Downloaded from https://www.everyspec.com MIL-STD-810D 19 July 1983 Functional:test levels are normally the maximum service levels. When there is signi~lcant non-linearity, testing at lower levels should be considered. When separate functional and endurance tests are required, the functional test duration should be split, with one half accomplished before the endurance test and one half after the endurance test (in each axis). The duration of each half should be sufficient to fully verify equipment functional or one half hour (1,hour.,per axis), whiChever iS greater.
This arrangement.has proven to..be a gooU way of adequately verifyingthat equipment survives,endurance testing in all respects. In-the Dast, ‘endurancetest duration was normally.set at one hour Der axis. Test le~els”were establishedby raising functional levels to accoount for equivalent fatigue damage. Another.approach is to establish levels and dura- tions to test to maximum service levels for a duration sufficient to reach the material endurance limit (approximate y 106 cycles at each resonant frequency). These techniques,are.basically valid; however, both have shortcomings. The -. first technique,results in test levels higher than field levels -- in SOtIIe . caseg, much higher,.
The fatigue relationships (I-4.9) used to generate these criteria are simplified.representationsat best and when structural nonlinearity at high vibration.levels becomes a factor, the validity of the relationships is questionable. The second,techniquedepends on the definition of endurance limits. This is a further simplification of the already simplied fatigue relationship. Further,.it is shown that some materials do not exhibit endurance limits. ,. o .Basedon,the above, the following approach is reco~ended.
Uae the simplified fatigue relationship to determine the time at aximum service levels (functional levels) which is equivalent to a vibration lifetime (levels are different for different mission profiles). Appendix A contains an example of this process. Use the equivalent time as the functional test duration, thereby combining functional and’endurance tests. There may be caaes when this test duration is too long to be compatible with program restraints. In this case uae as long a test duration as is practical and use the fatigue relationship to define the test leve,l. However, in no case should endurance test levels. and durations be less than those specified in I-3.2.12. ,.. .
I-4.9 htircue rela ti~e, The following relationship may be used to determine the required test times at functional levels to satisfy endurance requirements or when necessary to develop the ratio between functional and endurance leveIs: . Vibration . where w = levelS (acceleration spectral density) T= Time (hours) M= Material constant (slope of log/log.random s/N curve.) 0 19 JUly 1983 514.3-63 MSTHOD 514.3