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Park C.,KAIST | Kim J.,KAIST | Huh H.,KAIST | Ahn C.,Hyundai and Kia Corporate Research and Development Division
Conference Proceedings of the Society for Experimental Mechanics Series | Year: 2011

This paper is concerned with tensile characteristics of auto-body plastics at various strain rates ranging from 0.001/sec to 100/sec. Tensile characteristics at the high strain rate are important in prediction of deformation modes of plastic components which undergo the high-speed deformation during car crash. Uniaxial tensile tests at the quasi-static strain rate were conducted at strain rates ranging from 0.001/sec to 0.01/sec by using a tensile testing machine, INTRON 5583. Uniaxial tensile tests at intermediate strain rates were conducted at strain rates ranging from 0.1/sec to 100/sec by using a high-speed material testing machine developed. Since the deformation of plastics is accompanied with localized deformation and a conventional extensometry method(CEM) is no longer valid for strain measurement, a force equilibrium grid method(FEGM) is newly proposed in order to acquire accurate true stress-true strain curves of plastics. FEGM is utilized with image capture of non-uniform distribution of deformation at each elongation stage from a high speed camera in aids of grid methods. The relation between true stress and true strain at the designated strain rate and increment were obtained by collecting the load data by the equilibrium and the deformation images. ©2010 Society for Experimental Mechanics Inc. Source


Suh J.-Y.,Korea Institute of Science and Technology | Lee Y.-S.,Korea Institute of Science and Technology | Shim J.-H.,Korea Institute of Science and Technology | Park H.M.,Hyundai and Kia Corporate Research and Development Division
Computational Materials Science | Year: 2012

A methodology is proposed for predicting the elastic properties of precipitation-hardened alloys by combining different modeling techniques: the CALPHAD method, first-principles calculation, and elasticity models. The proposed procedure was applied to conventional aluminum cast alloys to predict their elastic moduli. The predicted Young's moduli are in reasonable agreement with values reported in the literature, which verifies the potential applicability of the methodology to the development of high-stiffness aluminum cast alloys. © 2011 Elsevier B.V. All rights reserved. Source


Park C.,KAIST | Huh H.,KAIST | Kim J.,Korea Railroad Research Institute | Ahn C.,Hyundai and Kia Corporate Research and Development Division
Journal of Composite Materials | Year: 2012

This article is concerned with the tensile characteristics of polymers at various strain rates. Tensile characteristics at the high strain rate are important in the prediction of deformation modes of polymeric components which undergo high-speed deformation during car crashes. Uniaxial tensile tests at strain rates ranging from 0.001 to 100 s-1 were conducted using a tensile testing machine (INSTRON 5583) and developed high-speed material testing machine. Since the deformation of polymers is accompanied by localized deformation and a conventional extensometry method is no longer valid for strain measurement, a force equilibrium grid method (FEGM) is newly proposed to acquire accurate true stress-true strain curves of polymers. FEGM is utilized with images of the non-uniform distribution of deformation at each elongation stage captured by a high-speed camera in combination with a grid method. The relation between true stress and true strain at the desired strain rate and increment was determined by collecting the load data from the equilibrium and deformation images. © 2012 The Author(s). Source


Kwon J.B.,Korea Advanced Institute of Science and Technology | Huh H.,Korea Advanced Institute of Science and Technology | Ahn C.N.,Hyundai and Kia Corporate Research and Development Division
Conference Proceedings of the Society for Experimental Mechanics Series | Year: 2016

This paper describes the experimental procedure to reduce the load ringing phenomenon in dynamic tensile tests. Reduction and prevention of oscillations in the force signal is an important criterion in the selection of the test jigs. A slack adaptor type jig system has been newly developed for acceptable response at high strain rates. Dynamic tensile tests were conducted using a servo-hydraulic machine with high strength steel sheets at the strain rate of 200 s-1. A piezo-electric load cell is used to measure the force. To confirm and determine the proportion of oscillations from bending effects on a specimen, two strain gauges are attached on the both sides of the gauge section for measurement of the difference in signals with deformation. A digital image correlation (DIC) method is employed to measure the strain during tensile tests. Experimental results show that the load ringing phenomenon in raw data of measured load signals has remarkably diminished with the slack adaptor jig newly developed at a strain rate of 200 s-1. © The Society for Experimental Mechanics, Inc. 2016. Source


Lee C.-W.,Sungkyunkwan University | Hwang T.,Sungkyunkwan University | Nam G.-Y.,Sungkyunkwan University | Hong J.-P.,Sungkyunkwan University | And 12 more authors.
Composites Part A: Applied Science and Manufacturing | Year: 2011

A novel synthetic route to the highly-loaded rubber nanocomposite was developed by a stabilization-destabilization process of colloidal mixtures using montmorillonite (MMT) and natural rubber (NR) as a model system. By analyzing the zeta potentials of the MMT and NR colloids, the stable and unstable conditions of their mixture were identified and subsequently used as the mixing and precipitating process conditions, respectively. The NR drops and MMT nanoplatelets were homogeneously mixed due to their electrostatic repulsion in the stabilized condition of pH > 10.5 and, then the stabilized colloidal mixture were forced to precipitate quickly by changing to pH < 4.0 for destabilization, where the surface charge of the NR drops became positive and attracted the negatively-charged MMT particles resultantly to coagulate together. The developed methodology enabled a maximum loading content of MMT up to 25 phr (20.0 wt%) with a surprisingly large increment in mechanical properties: e.g., tensile modulus by 198% and tear strength by 69%. © 2011 Elsevier Ltd. All rights reserved. Source

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