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홍창섭,이학,오재윤 한국기계기술학회 2016 한국기계기술학회지 Vol.18 No.6
This paper studies the effect of a playtykurtic excitation signal on fatigue life. In general, a vibration test uses an excitation signal having a normal distribution of kurtosis 3. However, a vibration signal generated in a product’s operation environment has usually a non-normal distribution. This paper uses ZMNL method to generate a playtykurtic excitation signal having the equivalent power spectrum density with a reference vibration profile. This paper proposes a method which uses a fatigue damage spectrum ratio for studying the effect of a playtykurtic excitation signal on fatigue life. The fatigue spectrum damage ratio is obtained by dividing a fatigue damage spectrum acquired using the acceleration profile in which all conditions are the same except for the kurtosis by a fatigue damage spectrum acquired theoretically. This paper shows that the signal of kurtosis less than 3 can increase the fatigue damage spectrum by more than 2 to 4 times compared to the signal of kurtosis 3 using the fatigue damage spectrum ratio.
홍창섭,양홍준,강윤식,오재윤,오택열 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.12
In this paper, we study the correlation between a sinusoidal sweep durability test and a random vibration durability test through specimen tests. We compute random vibration durability test conditions having the same fatigue damage spectrum as a sinusoidal sweep durability test using the numerical analysis method. We use two kinds of specimens of different shape to perform durability tests. This paper proposes a normalization process that uses the average of the fatigue damage time caused only by a sinusoidal sweep durability test, and the average of the fatigue damage time caused only by a random vibration durability test. The normalization process makes it possible to remove the difference of fatigue life due to the difference of specimen shape. Thus, we determine one trend equation that can predict the test results of two kinds of specimen with high reliability. Through the trend equation, we can find the correlation between the fatigue life due to sinusoidal sweep vibration, and the fatigue life due to random vibration, which depends only on the specimen material and the excitation method.
백서에서 동종 신경이식시 항 T임파구 단일클론항체 분포에 관한 조직화학적 연구
홍창섭,김경욱,임창준,정대현 단국대학교 치의학연구소 1991 논문집 Vol.3 No.-
Nerve allografts as a bridge through which lost nerve can regenerate is useful in the repair of peripheral nerve defect resulting from trauma, neoplasm and leprosy. But immunological rejection and complicated scar formation is an unaboidable problem in the application of allogenic nerves. This article is intended to study histopathological and immunohistochemical response after fresh allogenic sciatic nerve grafts in rats. 12 male Sprague- Dawley rats were used as the experimental animals. A 2cm skin incision was made on the lateral aspects of limb, parallel to the femur. 1cm-long sciatic nerve trunk taken from the one rat was resected at the middle of the to high, and it was transplanted to the same area of the other rat with perineural suture method. Observation was made at the postoperative 1, 3, 8, 16 day. The results were as follows. 1. Histopathologically, destruction of the perineural sheath was observed only in 1-day group. 2. Mild degenerative changes of the nucleus and cytoplasm of Schwann cells were ovserved in the 1-day and 3-day groups. These changes gradually resolved. 3. Hollow space phenomena of the nucleus and cytoplasm of schwann cells were observed. The response was mild in the 1 day and 3 day groups, and moderate in the 8 day group. The phenomena were not identified in the 16 day group. 4. Immunohistochemical studies revealed pan T cells and cytotoxic T cells in the 1 day group. Increased numbers of cytotoxic T Cells and helper T cells were observed in the 3 and 8 day groups. 5. According to these results, after transplantation of fresh allogenic sciatic nerve an inflammatory response was observed up to 8 days and then gradually resolved. Degenerative changes were more severe up to 8 days, but an the 16th day they had resolved histopathologically and immunopathologically.
홍창섭,오재윤 한국기계기술학회 2015 한국기계기술학회지 Vol.17 No.4
This paper studies on the effect of kurtosis on fatigue life. A typical vibration test machine uses a normal distribution signal. However, the vibration signal generated in the actual operating environment is a non-normal distribution signal with kurtosis. In this paper, a signal which has the same power spectral density, but has different kurtosis is generated using the Zero Memory Non-Linear (ZMNL) method. The power spectral densities of these two signal will coincide within ±3dB. Fatigue damage spectrum(FDS) computed with a normal distribution signal and FDS computed with a non-normal distribution signal generated using the ZMNL method are compared. FDS computed using the normal distribution signal of kurtosis 3 will show a big difference over the 100Hz with FDS computed using the signal of kurtosis 6. This paper shows through such FDS comparison that a difference in fatigue life prediction may result in if a vibration profile which does not consider kurtosis occurring in the operating environment of a product is used in a vibration test.
