Kevlar Epoxy Composites Research Articles

Development and characterization of kevlar and glass fibers reinforced epoxy/vinyl ester hybrid resin composites

AbstractThis research investigates the influence of kevlar and glass fiber reinforcements on the mechanical and thermal properties of epoxy/vinyl ester (hybrid resin) composite. The hybrid resin was synthesized by achieving an interpenetrating network between epoxy and vinyl ester. The composites were characterized using tensile, flexural, impact, and thermo‐gravimetric analysis (TGA). Scanning electron microscopy was employed to analyze surface morphology whereas Fourier‐Transformation Infrared Spectroscopy (FT‐IR) was used to investigate the possible interaction between the constituents of the composites. The findings have shown a notable improvement in the mechanical properties after the hybridization of the resin. For reference, the tensile strength of glass/hybrid resin and kevlar/hybrid resin composites were observed to increase by 8.33% and 23.65%, as compared to glass/epoxy and kevlar epoxy composites respectively, whereas, the bending strength of these composites was improved by 8.36% and 30.61%, respectively. TGA also showed an enhanced thermal stability of the hybrid resin‐based composites. Such improvements are noticed due to multi‐resin incorporation (the oxirane group of epoxy reacts with the hydroxyl group of vinyl ester), confirmed by the FTIR, TGA, and morphological analysis. This study signifies that the proposed hybrid composites are better in terms of strength and modulus relative to conventional metallic materials.Highlights The paper presents the development of novel hybrid resin, reinforced with synthetic fibers. Hybrid resin is imparted positively and is highly favorable in improving the mechanical properties of composites. The tensile strength of novel composites is increased by 8.33% and 23.65% relative to their base specimens, and a similar trend is observed in flexural and impact analysis. Fractured analysis showed that composite laminates deteriorated more intensely due to cohesive matrix fracture; adhesion failure was not observed at all, as evidenced by the emergence of micro‐cracks in resin. Developed novel composites exhibited maximum thermal stability; residual char in glass/epoxy/vinyl‐ester composite attained 17.81% higher, whereas kevlar/epoxy/vinyl‐ester achieved 3.56% relative to glass/epoxy and kevlar/epoxy base samples.

Ballistic performance of nanopowder intruded Kevlar polymeric composite targets

The effect of nano-filler addition on the mechanical and impact properties of Carbon Nano Tubes (CNT) reinforced Kevlar Epoxy composites were studied. Three different laminates (one without fillers and two with increasing concentration of fillers) were prepared using the hand layup process. Tensile, Inter Laminar Shear Stress (ILSS) and Low-velocity ballistic impact experiments were done and the fractured samples were investigated for microanalysis. All the three experimental results showed better properties for the laminate which contains nano-fillers. Laminates with 0.5% CNT addition showed better tensile, ILSS and energy-absorbing properties when compared with the 1% CNT filled and reference composite. From the fractographic study, the front side damage was minimum for the KC0.5 sample while the back face deformation was lower for the KC1 sample. This increase is mainly attributed to the nanofillers which act as a resistance layer to the projectile impact and also by increasing the interfacial bonding between the layers and the matrix. The brittle nature of the front face with nanofiller matrix toughening is the main phenomenon that significantly improved the composite properties.

Design and finite element study of Kevlar based combat helmet for protection against high-velocity impacts

High-velocity impact-resistant helmets are used by police forces, law enforcement and military personnel, firefighters, as well as civilians working in construction, manufacturing, mining and material handling industries among other sectors as protection against impact damage caused by projectiles of various shapes and sizes. In this study, an attempt was made to investigate the impact-resistance of fiber-reinforced polymer composite based helmets through finite element analysis. The composite helmets were modelled in different sacking sequences using bi-directional woven fabrics such as Kevlar-129 (K), 3 K-Carbon (C) and EC9-Glass (G) fabrics as reinforcements and an epoxy matrix formulation. Investigation was focused to study the high-velocity impact resistance and energy absorption performance of composite helmets in hybrid and non-hybrid stacking sequences such as KKK, KGK, KCK, KCG and GCK subjected to high-velocity impact simulations at 398 m.s−1. It was observed that neat Kevlar and Kevlar-glass sandwich hybrid composite helmets withstood the projectile, while all other hybrid helmets were completely perforated during impact. It was also found that Kevlar-glass sandwich helmets offered cost savings of about 21% compared to neat Kevlar-epoxy composite. Hence Kevlar-glass sandwich composite can be used to develop protective helmets due to their attractive impact resistance properties and lower cost. The variation in helmet weight among all the considered composite material combinations was only about 5%.

