Evaluation of Impact Strength of Epoxy Based Hybrid Composites Reinforced with E-Glass/Kevlar 49 SUBHAN ALI JOGI*, MUHAMMAD MOAZAM BALOCH**, ALI DAD CHANDIO***,

In hybridization different fibers are stacked layer by layer to produce laminates have specific strength and stiffness and employed in light weight high strength applications. Physically mean fabricated hybrid composites used in aerospace, under water, body armors and armed forces establishment. In present work drop-weight impact response of hybrid composites were investigated by making laminates of hybrid composites. In Hybridization layers of E-glass (roving) and Kevlar 49 fabrics stacked with epoxy resin. The layers formulation was set up by hand layup method. Impregnationsof epoxy resin of commercial grade (601A) in fabrics were accomplished by VRTM (Vacuum Bagging Resin Transfer Molding) technique. Layup placementof Glass fibers/ Kevlar at 0°/90°, 45°/45° and 30°/60° were set for this work. Mechanical properties such as impact strength, bear resistance and break resistance were analyzed by usingASTM D-256 and D-3763 standard.Experimental investigation was conducted using instrumented Dart impact and Izod Impact test. E-glass/Kevlar 49 at layup 0°/90°and 30°/60°exhibited improvedimpact strength than 45°/45°. The surface morphology and fractography were also investigated by capturing different images of Specimens by using the SEM (Scanning Electron Microscopy). The fiberreinforcement and matrix fracture were also observed by using SEM.The SEM images suggest that epoxy resin tightly bonded with Kevlar fibers whereas Glass fibers were pulled out from laminations.


INTRODUCTION
H igh strength aramid fibers placed as core materials in laminates for combination of strength and ductility. Hybrid composites known for their strength-to-weight ratio and ability to absorb energy when struck by bullet therefore used for making body armors for armed forces establishment.
Aramid fibers have symmetricin their internal structure (Zhu et. al. [1]). Aramid fibers extensively used in air craft design, boat hulls, sports goods and armed forces applications (Reis et. al. [2]). Kevlar fibers cross-linked with thermosetting resin to produced hardened product.
Aramid fibers have specific strength and stiffness and incorporated matrix where toughness is required (Reis et. al. [3]). Layup placement and reinforcement fibers are effective tools for fabrication of hybrid composites. Eglass fibers have high tensile strength and placed out for making stiff sandwich structure (Alam et. al. [4]). For light weight high strength applications reinforcement of Kevlar fibers with glass fibers have significant achievement to fabricate low density materials having enhanced impact strength (Wang et. al. [5]). Impact strength of hybrid composites strongly depends upon the selection of reinforcement and layup placement. Kevlar fibers have inter-laminar fracture toughness and working as core material for effective hybridization.Hybrid composites are fabricated by stacking layers by layers with vacuum bagging resin transfer molding technique. Thickness of the laminate maintained at around 3-4mm according to ASTM standard (Reis et. al. [2]).Glass fiber reinforcement polymer has considerable application where light weight and high strength is required. Mechanical strength of composites material relies on the way of layup placement. The glass fibers as reinforcement materials are frequently used in aerospace and construction industries. Aramid fibers reinforcement polymers exhibit superior ultimate tensile strength, elastic modulusand impact energy (Reis et. al. [3]). Kevlar fiber of 5-7mm enhanced the delamination toughness. Kevlar fibers used as core material in lamination and improve the fracture toughness of the composite structures (Sohn et. al. [6]). Kevlar fibers have specific strength associated with failure mechanism and used in impact performance at low weight. Aim of present work is to discuss the experimental results obtained by changing angle ply orientation of reinforced materials. Impact properties of the materials are analyzedby calculating potential energy in joules by observing break and bear resistance of the materials using instrumented dart impact test. Izod impact test also conducted using izod impact tester to observe impact energy joules/meter.

Specimen Fabrication
Laminate of 9 layers 4mm thick were fabricated at room temperature under pressure of 30-100 Psi. Fabrication process is shown in Fig. 1

DART IMPACT TEST
Drop weight impact tester designed to calculate break and bear resistance of fibers reinforcement in polymers.
The drop-dart test conducted with various loading conditionsat room temperature. The adjusted falling speed of impactor was 4.43m/s and 50 Joules of energy. Falling height in dart impact tester is 1000mm and falling mass is in range from 510-550g (Fig. 2).
ASTM D-3763 standard specimens for dart impact test were in square shape measuring 2x2in. Impact energy in form of potential energy(joules)was calculated by using PE= mgh.

Izod Impact Test
Izod impact test measure the toughness of the materials.The Izod impact powerfully dependson size of the specimen being tested because number of imperfection acts as stress raisers and deduce the fracture toughness of the laminate.The Izod impact test was conducted by selecting different specimens and these specimens were designedas per ASTM D-256 standard. The dimension of the specimens were 6.4x12.7x3.2 mm and radius of the notch was 0.25R havingnotch lengthof 2mm ( Fig. 3 and Fig. 4 (a-d)).

