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Huh J.,KAIST | Huh H.,KAIST | Lee C.S.,KAIST | Lee C.S.,Korea Automotive Technology Institute
International Journal of Plasticity | Year: 2013

This paper investigates the effect of strain rate on plastic anisotropy of advanced high strength steel sheets at static and intermediate strain rates. Uniaxial tensile tests were performed at different strain rates to obtain yield stresses and r-values at various loading angles to the reference rolling direction on two advanced high strength steel sheets of TRIP590 and DP780 and a conventional cold-rolled steel sheet of SPCC for comparison. A new method was proposed to measure r-values at intermediate strain rates with the aid of digital image correlation to investigate the deformation history during tensile tests. Plastic anisotropy of the steels was modeled with Hill48, Yld89 and Yld2000-2d yield functions at strain rates between 0.001s-1 and 100s-1. The performance of the three yield criteria was evaluated by comparisons of theoretically calculated planar distributions of the uniaxial yield stress and the r-value with experimental data. Yld2000-2d yield function was found to accurately describe the in-plane anisotropy of the uniaxial yield stress and the r-value of the advanced high strength steels since it has great flexibility due to a larger number of the mechanical parameters incorporated than that of Hill48 yield function with which the anisotropy of SPCC can be described acceptably. Yld2000-2d yield loci were constructed on the two advanced high strength steel sheets and SPCC in order to investigate the effect of the strain rate on their plastic anisotropy at the given range of strain rates. For the materials that we investigated, it is evident that strain rate has a distinct effect both on the shape and magnitude of the yield surface, and the plastic anisotropy tends to diminish at a higher strain rate. © 2013 Elsevier Ltd. All rights reserved. Source


Park S.W.,Japan National Institute of Information and Communications Technology | Park S.W.,Korea Automotive Technology Institute | Wake K.,Japan National Institute of Information and Communications Technology | Watanabe S.,Japan National Institute of Information and Communications Technology
IEEE Transactions on Microwave Theory and Techniques | Year: 2013

We conducted a dosimetry study of a wireless power transfer (WPT) system, which is based on magnetically coupled resonances. The electric and magnetic fields produced by the system have been calculated using the method of moments. We calculated the induced electric fields and the specific absorption rates in a Japanese adult male model by the scattered-field finite-difference time-domain method, taking into account both the incident electric and magnetic fields, and also by the impedance method, but only taking into account the incident magnetic fields. We discuss the differences between the results obtained by the two methods. We also discuss the compliance of the WPT system with international safety guidelines. © 1963-2012 IEEE. Source


Patent
Korea Automotive Technology Institute | Date: 2013-11-05

The present invention provides an apparatus for controlling the temperature of a battery, which is capable of cooling a battery such as a lithium ion battery and the like by using the circulation of a liquid refrigerant and controlling the temperature of the battery through an endothermic reaction or an exothermic reaction caused by a phase transformation process of the corresponding supersaturated liquid refrigerant. To this end, the present invention comprises: at least one temperature sensor for sensing the temperature of a battery pack so as to generate a temperature detection signal; a refrigerant pipe which is extended between arrangement spaces of a plurality of battery cells included in the battery pack and circulates the supersaturated liquid refrigerant through the inside thereof; a refrigerant circulation driving unit which drives a cooling operation by circulating the supersaturated liquid refrigerant through the refrigerant pipe when the temperature of the battery pack rises; and a control unit for driving and controlling the refrigerant circulation driving unit when the rise in the temperature of the battery pack is detected according to a temperature detection signal received from at least one temperature sensor.


Patent
Korea Automotive Technology Institute | Date: 2011-11-21

Provided are an extruded aluminum (Al)-magnesium (Mg) material and a method of producing the same. An AlMg master alloy having a first Mg content is provided. An AlMg alloy having a second Mg content less than the first Mg content is prepared by adding the AlMg master alloy into molten Al and then casting the molten Al. An extruded AlMg material is prepared by extruding the AlMg alloy.


Patent
Korea Automotive Technology Institute | Date: 2010-01-25

Disclosed is a heat-resistant aluminum alloy including aluminum and two types of alloy elements which are combined while forming a homogeneous solid solution reinforcing phase. The disclosed heat-resistant aluminum alloy includes the alloy elements that form a homogeneous solid solution and do not have a solvus line with respect to aluminum as a matrix metal and, therefore, the formed homogeneous solid solution reinforcing phase does not react with aluminum even at a temperature up to 300 C., thus not becoming coarse or undergoing phase decomposition. Consequently, the disclosed aluminum alloy may have remarkably enhanced heat resistance.

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