| Ultra-high molecule weight polyethylene (UHMWPE) fiber is one of the main high performance fiber utilized in personal ballistic equipment because of its excellent mechanical property. However, disadvantage of low surface energy and weak temperature endurance make it difficult to choose proper resin system and manufacturing process for UHMWPE ballistic composite. Electron beam (EB) radiation curing is a newly emerging technique for manufacturing polymer-based composite. This technique not only makes effective curing of resin under a relative low temperature possible, but also enables the surface modification of UHMWPE fiber by irradiation grafting. Although EB curing has been utilized in aerospace composite industry nowadays, the use of this technique in UHMWPE ballistic composite has not been reported. In this paper, EB curing technique for UHMWPE/vinlyester resin (VER) ballistic composite is studied. Radiation effects on UHMWPE fiber and VER have been investigated. VER has been toughened according to the needs of ballistic composite. Ballistic plates have beenmanufactured based on the selected processing of UHMWPE fiber surface modification and EB curing.The main content and conclusion of the paper are as follows:EB radiation effect of UHMWPE fiber has been thoroughly investigated. It is demonstrated from the gel fraction analysis that gel fraction of the fiber increases at first stage of irradiation as the radiation dose increases, but decreases afterwards. There is a more significant chain scission effect for UHMWPE fiber compared to ordinary LDPE and HDPE because of its high crystalline. Recrystallization in localized microstructure occurs because of the chain scission under low dose irradiation, which leads to an increase in the fiber crystalline within a limited scale. The melting point and enthalpy increases. However, as the irradiation dose increases, crystallinity decreases and the regularity of microstructure is destroyed. Tensile strength and breaking elongation of the fiber decrease after irradiation. Fiber modulus increases at low dose irradiation due to crosslinking between macromolecule chains, then it declines as dose increases. The failure behavior of the fiber exhibits a ductile–brittle transition. Dose rate and irradiation atmosphere also influence the irradiation effects.The effect of EB irradiation on fiber surface and surface grafting of UHMWPE fiber by EB irradiation are studied. An etch effect on the fiber surface is confirmed. Polar group, such as ester, carboxyl, and ether, appears on fiber surface, which may result in surface activation. However, less oxygen-content polar group is found when irradiated under vacuum. Co-irradiation grafting process is utilized for UHMWPE fiber surface modification. Homopolymerization is restricted by using acrylic acid (AA)/ acrylamide(AM) binary grating system. Carboxyl and carbonamide group are grafted to the fiber surface. Formula with equal content of AA and AM yields the highest graft at the dose rate of 100Gy/s. Fiber irradiated inγ-MPS solution is grafted by siloxanol group. EB irradiation may strengthen the condensation of primary hydrolysate, which results in the formation of polysiloxane and decrease the coupling activity of grafted group. The graft yielding of GMA by co-irradiation process is rather limited. However, it can be utilized to further modify AA grafted UHMWPE fiber by introducing vinyl group to fiber surface. Results from T-peel strength testing demonstrates that boundary strength between the UHMWPE fabric and VER increases. The analysis of interfacial strengthen mechanism reveals that hydrogen bond can be formed between hydroxyl group of VER and carboxyl or carbonamide group on the fiber surface. Covalent bond is formed by dehydration reaction between the siloxanol group and hydroxyl group. Vinyl group on the fiber surface will react with the same group in VER during the EB curing process and thus strengthen the interface between fiber and resin.The study of EB curing process of VER indicates that it can be cured without any initiator by EB irradiation under free radical mechanism. ESR analysis confirms that polyenoic radicals are formed during the EB curing process as the radical content increases with the irradiation dose. Trapped radical is fairly stable under low temperature but can be reactivated by heating to further initiate polymerization.. Analysis of gel fraction indicates that the increasing rate of gel fraction is influenced by irradiation dose rate and the irradiation processing style. Gel fraction increases faster under high dose rate irradiation. Curing rate under discontinuous irradiation is more tender than that under continuous irradiation. Crosslinking density and structure regularity of the resin increases with irradiation dose. Tensile strength and bending strength increases. However, the impact toughness is better under low dose irradiation. The influence of dose rate on the resin property is not distinct in this study. VER is toughened by a series of liquid rubber, including hydroxyl-terminated and carboxyl-terminated butyl rubber(HTPB,CTPB),hydroxyl-terminated and carboxyl-terminated butyronitrile rubbe(rHTBN,CTBN), hydroxyl-terminated styrene butadiene rubbe(rHTBS), maleic anhydride modified butyl rubber(MLPB)and vinyl-terminated polyurethane (PU). Investigation of gel fraction reveals the influence of liquid rubber on the VER curing. There is an acceleration effect under high dose irradiation. Microstructure analysis of blend system shows that free volume of the resin decreases with the inducing of liquid rubber. Damp property of the resin increases and phase separation occurs. Mechanical property testing reveals that MLPB/PU/VER system acquires the highest impact toughness among the toughen resin. Surface tension of the toughen resin and the T-peel strength between resin and surface modified UHMWPE fabric have been tested. The results indicate that resin with moderate surface tension may result in better interfacial strength.The ballistic property of EB curing UHMWPE ballistic composite has been studied along with the processing parameters. The investigation of irradiation dose distribution in the ballistic plate concludes that penetration depth of 6MeV electron beam is about 2.4cm..The number of layer for relative uniform distribution is 30~35. Surface temperature of ballistic plate during curing process increases with the irradiation dose but levels off when resin reaches a rather high curing degree. Maximum temperature during the process is less than 90°C.The plate acquires the best ballistic property when the irradiation dose is 50kGy. Decline of the ballistic property occurs with high irradiation dose. Plate with MLPB/PU/VER resin system exhibits the best ballistic property. Surface modification of UHMWPE fiber also benefits the ballistic property. Heat pressing process following low dose irradiation can improve the property of plate by adopting the advantages of both processes.Ballistic mechanism of UHMWPE composite has been discussed based on the morphology analysis of ballistic perforation. It is demonstrated that multiple energy absorbance mechanism effects during the ballistic process. At the first stage of fragment penetration, fiber is cut by the fragment without enough elongation. Debonding between fiber and resin, and the fracture of resin occurs. Melting phenomenon may occur for some fibers. In the middle thickness of the plate, more fibers have been broken by elongation, debonding between layers, and the fracture of resin are more distinct. The fracture ends of fiber are enveloped by the same material. There is nearly no fibrillated fracture morphology characterizing aramid fiber. This suggests that the fracture mechanism of UHMWPE fiber under high strain velocity is plastic flow and melting fracture. At penetration side of the plate, shear failure, stretch failure, and twisting deformation of the fiber are dominated. Debonding between layers and fracture of resin may occur before the fragment is reached and thus do not play an important role in anti-penetration at this stage.
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