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.

R. Velmurugan

Department of Aerospace Engineering

Analytical expressions

composite laminate

COMPRESSION-MOLDING TECHNIQUE

Energy absorption capacity

GLASS/EPOXY COMPOSITE

IMPACT BEHAVIOR

Residual velocity

Strain rate sensitivity

Ballistics

Laminated composites

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.

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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

Composites Part B: Engineering

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.

International Journal of Crashworthiness

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

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.

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

Journal	Composites Part B: Engineering
ISSN	13598368
Open Access	No