Strain-based experimental modal analysis on planar structures: Concepts and practical aspects

Abstract

Strain modal analysis has been used for a long time as an alternative way of identifying the vibration modes of a structure, whenever the use of accelerometers is not suited (such as in aerospace applications) or when information about the dynamic strain levels in the structure is required (e.g. structural health monitoring or durability applications). However, some practical aspects of strain-based modal analysis are not always studied in such applications. For instance, how to visualize and interpret multi-directional modal strain is still an open topic. Similarly, the optimal way to correlate and distinguish these strain modes is also not usually discussed. This work will focus on clarifying some concepts related to multi-directional strain, and will show some examples on how modal strain in multiple directions can be better interpreted. For this purpose, the use of strain gauges (and strain rosettes) for modal analysis in two-dimensional structures will be introduced and some insights will be given on how to properly measure and interpret normal and shear strain modes and how to carry out modal correlation. Finally. these concepts will be applied to numerical and experimental examples.