Papers by Author: Hoon Huh

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Authors: Geun Su Joo, Min Kuk Choi, Hoon Huh
Abstract: The tension/compression hardening behavior is important in sheet metal forming processes because of complicated loading paths. Experimental methods to measure the tension/ compression behavior have not considered the effect of the strain rate although the strain rate is related to the hardening behavior of sheet metal. The tension/compression tests need to be conducted considering the strain rate to acquire accurate hardening behavior.This paper deals with an experimental technique to measure the tension/compression behavior of sheet metal at various strain rates. A new clamping device was developed to prevent a sheet specimen from buckling under compression loading condition. Compared to previous clamping devices, the clamping device was devised to uniformly impose a clamping force and easily measure the strain from side of a specimen. Tension/compression tests have been conducted at various strain rates for SPCC and DP590 with displacement of 10%. Hardening curves under the tension or compression loading condition were obtained and analyzed with respect to the strain rate.
Authors: Kee Sun Yeom, Seh Wan Jeong, Hoon Huh, Jung Su Park
Abstract: PBX is known to exhibit highly nonlinear behaviors of deformation such as the Mullins effect of stress softening, hysteresis, residual strain, and frequency dependant responses. This paper proposes a phenomenological energy-based model for PBX considering the Mullins effect for isotropic, incompressible, hyperelastic, particle-filled materials. Uniaxial compressive loading and unloading tests at quasi-static states were undertaken in order to obtain the mechanical properties of the PBX simulants. The phenomenological energy-based model by Ogden-Roxburgh is, then, modified to make it consistent with the test result of PBX simulants in the case that the Mullins effect is dominant. Prediction with the new model shows a good correspondence to the experimental data demonstrating that the model properly describes the Mullins effect and the loading-unloading behavior of deformation.
Authors: Ji Ho Lim, Jin-Sung Kim, Hoon Huh, Jong Seub Kim
Authors: Jin Sung Kim, Hoon Huh, Won Mog Choi, Tae Soo Kwon
Abstract: This paper demonstrates the jig set for the crash test and the crash test results of the tension bolts with respect to an applied pre-tension. The tension and shear bolts are adopted at Light Collision Safety Devices as a mechanical fuse when tension bolts reach designed failure load. The kinetic energy due to the crash is absorbed by secondary energy absorbing devices after the fracture of tension bolts. One tension bolt was designed to be failed at the load of 375 kN. The jig set was designed to convert a compressive loading to a tensile loading and installed at the high speed crash tester. The strain gauges were attached at the parallel section of the tension bolts to measure the level of the pre-tension acting on the tension bolts. Crash tests were performed with a barrier whose mass was 250 kg and initial speed of the barrier was 9.5 m/sec. The result includes the load response of the tension bolts during both the crash tests and finite element analysis.
Authors: Kwanghyun Ahn, Hoon Huh, Tae Soo Kwon
Abstract: A railway buffer stopper is a crash energy absorbing device which is installed at the end of rail lines in order to prevent derailment. To stop a train which cannot otherwise stop at the rail end due to some kind of trouble, this device should be installed in a railway station or depot where the rail line finishes. Friction type buffer stoppers have been installed at railway stations in most European countries. These devices can absorb the crash energy of the train by using the friction between a friction element and the rail when the train crashes into the buffer stopper. This paper proposes a new concept for the buffer stopper which can replace the friction type buffer stopper. More economical and effective buffer stopper can be suggested by using a progressive compression process. When the train crashes into the new type buffer stopper, a metal strip installed at the rail is progressively compressed and absorbs the kinetic energy of the train through its own plastic deformation. The feasibility of the buffer stopper using the progressive compression process is first investigated using numerical analysis and then the design and concept for the new system are suggested by a parametric study. The design of the progressive compression type has been verified by a series of experiments.
Authors: Jung Han Song, Hoon Huh
Abstract: This paper is concerned with the dynamic characteristics of sinter-forged Cu–Cr alloy for various strain-rates. The amount of the chrome content is varied from 10 %wt to 30 %wt in order to investigate the influence of the chrome content on the dynamic characteristics. The dynamic response at the corresponding level of strain-rate should be obtained with an adequate experimental technique and corresponding apparatus due to the inertia effect and the stress wave propagation. In this paper, the high speed tensile testing machine is utilized in order to identify the dynamic response of the Cu–Cr alloy at the intermediate strain-rates and the split Hopkinson pressure bar is used at the high strain-rates. Experimental results from both the quasi-static and the high strain-rates up to the 5000/s are interpolated with respect to the amount of the chrome content in order to construct the Johnson–Cook and the modified Johnson–Cook model as the constitutive relation for numerical simulation of the dynamic impact behavior of electrodes.
Authors: Kwanghyun Ahn, Hoon Huh
Abstract: The dynamic response of the turbine blade materials is indispensable for analysis of erosions of turbine blades as a result of impulsive loading associated with gas flow. This paper is concerned with the dynamic hardening equation of the Nickel-based superalloy Inconel 718 which is widely used in the high speed turbine blade. Reported representative dynamic hardening equations have been constructed and evaluated using the dynamic hardening characteristics of the Inconel 718. Dynamic hardening characteristics of the Inconel 718 have been obtained by uniaxial tensile tests and SHPB tests. Uniaxial tensile tests have been performed with the variation of the strain rate from 0.001/sec to 100/sec and SHPB tests have been conducted at the strain rate ranging up to 4000/sec. Several existing models have been constructed and evaluated for Johnson-Cook model, Zerilli-Armstrong model, Preston-Tonks-Wallace model, modified Johnson-Cook model, and modified Khan-Huang model using test results at various strain rate conditions. The most applicable equation for the Inconel 718 has been suggested by comparison of constructed results.
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