Effects of Fiber Orientation on Mechanical Properties and Analysis of Failures for Kevlar Epoxy Reinforced Composites

This paper is an outcome of investigation made on Kevlar epoxy composites made by altering the fiber orientation. It is an important region to emphasize the effect of fiber angle in the composite that results in performance. In the present research the Kevlar fiber is made by 18 layers with different angular orientation from 0o to 90o. While preparing the composite the reinforcement is made by the addition of SiC and acetone to have the firm binding ability. In addition to that right from the first layer of the fiber to the 18th layer the angle is varied progressively from 0o to 90o. After the fabrication process the Kevlar composite is tested as a flat plate and a flat plate with a circular hole in it. The analysis has involved the maximum stress theory and Tsai-wu theory for the findings on fiber orientation against failure. The test results have yielded that the fiber orientation has the significant effect on the composite plate with a circular hole in it. Index Terms: Kevlar epoxy composites, Mechanical characterization, Failure analysis

Strain Rate Effect on Progressive Failure and Tensile Behaviour of Kevlar Epoxy Composites

This study investigates about the effect of different strain rates on the tensile behaviour of kevlar epoxy composites and progressive failure of kevlar epoxy composites under displacement controlled axial loading. A series of experimental tests were conducted under different strain rates to find out the tensile behaviour of kevlar epoxy composites. Two different strain rates 0.5mm/ min and 1.5mm/ min were applied to the kevlar epoxy specimen in order to understand the difference in mechanical properties and progressive failures of composites. Tensile strength increases with an increase in strain rates. Failure in kevlar epoxy composites is analysed under different stages for both 0.5mm/min and 1.5 mm/min. For all the tests, failure starts with matrix cracking followed by delamination and ends with fracture.

Impact Strengthening of Laminated Kevlar/Epoxy Composites by Nanoparticle Reinforcement.

Herein, we report the fabrication and characterization of high-strength Kevlar epoxy composite sheets for structural application. This process includes optimization of the curing conditions of composite preparation, such as curing time and temperature, and the incorporation of nanofillers, such as aluminum oxide (Al2O3), silicon carbide (SiC), and multi-walled carbon nanotubes (MWCNT) in different weight percentages. Differential scanning calorimetry (DSC) was utilized to investigate the thermal stability and curing behavior of the epoxy, finding that a minimum of 5 min is required for complete curing under an optimized temperature of 170 °C. Moreover, mechanical characterization, including flexural and drop-weight tests, were performed and found to be in good agreement with the DSC results. Our results show that nanofiller incorporation improves the mechanical properties of Kevlar epoxy composites. Among the tested samples, 0.5% MWCNT incorporation obtained the highest mechanical strength.

Failure Analysis of Silane-Treated Kevlar-Reinforced Nano-silica-Toughened Epoxy Composite in Laminar Shear Strength, Drop Load Impact and Drilling Process

In this research, the role of silane surface modification on Kevlar fiber and nano-silica and their failure analysis on inter-laminar shear strength and drilling process were studied. The main objective of this research is to explicate the importance of silane surface modification on the reinforcements and their failure effects on proposed properties. The Kevlar fiber and nano-silica were surface-treated using 3-aminopropyltrimethoxysilane using aqueous solution method. The composites were prepared using hand layup technique followed by post-curing at 120 °C. The inter-laminar shear strength results show that the silane-surface-modified fiber and filler in epoxy composite give the highest strength of 32 MPa for EKS2. The highest drop load impact energy of 16.3 J was observed for surface-modified composite designation EKS2. Similarly, the surface-modified epoxy composite designations show highest dimensional stability than as-received designations in drilling process. There are no fiber pullout and edge damage observed in optical microscopy images after drilling process. These high shear strength, high energy absorption and high de-lamination-resisted Kevlar-epoxy composites could be used in defense, armor equipment, automobile bumpers and small aircraft manufacturing applications.

