Design Of Modulus Matching And Ballistic Resistance Of Polyimide Fiber Composites

Polyimide(PI)fibers and their composites have excellent mechanical properties and comprehensive performance,which can meet the needs of ballistic performance and light weight of bulletproof products,and have a wide application prospect in the field of ballistic protection.The key to improving the ballistic performance of composite materials is to take advantage of high-strength PI fibers and high-modulus PI fibers through structural design.In this paper,the initial evaluation of the ballistic performance of PI fibers and various organic fibers was firstly conducted by fiber tensile test.The dynamic mechanical properties of PI single fiber and the fracture failure mechanism are studied.The research idea of modulus matching design is proposed,and the composite target plate is prepared by laying high modulus PI fibers on the impact surface and high strength PI fibers on the back surface.The ballistic test was used to study the ballistic performance of the target plate,and the failure mode and energy absorption mechanism were investigated by combining macroscopic morphology,CT inspection and finite element analysis;the effects of resin matrix,lay-up angle and fabric/UD(uni-directional)reinforcement matching on the ballistic performance of the target plate were explored and studied to provide reference for further improving the ballistic performance of the target plate.The research results show that:(1)High-modulus PI fibers have high stress wave velocities,and high-strength PI fibers have high toughness and bullet-proof effectiveness values.As the strain rate increases,PI fiber monofilament tensile strength increases,elongation at break decreases,dispersion increases,and PI fiber fracture morphology changes from necking to necking weakening,which then changes to protofibrillation and axial cleavage.The tensile strength of high modulus PI fibers is more sensitive to strain rate changes.The Weibull distribution with strain rate term can describe the mechanical behavior of PI fibers at high strain rates.(2)When the proportion of high modulus fibers is lower,the ballistic performance of the modulus-matched design target plate is significantly improved.When the penetrator is 5.6 g lead bullet,the delamination area and fiber stretching degree of the modulus-matched design target plate are larger,and when the penetrator is 1.1 g fragment,the delamination area of the modulus-matched design target plate decreases and the pore volume and fiber stretching degree increase.The finite element analysis results further indicate that the modulus-matched design target plate has better energy absorption,and the high modulus fiber disperses the energy rapidly to increase the number of high-strength fibers involved in energy absorption,thus improving the ballistic performance.(3)The ballistic performance of different resin PI fiber composite target plates is from high to low: PPS,PEI,PVB,TPU;changing the lay-up angle can limit the back face signature(BFS).Introducing a small amount of fabric on the impact face of the UD reinforced PI target plate can reduce the BFS value of the target plate.