Tae-Rin Lee

Surface thermochemical reaction control utilizing planar anisotropic thermal conduit

Surface exothermic chemical reaction was amplified by the carbon nanotube film on a polymer substrate. Heat was transferred along the nanotubes with high thermal conductivity/low heat capacity and fed back to the reactants, leading to the amplification of reaction rate, while suppressing perpendicular heat transfer to the thermally insulating substrate.

Cleavage Fracture Evaluation Using Local Approach for SA508 Carbon Steel at -60°C

The scatter of measured fracture toughness data and transferability problems for specimens with different crack configurations and loading conditions are major obstacles for integrity assessment of ferritic steels in ductile-brittle transition region. To address these issues, recently, concerns for local approach adopting micro-mechanical damage models are being increased again in connection with a progress of computational technology. In this paper, cleavage fracture evaluation based on Weibull statistics was carried out for SA508 carbon steel. A series of three dimensional finite element analyses as well as corresponding fracture toughness tests were performed for 1T-CT and PCVN specimens at -60°C. Also, failure probability analyses for different configurations and sensitivity analyses for Weibull parameters were conducted. Thereby, promising results have been derived through comparison between measured and estimated fracture toughness data, which can be utilized to make the basis for demonstrating real safety margins of components containing defect.

Weibull Statistics as a Basis for Assessment of Ductile-Brittle Transition Behavior

The objective of this paper is to investigate failure characteristics of SA508 carbon steel in ductile-brittle transition temperature region. To achieve this goal, a series of finite element analyses as well as fracture toughness tests are performed for pre-cracked V-notch specimens. An assessment of failure probabilities is, then, carried out employing Weibull stress models with different rank probability options. Finally, a prototype of toughness scale diagram is derived through comparison of estimated fracture toughness data with those for compact tension specimens. The present results can be utilized to found a basis of realistic integrity evaluation on major nuclear components containing defect.

Assessment of Geometry Independent Fracture Resistance Characteristics Based on Local Approach

The influences of stress triaxiality on ductile fracture have been emphasized to explain the geometry independent fracture resistance characteristics of specimens and structures during past two decades. For the estimation of this material behavior, two-parameter global approach and local approach can be used as case by case manner. Recently, the interests for the local approach and micro-mechanical damage model are increased again due to progress of computational environments. In this paper, the applicability of the local approach has been assessed through a series of finite element analyses incorporating both modified GTN model and Rousselier model. The ductile crack growth behaviors are examined to guarantee the transferability on different sizes and geometries of C(T) specimens and SE(T) specimens. The material fitting constants are determined from calibration of tensile tests and numerical analyses results, and used to simulate the fracture behaviors of typical specimens. Then, a comparison is drawn between the numerically estimated crack resistance curves and experimentally determined ones. The comparison results show a good agreement and the two damage models are regarded as promising solutions for ductile crack growth simulation.

Assessment of Ductile Crack Growth Based on a Local Approach

The influence of stress triaxiality was a matter of concern on ductile fracture to explain geometry dependent fracture resistance characteristics of specimens and real structures during past two decades. Regarding the issue, recently, interests for local approach and micro-mechanical damage models are increased again in accordance with progress of computational environments. In this paper, the applicability of a local approach is investigated through a series of finite element (FE) analyses incorporating both a modified GTN model and a Rousselier model as well as fracture toughness tests. The ductile crack growth behaviour of SA515 Gr.60 carbon steel is assessed to guarantee transferability of fracture resistance curve from typical specimens with different in-plane and out-of-plane sizes. The material parameters are determined by calibration of test results and corresponding numerical analyses results, and used to simulate the fracture behaviour of CT specimens. Then, a comparison is drawn between the numerically estimated crack resistance curves and experimentally determined ones. Finally, the Rousselier model is applied to estimate J-R curves of circumferential through-wall cracked pipe. The comparison results showed that the two damage models can be used as promising solutions for ductile crack growth simulation.Copyright

Assessment of In-plane Size Effect of Nuclear Materials Based on Damage Mechanics

The influences of stress triaxiality on ductile fracture have been investigated for various specimens and structures. With respect to a transferability issue, recently, the interests on local approaches reflecting micromechanical specifics are increased again due to rapid progress of computational environments. In this paper, the applicability of the local approaches has been examined through a series of finite element analyses incorporating modified GTN and Rousselier models as well as fracture toughness tests. The ductile crack growth of nuclear carbon steels is assessed to verify the transferability among compact tension (CT) specimens with different in-plane size. At first, the basic material constants were calibrated for standard CT specimens and used to predict fracture resistance (J-R) curves of larger CT specimens. Then, the in-plane size effects were examined by comparing the numerically estimated J-R curves with the experimentally determined ones. The assessment results showed that the in-plane size effect should be considered for realistic engineering application and the damage models might be used as useful tool for ductile fracture evaluation.

Quantification of Crack Length and Thickness Effects on J-R Curves by Ductile Damage Models

In this paper, the applicability of local approach is examined for SA515 Gr.60 nuclear steel through a series of finite element analyses incorporating modified GTN and Rousselier models as well as fracture toughness tests. To achieve the goal, fracture toughness test data of standard compact tension (CT) specimens are used for calibration of micro-mechanical parameters. Then, from finite element analyses employing the calibrated parameters, fracture resistance (J-R) curves of CT specimens with different crack length to width ratio, with different thickness and with/without 20% side-grooves are predicted. Finally, suitability of the numerically estimated J-R curves was verified by comparison with the corresponding experimental J-R curves.