• Proceedings of the Korean Fiber Society Conference
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• 2002.04a
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• pp.63-68
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• 2002

크림프를 가지는 섬유 캔틸레버의 대변형을 해석함에 있어서 크림프를 반원모양의 교대 접합으로, 섬유를 선형 탄성 보로 간주하여 해를 구하였고 구하여진 해를 단순화하여 기존의 1원소 선형 보의 변형[1], 1원소 선형 보의 끝단 회전 하중시의 변형[2], 1원소 원형 굽힘보의 변형[3]의 결과와 비교함으로써 해의 정확성을 확인하였고 본 연구의 일반해의 가장 단순한 경우인 2원소 원형 굽힘보의 처짐의 해를 구하였다. (중략)

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.04b
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• pp.449-453
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• 1994

공작기계의 가공정밀도는 공구와 공작물간의 상대변위 크기로서 평가되는데, 이 상대변위는 가공중에 발생 하는 절삭력이 공구-척-주축-기계구조물-안내면-가공테이블-공작물로 이어지는 하중전달 폐곡선을 흐르면서 경로상의 정적, 동적 취약부의 주된 영향을 받아 생기거나 각 요소부품의 변형이 누적되어 생겨난다. 본 연구에서는 주축의 취약부를 규명하기 위하여 정적으로는 정적 처짐곡선을 이용하고, 동적으로는 진동모우드의 굽힘곡선을 이용하여 주축선단의 처짐에 가장 영향을 많이주는 부위를 파악하였다. 취약부의 개선방법으로는 주축지름을 변화시켜 주축선단 근처에서 굽힘이 집중되지 않도록 유도하였다. 그리고 구조개선의 효과를 확인 하기 위해서 기존 주축시스템과 개선 주축시스템의 정적, 동적 특성변화를 비교하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.8
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• pp.3638-3643
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• 2013

These days, workers in a construction site conduct a rebar bending process with a machine. This bending process has some problems such as long processing time and bad quality of the rebar. In order to manufacture a rebar having precision and machinability, we should study on Spring-back phenomenon. This phenomenon affects a shape of rebar after unloading due to restoration ability of material and it is influenced by bending angle, bending radius and a rebar diameter. The change of spring-back ratio according to the change of the parameters are analyzed by FEM. Consequently, Spring-back increases around $0.1^{\circ}$ as bending angle increases $10^{\circ}$. and it also increases around $0.6^{\circ}$ as diameter of rebar increases from ${\varphi}$ 10mm to ${\varphi}$ 16mm. while we can confirm that it decreases around $0.2^{\circ}$ as bending angle increases $10^{\circ}$.

• Composites Research
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• v.17 no.6
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• pp.22-27
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• 2004

The objective of this work is to design Surface Antenna Structure (SAS) and investigate fatigue behavior of SAS that is asymmetric sandwich structure. This term, SAS, indicates that structural surface becomes antenna. Constituent materials are selected considering electrical properties, dielectric constant and tangent loss as well as mechanical properties. For the antenna performance, SSSFIP elements inserted into structural layers were designed fur satellite communication at a resonant frequency of 12.5 GHz and final demonstration article was $16{\;}{\tiems}{\;}8$ array antenna. From electrical measurements, it was shown that antenna performances were in good agreement with design requirements. In cyclic 4-point bending, flexure behavior was investigated by static and fatigue test. Fatigue life curve of SAS was obtained. The fatigue load was determined experimentally at a 0.75 (1.875kN) load level, Experimental results were compared with single load level fatigue life prediction equations (SFLPE) and in good agreement with SFLPE. SAS concept is the first serious attempt at integration fur both antenna and composite engineers and promises innovative future communication technology.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.8
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• pp.703-709
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• 2017

