In this study, the elastic modulus of single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposite was studied using the 3D finite element method and compared with experimental results to investigate the effect of SWCNTs interphase, curvature, and agglomeration on the prediction of the elastic modulus. Nanocomposite specimens containing 0.1, 0.3, and 0.5 wt% SWCNTs were fabricated to obtain SWCNTs/epoxy elastic modulus. The elastic modulus increased until SWCNTs was incorporated up to 0.3 wt% and after that, the trend of increasing elastic modulus declined. TEM images showed that in higher contents of filler, there were some local SWCNTs agglomerations within the composites which caused a dropped in elastic modulus of specimens containing 0.5 wt% SWCNTs. Also, six different 3D representative volume element (RVE) of SWCNTs/epoxy including incorporated cylindrical, cylindrical with agglomeration, curved-cylindrical, cylindrical with interphase, cylindrical with interphase and agglomeration and curved-cylindrical with agglomeration SWCNTs in the epoxy matrix have been generated using Digimat-FE and their elastic modulus evaluated by Digimat-FE solver. The numerical results cleared that the simplest cylindrical RVE has the greatest discrepancy with experimental results which showed the necessity of consideration of three important parameters including SWCNTs interphase, curvature, and agglomerations. By considering SWCNTs interphase and agglomeration the difference of numerical and experimental results decreased so that in specimens containing 0.1 wt% SWCNTs the error was only 6.8%. Also, the best results obtained from RVE of curved-cylindrical with agglomeration in specimen containing 0.1 wt% SWCNTs with only 4.1% error which showed the importance of considering SWCNTs agglomeration and curvature for modeling of nanocomposites.

Effect of interphase, curvature and agglomeration of SWCNTs on mechanical properties of polymer-based nanocomposites: Experimental and numerical investigations

In this paper, theoretical and experimental studies are carried out to investigate the damping characteristics of carbon nanotube (CNT) reinforced epoxy nanocomposite beams. A modified Biot model is proposed to simulate the frequency-dependent damping characteristics of CNT reinforced epoxy nanocomposites and implemented into the finite element model for composite beams. The natural frequencies and modal damping ratios of CNT reinforced epoxy beams are predicted using the proposed finite element model. Then, CNT reinforced epoxy beam specimens are fabricated, upon which dynamic mechanical analysis and vibration tests are carried out. Comparison studies between theoretical and experimental results show that modified Biot model proposed here is more accurate than the original one in predicting loss factors of CNT reinforced epoxy nanocomposites. It is revealed that the damping ratios associated with the first three vibration modes of composite beam specimens initially increase and then decrease with the increment of CNT weight ratio. The first order damping ratio with 0.4 wt% CNT reinforcement has the maximum value of 0.591%, which is improved by 41% compared with that of pure epoxy.

Damping characteristics of carbon nanotube reinforced epoxy nanocomposite beams

Viscoelastic nature of polymers makes their properties strongly dependent on temperature and strain rate. Characterization of material properties over a wide range of strain rates and temperatures requires an expensive and time consuming experimental campaign. While viscoelastic properties of materials are widely tested using dynamic mechanical analysis (DMA) method, the frequency dependent component of the measured properties is underutilized due to a lack of correlation between frequency, temperature, and strain rate. The present work develops a method that can extract elastic modulus over a range of strain rates and temperatures from the DMA data for nanocomposites. Carbon nanofiber (CNF) reinforced high-density polyethylene (HDPE) matrix nanocomposites are taken as the study material. Four different compositions of CNF/HDPE nanocomposites are tested using DMA from 40 to 120 °C at 1–100 Hz frequency. First, time-temperature superposition (TTS) principle is used to develop an extrapolation for the results beyond the test parameter range. Then the TTS curve is transformed to a time domain relaxation function using integral relations of viscoelasticity. Finally, the strain rate sensitive elastic modulus is extracted and extrapolated to room temperature. The transform results are validated with tensile test results and the error found to be below 13.4% in the strain rate range 10−5 to 10−3 for all four nanocomposites. Since the materials are tested with the aim of finding a correlation among the test methods, the quality of the material is not a study parameter and the transform should yield accurate results for any material regardless of composition and quality.

Extracting elastic modulus at different strain rates and temperatures from dynamic mechanical analysis data: A study on nanocomposites

A multi-stage hierarchical micromechanical approach is presented to predict the elastic properties of unidirectional carbon fiber (CF)-reinforced polymer hybrid composites containing carbon...

Multi-stage micromechanical modeling of effective elastic properties of carbon fiber/carbon nanotube-reinforced polymer hybrid composites

In this study the dynamic stability of viscoelastic functionally graded cylindrical shells (VEFGCSs) under an axial load with different initial conditions is investigated. Mathematical models are constructed for the problem of dynamic stability of the VEFGCSs, which is characterized simultaneously by taking into account both viscoelastic and FGM features. The basic equations of VEFGCSs are described by integro-differential equations using the linear viscoelasticity theory. An approach is developed to the determination of the critical times (CTs) for VEFGCSs with different initial conditions. Finally, the numerical analyzes are performed to demonstrate the influences of the initial conditions, the FGM profiles and the rheological parameter on the critical times for various geometric characteristics of the cylindrical shells.

