Amal M.K. Esawi

Cost Estimates to Guide Pre-selection of Processes

Abstract 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 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.

Characterization and Spark Plasma Sintering of Mechanically Milled Aluminum-Carbon Nanotube (CNT) Composite Powders

Carbon nanotube (CNT) reinforced metallic composites have been recently gaining a significant amount of scientific interest. The promise of transmitting part of the remarkable and outstanding properties of CNTs to metals has spurred efforts to design and manufacture metallic composites reinforced with CNTs. Out of the metallic matrices investigated, Al has received significant attention. The stability of these powders at high temperatures is important to investigate, since they would ultimately be consolidated at elevated temperatures into useful products, and service temperature limits will be important. In this article, we discuss the detailed characterization of SPEX milled Al-CNT powders (well-dispersed CNTs in an Al matrix at 2.5 and 5.0 wt% loading), their heat treatment and consolidation using spark plasma sintering.

Fabrication and Properties of Nylon-6/Layered Silicate Nanocomposites by Melt Blending

Polymer/clay nanocomposites currently attract immense interest from both research and industrial communities. By dispersing at the molecular level a tiny amount of clay within a polymeric matrix, a wide range of properties can be significantly improved. The efficiency of the clay (layered silicate) in improving the properties of the polymer materials is primarily determined by the degree of its dispersion in the polymer matrix. To promote the molecular and stable dispersion of the clay layers, the clays should be organically-modified with onium salts. In this work, nylon-6 nanocomposites based on two types of commercial organoclays were prepared by melt blending via single-screw extrusion. The good dispersion of clay in the nylon-6 nanocomposites was confirmed by X-ray diffraction and transmission electron microscopy. The influence of the dispersed nano-clay fillers on the thermal and mechanical properties of the resulting nanocomposites was characterized using thermogravimetric analysis and nanoindentation.Copyright

Effect of Milling Time and Annealing on the Mechanical Response of Mechanically Milled Aluminium

Owing to its many exceptional properties, aluminium finds many applications in theaerospace, automotive, building and packaging industries. Enhancing its properties through alloyingor thermal treatments has been the focus of researchers’ interests for a long time. In this work, purealuminium powders were mechanically milled for up to 12 hrs and then were cold compacted andextruded to produce bulk nanostructured material. Both tensile and compressive tests wereconducted and the results compared. Post extrusion annealing treatments for up to 3 hrs wereconducted on additional samples.It was found that increasing the process control agent (PCA) content as well as the milling durationresulted in a finer microstructure and hence enhanced mechanical strength. This was accompaniedby a reduction in the ductility of the material. Moreover, compression tests revealed that thesamples are significantly more ductile in compression than in tension and that the decrease inductility with increase in milling time is less significant than in the case of tension. The differencein mechanical response is attributed to plastic instabilities. Annealing was found to enhance thetensile ductility of the samples without sacrificing strength.

Fabrication of Carbon Nanotube/Low Density Polyethylene Composites for Strain Sensing

Carbon Nanotubes (CNTs) have shown remarkable electrical, piezoresistive properties as well as other physical properties. The aim of this study is to investigate the potential of CNT-polymer composites in strain sensing using low density polyethylene (LDPE) polymer. Different CNT loadings were used (0, 1, 2, 3.5, 5, 6.5 and 8 weight %). CNT/LDPE composite films of 1mm thickness were fabricated using compression molding. The electrical resistance at no load condition was measured and the percolation behavior was obtained. The percolation threshold was found to be in the range of (2-5) wt%, where a decrease in resistivity by 5 orders of magnitude was observed. The sensitivity (gauge factor – GF) of the films was evaluated by correlating the strain applied with the simultaneously measured resistance. For a strain range of up to 320 µε, a gauge factor of 200 was achieved at a CNT loading of 5 wt%.

