In this study, microstructure and mechanical properties of Cu-based amorphous alloy matrix composites consolidated by spark plasma sintering (SPS) equipment were investigated. Amorphous alloy powders were mixed with 10∼40 vol.% of pure Cu powders, and were consolidated at 460°C for 1/2 minute under 300 or 700 MPa. The consolidated composites contained Cu particles homogeneously distributed in the amorphous matrix, and showed a considerable plastic strain, whereas their compressive strength was lower than that of the monolithic amorphous alloys. The compressive strength and plastic strain of the composites consolidated under 700 MPa showed 10∼20% and two times increases, respectively, over those of the composites consolidated under 300 MPa. The increase in consolidation pressure could play a role in sufficiently bonding between prior amorphous powders, in preventing micropores, and in suppressing the crystallization, thereby leading to the successful consolidation of the high-quality composites. Microfracture mechanisms were investigated by directly observing microfracture processes using an in situ loading stage. Cu particles present in the composites acted as blocking sites of crack propagation, and provided the stable crack growth. These findings suggested that the composites consolidated by the SPS presented new possibilities of application to structural materials or parts requiring excellent mechanical properties and large sizes.

The Equal Channel Angular Extrusion (ECAE) process is one of the most promising processes used for producing nanostructured consolidates making use of the severe plastic conditions that the powder particles experience during the extrusion. The intrinsic heat generated during extrusion in addition to 1.16 total strain imposed on the powder per pass can substitute for the elevated temperature required for sintering. The consolidation conditions of the Nanocrystalline-Micropowder (NCMP) prior to ECAE influences significantly the structural evolution and hence mechanical properties of the produced bulk product. Through the current research work, consolidation maps of hardness and density variation for NCMP Al-2124 powders hot compacts were constructed. A NCMP of about 45μm particle size and 87nm internal structure average size was used. Hot compacts of height-to-diameter (h/d) ratio of 4 were obtained by combinations of temperatures (360, 420 and 480°C), durations (30, 60, and 90 minutes), and pressures (4, 5, and 6) multiples of the yield strength (σ ys ) of as received Al-2124. For the NCMP hot compacts, an optimal combination of compaction conditions was for 60min duration at 420-to-480°C range of temperatures, and 375–450MPa (5–6σ ys ) range of pressure. For the 30 and 90min compaction durations the optimum properties were limited to 480°C over a stress range of 5.2 to 5.8σ ys . Uniformity of density along the sample’s length was achieved for NCMP hot compacts at the conditions of (6σ ys (450MPa), 420°C–480°C and 60 minutes), and (5σ ys (375MPa), 420–480°C and 90 minutes). Fully dense uniformly deformed bulk products with enhance hardness up to 178% compared to the hot compact was achieved post one-pass and 2-pass routes A and C at extrusion temperature of 235°C.

Electron back scattered diffraction (EBSD) was used to document the texture developed during ECAP. Samples of commercial purity aluminum processed to 8 passes through route B C and route C were examined on two planes (flow plane and the plane normal to the extrusion direction) and pole figures and orientation distribution function plots (ODFs) were generated. The results of the texture evolved in the as ECAPed samples gave some interpretation for the different mechanical properties realized via the two routes, though the amount of imposed equivalent accumulated strain was the same. Furthermore, the texture developed when ECAPed samples were subsequently compressed was also documented, and the examination of pole figures, ascertained that there is a transition of texture accompanied with the strain path change from simple shear to simple compression.

Nanostructured and conventional titania (TiO2) coatings were thermally sprayed using air plasma spray (APS) and high velocity oxy-fuel (HVOF) processes. The fatigue and mechanical properties of these coatings were investigated. The fatigue strength of coatings deposited onto low-carbon steel showed that the nanostructured titania coated specimens exhibited significantly higher fatigue strength compared to the conventionally sprayed titania. SEM analysis of fracture surfaces revealed valuable information regarding the influence of these coatings on the performance of the coated component. Analysis of surface deformation around Vickers indentations was carried out. This investigation gives new understanding to the nature of fatigue and deformation of these coatings.

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.

It is frequently reported that carbon nanotubes can efficiently be used to reinforce composite materials and considerably improve their structural mechanical properties. Therefore, it is essential to investigate the effective properties of such nanocomposites. In this work, an analytical approach is employed to derive the analytical exact solutions for the effective Young’s modulus and major Poisson’s ratio of a three-phase composite cylinder model representing a matrix filled single-walled carbon nanotube (SWCNT) embedded in another host material. In this study, all three constituents are considered generally cylindrical orthotropic. For validation, results from finite element analysis of an identical 3-D model are compared to those obtained analytically. It is shown that both techniques are in excellent agreement and therefore analytical exact solutions for the prediction of effective axial Young’s modulus and major Poisson’s ratio of the filled SWCNT embedded in another host material and all having orthotropic properties are verified.

