The influence of measurement temperature on the high velocity (>100 m/s) impact performance was investigated for three thermosetting epoxy resin S-2 glass composite systems. These three model resins were chemically similar but have different glass transition temperatures (T-g) and molecular weights between crosslinks (M-c) through the use of different diamine curing agents (Jeffamine (R) D230, D400, and D2000). Impact performance was quantified by the projectile kinetic energy absorbed (KE50) as calculated from the characteristic ballistic velocity (V-50) of the composites during high velocity impact. Among the resin systems, the KE50 remained essentially constant over a broad range of temperatures for each composite set and modestly increased with decreasing M-c. The superficial damage area associated with delamination showed remarkable sigmoidal behavior as a function of the testing temperature relative to the T-g (T-T-g). Damage was high for low T-T-g values (glassy resin) and decreased as the resin traversed its Tg into the rubbery region. These damage area trends were found to depend on the resin M-c, with higher M-c values resulting in lower overall damage area and a lower inflection point temperature. High speed videography of the back surface of the samples showed that lower damage areas correlated with an increased back face deflection, which enabled energy absorption with relatively less delamination. Composite mechanical tests were performed to validate the impact performance and explain the deformation mechanisms observed during impact energy dissipation. Our results illustrate the critical importance of the resin architecture and temperature-dependent viscoelastic behavior on the impact properties of composites for impact-resistance applications.

An understanding of the dynamic failure of damaged ceramics is important in protection applications, where the interaction of the projectile with cracked material is a contributing factor in the overall system performance. In this paper, we investigate the effects of pre-existing internal cracks on the quasi-static and dynamic compressive behavior of an advanced ceramic. We present experiments on a hot-pressed boron carbide in which internal cracks are generated through thermal shocking after which the initial material damage is quantified. Damage characterization was performed via Resonant Ultrasound Spectroscopy (RUS) and high-resolution Computed Tomography (CT). A computational procedure is developed to determine the three-dimensional structure of the internal crack network in the initially damaged material from a series of CT images. The failure and strength of the material is then evaluated experimentally. The uniaxial compressive strength of the predamaged boron carbide samples is determined under both quasistatic and dynamic loading scenarios and this is correlated with the pre-existing crack structure as determined by CT. Damaged samples were found to have average compressive strength of 1.14 GPa in quasistatic loading and 0.68 GPa in dynamic loading compared to 2.98 +/- 0.6 GPa and 3.70 +/- 0.3 GPa for pristine material, respectively. High speed photography employed during dynamic testing indicates that pre-existing cracks may lead to different failure mechanisms from what is normally seen in pristine material. Ultimately, these insights can be used to design improved materials that are more resistant to dynamic failure.

The influence of measurement temperature on the high velocity (>100 m/s) impact performance was investigated for a model thermosetting resin composite system. Plain weave S-2 glass composite panels were fabricated using VARTM and an epoxy resin cured with a polyetheramine curing agent. Overall, the energy absorption for the composite remained approximately constant over a broad testing temperature (T) range. The damage area caused by high-strain rate delamination, however, showed remarkable dependence on the T-Tg. The damage area was high in the glassy state (low T-Tg values) and decreased as the resin traversed its Tg into the rubbery region. Impacted samples showed that an increase in back face deflection correlated to lower damage areas and enabled more energy absorption. These results illustrate the critical importance of the temperature dependent viscoelastic behavior on the impact properties of composites.

Abstract : The use of cartridge projectiles in the ballistic evaluation of armor can result in measurement uncertainty if there is variability in their construction. This report details a method that was developed to batch analyze and compare the volumes of (210) BS41 surrogate projectiles that were scanned using X-ray computed tomography. The method described automatically segments and obtains the axial-symmetric radii profiles of components contained within the projectile (outer jacket, inner jacket, core), which can then be used to quantify and compare projectiles to one another numerically using a root-mean-square-error calculation. Projectiles are then grouped together according to the similarity of their components. Also discussed is graphical-cluster analysis of the projectiles, which aids in understanding the source of their variability as well as an approach to use this methods numerical component values to account for projectile variability in the ballistic evaluation of armor.

This chapter contains sections titled: Introduction Theory Experiments Eclipse TEC Performances, Properties and Applications Conclusions

This chapter contains sections titled: Scanner-Based Tile Dimensioning Genetic Algorithm Measurement Error Considerations Conclusions Acknowledgements

In the past, the dispersion of carbon nanotubes (CNTs) in both liquids and solids has been difficult due to the high surface interactions between the tubes. Dispersion of polymer CNT composites is important for such benefits as structural reinforcement of composites, the percolation threshold of CNT based conducting materials, and the thermal properties with the exploitation of the high surface area of CNTs. Here we discuss two approaches towards addressing dispersion of multiwalled nanotubes (MWNTs). One approach is the use of surfactant chemicals selected on the basis that they interact with CNT chemical groups. The second approach is the functionalization through covalent bonding of the CNTs with various polymers including polyethylenimine (PEI), and poly(methyl methacrylate) (PMMA). The two approaches were evaluated to determine whether covalent functionalization was more beneficial than the use of surfactants. Characterization of the dispersion was performed using various microscopy techniques.

