Publications
Mechanical environment test specifications derived from equivalent energy in fixed base modes
The main point of mechanical environment testing is to prove that designs can withstand the loads imparted on them while being exposed to in-service conditions. This is dependent not only on the test article construction, but also the loads imparted through its boundary conditions. Current practices for developing environment test specification are typically based on inadequate information reduced to single input point control with large uncertainty as compared to the field environment. Yet the test specifications are considered conservative, with the assumption that most of the adjustment for uncertainty is conservatism. For base mounted components, a modal model is presented that can be used to generate specifications with much lower uncertainty and with guaranteed quantifiable conservatism. In this method, the modal energies in the fixed base modes of the article due to the in-service loads are determined. Using the fixed base modes of the test article as a basis, the test specification is derived by determining what fixture motion is required to emulate the in-service environment. The specification method accounts for frequency shifts between the in-service and test configurations. Variability in nominal test articles can be included in the derivation of the test specifications. Real hardware under in-service environment loads and in a ground test fixture and loading configuration are considered.