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Dave Kim,Sina Alizadeh Ashrafi,Kangwoo Shin,김태곤 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.8
This paper investigates how tool geometries and process conditions influence fiber pull-out formations, drilling forces, and hole quality parameters during the drilling process of quasi-isotropic CFRP laminates. The dry drilling experiments with the tools having three different point angles (two single point angles of 166° and 118°, and one double point angle of 100°/60°) were conducted with the feed conditions of 0.08 mm/rev to 0.2 mm/rev and the spindle speed conditions of 1500 rpm to 5000 rpm. A destructive method was used to quantify the fiber pull-out area and depth concerning the interaction angle of the cutting tool edge and fiber directions. The feed condition and the drill point angle affect the drilling forces and undeformed chip thickness, which influence the fiber pull-out formation mechanisms. The drill with the higher point angle produced less fiber pull-out area; however, it resulted in deeper fiber pullouts, causing higher surface roughness.
Dave Kim,Aaron Beal,Kiweon Kang,Sang-Young Kim 한국탄소학회 2017 Carbon Letters Vol.23 No.-
Polycrystalline diamond (PCD) tools possessing high hardness and abrasive wear resistance are particularly suited for drilling of carbon fiber reinforced plastic (CFRP) composites, where tool life and consistent hole quality are important. While PCD presents superior performance when drilling CFRP, it is unclear how it performs when drilling multi-stack materials such as CFRP-titanium (Ti) stacks. This comparative study aims to investigate drilling of a Ti plate stacked on a CFRP panel when using PCD tools. The first sequence of the drilling experiments was to drill 20 holes in CFRP only. CFRP-Ti stacks were then drilled for the next 20 holes with the same drill bit. CFRP holes and CFRP-Ti stack holes were evaluated in terms of machined hole quality. The main tool wear mechanism of PCD drills is micro-fractures that occur when machining the Ti plate of the stack. Tool wear increases the instability and the operation temperature when machining the Ti plate. This results in high drilling forces, large hole diameter errors, high surface roughness, wider CFRP exit thermal damage, and taller exit Ti burrs.
Dave Kim,Sam R. Swan,Bin He,Viktor Khominich,Eric Bell,Seok‑Woo Lee,Tae‑Gon Kim 한국탄소학회 2021 Carbon Letters Vol.31 No.3
This study aims to investigate the effect of an aluminum chromium nitride (AlCrN) coating on tool wear and hole quality in the conventional drilling process of carbon fiber-reinforced plastic (CFRP) composites, titanium alloy (Ti), and CFRP–Ti stack workpieces popular in the aerospace industry. The advanced arc plasma acceleration (APA) method of physical vapor deposition (PVD) was used for all AlCrN coatings. The drilling experiments were conducted with uncoated drills as well as AlCrN-coated drills. When drilling CFRP only, the AlCrN coating was removed at the drill cutting edges and the margin area, which suggests the carbon fibers abraded the coatings. When drilling Ti only, the AlCrN-coated drill mitigated the Ti adhesion formation, which resulted in less tool wear. In addition, hole quality for both CFRP and Ti was improved when the coating was used versus the uncoated tool. The machinability of CFRP–Ti stacks in the drilling process was improved by utilizing the advanced AlCrN coating on the WC tool in terms of drilling forces and hole quality parameters such as average hole size, average hole roundness, hole surface roughness, and Ti exit burr height.
