Mechanical Engineering

Powder metallurgy techniques have emerged as promising routes for the fabrication of carbon nanotube (CNT) reinforced metal matrix composites. In this work, planetary ball milling was used to disperse 2wt% MWCNT in aluminum (Al) powder. Despite the success of ball milling in dispersing CNTs in Al powder, it is often accompanied with considerable strain hardening of the Al powder, which may have implications on the final properties of the composite.

Choosing the right manufacturing process for making a component is an important consideration at the early stages of design. Frequently, the choice of process is based on previous experience or tradition, thereby missing the opportunity to use a new or more suitable process. Lost opportunities could be avoided if the designer had access to a quick efficient selection tool that would guide the selection. In this paper, a systematic procedure for selecting the optimum process to manufacture a component is described.

RESUME La sélection d'un procédé de fabrication comprend deux étapes. La première consiste a évaluer les différents procédés afin de vérifier qu'ils permettent, d'un point de vue technique, d'obtenir un produit en accord avec les spécifications. La seconde étape consiste a classer les procédés retenus selon des critères économiques. Cette phase fait intervenir des techniques simples d'estimation de coût. Cependant, on rencontre au cours de cette sélection deux types de problèmes.

A process is a method of shaping, joining or surface-treating a material. Process selection has three steps. The first is to identify from the 'menu'of all available processes, the subset, which can give a chosen material the desired shape with the desired detail, precision and finish. The second is to choose, from among these, the ones that will do so at the lowest cost.

The effect of high energy ball milling under different conditions on the structure of Na + -montmorillonite (Na-MMT), and the organo-montmorillonite (Cloisite 30B) was investigated. Ball milling increased the structural disorder: peeling off of layers from the particles was observed, followed by the exfoliation of the particles, indicated by the disappearance of the (001) reflection. X-ray diffraction and infrared spectra revealed that the exfoliated layers did not show deteriorated structures. The presence of the alkylammonium ions seemed to stabilize the structure by reducing exfoliation.

Powder metallurgy techniques have emerged as promising routes for the fabrication of carbon nanotube (CNT) reinforced metal matrix composites. In this work, planetary ball milling was used to disperse 2 wt% MWCNT in aluminum (Al) powder. Despite the success of ball milling in dispersing CNTs in Al powder, it is often accompanied with considerable strain hardening of the Al powder, which may have implications on the final properties of the composite. Both un-annealed and annealed Al-2 wt% CNT composites were investigated. It was found that, ball-milled and extruded (un-annealed) samples of Al-2 wt% CNT demonstrated high notch-sensitivity and consistently fractured outside the gauge length during tensile testing. In contrast, extruded samples annealed at 400 and at 500 • C for 10 h prior to testing, exhibited more ductile behavior and no notch sensitivity. Under the present investigated processing conditions, ball milling for 3 h followed by hot extrusion and annealing at 500 • C resulted in enhancements of around 21% in tensile strength compared with pure aluminum with the same process history. The ball-milling conditions used were found to result in the creation of a nanostructure in all samples produced, as shown by XRD and TEM analysis. Such nanostructure was retained after prolonged exposures to temperatures up to 500 • C. The tensile testing fracture surfaces showed uniform dispersion and alignment of the CNTs in the aluminum matrix but also showed CNTs acting as nucleation sites for void formation during tensile testing. This has contributed to the observation of CNT pull-out due to the poor bond between the CNTs and the matrix.

Choosing the right manufacturing process for making a component is an important consideration at the early stages of design. Frequently, the choice of process is based on previous experience or tradition, thereby missing the opportunity to use a new or more suitable process. Lost opportunities could be avoided if the designer had access to a quick efficient selection tool that would guide the selection. In this paper, a systematic procedure for selecting the optimum process to manufacture a component is described. It is based on ...

