14 research outputs found
Nonlinear Damage Modeling and Analysis of Viscoplastic Composite Materials
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Όλ¬Έ (λ°μ¬)-- μμΈλνκ΅ λνμ : νλκ³Όμ κ³μ°κ³Όνμ 곡, 2014. 8. μ μΈμ.ν곡기 κ²½λνλ₯Ό ν΅ν μ΄νν¨μ¨μ μ¦μ§μν€κΈ° μν΄ μ΅κ·Ό ν΄λ¦¬λ¨Έ 볡ν©μ¬λ£λ₯Ό μ μ©ν ν곡기 μ£Ό ꡬ쑰물μ κ°λ°μ΄ 보νΈνλκ³ μλ μΆμΈμ΄λ€. 볡ν©μ¬λ£μ ν곡기 ꡬ쑰μ¬λ£λ‘μ μ μ© νλλ μΌλ°μ μΈ ν곡기 μ΄μ© 쑰건μ λνλ΄λ μ ν, μ μ νμ€ νμ ν곡기 ꡬ쑰 μ€κ³ λ° ν΄μμ μꡬλλ ν΄μ κΈ°λ²κ³Ό μ¬λ£ λ¬Όμ±ν보 λ± κ³΅νμ κΈ°λ²μ λ°μ μΌλ‘ μ΄μ΄μ‘λ€. κ·Έλ¬λ ν곡기 ꡬ쑰μ¬λ£λ‘ λ리 μ μ©λλ 볡ν©μ¬λ£μ λμ κ±°λ λ° λΉμ ν λ³ν λ±μ ν΄μμ μ νλκ° μ ν, μ μ ν΄μμ λΉν΄ μλμ μΌλ‘ λμ§ μμΌλ©°, νΉν 좩격 λλ μΆ©λμ μν΄ λ°μλλ λΉμ ν κ±°λμ ν΄μμ λ°©λ²μ ν΅ν μμΈ‘μλ νκ³λ₯Ό λνλ΄κ³ μλ€. κ·Έλ¬λ―λ‘ μ΄λ¬ν λΉμ ν κ±°λκ³Ό μΆ©λμλμ λ°λΌ λ³ννλ 볡ν©μ¬λ£μ κ±°λμ μμΈ‘νκΈ° μ ν©ν ν΄μ λͺ¨λΈκ³Ό λ°©λ²μ κ°λ°μ ν΅ν΄ ν곡기 ꡬ쑰물μ λ΄μΆλ½ μ±λ₯ ν₯μμ΄ κ°λ₯ν κ²μΌλ‘ νλ¨ν μ μλ€.
λ³Έ μ°κ΅¬λ μΈμ°μ μ νμμν΄μκΈ°λ²μ μ μ©νκΈ° μν λ³νλ₯ μλμ λ°λΌ λ³ννλ ν΄λ¦¬λ¨Έ 볡ν©μ¬λ£μ λΉμ ν μμ λͺ¨λΈμ κ΄ν κ²μΌλ‘, μ¬λ£μ λΉμ ν μμ κ±°λμ ν¨κ³Όμ μΌλ‘ μμΈ‘νκΈ° μν΄ μνλμλ€. 볡ν©μ¬λ£μ νμμ΄ λ°μνκΈ° μ κ±°λμ μμΈ‘νκΈ° μν μμ λͺ¨λΈμ λ€μ€μ€μΌμΌ μ κ·Όλ²μ μ΄μ©ν ν΄λ¦¬λ¨Έ 볡ν©μ¬λ£μ μ νμ±, μ μμ± κ΅¬μ±λ°©μ μμΌλ‘ ꡬμ±λμ΄ μλ€. νμνμ μΌλ‘, λ©΄λ΄ μ λ¨νμ€μ΄ μμ©νλ 볡ν©μ¬λ£μ λΉμ ν λ³ν κ±°λμ κΈ°μ§μ μ μμ± κ±°λκ³Ό 볡ν©μ¬ λ΄λΆμ λ―ΈμΈμμμ μν μμκ±°λμ μν΄ λνλλ κ²μΌλ‘ μλ €μ Έ μλ€. λμ νμ€μ΄ μμ©νλ κ²½μ° λ³νλ₯ μλμ λ³νλ 볡ν©μ¬λ£ λ΄ κΈ°μ§μ κ±°λμ λ³ν λΏ μλλΌ, 볡ν©μ¬ μμκ±°λμ λ³νλ₯Ό μ΄λνκ² λλ€. λ©΄λ΄ μ λ¨ κ±°λμ λν μ νλκ° ν₯μλ λ―Έμμνλͺ¨λΈμ μ μ©μ ν΅ν΄ λ³νκ±°λμ νΉμ±μ΄ μμ΄ν μ¬μ μ κΈ°μ§μ κ±°λμ λμμ κ³ λ €νμλ€. ν΄μ λͺ¨λΈμ μ νλ ν₯μμ μν΄ λ³Έ μ°κ΅¬μμλ κ±°μμνμ μ΄λ°©μ± μ°μ체 μμμνμ΄λ‘ μ λ°νμΌλ‘ λ³νλ₯ μλμ λ°λΌ νμ±μμλͺ¨λΈμ μνλ³μκ° λ³ννλ μμλͺ¨λΈμ μ μνμλ€.
