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Numerical investigations on the effect of pit on two-step dimple forming of atomic fuel spacer grid
Marimuthu, Karuppasamy Pandian,Choi, Wanseop,Kim, Naksoo,Lee, Hyungyil Springer-Verlag 2018 INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TE Vol.94 No.1
<P>Surface defects, known as pits, due to intervention of impurities are difficult to control during the production of sheet metals for atomic fuel spacer grids. These surface defects can increase the fracture risk during sheet metal forming (SMF) processes and lead to failure due to cracking. In this research, an effect of pits on the formability of zircaloy-4 sheets in two-step stamping process is numerically investigated. Experimentally measured pits with averaged sizes are introduced into finite element (FE) models to investigate the effect pit size and the location on plastic strain distribution around weaker sections. By performing one-step and two-step stamping analyses, strains at the pit locations are compared with an experimental forming limit curve (FLC). Although the two-step stamping model reduces the susceptibility to cracking of the atomic fuel spacer grids over one-step stamping model, this study reveals that the fracture risk is higher, if a pit with relatively small radius and deep depth is located near the edge of the metal sheets. Therefore, it is recommended to identify the pits with critical size around the weaker sections before the SMF processes.</P>
Spherical indentation for brittle fracture toughness evaluation by considering kinked-cone-crack
Marimuthu, Karuppasamy Pandian,Rickhey, Felix,Lee, Jin Haeng,Lee, Hyungyil Elsevier 2017 Journal of the European Ceramic Society Vol.37 No.1
<P><B>Abstract</B></P> <P>This work aims at evaluating the fracture toughness of brittle materials by spherical indentation. The cone-cracking is simulated by the extended finite element method (XFEM) in Abaqus. The formation of a kinked-cone-crack is observed when the indenter comes into (second) contact with the surface part outside the ring-crack. The effects of friction, Poisson’s ratio and cone-crack kinking on the Roesler’s constant <I>κ<SUB>c</SUB> </I> are analyzed. Based on numerical results, the Roesler’s method for evaluating the fracture toughness is enhanced by considering kinked-cone-crack. By performing systematic XFE analyses, a database for enhanced Roesler’s constant <I>κ<SUB>c</SUB> </I> | <SUB>kink</SUB> is provided for the fracture toughness evaluation of brittle materials. Finally, the proposed method is verified by conducting spherical indentation tests on soda-lime glass specimens.</P>
수정된 Chaboche 이동 경화 모델의 수치 구현과 압입라체팅 FE 해석
한정무,MARIMUTHU KARUPPASAMY PANDIAN,이형일 대한기계학회 2020 大韓機械學會論文集A Vol.44 No.1
Mechanical components operating under cyclic loading conditions exhibit multiaxial ratcheting behavior. The kinematic hardening model supported by commercial finite element (FE) software (Abaqus, Ansys) is limited to the initial theory and is not applicable to multiaxial ratcheting analysis. However, the modified kinematic hardening model, which is suitable for multiaxial conditions, is difficult to numerically implement because of the existence of complex constitutive relationships, such as those related to the added multiaxial dependence term and hardening law. In this study, the modified Chaboche kinematic hardening model was numerically implemented by using the framework of a small-strain, elastic-plastic theory; then, the applicability to multiaxial ratcheting analysis was explored by performing indentation ratcheting FE analysis. The numerical model can be practically applied to the analysis of multiaxial ratcheting caused by cyclic indentation, as well as biaxial ratcheting. 반복 하중 조건에서 작동하는 기계 요소들은 다축 반복 하중에 의한 다축라체팅 거동을 보인다. 상용 해석 소프트웨어(Abaqus, Ansys)에서 지원하는 이동 경화 모델은 초기 이론에 제한돼 다축라체팅 분석이 불가능하다. 반면, 다축 조건에 적합한 수정된 이동 경화 모델은 기존 모델에서 추가된 다축항과 경화 법칙 등 복잡한 구성 관계식으로 인해 수치 구현이 난해하다. 본 연구에서는 소변형 탄소성 이론에 입각해 수정된 Chaboche 이동 경화 모델에 대해 Abaqus(6.13 ver)로의 효과적인 수치 구현과 검증 방법을 제안하고, 이를 이용한 압입라체팅 유한요소해석을 수행함으로써 다축라체팅 분석에 대한 활용성을 제시한다. 본 연구로부터 수치 구현된 이동 경화 모델은 반복 압입으로 발생하는 다축라체팅 분석에 실용적으로 활용될 수 있다.
A. Kathalingam,Karuppasamy Pandian Marimuthu,K. Karuppasamy,Yeon‑Sik Chae,Hyungyil Lee,Hyun‑Chang Park,Hyun‑Seok Kim 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6
We report the structural characterization and nanomechanical properties of platinum (Pt) thin films prepared through facileelectrochemical synthesis. The Pt thin films were coated onto indium tin oxide (ITO)/glass substrates by two-electrode electrochemicaldeposition at room temperature. They were characterized using X-ray diffraction, scanning electron microscopy,and atomic force microscopy for structural and morphological analyses. Indentation depth-dependent hardness and elasticmodulus of the prepared films were analyzed using the nanoindentation technique. Furthermore, the mechanical propertiesof the ITO/glass substrates were also investigated to understand the influence of the substrate on the film properties. Theprepared films showed reasonable mechanical and structural properties suitable for device applications. Finally, the photoconductivityeffect of the prepared Pt film was also studied to determine its suitability for device applications. The Pt filmwas also coated on Cu plates to check substrates effects on this electrochemical deposition, and found that the Cu platesproduced well adherent smooth films.