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Yanggu, South Korea

Nam J.S.,Korea Institute of Machinery and Materials | Park Y.J.,Korea Institute of Machinery and Materials | Chang H.S.,Taewoong Co.
Journal of Mechanical Science and Technology | Year: 2016

The design guideline of the National Renewable Energy Laboratory (NREL) is a standard for designing and verifying pitch and yaw bearings of wind turbines. The usability of the guideline was evaluated by comparing with analytical results obtained by a commercial software. Results from calculation equations of the NREL guideline and from a commercial software were compared in terms of the main design evaluation items of pitch and yaw bearings, such as dynamic life, static load factor, and case-core interface models. Calculation and analysis were conducted using specifications and loading conditions for the yaw bearing of a 2.5 MW wind turbine. Results showed that the values computed using the NREL guideline were more conservative than those derived using the commercial software. Although the guideline showed some differences from the analytical results obtained using the software, they can be used in the initial design of pitch and yaw bearings because of the advantage of the simplicity and the characteristics of conservative output. © 2016, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg. Source


Yeom J.-T.,Korea Institute of Materials Science | Jung E.J.,Korea Institute of Materials Science | Kim J.H.,Korea Institute of Materials Science | Hong J.-K.,Korea Institute of Materials Science | And 3 more authors.
Surface Review and Letters | Year: 2010

In this study, the modeling of recrystallization and grain growth was investigated to predict the microstructure evolution during hot working of INCONEL 783 superalloy (Alloy 783). The recrystallization model was constructed on the basis of the Avrami formation. A least-square optimization technique was used to determine several important parameters within the model from isothermal heat treatment and hot compression test results. High temperature compression tests were carried out under different temperatures, strain rates and strain conditions. The model for describing the recrystallization and grain growth behaviors of Alloy 783 was implemented onto the user-subroutine of a commercial FE code. In order to demonstrate the reliability of the model, the microstructure evolution of Alloy 783 alloy during the hot compression test was simulated and was accorded well with the experimental results. © 2010 World Scientific Publishing Company. Source


Zhao J.,Pohang University of Science and Technology | Kim Y.W.,Pohang University of Science and Technology | Lee J.H.,Pohang University of Science and Technology | Lee J.M.,Taewoong Co. | And 2 more authors.
Metals and Materials International | Year: 2012

A study was made to investigate the effect of tungsten (W) addition on the microstructure, tensile properties, Vickers hardness, and corrosion resistance of S355NL forging steel. Mechanical properties were evaluated and considered in the context of the interlamellar spacing of pearlite. Microstructural analysis revealed that the addition of W favors the formation of intragranular acicular ferrite and leads to a decrease in the interlamellar spacing of pearlite. After W addition, the corrosion rust film was intact. The steel containing W showed fewer microcracks distributed in the corroded surface compared with that without W. It was concluded that the addition of W is beneficial for improvement of both the mechanical properties and corrosion resistance of S355NL forging steel. © KIM and Springer. Source


Yeom J.-T.,Korea Institute of Materials Science | Jung E.-J.,Korea Institute of Materials Science | Kim J.H.,Korea Institute of Materials Science | Hong J.-K.,Korea Institute of Materials Science | And 4 more authors.
7th International Symposium on Superalloy 718 and Derivatives 2010 | Year: 2010

In this study, microstructure evolution during ring rolling process of INCONEL alloy 783 (Alloy 783) was investigated with the combined approaches of 3-D FEM (Finite Element Method) simulation and microstructure prediction model. A microstructure prediction model was developed by considering the effects of process variables on recrystallization and grain growth behavior. The model was established by the analysis of hot compression and isothermal heat treatment test results. From the analysis of isothermal heat treatment tests, it can be found that the rate of grain growth dramatically increases after the dissolution of β phase, which acts as an obstacle to grain boundary movement. In order to consider the effect of β phase on grain growth, an additional equation in the transition temperature region was interposed. Microstructure evolution during ring rolling process of Alloy 783 was calculated by de-coupled approach between FEM analysis and microstructure prediction model. The prediction results were compared with the experimental ones. Source


Yeom J.-T.,Korea Institute of Materials Science | Kim J.H.,Korea Institute of Materials Science | Hong J.-K.,Korea Institute of Materials Science | Lee J.M.,Taewoong Co. | And 4 more authors.
Metals and Materials International | Year: 2014

In this work, a ring-rolling process to formulate ring-shaped components for a wind turbine is designed by means of a simulation and in an experimental approach. The target of the ring-rolling design is a yaw ring with an outer diameter of approximately 3,130 mm. The ring-rolling design includes the design of the geometry and the optimization of the process variables. A calculation method was used for the geometry design, in this case for the initial billet and the pre-form (or blank) sizes, and for the final rolled ring shape. Also, a deformation map-based approach was utilized to determine the initial ring-rolling temperature and feed rate of the mandrel. A three-dimensional finite element method was used to predict the formation of rolling defects and the deformed shape in the ring-rolled components. The design criteria are to achieve uniform distributions of the strains and temperatures as well as defect-free ring-shaped components. Finally, an optimum process design to obtain a sound large-scale yaw ring without defects is proposed. It is validated by comparisons between the experimental data and the FE analysis results. © 2014 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht. Source

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