Downloaded from https://www.everyspec.com MIL-STD-810D 19 July 1983 This teehnique differs from the traditional sinusoidal resonance dwell test. A resqnance dwell emphasizes those frequencies at which the test item resonates. A source dwell emphasize9 those frequencies which predominate in the platform environment. Obviously the source dwell spectrum provides a more realistic test. Source dwell testing should be performed using one of the following techniques: ., (1) Broadband random excitation with vibration peaks centered at the fundamental and harmonic frequencies of the platform.
(2) Narrowband random superimposed over a low-level background broadband random signal with the narrowband.portion oentered at the fundamental and harmonic frequencies. (NOTE: The narrowband signals may also be cycled through a frequency band representative of the platform conditions). (3) Sinusoidal inputs.at the fundamental frequencies and harmonic frequencies either singularly or simultaneously. A low-level random background may also be added to the sinusoids. (NOTE: The sinusoidal inputs may be cycled through a frequency band representative of the platform conditions). . I-4.2.3 woidal vi~.
Tbe service vibration environment in some propeller airoraft and helicopters contains excitation which is’basically , sinusoidal in nature. The excitation derives from engine rotational speeds, propeller and turbine blade passage frequencies, rotor blade passage and velocity, and their harmonics. Environments such as this may be best simulated by a sinusoidal test. Caution must be exercised to assure that the frequency range of the sinusoidal exposure is representative of the platform environment. Most vibration problems are associated with a resonant response of the equipment item or comporientto the platform source excitation.
Thus, the traditional sweep sinusoidal vibration test technique is not used in this method for representation of the actual service condition. Swept sinusoidal testing is a useful engineering development technique. 1-4:2.4 J@wonse Qharacteriza lm. t. Response characterization“isa technique for measuring the structural response of equipment or test fixtures to applied vibration. Response characterizations may either use broadband or swept-sine excitation. They are performed for reasons which include, but are not limited to: (1) Identifying the frequencies at which an item resonates, especially when those frequencies might be present in the service vibration environment. .
(2) Evaluating fixture/test item interaction to ensure reasonable duplication of known or expected service-induced responses. (3) Determining appropriate locations for’test control instrumentation. METHOD 514.3 . 19 July 1983 514.3-59