Use this Method to demonstrate that the materiel of interest can structurally and functionally withstand a specified dynamic environment that is defined in more than a single-degree-of-freedom (SDOF) motion; i.e., in multiple-degree-
of-freedom (MDOF) motion. Establishing confidence intervals may also be of interest if multiple like items are under test. Specification of the environment may be through a detailed summary of measured field data related to the test materiel that entails more than one degree-of-freedom, or analytical generation of an environment that has been properly characterized in MDOF. In general, specification of the environment will include several degrees of freedom in a materiel measurement point configuration, and testing of the materiel in the laboratory in a SDOF mode is considered inadequate to properly distribute vibration energy in the materiel in order to satisfy the specification. As a result of the increased complexity of application of MET over multiple application of SDOF single-exciter testing (SET), an analyst, after careful review of the available data and specification, will need to provide rationale for selection of this Method. Methods 514.8, 516.8, 519.8, and 525.2 provide guidance in developing the rationale and requirement for MET.
Reasons for selection of MET over SET may include the following.
- a. MET provides a distribution of vibration or shock energy to the materiel in more than one axis in a controlled manner without relying on the dynamics of the materiel for such distribution.
- b. MET may be selected when the physical configuration of the materiel is such that its slenderness ratio is high, and SET must rely on the dynamics of the materiel to distribute energy.
- c. For large and heavy test materiel, more than one exciter may be necessary to provide sufficient energy to the test item.
- d. MET allows more degrees-of-freedom in accounting for both the impedance matches and the in service boundary conditions of the materiel.