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This investigation focused on identifying the impact of various steel fiber types on the mechanical response of an ultra-high performance concrete (UHPC) known as Cor-Tuf (CT). CT specimens were fabricated with four steel fiber types: hooked-end 3D 55/30 BG fibers, undulated NYCON type V fibers, straight brass coated OL 10mm fibers, and straight brass coated OL 6mm fibers. Fiber shape and size had a limited impact on quasi-static properties in compression but had a significant impact on quasi-static tensile properties and dynamic penetration resistance. The use of smaller fibers resulted in up to a 100 percent increase in component/test article tensile strength compared with their larger fiber size counterparts. However, the benefits offered by the smaller fibers primarily occurred prior to reaching the ultimate load carrying capacity. Once the ultimate strength was reached, larger fibers were more effective at bridging larger cracks. Smaller fibers provided improved penetration resistance, with reduced residual projectile velocities and loss of material from cratering and/or spallation. The overall goal of the study was to identify the relationships between fiber characteristics and the multi-strain rate response of UHPCs in order to better optimize fiber reinforcement for various loading conditions.

A mass spectrometric analysis of the anionic and cationic species generated by laser ablation of graphite fluoride (GF) and graphite targets performed under identical sets of conditions is presented. Under conditions that produce typical C n – cluster mass distributions from ablation of graphite, the mass spectra of anionic species generated by ablation of GF are congested with overlapping stoichiometric patterns such as C n F2n and C n F(2n–2). Some of the molecular formulas for these clusters, such as C6F6, C6F12, and C7F8, are evocative of stable neutral fluorocarbons. Additionally, the GF-ablation generated mass peaks broaden at higher masses more than the graphite-based counterparts, which may indicate cluster fragmentation. Furthermore, a pattern of fragmentation via loss of CF2 is observed and is reminiscent of previous studies which determined CF2 loss during thermal decomposition. No species were seen in the mass spectra of the cationic species generated from laser ablation of GF, while, under the same conditions, typical C n + cluster distributions were observed.

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Anion photoelectron (PE) spectroscopy was used to characterize several perfluorocarbon (PFC) species generated from pulsed-laser ablation of graphite fluoride (GF) and compare them to PFCs introduced into the gas phase and negatively charged by using a gentle photoemission source. The PE spectra of C6F6 –, C7F8 –, and C5F8 – produced by ablation of GF are nearly identical with the PE spectra of the anions of hexafluoro­benzene, perfluoro­toluene, and perfluoro­cyclopentene, respectively, generated by electron attachment to the neutral perfluorocarbon molecules. This result suggests that laser ablation of GF, which is a hyperthermal decomposition event, produces species larger than CF2 and with stable molecular structures. In addition, anion PE spectra were obtained for several larger PFC molecular anions, some of which have been the subject of past computational studies. The electron affinities of these species cannot be determined unambiguously from the broad PE spectra, though a systematic approach to identifying the onset of detachment signal was used to approximate the electron affinities. The vertical detachment energy of perfluoro­ethylcyclohexene was determined to be 2.98 ± 0.05 eV. The vertical detachment energies of additional perfluorocarbon radical anions, including perfluoroheptene, perfluoro­methylcyclohexane, perfluoro-1,3-dimethyl­cyclohexane, and perfluorodecalin, all exceed 3.495 eV. We also demonstrated that photoemission from gadolinia (Gd2O3) using a pulsed laser is an efficient and effective method of generating radical anions of larger volatile molecules in the gas phase.