This paper presents the properties of the EclipseTEC (TM) transparent conductor. EclipseTEC (TM) is a room temperature deposited nanostructured thin film coating system comprised of metal-oxide semiconductor elements. The system possesses metal-like conductivity and glass-like transparency in the visible region. These highly conductive TEC films exhibit high shielding efficiency (35dB at 1 to 100GHz). EclipseTEC (TM) can be deposited on rigid or flexible substrates. For example, EclipseTEC (TM) deposited on polyethylene terephthalate (PET) is extremely flexible that can be rolled around a 9mm diameter cylinder with little or no reduction in electrical conductivity and that can assume pre-extension states after an applied stress is relieved. The TEC is colorless and has been tailored to have high visible transmittance which matches the eye sensitivity curve and allows the viewing of true background colors through the coating. EclipseTEC (TM) is flexible, durable and can be tailored at the interface for applications such as electron-or hole-injecting OLED electrodes as well as electrodes in flexible displays. Tunable work function and optical design flexibility also make EclipseTEC (TM) well-suited as a candidate for grid electrode replacement in next-generation photovoltaic cells.

Hyperbranched polyethyleneimines were modified with methacrylated fluorosurfactants and aliphatic epoxides to provide a library of macromolecules with controlled chain ends and residual amine functionality. These materials were co-dissolved with a thermoplastic polyurethane-ether and the blends were subsequently deposited as films cast from solution. The surface chemistry of the cast films was determined using angle resolved X-ray photoelectron spectroscopy (AR-XPS) and Rutherford backscattering spectroscopy (RBS). Experimental results indicate that the modified hyperbranched polymers (HBPs) concentrate at the air–polymer interface. Furthermore, HBPs that were complexed to polyoxometalates (POMs) using electrostatic interactions also exhibited surface segregation in cast polymer films, resulting in ca. 10-fold increase of metal at the film surface relative to the known bulk concentration. Results from XPS and RBS examination of the films are consistent with surface segregation of the HBP–POM hybrids, exhibiting increased metal, fluorine, and nitrogen content near the surface of the film, as well as significant changes in wetting behavior. This study indicates that modified HBPs may be used to selectively transport inorganic species such as polyoxometalates to polymer film surfaces.

Grafting reactions of living polystyryllithium (PSLi) with acid chloride containing multi-walled carbon nanotubes (MWNTs-COCI) were performed under vacuum in benzene at room temperature. Covalent grafting of polystyrene (PS) was characterized using spectroscopic, microscopic, and thermogravimetric analyses. Grafting at different ratios of macroanion to acylchloride of the carbon nanotubes showed that the grafting efficiency was not dependent on the concentration of the macroanions. The mole percent of PS present in the MWNTs-g-PS samples was inversely proportional to the precursor molecular weight of PSLi. Direct reactions of PSLi, polybutadienyllithium and n-butyllithium with pristine MWNTs without any functional groups were also performed in the presence and in the absence of tetrahydrofuran in benzene. The grafting reactions of living macroanions either with MWNTs-COCl or with pristine MWNTs indicated a partial grafting of polymer on the carbon nanotubes in benzene at room temperature.

Single- and multiwalled carbon nanotubes have been covalently functionalized with free-base porphyrin. The quantity of porphyrin linked to the surface was determined from thermogravimetric and UV-vis analysis. A reversible protonation equilibrium between the attached porphyrin and the residual acid groups of the carbon nanotubes has been identified. Steady-state fluorescence emission spectrum of the solutions of porphyrin-linked carbon nanotubes shows that the porphyrins act as energy absorbing and electron transferring antennae, and the carbon nanotubes act as efficient electron acceptors. The porphyrin-linked carbon nanotubes show 95-100% emission quenching, indicating a fast photoinduced electron transfer.

Abstract : A series of hyperbranched materials have been developed that allow for the transportation of desired functional groups to the surface of a polymer blend by simple solution casting techniques. These materials have been employed to transport polyoxometalates, or POMs, to the surface of a polyurethane- polyether copolymer film. providing for a 10x increase in POM concentration at the surface compared to the bulk. The films were evaluated using x-ray photoelectron spectroscopy (XPS) and contact angle analysis, and their surface chemistry was dominated by the hyperbranched polymer incorporated into the blend.

: The photo induced formation of silver (Ag) clusters and particles in poly(vinyl alcohol) poly(acrylic acid) blend films is described. The photo reduction of the Ag+ is achieved by subjecting the Ag+ doped films to 350 nm photons. The formation of Ag clusters and particles is monitored using UV-VIS spectroscopy. Films treated with H2O2 exhibit bleaching of the UV-VIS signals corresponding to Ag clusters and Ag particles that were generated during the photo reduction. This paper describes the process for generating these films and provides results from the initial investigation into the formation and decay process observed.