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EFFECT OF HEAT TREATMENT ON CRACK PROPAGATION AND PERFORMANCE OF DISK BRAKE WITH CROSS DRILLED HOLES
Yunhwa Hong,Taeksu Jung,Chongdu Cho 한국자동차공학회 2019 International journal of automotive technology Vol.20 No.1
A vehicle disk brake, which has cross drilled hole patterns on a frictional surface for improving cooling and braking performance, has propensity to cause crack problem under the harsh braking condition. In this study, the finite element analysis by using ABAQUS was adopted to investigate a cause of crack occurrence by the thermo-mechanical phenomenon around drilled hole patterns. As a remedy of the crack generation, the disk brake rotor with stress relieving and ferritic nitrocarburizing was prepared and tested on brake dynamometer in harsh condition. The test result was examined in terms of pad wear, the braking torque variation, the braking temperature changes, the crack initiation timing, and the crack propagation speed. As a test result, the disk after heat treatment showed 3.61 % higher average braking temperature than the disk without heat treatments, to suggest decreased heat dissipation performance, however, it also showed 14 % lower pad wear amount, and 0.1 % smaller braking torque variance than the disk without heat treatments, to stand for improved contact characteristics. Also, the heat treated brake rotor showed 51.3 % lower crack propagation rate which is considered as proper countermeasure of the fracture phenomenon at the edge of cross drilled hole.
NUMERICAL STUDY FOR BRAKE SQUEAL BY MACHINING PATTERNS ON FRICTIONAL SURFACE
Taeksu Jung,Yunhwa Hong,Sungsu Park,Cheongmin Kim,Younghoon Hong,Chongdu Cho 한국자동차공학회 2018 International journal of automotive technology Vol.19 No.2
Automotive brake noise has become a stubborn problem as automotive cars achieve higher driving torques, since that the increased torque induces the generation of severe noise dissipation during brake operation. Moreover, the global brake tuning market for achieving higher performance of the vehicle has expanded recently. The need to control the noise grows more in this connection. The tuning brake kits have employed cross-drilled and slotted machining pattern on the surface of the rotor. These designs have advantages to improve air ventilation, temperature control, and surface cleaning of brake pad. However, the effects of modal frequency by patterned rotor surfaces are rarely discussed, even if it is highly related with brake squeal phenomenon. Therefore, this study deals with the relationship between patterned surfaces and brake squeal through the numerical methods. The commercial software of a finite element analysis is employed for calculation by varying geometric design factors of each rotor pattern. As a result, the cross-drilled machining patterns are concluded to be an influential factor for in-plane mode frequency while the slotted patterns have more leverage for out-of-plane mode frequency.
변부형,Yunhwa Jung 한국분자세포생물학회 2008 Molecules and cells Vol.25 No.2
The role of SPOP in the ubiquitination of ERα by the Cullin3-based E3 ubiquitin ligase complex was investigated. We showed that the N-terminal region of SPOP containing the MATH domain interacts with the AF-2 domain of ERα in cultured human embryonic 293 cells. SPOP was required for coimmunoprecipitation of ERα with Cullin3. This is the first report of the essential role of SPOP in ERα ubiquitination by the Cullin3- based E3 ubiquitin ligase complex. We also demonstrated repression of the transactiva