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Kyeongsik Ha,Young Hoon Moon,Tae Hwan Kim,Gyeong Yun Baek,Ki Yong Lee,Do-sik Shim,Wookjin Lee 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.5
This study aimed to develop a computational methodology to estimate the residual stress formation behavior followed by direct energy deposition of high-speed tool steel hard materials. First, evolutions of substrate distortions followed by the depositions of AISI M4 tool steel layers were investigated by experiments and the results were analyzed using the elasticity-based Stoney’s approach. The results revealed significant additional distortion caused by the temperature gradient formed when depositing the first M4 layer. Distortions occurring on depositing the second and subsequent M4 layers could be approximated as linearly increasing with the total M4 layer thickness, indicating a stable inherent shrinkage strain for each layer deposition process. It was also clearly revealed that the elastic Stoney’s approach is not capable of predicting the residual stress in the studied direct energy deposition system as significant plastic deformations are expected to occur. Based on the experimental observations, a phenomenological finite element (FE) model was developed considering the elastoplastic behavior of materials. The FE simulation results showed very good agreement with the experimentally measured distortions during the M4 deposition process in a wide range of deposition areas and thicknesses. Thus, the proposed model can be used effectively for controlling the distortions and analyzing residual stress evolutions during hard-facing or repairing processes using direct energy deposition.
Phase‐contrast hard X‐ray microscopy using synchrotron radiation for the diagnosis of onychomycosis
Lee, Onseok,Ha, Seunghan,Lee, Gunwoo,Kim, Jaeyoung,Huang, Jungyun,Jin, Kyeongsik,Oh, Chilhwan Wiley Subscription Services, Inc., A Wiley Company 2010 Microscopy research and technique Vol.73 No.12
<P><B>Abstract</B></P><P>Onychomycosis, or fungal infection of the nail, is a disease seen frequently in clinical settings. However, the rates of positive identification using potassium hydroxide preparations or fungal cultures are relatively low. Precise diagnosis is possible via histopathologic examination to monitor the existence of fungus and performance of a fungal culture for confirmation. Phase‐contrast hard X‐ray microscopy using synchrotron radiation provides 70‐nm spatial resolution and enables imaging of minute internal cellular structures. This study confirms the feasibility of diagnosing onychomycosis using a phase‐contrast hard X‐ray microscope developed at 1B2 beam line using a Pohang light source. Microsc. Res. Tech. 73:1110–1114, 2010. © 2010 Wiley‐Liss, Inc.</P>