• Journal of the KSME
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• v.32 no.6
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• pp.536-553
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• 1992

하중 종류 중에서 가장 기본적인 하중 중의 하나인 순수 전단력과 순수 굽힘 모멘트를 발생시 키고자 할 때는 아래와 같은 장치를 사용하는 것이 좋다. 1) 등방성체나 이방성체의 횡 전단계수 (G$_{12}$)와 횡 응력 프린지치(f$_{12}$) 등을 측정 하고자 할 때, 또는 모드 II (mode II)상태의 파괴역학을 연구하고자 할 때는 그림 1, 그림 2, 그림 3 그리고 그림 4 등에 제시된 것 중에서 적당한 것을 사용할 수 있다. 그러나 순수 전단 력이 발생되는 면적이 크고, 순수 전단력을 정확하고 균일하게 발생시키고자 할 때, 각 재료의 전단 물성치(shear properties) 측정, 모드II(mode II) 상태의 파괴역학을 연구하고자 할 때는 본 연구자가 고안한 H.I.S.T. 장치를 이용하면 편리하다. 2) 직선 보에 순수 굽힘 모멘트를 균일하고 정확하게 가하고자 할 대는 N.B.M.장치를 사용하는 것이 좋다. 또 N.B.M. 장치는 어느 보의 장치보다도 곡선보나 변형이 큰 보에도 더 정확하고 균일하게 순수 굽힘 모멘트를 발생시킬 수 있다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.7
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• pp.505-511
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• 2020

The circular composite tubes have been used as a main spar of HALE-UAV(High Altitude Long Endurance-Unmanned Air Vehicle). In this paper, an analytical model is presented for the prediction of the failure load of unsymmetrically stiffened circular spar using a modified Brazier approach. This model was used to predict the moment carrying capacity of the unsymmetrically stiffened circular spar. From the results, we can know that a stiffened cap placed in the top sector of a spar increased the bending capabilities. Four point bending tests were conducted to estimate the effect of the cap on the failure load and compared with the proposed model. And numerical simulations were performed to analyze the behavior of stiffened circular spar. Comparisons of the results from the proposed model with those from experiments and numerical modes show good correlation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.4
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• pp.761-768
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• 1990

본 연구에서는 4-점 굽힘시험 장치를 이용하여 구멍의 표면에서 응력구배를 발생시켰을 때 (구멍의 깊이 방향으로는 응력구배가 없음), 구멍을 뚫기전 표면의 응 력구배를 고려하여 산정한 하중상태와 구멍을 뚫은 후 이완되는 잔류응력을 비교하였 다. 또한 잔류응력 측정시 구멍의 진원도에 대하여 실험적으로 연구하였으며, 구멍 직경의 측정오차가 잔류응력 측정에 미치는 영향을 분석하였다. 연구결과 4-점 굽힘 시험시 하중상태는 응력구배를 고려하여 계측되어야 하며, 응력구배장에서의 잔류응력 을 로젯트 게이지 중심에 존재하는 균일응력으로 나타낼 수 있다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.3
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• pp.427-431
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• 1986

3점 굽힘 시험편, 중앙균열 인장 시험편, 콤팩트 인장 시험편에 대한 J적분식을 하나의 일반화된 형태로 유도한다. 이 일반식은 Eftis와 Liebowitz에 의해 제안된 하중과 하중점 변위 사이의 관계와 Sumpter에 의한 탄성과 소성성분 J적분의 중첩개념을 이용함으로써 유도된다. 일반식에 포함된 .eta.계수를 위 3가지 시험편에 대해서 결정한다. 위 3가지 시험편에 대한 J적분의 최종식은 하중과 하중점 변위곡선 아래의 면적을 측정하지 않아도 되는 형태로 나타난다. 본 연구의 결과식은 Landes등에 의한 실험치와 비교하여 매우 잘 일치함을 보인다.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.299-304
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• 2008

This paper presents plastic limit loads of piping branch junctions with local wall thinning under combined pressure and in-plane bending, based on systematic three-dimensional finite element limit analyses using elastic-perfectly plastic materials. An ideal branch junction without weld or reinforcement around the intersection is considered with two locations of wall thinning; one in the run pipe, and the other in the branch pipe. Based on FE results, effects of thinning geometries on plastic limit moments are quantified and simple approximations of plastic limit loads are proposed.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.4 s.97
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• pp.178-188
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• 1999

