A Primer on Multiple Degree of Freedom Vibration Test for Aerospace and Military Applications

Abstract

The aerospace and military communities have performed vibration tests for decades using a single axis or single degree of freedom (SDOF) approach. In recent years, military standards have recognized a multiple exciter or multiple degree of freedom (MDOF) approach for conducting vibration testing. This primer on MDOF vibration testing serves to introduce the topic to the IMAC community and fits with IMAC-XXXVI’s theme: Engineering Extremes.

This presentation will review how SDOF and MDOF vibration environmental definitions are obtained. The concept of cloud plots will be reviewed and approaches for determining acceptable test levels will be discussed. The common approach in the MIL-STD-810 community for accelerating testing using the Palmgren-Miner Hypothesis will be reviewed.

Next, the presentation will shift from the actual real-world vibration environment to the laboratory environment with special consideration reviewed such as: non-linearity effects, boundary conditions, controllability and observability.

Analogies between the power spectral density for an SDOF test and the spectral density matrix (SDM) for an MDOF test will be reviewed. The author’s previous work will be adapted for illustrating how the SDM can take on a truly random nature for MDOF environments.