λ³Έ μ°κ΅¬μμ 볡ν©μ¬ μ μΈ΅νλ΄μ μ μΈ΅μ νμμ΄ λ°μν μ΄ν μ¬λ£ κ°μ± λ° κ°λμ λ³νλ₯Ό λνλ΄κΈ° μν μμ κ±°λ λͺ¨λΈμ μ μ©νκ³ μλ€. 볡ν©μ¬ μ μΈ΅ν λ΄μ 볡ν©μ¬ μ μΈ΅μ νμ λ°μ μμΈ‘μ Hashin νμ λͺ¨λΈμ κΈ°λ³Έννλ‘ λ³νλ₯ μλμ λ°λΌ νμκΈ°μ€μ΄ λ³ννλ νμ λͺ¨λΈμ μ μ©νμλ€. 볡ν©μ¬ μ μΈ΅ν λ΄ λ³΅ν©μ¬ μ μΈ΅μ νμμ μν κ°μ± λ° μμ© μλ ₯μ κ°μλ₯Ό λνλ΄κΈ° μν΄ λ³Έ μ°κ΅¬μμλ ν₯μλ μμ μ§μ λͺ¨λΈμ μ μνκ³ μλ€. μ΄ μμ μ§μ λͺ¨λΈμ κΈ°μ‘΄ μμ μ§μ λͺ¨λΈμ λ€μν ννμ μμ κ±°λ 곑μ μ λνλ΄κΈ° μν λ³μλ₯Ό μΆκ°ν¨μΌλ‘μ¨ κΈ°μ‘΄ λͺ¨λΈμ λΉν΄ λ€μν μμ κ±°λμ λͺ¨μ¬ν μ μμ΄, μΈμ°μ μ νμμν΄μμ μ΄μ©ν 볡ν©μ¬ μ μ§μ νμν΄μμ μ ν©ν λͺ¨λΈμ΄λ€.
λ³Έ μ°κ΅¬μμ μ μλ λ³νλ₯ μλμ λ°λΌ λ³ννλ μμ λͺ¨λΈμ μ μ©ν ν΄μ κ²°κ³Όλ λ€μν λ³νλ₯ μλμμμ μνμΉμ λΉκ΅λ₯Ό ν΅ν΄ κ²μ¦λμμΌλ©°, λμ ν΄μ μ νλλ₯Ό νμΈν μ μμλ€. λν λ³Έ μ°κ΅¬μμ μ μλ μμ μ§μ λͺ¨λΈμ μΈμ°μ μ νμμκΈ°λ²μ μν μ μ§μ νμν΄μκΈ°λ²μ λ§€μ° μ ν©ν λͺ¨λΈμμ νμΈν μ μμλ€.Recently, polymeric composite materials have been widely used as the primary structures for saving the weight and increasing the efficiency in the aerospace industry. As the application of composite airframes is promoted, it is almost equipped that the engineering properties and analysis method for the composite structural design for the quasi-static and linear conditions. However, analysis methods for of the dynamic and nonlinear behaviors of composite materials are relatively deficient to fully predict structural responses, and which nonlinear behaviors are typically caused by the impact or crash conditions. Therefore, appropriate analysis methods for the rate-dependent and nonlinear behaviors of composite materials can improve the crashworthiness performance of aerospace structures.
