Sharif Digital Repository

During the past decades, development of reinforcing materials caused a revolution in the structure of high strength and high performance cement-based concrete. Among the most important and exciting reinforcing materials, Steel Fiber (SF) becomes a widely used in the recent years. The main reason for addition of SF is to enhance the toughness and tensile strength and limit development and propagation of cracks and deformation characteristics of the SF blended concrete. Basically this technique of strengthening the concrete structures considerably modifies the physical and mechanical properties of plain cement-based concrete which is brittle in nature with low flexural and tensile strength... 

CNT-reinforced polymer composites have attracted attention due to their exceptional high strength. The high strength can be affected by the presence of defects in the nanotubes used as reinforcements in the practical nanocomposites. In this paper, a Molecular Structural Mechanics / Finite Element (MSM/FE) multiscale modeling is used to study the effect of carbon nanotube geometrical defects on the stability of SWCNT-polymer composites. Here, two types of representative volume elements (RVEs) for these nanocomposites are considered with perfect and defected CNT. These RVEs have the same dimensions. The nanotube is modeled at the atomistic scale using molecular structural mechanics whereas the... 

Hot isotherm compression tests were performed in temperature range of 350-500 °C and at strain rates of 0.0005 to 0.5 s-1 for Al6061 alloy reinforced with alumina nanoparticles. Effect of deformation parameters and optimal conditions for hot working this nanocomposite were comprehended thoroughly via hot working data analyses, electron microscopy images, and X-ray diffractograms. The results indicated the severity of hot deformation process and an increase in the activation energy to 320 kJ/mol due to the addition of nanoparticles. Dynamic recovery (DRV) was considered as the individual determinative softening mechanism during hot deformation of this nanocomposite, and no sign of dynamic... 

In this article, a Molecular Structural Mechanics/Finite Element (MSM/FE) multiscale modeling of carbon nanotube/polymer composites with viscoelastic (VE) polymer matrix is introduced. The nanotube is modeled at the atomistic scale using structural molecular mechanics. The matrix deformation is analyzed by nonlinear finite element method considering VE behavior. The nanotube and matrix are assumed to be bonded by van der Waals interactions based on the Lennard-Jones potential at the interface. Using the MSM/FE multiscale model, we investigate the effect of carbon nanotube (CNT) on the improvement of mechanical stability of the nanocomposite. Also, the buckling behavior of these... 

We investigate eigenvectors of rank-one deformations of random matrices B = A + θuu* in which A ∈ RN×N is a Wigner real symmetric random matrix, θ ∈ R+, and u is uniformly distributed on the unit sphere. It is well known that for θ > 1 the eigenvector associated with the largest eigenvalue of B closely estimates u asymptotically, while for θ < 1 the eigenvectors of B are uninformative about u. We examine O(1/N) correlation of eigenvectors with u before phase transition and show that eigenvectors with larger eigenvalue exhibit stronger alignment with deforming vector through an explicit inverse law 1/θ*-x with θ* := θ + 1/θ. This distribution function will be shown to be the ordinary...