• 한국안전학회지
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• 제31권1호
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• pp.19-24
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• 2016

Rubber parts are widely used in many applications such as dampers, shock absorbers, and seals used in railway and automotive industries. Much research has thus far been conducted on property estimation and life prediction of rubber parts. To predict the service life of rubber parts at room temperature, most prior work adopts the well-known Arrhenius model that needs the accelerated life test in high-temperature conditions. However, they may not reflect the actual conditions of use that rubber parts are usually used under a specific strain condition during long period of time. In this context, we propose a method for the life prediction of rubber parts in actual conditions of use. The proposed method is based on the accelerated life test using stress relaxation during which three relatively high elongation percentages (100%, 200%, and 300%) are applied to the rubber specimens. Rubber specimens were prepared in accordance with KS M 6518 standard and three stress relaxation testers were fabricated for actual experiments. Finally, a inverse power model for life prediction was derived from experimental results. The predicted life was compared with the actual test life for validation.

• 감성과학
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• 제4권2호
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• pp.33-38
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• 2001

본 연구는 가상현실을 이용하여 교통사고 후 경험하게 되는 불안감 및 공포감과 같은 심리적인 후유장애에 대한 치료 프로그램을 개발하기 위한 예비연구로 수행되었다. 가상현실을 통한 교통사고 후유장애 프로그램의 핵심내용이 되는 운전주행 시나리오의 효과를 검증하고, 이완훈련 등의 불안감소 훈련의 효과를 피험자를 통해 검증해 보았다. 총 8명의 피험자(정상인 7명, 교통사고 환자 1명)를 대상으로 세 가지 주행상황 시나리오를 제시하고, 이후 이완훈련을 실시하였다. 그 결과 이완훈련 후 유의미한 불안감소 효과가 나타났다. 하지만 각각의 주행상황에 따라서 불안이 증가되는 경향성은 나타났으나 통계적으로 유의미한 수준에 이르지는 못하였다. 이를 종합하여 볼 때, 주로 정상인을 대상으로 한 연구임에도 불안유발 경향성이 나타난 점은 고무적이나 교통사고자를 대상으로 한 경험적인 증명이 필요하며, 가상현실을 이용한 이완훈련은 효과적인 것으로 판명되었다.

• 한국유변학회:학술대회논문집
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• 한국유변학회 2006년도 춘계 학술발표회 논문집
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• pp.119-122
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• 2006

• Structural Engineering and Mechanics
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• 제2권4호
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• pp.383-393
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• 1994

The residual stress distribution in a unidirectional graphite/epoxy laminate induced during the fabrication process is investigated at the microstress level within the scope of linear viscoelasticity. To estimate the residual stresses, the fabrication process is divided into polymerization phase and cool-down phase, and strength of materials approach is employed. Large residual stresses are not generated during polymerization phase because the relaxation modulus is relatively small due to the relaxation ability at this temperature level. The residual stresses increase remarkably during cool-down process. The magnitude of final residual stress is about 80% of the ultimate strength of the matrix material at room temperature. This suggests that the residual stress can have a significant effect on the performance of composite structure.

• Food Science and Biotechnology
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• 제18권4호
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• pp.1013-1018
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• 2009

Several rheological terms were introduced to estimate the properties of cooked noodles with different starch content using tensile tests. Ring-shaped specimens were prepared by connecting both ends of the noodle strip before cooking. Hencky strain and rate, as well as true stress were applied in constant deformation tests. The elastic region on the curves of strain vs. stress was not clearly identified. Strain hardening in the subsequent plastic region was more prominent in low-starch noodles. Elongational viscosities at lower strain rates were used to differentiate noodles with different starch content, representing the dominant effect of protein content in the range of lower strain rates. In stress relaxation tests, the reciprocal of Peleg's constant $K_1$ (initial decay rate) and $K_2$ (asymptotic level) increased and decreased respectively, with an increase in starch content. This indicated that addition of starch contributed to the noodles becoming viscous liquid rather than elastic solid.

• 한국안전학회지
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• 제22권2호
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• pp.22-27
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• 2007

To assess a creep life of elevated temperature plant components, inspections and analysis are usually focused on the critical locations. In this study, stress analysis of a weld region in branch part of Y-piece was conducted by using a three-dimensional finite element analysis. The stresses at the inner and outer surface in the weld part were estimated by using elastic and elastic-creep analysis. For the elastic-creep analysis two kinds of elastic-creep analysis was conducted. The one was assumed that base and weld material properties were same and the other was that material properties were different between base and weld metal. The material properties of base and weld metal were used from reference data. The results showed the stress relaxation level and its location. The result stresses are also compared with elastic stresses.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.95-100
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• 2004

An analysis using FEM simulation was conducted to predict residual stresses and birefringence in simple compressed cylindrical glass as a preliminary part of the optimum design determination of optical lenses. The FEM simulation with the Maxwell viscoelastic constitutive model was used to predict thermal induced residual stresses and birefringence during the compression test considering stress relaxation. Also the linear photoelastic theory was introduced to calculate birefringence from the residual stress state. The simulation results were in good agreement with deformation and birefringence distribution in the existing experimental result.

• 한국정밀공학회지
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• 제20권2호
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• pp.129-135
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• 2003

The fatigue life of a structure can be enhanced by improving the mechanical and metallurgical aspects to strengthen the material around regions of high stress. Coldworking of holes in structures is one of the mechanical methods of strengthening material. The material for this research is A12024-T351 which is used for the primary member or aircraft. Specimens were tested under constant amplitude loading and residual stresses measured by X-ray diffraction technique. Fatigue crack initiation life was evaluated by a strain-life equation which was considered initial residual stress and residual stress relaxation exponent as a function of the strain amplitude. The predictions on fatigue crack initiation life were compared with experimental results. A wide range of discrepancies between them was found.

• 소성∙가공
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• 제5권4호
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• pp.327-336
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• 1996

The effect of dynamic strain aging on high temperature deformation behaviour of the A-Mg alloy was investigated by strain rate change tests and stress relaxation tests between 20$0^{\circ}C$and 50$0^{\circ}C$. Yield point, short stress transient and periodic discontinuities on the stress-strain curve were considered as an evidence of the effect of dynamic strain aging. With this criterion two distinct strain rate-temperature regimes could be manifested. Dynamic strain aging was considered to be effective in the high temperature-low strain rate regime, whereas dynamic recovery was a dominant deformation mechanism in the low temperature-high strain rate regime. It was found that dynamic strain aging in the high temperature deformation was governed by the mechcanism of diffusion-controlled, viscous dislocation movement.

• 한국세라믹학회지
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• 제43권8호
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• pp.479-485
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• 2006

The residual stress changes on thermo-mechanical loading in the interface region of the Thermal Barrier Coating (TBC)/Thermally Grown Oxide (TGO)/Bond Coat (BC) were calculated on the TBC-coated superalloys using a Finite Element Method (FEM). It was found that the residual stress of the interface boundary was dependent upon mainly the oxide formation and the swelling rate of the oxide by creep relaxation. During an oxide swelling, the relaxation of residual stress which is due to creep deformation increased the TBC's life. In the case of the fine grain size of TGO scale, the TBC stresses piled up by oxide swelling could be relaxed by diffusional creep effect of TGO.