Downloaded from https://www.everyspec.com MIL-STD-810D 19 July 1983 c. The test item shall consist of the unpackaged equipment in a nonoperational mode. It shall be subjected to a series of trapezoidal 30-g shock pulses having a time duration to be determined from table 516.3-I and the equation TD.2F The pulse will be in accordance with figure 516’”.3-5.A progra~able shock machine will more than likely be required to produce these test conditions because of the displacement limitations of shakers. . d. ~.
The trapezoidal w?tieshapewas chosen because the computation of velocit~ change it produces (for comparison with design drop height) is much easier to make and more reproducible than most shock spectrum synthesis routines.’ Also it provides an upper bound on primary and maximax shock response spectra for given peak acceleration input 1evels. I-3.5 III - CrXl . . accelera~ fraullj& a. Procedure III is used to determine an itemts fragility level so that packaging can be designed for it, or so the item can be redesigned to suit packaging requirements. b. ~. Procedure III ia to be used”when the critical acceleration for an item must be determined. ., c. lQaLJxmuiQw.
A deeign drop height will be selected based on ,measurementof the test item~s shipping environment, or from table 516.3-I when measured data are unavailable. (A design drop height is the height from which the test item might be dropped in its shipping configuration and be expected .to survive.) A maximum test item velocity change may be taken from table 516.3-I or determined by using the following relationship: where AV . maximum product velocity change cm/s (inla) (summation of impact velocity and rebound velocity) .h = design dro height cm (in) ,., 5 s = 980.6 Cm/s (386 in/s2) ,. ,, The:shock’&chine is set to a maximw” acceleration level (.Am)below.the anticipated failure level.
The approximate follows (see figure 516.3-5): pulse duration is determined ,aa V = Am.g (0.9 TD) V = 0.5 (g) Am (2TD-TF-TR) (TF and TR assumed to be 0.1 TD) (TF and TR are known) If an initial value for Am does not exist, 15 g!s may be used. If no damage occurs, then Am will be increased incrementally while the maximum test item velocity change is held constant until damage to the test item occurs. This will be .“@.abli?hedas the test item’s critical acceleration fragility level. d. E&i.mak. Test levels used in this procedure represent the correlation of the best information currently available from research and experience.
If more applicable test level data become available, they should be used (reference d),. MSTHOD 516.3 516.3-9 19 July 1983