Microstructure optimization to improve mechanical and corrosion properties of pure titanium and magnesium alloy using severe plastic deformation

DoctorLoss of body function occurs due to aging or unavoidable accidents. The loss is directly related to the quality of human life. Biomaterials contribute to improve the quality of human life by replacing or complementing tissue or organ that has lost its function. In particular, metallic biomaterials are used to permanently or temporarily replace or supplement the hard tissue in the human body. Metals are superior in mechanical properties and resistant to cracking compared to ceramics or polymers, thus metals are used for applications that are subject to external stress such as artificial dental implant, orthopedic implant, artificial joint, stent, and so on. Metallic biomaterials are divided into permanent or biodegradable materials. The commercialized permanent materials are Ti-6Al-4V and stainless steels. However, these materials contain toxic elements such as Al (Induction of Alzheimer’s disease), V (Neurotoxicity), Ni (Allergy), and Cr (Cell necrosis) which can cause problem to the body during long-term use. For this reason, pure Ti have recently attracted attention to replace commercial biomaterials. However, pure Ti are not suitable for long term use due to its low mechanical properties compared to the commercial materials. In addition, despite of the importance of etching in medical industries, the texture effect on etching behavior of pure Ti has not been investigated. Mg alloys have mainly been studied as biodegradable material for orthopedic fixation devices. Biodegradable materials are expected to change the existing implant procedures, which not only require a secondary surgery to remove implants after bone healing process, but also carry infection risk at the exposed site after surgery. However, fast and uncontrolled corrosion rate of Mg alloys are problematic because mechanical strength reduction, gas evolution, and pH change are correlated with corrosion behavior. Severe plastic deformation (SPD) process improves the mechanical properties of materials by grain refinement and produces the ultrafine-grained (UFG) and nanocrystalline structure. Typical SPD processes include high pressure torsion (HPT) and equal-channel angular pressing (ECAP) while surface modified SPD process includes ultrasonic nanocrystalline surface modification (UNSM). The SPD process not only affects the microstructure development of the materials, but also changes the texture of the materials. The purpose of this thesis in achieving two specific goals using the SPD process. The first goal is to increase mechanical and surface properties of commercially pure (CP)-Ti by controlling the microstructure and texture for development of rough surface through etching. And the second goal is to improve corrosion resistance of Mg alloy considering mechanical properties

Establishing Micro-Scale Sediment Transport Model for Wurf-zone Dynamics Using LES Turbulence Modeling Scheme

한국해양과학기술

순 타이타늄 인장 물성에 미치는 표면 거칠기의 영향에 대한 유한요소해석

Titanium based implants are known to improve their osseointegration by controlling surface roughness from nanometers to micrometers. Implants continuously and/or repeatedly receive irregular loads in the human body, and require a deeper understanding of the tensile and fatigue properties that can determine the fracture characteristics of the materials. In this study, the plastic deformation behavior which depends on the surface geometry of the materials during tensile tests was analyzed using the finite element method. As a result, the tensile properties were greatly decreased with increasing the sharpness of the surface. On the other hand, the average roughness had no significant effect on tensile properties. This investigation shed a light on developing titanium implants with improved osseointegration by surface treatments.22kc

Development of Cementitious Materials for Life Time Extension of Floating Concrete Structures

◦ 본 연구에서는 부유식 콘크리트 구조체의 수명연장을 위한 시멘트 모르타르 계열 보수재료개발을 목표로 실험적 연구를 수행함 ◦ 표면보호재료의 성능평가를 위해서 압축, 휨강도를 측정할 수 있는 200 kN급 만능재료시험기, 부착강도를 측정할 수 있는 Pull-off 부착강도 시험장비, 염화물 침투저항성 측정을 위한 Rapid Chloride Permeability Test 장비를 구축함 ◦ 구축된 실험 장비들을 사용하여 시멘트 모르타르 계열 표면보호재료의 강도와 내구성에 양생환경(수돗물과 해수), 혼화재료의 종류, 혼화재료의 치환율, 그리고 양생기간이 미치는 영향을 평가함 ◦ 또한, 시멘트 모르타르 표면보호재료의 강도와 내구성이 변화하는 원인을 보다 정확히 규명하고자 미세구조분석을 실시하였으며, 개발된 표면보호재료를 부유식 콘크리트 구조체에 적용하기 위한 믹싱가이드라인과 시공방법을 제시함 ◦ 추후 개발된 표면보호재료의 실구조물 적용을 위한 경제성 평가 및 장기양생 (6개월, 1년,2년) 시험을 계획하고 있음한국해양과학기술

Development of advancement technology for real-time marine environment monitoring system(Echo-buoy)

한국해양과학기술

저탄소강-고망간강-저탄소강 3층 적층재의 딥 드로잉 거동

2

TWIP기반 3층 복층 강판의 초기 인장 변형

2

Development of Cementitious Materials for Life Time Extension of Floating Concrete Structures

◦ 본 연구에서는 부유식 콘크리트 구조체의 수명연장을 위한 시멘트 모르타르 계열 보수재료개발을 목표로 실험적 연구를 수행함 ◦ 표면보호재료의 성능평가를 위해서 압축, 휨강도를 측정할 수 있는 200 kN급 만능재료시험기, 부착강도를 측정할 수 있는 Pull-off 부착강도 시험장비, 염화물 침투저항성 측정을 위한 Rapid Chloride Permeability Test 장비를 구축함 ◦ 구축된 실험 장비들을 사용하여 시멘트 모르타르 계열 표면보호재료의 강도와 내구성에 양생환경(수돗물과 해수), 혼화재료의 종류, 혼화재료의 치환율, 그리고 양생기간이 미치는 영향을 평가함 ◦ 또한, 시멘트 모르타르 표면보호재료의 강도와 내구성이 변화하는 원인을 보다 정확히 규명하고자 미세구조분석을 실시하였으며, 개발된 표면보호재료를 부유식 콘크리트 구조체에 적용하기 위한 믹싱가이드라인과 시공방법을 제시함 ◦ 추후 개발된 표면보호재료의 실구조물 적용을 위한 경제성 평가 및 장기양생 (6개월, 1년,2년) 시험을 계획하고 있음한국해양과학기술

Development of Design Technologies for Harbor Structures Based on Open-cell Caissons

한국해양과학기술

CoWiTA를 이용한 구속효과가 고려된 범용구조해석 프로그램 비선형 모듈 개발

한국해양과학기술