Powder Rolling of Carbon Nanotube-Reinforced Aluminium

Powder Rolling is a traditional technique for the fabrication of metal strips in which metal powder is continuously fed into a rolling mill and compacted into strip. Recently, carbon nanotubes (CNTs) have emerged as promising new materials with exceptional properties. This has stimulated interest in their use to reinforce polymer, and ceramic matrices. In spite of their potential technological importance, a few research groups have investigated their use to reinforce metal matrices. In this paper, the powder rolling technique is used for the first time to fabricate aluminium strips reinforced with carbon nanotubes. Mixtures of aluminium powder and various wt% catalytic multi-wall carbon nanotubes (MWCNT) were roll compacted and sintered to form thin strips. CNTs were observed to be aligned in the in-plane direction. Tension tests were conducted on the strips to investigate the effect of the carbon nanotubes on the mechanical properties. Although the yield strength for the 0.5 wt% CNT samples increased, the ultimate strength and strain-to-failure for all samples with CNT were mostly lower than the base metal. This was attributed to the observed clustering of the CNTs, especially in higher wt% CNT samples. Provided the CNT clustering problem is overcome, the process promises many advantages; namely, its low cost, the ease of incorporating the carbon nanotubes and the potential important applications for the carbon nanotube-metal strips.Copyright

Development of an Electroless Plating Process for Multi-wall Carbon Nanotubes (MWCNTS) to Improve Their Dispersion and Wettability in Molten Aluminum

Embedding CNTs in molten aluminum by mechanical stirring represents one approach of producing Aluminum-Carbon Nanotube (Al-CNT) composites. Molten aluminum is known for its high surface tension with CNTs resulting in extremely poor wettability. One approach to tackle this problem is done by metallizing CNTs via electroless plating . The new interfacial metallic layer on CNTs improves their dispersion and wettability in molten aluminum. One of the challenges, however, is the rapid growth of the plated layer on CNTs during microfiltration of the prepared powder resulting in aggregates of metal-coated CNTs and grown copper crystals. This results in poor dispersion of the powder in molten aluminum making the industrial upscaling of the process not viable. In this work, chemical constraints were put to control electroless plating kinetically. Instead of growing catalytic palladium particles on top of CNTs via what is known as a two-step process sensitization and activation, colloidal ready grown Palladium-tin (Pd-Sn) particles of a fixed size were used to ensure the conformity of the coat, the concentration and volume of the catalytic solution was optimized to ensure the coverage of the surface area of CNTs. After the surface of CNTs was covered with the catalyst, a Copper-Cobalt (Cu-Co) electrolyte of extremely high deposition rate was used to ensure a reaction stopping mechanism before filtering the Copper coated CNTs ensuring that copper does not grow on aggregates of the tubes. Copper coated CNTs of an average size of 85 nm were obtained. Percentages from 0.5 to 2% of the prepared powder (containing less than 0.1% of CNTs for each 2 gm) were dispersed in molten aluminum and casted resulting into 12.2–52.1% increase in the Vickers hardness indicating the effectiveness of the copper coated CNTs in improving the properties of commercial pure aluminum.

Characterization of Nano- and Micro-Filled Resin Composites Used as Dental Restorative Materials

Adhesively-bonded resin composites have the advantage of conserving sound tooth structure with the potential for tooth reinforcement, while at the same time providing an aesthetically acceptable restoration. However, no composite material has been able to meet both the functional needs of posterior restorations and the superior aesthetics required for anterior restoration. In an attempt to develop a dental resin composite that had the mechanical strength of hybrid composite materials and the superior polish and gloss retention associated with microfilled materials, nanofilled resin composites have been introduced in the market. Although nanofillers are the most popular fillers utilized in current visible light-activated dental resin composites and are claimed to be the solution for the most challenging material limitations as a universal restorative material, the mechanisms by which these fillers influence the resin composite properties are not well explained. In this study, some physical and mechanical properties of a nanofilled resin composite containing 60 vol. % zirconia and silica fillers were evaluated and compared to those of a microhybrid resin composite of the same composition. The nanofilled resin composite was found to have equivalent polymerization shrinkage and depth of cure to the microhybrid material but a slightly lower degree of conversion and density. Regarding mechanical behaviour, although the nanocomposite was found to exhibit significantly higher wear resistance, and equivalent flexural strength, its indentation modulus and nanohardness were slightly lower. Field-emission scanning electron microscopy (FE-SEM) analysis was conducted in order to evaluate the microstructure and to obtain a better understanding of the effect of the nanofillers on the behaviour of the nanocomposite.Copyright