توجه: محتویات این صفحه به صورت خودکار پردازش شده و مقاله‌های نویسندگانی با تشابه اسمی، همگی در بخش یکسان نمایش داده می‌شوند.
۱Effect of wall thickness on the mechanical properties of single–walled carbon nanotubes
نویسنده(ها): ، ،
اطلاعات انتشار: هفتمین همایش انجمن هوافضای ایران، سال
تعداد صفحات: ۶
A three–dimensional finite element (FE) model for the prediction of mechanical properties of defect–free carbon nanotubes (CNTs) is developed by incorporating the modified Morse potential energy with an analytical molecular structural model. The model is capable of predicting Young’s and shear modulus of elasticity and Poisson’s ratios of Armchair and Zigzag single walled–carbon nanotubes (SWCNTs) under tension and torsion loading conditions. Additionally, the effects of wall thickness on mechanical properties of SWCNTs were studied in details. The results show that with increasing tube diameter, the elastic and shear modulus of both Armchair and Zigzag CNTs increase monotonically and approach the elastic properties of Graphene, but the variation trend of Poisson’s ratio is reverse, also the Young’s modulus values are inversely proportional to the wall thickness and if the value of 0.066nm is used for the wall thickness, the Young’s modulus is estimated about 1TPa which agree very well with the corresponding theoretical and experimental measurements.<\div>

۲Mechanical properties of double–walled carbon nanotubes
نویسنده(ها): ، ،
اطلاعات انتشار: هفتمین همایش انجمن هوافضای ایران، سال
تعداد صفحات: ۶
In the past decade a large interest is developed to carbon nanotubes (CNTs) that exhibit exceptional mechanical and electrical properties. In this paper, the finite element model (FE) is combined with the modified Morse interatomic potential and the molecular structural mechanics approach in order to study the role of diameter and chirality in the mechanical properties of Armchair and Zigzag double–walled carbon nanotubes (DWCNTs). The interlayer van der Waals (vdW) forces are represented by the ‘6–12’ Lennard–Jones (LJ) potential and simulated by a nonlinear truss rod model. The results show the Young’s and shear modulus of DWCNTs increases with increasing the nanotube diameter. The computational results agree well with the previous experimental and theoretical results.<\div>

۳The investigation of damage effect in the buckling load of laminated composite plates
نویسنده(ها): ،
اطلاعات انتشار: دومین کنفرانس ملی مهندسی ساخت و تولید، سال
تعداد صفحات: ۷
In the present paper, the linear buckling analysis of laminated composite plates with cut out and subjected to axial compression is investigated. The critical buckling capacity of the structure is found using the geometric linear analysis based on degenerated shell element (Ansys, shell91) with conjunction of the progressive damage modeling. Various failure modes such as fiber breakage, matrix cracking and so forth with assessment of interlaminar stresses are developed. The present results are found to compare well with those available in the literature.<\div>

۴A New Procedure for Dynamic Calibration of Drop Weight Impact Testers
نویسنده(ها): ،
اطلاعات انتشار: دومین کنفرانس بین المللی و هشتمین کنفرانس ملی مهندسی ساخت و تولید، سال
تعداد صفحات: ۸
In this paper, a new procedure for dynamic calibration of Drop Weight Impact Testers (DWIT) is developed. The DWIT is calibrated by measuring velocities before and after rebounding and using impulse balance equation. By performing a stage of numerical integration, linear dynamic calibration factor can be extracted. This procedure is very simple, and can be performed during tests. No additional accessories and equipments are needed during execution of the procedure. More over, different calibration methods are reviewed here. Controlling and decreasing of errors and related sources have been developed in this procedure.<\div>

۵A New Technique in Recovering Corroded Pipelines Using Unidirectional Composites
نویسنده(ها): ، ،
اطلاعات انتشار: اولین کنفرانس بین المللی و هفتمین کنفرانس ملی مهندسی ساخت و تولید، سال
تعداد صفحات: ۹
Repairing and maintenance of gas transmission pipelines have always been a major concern of the gas industry. Considering the obsolete and problematic nature of the old repairing methods, it seems necessary to present new methods of repairing that are safe and cost effective. In this paper we study a new method of repairing gas transmission pipelines using glass\epoxy composite materials. Using the numerical and analytical solutions, corroded gas pipes are stress analyzed and suitable composite along with the number and direction of needed layers for repairing the pipes are obtained. Employing unidirectional Glass\Epoxy composites, corroded pipes are finally repaired according to the result of the design and then tested based on standards. Laboratory results justify the possibility of replacing old methods with the new one.<\div>

۶Development of a Full Range Multi–scale Model to Obtain Elastic Properties of CNT\Polymer Composites
نویسنده(ها): ،
اطلاعات انتشار: دومین کنفرانس بین المللی کامپوزیت، سال
تعداد صفحات: ۶
The main goal of this research is to develop a full range multi–scale modeling approach to extract Young’s modulus and Poisson’s ratio of carbon nanotube reinforced polymer (CNTRP) composites covering all nano, micro, meso and macro scales. The developed model consists of two different phases as top–down scanning and bottom–up modeling. At the first stage, the material region will be scanned from the macro level downward to the nano scale. Effective parameters associated with each and every scale will be identified through this scanning procedure. Accounting for identified effective parameters of each specific scale, suitable representative volume elements (RVE) will be defined, separately for all nano, micro, meso and macro scales. In the second stage of modeling, a hierarchical multi–scale modeling approach is developed. This modeling strategy will process the material at each scale and feed the obtained information to proceeding scale as input information. It has been shown that the developed modeling procedure provides a clear insight to the properties of CNTRP and it is a very efficient tool for simulation of mechanical behavior CNTRP composites<\div>

