• Composites Research
• /
• 제17권5호
• /
• pp.78-84
• /
• 2004

본 연구에서는 $\textrm{Al}_2\textrm{O}_3$와 Ti-6Al-4V로 이루어진 두 가지 유형의 경사기능재료 평판에 대한 열적 거동을 조사하였다. 경사기능 평판의 재료 물성치는 체적비의 멱지수 값에 따라 두께방향으로 연속적으로 변화하고, 평판의 윗면과 아랫면에 열하중이 가해지며 일정한 온도 조건을 유지한다고 가정하였다. FCM 사각 평판의 운동방정식은 해밀턴 변분 원리로 구하였으며, 나비에 기법으로 수치해를 얻었다. 체적비와 온도 변화에 대한 FCM 평판의 정적처짐과 고유진동수의 영향에 대하여 고찰하였다.

• Composites Research
• /
• 제12권1호
• /
• pp.47-58
• /
• 1999

다양한 형상 및 경계조건을 갖는 적층 복합재료 및 혼합적층 복합재료 판의 자유진동해석을 위한 실험적 연구결과에 대하여 고찰하였다. 실험에 사용한 판의 재료는 탄소섬유강화(CFRP), 유리섬유강화(GFRP) 복합재료, 알루미늄-GFRP, CFRP-GFRP 혼합적층 복합재료이다. 충격해머와 가속도계를 이용한 충격가진법을 통하여 판의 고유진동수 및 노달패턴을 얻었고, 결과는 무차원화된 진동수매개변수로 제시하였다. 복합재료의 물성, 적층강도, 판의 기하학적 형상과 경계조건 등이 복합재료 판의 진동특성에 미치는 영향에 대하여 평가하였다. 실험결과의 비교/검증을 위하여 유한요소해석을 수행하였고, 서로 잘 일치함을 보였다.

• Composites Research
• /
• 제24권3호
• /
• pp.39-45
• /
• 2011

접착제에 의한 접합은 일반적으로 구조물의 접합에 널리 사용되고 있다. 폴리우레탄 접착제와 에폭시 접착제는 현재 극저온에서 운항되고 있는 LNG 선박의 화물창에 적용되고 있다. 본 연구에서는 화물창용 소재인 트리플엑스와 폴리우레탄 및 에폭시 접착제와의 상온과 극저온에서의 접착강도를 평가하였다. 연구결과 모든 접착시스템에서 극저온에서 박리강도의 감소가 있었으며 그 원인은 접착제마다 다르게 검토되었다. 결과적으로는 폴리우레탄 접착제와 트리플엑스가 극저온에서의 강도 값이 에폭시에 비해 우수하였으며 LNG 선과 같은 극저온 환경에 접합한 것으로 평가되었다.

• 식물병연구
• /
• 제24권2호
• /
• pp.99-112
• /
• 2018

Certain agrochemicals may be tuned for increased effectiveness when downsized to nanoparticles (NPs), where one dimension is less than 100 nm. The NPs may function as fertilizers, pesticides and products to improve plant health through seed priming, growth promotion, and induction of systemic tolerance to stress. Formulations will allow targeted applications with timed release, reducing waste and pollution when compared to treatments with bulk-size products. The NPs may be a single component, such as nano-ZnO as a fertilizer, or be composites of compatible materials, for example where N, P, and K plus micronutrients are available. The active materials could be loaded into porous carriers or tethered to base nanostructures. Coatings could include such natural products alginate, chitosan, zein, or silica. Certain NPs are taken up and transported in the plant's phloem and xylem so systemic effects are feasible. Timed and targeted release of the active product could be achieved in response to changes in pH or availability of ligands within the plant or the rhizosphere. Global research has revealed the many potentials offered by NP formulations to aid sustainability in agriculture. Current work will provide information needed by regulatory agencies to assess their safety in the agricultural setting.

• Elastomers and Composites
• /
• 제53권3호
• /
• pp.150-157
• /
• 2018

Fatigue properties of rubber are one of the most important characteristics in the rubber industry. In this study, the fatigue properties of MREs (magneto-rheological elastomers) based on NR (natural rubber), EPDM (ethylene-propylene diene monomer), and AEM (ethylene/acrylic elastomer) were investigated. For comparison, MREs with a Shore hardness of 60A were prepared. According to the relative results, the fatigue properties of EPDM MRE were the worst. Thus, we investigated methods to improve the fatigue properties of EPDM MRE by varying the carbon black content and curing systems of EPDM as the matrix of the MRE. Dynamic properties were measured using a fatigue tester and an RPA (rubber process analyzer), and the XPS (X-ray photoelectron spectroscopy) was used to analyze the curing system of the EPDM matrix. According to the results, the Payne effect increased and the fatigue resistance decreased as the carbon black content increased. In case of the curing system, the CV (conventional vulcanization) system was superior to the EV (efficient vulcanization) system in terms of the fatigue resistance. This was because the number of flexible bonds in the case of the CV system was higher than that in the case of the EV system. However, the EV system showed excellent mechanical properties because it had many monosulfidic bonds with strong binding energy.

