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[en] Non-contacting acoustical methods can be used to extract various material properties of liquid or solid samples without disturbing the sample. These methods are useful even in the lab since they do not involve coupling anything to the sample, which might change its properties. A forteriori, when dealing with potentially dangerous materials, non-contacting methods may be the only safe solutions to mechanical characterization. Here, we show examples of using laser ultrasound to remotely insonify and monitor the elastic properties of several granular explosive simulants. The relatively short near-infrared laser pulse length (a few hundred nanoseconds) provides a broad-band thermoelastic source of ultrasound; we intentionally stay in the thermoelastic regime to avoid damaging the material. Then, we use a scanning laser Doppler vibrometer to measure the ultrasonic response of the sample. LDV technology is well established and very sensitive at ultrasonic frequencies; atomic level motions can be measured with modest averaging. The resulting impulse response of the explosive simulant can be analyzed to determine decay rates and wave speeds, with stiffer samples showing faster wave speeds and lower decay rates. On the other hand, at the low-frequency end of the acoustic spectrum, we use an electronically phased array to couple into a freely suspended sample's normal modes. This allows us to gently heat up the sample (3 °C in just under 5 min, as shown with a thermal IR camera). In addition to the practical interest in making the sample more chemically visible through heat, these two measurements (low-frequency resonant excitation vs high-frequency wave propagation) bracket the frequency range of acoustic non-destructive evaluation methods available.
[en] Highlights: • Developed model-based efficiency performance metrics for industrial pneumatic systems. • Quantified system efficiency increases due to the Pneumatic Strain Energy Accumulator. • Experimentally validated model efficiency increases ranging from 32% to over 78% - Abstract: A number of national organizations have recently expressed interest in research to develop materials and devices that achieve greater energy storage capacity, power density and increased energy efficiency on the heels of a report finding that the pneumatic sector of the fluid power industry averages only 15% efficiency. One way of improving efficiency is the use of compressed air storage and recycling devices. The pneumatic Strain Energy Accumulator is a recently developed device that recycles exhaust gas from one pneumatic component, stores it in a highly efficient process, and reuses the stored exhaust gas at a constant pressure to power another pneumatic component. This work analyzes system efficiency increases directly attributable to the implementation of a pneumatic strain energy accumulator by applying an analytical methodology for system level efficiency improvement calculations, experimental validation, and compressed air savings projections. Experimentally determined efficiency increases ranged between 32% and 78%, demonstrating that the pneumatic strain energy accumulator can be a viable part of the solution to the fluid power efficiency challenge.