• 대한의용생체공학회:의공학회지
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• 제21권3호
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• pp.295-301
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• 2000

뼈의 성장에 미치는 많은 요소들 중에서 implant의 상대적인 미세운동(relative micromotion)은 뼈의 implant와의 접합을 방해하는 것으로 알려져 왔다. 그런데 이러한 상대적인 운동 및 spinal stability에 직접적으로 영향을 주는 하중조건, spinal material의 물성치, spinal geometry 및 뼈와 implant의 접촉면에서의 마찰계수를 고려하기 위하여, 하나의 titanium interbody cage 가 삽입된 human lumbar segments (L4-L5)의 유한요소 모델이 개발되었다. 이러한 유한요소 모델의 해석을 통하여 상대적인 미세운동, Posterior의 수직적인 변위, von Mises 응력 및 마찰력이 예측되었다. Cancellous bone. annulus fibers 및 ligaments의 기계적인 물성치의 감소 또는 접촉면에서의 마찰계수의 감소는 상대적인 미세운동 (relative micromotion or slip distance)을 증가 시켰다. 접촉면에서의 normal force는 뼈의 밀도 (cancellous bone density) 가 감소하거나 접촉마찰계수가 증가하면 감소했다. 특히 하중조건에 있어서, compressive preload에 대한 torsion의 추가는 접촉면의 anterior부위에서 상대적인 미세운동을 증가 시켰다. 하지만 디스크면적이 증가할수록 상대적인 미세운동은 감소했다. 결론적으로, 접촉면의 기계공학적 거동 (Relative micromotion, stress response, posterior axial displacement and contact normal force)은 접촉면의 마찰계수 뼈의 밀도, 하중조건 및 노화에 따른 형상/물성의 변화에 매우 민감함을 보이고있다.

• 대한기계학회논문집
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• 제15권6호
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• pp.1831-1838
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• 1991

본 연구에서는 와핑과 두 단면중심의 불일치에 의해 발생하는 기하중심의 이 동을 고려한 등매개변수보요소를 개발하여 스프링단면의 응력해석을 수행하고 그 결과 를 다음과 같이 검증할 것이다.우선 본 연구에 사용된 보요소가 이 두 효과를 효과 적으로 표현하고 있는지를 확인하기 위해서 간단한 비틀림실험과 비교할 것이다. 또 한 2차원문제에 대해서 입체요소를 이용한 결과와 비교하고, 원통형 스프링모델의 해 석결과를 Nagaya의 해석결과와 비교함으로써 실제 스프링해석에 효과적으로 적용될 수 있음을 보일 것이다.

• 한국군사과학기술학회지
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• 제18권5호
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• pp.485-491
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• 2015

In this study, the experimental and analytical investigation on structural integrity evaluation of spline shaft of self propelled artillery' generator were carried out. For this work, macro and microstructure fractography of spline shaft were observed. According to the results of the structure analysis and simulation, the shaft was redesigned and optimized. To improve the stiffness and shear stress, the material was changed from the SNCM220 to SNCM439 and surface roughness and protective coating treatment are changed to increase the stress relaxation, respectively. From the result of the torsion test of shaft and accelerated life test of generator, the shaft of a SNCM439 with heat-treatment(Q/T) and electroless nickel plating was superior quality reliability and durability than the others. Therefore, modeling and simulation corresponded well with the experimental result and structural safety was confirmed by generator performing.

• 한국기계가공학회지
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• 제12권4호
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• pp.69-74
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• 2013

According to the axial torsion applied at power transmission and the vibration from the roughness of road surface, this paper analyzes the stresses on two kinds of universal joint model. As stress and deformation at model 2 becomes smaller than model 1 on structural analysis, model 2 is more stabilized than model 1. The natural frequencies at model 1 and 2 are 7,040 and 9,540 Hz respectively. As the natural frequency range of model 2 becomes higher than model 1, model 2 becomes safer than model 1. Critical frequencies at these models are calculated through harmonic response analyses. On critical frequencies at model 1 and 2, the stress at model 2 becomes lower than 2 times as much as model 1 and the deformation at model 2 becomes lower than 4 times as much as model 1. Model 2 on durability is thought to become better than model 1. This study result is applied with the design of safe universal joint and it can be useful to improve the durability by predicting prevention against the deformation due to its vibration.

• 소성∙가공
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• 제7권2호
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• pp.168-176
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• 1998

Hot workability of the AA5083 alloy ws investigated by torsion test at temperature ranges of $350{\sim}520^{\circ}C$ and strain rates of 0.5, 1.0, and 3.0/sec. The flow stress and hot ductility of the AA5083 alloy as a function of deformation variables such as temperature and train rate were studied. The microstructural evolution of the AA5083 alloy was studied in relation to Zener-Hollomon parameter (Z=exp( /RT) Also the hot restoration mechanism of the AA5083 alloy was small when Z val-ues were higher than $1.73{\times}1016/sec(370^{\circ}C,\;0.5/sec)$ In addition the difference microstructures during hot deformation. It was found that the increase of flow curves and deformed microstructures during hot deformation. It was found that the increase of flow stress of the AA5083 alloy was small when Z val-ues were higher than $1.73{\times}1016/sec(370^{\circ}C.\;0.5/sec)$. However under the low Z values less than $1.73{\times}1016/sec(370^{\circ}C,\;0.5/sec)$ the flow stress increase with increasing the Z values. The large dispersoid particles in the matrix grain decreased the flow strain of the AA5083 alloy because it caused the stress concentration during hot deformation.

