As polymers are rate sensitive to mechanical properties, dynamic tensile tests are carried out on drop mass setup, to obtain medium strain rate stress-strain response which fills the gap between quasi-static strain rate (&lt;10 s-1) and split Hopkinson pressure bar (SHPB) technique (&gt;1000 s-1). The present research work is to study the effect of medium strain rate on tensile behavior of epoxy/clay nanocomposites. Neat epoxy and nanocomposites containing 1.5, 3 and 5 wt% clay content are fabricated using mechanical stirrer. The dispersion of nanoclay in epoxy is examined using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The digital image correlation (DIC) technique is employed for evaluating full-field strain and strain rate using high speed CCD camera, which captures about 100,000 frames per second. Stress-strain measurements are reported for epoxy/clay nanocomposites for strain rates ranging from 0.008 to 450 s-1. The results reveal that the tensile strength and modulus increase with increase in strain rate for epoxy and its clay nanocomposites. The fracture surfaces of tensile specimens are investigated using scanning electron microscopy (SEM). © 2015 Elsevier Ltd. All rights reserved.

R. Velmurugan

Department of Aerospace Engineering

CCD CAMERAS

Clay

Electrons

Epoxy resins

Fractography

FRACTURE MECHANICS

High resolution transmission electron microscopy

Image analysis

Nanocomposites

Scanning electron microscopy

strain measurement

Stress-strain curves

Tensile strength

Tensile testing

Transmission electron microscopy

X ray diffraction

D. DIGITAL IMAGE CORRELATION (DIC)

EPOXY/CLAY NANOCOMPOSITES

HIGH SPEED CCD CAMERAS

High strain rates

QUASI-STATIC STRAIN RATES

STRAIN AND STRAIN RATES

STRESS-STRAIN MEASUREMENT

STRESS-STRAIN RESPONSE

Strain rate

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Polymer

Glass/epoxy, carbon/epoxy and hybrid (glass-carbon/epoxy) composites are subjected to quasi-static to high strain rate (542 s−1) studies to obtain the tensile strength. The two-parameter Weibull distribution is employed to measure the variability of the tensile strength of cross ply laminates. The Weibull parameters are obtained using the linear curve fit method. The theoretical tensile strength values are determined for the GFRP, CFRP and hybrid composites. The experimental and theoretical strength values are in good agreement. Using Hitachi scanning electron microscope instrument, the failure mechanisms are investigated in the fracture surfaces of glass/epoxy, carbon/epoxy and hybrid specimens, and discussed. © 2016 Elsevier Ltd

Thin-Walled Structures

Statistical analysis of the tensile strength of GFRP, CFRP and hybrid composites

In the current work, the energy absorption, ballistic limit and residual velocities for different laminate ply orientations [(0/90), (0/90/30/-60), (0/90/45/-45) and (30/-60/60/-30)] and thicknesses [2 mm and 4 mm] of woven roving carbon fiber reinforced polymer [CFRP] composites are experimentally and theoretically studied. High strain rate tensile test results are used as reference values for the theoretical studies. Using an air gun, experiments are carried out to impact the carbon/epoxy laminates by a rigid conical steel bullet of 9.5 mm diameter and mass of 8 g. The results obtained from this study indicate that the (0/90) laminates absorb more energy and also have a higher ballistic limit than other lay-up sequences while energy absorption and ballistic limit are minimum for (30/-60/60/-30) laminates. The ballistic limit and energy absorption capacity of the plates increase whereas the residual velocity of the projectile decreases with the increase in thickness for laminates of all orientations. Using an Instron universal testing machine, end-notched flexure (ENF) tests are performed to determine the mode-II fracture toughness for the carbon/epoxy composites of different orientations. These results are used in the energy calculations and the influence of the mode -II fracture toughness on the energy absorption studies is discussed. © 2017, © 2017 Informa UK Limited, trading as Taylor &amp; Francis Group.