Carbon nanofibers, such as single walled carbon nanotubes (SWNT), multiwalled carbon nanotubes (MWNT) and vapor-grown carbon nanofibers (VGCF or VGCNF) are routinely compounded with polymers to create thermally and electrically conductive polymer nanocomposites. Our group is interested in combining the conduction with structural functionality by reinforcing a high-performance thermotropic liquid crystal polymer (LCP) matrix with vapor-grown carbon nanofibers and single walled carbon nanotubes. High strength and stiffness can be achieved in LCPs through the alignment of molecular domains during high-shear mixing and extrusion. Further strength and stiffness enhancements are potentially possible if the carbon nanofibers could also be aligned, perhaps, with the assistance of the aligned domains of the LCP matrix. However, the geometrical structure of VGCF is quite different and the diameter is one to two orders of magnitude larger than that of SWNT. Therefore, the processing conditions and the interactions between the LCP domains and the nanofibers are expected to lead to different dispersion and alignment characteristics of VGCF and SWNT within the LCP matrix. In this work, twin-screw and Maxwell-type mixer-extruders were used to produce neat LCP filaments and LCP-nanofiber composite filaments with various concentrations of VGCF and SWNT. The dispersion and orientation of the VGCF and SWNT reinforcements were determined by X-ray diffraction and electron microscopy. The filaments were loaded in quasi-static uniaxial tension until fracture to determine the tensile modulus, strength and strain-to-failure. The mechanical properties showed a strong dependence on the filament diameter, nanofiber concentration and processing parameters. A significant increase in mechanical performance was observed with decreasing filament diameter irrespective of the carbon nanofiber concentration. Fracture surfaces examined under electron microscopy revealed hierarchical features at multiple length scales. At the macroscopic scale, a skin-core configuration was observed in the filament cross-section with the skin possessing a greater degree of LCP molecular alignment and nanofiber alignment than the core. The mechanical and electrical properties of the LCP, LCP-VGCF and LCP-SWNT nanocomposite filaments will be described and related to processing parameters, the type of carbon nanofibers (VGCF or SWNT) and the resulting composite microstructure.

This paper presents activities related to the development of nanocomposites and hierarchical nanocomposites; at the Hawaii Nanotechnology Laboratory of the Department of Mechanical Engineering of the University of Hawaii at Manoa. On nanocomposites, developments on toughening of polymeric materials employing nanoparticles and carbon nanotubes are reported. On hierarchical nanocomposites, first, mechanical properties improvements for continuous fiber ceramic composites using nanoparticles are discussed. Second, a multifunctional micro-brush using carbon nanotubes is discussed. Third, the structure of a micro-foam using carbon nanotubes is explained. Finally, the multifunctional properties improvement of a novel three-dimensional hierarchical nanocomposite employing carbon nanotubes is discussed. In closing, the effect of chirality of single-walled nanotubes on their thermomechanical properties evaluated analytically using asymptotic homogenization method and numerically employing finite element method will be explained, and analytical closed form solutions for matrix filled nanotube nanocomposites, also verified numerically, assuming generally cylindrical orthotropic properties will be reported.

Understanding the stress transfer between nanotube reinforcements and matrix is an important factor in determining the overall mechanical properties of nanotube-reinforced composites. The classical shear-lag model in which the fiber and the matrix are equally long can not be applied to nanotube-based composite structures. Recently, a shear-lag model under mechanical loading for a concentric composite cylinder embedded with a capped nanotube has been introduced as the representative volume element (RVE). In this study, using similar approach the shear lag model is extended for a system under both mechanical and thermal loadings. The outer surface of RVE is prescribed to heating and cooling conditions, and transient heat transfer concept is used to find the temperature distribution in the matrix and on the surface of the nanotube. Using constitutive, geometrical and equilibrium equations for a given RVE, new shear-lag model for a nanotube-reinforced composite is then derived. It is demonstrated that the proposed model at room temperature could reduce to the same results obtained previously. These equations can be used to predict the mechanical properties of nanocomposite systems in real applications.

Tensile behavior of a carbon nanofiber reinforced vinyl ester polymer composite was studied using dog-bone shaped specimens to obtain its mechanical properties. Pyrograf III which is a very fine, highly graphitic and yet low cost carbon nanofiber was used as the fiber material. Vinyl ester with low molecular weight which was used as the matrix material is a thermoset with high tensile strength at room temperature. When small amounts of carbon nanofibers are combined with vinyl ester, the stiffness of the resulting composite can improve if the fiber-matrix adhesion is good. The mechanical properties can improve further after surface treatment (functionalization) of carbon nanofibers. This surface treatment adds some functional groups chemically to the nanofiber’s surface which increases the adhesion between nanofiber and matrix resin. Understanding the mechanical behavior of these composites is crucial to their effective application. In this research the stiffness, strength, and tensile deformation behavior of these nanocomposites were investigated. The effects of matrix curing systems and composition, strain rate, nanofiber concentration, nanofiber surface treatment and environment such as low and high temperatures and humidity were also characterized. Based on the mechanical properties simple models were used to represent tensile stress-strain and deformation behaviors of the nanocomposite. The experimental results were also applied to these models to examine their predictive capability.

