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.

R. Velmurugan

Sikarwar R.S

Velmurugan R

Gupta N.K.

Analytical models

Ballistics

Damage detection

Energy absorption

Failure (mechanical)

Fibers

Glass

Kinetics

Laminates

Projectiles

ballistic limit velocity

DAMAGE AREA

Experimental approaches

Hybrid composites

Impact

PROJECTILE VELOCITY

SPECIFIC ENERGY ABSORPTION

TOTAL KINETIC ENERGY

Laminated composites

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

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

International Journal of Crashworthiness

Examination of stacking sequence effect is essential in optimising the properties of synthetic fibre reinforced hybrid polymer composites for protecting the aircraft structure from the barely visible impact damage during low-velocity impact (LVI) events. It is important to know the quasi-static mechanical properties of polymer composites before analysing the LVI damage. Therefore, in this study, both quasi-static mechanical (tensile, flexural and punch-shear) and LVI properties of epoxy reinforced woven roving, E-glass and three different interply hybrid fabric (S-glass-E-glass, Carbon-E-glass and Kevlar-E-glass) composites are investigated. In all these hybrid composites, E-glass fabric layers are placed in the interior. Analysis of LVI properties indicated a 7.5% increase in the maximum energy absorption for laminates having Kevlar fibre as surface layers as against 3.4% decrease in energy absorption and 13.5% for laminates with carbon fibre and S-glass fibre as surface layers, respectively, compared to the E-glass/epoxy composite. An X-ray computed tomography is used for observing the layer-wise damage mechanisms of the LVI tested specimens from damage initiation to final perforation, which predicts that the bottommost layers of the plate are subjected to more damage. The damage area for each layer of the composite plates are measured using Image J software. Carbon-E-glass/epoxy composites are found to have more damage area than the other laminates. The delamination and damage zone of the plates are detected using the ultrasonic C-scan. The scanning electron microscopy is used to examine the fractured surfaces of tensile, flexural and punch-shear tested specimens. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.

Layer-wise damage prediction in carbon/Kevlar/S-glass/E-glass fibre reinforced epoxy hybrid composites under low-velocity impact loading using advanced 3D computed tomography

The effect of separation of fiber orientation through the thickness of thin composites on their low velocity impact response is studied. The composites are prepared using unidirectional glass fiber reinforced epoxy through hand layup followed by vacuum bagging. The two dissimilar layups of composites considered have separation of composite layers with fibers having the same and different orientations through the thickness. The composites are subjected to low velocity impact using a drop-weight testing machine. The composites are evaluated using different performance parameters such as damage degree, first damage and maximum forces, first cracking energy, bending stiffness, elastic strain energy, elastic, residual and maximum displacements, permanent deformation, square-root delaminated area, delamination length and width, and contact duration. Among the two composites, it is observed that [90/-45/45/0] composite in which two layers with fibers having 90° and 0° orientations separating by two layers with fibers having -45° and 45° orientations, levels of deformation are lower and recorded force and square-root delaminated area are higher and lower, respectively for the same level of impact energy. Whereas, in case of [0/90/90/0] composite in which two layers with fibers having 0° orientations separating by two layers with fibers having 90° orientations, recorded force is lower and deformation and square-root delaminated area are higher. The [0/90/90/0] composite is having a comparatively more lateral spread of delamination and inter-layer opening than that of [90/-45/45/0] composite considering extensional and bending stiffnesses along longitudinal (A11, D11) and transverse (A22, D22) directions. This facilitates that lateral spread of damage within composite can be decreased by separating two layers of composite with 90° and 0° fiber orientations by two layers with -45° and 45° fiber orientations, i.e., [90/-45/45/0] composite. © 2019Materials science; Mechanical engineering; Composites; Low velocity impact; Delamination; Energy absorbed; Structural analysis; Composite materials; Materials characterization; Mechanical property; Structural behavior © 2019

Fulltext

Heliyon

Effect of through thickness separation of fiber orientation on low velocity impact response of thin composite laminates

