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Heerok Hong,Ho-Yong Lee,Nak-Tak Jeong,Keon-Hee Baek,Myung-Won Suh 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.3
The threaded fasteners are typical machine components in tightening of the machine parts and structures. In addition, as threaded fasteners are easy to maintenance, these are used extensively from large structures to small electronic devices. However, after the clamping, if repetitive load is applied to the bolt/screw, loosening of the screw occurs. In this study, clamping analysis and loosening analysis are carried out for the M12 bolts which are used for the wheels of commercial vehicles. Since it is difficult to carry out test and finite element analysis (FEA) for the wheels of commercial vehicles, we propose a complex structure to deal with these problems. Through the test and FEA, the clamping force and the loosening load of bolt are derived. Not only the reduction of clamping force but also displacement of the complex structure subjected to load can indicate the loosening of the bolt. Three equivalent models are proposed to replace a detailed model for reduction of the analysis time and cost. Then, the three equivalent models are forms of rigid beam – beam – pretension (RBP), shell – beam – pretension (SBP) and shell – beam – temperature (SBT), respectively. Among these forms, the SBT model is most similar with analysis results of the detailed model. The difference between the analysis results of the detailed model and the SBT model was only 5 %. Based on the SBT model and the detailed model, it is applied to the wheel of the commercial vehicles to be verified. Then, the changes in the clamping force of the detailed model and the SBT model are identified as similar, proving the validity of the equivalent.
Heerok Hong,김경필,Ho-Yong Lee,김재식,이다솜,김민수,Myung-WonSuh,이정환 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.3
During the braking process, frictional heat generated between a disc and a pad can lead to high temperatures. The location of friction blocks on the brake pad can lead directly to differences in friction contact time and friction speed at each point on the brake disc surface, this can lead to non-uniform temperature distribution on the brake disc surface. In this paper, the optimum design for friction blocks on a brake pad is investigated using the design of experiments (DOE) of Taguchi approach and response surface method (RSM) with an aim to minimize the deviation in the rate of friction heating in each area along the radial direction of brake disc. 18 design variables on 2 levels are adjusted. A table of orthogonal arrays, L32 (218), is used. Finite element analysis (FEA) is performed to analyze the mean squared error (MSE) values in the temperature deviations from frictional heat, the disc’s thermo-mechanical characteristics are taken into account. Analysis of variance (ANOVA) is carried out using the data gathered from the DOE stage, we find 7 significant factors among the design variables. A meta-model using RSM is proposed for reduction of temperature deviations over the brake disc. An optimized brake pad is analyzed in terms of the temperature and thermal stress imparted on the brake disc, this optimized pad is then compared with the original pad. The maximum temperatures of the optimized pad and original pad were 399.8 °C and 480.6 °C, respectively. The thermal stress of the optimized pad and original pad were 640.4 MPa and 721.4 MPa, respectively. In the optimized model, the size of the hot band on the disc is larger than that from the original model, so the thermal stress distribution on the disc is smaller. Finally, the optimized pad was found to give significant performance benefits with a 16.8 % decrease in maximum temperature and 11.2 % decrease in thermal stress.