Numerical and experimental studies on surface peening behaviors of 6061 T6 Al sheet processed by ultrasonic nanocrystal surface modification = 초음파 나노 표면 개질 처리된 6061 T6 Al 판재의 표면 피닝 거동에 관한 수치적, 실험적 연구

다국어 초록 (Multilingual Abstract)

UNSM (Ultrasonic Nanocrystal Surface Modification) can induce surface hardening and compressive residual stress on the surface by striking metal surface with static force, ultrasonic vibration in the hard micro WC-tip. This is a type of "surface micro cold forging" technique. In this study, a numerical and experimental approach was taken to the local deformation behavior of the surface caused by a UNSM strike. Using finite element analysis (ABAQUS Dynamic/Explicit), the striking control of the micro-tip was divided into displacement-controlled and force-controlled, comparing the distribution of residual stress and strain field after 300 strikes on the 6061 T6 Al sheet. Here, the strain field distribution and surface morphology in strain hardening have different results. With experimental approaches, observing the surface morphology of a single path UNSM-treated sheet is similar to simulation results of a force-controlled striking. This confirms that the strain field distribution takes place on the sheet, such as a force-controlled striking, and that the strain hardening exponent and strain rate sensitivity of the metallic materials are variables that affect the local deformation behavior during a UNSM strike.

목차 (Table of Contents)

• CONTENTS
• List of tables 1
• List of figures 2
• Abstract 5
• 1. Introduction 7
• 1.1 Research objective 11
• 2. Theoretical Background 17
• 2.1 Surface peening 17
• 2.2 UNSM 19
• 2.2.1 Striking mechanism of UNSM process 19
• 2.2.2 High Strain Rate Behavior 21
• 2.3 Residual Stress of Surface Peening 23
• 2.3.1 Residual Stress 23
• 2.3.2 Macro Types of Compressive Residual Stress 26
• 3. Experimental approach 28
• 3.1 Single path UNSM 28
• 3.2 Surface Topology and Instrumented indentation 31
• 4. Numerical approach 34
• 4.1 Mechanics of UNSM striking 34
• 4.2 Simulation Details 37
• 4.2.1 Numerical Framework 37
• 4.2.2 High strain rate constitutive model 40
• 5. Result and Discussion 44
• 5.1 Residual Stress Distribution with Simulations and Experiments 44
• 5.2 Strain Distribution and Surface Topology comparing with Simulation and Experiments 49
• 5.3 Different vertical displacement in Simulation 59
• 5.4 In terms of Materials Constitutive Parameters 62
• 6. Conclusion 63
• Reference 65
• Abstract 71