Most of the aircraft and ship structural components are exposed to different environmental conditions (different temperatures) in various places. Furthermore, helicopter main and tail rotor blades are subjected to turbulence at various frequencies during heavy winds and bird strikes on it. To overcome this, conventional metal components and propeller blades need to be replaced with light weight, advanced hybrid composite materials and also frequency characterization studies are required at different temperatures. Therefore, in this study, the viscoelastic behavior of pure epoxy, E-glass/epoxy and three different hybrid composites (S-glass-E-glass/epoxy, carbon-E-glass/epoxy and Kevlar-E-glass/epoxy) are characterized using dynamic mechanical analyzer (DMA) over the temperature range of 30–150 °C at four different frequencies (1, 10, 50 and 100 Hz). The experimentally obtained storage modulus and loss tangent (tan δ) values are theoretically validated. The least square regression lines are used to obtain the activation energy. The results indicate that the carbon-E-glass/epoxy composites exhibit the highest storage and loss moduli due to stiffening effect whereas pure epoxy exhibits the least storage modulus and highest tan δ peak at all frequencies, as the temperature changes from 30 to 150 °C when compared with other combinations. The glass transition temperature (Tg) increases with the increase in frequency. The sharp decrease in storage and loss moduli are observed in the glass transition zone, which can be attributed to the enhanced mobility of polymer chains owing to matrix softening. Using scanning electron microscopy, the higher debonding regions are seen in tested samples of Kevlar-E-glass/epoxy hybrid composites at higher frequencies. © 2018, © 2018 Taylor & Francis Group, LLC.

International Journal of Polymer Analysis and Characterization

Experimental and analytical investigation of thermo-mechanical responses of pure epoxy and carbon/Kevlar/S-glass/E-glass/epoxy interply hybrid laminated composites for aerospace applications

This work focuses on quasi-static mechanical (tensile, flexural, indentation), low velocity impact (LVI) and viscoelastic behaviour of different stacking sequences [(30 K 1 /0 G 14 /30 K 1 ) and (45 K 1 /0 G 14 /45 K 1 )] of 16 layers woven roving Kevlar-E-glass/epoxy interply hybrid composites. The outermost layers are Kevlar and remaining 14 E-glass layers are placed as interior for making these hybrid laminates. The viscoelastic properties are measured over the temperature range from 25&nbsp;°C (room temperature) to 180&nbsp;°C at three different frequencies (1, 10 and 50&nbsp;Hz) by using the dynamic mechanical analyzer (DMA). The LVI results indicated that (45 K 1 /0 G 14 /45 K 1 ) Kevlar-glass/epoxy hybrid laminates exhibit the highest damage threshold load (DTL) whereas (30 K 1 /0 G 14 /30 K 1 ) laminates possess the higher peak load and threshold and maximum energies. Advanced non-destructive testing techniques (NDT) such as X-ray computed tomography (X-CT) and ultrasonic C-scan are employed to evaluate the micro and macro damage mechanisms of LVI tested specimens, respectively. Detailed observations have been made on the onset and growth of cracks in 30°, 45° and 0° plies using X-CT scan imaging. These images show that the bottommost plies subjected to more impact than the topmost plies, the outer Kevlar plies protect the inner 0° glass plies and delays the delamination propagation. ‘C’ scan images indicate that (30 K 1 /0 G 14 /30 K 1 ) laminates spread the damage to more area. The scanning electron microscopy (SEM) is used for examining the failure mechanisms of indentation specimens. © 2018, © 2018 Informa UK Limited, trading as Taylor &amp; Francis Group.

Advances in Materials and Processing Technologies

Advanced 3D and 2D damage assessment of low velocity impact response of glass and Kevlar fiber reinforced epoxy hybrid composites

Journal of Sandwich Structures & Materials

A modified new analytical model for low-velocity impact response of circular composite sandwich panels

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

Procedia Engineering

Analytical Model to Describe Damage in CFRP Specimen When Subjected to Low Velocity Impacts

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.

Composites Part B: Engineering

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

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

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