Foam - Speed of Sound

Speed of Sound

The acoustical property of the speed of sound through a foam is of interest when analyzing failures of hydraulic components. The analysis involves calculating total hydraulic cycles to fatigue failure. The speed of sound in a foam is determined by the mechanical properties of the gas creating the foam: oxygen, nitrogen, or combinations.

An assumption that the speed of sound based on the fluid properties of the liquid will lead to errors in calculating fatigue cycles to failure of mechanical hydraulic components. Using acoustical transducers and related instrumentation that set low limits (0 - 50,000 Hz with roll-off) will result in errors. The low roll-off during measurement of actual frequency of acoustic cycles results in miscalculation due to actual hydraulic cycles in the possible ranges of 1-1000 MHz or higher. Instrumentation systems are most revealing when cycle bandwidths exceed the actual measured cycles by a factor of 10 to 100. Associated instrumentation costs also increase by factors of 10 to 100.

Most moving hydro-mechanical components cycle at 0-50 Hz, but entrained gas bubbles resulting in a foamy condition of the associated hydraulic fluid results in actual hydraulic cycles that can exceed 1000 MHz even if the moving mechanical components do not cycle at the higher cycle frequency.