The present study aims at the nonlinear damage models for the explicit finite element method with respect to strain rates which are to predict nonlinearly damaging behaviors of polymeric composite materials. The damage model for prior to material failure, which represents the rate-dependent damage modeling for polymeric composite materials with the viscoelastic and viscoplastic constitutive model using a multi-scale approach. Phenomenologically, the nonlinear response of a composite under the in-plane shear loading condition is originated from the viscoplasticity of a matrix and the damage behavior of composite materials. In case of dynamic loading conditions, the strain-rate effects the change of the damage behavior of composite materials, as well as the behavior of the matrix. The enhanced micromechanical model which improves the in-plane shear behavior, is used for analyzing the rate-dependent behaviors of the fiber and matrix constituents. The rate-dependent elastic damage model based on orthotropic continuum damage mechanics theory at the macromechanical level is applied to improve the accuracy of the analysis model.
The damaging behavior after the material failure in this study, which represents the degradation after the composite failure. The rate-dependent composite failure criteria based on Hashin failure model is employed in this study. In order to degrade the stiffness and reduce the stresses, the enhanced damage progression model is proposed in this study. This model is suitable for the progressive failure analysis of composite materials using the explicit FE analysis, because it has one more variable than the original model which can adjust the progressive failure behaviors of composite laminates.
Predictions by presented the rate-dependent damage model are shown to agree fairly well with experimental results over a wide range of strain rates. The enhanced damage progression model is shown that it is quite suitable for the progressive failure model for the explicit finite element method.ABSTRACT i
1. INTRODUCTION 1
1.1 Backgrounds 4
1.2 Scope of this works 11
2. RDM MODEL FOR POLYMERIC COMPOSITES 14
2.1 Phenomenological description for polymeric composite materials under in-plane shear dynamic loading 15
2.1.1 Orthotropic behavior of fiber reinforced composite materials 15
2.1.2 Nonlinear behavior of in-plane shear loaded composite materials 17
2.1.3 Rate-dependent behavior of polymeric composite laminates 23
2.2 Rate-dependent polymer model 26
2.2.1 Viscoelastic model for polymer 27
2.2.2 Viscoplastic model for polymer β State variable constitutive equation 30
2.2.3 Viscoplastic model for polymer β Material constants determination 33
2.2.4 Viscoplastic model for polymer β Compressive loading consideration 37
2.3 Composite micromechanical model 39
2.3.1 Original micromechanical model β Slicing algorithm 40
2.3.2. Enhanced micromechanical model β Modified slicing algorithm 47
2.4 Rate-dependent damage model prior to failure 51
2.4.1. Theoretical modeling of reference damage model 52
2.4.2. Development of rate-dependent damage modeling 57
3. PROGRESSIVE FAILURE ANALYSIS USING EDPM 64
3.1 Material failure detection model 65
3.1.1. The Hashin composite failure criteria 65
3.1.2. The Rate-dependent Hashin failure criteria 68
3.2 Damage progression after material failure 71
3.2.1. Material degradation model β micromechanical approach 72
3.2.2. Enhanced damage progression model (EDPM) 81
3.3 Damaged element deletion 97
4. IMPLEMENTATION AND MODEL VERIFICATION 98
4.1 Implementation in the FE element analysis 99
4.1.1. Implementation of RDM using multi-scale approach 101
4.1.2. Implementation of PFA 103
4.2 Model verification 106
4.2.1. Verification for RDM 106
4.2.2. Verification for PFA model 116
5. DISCUSSION 127
6. CONCLUSIONS 135
REFERENCES 139Docto
Optimized rotor design of UAV cyclocopter with cycloidal blades system
Thesis (master`s)--μμΈλνκ΅ λνμ :κΈ°κ³ν곡곡νλΆ,2004.Maste