Validating the design and reliability of equipment prior to fielding is a critical step in the materiel development and manufacturing process. Success requires that the new equipment undergo and survive testing. Stress screen vibration testing determines the equipment's design capability. Traditionally, stress screen vibration tests have been conducted by sequentially applying uniaxial excitation to test articles along three orthogonal axes. Simultaneous multiaxial excitation is an advanced method of vibration testing with the goal of more closely approximating real-world operating conditions. Multiaxial testing achieves the synergistic effect of exciting all modes simultaneously and induces a more realistic vibrational stress loading condition. This research begins an effort to explore the difference in predicting fatigue failure between sequentially applied uniaxial and simultaneous triaxial tests. The research plan starts with simple cantilever beam structures. Once initial results are complete, more complex and typical components in actual vehicles will be tested. This paper provides results that reveal inadequacies in traditional uniaxial test methods. It is shown that the order in which orthogonal uniaxial excitation is applied has a significant effect on fatigue failure.

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