Terahertz dynamic scanning reflectometry (TDSR) was used for measuring layered materials’ deformation kinetics
spectra. Multi-layered materials are used for protective devices such as helmet and body armor. An in-situ measurement
of deformation profile and other dynamic characteristics is important when such material is subjected to ballistic
impacts. Current instrumentation is limited in their abilities to provide sub-surface information in a non-destructive
fashion. A high sensitivity TDSR has been used to measure dynamic surface deformation characteristics in real-time
(in-situ) and also at post deformation (ex-situ). Real-time ballistic deformation kinetics was captured with a high speed
measurement system. The kinetics spectra was used to compute a number of crucial parameters such as deformation
length and its propagation profile, the relaxation position, and the macroscopic vibration profile. In addition, the loss of
mass due to impact was quantified for accurate determination of the trauma causing energy. For non-metallic substrates,
a transmitted beam was used to calibrate mass loss, a priori, of the laminate layers due to impact. Deformation kinetics
information may then be used to formulate trauma diagnosis conditions from blunt hit via the Sturdivan criterion [1].
The basic difference in the proposed approach is that here diagnostic criteria are inferred by measuring the helmet itself;
no need to draw blood or any biopsy from the patient.
Innovations in x-ray imaging are described to evaluate spatial and temporal dissipation and relaxation dynamics in materials. A system is constructed employing five sets of image planes orthogonal to the target, such that the centerline image-plane orthogonal axes are coplanar. Variable pulser firing sequences flash five x-ray tubes, capturing temporal sequences of interest, and controlled coincident firing sequences characterize ballistic impact events in three dimensions.
Ballistic characterization of improved materials for Soldier personal protective equipment is an ever-challenging
task, requiring precise measurement of materials during ballistic impact. Current dynamic deformation
technologies, such as high-speed digital image correlation, and laser velocimetry and vibrometry, are only able to
provide surface measurements. However, there is a need to measure the dynamic delamination and mass loss of
composite material, allowing calculation of available kinetic energy remaining in the material. A high sensitivity
terahertz dynamic scanning reflectometer may be used to measure dynamic surface deformation and delamination
characteristics in real-time. A number of crucial parameters can be extracted from the reflectance measurements
such as dynamic deformation, propagation velocity, and final relaxation position. As proof of principle, an acrylic
plate was struck with a blunt pendulum impactor and dynamic deformation was captured in real-time. Reflectance
kinetics was converted to deformation and the velocity was calculated from the kinetics spectrum. Kinetics of a
focused pendulum impactor on a steel plate was also acquired, characterizing plate relaxation from maximum
deformation to equilibrium with discernible vibrations before reaching stable equilibrium.
Laser illumination systems for high brightness imaging through the self-luminosity of explosive events, at Aberdeen
Proving Ground and elsewhere, required complex pulse timing, extensive cooling, large-scale laser systems (frequencydoubled
flash-pumped Nd:YAG, Cu-vapor, Q-switched ruby), making them difficult to implement for range test
illumination in high speed videography. A Vertical Cavity Surface-Emitting Laser (VCSEL) array was designed and
implemented with spectral filtering to effectively remove self-luminosity and the fireball from the image, providing
excellent background discrimination in a variety of range test scenarios. Further improvements to the system are
proposed for applications such as imaging through murky water or dust clouds with optimal penetration of obscurants.
Previous laser illumination systems at Aberdeen Proving Ground and elsewhere required complex pulse timing, extensive cooling, large-scale laser systems (frequency-doubled flash-pumped Nd:YAG, Cu-vapor, Q-switched ruby), making them difficult to implement for range test illumination in high speed videography. Requirements to illuminate through the self-luminosity of explosive events motivate the development of a high brightness imaging technique obviating the limitations of previous attempts. A lensed vertical cavity surface-emitting laser array is proposed and implemented with spectral filtering to effectively remove self-luminosity and the fireball from the image, providing excellent background discrimination in a variety of range test scenarios.
X-ray imaging requires unique optical detector system configuration for optimization of image quality, resolution, and
contrast ratio. A system is described whereby x-ray photons from multiple anode sources create a series of repetitive
images on fast-decay scintillator screens, from which an intensified image is transferred to a fast phosphor on a GEN II
image intensifier and collected as a cineradiographic video with high speed digital imagery. The work addresses
scintillator material formulation, flash x-ray implementation, image intensification, and high speed video processing and
display. Novel determination of optimal scintillator absorption, x-ray energy and dose relationships, contrast ratio
determination, and test results are presented.
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