• Journal of Welding and Joining
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• 제6권3호
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• pp.43-55
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• 1988

An experimental study was carried out to identify the fatigue fractue behavior of weld zone in generally rolled steel for marine structure. The bending an shear loads were applied simultaneously on the specimens to simulate real load condition for marine structure. The effect of the stress intensity factor under mode I with II loading condition on the initiation and the propagation of a crack were investigated, with particular emphaiss on mode II. When the $K_{II}$ stress intensiy factor in mode II was applied under mode I load condition, the growth behavior of a crack seems to be affected mainly by the anisotropic characteristic of materials. Especially, when the crack was located in and near the weld zone and parallel to th weld line, the propagation behaviour was turned out to be quite different from that of the base metal along the direction transverse to the weld line. In general, the propagation veiocity of the cracks in and near the weld zone was found to be slower that the velocity in base metal.

• 동력기계공학회지
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• 제22권1호
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• pp.25-33
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• 2018

The safety of structure was evaluated by taking into consideration the complex marine environmental conditions of the Lattice boom crane, which is widely used in offshore plants due to less influence by wind. CFX analysis was carried out to take into account the influence of wind speed, and the result was applied as a boundary condition to perform static analysis according to the luffing angles of $28^{\circ}$, $61^{\circ}$, and $80^{\circ}$ in the on board and off board, respectively. In addition, the Lattice Boom Crane is large slender structure, and the possibility of buckling is interpreted under three conditions where the biggest stress occurs. All conditions satisfied the safety requirements of the Classification Regulations. Also, as a result of the buckling analysis, the load less than the critical load was applied so buckling does not occur.

• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.377-389
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• 2017

Tests of the lateral and torsional stability are quite sensitive to the experimental conditions, such as support conditions and loading system. Controlling all of these conditions in a full-size test is a very challenging task. Therefore, in this paper, an experimental measurement method that can control the experimental conditions using a small-scale model was proposed to evaluate the lateral and torsional stability of beams. For this, a loading system was provided to maintain the vertical direction of the load applied to the beam, and a support frame was produced to satisfy the in-plane and out-of-plane support conditions. The experimental method using a small-scale model was applied successively to the lateral and torsional behavior and stability of I-shaped beams. The proposed experimental methods, which effectively accommodate the changes in the geometry and length of the beam, could contribute to further experimental studies regarding the lateral and torsional stability of flexural members.

• Steel and Composite Structures
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• 제47권2호
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• pp.289-296
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• 2023

The failure of a thin-walled tube was studied in this paper based on three failure models. Both proportional and non-proportional loading paths were applied. Proportional loading consisted of combined tension-torsion. Cyclic non-proportional loading was also applied. It was a circular out-of-phase axial-shear stress loading path. The third loading path was a combination of a constant internal pressure and a bending moment. The failure models under study were equivalent plastic strain, modified Mohr-Coulomb (Bai-Wierzbicki) and Tearing parameter models. The elasto-plastic analysis was conducted using J2 criterion and nonlinear kinematic hardening. The return mapping algorithm was employed to numerically solve the plastic flow relations. The effects of the hydrostatic stress on the plastic flow and the stress triaxiality parameter on the failure were discussed. Each failure model under study was utilized to predict failure. The failure loads obtained from each model were compared with each other. The equivalent plastic strain model was independent from the stress triaxiality parameter, and it predicted the highest failure load in the bending problem. The modified Mohr-Coulomb failure model predicted the lowest failure load for the range of the stress triaxiality parameter and Lode's angle.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2022년도 봄 학술논문 발표대회
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• pp.247-248
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• 2022

3D printer-based self-healing capsules have been proposed to heal cracks by enabling various structural designs, repeatable fabrication, and strength analysis of the capsules. The Fusion Deposition Modeling (FDM) method was used to design, analyze, and produce new self-healing capsules that are widely used at low cost. However, PLA extruded from FDM has low interlayer adhesion energy, and thus strength varies depending on the angle of load applied to the laminated layer and the concrete structure, thereby degrading the performance of the self-healing capsule. Therefore, in this paper, the structure of the capsule manufactured by the FDM PLA method has isotropic strength was designed. In addition, the fracture strength in the x, y, and z directions of the load applied through the compression test was analyzed. As a result, it was confirmed that the newly proposed capsule design has an isotropic fracture strength of 1400% in all directions compared to the existing spherical thin-film capsule.

• 드라이브 ㆍ 컨트롤
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• 제19권4호
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• pp.19-28
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• 2022

This paper introduces an automatic steering system for straight traveling capable of being mounted on drivable agricultural machinery which user can handle it such as a tractor, a transplant, etc. The modular automatic steering device proposed in the paper is composed of RTK GNSS, IMU, HMI, hydraulic valve, and wheel sensor. The path generation method of the automatic steering system is obtained from two location information(latitude and longitude on each point) measured by GNSS in advance. From HMI, a straight path(AB line) can be created by connecting latitude and longitude on each point and the device makes the machine able to follow the path. During traveling along the reference path, it acquires the real time position data every sample time(0.1s), compares the reference with them and calculates the lateral deviation. The values of deviation are used to control the steering angle of the machine using hydraulic valve mounted on the axle of front wheel. In this paper, Pure Pursuit algorithm is applied used in autonomous vehicles frequently. For the analysis of traveling characteristics, field tests were executed about these conditions: velocity of 2, 3, 4km/h which is applied to general agricultural work and ground surface of solid(asphalt) and weak condition(soil) such as farmland. In the case of weak ground state, two experiments were executed about no-load(without work) and load(with work such as plowing). The maximum average deviations were presented 2.44cm, 7.32cm, and 11.34cm during traveling on three ground conditions : asphalt, soil without load and with load(plowing).