This paper describes the first steps in the area of prediction mechanical properties of nanotubes-plastic composites. Multi-level approach is used in order to take into account all the known data about all levels of composite material. Effective (macroscopic) mechanical properties are produced from solution of inverse boundary problem of continuum medium mechanics with coordinate-dependent elastic tensor. Theoretical results are compared with known experiment [1] on reinforcing polystyrene film.

In this study we are presenting a novel method for introducing nanoclay in epoxy matrix composites. The method involves vacuum-assisted deposition of fine clay particles directly onto the surface of commercially available prepregs. A deposition chamber is developed that is capable of breaking down nanoclay particles by subjecting them to shear and depositing them uniformly onto prepregs at room temperature. By using the deposition chamber, a thin layer of nanoclay is deposited on 101.6mm×101.6mm woven glass/epoxy prepregs. Twelve of these prepregs are stacked and cured by an autoclave at a temperature of 121°C under a constant pressure of 0.2MPa (30psi) for 1 hour. After the curing is complete, the laminates are cut into 10.8mm×31.7mm samples for three-point bending tests, glass transition temperature measurements and microstructural characterization. The improvements in mechanical properties such as flexural strength, flexural stiffness, and glass transition temperature by the addition of nanoclay are presented. Nanocomposite morphology is studied by light microscopy and scanning electron microscopy. Marginal improvements in mechanical properties are observed with only 0.6% nanoclay content. The flexural stiffness improved by 4% while maintaining the flexural strength constant at around 400Wa. Glass transition temperature is measured as 128°C for samples with and without nanoclay. However, significant differences in microstructure are observed. Although both samples contain micro-voids, these voids are observed to be more extensive in samples involving nanoclay.

Silicate minerals have been found to improve physical and mechanical properties of polymers significantly through clay/polymer nanocomposites. This class of materials uses smectite-type clays, such as hectorite, montmorillonite, magadiite, and synthetic mica, as fillers to enhance the properties of polymers. One of the most important properties of smectite-type clays is their layered structure, in which each layer is constructed from tetrahedrally coordinated Si atoms fused into an edge-shared octahedral plane of either Al(OH) 3 or Mg(OH) 2 . The layers exhibit excellent mechanical properties parallel to the layer direction due to the nature of the bonding between these atoms. It has been found that Young’s modulus in the layer direction is 50 to 400 times higher than that of a typical polymer [1–5]. The layers have a high aspect ratio and each one is approximately 1 nm thick, while the diameter may vary from 30 nm to several microns or larger. Hundreds or thousands of these layers are stacked together with weak van der Waals forces to form a clay particle. With such a configuration, it is possible to tailor clays into various different structures in polymer [1,6,7].

Polymer nanocomposites based on poly(ethylene terephthalate) PET and with an intercalated and fairly dispersed nanostructure have been obtained in the melt state using a twin screw extruder. The intercalation and dispersion levels as well as the mechanical properties were studied varying the chemical nature and amount of the organic modification of the clay as well as the clay content. The intercalation level of PET into the organoclay galleries was measured by the increase in the interlayer distance upon mixing. The surfactant content did not influence the intercalation level but an interaction between the polymeric matrix and the surfactant, through a common polar character led to easier intercalation. The observed modulus increases and consequently the overall dispersion did not almost depend on either the amount or chemical nature of the used organic modification of the clay, suggesting that the parameters leading to high intercalation differ from those lead to a high modulus of elasticity and therefore to a high dispersion level. The obtained increases in the modulus of elasticity that reflect the dispersion level were large attaining a 41% increase with respect to that of the matrix after a 6wt% clay addition.

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.

The rapid prototyping (RP) technology has been advanced for various applications such as verification of design, functional test. Recently, researchers have studied various materials to fabricate functional RP parts. In this research, a nano composite deposition system (NCDS), which can fabricate various nano composites using polymer resins with various nano particles, was introduced. The NCDS is a hybrid system in which material removal process by mechanical micro machining and/or the deposition process is combined. To predict the mechanical behavior of nano composite part made by NCDS, it is critical to understand the mechanical properties of the NCDS material. The NCDS process was characterizes by process parameters such as raster orientation, bead width, weight percent, and curing condition. Tensile strengths and compressive strengths of fabricated specimens with various raster orientation were measured, and various sample parts made of nano composites were fabricated using NCDS.