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Effect of hydro co-extrusion on microstructure of duo-cast Al 3003/Al 4004 clad materials
SON, In-Soo,LEE, Sang-Pill,LEE, Jin-Kyung,KIM, Woo-Cheol,MOON, Ji-Seon,LEE, Sangmok,LEE, Jong-Sup,KIM, Yong-Bae,LEE, Geun-Ahn,BAE, Dong-Su Elsevier 2014 Transactions of Nonferrous Metals Society of China Vol.24 No.suppl1
Lee, Sanghwan,Kim, Bonghwan,Lee, Sangmok The Japan Institute of Metals 2011 Materials transactions Vol.52 No.6
<P>The effects of Fe content and cooling rate on the solidification path and formation behavior of the Al<SUB>5</SUB>FeSi (β) phase in Fe-containing eutectic Al-Si alloys were studied based on thermodynamic analysis and pertinent experiments. To predict solidification path in Fe-containing eutectic Al-Si alloys, the thermodynamic calculations in the Al-Si-Fe ternary system, including the high Fe region, were systematically performed using the Thermo-Calc program and updated database. To experimentally verify the predicted results, designed two eutectic Al-Si alloys with different Fe levels were solidified under slowly- and rapidly-cooled conditions, respectively. The cooling curves of the solidified alloys were recorded by thermal analysis. Microstructures of the casting samples were studied by the combined analyses of optical microscopy (OM) and scanning electron microscopy (SEM). For the slowly-cooled condition with the high Fe level, the primary β phase was mainly formed by the quasi-peritectic reaction of L+γ→α+β (656°C). For the rapidly-cooled condition with high Fe level, the primary β phase was mainly formed by the reaction of L→β (583∼649°C).</P>
Effect of plateau distribution on friction instability of brake friction materials
Lee, Sangmok,Jang, Ho Elsevier 2018 Wear: An international journal on the science and Vol.400 No.-
<P>The effect of contact plateau distribution on stick-slip of brake friction materials was studied based on experimental results and computer simulation of the sliding interface. Experimental results showed that plateau distribution determined the amplitude and frequency of friction oscillation, which were governed by the tangential stiffness and failure strength of each plateau. The numerical analysis showed that the surface with few large plateaus produced larger stick-slip amplitudes than one with several small contact plateaus. This study suggested that the friction material should be designed to produce small contact plateaus on the sliding surface to diminish its noise propensity during brake applications.</P>
Hybrid fragility curve derivation of buildings based on post-earthquake reconnaissance data
Sangmok Lee,Do-Soo Moon,Byungmin Kim,Jeongseob Kim,Young-Joo Lee 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.28 No.4
This study proposes a new hybrid method that uses both of post-earthquake reconnaissance data and numerical analysis results based on a finite element (FE) model. As the uncertainty of a capacity threshold for a structural damage state needs to be estimated carefully, in the proposed method, the probabilistic distribution parameters of capacity thresholds are evaluated based on post-earthquake reconnaissance data. Subsequently, the hybrid fragility curves were derived for several damage states using the updated distribution parameters of capacity thresholds. To illustrate the detailed process of the proposed hybrid method, it was applied to piloti-type reinforce concrete (RC) buildings which were affected by the 2017 Pohang earthquake, Korea. In the example, analytical fragility curves were derived first, and then hybrid fragility curves were obtained using the distribution parameters of capacity thresholds which were updated based on actual post-earthquake reconnaissance data about the Pohang city. The results showed that the seismic fragility estimates approached to the empirical failure probability at 0.27 g PGA, corresponding to the ground motion intensity of the Pohang earthquake. To verify the proposed method, hybrid fragility curves were derived with the hypothetical reconnaissance data sets created based on assumed distribution parameters with errors of 10% and 1%. As a result, it was identified that the distribution parameters accurately converged to the assumed parameters and the case of 1% error had better convergence than that of 10% error.
An Examination of Kant's Space
Lee,Sangmok 영남철학회 1987 哲學論叢 Vol.3 No.-
There are the many arguments produced against Kant's theoretical philosophy. Among them there are some arguments that Kant's doctrine of space as a priori intuition must be abandoned. The criticism is as follow; Kant's theory of space as a priori intuition is only possible the validity of the propositions of the Euclidean geometry, since the latter works on the assumption that space is infinite, and since this geometry is supposed to be capable of determining the properties of space in a synthetic and yet a priori manner. Now, the assumption of the infinity of space is by no means necessary. Therefore, Kant's theory of geometry is untenable and along with it his concept of space. It is widely assumed that Kant's real argument for the ideality of space turn on his conception of Eucledean geometry as a synthetic a priori science of space. Since this conception is almost universally rejected, there is little sympathy for the central claims of transcendental Aesthetic. The wrongness of his doctrine of space as pure intuition. Therefore, his doctrine of space as pure intuition can no longer be maintained. In opposition to this interpretation, I suggest that Kant's argument from the representation of space is still worthy, and that the rejection of Kant's view on geometry does not entail the rejection of the doctrine of the a priori intuition character of space. In order to examine it, we must look more closely at Kant's Metaphysical Exposition of the concept of space. It is to show that space must be regarded as a priori intuition.
Lee, Sanghwan,Kim, Bonghwan,Lee, Sangmok The Japan Institute of Metals 2011 Materials transactions Vol.52 No.5
<P>The effects of Fe content and cooling rate on the solidification path and formation behavior of the Al<SUB>5</SUB>FeSi (β) phase in Fe-containing hypoeutectic Al-Si alloys were studied based on thermodynamic analysis and pertinent experiments. The thermodynamic calculations were performed using the Thermo-Calc program. For analyses in the high alloy region of the Al-Si-Fe ternary system, a thermodynamic database for Thermo-Calc was correctly updated and revised by the collected up-to-date references. For thermodynamics-based predictions of the solidification path in Fe-containing hypoeutectic Al-Si alloys, liquidus projection (including various invariant, monovariant, and bivariant reactions and isotherms) and equilibrium phase fraction were calculated as functions of composition and temperature in the Al-Si-Fe ternary system. The calculated results were compared to experimental results using various casting runs. In order to analyze the solidification path as a function of Fe content, two representative hypoeutectic Al-Si alloys with different Fe levels were designed. To better understand the influence of cooling rate on the formation behavior of the β phase, the two alloys were solidified under slowly- and rapidly-cooled conditions, respectively. The cooling curves of the solidified alloys were recorded by thermal analysis and various important solidification events were detected using the first derivative of the cooling curves. Microstructures of the casting samples were studied by combined analyses of optical microscopy (OM) and scanning electron microscopy (SEM). For the slowly-cooled condition with the high Fe level, the primary β phase enveloping the Al<SUB>8</SUB>Fe<SUB>2</SUB>Si (α) phase was mainly formed by the quasi-peritectic reaction of L + α → (Al) + β (612°C). For the rapidly-cooled condition with the high Fe level, the primary β phase with morphology of a curved needle was mainly formed by the reaction of L → (Al) + β (579∼612°C).</P>