Tech Briefs

Measuring Propellant Stress Relaxation Modulus Using Dynamic Mechanical Analyzer

New testing technique requires less material, gives more accurate results.

Structural analysis of solid rocket motors is challenging for several reasons, but the most important of these is the complex behavior of the propellant. The mechanical response of a solid propellant is time and temperature dependent. The complexity of the mathematical analysis of the propellant depends on the loading conditions, but for some loading situations, the linear viscoelasticity assumption is reasonable. In particular, linear viscoelasticity is perhaps the most appropriate material behavior description for use in the simulations of stresses related to storage conditions. Typically, simulations use a viscoelastic model in the form of a Prony series and a Williams–Landel–Ferry (WLF) equation. The parameters in these models are derived from stress relaxation experiments, making the stress relaxation experiment a key viscoelastic test, analogous to the tensile test for linear elastic materials.

Posted in: Briefs, Aerospace, Defense
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Combustion Characteristics of Hydrocarbon Droplets Induced by Photoignition of Aluminum Nanoparticles

Test methodology allows analysis of combustion dynamics for subscale rocket injectors under super critical conditions.

In the study of combustion characteristics of liquid rocket fuels, it is customary to either study the combustion of liquid fuel droplets or the combustion of fuel sprays. However, the two are closely related to each other, because in a typical rocket combustion chamber, the burning of droplets, droplet clusters, and fuel sprays occur simultaneously.

Posted in: Briefs, Aerospace, Defense
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Vapor Pressure Data and Analysis for Selected Organophosphorous Compounds: DIBMP, DCMP, IMMP, IMPA, EMPA, and MPFA

Determining the thermophysical properties of chemical warfare agent simulants can help evaluate the performance of defensive equipment.

Knowledge of the physical properties of materials is critical for understanding their behavior in the environment as well as in the laboratory. Vapor pressure is an important physical property for a wide variety of chemical defense-related applications, including estimation of persistence, prediction of downwind time-concentration profiles after dissemination, generation of controlled challenge concentrations for detector testing, evaluation of toxicological properties, and assessment of the efficiency of air filtration systems.

Posted in: Briefs, Aerospace, Defense
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Coupling of Coastal Wave Transformation and Computational Fluid Dynamics Models for Seakeeping Analysis

New analytical tools improve understanding of vessel operating environments in the littorals.

This research focused on depth-integrated modeling of coastal wave and surf-zone processes in support of computational fluid dynamics (CFD) simulation of ship motions. There were two components of the project. The first was the development of a numerical dispersion relation for a family of Boussinesq-type equations commonly used in modeling of coastal wave transformation. The relation depicts numerical dissipation and dispersion in wave propagation and provides guidelines for model setup in terms of temporal and spatial discretization. The second component was an extension of existing depth-integrated wave models to describe overtopping of coastal reefs and structures along with a series of CFD and laboratory experiments for model validation. The basic approach utilizing the HLLS Riemann solver performs reasonably well and produces stable and efficient numerical results for practical application.

Posted in: Briefs, Aerospace, Defense
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Assessment of Non-Traditional Isotopic Ratios by Mass Spectrometry for Analysis of Nuclear Activities

Technique can be used to distinguish between commercial nuclear reactor fuel cycles, fuel cycles for weapons grade plutonium, and products from nuclear weapons explosions.

The objective of this work is to identify isotopic ratios suitable for analysis via mass spectrometry that distinguish between commercial nuclear reactor fuel cycles, fuel cycles for weapons grade plutonium, and products from nuclear weapons explosions. Methods will also be determined to distinguish the above from medical and industrial radionuclide sources.

Posted in: Briefs, Aerospace, Defense
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Imaging Detonations of Explosives

Using high-speed camera pyrometers to measure and map fireball/shock expansion velocities.

An effort has been made within the US Army Research Laboratory (ARL) to extract quantitative information on explosive performance from high-speed imaging of explosions. Explosive fireball surface temperatures are measured using imaging pyrometry (2-color 2-camera imaging pyrometer; full-color single-camera imaging pyrometer). Framing cameras are synchronized with pulsed laser illumination to measure fireball/shock expansion velocities, enabling calculation of peak air-shock pressures. Multicamera filtering at different wavelengths enables visualization of light emission by some reactant species participating in energy release during an explosion. Measurement of incident and reflected shock velocities is used to calculate shock energy on a target.

Posted in: Briefs, TSP, TSP, Aerospace, Imaging, Imaging, Imaging and visualization, Imaging, Imaging and visualization, Thermodynamics, Thermodynamics, Defense industry, Missiles
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Laser Integration on Silicon Photonic Circuits Through Transfer Printing

New fabrication approach allows the massively parallel transfer of III-V coupons to a silicon photonic target wafer.

The purpose of this project was to develop a transfer printing process for the massively parallel integration of III-V lasers on silicon photonic integrated circuits. Silicon has long offered promise as the ultimate platform for realizing compact photonic integrated circuits (PICs). That promise stems in part from the material's properties: the high refractive-index contrast of silicon allows strong confinement of the optical field, increasing light-matter interaction in a compact space—a particularly important attribute for realizing efficient modulators and high-speed detectors.

Posted in: Briefs, TSP, TSP, Aerospace, Photonics, Integrated circuits, Lasers, Integrated circuits, Lasers, Fabrication, Materials properties, Semiconductors
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