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Hybrid composite armors consisting of Kevlar short fibers reinforced high-density polyethylene were prepared and the effects of the addition of micro and nano-fillers on the dynamic impact response and the energy absorption under ballistic impact were investigated. Five groups of specimens were manufactured using compression molding of pellets containing mixtures of high-density polyethylene and the reinforcing materials. The first group consist of high-density polyethylene reinforced with 10 wt% Kevlar pulp (KN-1). The rest are hybrid composites created by the addition of 20 wt% of micro and nano-fillers. The natural micro-fillers used are particles of chonta palm wood (KN-2) and potato flour (KN-3). The synthetic nanofillers are colloidal silica (KN-4) and gamma alumina (KN-5). Microstructure (scanning electronic microscope) and compositional (energy-dispersive spectroscopy) analysis of the hybrid composites were carried out to evaluate matrix-reinforcements-interface. The fabricated composites plates were subjected to high velocity impact using split Hopkinson pressure bar system and ballistic impact, according to NIJ standard–0101.06 for ballistic resistance. Significant stiffness improvements of up to 43.5% were achieved as a result of the addition of synthetic nano-particles to Kevlar fiber reinforced high-density polyethylene. X-ray diffractometer analysis revealed that the crystalline structure of the Kevlar reinforced high-density polyethylene is unaffected by addition of the nano-particles as fillers. However the intensity of the crystalline peaks decreased depending on the type of the added fillers. The results of dynamic impact test using split Hopkinson pressure bar revealed improved impact resistance by addition of synthetic nanofillers (silica and alumina). The results of the ballistic impact test showed the gamma alumina nano-particles (KN-5) exhibited the highest energy absorption capability. The results of these investigations indicate that hybridization Kevlar short fibers reinforced high-density polyethylene by micro and nano-fillers addition enhances the stiffness, impact resistance and ballistic energy absorption capability of the composites. [ABSTRACT FROM PUBLISHER]

We have studied a relationship between magnetic hysteresis and microstructures on high-tensile AISI 4340 steels after impact loading with a strain rate up to 2100 s-1 We find that coercivity, and minor-loop coefficient which is deduced from a power-law scaling between minor-loop parameters increase with strain rate, show a maximum at around a strain rate of 1400 s-1, followed by a decrease at a higher strain rate, associated with magnetic anisotropy with respect to impact direction. These observations are explained from the viewpoints of heat generation and heterogeneous microstructures characteristic to steels subjected to high strain rate deformation. [ABSTRACT FROM AUTHOR]

In the present study, the texture evolution, microstructure and mechanical behavior of WE43 magnesium sheet at high strain rates are investigated. Samples cut along the rolling direction (RD), 45° from the RD, transverse direction (TD) and perpendicular to the RD-TD plane were tested at strain rates of 800, 1200 and 1400 s-1 using Split Hopkinson Pressure Bar. It is observed that after shock loading, the initial weak texture converts to a weak (00.2) basal texture in all samples. Besides, it is found that the strength and ductility increase and twinning fraction decreases with increase in strain rate. Moreover, another effect of increase in strain rate is found to be the higher activation of pyramidal 〈c + a〉 slip systems. In addition, degree of stress and strain anisotropy is low particularly at higher strain rates, which is mainly related to the weak initial texture of the samples. A viscoplastic self-consistent model with a tangent approach is used to analyze the deformation mechanism during shock loading. [ABSTRACT FROM AUTHOR]

Alumina particle-reinforced aluminum 6061-T6 composites are subjected to deformation at high strain rates in torsion and in compression using Hopkinson bars. The volume content of alumina particles in the aluminum alloy are 10 and 20 pct. While occurrence of adiabatic shear bands is evident under compression, the specimens fractured rapidly in torsion at high strain rates. Fracture occurs in both testing modes by ductile shear failure with elongated dimples originating mostly from the particle matrix interface. Most of the reinforcing particles along the crack propagation path fractured in torsion. However, excessive thermal softening inside the shear bands in the specimens under compression loading caused debonding rather than fragmentation of most particles as the crack propagates along the shear bands. [ABSTRACT FROM AUTHOR]

Cylindrical specimens of AA 2017 alloy in T451, T651 and O temper conditions were subjected to quasi-static compressive loading at a strain rate of 3.2 × 10-3 s-1 and dynamic impact loading at strain rates between 3000 s-1 and 8000 s-1. The effects of strain rates and temper condition on damage evolution were investigated. Deformation under quasi-static loading was dominated by strain hardening while high strain rates deformation was characterized by two-peak stress-strain curves, indicating simultaneous occurrence of hardening and softening controlling deformation. The degree of softening after the first peak is highest in the annealed sample while the age-hardened specimens showed higher degree of softening beyond the second peak. Both deformed and transformed shear bands were observed in the impacted age-hardened specimens, whereas only deformed bands developed in the annealed specimens. The critical strains for the onset of the thermomechanical instability leading to the formation of adiabatic shear bands are about the same for both T451 and T651 specimens, but much higher for the annealed (O) specimens. The age-hardened specimens fractured in a manner consistent with ductile fracture mode that is characterized by the sequential nucleation, growth and coalescence of micro-voids inside transformed shear bands. [ABSTRACT FROM AUTHOR]