Kim, Dave Dae-Wook,Hennigan, Daniel John,Beavers, Kevin Daniel The Society of Naval Architects of Korea 2010 International Journal of Naval Architecture and Oc Vol.2 No.1
Polymer composite materials offer high strength and stiffness to weight ratio, corrosion resistance, and total life cost reductions that appeal to the marine industry. The advantages of composite construction have led to their incorporation in U.S. yacht hull structures over 46 meters (150 feet) in length. In order to construct even larger hull structures, higher quality composites with lower cost production techniques need to be developed. In this study, the effect of composite hull fabrication processes on mechanical properties of glass fiber reinforced plastic (GFRP) composites is presented. Fabrication techniques investigated during this study are hand lay-up (HL), vacuum infusion (VI), and hybrid (HL+VI) processes. Mechanical property testing includes: tensile, compressive, and ignition loss sample analysis. Results demonstrate that the vacuum pressure implemented dining composite fabrication has an effect on mechanical properties. The VI processed GFRP yields improved mechanical properties in tension/compression strengths and tensile modulus. The hybrid GFRP composites, however, failed in a sequential manor, due to dissimilar failure modes in the HL and VI processed sides. Fractography analysis was conducted to validate the mechanical property testing results.
The Impact of Fasciation on Maize Inflorescence Architecture
Kim Da Eun,Jeong Jin-hee,Kang Yu Mi,Park Young-Hoon,Lee Yong-Jae,강점순,최영환,손병구,Kim Sun Tae,Jackson Dave,제병일 한국식물학회 2022 Journal of Plant Biology Vol.65 No.2
How functional genetics research can be applied to improving crop yields is a timely challenge. One of the most direct methods is to produce larger inflorescences with higher productivity, which should be accompanied by a balance between stem cell proliferation and lateral organ initiation in meristems. Unbalanced proliferation of stem cells causes the fasciated inflorescences, which reflect the abnormal proliferation of meristems, derived from the Latin word ‘fascis’, meaning ‘bundle’. Maize, a model system for grain crops, has shown tremendous yield improvements through the mysterious transformation of the female inflorescence during domestication. In this review, we focus on maize inflorescence architecture and highlight the patterns of fasciation, including recent progress.
Kim, Sang-Young,Shim, Chun Sik,Sturtevant, Caleb,Kim, Dave Dae-Wook,Song, Ha Cheol The Society of Naval Architects of Korea 2014 International Journal of Naval Architecture and Oc Vol.6 No.3
Glass Fiber Reinforced Plastic (GFRP) structures are primarily manufactured using hand lay-up or vacuum infusion techniques, which are cost-effective for the construction of marine vessels. This paper aims to investigate the mechanical properties and failure mechanisms of the hybrid GFRP composites, formed by applying the hand lay-up processed exterior and the vacuum infusion processed interior layups, providing benefits for structural performance and ease of manufacturing. The hybrid GFRP composites contain one, two, and three vacuum infusion processed layer sets with consistent sets of hand lay-up processed layers. Mechanical properties assessed in this study include tensile, compressive and in-plane shear properties. Hybrid composites with three sets of vacuum infusion layers showed the highest tensile mechanical properties while those with two sets had the highest mechanical properties in compression. The batch homogeneity, for the GFRP fabrication processes, is evaluated using the experimentally obtained mechanical properties.
Christian N. Svinth,Scott Wallace,Daniel B. Stephenson,Dave Kim,Kangwoo Shin,Hyo-Young Kim,Seok-Woo Lee,Tae-Gon Kim 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.23 No.6
This study aims to conduct abnormality detection by applying machine learning algorithms when drilling a carbon fiber reinforced plastic laminate. In-process signals including current, thrust force, and vibration were captured during the dry drilling experiments using a 6 mm physical vapor deposit diamond-coated drill at the consistent spindle speed of 6500 RPM and 0.05 mm/rev. Across measurements from out-of-process variables, including hole diameter, roundness, surface roughness, entry/exit delamination, and entry/exit uncut fiber area, in-process measurements were most able to find outliers with respect to diameter. Both Principal Component Analysis, an unsupervised dimensionality reduction technique, and Linear Discriminant Analysis, a supervised dimensionality reduction technique, could separate oversize or undersize holes from average-sized holes when using fast Fourier transformation data of in-process vibration. Predictive performance with k-Nearest Neighbors shows that our machine learning pipeline can predict oversized vs. non-oversized holes with over 85% accuracy in this dataset. Peak prediction performance is obtained when in-process measurement data is viewed from the frequency domain, and predictions are weighted based on the relative distances of the nearest neighbors.