The effect of carbon nanotube (CNT) damage on the mechanical properties of aluminium (Al)-CNT composites is investigated using mildly and severely damaged CNTs. Composites prepared with mildly damaged CNTs are found to have 97.5% higher strength and 14.2% higher modulus than pure Al. Increased carbide formation-due to the damage sustained-is observed and is believed to be in the form of isolated secondary particles within the matrix which do not contribute to enhancing the Al-CNT bonds. The strength and modulus of composites with severely damaged CNTs are found to be higher by 71% and 3.3% than pure Al, suggesting that even fragmented CNT particles can contribute to enhancing the strength and modulus of the Al matrix. The results are analyzed in light of strengthening mechanisms expected to be playing different roles in Al-CNT composites. The enhancement in strength is believed to be mainly due to matrix strengthening mechanisms and is not affected by CNT damage whereas the gain in Young's modulus is due to load transfer to the CNTs and accordingly is more significant in the case of the mildly damaged CNTs which have retained their tubular structure and high aspect ratio.

Carbon nanotube-reinforced polymer composites are being investigated as promising new materials having enhanced physical and mechanical properties. With regards to mechanical behavior, the enhancements reported thus far by researchers are lower than the theoretical predictions. One of the key requirements to attaining enhanced behavior is a uniform dispersion of the nanotubes within the polymer matrix. Although solvent mixing has been used extensively, there are concerns that any remaining solvent within the composite may degrade its mechanical properties. In this work, a comparison is carried out between solvent and ''solvent-free'' dry mixing for dispersing multiwall carbon nanotubes in polypropylene before further melt mixing by extrusion. Various weight fractions of carbon nanotubes (CNTs) are added to the polymer and their effect on the mechanical properties of the resulting composites is investigated. Enhancements in yield strength, hardness, and Young's modulus when compared with the neat polymer, processed under similar conditions, are observed. Differences in mechanical properties and strain as a function of the processing technique (solvent or dry) are also clearly noted. In addition, different trends of enhancement of mechanical properties for the solvent and dry-mixed extrudates are observed. Dry mixing produces composites with the highest yield strength, hardness, and modulus at 0.5 wt% CNT, whereas solvent mixing produces the highest mechanical properties at CNT contents of 1 wt%. It is believed that this difference is primarily dependent on the dispersion of CNTs within the polymer matrix which is influenced by the processing technique. Field emission scanning electron microscopy analysis shows the presence of clusters in large wt% CNT samples produced by dry mixing. Samples produced by solvent mixing are found to contain homogeneously distributed CNTs at all CNT wt fractions. CNT pull-out is observed and may explain the limited enhancement in mechanical properties.

Aluminum (Al)-carbon nanotube (CNT) composites are promising candidates for friction and wear applications. The wear behavior of Al-CNT composites, with up to 5 wt% homogeneously dispersed CNTs, is investigated in the present study and compared to that of pure aluminum processed using the same technique of cold compaction and hot extrusion. The effects of CNT content, sliding speed and applied load, on the wear behavior of the composites were studied. The morphologies of the wear surfaces were investigated using scanning electron microscopy (SEM). Hardness and wear resistance were found to increase significantly with CNT content. The wear rate of the 5 wt% CNT composite decreased by 78.8% compared to pure aluminum. This was accompanied by a decrease in the coefficient of friction. For samples with 5 wt% CNT, the wear rate and coefficient of friction were found to decrease with increasing sliding speed. The SEM investigation of the worn surfaces confirmed the dominant role played by the CNTs in enhancing the wear characteristics. CNTs were observed to be either partially or fully crushed forming a carbon film that covered the surface and acted as a solid lubricant enhancing the wear behavior significantly.

Nanocomposite membranes of Ethylene Vinyl Acetate (EVA) with Cloisite 20A and 30B montmorillonite clays were prepared by a novel combination of solution compounding, extrusion and compression molding in order to achieve a good dispersion of the clay within EVA. X-ray diffraction and TEM analysis showed that the EVA-C20A nanocomposite primarily contained intercalated clay structures, whereas the EVA-C30B primarily contained exfoliated clay structures. This difference was found to lead to different gas permeability and selectivity behaviors.

