An overview of experimental strain-based modal analysis methods

Abstract

The most established way of performing experimental modal analysis is to use acceleration or velocity based transducers that lead to the calculation of the displacement mode shapes. However, there are applications where the use of strain measurements makes for a more attractive and interesting option. Strain gauges have been commonly used for static load testing of mechanical products in the aeronautic, automotive and mechanical industry. Moreover, fatigue testing, durability analysis and lifetime prediction has also been a common application where strain gauges are used. This sort of testing is a common part of the product development process, and additional information on product durability and dynamic performance can be assessed by obtaining the modal parameters of the system, while still using the same instrumentation. Moreover, since strain measurements are more directly related to stress, fatigue and failure, strain-based measurement methods can be a good option for structural health monitoring methods and monitoring systems. Applications where sensor size and placement might be critical are also good candidates for strain-based methods. Helicopters, wind turbines and gas turbines are a good example where strain gauges are more suited for vibration measurements. Some application cases of dynamic strain measurements and dynamic strain modal analysis are shown in this work, with test subjects such as a composite helicopter blade.