No abstract

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. Inhouse 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.

In this study, the mechanical performance of electrospun ultra-high molecular weight polyethylene (UHMWPE) fiber was successfully improved by postprocessing treatment. It is performed by stretching the electrospun UHMWPE mat under constant load at temperatures ranging from 90 to 150 C. The temperature is varied in order to achieve the highest possible draw ratio. The prepared fibers were characterized for their morphological and thermal properties. Moreover, the induced fiber morphology and their performance due to the effect of high-temperature stretching were evaluated using different characterization techniques such as scanning electron microscopy, wide-angle X-ray diffraction, and tensile testing analysis. In addition, the characteristics of prepared yarns were also compared with a commercial grade of Spectra ® fibers. This analysis shows that the post-processing of the mat resulted in the production of axially elongated microfibrillar yarn. Maximum tensile strength of 11.14 ± 3.65 GPa was attained at a stretching temperature of 130 C. However, further raising the temperature causes a decline in performance, demonstrating that the stretching temperature dramatically influences the properties of the fiber.