Development of a predictive model for kerf taper angle in AWJM of Kevlar epoxy composite

This paper describes the research work involved in studying the influence of process parameters on kerf taper and development of predicative model for the response in abrasive water jet machining (AWJM) of Kevlar epoxy composite. Four process parameters namely water pressure, stand-off distance, traverse speed and abrasive mass flow rate are considered. To investigate the influence of process parameters on kerf taper, experiments are designed using response surface methodology. Experiments are conducted on flying arm AWJM setup. Kerf taper of machined work pieces is measured using vision measurement system. It is found that water pressure and traverse speed are most significant process parameters influencing kerf taper angle. Based on the analysis, a predictive model is developed to predict kerf taper angle. The confirmation tests are performed to verify the predicative model. The findings of present work is useful in minimizing the kerf taper during AWJM of composite materials.

Improved static and dynamic mechanical properties of multiscale bucky paper interleaved Kevlar fiber composites

Herein, the influence of bucky paper interleaves and dispersed MWCNT network on static and dynamic mechanical properties of Kevlar-epoxy composites, subjected to different loading conditions is investigated. Multiscale hybrid laminar Kevlar composites are prepared by vacuum impregnation followed by compression moulding technique. Subsequently, these hybrid composites are subjected to tensile, flexural, dynamic mechanical and low velocity impact and directly compared with basic Kevlar composite (KE) laminate. It is found that bucky paper interleaves along with dispersed MWCNT (KEBC) improve interlaminar and interfacial properties respectively. It is found that the maximum dynamic impact energy absorption and load carrying capacity of KEBC increase to 13.8 J and 2650 N respectively which shows an overall improvement of 31% over KE. These results are further confirmed by Charpy's impact test, in which maximum impact toughness reaches to 90.4 J/mm2, which is consistent with dynamic impact test results. After conducting various lab scale mechanical tests, ballistic test is also performed over KEBC and KE. It is found that, in case of KEBC, back face signature is reduced to 30% over KE, which confirms the collective effort of bucky paper interleaves and dispersed MWCNT in enhancing the energy absorption capability of hybrid laminar composite.

EXPERIMENTAL STUDY OF ABRASIVE WATER JET MACHINING OF KEVLAR EPOXY COMPOSITE

The present paper describes an experimental study of abrasive water jet machining (AWJM) of Kevlar epoxy composite. Influence of process parameters namely stand-off distance, water pressure, traverse speed and abrasive mass flow rate on surface roughness and kerf taper is investigated. Taguchi orthogonal approach is applied to plan the design of experiments; and subsequent analysis of experimental data is done using analysis of variance (ANOVA). It is found that water pressure and traverse speed are most significant parameters followed by stand-off distance and abrasive mass flow rate influencing surface roughness and kerf taper. With increase in water pressure and decrease in traverse speed, kerf taper and surface roughness decreases.

Viscoelastic Behavior of Cellulose Coated Glass/Kevlar Epoxy Composite Laminates using Dynamic Mechanical Analyzer

The dynamic behaviour of fiber reinforced composites plays a significant role on the performance of the laminated composite materials. In the present study the dynamic characteristics of cellulose Glass Epoxy Composites (CGEC) and Cellulose Kevlar epoxy composites (CKEC) were investigated and compared with pristine glass epoxy (GE) and Kevlar Epoxy (KE) composites using Dynamic Mechanical Analyzer (DMA). Cellulose particles were liquefied in organic solvents such as Acetone, Dimethylformamide (DMF), Ethanol and Sodium Hydroxide (NaOH) to inspect the settling time and it was found that cellulose particles settled in short interval of time in solvents and hence NaOH was used to make solution as better dispersion with high settling time was observed with NaOH. The Glass and Carbon plies were coated with Cellulose using semi automated coating technique. The DMA test was conducted in accordance with ASTM 1867-13. The tests results revealed that initially all the samples exhibited high storage modulus but there was a small drop in storage modulus in the temperature range of 50-70˚C and considerable drop in storage modulus was observed in the temperature range of 70-90˚C and also it was found that composite laminates changed in state from solid to elastic beyond glass transition temperature (Tg)

