LYCOS RETRIEVER 
Random Vibration Testing
built 674 days ago
Random vibration theory, including power spectral density theory, is discussed and video demonstrations show the effects of sinusoidal and random vibration. Various types of vibration exciters or shakers are discussed and the concept of test fixture design for vibration testing is covered.
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Random vibration is exactly what the name describes: vibrations that occur randomly. Driving down the road makes your car vibrate. You never know when you will hit a bump in the road because they occur randomly. This is different from the vibration caused by your engine or tires rotating in regular cycles.
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Subsystem vibroacoustic testing - Subsystems must be exposed to random vibration testing unless analyses show that the test exposures are not needed. Specific test levels are determined on a case-by-case basis. The test levels must be equal to the qualification level (highest predicted flight level +3 dB) predicted at the location where the input is controlled. Subsystem acoustic tests must ... be performed if the subsystem is judged to be sensitive to this environment.
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The third vibration test , SAE J1455 Section 4.9.4.3, is to operate the vehicle over a non-paved road with rocks, ruts, pot holes, etc. (complex surfaces) for at least 100 miles in less than 8 hours. The unit shall be on, running, and shall not fail during the test.
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The imager was tested in the vibration test facility at Oerlikon Contraves Space in Zurich, Switzerland. For testing, the imager was mounted to a substantial test fixture, which was mounted to the vibration slip table. Three force gauges were mounted between the imager hard point mounts and an interface ring to the vibration test fixture. Three triaxial piezoelectric force transducers (Kistler model 9167A1.5) were used. The force transducers were preloaded to 80,000 N so that they would operate in compression and effectively transmit the shear forces without exceeding the manufacturer's specifications. Figure 2 is a sketch of the vibration test fixture and shows the location of the imager mounting points for testing in the X- and Z-axes.
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Whatever the size of shaker, for random vibration, its capacity directly relates to the psd plot. The shaker force rating must exceed the product of the grms requirement and the total mass being shaken including the shaker armature and any fixture that may be used. For example, if an experiment to fly on NASA’s F-15B weighs 300 lb and a fixture and shaker armature add 200 lb more, a shaker with at least a 4,000-lb rms force rating is required to test to the 8 grms of profile A.
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Random Vibration Testing