Downloaded from https://www.everyspec.com AMCP 706.1W prior to environmental testing to simulate and money on an independent study. This the historical effects must be considered. is essentially the "build-and-test" approach, This conditioning is sometimes necessary to which has limited value for large and ex- assure that the response during the test is pensive Items, but, when used with dic.,'re- representative of that in operational use. tion, it can be useful for new designs or for Knowing the environmental history is not new applications of old designs.
important when the effects are reversible, but the reversibility of all important re- 6-3 SIMULATING ENVIRONMENTAL sponses can be determined only through CONDITIONS careful analysis. Ignoring the nonreversible effects that have occurred in previous tests The emphasis on environmental testing and operations can result in misleading on- has led to the development of some very vironmental test results. Of course, these vlaborate test facilities (Ref. I). Several good effects may be difficult to assess or simu- surveys of older environmental test capabi. ilate, but just knowing of their existence can •.lilteo are presented in Refs. 2 and 3.
The be very valuable for the test designer, most frequently used standard for military procurement is MIL-STD-810 (Ref. 4). Experience is frequently the most useful guide for selecting the environmental factors It is not always possible to generate com- and the severity levels and combinations of plex conditions, even with the most elabor- them to be used in a test. This prior know- ate facilities, Air turbulence, gases, or in- le~dge and experience can help reduce the sect conditions can be difficult to simulate. number of environmental tests needed to Many facilities are even limited in their ensure the successful operation of the item. capability to generate complex temperature profiles.
The difficulties associated with common environmental factors - such as tempeitturo, Because of these probt[jms, a great d,.*l of vibration, and thermal shock - nearly al- effort has been devoted to developing so- ways receive attention. Less familiar factors phisticated simulation facilities. But there can sometimes be equally or even more im- may be other ways to resolve the question. portant, e.g., hall and insects demand special First of all,,it is the effect of the environ- attention to determine what characteristics mental conditions that is of interest, not and severity levels are required. With hall, just the conditions themselves.
Therefore, for example, if mechanicel impact damage substitutes should be considered, For ex- is the major effect, the size, shape, velocity, ample, pebbles might be used as a substitute and number per unit area of the simulated for hailstones if mechanical damage from hailstones are the Important chutEracteritics. impact is of interest. Or, if vibration in- On the other hand, the vibration induced by duced by hailstones is of interest, then a the Incident hall may be the most signtif- vibration test already r cheduled may be cant factor, Insects can cause both mechan- adequate. ical and chemical daynage, and both charsac- teristics must be evaluated.
Some effects are invustiapted more easily froni a more fundamental Itvel. Also, the When there is little available knowledge environmental conditions sometimes may be about the operational environment or its separable into fundamental components. For effect on an item, it is often sWnipler and example, a temperature profile may be more economical to test and see what hap. simuilated by high and low temperature pens than to spend a great deal of time levels and thermal shock. In such cases, ef- i!. '• "i.i',•'