This Method addresses very general testing configurations for applying excitation in multiple axes to materiel. Generally, field deployed materiel has boundary (or impedance) conditions that are very difficult and often cost prohibitive to replicate in laboratory testing. The overall goal of a MET is to achieve a distribution of materiel excitation energy that approaches that appearing during in-service deployment, while minimizing the difference between in-service and laboratory boundary conditions. Fixturing design limitations and/or other physical constraints may limit application of in-service environment in the laboratory. Also, in-service measurements may not be adequate to specify the laboratory test configuration. As always, engineering analysis and judgment will be required to ensure the test fidelity is sufficient to meet the test objectives.
The following limitations also apply to this Method:
- a. It does not address aspects of vendor-supplied software control strategy for a MET.
- b. It does not address advantages or disadvantages of Procedure I and Procedure II MET as defined in paragraph 2.2. The state of the art in a MET is not such that a comprehensive comparison can be made at this time.
- c. It does not address optimization techniques of the laboratory test configuration relative to distribution of the excitation energy within the test item.
- d. It does not address technical issues related to axes of excitation and materiel mass and product moments of inertia. Nor does it address the need for specialized software for optimizing the axes of excitation with respect to mass and products of inertia.
- e. It generally does not provide specific test tolerance information that is highly dependent on the (1) test objective, (2) test laboratory measurement configuration, and (3) vendor software control strategy.
- f. It does not discuss, in detail, the potential for efficiencies and efficacies of a MET over SET, leaving this as a part of specification of MET peculiar to the in-service measured environment.
- g. It does not discuss optimum in-service measurement configuration factors consistent with a MET.
- h. It assumes that excitation is provided mechanically through electro-dynamic or servo-hydraulic exciters, and does not consider combined acoustic (refer to Method 523.4) or pneumatic induced modes of excitation.