Loosening analysis for fastening screw of automotive door trim parts : 자동차 도어트림부품 체결나사의 풀림해석

다국어 초록 (Multilingual Abstract)

While a screw is a fastening element that can implement the tightening of two materials at low cost, the loosening of the screw is generated due to external forces such as repetitive load, vibration, and thermal stress. This phenomenon decreases the initial clamping force, and this can be a serious problem to the safety of the product. However, while fastening parts are managed through
experiment and experience, there is a lack of research on the screw loosening of plastic fastening parts. For example, vehicles have various fastening parts. Among
the fastening elements, screws are typically used for tightening parts of the vehicle door trim. Vehicle interior materials are mainly composed of plastic parts.
Especially, the temperature of the vehicle interior changes from a sub-zero temperature to 100 degrees due to solar radiation. Unlike metals, plastic materials are commonly susceptible to the environment. In this study, the fastening screw of automotive door trim parts is selected. First, a screw loosening mechanism is implemented through Computer Aided Engineering (CAE) analysis and the impact of degradation is then analyzed. Secondly, the selecting method of clamping force is suggested through the analysis result of reduction according to the tightening
torque.

목차 (Table of Contents)

• * Nomenclature ⅳ
• * List of Tables ⅵ
• * List of Figures ⅶ
• * Abstract ⅸ
• Chapter 1 Introduction 1
• 1.1 Research background 1
• 1.2 Research purposes 2
• 1.3 Researches trend 3
• 1.4 Composition of paper 4
• Chapter 2 Basic theory 8
• 2.1 Torque and clamping force at screw 8
• 2.1.1 Required torque when tightening screw 8
• 2.1.2 Required torque when loosening screw 9
• 2.2 Plastic material properties 11
• 2.2.1 Viscoelastic behavior 11
• 2.2.2 Creep behavior 12
• 2.3 Screw loosening mechanisms 13
• 2.3.1 Screw loosening mechanism due to slipping 13
• 2.3.2 Screw loosening mechanism by degradation 15
• Chapter 3 Screw loosening analysis 24
• 3.1 Plastic material properties test 24
• 3.1.1 Tensile test 24
• 3.1.2 Creep test 25
• 3.2 Finite element model of screw fastening parts 26
• 3.3 Screw loosening analysis by the external force 26
• 3.3.1 Screw fastening by torque 27
• 3.3.2 Screw loosening by shear load 27
• 3.4 Screw loosening analysis by degradation 28
• 3.4.1 Heat cycle 28
• 3.4.2 Reduced clamping force by degradation 28
• 3.4.3 Screw loosening by shear load after degradation 29
• 3.5 Closing remarks 30
• Chapter 4 Discussion on clamping force considering degradation 43
• 4.1 Degradation effect according to friction coefficient 43
• 4.1.1 Relation between the friction coefficient and clamping force 43
• 4.1.2 Relation between the friction coefficient and clamping force after degradation 44
• 4.2 Selection for tightening torque according to the friction coefficient 44
• 4.2.1 General selection method for tightening torque 44
• 4.2.2 Selection method for tightening torque in case of plastic parts 45
• 4.3 Closing remarks 46
• Chapter 5 Conclusion and future research project 51
• 5.1 Conclusion 51
• 5.2 Future research project 52
• References 53
• Korean Abstract 57