• 소성∙가공
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• 제7권2호
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• pp.158-167
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• 1998

Hot restoration mechanism flow stress and stain of the Al2024 composites reinforced with 1,8,15,36, and $44{\mu}m\;SiC_p$(10 vol. %) were studied by hot torsion tests. The hot restoration mechanism of all the composites was found to be dynamic recrystallization(DRX) at $320^{\circ}C$ while that of the composites reinforced with 1 and $8{\mu}m\;SiC_p$ was found to be dynamic recovery(DRX) at $480^{\circ}C$. It was found that the Al2024 composite with $15{\mu}m\;SiC_p$ showed the highest flow stress(${\sim}$223 MPa) at $320^{\circ}C$ under a strain rate of 1.0/sec. Also the highest flow strain of the composites was obtained at $430^{\circ}C$. The com-posites reinforced with 1 and $8{\mu}m\;SiC_p$ showed lower flow stress and higher flow strain at $480^{\circ}C$ than those of the composites reinforced with 15, 36, and $44\;{\mu}m\;SiC_p$ These result were discussed in relation to the transition of the hot restoration mechanism. $DRX{\leftrightarrow}DRV$. The dependence of flow stress on strain rate and temperature was attempted to fit with the hyperbolic sine equation ($\dot{\varepsilon}=A[sinh({\alpha}{\cdot}{\sigma}_p]^n$ exp(-Q/RT)and Zener-Hollomon parameter($Z=\;\dot{\varepsilon}\;exp(Q/RT))$.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1446-1455
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• 2000

Fatigue crack initiation and propagation behavior under cyclic biaxial loading has been investigated using thin-walled tubular specimen with a hole. Two types of biaxial loading system, i.e. cyclic tensile loading with super-imposed static torsional load and cyclic torsional loading with superimposed static tensile load, with various values of the biaxial loading ratio, $\tau$ s/ $\sigma$ max (or $\tau$ max/ $\sigma$s) were employed. Fatigue tests show that fatigue crack near the hole initiates and propagates at 900 and 450 direction to the longitudinal direction of the specimen under cyclic tensile and torsion loading with static biaxial stress, respectively, and the static biaxial stress doesn't have any great influence on fatigue crack initiation and growth direction. Stress analysis near the hole of the specimen shows that the crack around the hole initiates along the plane of maximum tangential stress range. Fatigue crack growth rates were evaluated as functions of equivalent stress intensity factor range, strain energy density factor range and crack tip opening displacement vector, respectively. It is shown that the biaxial mode fatigue crack growth rates can be relatively consistently predicted with these cyclic parameters.

• 한국산학기술학회논문지
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• 제14권1호
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• pp.57-62
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• 2013

카트 차체에는 현가장치와 차동장치가 존재하지 않으므로 카트주행 중 발생하는 프레임의 변형은 탄성변형으로 인한 주행성능과 프레임의 피로수명에 영향을 미친다. 선회주행 시 비틀림 변형에 의한 카트의 거동은 이 두 가지 변형에 결정적 원인을 제공한다. 이러한 곡선구간에서 카트의 동적 거동을 분석하기 위하여 GPS를 이용하여 차량의 궤적을 추적하고 카트 프레임 강에 작용하는 비틀림 응력을 측정하였다. 레저와 레이싱 카트 프레임의 기계적 성질을 파악하기 위해 재질 분석과 인장시험을 실시하여 각 프레임의 재료 특성을 분석하였다. 비틀림 응력집중과 프레임 비틀림은 프레임 해석을 통해 조사되었다. 또한 주행 분석 장치를 이용하여 레저와 레이싱 카트를 각 조건별로 실차실험을 수행하였고, 이를 통해 곡선구간에서 카트의 주행거동을 분석하였다. 선회주행 시 차량에 원심력에 의한 하중이동의 현상이 발생했으며, 이로 인해 카트 프레임 강에 비틀림 응력이 발생하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 봄 학술발표회 논문집
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• pp.177-184
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• 2004

Orthotropic steel deck bridge has much advantages such as the light deadweight, so the construction of orthotropic steel deck is profitable for the long-span bridges Although the system has a lot of merits, it happens some damages by the traffic density and the fatigue cracks of welding. The cross-connection of longitudinal rib and transversal rib is one of the weakest at the fatigue. The secondary stresses which are from the out-plane deformation of transversal rib and the torsion of longitudinal rib make the topical stress concentration phenomenon. The Bulkhead Plate for prevention of this stress concentration phenomenon was applied by changing the orthotropic steel deck of Williamsburg bridge in USA. But, it is principle that a Bulkhead Plate is not established in the domestic design standard. Therefore, it is estimated that the study for installation of Bulkhead Plate is needed. This study with considering these circumstances proves efficiency of Bulkhead Plate and will be presented optimal design details through finite element analysis according to change the geometrical of Bulkhead Plate and the cross-connection area of longitudinal and transversal rib

• Structural Engineering and Mechanics
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• 제44권2호
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• pp.197-217
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• 2012

Detailed analysis of internal forces of exterior beam-column joints of RC frames under seismic action is reported in this paper. A formula is derived for calculating the average joint shear from the column shears, and a formula is proposed to estimate torque in eccentric joints induced by seismic action. Average joint shear stress and strain are defined consistently for exterior joints, which can be used to establish joint shear constitutive relationship. Numerical results of shear, bending moment and torque in joints induced by seismic action are presented for a pair of concentric and eccentric exterior connections extracted from a seismically designed RC frame, and two sections located at the levels of beam bottom and top reinforcement, respectively, are identified as the critical joint sections for evaluating seismic joint behavior. A simplified analysis of the effects of joint shear and torque on the flexural strengths of the critical joint sections is made for the two connections extracted from the frame, and the results indicate that joint shear and torque induced by a strong earthquake may lead to "joint-hinging" mechanism of seismically designed RC frames.