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2017
the chairman of my supervisory committee, for his excellent supervision, constructive comments. My thanks also goes to the members of my supervisory committee, Dr. Al-Khawad Ali Elfaki for his ennobling association, and for giving me another dimension to life and taking time off from his busy schedule to serve in the committee. My thanks also go to Dr.
International Journal of Smart and Nano Materials, 2014
A study on the mechanical and thermo-mechanical properties of carbon nanotube (CNT) reinforced nanocomposites is presented in this article. Mori-Tanaka method is used for modeling the effective stiffness and coefficient of thermal expansion. Regression formulas were developed to describe the effects of CNT orientation, aspect ratio, and CNT volume fraction. Given the statistical distributions of CNT orientations and aspect ratios, the effective properties can be conveniently derived by numerical integration using these formulas.
Aluminum matrix composites reinforced with 0-5.0 wt.% multi-walled carbon nanotubes (MWNTs) were produced by spark plasma sintering (SPS). The composites with 61.0 wt.% MWNTs additions had higher thermal conductivity than the pure aluminum produced by the same SPS processing. The MWNTs/Al composites exhibited the maximum thermal conductivity of 199 W/m/K at 0.5 wt.% MWNTs. The enhancement of thermal conductivity is supported by the measured tensile strength. The MWNTs/Al composites exhibited the maximum tensile strength of 130 MPa also at 0.5 wt.% MWNTs. The contribution of carbon nanotubes to thermal conductivity of the composites was demonstrated by theoretical analysis. The results show that MWNTs reinforced aluminum matrix composite is a potential material for high thermal conductivity applications.
Metal matrix composites are grabbing more attention by researchers due to their outstanding properties which meet the requirements of a specific application. This paper deals with the experimental investigations done to examine the thermal stability of Matrix under various thermal applications and also to study the effect of MWCNT content and particle size on thermal properties of the Al-CNT metal matrix. Different characterization techniques such as Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry analysis (DSC) were performed for the Aluminium-CNT metal matrix. Thermal gravimetric analysis revealed that maximum weight loss is found to be 0.44% for 1.5 wt % of CNT (type2) in Aluminium which is less compared to the weight loss of pure Aluminium. Hence a minimum of 0.24% weight loss was found for 1.0 weight % of CNT (type 2) in Aluminium. Differential Scanning Calorimetry analysis revealed that rate of heat flow increase gradually with the increase in outer diameter of selected carbon nanotubes and maximum heat flow of 106.6 mW for 1.5 wt% of CNT (type3) in Aluminium which was 40% greater than that of pure Aluminium. Thus TGA-DSC tests help in investigating the thermal stability of selected Al-CNT metal matrix.
2011
Carbon nanotubes (CNTs), since their discovery by Lij ima in 1991 [1], are considered a new generation of reinforcement [2]. Their "nano" size structure makes them potentially free of defects, which provides them with excellent physical properties [3,4]. There are two main nanotube types: single wall nanotubes (SWNT), which are made of a single wall tube; and multiwall nanotubes (MWNT), which consist in several concentric walls, one inside the other. In a composite, one the most important factor is the interfacial tension between matrix and reinforcement. In general, the loads in a composite structure are introduced through the matrix and then are transferred to the reinforcement through the interface [5]. Therefore, the interface can be defined as the region surrounding the reinforcement where this stress transfer takes place. The properties of the composite depend on the properties of this region and its ability to transfer the load efficiently. This work proposes a new ...
Composite Structures, 2012
Carbon nanotubes (CNTs) have been regarded as ideal reinforcements for high-performance composites. A key factor for the reinforcement efficiency is the interface bonding between the CNTs and the matrix. This paper presents a new constitutive model to predict the mechanical performance of composites made with CNTs. The model takes into account explicitly the performance of the interface between the matrix and the CNTs. The formulation developed is based in the mixing theory. It divides the composite in matrix and in a new material result of coupling the CNTs with the interface. The relation defined between interface and CNTs assumes that the load is transferred to the nanotubes along their ends and that in the central part the CNTs can develop their full strength. The composite non-linear behavior results from the non-linearities of its constituents. In case of interface damage, it also becomes non-linear the law defined to couple the interface with the CNTs. After describing the formulation, it is validated studying the elastic response of several composites made with different types of CNTs reinforcements. The non-linear behaviour provided by the formulation is also studied. In both cases the numerical results are compared with experimental data showing good agreement.
