SMP under magnetic field 98
4.4. Results and discussions 99
4.4.1 One way shape memory test under magnetic field 99
4.4.2 Reversible deformation behavior of ma-SMP under magnetic field 103
4.5. Summary 108
5. Applications and considerations 109
5.1. Applications 109
5.1.1 Analysis of cylindrical stent 109
5.1.2 Reflector 114
5.1.3 Lens 118
5.2. Variations of this model 122
5.2.1 Elimination of viscoplastic element 122
5.2.2 Unification of viscoplastic and non-mechanical strain elements 124
5.2.3 Quasi-equivalent equation of non-mechanical strain 128
5.3. Limitations of this model 134
5.3.1 Thermal expansion 134
5.3.2 Overcooling test 134
5.3.3 Unique volume fraction profile for the cooling and heating 136
5.3.4 Plasticity in rubbery phase 137
5.3.5 Volume fraction of the hard segment 138
5.3.6 Other effects on the non-mechanical strain 139
6. Concluding remarks 140
Appendices 142
Appendix A - proof of Equation (20) 142
Appendix B - proof of Equations (34) and (35). 142
Appendix C - proof of Equations (36) and (37). 146
Appendix D - Viscoplastic element 147
Appendix E - Determination of material parameters 147
E.1. Parameter determination for Viscoplasticity 149
E.2. Parameter determination for the non-mechanical strain 150
Appendix F - proof of section 5.2.3 151
References 154
Korean abstract 170
dc.format.extent48185689 bytes-
dc.publisher서울대학교 대학원-
dc.subjectshape memory polymers-
dc.subjectconstitutive equation-
dc.subjectmultiplicative decomposition-
dc.subjectnon-mechanical strain-
dc.subjectshell structure-
dc.titleThree dimensional constitutive equation for shape memory polymers and its applications-
dc.title.alternative형상 기억 고분자의 3차원 구성 방정식과 그 응용-
dc.citation.pagesxv, 171-
dc.contributor.affiliation공과대학 재료공학부-
Appears in Collections:
College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Material Science and Engineering (재료공학부) Theses (Ph.D. / Sc.D._재료공학부)
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