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.

R. Velmurugan

Department of Aerospace Engineering

Cantilever beams

Delamination

Fracture

Fracture testing

Impact testing

velocity

DOUBLE CANTILEVER BEAM

END-NOTCH FLEXURES

GFRP LAMINATES

Low velocity impact

MULTIMODE FAILURES

Numerical and experimental study

Numerical results

quasi-isotropic

Numerical models

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

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

International Journal of Crashworthiness

Embedding shape memory alloys (SMAs) in composites is a promising method resistance against impact loading.In the present paper, an attempt is made to quantify the improvement in damage mitigation properties of FRP (fibre reinforced plastic)composites by embedding SMA.Numerical modelling of low velocity impact was carried out topredict the delamination in composites and composites embedded with SMA and steel wires. Through modelling, effect of location and quantity of SMA material in decreasing the impact induced delamination size was also studied.Compression after impact (CAI) tests were carried out on pristine and SMA hybrid composite (SMAHC)specimens to quantify the change in damage resistance. Experimental results show an improvement in compressive load-carrying capacity after impact in SMAHC as compared to pristine composites.Experimental results match well with numerical findings in terms of; location of placement of SMA wire and optimum quantity of SMA wires. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.

Studies on shape memory alloy-embedded GFRP composites for improved post-impact damage strength

Composites are efficient to deal with tensile loads than metals. Now-a-days, metals are replaced with composites owing to their higher strength to weight ratio and are extensively used in aircraft wing and fuselage structures. These structures are subjected to high strain rates during impact loadings, such as bird hit or run-way debris impact. In order to design robust composite structures, it is important to understand the strain-rate-dependent behavior of composite materials. In this study, influence of strain rate on the tensile properties of glass/epoxy, carbon/epoxy and hybrid (glass-carbon/epoxy) composites are experimentally and theoretically investigated in the range of strain rates from 0.0016&nbsp;s−1 to 542&nbsp;s−1. Drop mass setup is used for high strain rate tests. Quasi-static tests are performed on Instron universal testing machine in accordance with ASTM D638. The results indicate that the tensile strength and tensile modulus of GFRP and hybrid composites increase and percentage of failure strain for GFRP, CFRP and Hybrid composites decreases with the increase in strain rate, whereas tensile strength and tensile modulus of CFRP composites remains approximately constant. The scanning electron microscopy is used for analyzing the failure modes of the failed region (surface) of the tested specimens. Non contact DIC system is used to capture the strain field with the help of high speed camera. © 2016 Elsevier Ltd

Composites Part B: Engineering

Effect of high strain rate on glass/carbon/hybrid fiber reinforced epoxy laminated composites

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.

Polymer

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

Composite laminates, made of glass/epoxy using compression molding technique, were subjected to impact loading. The ballistic limit and energy absorption capacity of the laminates were obtained. Experiments were carried out to study the effect of fiber orientation and thicknesses on ballistic limit and energy absorption of the laminates, by using a rigid conical bullet having 9.5 mm diameter and mass of 7.5 g in an air gun. Analytical expressions were obtained to find the ballistic limit, residual velocity and energy absorption capacity of the laminates. The expressions obtained by considering the various damage modes, which were involved in penetration, when laminates subjected to impact loading. The values obtained from analysis were compared with experimental results and good agreement was found. The strain rate sensitivity of the glass/epoxy composites was considered for analysis. © 2013 Elsevier Ltd. All rights reserved.

Influence of fiber orientation and thickness on the response of glass/epoxy composites subjected to impact loading

In the present study, impact behavior of Kevlar/Epoxy composite plates has been carried out experimentally by considering different thicknesses and lay-up sequences and compared with analytical results. The effect of thickness, lay-up sequence on energy absorbing capacity has been studied for high velocity impact. Four lay-up sequences and four thickness values have been considered. Initial velocities and residual velocities are measured experimentally to calculate the energy absorbing capacity of laminates. Residual velocity of projectile and energy absorbed by laminates are calculated analytically. The results obtained from analytical study are found to be in good agreement with experimental results. It is observed from the study that 0/90 lay-up sequence is most effective for impact resistance. Delamination area is maximum on the back side of the plate for all thickness values and lay-up sequences. The delamination area on the back is maximum for 0/90/45/-45 laminates compared to other lay-up sequences. © Versita sp. z o.o.

Central European Journal of Engineering

Experimental and analytical study of high velocity impact on Kevlar/Epoxy composite plates

This study evaluates the energy absorption, perforation and damage evolution created by cylindrical projectile of different nose geometries in woven roving mat/epoxy laminates with 0.45° orientation. A series of ballistic impact tests have been carried out on the laminate with projectile nose geometries representing hemispherical, conical, and conical with round nose and truncated tip. A gas gun projectile launcher set-up was employed to impact the target at different speeds. The damage pattern, perforation mechanism and ballistic limit for each type of projectiles have been studied. Truncated-nose projectile shows the highest ballistic limit while sharp-nose shows the lowest. A quasi-static punch test was carried out on targets with projectiles of above-mentioned nose geometries to assess the damage evolution at a constant strain rate. The maximum load required to cause perforation during punch test was noted for hemispherical-nose projectile. An in-depth layerwise analysis was carried out to analyse the damage in each layer. Copyright © 2008 Taylor & Francis.

Journal	Data powered by TypesetInternational Journal of Crashworthiness
Publisher	Data powered by TypesetTaylor and Francis Ltd.
ISSN	13588265
Open Access	No