Mechanics of Advanced Composite Structures
Volume:1 Issue: 2, Winter and Spring 2014

This paper investigates axial compression process of multi-layered tubes with circular cross-section under the axial loading in the quasi-static condition using experimental method. Some specimens are prepared in seven different groups, namely; empty carbon/epoxy composite tubes, solid carbon/epoxy composite rods, empty copper tubes, composite tubes with silicon sealant filler, concentrically solid carbon/epoxy composite rod and copper tube with silicon sealant-filler between them, double-walled copper and carbon/epoxy composite tubes with silicon sealant-filler between them, and double-walled copper and carbon/epoxy composite tubes with silicon sealant-filler between them and into the inner tube. For each test, diagrams of axial load-displacement and absorbed energy-displacement are sketched and also, specific absorbed energy by each specimen is measured. The experiments show that filling the copper tube with the composite tubes and also, filling the carbon/epoxy composite tubes with the silicon sealant increase instantaneous axial load and consequently, increase energy absorption capability of the structure. Then, comparing the experimental measurements in viewpoint of energy absorption capacity and specific absorbed energy, an optimum sample is introduced. Furthermore, the effects of geometrical characteristics of composite and copper tubes such as tube diameter and different filling conditions are investigated, based on the axial compression tests. The experiments show that absorbed energy of the circular copper tubes that are filled with the carbon/epoxy composite tubes is higher than sole copper tubes. Also, it is found that copper tubes have less absorbed energy per unit of mass, compared to the empty carbon/epoxy composite tubes and also, the filled composite tubes by the silicon sealant.

Most impact tests are carried out on specimens with specific stacking sequence and dimensions to meet standard and experimental limitations. The damaged areas and the resulted reduction in the strength values of specimens may not agree very well with those of real application. In this paper an attempt is made to study the variation in the size of damaged areas due to varying the dimension of test specimens. Three different types of specimens, namely, A, B and C are examined under the same impact energy. It is found that the area of damage in the smaller size test specimens is larger. It is also concluded that the mode of failure is different for various specimens. The study of impact energy/damage area reveals that the types B and C tend to agree more than the smaller type suggesting a convergence of results as the specimen size approaches the actual size of larger nature. These graphs may be utilized to find impact energy in real structures with a specific stacking sequence and layout, if the size of damaged area is known.

In this research, using pyrolysis of phenolic resin in the presence of silicon particles, the SiC ceramic composite is formed. The samples were prepared by introducing 30, 35, 40, 45 and 50 wt% of Si particles to the phenolic resin. The samples were cured at 180°C then carbonized at 1100°C. The final carbonized C/Si composites are hot-pressed at 1500°C in inert atmosphere, which is more than the melting point of Si particles. In this temperature, Carbon vapor and melted Si react and SiC ceramic is formed. The XRD analysis of samples showed that SiC peak was observed in the final product while carbonized phenolic and Si particles also existed in the matrix. The samples were so brittle and therefore, several impregnation processes should have been used to reduce the porosity of composite. SEM images of in situ composite reveal extraordinary phenomenon which is related to the formation of CNT and nanostructures on the base of Si particles that grow like flower in the matrix. These nanostructures are one of the reasons for higher mechanical properties of final nanocomposite. Three-point flexural tests are also conducted for better understanding of mechanical improvement.

In the present research, the effects of delamination size and location on vibration characteristics of laminated composite beams are investigated both analytically and numerically. In the analytical method, the delaminated beam is modeled as four interconnected Euler–Bernoulli beams and the constrained and free mode models are both simulated. The differential stretching and the bending-extension coupling are considered in the formulation. Analytical expressions for displacement functions are presented in a simple form based on the basic standard trigonometric and hyperbolic functions. This new technique considerably simplifies the calculations regardless of the number of delaminations. In finite element method, delaminated composite beams are modeled in commercial finite element software, ABAQUS, and natural frequencies and mode shapes are extracted from the modal analysis. Analytical results are compared with finite element ones and available experiments in the literature. Finally, the generated database for different sizes and locations of delamination can be used to detect the existence of delamination in laminated composite beams and thento specify the size and location of delamination.

One of the most important applications of carbon nanotubes (CNTs) is as reinforcement of metal matrix composites, because of their excellent mechanical properties. In this study, Al-TiO2-multi walled carbon nanotubes (MWCNTs) nanocomposite is fabricated using isostatic pressing followed by hot extrusion. Mechanical alloying is used to mix powders of aluminium, TiO2 and MWCNTs. TiO2 with the amounts of 1, 2 and 3 wt% and CNTs with 0.5, 1, 1.5 and 2 wt% are used. Mechanical properties of Al-TiO2-CNT Nano composites were characterized with tensile and microhardness test. The morphology and microstructure of fabricated nanocomposites were characterized using field emission scanning (FESEM) and Transmission electron microscopy (TEM). The results showed that the maximum ultimate tensile strength (UTS) was observed for the Al-0.5 wt% CNT–1wt% TiO2 nanocomposite, which exhibited about 28% increase compared to the 1wt%TiO2- Al sample. The results showed that the addition of MWCNTs with uniform distribution improved the tensile strength and micro hardness.

The The main objective of this research paper is to present 3-D elasticity solution for free vibration analysis of elastically supported continuously graded carbon nanotube-reinforced (CGCNTR) annular plates. The volume fractions of oriented, straight single-walled carbon
nanotubes (SWCNTs) are assumed to be graded in the thickness direction. An equivalent continuum model based on the Eshelby-Mori-Tanaka approach is employed to estimate the effective constitutive law of the elastic isotropic medium (matrix) with oriented, straight carbon nanotubes (CNTs). A semi-analytical approach composed of 2-D differential quadrature method and series solution is adopted to solve the equations of motion. The novelty of the present work is to exploit Eshelby-Mori-Tanaka approach in order to reveal the impacts of the volume fractions of oriented CNTs and different CNTs distributions on the vibrational characteristics of CGCNTR annular plates.

This study investigates natural frequency analysis of an FG composite rectangular plate partially contacting with a bounded fluid. The material properties are assumed to be varying continuously through the thickness direction according to a simple power law distribution in terms of volume fraction of material constituents. Wet dynamic transverse displacements of the plate are approximated by a set of admissible trial functions which are required to satisfy the clamped and simply supported geometric boundary conditions. Fluid velocity potential satisfying fluid boundary conditions is derived and wet dynamic modal functions of the plate are expanded in terms of finite Fourier series for compatibility requirement along the contacting surface between the plate and the fluid. Natural frequencies of the plate coupled with sloshing fluid modes are calculated using Rayleigh–Ritz method based on minimizing the Rayleigh quotient. The proposed analytical method is validated by available data in the literature. The numerical results show the effects of boundary conditions, aspect ratios, thickness ratios, gradient index, material properties of the FG plate, depth of the fluid and dimensions of the tank on the wet natural frequencies.