• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.762-769
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• 2017

The extensional stiffness in quasi-isotropic laminates is uniform in the radial direction, but the bending stiffness varies radially due to the stacking sequence. This paper addresses the directional dependency of the bending stiffness and its radial variation in three types of quasi-isotropic laminate reflectors consisting of unidirectional fiber composite materials (UDM) and randomly distributed composite materials (short fiber, RDM). The extensional stiffness and bending stiffness in optical reflectors using RDM are uniform, while the bending stiffness in those using UDM varies radially from 11% to 26%. Also, the stiffness sensitivity, such as the bend-twist or bend-torsion effect, due to the differences in the stiffness value in the composite, is large. These factors are problematic in the optical field requiring precision surfaces. Utilizing RDM might be one way to eliminate the presence of bending stiffness in composite mirror substrates.

• Composites Research
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• v.17 no.5
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• pp.25-38
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• 2004

In this study, the stiffness of spatially reinforced composites (SRC) are predicted by using superposition of a rod and matrix stiffnesses in an arbitrary direction. To confirm the predicted values, the material properties of SRC are measured. The predicted values from the volume average of stiffness matrix are consistent with the tested values in a rod direction, but are inconsistent in an off-rod direction while reverse is true fur the volume average of compliance matrix. Therefore, the harmony function from superposition of stiffness and compliance matrix is introduced. The predicted values from the harmony function are consistent with the tested values in both the rod and the off-rod directions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.11
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• pp.941-948
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• 2016

Textile composite materials have been widely applied in aerospace structures due to their various advantages such as high specific stiffnesses and strengths, better out-of-plane performances, impact and delamination resistances, and net shape fabrications. In this paper, a modified geometric model of repeating unit cell (RUC) is suggested based on the Naik's model for 2D plain weave textile composites. The RUC geometry is defined by various parameters. The proposed model considers another parameter which is a gap length between adjacent yarns. The effective stiffnesses are predicted by using the yarn slicing technique and stress averaging technique based on iso-strain assumption. And the stiffnesses of RUC are evaluated by adjusting the gap ratio and verified by comparing with Naik's model and experimental data for 2D plain weave composite specimens.

• Journal of Korean Society of Steel Construction
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• v.10 no.3 s.36
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• pp.463-472
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• 1998

The purpose of this paper is to analyze the buckling characteristics of rigidly-jointed single-layer latticed domes with square network by using the experimental and the theoretical techniques in order to develop a reasonable method of theoretical analysis for these domes. Two methods of theoretical analysis are applied; one is based on the Yamada's method of shell analogy and the other is based on the frame analysis method using the finite element method. The effects of the nonuniformity of rigidity-distribution in the circumferential direction and the rigidity of the covering material on both the prebuckling and the buckling characteristics are examined. The results indicate that these effects should be considered reasonably in the theoretical analyses.

• Journal of the Korean Geotechnical Society
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• v.31 no.4
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• pp.31-43
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• 2015

A numerical analysis on the effect of increasing tensile stiffness of the geosynthetics on the soil displacement and pile efficiency was conducted. Parametric studies by changing the stiffness of soft soil, internal friction and dilatancy angles of the embankment material, and flexual stiffness of the composite layer including the geosynthetics were carried out. In general, increasing stiffness of the geosynthetics improves the pile efficiency, whereas the amount of its improvement depends on the condition of parameters. In case of the sufficiently low stiffness of the soft soil or high flexual stiffness of the composite layer including the geosynthetics, a noticeable increase in the pile efficiency can be observed. When the stiffness of the soft soil is very low, the increase in the stiffness of the geosynthetics can significantly reduce the vertical displacement in the piled embankment. When the flexual stiffness of the composite layer is sufficiently high, increasing stiffness of the geosynthetics can greatly improve the pile efficiency.

• Composites Research
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• v.19 no.2
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• pp.13-19
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• 2006

In this paper, parametric study was carried out to design sandwich structures for EDM machines controlling stacking sequence, stacking thickness of composites and rib configuration. Sandwich structures which are dealt with in this paper are composed of fibre reinforced composite for skin material and foam or resin concrete for core materials. The sandwich column has cruciform rib to enhance bending stiffness of the structure and the bed has several vertical ribs to resist the normal forces and vibration. The design parameters such as rib thickness and stacking sequence were controlled to enhance the system robustness. Finite element analysis was also carried out to verify the variation of static and dynamic stiffness of the structures according to the variation of the parameters. Vibration tests were performed to verify the natural frequencies and damping ratios of the manufactured composite structures. The appropriate shape and configuration conditions for micro-EDM machine structures are proposed.

