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Lee, Hyungsoo,Sohn, Seok Su,Jeon, Changwoo,Jo, Ilguk,Lee, Sang-Kwan,Lee, Sunghak Elsevier Sequoia 2017 Materials science & engineering Structural materia Vol.680 No.-
<P><B>Abstract</B></P> <P>In this study, A356 Al alloy composites reinforced with SiC particulates (SiC<SUB>p</SUB>), whose SiC<SUB>p</SUB> volume fraction was quite high (about 56vol%) for a candidate surface material of multi-layered armors, were fabricated by a liquid pressing process, and their dynamic compressive properties were investigated by using a split Hopkinson pressure bar. Defects such as misinfiltration or pores were eliminated, but about 2vol% of eutectic Si particles and about 3vol% of Fe-Al intermetallic compound particles were contained in the Al matrix. According to the dynamic compressive test results, dynamic compressive strength and strain were much higher than quasi-static ones because of strain-rate hardening effect and existence of molten Al matrix formed by adiabatic heating. The as-cast composite showed the best combination of dynamic strength and strain, together with the highest dynamic toughness, because the crack propagation was effectively blocked by the molten Al matrix and deformation band formation, while the T6-heat-treated composite showed the lowest compressive strain in spite of the highest strength. These findings suggested that the present Al-SiC<SUB>p</SUB> composites could be reliably applied to armors because the dynamic toughness or resistance to fracture was much higher under the dynamic loading than under the quasi-static loading.</P>
Effects of Strain Rate on Compressive Properties in Bimodal 7075 Al-SiCp Composite
Lee, Hyungsoo,Choi, Jin Hyeok,Jo, Min Chul,Jo, Ilguk,Lee, Sang-Kwan,Lee, Sunghak Springer-Verlag 2018 METALS AND MATERIALS International Vol.24 No.4
<P>A 7075 Al alloy matrix composite reinforced with SiC particulates (SiC(p)s) whose sizes were 10 and 30 mu m, i.e., a bimodal Al-SiCp composite, was made by a liquid pressing process, and its quasi-static and dynamic compressive properties were evaluated by using a universal testing machine and a split Hopkinson pressure bar, respectively. Mg-Si-, Al-Fe-, and Cu-rich intermetallic compounds existed inside the Al matrix, but might not deteriorate compressive properties because of their low volume fraction (about 2.6%) which was much lower than that of SiCp. The dynamic compressive strength was higher than the quasi-static strength, and was higher in the specimen tested at 2800 s(-1) than in the specimen tested at 1400 s(-1) according to the strain-rate hardening. For explaining the strain data, the blocking extent of crack propagation by the Al matrix was quantitatively examined. The melting of Al matrix occurred by adiabatic heating was favorable for the improvement in compressive strain because it favorably worked for activating the shear band formation and for blocking the crack propagation, thereby leading to the excellent compressive strain (10.9-11.6%) as well as maximum compressive strength (1057-1147 MPa). Thus, the present bimodal 7075 Al-SiCp composite provides a promise for new applications to high-performance armor plates.</P>
Printed cylindrical lens pair for application to the seam concealment in tiled displays
Lee, Seunghwan,Lee, Seungjae,Yoon, Hyungsoo,Lee, Chang-Kun,Yoo, Chanhyung,Park, Jongjang,Byun, Junghwan,Kim, Geonhee,Lee, Byeongmoon,Lee, Byoungho,Hong, Yongtaek The Optical Society 2018 Optics express Vol.26 No.2
Lee, Hyungsoo,Choi, Jin Hyeok,Jo, Min Chul,Lee, Donghyun,Shin, Sangmin,Jo, Ilguk,Lee, Sang-Kwan,Lee, Sunghak Elsevier 2018 Materials science & engineering. properties, micro Vol.738 No.-
<P><B>Abstract</B></P> <P>Quasi-static and dynamic compressive properties of 7075-T6 Al matrix composites reinforced with SiC<SUB>p</SUB>s (size; 10 µm, 30 µm, and bimodal (10 + 30) μm), <I>i.e</I>., 10S, 30S, and BS composites, respectively, were investigated in relation with fracture mechanisms. SiC<SUB>p</SUB>s were homogeneously distributed without SiC<SUB>p</SUB> agglomeration, pores, or cracks, and their volume fractions were 49.5 vol%, 54.1 vol%, and 56.5 vol% in the 30S, 10S, and BS specimens, respectively. Compressive properties could be explained by a rule of mixtures based on SiC<SUB>p</SUB> volume fraction and by three major fracture phenomena including deformation of Al matrix, cracking of SiC<SUB>p</SUB>s, and interfacial debonding between SiC<SUB>p</SUB> and Al. As the SiC<SUB>p</SUB> size decreased, crack initiation sites changed from SiC<SUB>p</SUB>s themselves to SiC<SUB>p</SUB>/Al interfaces, which mainly affected the compressive strength. In the BS composite, coarse SiC<SUB>p</SUB>s additionally worked for the strengthening by increasing the total reinforcement fraction, and the three fracture phenomena were well homogenized, thereby leading to the highest strain energy density as well as the best combination of strength and strain.</P>
Hyungsoo Lee,Gyeong Su Kim,전창우,Seok Su Sohn,Sang-Bok Lee,Sang-Kwan Lee,Hyoung Seop Kim,이상관 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.4
Zr-based amorphous alloy matrix composites reinforced with tungsten (W) or tantalum (Ta) continuous fibers were fabricated by liquid pressing process. Their dynamic tensile properties were investigated in relation with microstructures and deformation mechanisms by using a split Hopkinson tension bar. The dynamic tensile test results indicated that the maximum strength of the W-fiber-reinforced composite (757 MPa) was much lower than the quasi-statically measured strength, whereas the Ta-fiber-reinforced composite showed very high maximum strength (2129 MPa). In the W-fiber-reinforced composite, the fracture abruptly occurred in perpendicular to the tensile direction because W fibers did not play a role in blocking cracks propagated from the amorphous matrix, thereby resulting in abrupt fracture within elastic range and consequent low tensile strength. The very high dynamic tensile strength of the Ta-fiber-reinforced composite could be explained by the presence of ductile Ta fibers in terms of mechanisms such as (1) interrupted propagation of cracks initiated in the amorphous matrix, (2) formation of lots of cracks in the amorphous matrix, and (3) sharing of loads and severe deformation (necking) of Ta fibers in cracked regions.