• 한국운동역학회지
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• 제34권1호
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• pp.25-33
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• 2024

Objective: The purpose of this study was to compare the lower extremity muscle activity and knee joint load according to movement speed conditions during the barbell back squat. Method: Nine males with resistance training experience participated in this study. Participants performed the barbell back squat in three conditions (Standard, Fast, and Slow) differing movement speed. During the barbell back squat, muscle activity of the rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris long head (BFL), semitendinosus (ST), gluteus maximus (GM), gastrocnemius (GCN), and tibialis anterior (TA) was collected using an 8 channel wireless EMG system. The peak flexion angle of the lower extremity joints and the peak resultant joint force in each direction of the knee joint were calculated using eight motion capture cameras and ground reaction force plates. This study was to used the Friedman test and the Wilcoxon signed rank test, to compare lower extremity muscle activity and peak resultant joint force at knee joint according to movement speed conditions during the barbell back squat, and the statistical significance level was set at .01. Results: In the downward phase of the barbell back squat, the RF and TA showed the higher muscle activity in the fast condition, and in the upward phase, RF, VL, VM, BFL, ST, GM, and TA showed the higher muscle activity in the fast condition. As a results, analyzing of the load on the knee joint, in the downward phase, and in the upward phase, the higher peak compressive force of the knee joint was showed in the fast condition. Conclusion: The barbell back squat with fast movement speed was more effective due to increased muscle activity of lower extremity, but one must be careful of knee joint injuries because the load on the knee joint may increase during the barbell back squat with fast movement speed.

• Composites Research
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• 제16권6호
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• pp.23-32
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• 2003

복합 신소재의 건설 분야 적용은 확대되고 있는 추세이고, 높은 비강도 비를 지닌 복합 신소재 교량 바닥 판의 개발은 국내외에서 활발히 진행되고 있다. 본 연구의 목적은 이동 하중을 받는 비등방성 복합재료 적층판의 동적 응답을 정식화하고, 유한요소법을 사용하여 적층에 따른 동적거동 특성을 분석하는 것이다. 수치 해석 모델에 대해서 이동하중의 속도를 증가시키면서 동적 확대 계수를 계산하였다. 또한 적층형식 및 순서, 섬유 보강 각도 등의 변화에 따른 동적 거동 특성을 분석하였다. 본 연구 프로그램의 타당성을 확보하기 위해 휨과 자유 진동 해석에 관한 기존 문헌 결과와 비교하여 검증하였다. 또한 이동 하중에 의한 동적 해석에 대해 모우드 중첩법과 Newmark 직접 적분법을 사용하였다. 이러한 이동 하중과 적층 수, 적층 순서 및 섬유 보강 각도에 따른 수치 해석 결과는 완전 복합 신소재 교량 바닥 판을 개발하는데 있어서 중요한 기초 자료로 제시될 수 있을 것이다.

• 대한기계학회논문집A
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• 제24권1호
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• pp.69-78
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• 2000

The one-parameter singular expression for stresses and displacements near a crack tip has been widely thought to be sufficiently accurate over a reasonable re ion for any geometry and loading conditions. In many cases, however subsequent terms of the series expansion are quantitatively significant, and so we now consider the evaluation of such terms and their effect on the predicted crack growth direction. For this purpose the problem of a cracked orthotropic plate subjected to a biaxial load is analysed. It is assumed that the material is ideal homogeneous anisotropic. BY considering the effect of the load applied parallel to the plane of the crack, the distribution of stresses and displacements at the crack tip is reanalyzed. In order to determine values for the angle of initial crack extension we employ the normal stress ratio criterion.

• 대한기계학회논문집A
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• 제33권4호
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• pp.360-365
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• 2009

In the manufacture of CFRP(Carbon Fiber Reinforced Polymer Composite) composite structures, various independent components join by bolts and pins. Holes for bolts and pins have an effect on the failure strength of such structures, because those act as notches in structures. The failure characteristic of such structures are different from those of plain plate subject to remote load. In this paper, tensile properties of woven CFRP composite plates with laminates of $0^{\circ}$, $30^{\circ}$ and $45^{\circ}$ were obtained according to ASTM D 3039. By using obtained tensile failure strength and Tan-Cheng failure criterion, tensile failure strength of CFRP laminate with arbitrary fiber angle were evaluated. Also, the degradation of tensile properties by center hole(${\phi}10mm$) with a remote load was evaluated and the failure strengths were applied to Tan's failure criterion, similarly.