Study On Ballistic Impact Failure Mechanism Of STF Fiber Reinforced Composites

High strength and high modulus fiber materials have high specific strength,high specific modulus,low density,high protection and high designability,so they are widely used in the field of individual impact protection.At present,the research on ballistic impact protection materials has made progress from various perspectives at home and abroad,but there is still a lack of theoretical guidance on the ballistic impact response process of fiber-reinforced flexible composites and their failure mechanisms.This topic takes the ballistic impact process of high-strength and high-modulus fiber-reinforced flexible composites as the starting point,conducts ballistic impact experiments on single-layer,multi-layer,and turn-angle layered flexible composites,analyzes the impact response of flexible composites under the action of ballistic impact,establishes the fluid-solid coupling model of flexible composites by finite element simulation method,and analyzes the response mode and energy absorption distribution of fabric to bullet impact and its ballistic impact failure mechanism.In this project,shear thickening fluid（STF）was prepared by mixing silicon dioxide（SiO₂）nanoparticles with polyethylene glycol solution by a combination of mechanical stirring and ultrasonic oscillation,and STF fiber-reinforced composites were prepared by impregnation method with UHMWPE fiber woven fabric.The presence of STF on the fabric was investigated by Scanning electron microscope,X-ray diffraction,and Fourier transform ioncyclotron resonance characterization tests on STF fiber-reinforced composites,and the effect of STF on the interfacial behavior of the composites was verified by yarn pull-out tests.Ballistic impact tests of STF fiber-reinforced composites to investigate the damage pattern and ballistic protection mechanism of flexible composites through energy absorption,failure shape,and impact morphology.LS-DYNA software was used to perform fluid-structure coupled finite element analysis on the composite material to simulate the failure behavior and energy absorption of the fabric after being hit by a bullet,and to investigate the response shape of the flexible composite material to the bullet impact.The results showed that the SiO₂ particles were uniformly adhered to the fibers and the STF was in a near viscous flow state on the UHMWPE fiber fabric.The peak extraction force of the flexible composite yarn shows an increasing and then decreasing trend with increasing extraction speed,similar to the rheological properties of the STF.According to the ballistic test results,STF fiber-reinforced composites absorb higher energy than pure fabrics,and single-layer fiber-reinforced composites absorb up to 37.1%of the kinetic energy of the impact.The damage sequence of the reinforced fabric is correlated with the STF impregnation;the damage of the pure fabric pavement is from outside to inside;the damage of the fabric pavement after STF impregnation is from inside to outside.The deformation and failure of the composite during the impact were reproduced by finite element simulation,and the energy and impact morphology were analyzed to confirm the impact response of the STF fiber-reinforced composite fluid-solid coupling model to the bullet.In addition,the effect of STF on the weave is divided into two parts within the weave,while in multi-layered angular weave,STF also plays an important role in limiting the slippage between weave layers.