Downloaded from https://www.everyspec.com MIL-STD-81OD 19 July 1983 0 f. Develop an equivalent scenario and,an equivalent duration,by deleting negligible stress levels, oombining similar data and using maximum measured field levels. g. Apply conservation (additional severity) to cover’unknown conditions. A factor of 1.2 mav be used as a base. However. the conservative,factor is determined by: - (1) The tester’s confidence in definitions of servioe conditions. ,- (2). The aocuricy required (the versus the consequences of failing a good consequences of passing a bad item , item).. . . h. Conduct the laboratory test. .,, . . i.
,Evaluste.the resulte with consideration to overall specification development. ,, ,. A - 3 . TYPICAL VIBRATION TEST SPECIFICATION DEVELOPMENT - This section describes.the development of a laboratory sp.5cificationfor a tracked vehicle. This.example is to be used as a guide.and may be modified as appropriate for other types of platforms and forcing functions. ,.- A-3.1 ~sd SCQll@J2. The materiel user’s requirements.and service soenarios are identified. The required scenario defines the,’road,speed, and mileage distributions as well as the frequency of miseione and the test item configuration. The test specification ie based on these required scenarios. A - 3 . 2 ~ .
The dynamio stresses occurring duringn service conditions are measured during instrumented road tests. Road test data require- ments are specified to obtain representative data for service conditions whioh are to be accounted for, Requirements inolude instrumentation, locatione, frequenty response, roads, speeds, and provisions for validation of field data. A-3.3 A-3.3.1 reduc~ .- The overall data reduction and specification document ii summarized in flow chart format in figure Al. In the following discussion, it is assumed that the reader is familiar with basic vibration data reduction techniques and laboratory test conduct. Detailed data reduction procedures may be found in referenoe A1.
,. The final vibration oriteria will be’in the form of a shaped random speotrum with a periodio component mixed in to account for the traoklaying response. . Certain key features of the,specification development are discuaaed below. . A - 3 . 3 . 2 ~ . This provides a model for the failure mechanism.,,It is asaumed that the failure meohanism is fatigue. (Other possible failure modes: fracture, wear, loosening, operational, and heat-related failuree.) As.detailed in reference A2, fatigue damage can be accelerated ,byincreasing the stress levels along a test exaggeration curve. The specification development will use the composite teet exaggeration curve developed in reference A2.
The curve is presented in figure A2. METHOD.514.3 514,.3-7’7 APPENDIX A 19 July 1983