Hossein Golestanian

EVALUATION OF EFFECTIVE MECHANICAL PROPERTIES OF NANOCOMPOSITES REINFORCED WITH SINUSOIDAL CARBON NANOTUBES

Carbon nanotubes (CNTs) possess exceptional mechanical properties and are therefore suitable candidates for use as reinforcements in composite materials. Substantial improvements in mechanical properties of polymers have been attained through the addition of small amounts of CNTs. The CNTs, however, form complicated shapes and do not usually appear as straight reinforcements when introduced in polymer matrices. In this paper, theory of elasticity of anisotropic materials and finite element method (FEM) are used to determine effective mechanical properties of sinusoidal-nanotube reinforced polymers. The effects of CNT shape, orientation, and CNT distribution on nanocomposite effective properties are investigated by modeling different CNT-reinforced polymers. Also, the effects of interface strength on nanocomposite properties are investigated using an elastic interface model. The results indicate that even a slight nanotube curvature significantly reduces the reinforcing efficiency of sinusoidal — nanotubes...

A Comparison between the Properties of Solid Cylinders and Tube Products in Multi‐Pass Hot Radial Forging Using Finite Element Method

Radial forging is an open die forging process used for reducing the diameter of shafts, tubes, stepped shafts and axels, and creating internal profiles for tubes such as rifling of gun barrels. In this work, a comprehensive study of multi‐pass hot radial forging of short hollow and solid products are presented using 2‐D axisymmetric finite element simulation. The workpiece is modeled as an elastic‐viscoplastic material. A mixture of Coulomb law and constant limit shear is used to model the die‐workpiece and mandrel‐workpiece contacts. Thermal effects are also taken in to account. Three‐pass radial forging of solid cylinders and tube products are considered. Temperature, stress, strain and metal flow distribution are obtained in each pass through thermo‐mechanical simulation. The numerical results are compared with available experimental data and are in good agreement with them.

NEURAL NETWORK ANALYSIS APPLICATION TO PERMEABILITY DETERMINATION OF FIBERGLASS AND CARBON PREFORMS

Preform permeability is an important process parameter in liquid injection molding of composite parts. This parameter is currently determined with time consuming and expensive experimental procedures. This paper presents the application of a back-propagation neural network to predicting fiber bed permeability of three types of reinforcement mats. Resin flow experiments were performed to simulate the injection cycle of a resin transfer molding process. The results of these experiments were used to prepare a training set for the back propagation neural network program. The reinforcements consisted of plain-weave carbon, plain-weave fiberglass, and chopped fiberglass mats. The effects of reinforcement type, porosity and injection pressure on fiber bed permeability in the preform principal directions were investigated. Therefore, in the training of the neural network reinforcement type, these process parameters were used as the input data. Fiber bed permeability values were the specified output of the program. As a result of the specified parameters, the program was able to estimate fiber bed permeability in the preform principal directions for any given processing condition. The results indicate that neural network may be used to predict preform permeability.

Thermal Conductivity of SWCNT Nanocomposites Determined Using Finite Element Methods

This research focuses on the determination of thermal conductivity of single‐walled carbon nanotube (SWCNT) composite materials using Finite Element Methods (FEM). The effects of SWNT array distribution on effective thermal conductivity of composites are investigated. The composite is analyzed at a microscopic scale by considering two fiber distribution patters: 1‐ a moderately aligned nano‐array distribution, and 2‐ a random SWCNT nano‐array distribution. A thermal conduction problem is solved in the composite domain to obtain the effective thermal conductivity in each case. A composite lamina with 12 percent SWCNT fiber volume fraction is investigated. ANSYS finite element software is used to perform the analysis. The results of FEM models are compared to thermal conductivities obtained using the weight‐average formulations. Weight average formulations under‐estimate the value of composite thermal conductivity. The effective thermal conductivity values obtained using the FEM models turned out to be much...

Evaluation of fracture energy for nanocomposites reinforced with carbon nanotubes using numerical and micromechanical methods

ABSTRACT This research presents numerical and micromechanical investigations of the effects of carbon nanotube (CNT) weight fraction on nanocomposites fracture energy. For this reason, numerical models consisting of 0.1, 0.2, and 0.5% CNT weight fractions are developed based on TEM image taken from nanocomposite samples. Fracture energy of these nanocomposites is determined using finite element simulations and micromechanics models. To determine the crack growth path and fracture parameters, mixed mode loading was applied on the nanocomposites. Also, fracture energy is determined using FESEM images along with numerical analysis. Finally, the numerical results were compared with experimental measurements found in the literature.

Experimental and numerical determination of compressive mechanical properties of multi-walled carbon nanotube reinforced polymer

Abstract In this paper, experimental and numerical methods were used to determine compressive mechanical properties of multi-walled carbon nanotube (MWCNT) reinforced epoxy. Standard samples with varying weight fractions of MWCNTs were prepared and were tested in compression. Nanocomposite modulus of elasticity, yield strength and compressive strength were determined experimentally. Experimental results show that incorporation of CNTs improves yield and compressive strengths of the epoxy resin to a large extent. Also, numerical simulation of nanocomposites was conducted in ABAQUS finite element (FE) software. In these simulations, the effects of the interface strength between individual nanotubes and between the outer nanotube and matrix were also investigated. Two different mechanisms were used to model these interfaces. In one set of the models, connector constraints were used as the interface. In the second set, an interface consisting of thin shells surrounding the nanotubes was used. The results of this investigation suggest that nanocomposite longitudinal modulus increases with increasing interface strength. Also, numerical results suggest that the connector model predicts values lower than the thin shell interphase model. Finally, experimental and numerical results were compared and a good correlation is observed between the results.

Fracture Analysis of Sinusoidal CNT-Based Nanocomposites with Uniform and Nonuniform CNT Distributions

In this investigation, the effects of carbon nanotube (CNT) shape and distribution on nanocomposite failure are investigated. To achieve our goals, nanocomposites consisting of straight and sinusoidal CNTs with uniform and nonuniform distributions have been modeled. Failure of these nanocomposites is investigated using finite element simulations and micromechanics models. Initially, straight CNT-reinforced polymer is simulated and the stress–strain diagram for this nanocomposite is obtained. To validate our models, the simulation results of this nanocomposite are compared with those found in the literature. Then, sinusoidal CNT-reinforced polymers with uniform and nonuniform CNT distributions are modeled. The results are compared to determine the influence of CNT shape and distribution on nanocomposite failure mechanisms.

Resin Flow Analysis in the Injection Cycle of a Resin Transfer Molded Radome

Resin flow analysis in the injection cycle of an RTM process was investigated. Fiberglass and carbon fiber mats were used as reinforcements with EPON 826 epoxy resin. Numerical models were developed in ANSYS finite element software to simulate resin flow behavior into a mold of conical shape. Resin flow into the woven fiber mats is modeled as flow through porous media. The injection time for fiberglass/epoxy composite is found to be 4407 seconds. Required injection time for the carbon/epoxy composite is 27022 seconds. Higher injection time for carbon/epoxy part is due to lower permeability value of the carbon fibers compared to glass fiber mat.