High Speed Impact Mechanism Of STF-Kevlar Fabric And Its Influencing Factors

Kevlar fabric is widely used in high bypass ratio turbofan engine soft wall containment system due to its good impact resistance.It can guarantee good containment and reduce the weight of the engine at the same time.Shear thickening fluid（STF）,a kind of non-Newtonian fluid,shows mechanical behavior of solid by improving viscosity under high velocity impact.Kevlar fabric impregnated with STF can improve the impact resistance,often used in body armor,making it lighter and more flexible.Replace the Kevlar fabric in soft casing with STF-Kevlar,can reduce the fabric layers and containment system volume.It is expected to further reduce the structural weight of the engine,improve the engine thrust weight ratio.However,the mechanism of high speed impact on STF-Kevlar fabric is not clear at present,which limits its development and application.In this paper,the high speed impact mechanism of STF-Kevlar fabric and influence factors are studied.The main work and conclusion are as follows:（1）With 100nm and 650nm diameter SiO₂ particles and polyethylene glycol as raw materials,different concentrations of STF were prepared by mixing method with ultrasonic dispersion,adding carbon nano materials to the STF of 100nm diameter SiO2 particles（20%mass concentration）to make multi disperse phase STF and the rheological properties of three systems were tested.Kevlar fabric impregnated with STF was observed by scanning electron microscope.It was found that the shear thickening phenomenon appeared in the three STF systems.The weight gain of the STF-Kevlar was related to the concentration of STF.From the micro morphology of the fabric,it can be observed that the nano SiO₂ particles were uniformly attached to the surface of the fiber,and the fibers were bonded together by STF.（2）Ballistic tests of different kinds of STF-Kevlar and Neat Kevlar fabrics were carried out using simulated blades of titanium alloy.The impact process was recorded by high-speed camera,and the ultimate deformation degree and elongation at break were obtained through analysis.The results show that the STF made of 100nm can improve ballistic limit of the Kevlar fabric,and increase the energy absorption in a certain impact speed,maximum increase of 36%.The energy absorption increases first and then decreases with the increase of energy projectile speed.Yarn strain energy and kinetic energy increase,yarn friction energy dissipation is the main way of energy absorption.It can be observed from the SEM of the fracture that untreated Kevlar fibers are disorderly,coiled,and the fracture of STF-Kevlar fiber is neatly.（3）The influence of pressure,number of layers and disperse phase on the impact resistance of STF-Kevlar fabric has been studied,and the results show that the ballistic limit and energy absorption of the fabric is maximum under the pressure of 1bar.The unit fabric surface density of absorbed energy under the pressure of 1bar and 2bar is close to the fabric with no padding.The ballistic limit of the 4 layer fabric is about 45%higher than that of the 2 layer fabric,and the energy absorbed by the unit surface density of the fabric increases slightly with the increase of layers.The impact properties of the fabric can be enhanced by the multi disperse phase STF,and the energy absorption of the composite fabric is related to the critical shear rate of STF.The research of this paper lays the foundation for the application of STF-Kevlar fabrics in soft-containment systems.