Downloaded from https://www.everyspec.com MIL-STD-81OD 19 JUly 1983 Response characterizations should ultimately be performed at realistic ~ vibration levels since nonlinearities in equipment response render charac- terization at other levels inconclusive. I-4.2.5 lest axes. Unless otherwise stated in specific procedures, test items shall be excited along three orthogonal axes. Excitation shall either be directed along each axis, one axis at a time or applied along two or three of the axes simultaneously. -: !..,! ,’:,, ~ I-4.2.6 -t “contro 1 versus resoonse -. ned control. Input control is the traditional approach to vibration testing.
‘Ideally,this form of testirig’” should represent the input from a carrying platform into equipment on the’ ., platform. It should not be used when the equipment mass-loading could significantly alter the platform behavior or when the actual service excitation is applied to all parts of”the structure simultaneously (i.e., aerodynamic turbulence) rather than through a few distinct attachment points. ,, . Respoxrae-definedtesting uses an essentially undefined input and instead tries to achieve an equipment structural response representative of that anticipated or measured”in service.
This approach is especially appropriatee when service vibration measurements exist and close correlation between laboratory and service conditions is readily achieved. I-4.2.7 Is@ duratiQDso Test durations should be chosen along’with test levels to accomplish the”test purpose. Guidance is included in the “individual test technique discussions of I - 3 , i n 1 - 4 . 6 , 1 - 4 . 7 , 1 - 4 . 8 , . and i n ww f i d i x ~ . , . . aid are implemented as a continuous exposure. However, service exposure Usually vibration criteria are written in terms of total‘time at a given level’ usually made up of a series of discrete”or short-term events.
Thus, centinuo’us application of vibrstion could result in unrealistic structural, isolator, or other heat buildup effects. Vibration should be applied for short’periods re- presentative of service conditions. Vibration-on periods should be alternated with vibration-off periods of sufficient length to allow heat to dissipate: Examples of intermittent vibration events requiring such treatment are gunfire and aircraft maneuver buffet. .. .. I-4.3 FWLurance vsrs~l testti. Functional tests are intended demonstrate that the equipment will function satisfactorily in the service environment.
Thus, functional test levels normally are the maximum levels expected in normal use at which full function of the equipment is required. Where partial or degraded functioning is permitted or under particular environmental extremes, an additional functional test should be accomplished accordingly. In cases where the relationship between vibration stress’level and equipment1s degree of performance is uncertain, functional testing at lower levels should be considered. Endurance testing is conducted to demonstrate that the equipment has a .! structural and functional life which is compatible with the system/subsystem life requirements.
An endurance environment is one in which the equipment is not required to meet all performance specifications. No damage is allowed while it is operating and the system must exhibit unimpaired performance when the endurance environment is removed. MSTHOD 514.3 19 July 1983 514.3-60