A process is a method of shaping, joining or surface-treating a material. Process selection has three steps. The first is to identify, from the "menu" of all available processes, the subset which can give a chosen material to the desired shape with the desired detail, precision and finish. The second is to choose, from among these, the ones that will do so at the lowest cost. The final step is to investigate the most promising processes in depth, exploring considerations such as availability, in-house experience, safety and environmental issues. The first two steps can be thought of as process pre-selection. Components have to be assembled and finished to create products. Here too, the ability to rank by cost, however crudely, helps guide pre-selection. Cost models are reviewed from the perspective of material and process selection. An approximate model is useful provided it has generality-that is, it must allow comparison of very different processes. Many approaches fail in this. One that works, based on resource consumption, is developed here and its use for selection is illustrated. It has been implemented as part of a tool that allows rapid pre-selection from a database of 112 processes. 1. Process pre-selection. A process, in the sense used in this paper, is a method for shaping, joining or surface-treating a material. There are many processes, each with its own characterising attributes: the materials with which it is compatible, the shapes it can make, the features it can create, and so forth. Process selection is the act of identifying, from among these, the process best suited to meet the requirements of a design. As detailed elsewhere (Esawi and Ashby, 1998b; Ashby, 1999), process selection has three steps: screening, ranking and a search for supporting information. In the first step, all processes that cannot meet the design requirements are screened out, leaving only those that can achieve them. In the second, the surviving candidates are ranked by cost, identifying the small number that are most promising for deeper exploration. In the final step, supporting information is sought for each of the top-ranked candidates-details of the shapes it can make, the materials with which it is compatible, and case studies of its application in other products and so forth. The first two steps can be thought of as pre-selection. They identify the subset of processes that are worth exploring in depth. The last step, in which detailed information for the most promising candidates is assembled and reviewed, is the one in which the final selection is made. We are here interested in pre-selection, requiring methods for screening the large population of processes to identify those that have promise, and for ranking them to guide the final, in-depth exploration,. The ranking, almost always, involves consideration of cost.

The review paper presents a systematic understanding of different synthesis routes to obtain holey graphene, its properties, and key applications in different fields. The article also evaluates the current progress and future opportunities of HG.

In this work, Carbon Nanotube Buckypapers (CNTBPs) were prepared using vacuum filtration. Morphology and pore size distribution were investigated using scanning electron microscopy (SEM), and nitrogen gas adsorption. The prepared BPs were subsequently exposed to four different boiling solvents (acetone, IPA, THF and DMF) for 40 min and the morphology and pore size were reevaluated. Results indicated that the type of solvent affects the pore size distribution with DMF giving more pores in the smaller pore size ranges. The findings confirm the potential of the solvent evaporation technique in tailoring the porosity of BP membranes for filtration applications.

Melt compounding has been favored by researchers for producing nylon 6/montmorillonite clay nanocomposites. It was reported that high compatibility between the clay and the nylon6 matrix is essential for producing exfoliated and well-dispersed clay particles within the nylon6 matrix. Though solution compounding represents an alternative preparation method, reported research for its use for the preparation of nylon 6/montmorillonite clay is limited. In the present work, solution compounding was used to prepare nylon6/montmorillonite clays and was found to produce exfoliated nylon 6/montmorillonite nanocomposites, for both organically modified clays with known compatibility with nylon 6 (Cloisite 30B) and clays with low/no compatibility with nylon 6 (Cloisite 15A and Na+-MMT), though to a lower extent. Additionally, solution compounding was found to produce the more stable α crystal structure for both blank nylon6 and nylon6/montmorillonite clays. The process was found to enhance the ...

Thin-film nanocomposite (TFN) membranes have been widely investigated for water treatment applications due to their promising performance in terms of flux, salt rejection, and their antifouling properties. This review article provides an overview of the TFN membrane characterization and performance. It presents different characterization techniques that have been used to analyze these membranes and the nanofillers within them. The techniques comprise structural and elemental analysis, surface and morphology analysis, compositional analysis, and mechanical properties. Additionally, the fundamentals of membrane preparation are also presented, together with a classification of nanofillers that have been used so far. The potential of TFN membranes to address water scarcity and pollution challenges is significant. This review also lists examples of effective TFN membrane applications for water treatment. These include enhanced flux, enhanced salt rejection, antifouling, chlorine resistan...