Ballistic impact response of Kevlar Composites with filled epoxy matrix

Impact resistance and weight are important features for ballistic materials. Kevlar fibres are the most widely reinforcement for military and civil systems due to its excellent impact resistance and high strength-to-weight ratio. Kevlar fibres or spectra fiber composites are used for designing personal body armour to avoid perforation. In this study, the ballistic impact behaviour of Kevlar/filled epoxy matrix is investigated. Three different fillers, nanoclay, nanocalcite and nanocarbon, were used in order to increase the ballistic impact performance of Kevlar-epoxy composite at lower weight. The filler, nanoclay and nanocalcite, content employed was 1 wt.% and 2 of the epoxy resin–hardener mixture while the nanocarbon were dispersed into the epoxy system in a 0.5%, 1% and 2% ratio in weight relating to the epoxy matrix. Specimens were produced by a hand lay-up process. The results obtained from ballistic impact experiments were discussed in terms of damage and perforation. The experimental tests revealed a number of damage mechanisms for composite laminated plates. In the ballistic impact test, it was observed whether the target was perforated completely penetrated at the back or not. The presence of small amounts of nanoclay and nanocalcite dispersed into the epoxy system improved the impact properties of the Kevlar/epoxy composites. The laminates manufactured with epoxy resin filled by 1 wt.% of nanoclay and 2 wt% nanocalcite showed the best performance in terms of ballistic performance. The addition of nanocarbon reduced ballistic performance of Kevlar-epoxy composites when compared the results obtained for laminates with 0% nanoparticles concentration.

Impact simulation of three-dimensional woven kevlar-epoxy composites

The focus of this work is to find the impact loading properties of three types of three-dimensional woven kevlar fabric structures before and after impregnation with epoxy resin. The analysis has been done at different impact times and different magnitude of forces. Total deformation, equivalent strain and equivalent stress created on these fabrics have been noted. First a model of three-dimensional woven fabric composite is generated using SolidWorks 2011. The model is constructed in such a way that it can be readily integrated into commercial finite element programs like ANSYS. Then impact resistance of this model is simulated and studied with impacts at different initial velocities. By incorporating the interface of fabric and matrix, the impact resistance is predicted. The simulated results are validated with experimental data. A compatible resin/matrix system has to be selected along with the fabric in order to develop sufficient resistance to impact. The three-dimensional woven kevlar-epoxy composites prove to be effectively resistant to impact due to interface of fiber and matrix system.

Impact and Ballistic Behavior Optimization of Kevlar–Epoxy Composites by Taguchi Method

In this research, the experimental method of Taguchi design has been used in order to establish a relationship between the penetrating impacts with different parameters used in developing Kevlar–epoxy composites. Therefore, different parameters like the fiber type, the sedimentation ratio, amount of filling materials and sample thickness have been studied. The effective parameters on material resistance in the ballistic test have been optimized using Taguchi test design method (Minitab15 software). The obtained results show that the best property combination between penetrating impact and impact resistance have been obtained by the layering ratio of 0.6, filling materials weight percentage of 50 % and thickness of 6 mm, respectively, for the composite of Kevlar 49 fibers in epoxy matrix.

Abrasive waterjet hole trepanning of thick Kevlar-epoxy composites for ballistic applications – experimental investigations and analysis using design of experiments methodology

Abrasive water jet (AWJ) is widely useful for producing cutouts/holes in difficult-to-cut materials. However, in AWJ hole trepanning, due to the jet trailback, the diameter of the hole tends to increase with an increase in workpiece thickness and striation marks are observed at the exit side. This results in an inferior quality hole due to poor dimensional tolerances, leading to assembly problems. Therefore, to obtain superior quality holes by AWJ trepanning, optimum selection of process parameters is absolutely critical. This paper embodies a Taguchi method based experimental investigation for finding the optimum parameter settings in AWJ hole trepanning of 6 mm thick Kevlar-epoxy composites, mainly used for anti-ballistic applications. Kerf taper and surface roughness has been chosen as the quality characteristics and four major operating parameters have been considered for experimentation. Visualisation studies using SEM and optical microscope have also been conducted for investigation of delamination induced during AWJ trepanning.

