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Computational mechanics of laser cladding process
Cho, Chongdu,Zhao, Guiping,Kwak, Si-Young,Kim, Chang Boo Elsevier 2004 Journal of materials processing technology Vol. No.
<P><B>Abstract</B></P><P>Laser cladding process accompanies phase transformations through melting (on heating) and solidifying (on cooling), which is an irreversible thermodynamic process. Most of analyses on material processing by laser as a heat source have been conducted on models of neglecting the latent heat in the process just for the reason of simplification. In this study the previous important works are summarized. And to further investigate the effects of latent heat on laser cladding process, this study develops a program accommodating an algorithm for enforcing the latent heat to run with ABAQUS™. The simulation technique of this study is verified by direct comparison of the present prediction with experimental publications elsewhere; the numerical results agreed accurately with the experiments. As a result, it is found that more accurate conclusions come out when considering the latent heat in process analyses.</P>
Thermo-Elastic Analysis for Chattering Phenomenon of Automotive Disk Brake
Cho, Chongdu,Ahn, Sooick The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.5
This study investigates the effects of operating conditions on the chattering of an automotive disk brake by experimental and computational methods. Design factors, which cause chattering in automobiles, have attracted great attentions for long time; but they are not well understood yet. For this study, we construct a brake dynamometer for measuring the disk surface temperature during chattering, and propose an efficient hybrid algorithm (combining FFT-FEA and traditional FEA program) for analyzing the thermo-elastic behavior of three-dimensional brake system. We successfully measure the judder in a brake system via the dynamometer and efficiently simulate the contact pressure variation by the hybrid algorithm. The three-dimensional simulation of thermo-mechanical interactions on the automotive brake, showing the transient thermo-elastic instability phenomenon, is presented for the first time in this academic community. We also find from the experimental study that the disk bulk temperature strongly influences the brake chattering in the automotive disk brakes.
STUDY ON DYNAMIC CRACK PROPAGATION AT IMPACT LOADED 3PB STEEL SPECIMENS
Jaeung Cho,Chongdu Cho,Moonsik Han 한국자동차공학회 2008 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
The crack propagation in ductile steel is investigated by means of impact loaded 3 point bending specimens. Results from experiments and numerical simulations are compared. The specimen has the size 320×75 ㎜ with a thickness of 10 ㎜. A newly designed 3PB specimen design with reduced width at the ends has been developed to avoid the influence of the uncertain boundary conditions at the impact heads. One static and two dynamic experiments with impact velocities of 30.2 ㎧ and 45.2 ㎧ are carried out. High speed photography is used to obtain crack growth and crack tip opening displacement data. Direct measurement of the relative rotation of the two specimen halves is made using by Moire interference pattern. The fracture surfaces of shear lip are obtained for all three loading conditions. The experiments indicate no or only a slight influence of the loading rate on the crack propagation.
디스크 브레이크에서 열섬 천이가 저더 현상 발생에 미치는 영향
조호준(Hojoon Cho),조종두(Chongdu Cho),맹주원(Joowon Maeng),이용산(Yongsan Lee),조기철(Kicheul Cho) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Hot judder phenomenon makes serious problems such as to be uneasiness to drivers or to decrease braking force of vehicle. Because judder vibration makes high magnitude vibration occurrence and thermal problem of brake disk in accordance with hot spots growth at the same time. Therefore it is necessary to reduce or eliminate judder phenomenon by understanding and analyzing origins of hot spot phenomenon. In this experimental study, mode shapes and frequencies related to hot spots were measured by modal testing. For increasing results of modal testing, mode analysis was calculated by finite element analysis. For coupled analysis of disk thickness variation (DTV) and judder vibration, temperature distribution of brake disk, DTV and vibration were measured by interval of 30 seconds in accordance with pressure of master cylinder at the same time. These were conducted by chassis-dynamometer. Hot spot measurements were photographed by using infrared camera. As results, coupled analysis of DTV and judder vibration was performed and relationship between temperature distribution and mode shapes was analyzed.
조호준(Hojoon Cho),조종두(Chongdu Cho),김명구(Myoung-Gu Kim),맹주원(Juwon Maeng),이용산(Yongsan Lee) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Hot spot phenomenon that occurs, during judder vibration, is locally concentrated heat due to friction between brake disk and pad. It is important to understand the reason behind hot spot phenomenon, for reduction of judder vibration. In this experimental study, experiments were performed in accordance with rotation speed of brake disk, pressure of master cylinder and pad length for achieving different aspects of hot spot phenomenon. Temperature distribution of hot spot was obtained by using the infrared camera. As the hot spot occurred, vibration was measured and frequency analysis was performed. Finite element analysis of thermal deformation of disk was performed by using temperature distribution that was achieved by experimental results. It was observed that the excitation frequency band of frictional contact and frictional force mainly affects the hot spot phenomenon.