I Downloaded from https://www.everyspec.com MIE-STD-81OD 19 JUIY 1983 J W . 3 . 3 ~ . The random and periodio levels are separated by means of the autooorrelation and acceleration spectral.density (ASD) functions, and tha required scenario of 3.1 ia “reducedto an equivalent scenario as indicated by the data. This operation consiate of combining road conditions which produce similar data and eliminating conditions which produoe levels that are 6dB below the maximum level. From a fatigue standpoint, these levels are considered insignificant. The equivalent scenario replaces the required scenario. A - 3 . 3 . 4 ~ . TO reduce the time required by the f3@ViikIt.
scenario without actually testing beyond tha field levels, the ASI)’sare collapsed (normalized) to the highest measured field level as indicated by the . individual random and periodic grm~ va speed”information. An axampla of thie operation is presented in table A-I. As table A-I illustrates, a service time of approximately 50 houra can be reduced to an equivalent duration of aPProximstelY 6 houre by using the test exaggeration curve and testing at mSxitIIUmmeasurad fiald level. -. If necessary, the equivalent test duration can be ‘reducedfurther by again using the test exaggeration curve, but this must be done with caution to avoid testing bayond peak, short duration levels. A-3.3.5 ~.
Conservatism (additional severity) is added to the random spectrum and periodic oomponent. The conservatism for tha periodic component is a factor of 1.2.“ For the random spectrum, a factor of 1.2 standard‘deviations ( G ) as a function of frequency is added at frequencies where the field levels are better defined (i.e..,lower u ). Conversely, more conservatism is added whare the variance of the field levels is greater (which indicates a poorer definition of field levels). The conservatism ia also used to account for items such ae: -0 a. Other terraina and vehicles for which no data was obtained. b. Effacta of vehicle wear, track tension, temperature, etc. c.
Available maximum field data that may not be true maximum. . d. Greater variance of field levele than laboratory levels. e. Test item differences within normal quality control requirements. “A - 3 . 3 . 6 ~ . To obtain realietic teat tolerances for’the random spactrum, the maximum and minimum envelopes of the collapsed ASDts or ~3dB (whichever is greater) is ueed. This results in a test tolerance which varies with frequency-but allows the response”to vary as it does during service . conditions. A-3.3.7 ~. Using the developed specification, a laboratory vibration test is performed. The physioal setup duplicate, as much as possible, the actual field configuration.
As much of the actual platform .. structure as practical is included in the test setup. The required overall g-rma is maintained.to preclude testing at extremes (over wide bandwidths) within the tolerance range. Control data eampling bandwidths and sample averages are consistent”with that used in the speci- fication development. ,. METHOD 514.3 APPENDIX A 19 July 1983 514 . ’ 3 - 78