Vibrationtest force limits derived from frequencyshift method
Abstract
An improved vibration testing technique has been recently developed and applied to eliminate overtesting caused by the infinite mechanical impedance of the shaker in conventional vibration tests. With the new technique, the acceleration input is notched at the resonance frequencies of the test item in order to limit the shaker force to that predicted for flight. Since few flight vibratory force data are available, the force limits must be calculated from measurements or analyses of the flight mounting structure and testitem mechanical impedances. An improved method of calculating these force limits is derived from evaluating the testitem apparent mass at the coupledsystem resonance frequencies. Application of the method to a simple and to a complex coupled oscillator system yields nondimensional results which may be used to calculate limits for future forcelimited vibration tests. For example, using the simple system results with Q = 50 and equal impedances of the flight mounting structure and test item, the input acceleration amplitude will be notched by a factor of 31.25 relative to a conventional test.
 Publication:

Journal of Spacecraft and Rockets
 Pub Date:
 March 1995
 DOI:
 10.2514/3.26611
 Bibcode:
 1995JSpRo..32..312S
 Keywords:

 Acceleration (Physics);
 Acoustic Impedance;
 Frequency Shift;
 Mechanical Impedance;
 Vibration Mode;
 Vibration Tests;
 Mechanical Oscillators;
 Resonance;
 Resonant Frequencies;
 Physics (General)