In this study, the fractal dimensions of failure surfaces of vinyl ester based nanocomposites are estimated using two classical methods, Vertical Section Method (VSM) and Slit Island Method (SIM), based on the processing of 3D digital microscopic images. Self-affine fractal geometry has been observed in the experimentally obtained failure surfaces of graphite platelet reinforced nanocomposites subjected to quasi-static uniaxial tensile and low velocity punch-shear loading. Fracture energy and fracture toughness are estimated analytically from the surface fractal dimensionality. Sensitivity studies show an exponential dependency of fracture energy and fracture toughness on the fractal dimensionality. Contribution of fracture energy to the total energy absorption of these nanoparticle reinforced composites is demonstrated. For the graphite platelet reinforced nanocomposites investigated, surface fractal analysis has depicted the probable ductile or brittle fracture propagation mechanism, depending upon the rate of loading.

This study explores the mechanical properties of an E-glass fabric composite reinforced with anchored multi-walled carbon nanotubes (CNTs). The CNTs were grown on the E-glass fabric using a floating catalyst chemical vapor deposition procedure. The E-glass fabric with attached CNTs was then incorporated into resin based composites and compared to similar composites without CNTs. Long and short beam bending tests, uniaxial compression measurements for energy dissipation, high strain-rate Split-Hopkinson pressure bar measurements, and ballistic performance (V50) tests were performed to characterize the mechanical properties of the CNT composites. The CNT composites showed a reduction in interlaminar shear strength by 25.9 %. They also showed an increase in the specific energy absorption by 106 % at high strain rates and an increase in energy density dissipation by 64.3 % after 5 cycles at quasi-static strain rates. In ballistic V50 tests, the CNT based composites showed a higher V50 value by 11.1 %. Due to their reduced weight and energy dissipation properties, the direct growth of CNTs on E-glass fabrics incorporated into composites have potential defense applications such as blast protection.

The dynamic mechanical behavior and high-strain rate response characteristics of a functionally graded material (FGM) system consisting of vertically aligned carbon nanotube ensembles grown on silicon wafer substrate (VACNT-Si) are presented. Flexural rigidity (storage modulus) and loss factor (damping) were measured with a dynamic mechanical analyzer in an oscillatory three-point bending mode. It was found that the functionally graded VACNT-Si exhibited significantly higher damping without sacrificing flexural rigidity. A Split-Hopkinson pressure bar (SHPB) was used for determining the system response under high-strain rate compressive loading. Combination of a soft and flexible VACNT forest layer over the hard silicon substrate presented novel challenges for SHPB testing. It was observed that VACNT-Si specimens showed a large increase in the specific energy absorption over a pure Si wafer.

Focus of our research is on developing stronger, safer and more cost-effective structures for the new generation naval ships; especially nanoparticle reinforced glass/carbon polymeric based composites and structural foams for blast/shock/impact mitigation. Punch-shear test at low velocity impact is significant for mechanical characterization. Gama et al. [1] performed QS-PST experimental methodology to define elastic energy and absorbed energies of composites as a function of penetration displacement. This paper describes the punch-shear response of nanoparticle reinforced vinyl ester plates, laminated face sheets and sandwich composites using Dynatup 8250 drop-weight impact test system according to ASTM D3763 Standard [2]. Low-velocity tests were performed on 4″ × 4″ square plate specimens with fixed circular boundary condition and impacted by a hemispherical-head plunger with added mass. The impact load, displacement, energy plots and visual inspection of the post damaged specimens depicted the failure characteristics and punch shear response of these composites.

This paper presents an investigation on energy absorption characteristics of nano-reinforced panels, laminated face sheets and sandwich composites in high velocity ballistic and low velocity punch-shear experiments. The vinyl ester panels were reinforced with 1.25 and 2.5 wt. percent nanoclay and exfoliated graphite platelets. Three different face sheets were manufactured with E-glass, Owens Corning HP ShieldStrand ® glass and T-700 Carbon woven fabric in vinyl ester; and one with the E-glass and graphite platelets impregnated vinyl ester matrix. The sandwich composites were fabricated with balsa, PVC foam, 3-D fiber reinforced Tycor ® and fire resistant fly-ash based Eco-Core ® cores in between E-glass/vinyl ester face sheets. Ballistic tests were conducted according to NIJ level III using a universal receiver equipped with a barrel to launch 0.308 caliber M80 ball round projectile at about 890 m/s. Low velocity punch-shear tests were performed at around 3 m/s according to ASTM D3763 Standard using a drop-weight impact test system. The tortuosity of the fractured surface in nanocomposite specimens has been investigated using digital microscope. In ballistic tests, the 3-D fiber reinforced Tycor ® core provided the most resistance when projectile strikes at the web-flange interface region. The 2.5 wt. pct. graphite platelet reinforced nanocomposite, HP ShieldStrand ® glass vinyl ester face sheets, and E-glass/Eco-Core ® sandwich composite showed the best energy absorption under low velocity punch-shear.