Materials Science and Engineering: A, 2014
Due to their remarkable mechanical properties, carbon nanotube (CNT) reinforced aluminum (Al) matrix composites have attracted a wide range of research interests. This work attempts to experimentally and numerically investigate the relationship between the micro-structures and mechanical behavior of CNT/ Al composites. Three-dimensional (3D) computational structural modeling of CNT/Al composites is performed, in which the size, morphology, orientation, location and volume fraction of CNTs are reproduced to be similar to those of the actual micro-structures of CNT/Al composites. The strengthening of the mechanical properties of the constituent materials of CNT/Al composites and reasonable load and boundary conditions are studied based on the models of CNT/Al composites developed. The tensile mechanical behavior of CNT/Al composites is numerically evaluated and experimentally verified. Results show that the enhanced mechanical properties of CNT/Al composites can be attributed to three factors: CNT reinforcements, matrix grain refinement and layered architectures. Through the microscopic structural modeling methods presented herein, the effects of model size, interfacial behavior, volume fraction of CNTs and layered structures on the mechanical behaviors of CNT/Al composites can be reproduced to understand the strengthening and deformation mechanisms of CNT/Al composites.
Carbon, 1995
This chapter discusses some aspects of the mechanical and thermal properties of carbon nanotubes. The tensile and bending stiffness constants of ideal multi-walled and single-walled carbon nanotubes are derived in terms of the known elastic properties of graphite. Tensile strengths are estimated by scaling the 20 GPa tensile strength of Bacon's graphite whiskers. The natural resonance (fundamental vibrational frequency) of a cantilevered single-wall nanotube of length 1 micron is shown to be about 12 MHz. It is suggested that the thermal expansion of carbon nanotubes will be essentially isotropic, which can be contrasted with the strongly anisotropic expansion in "conventional" (large diameter) carbon fibers and in graphite. In contrast, the thermal conductivity may be highly anisotropic and (along the long axis) perhaps higher than any other material. A short discussion of topological constraints to surface chemistry in idealized multi-walled nanotubes is presented, and the importance of a strong interface between nanotube and matrix for formation of high strength nanotube-reinforced composites is highlighted.
Materials Letters, 2008
The coefficient of thermal expansion (CTE) of aluminum matrix composite reinforced with 1.0wt.% multi-wall carbon nanotubes (MWNTs) fabricated by cold isostatic pressing and hot squeeze technique was measured between 25 and 400°C with a high-precision thermomechanical analyzer, and compared with those of pure aluminum and 2024Al matrix fabricated under the same processing. The results show that the CTE of the composite obviously reduces in relation to those of pure aluminum and 2024Al matrix due to the introduction of MWNTs. The addition of 1.0wt.% MWNTs to 2024Al matrix decreases the CTE by as much as 12% and 11% compared with those of pure aluminum and 2024Al matrix at 50°C, respectively, which indicates that carbon nanotube reinforced metal matrix composite may be a promising materials with low CTE.
Diamond and Carbon Composites and Nanocomposites, 2016
This chapter deals with the blending and processing methods of CNT-reinforced metal matrix bulk composites (Al/CNT, Cu/CNT and Ni/CNT) in terms of solid-state processing, referring mainly to the research works of the last ten years in this research field. The main methods are depicted in a brief way, and the pros and cons of each method are discussed. Furthermore, a tabular summary of the research work of the mentioned three systems is given, including the blending methods, sintering methods, the used amount of CNTs and the finally achieved relative density of the composite. Finally, a brief discussion of each system is attached, which deals with the distribution and interaction of the CNTs with the matrix material.
Mechanics of Composite Materials, 2010
Keywords: car bon nanotubes, com pos ites, me chan i cal prop er ties, modeling A lit er a ture re view on the pre dic tion of Young's modulus for car bon nanotubes, from both the o ret i cal and exper i men tal as pects, is pre sented. The dis crep an cies be tween the val ues of Young's modulus re ported in the liter a ture are an a lyzed, and dif fer ent trends of the re sults are dis cussed. The avail able an a lyt i cal and nu mer i cal sim u la tions for pre dict ing the me chan i cal prop er ties of car bon nanotube com pos ites are also re viewed. A gap anal y sis is per formed to high light the ob sta cles and draw backs of the mod el ing tech niques and fun da men tal as sump tions em ployed which should be over come in fur ther stud ies. The as pects which should be stud ied more accurately in modeling carbon nanotube composites are identified. 1 0191-5665/10/4602-01
Computational Materials Science, 2014
Exceptional mechanical properties like high strength, stiffness and aspect ratio exhibited by carbon nanotubes, make them ideal reinforcements for nanocomposites. In this paper load transfer in multi-walled carbon nanotube (MWCNT) composites is studied under tension and compression loading conditions. Continuum mechanics model is used to evaluate the effective material properties using a representative volume element (RVE) approach. Numerical results are obtained using Finite Element Modeling (FEM) and these results have been validated with rule of mixture results. FEM results are found to be quite closer to the results obtained from rule of mixture. In the present work we have considered a range of matrix material, the range covers the matrix material from metal to polymer, i.e. taken in a form of the ratio of effective modulus of elasticity of CNT to that of matrix material E t /E m from 5 to 200. With the addition of the multi-walled CNT in a matrix at the volume fractions of 5.1%, the stiffness of the composite is increased by 46% for compressive loading and 14.9% for tensile loading, as compared with that of the matrix in the case of long CNT at E t /E m = 10. Multi-walled carbon nanocomposite are found to provide better value of young's modulus in compression as compared in tension, this is due to the higher inter-tube load transfer in compression. Comparative evaluation of material properties with single walled carbon nanocomposite is also done. It is established that multi-walled carbon nanotube composite provide a better resistance against compression as compared to single walled carbon nanotube composite. Effect of change in diameter and length of multi-walled carbon nanotube on stiffness of nanocomposite have also been investigated. Longer multiwalled carbon nanotubes are found to be more effective in reinforcing the composite as compared to shorter ones. FEM results are also found to be in close approximation with the experimental results, which validates the current model.