• The Journal of the Convergence on Culture Technology
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• v.6 no.2
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• pp.535-541
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• 2020

A conventional elastic material replacement and performance evaluation are very complicated and time-consuming, and it is difficult to know when to replace the elastic material in advance. By comparing with the product limit and the functional limit, the necessity of elastic material replacement and the improvement of track support stiffness according to replacement can be immediately demonstrated based on experimental data. Using an evaluation system of track support stiffness, the performance evaluation data for elastic materials obtained through field tests using software for track support stiffness is integrated and managed on the administrator's computer. Therefore, the replacement plan is established and maintenance history is managed by identifying the replacement time and location of elastic materials. It is possible to evaluate the performance and condition of the elastic material at the various points during the working time of the track inspection and the track performance (track support stiffness) and durability of the elastic material (aging level, spring stiffness variation rate, etc.) at the operation condition. The elastic material could be replaced timely, and the deterioration of the elastic material can be continuously monitored.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.269-275
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• 2001

정밀가공기계 및 소음발생원의 방진재료로서 사용될 수 있는 재료는 우선 내부 및 외부진동의 흡수성과 감쇠성이 뛰어나야 하고, 시간 및 온도변화에 따라 형상 및 치수 정밀도가 안정되어야 하며, 불규칙한 외력과 운동전달기구의 변동 하중 하에서도 높은 정적, 동적 강성을 유지해야 한다. 본 연구에서 개발한 재료인 Ferrite-Resin 복합재료는 Resin-Concrete에 미세한 산화철을 filler 재료로 사용함으로써 주철 및 강의 구조재료가 갖는 강성과 비중의 값에 접근시킬 수이었다. 일반적으로 불포화 폴리에스테르 수지나 에폭시계 수지는 glass 전위점의 근처에서 진동에너지의 흡수가 큰 영역이 존재하며 이는 10 .mu.m 이내의 미세한 filler재료가 포함되었을 경우에도 그 종류에 관계없이 큰 변화가 없는 성질이다. 시험편을 통한 재료실험을 통하여 개발된 복합재료를 모델 구조물에 적용시킴으로서 그 적용성을 검토하였다. 앞으로의 수지와 Ferrite 함유량 및 제조 공정이 적절히 모색되면, 이 방진재료가 정밀기계의 구조재료로서 뿐만 아니라 냉동기, 소형선박의 기관실, 가전제품 및 기어박스 등의 케이싱 재료로 사용되는 방진재료로서 그 응용이 확대될 수 있을 것으로 본다.

• Composites Research
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• v.14 no.3
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• pp.1-9
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• 2001

A new non-destructive fatigue prediction model of the composite laminates is developed. The natural frequencies of fatigue-damaged laminates under extensional loading are related to the fatigue life of the laminates by establishing the equivalent flexural stiffness reduction as a function of the elastic properties of sublaminates. The flexural stiffness is derived by relating the 90-ply elastic modulus reduction, and using the laminate plate theory to the degraded elastic modulus and the intact elastic modulus of other laminates. The natural frequency reduction model, in which the dominant fatigue mode can be identified from the sensitivity scale factors of sublaminate elastic properties, provides natural frequency vs. fatigue cycle curves for the composite laminates. Vibration tests were also conducted on $[{90}_2/0_2]_s$ carbon/epoxy laminates to verify the natural frequency reduction model. Correlations between the predictions of the model and experimental results are good.

• Composites Research
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• v.15 no.4
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• pp.1-8
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• 2002

In this study, the rigidities of fiber-reinforced composite corrugated plates are derived to achieve the weight reduction, high strength, and high stiffness. The vibration of the corrugated plates for all the conventional boundary conditions in the plates is analyzed numerically by applying the derived rigidities, and so the analysis system is programmed to obtain the results by using Visual Basic language. Consequently, the characteristics of fiber-reinforced composite corrugated plates can be easily investigated from the results provided by the programmed system.