• Corrosion Science and Technology
• /
• 제16권2호
• /
• pp.85-89
• /
• 2017

One of the most challenging issues in the oil and gas industry is corrosion assessment and management in subsea structures or equipment. At present, almost all steel pipelines are sensitive to corrosion in harsh working environments, particularly in salty water and sulphur ingress media. Nowadays, the most commonly practiced solution for a damaged steel pipe is to entirely remove the pipe, to remove only a localized damaged section and then replace it with a new one, or to cover it with a steel patch through welding, respectively. Numerous literatures have shown that fiber-reinforced polymer-based composites can be effectively used for steel pipe repairs. Considerable research has also been carried out on the repair of corroded and gouged pipes incorporated with hybrid natural fiber-reinforced composite wraps. Currently, further research in the field should focus on enhanced use of the lesser and highly explored hybrid-biocomposite material for the development in corrosion prevention. A hybrid-biocomposite material from renewable resource based derivatives is cost-effective, abundantly available, biodegradable, and an environmentally benign alternative for corrosion prevention. The aim of this article is to provide a comprehensive review and to bridge the gap by developing a new hybrid-biocomposite with superhydrophobic surfaces.

• Structural Engineering and Mechanics
• /
• 제27권2호
• /
• pp.199-222
• /
• 2007

Composite laminated structures supported on elastic foundations are being increasingly used in a great variety of engineering applications. Composites exhibit larger dispersion in their material properties compared to the conventional materials due to large number of parameters associated with their manufacturing and fabrication processes. And also the dispersion in elastic foundation stiffness parameter is inherent due to inaccurate modeling and determination of elastic foundation properties in practice. For a better modeling of the material properties and foundation, these are treated as random variables. This paper deals with effects of randomness in material properties and foundation stiffness parameters on the free vibration response of laminated composite plate resting on an elastic foundation. A $C^0$ finite element method has been used for arriving at an eigen value problem. Higher order shear deformation theory has been used to model the displacement field. A mean centered first order perturbation technique has been employed to handle randomness in system properties for obtaining the stochastic characteristic of frequency response. It is observed that small amount of variations in random material properties and foundation stiffness parameters significantly affect the free vibration response of the laminated composite plate. The results have been compared with those available in the literature and an independent Monte Carlo simulation.

• Steel and Composite Structures
• /
• 제24권6호
• /
• pp.711-726
• /
• 2017

In the present work, by considering the agglomeration effect of single-walled carbon nanotubes, free vibration characteristics of functionally graded (FG) nanocomposite sandwich plates resting on Pasternak foundation are presented. The volume fractions of randomly oriented agglomerated single-walled carbon nanotubes (SWCNTs) are assumed to be graded in the thickness direction. To determine the effect of CNT agglomeration on the elastic properties of CNT-reinforced composites, a two-parameter micromechanical model of agglomeration is employed. In this research work, an equivalent continuum model based on the Eshelby-Mori-Tanaka approach is employed to estimate the effective constitutive law of the elastic isotropic medium (matrix) with oriented straight CNTs. The 2-D generalized differential quadrature method (GDQM) as an efficient and accurate numerical tool is used to discretize the equations of motion and to implement the various boundary conditions. The proposed rectangular plates have two opposite edges simply supported, while all possible combinations of free, simply supported and clamped boundary conditions are applied to the other two edges. The benefit of using the considered power-law distribution is to illustrate and present useful results arising from symmetric and asymmetric profiles. The effects of two-parameter elastic foundation modulus, geometrical and material parameters together with the boundary conditions on the frequency parameters of the laminated FG nanocomposite plates are investigated. It is shown that the natural frequencies of structure are seriously affected by the influence of CNTs agglomeration. This study serves as a benchmark for assessing the validity of numerical methods or two-dimensional theories used to analysis of laminated plates.

• Elastomers and Composites
• /
• 제35권3호
• /
• pp.215-226
• /
• 2000

고무 조성비가 다른 카본블랙으로 보강된 고무 배합물의 가황 특성을 연구하였다. 한 가지 고무로 이루어진 고무 배합물, 두 가지 고무로 이루어진 고무 배합물, 그리고 세 가지 고무로 이루어진 고무 배합물을 실험 대상으로 삼았다. NR/BR과 SBR/BR 배합물 중에서 BR의 함량이 높은 것의 델타토크는 단일 고무 배합물의 경우보다 높다. 삼중 고무 배합물의 델타 토크의 경우에는 세가지 고무의 함량비가 유사할수록 델타 토크가 낮아졌다. 스코치 시간과 적정 가황 시간은 NR이 증가할수록 빨라졌고 SBR이 증가할수록 느려졌다. 가황 속도는 SBR 함량이 증가할수록 느려졌다. 가교 역전(reversion) 현상은 SBR 함량이 증가할수록 감소하였다.

• Elastomers and Composites
• /
• 제45권4호
• /
• pp.291-297
• /
• 2010

차량에서 스트러트 인슐레이터는 도로노면으로부터 발생하는 소음과 진동을 방지하는 역할을 한다. 대부분의 점탄성 마운트들은 고무로 되어있으며 천연고무가 주성분이다. 이러한 고무 부품들은 초기에는 제 역할을 하지만 오랜 시간 고온과 반복하중에 노출되면 성능저하가 일어난다. 고무성능 변화는 NVH를 떨어뜨리고 승차감을 저하시킨다. 본 연구에서는 차량실험을 통해 스프링 변위를 측정하였고, 재현실험에서 가속도 센서를 이용하여 운행거리와 차량연식에 따른 인슐레이터 고무성능을 가속도 값, 고무 영구 변형량, 경도를 나타내었다.