Non-linearity Identification of Composite Materials by Scalable Impact Modal Testing

Abstract

The aim of experimental modal analysis is to determine the structural dynamic characteristics of a given component or assembly. However, modal models are based on linear systems of equations and assume material orthotropy and linear stiffness components. Many industrial elements made of highly-complex, composite materials, do not accomplish these assumptions due to their non-linear material behavior. One practical measurement method is performing iterative modal analyses; this is, measurements at different force input levels. Several iterations lead to the knowledge of different points of the structural force/response spring curve and how this behavior affects the modal test.

In this paper, a novel Scalable Automatic Modal hammer (SAM) is presented. The SAM allows exciting the structure with precisely adjustable and reproducible force amplitudes. The test device is designed in a way that only the inertia mass of the hammer tip impacts the structure with a finely amplitude-adjustable Dirac impulse. The non-linear behavior of composite materials and jointed structures can be investigated with the SAM in terms of impact force-depending natural frequencies and damping ratios. This leads to an increase in the accuracy of the experimental data and therefore, a more straightforward modal model correlation in regards to the real structure.