Advances in Materials and Processing Technologies

Influence of fibre orientation and thickness on the response of CFRP composites subjected to high velocity impact loading

Induced delamination due to low velocity impact results in degradation of load-carrying capacity of composite structures especially when loading is predominantly in compression. In this paper, size, shape and orientation of delamination that occur due to low velocity impact is obtained by numerical modelling and results are validated through experiments. Initially, numerical model is validated for single-mode fracture tests like double cantilever beam and end-notch flexure. Multimode failure phenomenon like low velocity impact was also simulated for different lay-ups such as cross-ply, angle-ply and quasi-isotropic and validated through experiments. Low velocity impact testing of laminates was done using drop weight impactor, and experimentally obtained force–time and energy–time history were compared with numerical results. Good match is obtained between simulations and experiments. Delamination size was also compared and it is found that numerical model correctly predicts the size, shape and orientation of delamination for all lay-ups. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

International Journal of Crashworthiness

Numerical and experimental study of multimode failure phenomena in GFRP laminates of different lay-ups

In this study, experiments are carried out to determine the tensile strength of laminates, for three different orientations [(0/90/30/-60), (0/90/45/-45) and (30/-60/60/-30)] of glass/epoxy and carbon/epoxy composites, for the strain rate range of 0.0083–542 s−1. Using two-parameter Weibull distribution, the theoretical tensile strength values are determined for Glass Fiber Reinforced Polymer (GFRP) and Carbon Fiber Reinforced polymer (CFRP) composites for different strain rates by a linear curve fitting. The theoretical and experimental values match well. The deviation between the theoretical and experimental values is less than 12% for GFRP laminates and less than 13% for CFRP laminates. Normally the mean values of mechanical properties are sufficient to use theoretical models, whereas all tested specimen data are considered (including the mean values) in Weibull distribution. Therefore, Weibull distribution contains more information and it will be useful for designers and composite manufacturers to ensure the reliability of structures. Studies show that the (0/90/45/-45) laminates have exhibited the highest scale parameter increment of 80.5% for glass/epoxy and 53% for carbon/epoxy composites with the increase of strain rate, when compared to laminates of other orientations. Using scanning electron microscopy (SEM), the failure mechanisms such as matrix microcracking and fiber-matrix interface microcracking are observed in quasi-static testing whereas the fiber pull-out, matrix damage and fiber-matrix interface cracking are seen in the high strain rate tests, which ensure the increase in strength values at high strain rate. © 2017 Elsevier Ltd

Composites Part B: Engineering

Reliability analysis of tensile strengths using Weibull distribution in glass/epoxy and carbon/epoxy composites

In the present work, an analytical model is proposed to obtain the damage area of the composite laminates at below ballistic limit velocities. The model is based on the fact that total kinetic energy of the projectile is absorbed by different energy absorbing mechanisms taking place in laminates during impact. Depending upon the projectile velocity, some or all energy absorbing mechanisms observed are; fibre breakage, deformation of fibres, delamination, matrix cracking and cone formation on the back face of the laminates. The accuracy of the model is then assessed by comparing its predictions for damage area and specific energy absorption with the experimental values for two different types of fibres (glass and kevlar) as well as glass/kevlar hybrid combinations. Experimental results are also used to quantify and compare the specific energy absorption capacity of the glass/epoxy, kevlar/epoxy and glass/kevlar/epoxy laminates. It is observed that the glass/kevlar/epoxy laminates in which kevlar percentage is 27.5% w/w showed 20% improvement in specific energy absorption as compared to the glass/epoxy laminates. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

Effect of velocity and fibres on impact performance of composite laminates–Analytical and experimental approach