Lee, Seoyoung,Lee, Seunghyun,Jo, Hyunjin,Bae, Sangki,Kim, Kimin,Song, Jiho,Cho, Younghwan,Kim, Jinsung,Ahn, Hyungsoo,Yang, Min 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.
<P>The growth temperature dependence of self-aligned beta-Ga2O3 nanostructures grown on an r-plane sapphire substrate by using metal-organic chemical vapor deposition is reported. Periodic self-alignment of the beta-Ga2O3 grains was observed for certain growth temperature windows and the grain size of the beta-Ga2O3 structure varied in response to the growth temperature. At temperatures under 800 A degrees C, self-alignment of the beta-Ga2O3 structures was not observed. The self-alignment tendency began to appear at 900 A degrees C, and obvious self-alignment characteristics in a certain direction were observed at approximately 950 A degrees C. However, as the growth temperature was increased to more than 900 A degrees C the growth mode of the beta-Ga2O3 structure gradually deviated from the self-alignment mode, finally exhibiting a two-dimensional thin film mode at 1100 A degrees C. We surmise that the driving force of beta-Ga2O3 grain self-alignment is the surface-potential difference between the planar and the step regions of the substrate on an atomic scale, which originates from misorientation occurring during the r-plane sapphire cutting process.</P>
Influence of Segregation on Microstructure and Hot Workability of Grade 250 Maraging Steel
Hyungsoo Lee,Hi Won Jeong,Seong Moon Seo,Dae Won Yun,Kyungmi Park,Kwang Hyuk Yim,Young Soo Yoo 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.4
The optimal process parameters of grade 250 maraging steel for hot forging were investigated with a process map and microstructureanalysis. To generate the process map, hot compression tests were performed at 800–1200 °C and strain rates of0.01–5 s−1. The flow stress–strain curves were calibrated by Bayesian artificial neural network (ANN) modeling to compensatethe heat generated by dynamic deformation. The Ni and Mo segregation during the solidification of the ingot causedalternating layers of Ni- and Mo-rich and -lean bands, which affected the recrystallization behavior during hot compression. According to the calculated process map, 1100–1200 °C × 0.01–0.7 s−1 and 1000–1200 °C × 0.01–0.2 s−1 are favorableprocess conditions that ensure wide process windows in terms of strain rate and temperature, respectively. The commonfeatures of the microstructure deformed under both conditions were relatively coarse martensite blocks and low values in theelectron backscattered diffraction (EBSD) kernel average misorientation (KAM) results (i.e., low residual stresses), whichwere attributed to a low fraction of fine martensite block region.
Lee, Hyungsoo,Lee, Jaehwan,Nam, Sanghyuck,Park, Sangoh Hindawi Limited 2018 Journal of sensors Vol.2018 No.-
<P>A cyber-physical system depends on stable control and interaction between the many systems and devices connected to the network. Dynamic control middleware, which considers the characteristics of a cyber-physical system, supports the dynamic search and control of devices existing on the global network using Internet protocol version 6 (IPv6). However, systems and devices may connect to a network using a variety of heterogeneous protocols, not just IPv6. To solve the problem of heterogeneous protocols, this paper proposes a routing technique which enables network devices to communicate using different protocols. The proposed network-routing module can register devices with various protocols and improve the stability of the efficient heterogeneous network.</P>
Lee, Hyungsoo,Jo, Min Chul,Sohn, Seok Su,Kim, Sang-Heon,Song, Taejin,Kim, Sung-Kyu,Kim, Hyoung Seop,Kim, Nack J.,Lee, Sunghak Elsevier 2019 Materials characterization Vol.147 No.-
<P><B>Abstract</B></P> <P>The weldability is one of the key factors governing applications of TWinning-Induced Plasticity (TWIP) steels to automotive industries demanding high economy, environmental friendliness, and high performance. During spot welding of Zn-coated Al-containing TWIP steel sheets, liquid metal embrittlement (LME) frequently occurs by Zn infiltration into grain boundaries to form cracks, but the direct observation and detailed analysis of LME cracking are quite difficult because it occurs instantaneously within a second. Here in the present study, the LME was investigated by detailed microstructural evolutions of small Zn infiltrations or cracks as well as formation behavior of various intermetallic phases. In the heat-affected zone, the applied tensile stress and spot-welding heat tore down a diffusion-inhibiting Fe<SUB>2</SUB>Al<SUB>5</SUB> layer formed between the Zn-coated layer and the TWIP steel substrate, and formed Zn-containing ferrite (α-Fe(Zn)) particles on the steel surface which provided paths for liquid Zn infiltration. α-Fe(Zn) particles played critical roles in accelerating the LME by reducing the ductility because they were brittle due to high contents of Zn and Al. In the present Al-containing TWIP steels, the increase in welding current generally aggravates the LME.</P>