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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]

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]

An investigation of the effect of strain rate on the dynamic compressive behavior of glass/polytetrafluoroethylene (PTFE) composite is presented. Experimental studies were carried out on two dimensional (2D), satin weave (SW) and three dimensional (3D) woven glass/PTFE composites using split Hopkinson pressure bar (SHPB) apparatus. Commercial grades of glass/PTFE fabrics were autoclaved to prepare the composite laminates and circular specimens were cut out using a high‐pressure water jet. High strain rate studies confirmed the rate‐dependent behavior of all the woven composite systems under consideration. The highest rates of loading were attained by 3D woven specimens for identical incident energies. The highest peak stress attained by 3D woven specimens was 501 MPa, which was trailed by 2D woven specimens with 482 MPa stress. The advantage of satin weave was not reflected in the small specimens as the peak stress attained for identical loading was limited to 405 MPa. Similarly, the highest strain and toughness were recorded for 3D woven composites. However, the SW pattern unlocked a new possibility of controlling the primary damage axis. Furthermore, an analytical method is presented based on variable rate power law to predict the dynamic compressive stress of glass/PTFE. [ABSTRACT FROM AUTHOR]

Kevlar reinforced composite material systems are widely used for personal body armors. Due to aging or minor damage while in service, body armor may get exposed to external weather conditions, including moisture. The present study investigates the effect of moisture on the high strain rate behavior of Kevlar/Polypropylene (K‐PP) composite. Flat K‐PP composite laminate was manufactured using a vacuum‐assisted compression molding followed by laser machining. Dynamic compressive loading tests were performed using split Hopkinson pressure bar setup. The phenomenological modeling approach was adopted to characterize the rate‐dependent behavior of dry and wet composites. For identical dynamic compressive loading, different strain rates, strains, and stresses were attained by the dry and wet composite specimens. Macroscopic and microscopic imaging was done to expose the variation in damage behavior as a function of moisture absorption. Significant property reduction as a function of moisture absorption emphasizes the need for moisture proofing and protecting the armor products from minor damages leading to sites for moisture ingress. [ABSTRACT FROM AUTHOR]