It is understood that small amount of nanoclay in the neat epoxy and fiber reinforced epoxy composite system improves the mechanical properties. The mechanical properties of most of polymer matrix composites are rate sensitive. Most of the researches have concentrated on the behavior of the polymer composites at high strain rates. The present research work is to study the effect of clay on neat epoxy and glass/epoxy composites, at low strain rates. The clay in terms of 1.5, 3 and 5wt% are dispersed in the epoxy resin using mechanical stirrer followed by sonication process. The glass/epoxy nanocomposites are prepared by impregnating the glass fiber with epoxy-clay mixture by hand lay-up process followed by compression molding. Characterization of the nanoclay is done by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Tensile stress-strain curves are obtained at strain rates of 10-4, 10-3, 10-2 and 10-1s-1 by a servo-hydraulic machine and the variation of modulus, strength and failure strain with strain rate are determined. The results show that, even at low strain rates, the longitudinal strength and stiffness increase as strain rate increases for all clay loadings. It is observed that the tensile modulus increases as the clay loading increases for both epoxy and glass/epoxy nanocomposites. Scanning electron microscopy is used to study the adhesion of composites in fracture surfaces. © 2014 Elsevier Ltd.

Materials and Design

Strain rate sensitivity of glass/epoxy composites with nanofillers

In the present work, the electrical, mechanical and thermal properties of epoxy nanocomposite materials were studied. The electrical insulation characteristics were analyzed through short time breakdown voltage test, accelerated electrical ageing test, and by tracking test. The breakdown voltage increases with increase in nano-clay content up to 5 wt%, under AC and DC voltages. The volume resistivity, permittivity and tan(δ) of the epoxy nanocomposites were measured. The Weibull studies indicate that addition of nanoclay upto 5 wt% enhances the characteristic life of epoxy nanocomposite insulation material. The tracking test results indicate that the tracking time is high with epoxy nanocomposites as compared to pure epoxy. Ageing studies were carried out to understand the surface characteristic variation through contact angle measurement. The hydrophobicity of the insulating material was analysed through contact angle measurement. The diffusion coefficients of the material with different percentage of clay in epoxy nanocomposites were calculated. The exfoliation characteristics in epoxy nanocomposites were analyzed through wide angle X-ray diffraction (WAXD) studies. The thermal behaviour of the epoxy nanocomposites was analyzed by carrying out thermo gravimetric-differential thermal analysis (TG-DTA) studies. Heat deflection temperature of the material was measured to understand the stability of the material for intermittent temperature variation. The dynamic mechanical analysis (DMA) results indicated that storage modulus of the material increases with small amount of clay in epoxy resin. The activation energy of the material was calculated from the DMA results. © 2006 Elsevier B.V. All rights reserved.

Materials Science and Engineering A

Understanding the thermal, mechanical and electrical properties of epoxy nanocomposites

Polymer/Clay nanocomposites consisting of an epoxy matrix filled with nanolayered silicate clay particles have been investigated. Recent and ongoing research has shown that dramatic enhancements can be achieved in mechanical and thermal properties by adding a small volume percent of clays. In the present work nanocomposites are processed by mechanical mixing of epoxy with organoclays and unmodified clays using a high speed electric shear mixer at room temperature. The addition of different organoclay wt% [1-3, 5 and 10] indicates good enhancement in hardness, dynamic mechanical properties, and also the molecular mobility of the polymer is reduced by the presence of the silicate layers, which in turn causes large stiffness improvements. X-ray diffraction (XRD) results show the intercalation/exfoliation of clays in the epoxy matrix. The influence of organoclay restricts the weight loss at varying temperatures. Experiments show improved elastic modulus for both modified and unmodified clays.

Journal of Materials Science

Room temperature processing of epoxy-clay nanocomposites

Materials & Design

The effect of strain-rate on the tensile and compressive behavior of graphene reinforced epoxy/nanocomposites

Epoxy clay nanocomposites – processing, properties and applications: A review

High strain rate sensitivity of epoxy/clay nanocomposites using non-contact strain measurement

Journal	Data powered by TypesetPolymer
Publisher	Data powered by TypesetElsevier Ltd
ISSN	00323861
Open Access	No