Objective Ultra-high molecular weight polyethylene (UHMWPE) fiber has the characteristics of high strength, mode and specific absorption energy, the UHMWPE composites has excellent impact resistance and has a place for military applications. However, UHMWPE fiber itself has high crystallinity and orientation, poor surface polarity, the interface properties formed between fiber and resins is weak, stress cannot be well transmitted, which in turn causes premature failure of the material. In this study, the duoplasmatron surface modification technology was used to improve the chemical bonding and mechanical interlocking ability of fibers and resins, so as to improve the impact resistance of composites.
Method In this study, the UHMWPE fiber fabric with a specification of 180 g/m2 modified by oxygen/argon duoplasmatron, and the vacuum-assisted resin infusion molding technology (VARI) technology was used to prepare composites from the surface modified UHMWPE fabric and epoxy vinyl ester resin. AFM(atomic force microscope), FT-IR(fourier transform infrared reflection)and other test methods were used to characterize the materials before and after modification, the impact load value was used as the response value, and the three-dimensional surface model was constructed by the response surface method to explore the influence of modification on the ballistic resistance of UHMWPE composites, the penetration process was recorded by high-speed cameras.
Results After ionizing the mixed gas, FT-IR results showed that more —OH hydrophilic groups are formed on the surface of the fiber, the hydrophilicity of the surface was improved on the basis of unmodified. The moisture permeability of the first and second modified materials after modification is increased by 33.3% and 30.6% respectively, compared with the unmodified materials. The fiber mean square root roughness value of the fiber modified by double plasma was 124, and the surface morphology was strip-like with terrain, which significantly increased the bonding area and promoted mechanical linkage. In this experiment, the discharge power, time and flow rate were taken as the independent variables, and the impact load value of UHMWPE composites was taken as the response values. Through analysis and optimization, the P = 0.011 2(<0.050 0), which proves that the model is significant. The influence of the three factor levels on the impact of the composites is ranked: flow rate> power > time. After the optimization of the response surface, the optimal power was 193 W, time was 118.29 s, and the flow rate was 14.637 mL/min.
The impact load of the modified material reaches 4 961 N. When the projectile penetrates, the projectile surface is almost presented as fiber shear failure, and the failure surface is smooth, with the deepening of penetration, the projectile velocity decreases, the energy absorption increases, there will be a certain stretching deformation on the back of the fiber impact point. If the target plate is penetrated, there will be a punch material flying out. With the impact point as the center, there is a clear empty drum area next to it, the resin is widely shed, and the target plate fails prematurely. After plasma modification of the material in the projectile impact, t=0.000 3 s can be seen that the instantaneous synergy between the fiber layers is strong, the holding force of the matrix on the fiber increases, and the UHMWPE fiber can play a good performance, when the high-speed bullet hits the surface, the fiber plays the main impedance penetration role, and the bullet is coated into the fiber. Moreover, the energy absorption value of the modified composite was increased by 45.59% compared with the unmodified composites.
Conclusion In this study, AFM, FT-IR and other methods were used to characterize the materials before and after modification, and it was concluded that more —OH hydrophilic groups were formed on the fiber surface, which improved the hydrophilicity of the surface. The moisture permeability of the first and second times was 33.3% and 30.6% higher than that of unmodified materials, respectively. The surface morphology modified by duoplasmatron and the strip-like terrain significantly increase the mating area, and promote the mechanical linkage. By constructing the 3-D surface model, it is concluded that the influence of three factor levels on the impact load resistance of the composites is ranked: flow rate> power > time. When the projectile penetrates the material, it almost appears as fiber shear failure on the projectile surface, and when the high-speed bullet hits the surface, the fiber plays a major impedance penetration role, which can wrap the bullet into the fiber. Moreover, the energy absorption value of the modified composites was increased by 45.59% compared with the unmodified composites.
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