Modeling of Depth of Cut in Abrasive Waterjet Cutting of Thick Kevlar-Epoxy Composites

Abrasive water jet cutting (AWJC) is one of the widely used non-conventional techniques for cutting difficult-to-cut materials like composites, super alloys and ceramics. However, while conducting initial trials the inability of the jet to cut through the workpiece is a major problem particularly in thicker materials. Therefore an accurate prediction of depth of cut (DOC) is absolutely necessary to achieve through cuts and more so to minimize delamination in polymer matrix composites. In this paper, a semi-empirical model is developed using non-linear regression analysis for prediction of DOC in AWJC of thick Kevlar-epoxy composites. Further, the model is verified by conducting experiments within the investigated range of process parameters and a good agreement is obtained between the two.

Predictive modelling of surface roughness and kerf widths in abrasive water jet cutting of Kevlar composites using neural network

Abrasive water jet cutting (AWJC) is one of the important non-traditional machining processes used for cutting of difficult-to-cut materials and intricate profiles. Cutting of Kevlar fibre reinforced polymer composites is a complex process, making it difficult to model, predict and improve the cut surface quality. This paper presents a detailed approach of the usage and effectiveness of a back-propagation neural network (NN) for modelling and prediction of three cut surface characteristics namely top kerf width, bottom kerf width and surface roughness (Ra) in AWJC of aerospace grade Kevlar-epoxy composites. Statistically designed full factorial experiments based on three process parameters [water jet pressure (WJP), abrasive flow rate (AFR) and quality level (QL)] at three levels each were conducted to generate the NN training database. The results demonstrate that the NN model was able to successfully model and predict the two kerf widths and surface roughness closely matching the experimental results.

Failure analysis of woven kevlar fiber reinforced epoxy composites pinned joints

An investigation was performed to determine the failure mode and the failure load of mechanically fastened joints in woven kevlar epoxy composite plates. Two-dimensional finite element code is developed to predict damage initiation, progression and strength of joints. Hashin, Hoffman and Maximum Stress criteria were used in this failure analysis. Experiments were performed to find the failure load and to predict the failure mode. Parametric studies were also carried out to evaluate the effect of joint geometry on this analysis. The obtained results were compared each other and comparison showed good agreement between numerical and experimental methods.

Anhydride and diamine epoxy–Kevlar composites: thermal and dynamic‐mechanical properties

Differential scanning calorimetry (DSC) and dynamic–mechanical thermal analysis techniques have been used to characterize different Kevlar–epoxy composites. Tetrafunctional aliphatic amine and anhydride–diglycidyl epoxy have been used as matrix, and different quantities of continuous Kevlar fibers as reinforcement. Kevlar fibers had different effects on curing kinetics and final thermal properties depending on epoxy matrix type. As Kevlar content increased DSC heat flow curves shifted to much lower temperatures in the anhydride matrix case, while there was very little difference in the diamine–epoxy one. A significant decrease in the glass transition temperature (Tg) was observed as Kevlar content increased when anhydride matrix was used, while little change was observed in the reinforced diamine systems. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal scans. The main dynamic–mechanical relaxation and its evolution versus frequency with fiber addition was studied. An important shift to high frequencies was observed in the anhydride system. Copyright © 1999 John Wiley & Sons, Ltd.

Anhydride and diamine epoxy-Kevlar composites: thermal and dynamic-mechanical properties

Differential scanning calorimetry (DSC) and dynamic–mechanical thermal analysis techniques have been used to characterize different Kevlar–epoxy composites. Tetrafunctional aliphatic amine and anhydride–diglycidyl epoxy have been used as matrix, and different quantities of continuous Kevlar fibers as reinforcement. Kevlar fibers had different effects on curing kinetics and final thermal properties depending on epoxy matrix type. As Kevlar content increased DSC heat flow curves shifted to much lower temperatures in the anhydride matrix case, while there was very little difference in the diamine–epoxy one. A significant decrease in the glass transition temperature (Tg) was observed as Kevlar content increased when anhydride matrix was used, while little change was observed in the reinforced diamine systems. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal scans. The main dynamic–mechanical relaxation and its evolution versus frequency with fiber addition was studied. An important shift to high frequencies was observed in the anhydride system. Copyright © 1999 John Wiley & Sons, Ltd.