۷Fabrication of Epoxy\Multi–Walled Carbon Nanotube–Nanoclay Nanocomposites: Investigation of Fracture Toughness
نویسنده(ها): ، ، ،
اطلاعات انتشار: دومین کنفرانس بین المللی کامپوزیت، سال
تعداد صفحات: ۶
The effect of concurrent presence of multi–walled carbon nanotube (MWNT) and nanoclay on fracture toughness of epoxy was studied. First, the effects of various contents of MWNT and nanoclay (as reinforcement factors) on fracture toughness of epoxy were investigated separately. Then, the optimum content of each reinforcement factor was used concurrently in epoxy and the changes in the amount of fracture toughness of the resulting nanocomposite compared with those of previous nanocomposites were studied. The SEM studies were used for the fractography of specimens and also for investigating the dispersion of MWNTs in the matrix which indicated that the MWNTs were dispersed well. The Xray diffraction (XRD) was applied to determine the d–spacing of nanoclay layers. The results show that d–spacing of layers increases from 18.42 A° to 42.28 A° and an intercalated nanocomposite is obtained<\div>

۸Investigation of mechanical properties of clay\epoxy nanocomposites
نویسنده(ها): ، ،
اطلاعات انتشار: دومین کنفرانس بین المللی کامپوزیت، سال
تعداد صفحات: ۶
Enhancing some mechanical properties of polymers by addition of nanoclay has attracted many attentions. In this paper, the effect of adding modified nanoclay (Cloisite 30B) to epoxy resin (ML– 506) on mechanical properties (Tensile, Compression and flexural) of their nanocomposites by applying a new fabrication method is studied. To fabricate the clay\epoxy nanocomposites, nanoclay and epoxy polymer are initially mixed by the aid of high speed mechanical stirrer and then the ultrasonication was utilized for complete dispersion of nanoclay. D–spacing and Dispersion of nanoclay layers in epoxy are characterized by X–ray diffraction (XRD) and transmission electron microscopy (TEM) respectively. The results indicate that d–spacing of layers are increased from 18.42 A° to 42.28 A° and an intercalated nanocomposite is obtained. The nanoclay is added from 1–5 wt% (stepwise 1 wt%) to epoxy and the mechanical properties are investigated. The results of mechanical examinations show that tension and flexural moduli and compression strength of nanocomposites are increased compared with those of pure epoxy. Also, the results reveal that as more Cloisite 30B is added to epoxy, the brittleness of nanocomposite is intensified and failure strains are decreased. Moreover, tensile and flexural strengths tend to reduce due to possible agglomeration and porosities<\div>

۹simple model for simulation of mode I strain energy release rate of a rectangular laminated composite
نویسنده(ها): ،
اطلاعات انتشار: دومین کنفرانس بین المللی کامپوزیت، سال
تعداد صفحات: ۶
The critical strain energy release rate for T300\913 carbon–epoxy laminated composites has been studied in this paper using ANSYS finite element software based on virtual crack closure technique (VCCT). Compact Tension (CT) specimen has been used for numerical analyses and the geometrical dimensions have been extracted from the existing references. The results obtained from the finite element analysis are compared with the existing experimental results in literature. There is good agreement between the critical energy release rate obtained from finite element analysis and the experimental results. Accuracy and simplicity of presented model make it appropriate for predicting the experimental results and improving experimental techniques. The simplicity of the presented model for simulation of the critical strain energy release rate for the laminated composites is the innovation of the present research.<\div>

۱۰The effect of multi–walled carbon nanotube dimensions on mechanical properties of epoxy–based nanocomposites
نویسنده(ها): ، ،
اطلاعات انتشار: دومین کنفرانس بین المللی کامپوزیت، سال
تعداد صفحات: ۶
The effects of multi–walled carbon nanotube (MWNT) diameter on the mechanical properties of epoxy\MWNT nanocomposites are studied and a correction factor for the Halpin–Tsai model is proposed based on the experimental results. This correction factor accounts for phenomena, such as filler bending or imperfect bonding, which are not included in the theory. To determine the suitable amount of filler, a number of test specimens based on different contents of MWNTs were prepared and tested and 0.5 wt% of MWNT was chosen as the best filler content based on the mechanical properties and the dispersion status. To compare Young’s modulus with the theoretical estimations, the Tsai–Halpin model was used which overestimated the experimental results. Therefore, a correction factor was introduced to the equation to fit the obtained experimental results. The proposed modified equation could predict the experimental result much more effectively. In addition, the modified Tsai– Halpin theory was successfully used to predict the tensile strength in the same fashion as the Young’s modulus<\div>

۱۱Damage in GFRPs due to Low Velocity Impact at Low Temperatures
نویسنده(ها): ، ،
اطلاعات انتشار: دهمین همایش انجمن هوافضای ایران، سال
تعداد صفحات: ۵
In order to study the impact behavior of glass\epoxy laminated composites, many test specimens are fabricated from glass fibers and epoxy matrix using hand layup method. Experimental analyses at different energy levels under variable temperatures in the range of –30 °C to 23 °C are performed. The configuration of laminates is quasi–isotropic. The effects of low temperatures on failure mode and energy absorption of composite specimens are investigated experimentally. Also the effects of exposure time at low temperatures on impact response of specimens are highlighted. Failure mechanisms of specimens are examined using microscopic examinations. Results indicated that impact performance (energy absorption and failure mechanism) of these composites is affected over the range of temperature considered<\div>
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