[안전] 트럭의 충돌 특성해석을 위한 유한요소 모델의 개발
홍창섭(Chang-Sup Hong),오재윤(Chae-Youn Oh),김학덕(Hak-Duck Kim),이대창(Dae-Chang Lee),송주현(Ju-Hyun Song) 한국자동차공학회 1999 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1999 No.11_2
This paper develops a finite element model for the crashworthiness analysis of a truck. A simulation for a truck frontal crash to a rigid barrier using the model is performed with PAM-CRASH installed in IBM super computer RS/6000. Full vehicle model is composed of 86467 shell elements, 165 beam elements and 98 bar elements, and 86769 nodes. The model uses four material model such as elastic, elastic-plastic(steel), rigid and elastic-plastic(rubber) material model which are in PAM-CRASH. Frame and suspension system are modeled with 28774 shell elements and 31412 nodes. Cab is modeled with 34680 shell elements and 57 beam elements, and 36254 nodes. Bumper is modeled with 2262 shell elements, and 2508 nodes. Axle, steering shaft, etc are modeled using beam or bar elements. Mounting parts are modeled using rigid bodies. Bodies are interconnected using nodal constrains or joint options. To verify the developed model, frontal crash test with 30mph velocity to a rigid barrier is carried out. In the crash test, vehicle pulse at lower part of b-pillar is measured, and deformed shapes of frame and driver seat area are photographed. Those measured vehicle pulse and photographed pictures are compared those from the simulation to verify the developed finite element model.
[안전] 트럭의 승객거동해석을 위한 유한요소 모델의 개발
홍창섭(Chang-Sup Hong),오재윤(Chae-Youn Oh),김학덕(Hak-Duck Kim),이대창(Dae-Chang Lee),송주현(Ju-Hyun Song) 한국자동차공학회 1999 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1999 No.11_2
This paper develops a finite element model for studying occupant behavior of a truck equipped with a driver side airbag. The developed model simulates an occupant behavior using PAM-SAFE in IBM super computer RS/6000. The model is developed based on a sled test. A 50% hybrid dummy I II is used for measuring head and chest accelerations and femur loads. and major injury coefficients such as HIC, CA and femur load. Interior parts of the truck compartment are modeled using rigid bodies and contact type II of PAM-CRASH. In the definition of contact type II, force-deflection relationships of each body is utilized. Airbag cushion is modeled using shell elements. Airbag cover groove is modeled using rivet elements. Airbag tether is modeled as nonlinear bar elements. Airbag model has two vent holes to ventilating the exploded gas. Airbag is folded close to the real airbag folding procedure, and folded cautiously in order not to have initial penetration. A vehicle pulse acquired from 31 mph frontal barrier test is used as input signal for the simulation. The simulation conditions are tuned to the sled test ones. The measured dummy accelerations and major injury coefficients and filmed dummy behavior and airbag inflation process using high speed camera are compared to the simulation results to verity the developed finite element model.
홍창섭,오재윤 한국기계기술학회 2015 한국기계기술학회지 Vol.17 No.4
This paper studies on the effect of kurtosis on fatigue life. A typical vibration test machine uses a normal distribution signal. However, the vibration signal generated in the actual operating environment is a non-normal distribution signal with kurtosis. In this paper, a signal which has the same power spectral density, but has different kurtosis is generated using the Zero Memory Non-Linear(ZMNL) method. The power spectral densities of these two signal will coincide within ±3dB. Fatigue damage spectrum(FDS) computed with a normal distribution signal and FDS computed with a non-normal distribution signal generated using the ZMNL method are compared. FDS computed using the normal distribution signal of kurtosis 3 will show a big difference over the 100Hz with FDS computed using the signal of kurtosis 6. This paper shows through such FDS comparison that a difference in fatigue life prediction may result in if a vibration profile which does not consider kurtosis occurring in the operating environment of a product is used in a vibration test.