충격하중을 받는 시험편 높이의 1/4 길이의 notch를 가진 3점 굽힘시험편들의 기계적 거동에 관한 컴퓨터 시뮬레이션을 하고 이 시뮬레이션에 대한 실험적 검증도 하여 그 타당성을 입증하였다. 시험편들의 양쪽 가장자리(지지점)에서 작용되어지는 여러 가지의 하중속도에 대한 경우들과 탄소성 von Mises 재질인 모델들을 시뮬레이션에 포함시켰으며 이들에 대한 결과들을 간극 개구 변위, 반력, 크랙선단 개구 변위 및 변형률등이 속도에 의존되는 재질(점소성 재질)에 대한 시뮬레이션 결과와 비교하였다. 또한 여러가지의 동적 하중을 받는 상황하에서의 안정성이 본 연구의 시뮬레이션을 통하여 비교되었으며 그 차이점들이 규명되었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.529-535
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• 2013

A new thin sandwich panel composed of an aluminum expanded metal core adhesively jointed with stainless steel face sheets is introduced, and its mechanical behavior under three-point bending is investigated. The strength and stiffness are analyzed theoretically, and the press-formability and strength enhancement are evaluated experimentally. The specimens with the specific configurations exhibit face yielding well before face-core separation, which means that the sandwich panel can be formed by a press without failure. The measured load levels corresponding to the face yielding and the face-core separation agree fairly well with the theoretical estimations. For a given weight, the sandwich panel is superior to a solid panel in terms of strength, stiffness, and press-formability.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1163-1169
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• 2014

In this study, a fatigue assessment method for vehicle suspension systems having welded geometries was established under a bending loading condition. For the fatigue life estimation of the actual product's welded joints made of different steels, bending fatigue tests were performed on welded specimens with a simplified shape for obtaining the moment-fatigue-life plot. Further, geometry modeling of the simplified welded specimens was conducted. Results of finite element analysis were used to obtain the stress-fatigue-life plot. The analysis results were also used to calculate the stress concentration factors for notch-factor-based fatigue life estimation. The test results were compared with results of the general notch-factor-based fatigue life estimation for improving fatigue assessment. As a result, it was concluded that both the welded fatigue tests and the notch-factor-based fatigue life estimation are necessary for accurate fatigue assessment.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.1 s.38
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• pp.63-72
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• 2006

Mobile products, such as cellular phones, PDA and notebook, are subjected to many different mechanical loads, which include bending, twisting, impact shock and vibration. In this study, a cyclic bending test of the BGA package was performed to evaluate the fatigue life. Special bending tester, which was suitable for electronic package, was developed using an electromagnetic actuator. A nonlinear finite element model was used to simulate the mechanical bending deformation of solder joint in BGA packages. The fatigue life of lead-free (95.5Sn4.0Ag0.5Cu) solder joints was compared with that of lead-contained (63Sn37Pb). When the applied load to the specimen is small, the lead-free solder has longer fatigue life than lead-contained solder. The fatigue crack is initialized at the exterior solder joints and is propagated into the inner solder joints.

• Composites Research
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• v.29 no.6
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• pp.369-374
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• 2016

In this study, a structural optimal design of 10 MW composite blade was performed using bend-twist coupled(BTC) design concept. Bend-twist coupling of blade means the coupling behavior between the bending and torsional deflections due to the composite lamina with fiber angle biased from the blade longitudinal axis. This can potentially improve the overall performance of composite blade and reduce the dynamic loading. Parametric studies on layup angle, thickness and area of off-axis carbon UD were conducted to find the optimum coupling effect with weight reduction. Comparing the results of fatigue load analysis between conventional model and BTC applied model, the damage equivalent load(DEL) of blade root area were decreased about 3% in BTC model. To verify the BTC effect experimentally, a 1:29 scaled model was fabricated and the torsion at the tip under deflection behavior of blade stiffener model was measured by static load test.