6. Assessment of Metrics Between Acceleration Power Spectral Density Metrics and Failure Criteria

Unlike traditional vibration testing that involves driving a single axis, Multi-Input/Multi-Output (MIMO) testing has become increasingly popular due to its ability to more accurately replicate field responses and failure modes. Quantifying the mismatch between test response and field response is critical to understanding whether the field environment was adequately replicated by the vibration test. Ideally, a vibration test would replicate the field response in terms of deflection shape and magnitude and therefore also the stresses in the test article. However, a clear and concise process or metric to quantify the difference with respect to stress between the test and field environment does not exist.

This paper first considers how the Cross Power Spectral Density (CPSD) metrics are affected by part to part variability between the field and the test. Basic properties of an analytical beam model, such as damping and stiffness, are incrementally varied and the effect on the metrics is observed. A more complex model is used to study the correlation between the CPSD metrics and failure mechanisms such as stress and fatigue. A synthetic field environment is generated so that the field stresses and fatigues are known. Many imperfect MIMO tests are constructed as samples for comparison, and several CPSD metric methods are computed for each MIMO case. The calculated CPSD metrics are correlated to the stress and fatigue differences, and the metrics that best correlate to the failure criteria are identified.