Effects of vertically aligned carbon nanotubes on shear performance of laminated nanocomposite bonded joints.

The main objective is to improve the most commonly addressed weakness of the laminated composites (i.e. delamination due to poor interlaminar strength) using carbon nanotubes (CNTs) as reinforcement between the laminae and in the transverse direction. In this work, a chemical vapor deposition technique has been used to grow dense vertically aligned arrays of CNTs over the surface of chemically treated two-dimensionally woven cloth and fiber tows. The nanoforest-like fabrics can be used to fabricate three-dimensionally reinforced laminated nanocomposites. The presence of CNTs aligned normal to the layers and in-between the layers of laminated composites is expected to considerably enhance the properties of the laminates. To demonstrate the effectiveness of our approach, composite single lap-joint specimens were fabricated for interlaminar shear strength testing. It was observed that the single lap-joints with through-the-thickness CNT reinforcement can carry considerably higher shear stresses and strains. Close examination of the test specimens showed that the failure of samples with CNT nanoforests was completely cohesive, while the samples without CNT reinforcement failed adhesively. This concludes that the adhesion of adjacent carbon fabric layers can be considerably improved owing to the presence of vertically aligned arrays of CNT nanoforests.

Toward wafer-scale patterning of freestanding intermetallic nanowires.

Individual metal alloy nanowires of constant diameter and high aspect ratio have previously been self-assembled at selected locations on atomic force microscope (AFM) probes by the method reported in Yazdanpanah et al (2005 J. Appl. Phys. 98 073510). This process relies on the room temperature crystallization of an ordered phase of silver-gallium. A parallel version of this method has been implemented in which a substrate, either an array of micromachined tips (similar to tips on AFM probes) or a lithographically patterned planar substrate, is brought into contact with a continuous, nearly planar film of melted gallium. In several runs, freestanding wires are fabricated with diameters of 40-400 nm, lengths of 4-80 µm, growth rates of 80-170 nm s( - 1) and, most significantly, with yields of up to 97% in an array of 422 growth sites. These results demonstrate the feasibility of developing a batch manufacturing process for the decoration of wafers of AFM tips and other structures with selectively patterned freestanding nanowires.

Chirality dependence of carbon single-walled nanotube material properties: axial Young's modulus.

The potential use of individual carbon nanotubes as nano devices warrants detailed investigation of their mechanical behavior based on structural and geometrical configurations. The objective of this paper is to unravel the structural and chirality dependence of the axial Young's modulus of a carbon single-walled nanotube by analytical and numerical approaches. In this work, we employ the general homogenization composite shell model developed based on the asymptotic homogenization technique for analytical modeling of single-walled nanotubes. We derive the working formulae for the effective elastic properties of carbon single-walled nanotube of any chirality and predict the structural and chiral dependence of the effective axial Young's modulus of the nanotube. Also, a finite element analysis on the chirality dependence of the axial Young's modulus of the carbon nanotube is reported. The outcomes of our analyses are compared with available experimental and simulation results.

Chirality dependence of carbon single-walled nanotube material properties: axial coefficient of thermal expansion.

Carbon nanotubes are one of the best candidates for applications where structural, thermal, and chemical stabilities are of great importance. Despite the fact that significant efforts have been devoted to study properties and behavior of the carbon nanotubes in recent years, there have not been sufficient results available on their thermoelastic properties. This paper investigates the chirality dependence of coefficient of thermal expansion of carbon single-walled nanotubes both analytically and numerically. The analytical approach in characterizing the chirality dependence of the coefficient of thermal expansion uses an asymptotic homogenization method. A second analytical interpretation follows a free-expansion strain method based on basic principles of thermoelasticity. The derived formulae make it easy to understand the dependencies of the nanotube thermoelastic properties on its geometrical parameters. The results from these analytical studies were verified using a finite element method. All three independent studies consistently demonstrate that the coefficient of thermal expansion of carbon single-walled nanotubes is independent of their chirality.