About an approach to the determination of the critical time of viscoelastic functionally graded cylindrical shells

The present work deals with the evaluation of elastic properties and dynamic analyses of thin hybrid composite shell structures, which consist of conventional carbon fiber as the reinforcing phase and multiwalled carbon nanotubes-based polymer as the matrix phase. The Mori-Tanaka and strength of material method has been implemented to determine the elastic properties of such hybrid composite structures without and with considering agglomerations. An eight-noded shell element, which considers stress resultant-type Koiter's shell theory and transverse shear effect as per Mindlin's hypothesis having five degrees of freedom at each node, has been utilized for discretizing and analysis of such hybrid shell structures. The Rayleigh damping model has been implemented in order to study the effect of carbon nanotubes (CNTs) on damping capacity of such hybrid composite shell structures. Different types of spherical shell panels have been analyzed in order to study the time and frequency responses. Results s...

Vibration damping characteristics of carbon nanotubes-based thin hybrid composite spherical shell structures

The present article deals with the viscoelastic modeling and dynamic responses of the carbon nanotubes (CNTs)-based carbon fiber-reinforced polymer (CNTs-CFRP) composite spherical shell panels where CNTs are reinforced in the polymer matrix phase. The Mori–Tanaka micromechanics in conjunction with weak interface theory has been developed for the mathematical formulations of the viscoelastic modeling of CNTs-based polymer matrix phase. Further, the strength of material method has been employed to formulate the viscoelastic material behavior of the homogenized hybrid CNTs-CFRP composite materials. An eight-noded shell element with five degrees of freedom per node has been formulated to study the vibration damping characteristics of spherical shell structures made by CNTs-CFRP composite materials. Frequency- and temperature-dependent material properties of such hybrid composite materials have been obtained and analyzed. Impulse and frequency responses of such structures have been performed to study the effects of various important parameters on the material properties and such dynamic responses. Obtained results demonstrate that quick vibration mitigation may be possible using such CNTs-based proposed composite materials.

Viscoelastic modeling and vibration damping characteristics of hybrid CNTs-CFRP composite shell structures

The carbon nanotubes (CNTs) are well known for its application in the areas of advanced composite materials for their improved elastic properties. The large specific interfacial surface area owing to tiny dimensions of CNTs may greatly escalation the interfacial sliding which may promote the dissipation of energy in a dynamic situation that makes them very ideal for damping applications in engineering structures/systems. The present article investigates the viscoelastic modelling and dynamic responses of the CNTs – based carbon fiber reinforced two dimensional woven fabrics (CNTs-CFRP-2DWF) composite spherical shell panels where CNTs are reinforced in the polymer matrix phase. The Mori – Tanaka (MT) micromechanics in conjunction with weak interface (WI) theory has been developed for the mathematical formulations of the viscoelastic modelling of CNTs-based polymer matrix phase. Further, strength of material (SOM) method has been employed to formulate viscoelastic material behavior of the yarn and finally the viscoelastic properties of the representative unit cell (RUC) is established based on the unit cell method (UCM). An eight-node shell element with five degree of freedom per node has been formulated to study the vibration damping characteristics of spherical shell structures made by CNTs-CFRP-2DWF composite materials. The shell finite element formulation is based on the transverse shear effect as per the Mindlin's hypothesis, and stress resultant-type Koiter's shell theory. Frequency and temperature dependent material properties of such CNTs-CFRP-2DWF composite materials have been obtained and analysed. Impulse and frequency responses of such structures have been performed to study the effects of various important parameters such as volume fraction of CNTs, interfacial condition, agglomeration, temperature, geometries of shell panel on the material properties and such dynamic responses. Obtained results demonstrate that quick vibration mitigation may be possible using such CNTs-CFRP-2DWF composite material which is desirable to overcome the drawbacks of conventional CFRP woven fabric composite materials.

Viscoelastic modelling and dynamic characteristics of CNTs-CFRP-2DWF composite shell structures

This article deals with the finite element (FE) modeling and dynamics analysis of bidirectional functionally graded (2D-FG) rotating shaft system considering temperature-independent (TID) and tempe...

Ashirbad Swain

Papers

Vibration damping characteristics of carbon nanotubes-based thin hybrid composite spherical shell structures

Viscoelastic modeling and vibration damping characteristics of hybrid CNTs-CFRP composite shell structures

Viscoelastic modelling and dynamic characteristics of CNTs-CFRP-2DWF composite shell structures

Dynamic responses of bidirectional functionally graded rotor shaft

Functionally Graded Carbon Nanotubes Reinforced Composite Structures: An extensive review