Application of Operational Modal Analysis for In Situ Deflection Shape Analysis During Shaker Tests

Shaker testing is an important step in evaluating the structural performance and fatigue of components and assemblies in many important areas like aerospace, automotive, and electronic products. In many of these tests, head expanders or slip tables are used for mounting the test specimen on the shaker. As these components may have significant impact on the overall dynamics of the system, a basic understanding of their structural properties is essential. Otherwise, depending on the positioning of the control transducers and the mounting points significant under or over testing may occur. Thus, it is important to understand the structural dynamics of the test assembly, shaker, and head expander to achieve testing in accordance with specifications. Especially, mounting the test specimen and the control accelerometers on nodes or antinodes of the head expander has significant impact on the test results and the vibration control algorithm. In this chapter a shaker with a head expander model is analyzed using three different approaches. Initially, the head expander’s mode shapes are examined via classical modal impact hammer testing. Additionally, Operational Deflection Shape (ODS) analysis and its applicability in evaluating the dynamic behavior of the vibrating system are investigated before the concept of Operational Modal Analysis (OMA) as an alternative method is introduced. To provide a comprehensive analysis, the results obtained from the traditional ODS analysis, impact analysis, and OMA are compared. By examining the strengths and limitations of each approach, insights into their suitability for different testing scenarios are provided. By considering the implications of these modes on structural integrity and test performance, the quality of shaker vibration test setups can be improved. Lastly, the feasibility of conducting in situ OMA analysis during complex shaker tests is discussed.