Creep analysis takes much more time than elastic or elastic-plastic analysis. In this study, we conducted elastic and elastic-plastic analysis and compared the results with creep analysis results. In the elastic analysis, we used primary stress, which can be classified by the $M{\alpha}-tangent$ method and stress intensities recommended in the ASME code. In the elastic-plastic analysis, we calculated the parameters recommended in the R5 code. For the FE models, a bending load, uniaxial load, and biaxial load were applied to the cross shaped welded plate, and a bending load and internal pressure were applied to the elbow pipe. To investigate the element size sensitivity, we conducted FE analysis for various element sizes for the cases where bending load was applied to the cross shaped welded plate. There was no significant difference between the creep stress and the alternative methods; however, in the $M{\alpha}-tangent$ method, the results were affected by the element size.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.687-694
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• 2019

A circular composite spar in the wing of ultra-light aircraft is subjected to both bending moment and transverse shear loads. However, the beam being used in the aircraft may be inefficient because the design would not take into account the characteristics of the circular tube that supports the bending moment in top and bottom arc parts and the transverse load in left and right ones. Therefore, it is necessary to efficiently fabricate the circular tube beam by properly selecting the stacking sequences or the laminated composite structure. In order to increase both bending and transverse shear strengths of the beams, in this study, a cross-section of circular tube is divided into four arcs: top, bottom, left and right ones. The commercial program, MSC/NASTRAN is used to calculate vertical displacement and the normal and shear strains with variation of parameters such as division angle of arc and fiber orientation. Based on the results, the effective parameters for the new circular composite beam are presented to increase its bending and shear strengths.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.2
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• pp.35-40
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• 2011

We have studied the impact and bending characteristics of a dual band antenna (1.575, 2.645 GHz) with composite sandwich construction. Mechanical performance of the antenna can be improved by reinforcing the antenna by sandwiching the planar antenna with layers of carbon fiber-reinforced plastic(CFRP) and glass fiber-reinforced plastic(GFRP) using an adhesive film. According to the ASTM D7137, ASTM C393 and MIL-STD401B, impact and bending test were performed and the S-parameters and gains of the antenna were measured in order to verify electrical and mechanical performance. The maximum contact load and the bending load of the antenna are 4 kN and 400 N and gains of the antenna are 6 dBi and 4.6 dBi in the GPS and DMB bands, respectively. The proposed antenna structure can be applied to surfaces of vehicles.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.12
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• pp.1013-1020
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• 2017

In this study, the failure prediction of composite laminates under flexural loading is investigated. A FEA(finite element analysis) using 2D strain-based interactive failure theory. A pregressive failure analysis was applied to FEA for stiffness degradation with failure mode each layer. A three-point bending test based on the ASTM D790 are performed for cross-ply $[0/90]_8$ and quasi-isotropic $[0/{\pm}45/90]_{2s}$ laminated composites. The accuracy of the applied failure theory is verified with the experimental results and other failure criteria such as maximum strain, maximum stress and Tsai-Wu theories.

• Composites Research
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• v.30 no.6
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• pp.331-337
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• 2017

The composite lattice structures have advantages of high specific stiffness and strength and are mainly applied to the structures of launch vehicles that carry the compressive load. However, since these structures are manufactured by filament winding technology, there are some defects and voids found in the knots. For these reasons, the stiffness and strength of the lattice structures have to be compared with finite element model for predicting design load. But, the full scale test is difficult because time and space are limited and the shape of structure is complex, and hence the simple and reliable test methods for examination of stiffness are needed. In this paper, subelements of composite lattice structures were prepared and compressive and bending test were conducted for examination of stiffness of helical and hoop rib. Test methods for subelements of composite lattice structures that has curved and twisted shape were supposed and compared with finite element analysis results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.107-115
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• 2002

A parametric study has been conducted to evaluate the effects of finite element modeling methods on the internal loads, sizing and the weight of the multi-spar aircraft wing structures. The wing is idealized into total 18finite element models and subjected to 4typical external load conditions. An automatic sizing algorithm based on MSC/NASTRAN and MSC/PATRAN is developed. The results show that the critical part affection the internal loads and weight of the structure is wing skin. Effect of modeling of the spar and rib on the structural behavior is not manifest. On the contrast to the general expectation, the models using the bending-resistant elements show the heavier weight than ones by the elements without bending stiffness. From this results, designers of multi-spar wing are recommended to construct the finite element model considering the bending stiffness, or to check the characteristics of the structure before modeling.