The use of strain and mixed strain/acceleration measurements for modal analysis

This paper shows some recent advances on the use of strain-based measurements and mixed strain/acceleration measurements for experimental modal analysis are shown in this work. The most common and established way of performing experimental modal analysis is to use accelerometers that lead to the identification of the displacement mode shapes. Since strain measurements are directly related to stress, fatigue and failure, strain-based measurement methods can be a good option for structural health monitoring systems or durability related measurements. Moreover, applications where sensor size and placement might be critical are good candidates for strain-based methods. Helicopters, wind and gas turbines are good examples where strain gauges are more suited for vibration measurements, since the sensors dont take up as much space when attached to the blade surfaces. The concepts of strain modal analysis, strain frequency response functions (SFRF), strain fields, as well as the identification of strain mode shapes are introduced in this paper. Similarly, the basic theory for strain-based modal analysis is presented, including the fundamental equations for dynamic strain. The similarities and differences between acceleration-based modal analysis and strain-based modal analysis are pointed out and a comparison is made.status: publishe