Papers by Neelanchali Asija
The high strain rate impact performance of STF is experimentally investigated on inhouse design... more The high strain rate impact performance of STF is experimentally investigated on inhouse designed and fabricated SHPB apparatus.
In order to face the grand challenge of characterizing soft and light armour material system shav... more In order to face the grand challenge of characterizing soft and light armour material system shaving polymers and shear thickening fluids under impacts at high strain rates lead to design and development of this particular SHPB set up. The developed set up is designed for a maximum firing pressure of 300 bar of nitrogen gas and it comprises automated gas filling and firing, striker bar velocity recording and data acquisition system. Pressure bars are made of titanium alloy due to its high yield strength and reasonably lower density which could protect plastic deformation, wave dispersion and reduces impedance mismatch with the intended soft specimens, unlike maraging steel bars. The maximum stresses on the critical parts of the setup are crosschecked with simulation results and compared with corresponding yield strengths. Velocity-pressure calibration of the developed setup shows higher velocities can be achieved at any particular pressure, when it is compared with the existing public domain velocity calibration of SHPB setup.
Shear thickening is a non-Newtonian flow behavior characterized by the increase in apparent visco... more Shear thickening is a non-Newtonian flow behavior characterized by the increase in apparent viscosity with the increase in applied shear rate, particularly when the shear rate exceeds a critical value termed as the critical shear rate (CSR). Due to this remarkable property of shear-thickening fluids (STFs), they are extensively used in hip protection pads, protective gear for athletes, and more recently in body armor. The use of STFs in body armor has led to the development of the concept of liquid body armor. In this study, the effect of particle size is explored on the low and high strain rate behavior of nanosilica dispersions, so as to predict the efficacy of STF-aided personal protection systems (PPS), specifically for ballistic applications. The low strain rate study was conducted on cone and plate rhe-ometer, whereas the high strain rate characterization of STF was conducted on in-house fabricated split Hop-kinson pressure bar (SHPB) system. Spherical nanosilica particles of three different sizes (100, 300, and 500 nm) as well as fumed silica particles of four different specific surface areas (Aerosil A-90, A-130, A-150, and A-200), respectively, were used in this study. The test samples were prepared by dispersing nanosilica particles in polypropylene glycol (PPG) using ultrasonic homogenization method. The low strain rate studies aided in determining the CSR of the synthesized STF dispersions, whereas the high strain rate studies explored the impact-resisting ability of STFs in terms of the impact toughness and the peak stress attained during the impact loading of STF in SHPB testing.
Modern and sophisticated ammunition systems have necessitated the development of advanced ballist... more Modern and sophisticated ammunition systems have necessitated the development of advanced ballistic protection personal armour systems that are damage resistant, flexible, lightweight and possess high energy absorbing/dissipating capacity. Although, exhaustive studies are available which show the improvement in impact resistance of STF-treated high performance fabrics, but there are limited studies which explore the efficacy of STF impregnation method. In this study, an attempt is made to understand this aspect. The low velocity impact studies were conducted on drop tower machine, while high velocity impact studies were accomplished on Split Hopkinson Pressure Bar (SHPB). High impact Poly Propylene Co-polymer (CO15EG) and UHMWPE variants Gold Shield ® and Spectra Shield were chosen for this study. It was observed that when STF was kept in liquid form between layers of ballistic fabrics, the composite exhibited reduced performance, whereas, when STF was impregnated in a ballistic fabric it had a synergistic effect to enhance the impact toughness of ballistic composite.
In the present work, dynamic compression response of polypropylene (PP) based composites reinforc... more In the present work, dynamic compression response of polypropylene (PP) based composites reinforced with Kevlar/Basalt fabrics was investigated. Two homogeneous fabrics with Kevlar (K3D) and Basalt (B3D) yarns and one hybrid (H3D) fabric with a combination of Kevlar/Basalt yarns were produced. The architecture of the fabrics was three-dimensional angle-interlock (3D-A). Three different composite laminates were manufactured using vacuum-assisted compression molding technique. The high strain rate compression loading was applied using a Split-Hopkinson Pressure Bar (SHPB) setup at a strain rate regime of 3633e5235/s. The results indicated that the dynamic compression properties of thermoplastic 3D-A composites are strain rate sensitive. In all the composites, the peak stress, toughness and modulus were increased with strain rate. However, the strain at peak stress of Basalt reinforced composites (B3D, H3D) decreased approximately by 25%, while for K3D specimens it increased approximately by 15%. The K3D composites had a higher strain rate as compared to the B3D and H3D composites. In the case of K3D composite, except strain at peak stress, remaining dynamic properties were lower than the B3D composite , however, hybridization increased these properties. The failure mechanisms of 3D-A composites were characterized through macroscopic and scanning electron microscopy (SEM).
A B S T R A C T Shear thickening fluids (STFs) are a special class of field responsive non-Newton... more A B S T R A C T Shear thickening fluids (STFs) are a special class of field responsive non-Newtonian fluids which exhibit transition from low viscosity to high viscosity state when these are subjected to shear deformation, particularly when the shear rate exceeds a critical value termed as the critical shear rate (CSR). Due to this unique characteristic of STFs, these are generally used for vibration mitigation or shock absorbance such as in vibration dampeners, hip protection pads, in protective gear for athletes etc. From the last two decades, STFs have found application in the field of ballistics, particularly in the development of special class of STF-intercalated armours called Liquid Body Armours (LBAs). These new age armours are lighter in weight and more flexible as compared to conventional heavy armours, which, infact seriously affect the mobility and agility of the soldier, especially in combat situations. Although, exhaustive studies are available which show the improvement in impact resistance of STF-treated high performance fabrics, but there are limited studies which explore the efficacy of STF treatment method. In this study, an attempt is made to understand this aspect. The low velocity impact studies were conducted on drop tower machine, while high velocity impact studies were accomplished on in-house designed and fabricated Split Hopkinson Pressure Bar (SHPB) experimental setup. It was observed that when STF was kept in liquid form between layers of ballistic fabrics, the composite exhibited reduced performance, whereas, STF-treated ballisic composites exhibited enhanced impact toughness at high strain rates in SHPB testing.
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Papers by Neelanchali Asija