2017
A micromechanical model is applied to examine the tensile properties of composite materials filled with multi-wall CNT oriented in in-plane and out-of-plane direction and a quantitative micromechanical model for the mechanical behavior of CNT-composites has been developed. Digimat-MF is used to generate a realistic three-dimensional microstructure for the current carbon nanotube/ epoxy composite. The Digimat model simulates a system of aligned carbon nanotubes arranged in-plane and another one having out of plane arrangement of reinforcements. A second model shows a representative volume element for the current nano-composite, in which the carbon nanotubes were simulated as a randomly (fully) dispersed, where all particles have been separated from each other. The predicted mechanical properties are compared with experimental tensile properties of composite materials reinforced with multi-wall CNTs arranged in in-plane and out-of-plane direction. A good agreement between the micromec...
Physica Status Solidi B-basic Solid State Physics, 2009
Thermal expansion exhibits considerable challenges developing residual stresses at the interfaces of different materials treated at high temperature. Electrical devices containing materials with different thermal expansion behaviour very often suffer this problem. Thermal expansion co-efficient (TEC) of different metals can be tuned by using carbon nanotube (CNT). Metal matrix composites (MMCs) using CNT are fabricated by hot-press sintering method and TEC of the composites are investigated throughout a wide range of temperature (À155 to 275 8C). Reduction of TEC of the composite materials was observed up to 20% compared to that of pure metals. The effect of CNTs in the matrix materials and the mechanism behind the improvement are explained from the microscopic investigation of the composites.
2000
Carbon nanotubes (CNT) possess many unique characteristics that promise to revolutionize the world of structural ma- terials resulting in significant impact on our capability to build lighter, smaller and higher performance structures for aerospace and many other industrial ap- plications. When the CNT are aligned, micromechanical studies showed the po- tential of an order of magnitude increase in mechanical properties
Meccanica, 2014
The scope of this work is the analysis of the reinforcement effect of carbon nanotubes in typical matrix systems, such as epoxy resins. As is well known, efficient dispersion is critical in achieving adequate reinforcement. However, dispersion processes are also well known to degrade the nano-phase. Degradation is manifested as reduction in the aspect ratio as the nanotubes de-agglomerate and break at the same time.
Journal of Thermal Analysis and Calorimetry, 2008
Nanoscale Research Letters, 2013
In this work, the thermal expansion properties of carbon nanotube (CNT)-reinforced nanocomposites with CNT content ranging from 1 to 15 wt% were evaluated using a multi-scale numerical approach, in which the effects of two parameters, i.e., temperature and CNT content, were investigated extensively. For all CNT contents, the obtained results clearly revealed that within a wide low-temperature range (30°C ~ 62°C), thermal contraction is observed, while thermal expansion occurs in a high-temperature range (62°C ~ 120°C). It was found that at any specified CNT content, the thermal expansion properties vary with temperature - as temperature increases, the thermal expansion rate increases linearly. However, at a specified temperature, the absolute value of the thermal expansion rate decreases nonlinearly as the CNT content increases. Moreover, the results provided by the present multi-scale numerical model were in good agreement with those obtained from the corresponding theoretical anal...
Materials Characterization, 2013
Mechanical characterization of copper coated carbon nanotubes reinforced aluminum matrix composites,
2009
With strength and stiffness properties several 100 times better than that of steel and conductivity better than copper, carbon nanotubes (CNT) have extraordinary intrinsic electrical, thermal and mechanical properties making them potentially attractive materials for use in lightweight spacecraft structures and subsystems. Research on the possibility of using such materials for improving the properties of known materials such as Carbon Fiber Reinforced Plastics (CFRP), has been performed, and the results indicate that some improvement is indeed possible as observed by Kostopoulos et al [1]. In the field of thermomechanics of space structures, the needs on material developments are focused on adjusting/increasing thermal properties for high temperature gradients or improving the stability of structural parts and the bonding of elements of sandwiched structures. The main objectives of the work presented in this paper are to identify and to investigate possible improvements on CNT reinf...
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