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Material systems capable of handling both the ballistic impact and blast waves are necessary for security forces. In this study, the high strain rate performance of monolithic and bonded ultra‐high molecular weight polyethylene (UHMWPE) with high‐temperature resistant basalt/polyetherimide (B/PEI) composite is presented. Individual composite laminates were fabricated using vacuum‐assisted compression molding. Subsequently, cylindrical test coupons were cut using a high‐pressure waterjet. A suitable adhesive grade was used for the bonding of two different composite types. The dynamic compression studies were conducted on a split‐Hopkinson pressure bar (SHPB). For identical incident energies, the range of strain rates attained by monolithic UHMWPE, B/PEI and bonded composites differed significantly. Monolithic UHMWPE achieved the highest rates of loading, whereas higher stresses were recorded for the B/PEI composite. Yet, monolithic UHMWPE, owing to higher constant stress plastic flow, results in higher toughness. Bonded composites revealed hybrid properties with delamination of UHMWPE as the primary failure mode. High‐speed imaging exposed severe deformation of UHMWPE during dynamic compression. SEM micrographs revealed fiber pull‐out and deforming behavior of UHMWPE and brittle failure of B/PEI composite. B/PEI in a bonded composite system never failed under dynamic compression within the experimental range, thus providing a window of opportunity to tailor‐make better ballistic and blast protection materials. [ABSTRACT FROM AUTHOR]

In this study, the effect of high strain rate on the dynamic mechanical properties of shear thickening fluid (STF) impregnated felt of ultra‐high molecular weight polyethylene (UHMWPE) was investigated by split‐hopkinson pressure bar. UHMWPE felts are randomly oriented nonwoven fabric that holds each other due to inter‐fiber coupling either by thermal calendaring or mechanical entanglement. Its lower areal density and highly porous structure can be utilized in lightweight ballistic resistance material. The junction points inside its porous structure make it easier to hold abundant STF. Shear thickening fluid was prepared by dispersing 100 nm dry silica powder into polypropylene glycol at 67.5 wt% concentration using probe ultrasonicator at 25°C. Rheological characterization of prepared STF was conducted using MCR702 advanced Anton Paar rheometer. It was done by performing a steady shear rate and thixotropy tests for shear thickening and structural regeneration behavior. In‐house fabricated split‐hopkinson pressure bar setup was used to evaluate dynamic compressive behavior at different strain rates by changing triggering pressure. It was found that STF impregnated felt shows a higher amplitude of strain rate augmentation and energy absorption than a neat felt. The impact energy absorption increases with increasing strain rate. However, the peak stress shows an opposite trend with an increased strain rate in STF impregnated felt. [ABSTRACT FROM AUTHOR]

In this study, the influence of hybridization on the compression response of thermoplastic matrix-based composites under high strain rate loading was investigated. The intra-ply and inter-ply hybrid composites were manufactured with Kevlar/Basalt yarns as the reinforcements with Polypropylene as a matrix. Cylindrical composite specimens were laser cut from the flat compression moulded laminates. The composite specimens were loaded under high strain rate using split-Hopkinson pressure bar setup at strain rates ranging from 2815/s to 5481/s. The study revealed differences in the rate-dependent growth of peak stress, peak strain and toughness with the strain rate. Intra-ply hybrid composites with alternate weaving of Kevlar and basalt yarns exhibited highest peak stress as compared to the Inter-ply hybrid composites (alternate layers of Kevlar and basalt fabrics) and another intra-ply composite containing Kevlar in the warp and basalt in the weft direction. Whereas in inter-ply hybrid composite, with Kevlar as the loading face attained higher stress, while composite with Basalt as the loading face attained higher strain. SEM micrographs revealed that Kevlar on the loading face can bear the impact with lesser delamination as compared to the Basalt on the loading face. Damage studies revealed that Kevlar fiber surface loading results in higher stress as compared to basalt (brittle) surface loading with lower overall damage. • The influence of hybization on the high strain rate resposne of thermoplastic composites. • Intra-ply hybridization excels over inter-ply hybridization. • Placement and direction of yarns is crucial in intra-ply hybridization. • Higher areal density fabrics are replacable with hybrid fabrics of lower areal density. [ABSTRACT FROM AUTHOR]

Shear thickening fluids (STFs) are a special class of field responsive fluids which exhibit change of phase from liquid to solid when subjected to imposed shear. This remarkable characteristic of STFs has led to their application in soft body armor technologies, leading the development of concept of Liquid Body Armors (LBAs). LBAs extensively rely upon the symbiotic relationship between STF and high strength FRP (Fiber Reinforced Polymer) composites comprising of high tenacity fibers such as Kevlar, UHMWPE (Ultra High Molecular Weight Poly Ethylene) etc. Although in the past, STFs have been widely characterized by rheometers at low strain rates (≤10 3 s −1 ), but in actual practical scenarios, body armours encounter much higher strain rates (of the order of 10 5 –10 7 s −1 ) under a ballistic impact. The main objective of this study is to capture the dynamics of STFs at such high strain rates by employing Split Hopkinson Pressure Bar (SHPB) technique. The STF sample was synthesized by dispersing 67.5 wt.% of 100 nm silica powder in Poly Propylene Glycol (PPG) and ethanol, using ultrasonic homogenization method. The mechanical response of STF was studied at high strain rates in terms of the stress-strain behavior and variation of the impact toughness with the loading rate of the fluid specimen. It was observed that the impact toughness of STF increased progressively with the specimen loading rate. The peak stress and peak strain rate attained in the SHPB tests were 147 MPa and 22,100 s −1 , respectively. The characteristic transition time of STF was found to be in the range of 13–25 µs. [ABSTRACT FROM AUTHOR]

The present study deals with the quasi-static and high strain rate characterization of Kevlar-129 based thermoplastic composites. Two different thermoplastic matrices, namely, Polypropylene (PP) and Polyetherimide (PEI) were used to manufacture composite laminates. Quasi-static compression tests were performed at strain rates of 0.041 s−1 and 0.045 s−1. High strain rate tests were performed using a split Hopkinson pressure bar apparatus within the strain rates ranging from 2548 s−1 to 4379 s−1. Stress-strain relations reveals the rate-sensitive behaviour of composites. Kevlar/PP (K-PP) showed higher peak stress under quasi-static loading as compared to the high strain rate test. Comparable peak stresses were revealed under quasi-static and high strain rate loading for Kevlar/PEI (K-PEI) composite. Also, high strain rate compression properties such as peak stress, peak strain and toughness of K-PP were 25%, 27% and 6% higher than that of the K-PEI composite. The failure mechanisms of both the composites were characterized through macroscopic and scanning electron microscopy. K-PP failed majorly due to matrix crush and fibre failure while K-PEI failed due to shear cracking. Damage study reveals that a single fibre based composite system can be tailored to act as an energy-absorbing or dissipating material system by varying the thermoplastic matrix materials. • Static and dynamic compressive properties of Kevlar reinforced high-performance polymers. • Kevlar/Polypropylene outperforms over Kevlar/Polyetherimide under both the quasi-static and high strain rate loads. • The quasi-static strength of Kevlar/Polypropylene is 25% higher than its high strain rate strength. • Polypropylene matrix results in ductile failure, while the Polyetherimide matrix results in brittle failure. [ABSTRACT FROM AUTHOR]