SCANNING ELECTRONIC MICROSCOPY
Izod impact test specimens were selected for SEM. Abrasive disc (V101) cutter was used to separate the fracture zone.
As received samples were investigated to analyze the angle ply orientation and surface morphology.SEM images with various magnifications were selected by using 5 KV secondary beam electrons. Experimental results such as

RESULT AND DISCUSSION
The load bearing capacity of hybrid laminates were characterizedby using Dart Impact Test. Specimens was tested with different angle ply orientation, their resistances to penetration were observed by analyzing bear and break resistance.Considerable data have been generated regarding the bear and break resistance mentioned in the bar graph shown in Fig. 6 at GF 0°/90°and GFK 0°/90°, 45°/ 45°and 30°/60°.  [7]) and Rajesh at. al. [8]), that experiments were conducted by designing 11 layers laminate composite as compared to our 9 layers laminate composite. The experimental results of impact energy (J) were carried by the study of different specimens. Bar graph in Fig. 6 shows variation in databy change in layup placementof laminates. Hybrid composite Sheet of GFK at 0°/90°has remarkable performance under loading conditions of dartdart. The GFK at0°/90°and 30°/60°have highenergy absorption capacity then 45°/45°orientation. It can also be analyzed from the reported results that bearand break resistance of glass fibers-Kevlar at angle ply 0°/90° was 46.71% greater than 45°/45°layup placement and 6.71% better than 30°/60°orientation. It is also be studied that impact energy ofglass fibers-reinforced epoxy at 0°/90°h as less energy results fromglass fibers-Kevlarreinforced epoxy at 45°/45° placement. Fig. 6 shows that GF-reinforced epoxy has low energy absorption than other layup placement. Fig. 7(a-d) shows the fracture specimen at different layup placement.  Fig. 8 shows variation of impact strength by different layup placement of glass fiber/epoxy and glass/Kevlar epoxy. Some difference in impact strength between the hybrids composites can be seen from the graph given in Fig. 8. Fig. 8 [9]). By the understanding of bar graph in Fig. 8 shows that change in fibers orientation does not effective in enhancement of impact strength of hybrid laminates but replacement of fibers is useful for the improvement hybrid composites.

Scanning Electronic Microscopy
For the fabrication of hybrid laminate aramid fibers 49/glass fibers reinforcedepoxy at different layup placement were considered for study. Aramid fiber has in-plane impact strength and placed in core for making sandwich structure. Aramid fiber has trade name Kevlar is effective tool to suppress the specific strength and stiffness. Kevlar fiber has resistance to penetration and bonding capability and used in civil and military establishment for making the components parts (Reis et. al. [3]). The scanning electronic microscopy discovered the layup placement and fractography of laminate. Fig.9identified the epoxy resin bonded with glass fibers at 0°/90° before fracture.
The cross-sectional view of glass fibers-reinforced epoxy was seen in Fig. 9 at 0°/90 orientations . The solution of epoxy resin and hardener were placed between the layers of hybrid composites laminate. Fig. 9 shows perfect sequential layers of glass fibers adhesive with epoxy.
Pictorial view of GF 0°/90°shows delimitation was taken place at the centre of impact zone. Impact strength of laminates was reduced by pull out the glass fibers from the sandwich structure by minimum energy absorptions. The placement of layers at different angles were not increase the impact energy of composites but selection fibers in hybridization is very important to enhance the impact strength. Izod tested specimens of GFK 0°/90° have
Nine layers of glass fiber-Kevlar at 0°/90° were seen in images of scanning electronic microscope. Five alternating layers of glass fibers and four layers of aramid fibers placed in sequence stacked layer by layer by epoxy were shown Fig. 11. Selected micrograph at different magnification reported that Kevlar adhesive with epoxy whereas some glass fibers were delaminated from hybrid composites. Young's modulus of laminates relies on fiber reinforced epoxy. The proper use of fibers improves the mechanical strength of hybrid laminates. Similar findings were also reported by number of researchers Satish et. al. [10]) and Reis et. al. [2]). In order to understand the inplane fracture toughness, hybrid compositesstrongly depends on fibers matrix bond strength and selection of fibers. The finding from experimental data is good agreement with literature.
SEM micrograph in Fig. 12 shows that Kevlar fibers bonded with epoxy, whereas the glass fibers deboned from the hybrid laminates. By the investigation of image given in the Fig. 13 it was understood that impact strength of hybrid composites depend son way of layup placement. By insightful of experimental results at 0°/90°, 45°/45°a nd 30°/60° it was observed that that fibers orientation 0°/90° have better impact strength and stiffness.

CONCLUSION
Experimental investigations were conducted to enhance the impact toughness of glass/epoxy and glass/Kevlar epoxy composites. From Dart impact test it was concluded that orientation GFK 0°/90°and 30°/60°have improved impact toughness than 45°/45 whereas GF 0°/90° have lowest value. But the surface and fracture study suggest that at 0°/90°orientation has better fracture strength than other orientations. Therefore, it can concluded that best results can be obtained for designing the structures at 0°/90°layup placement but as far as specific strength is concern angle ply orientation 45°/45°is suitable.

ACKNOWLEDGEMENT
This paper best supported by SUPARCO under the supervision of Anwar Ghyio,Project Director and well