Determining material damping type by comparing modal frequency estimators

Abstract

Abstract:The accuracy of modal frequency and damping estimators for non-lightly damped single degree of freedom systems depend on the response parameter used as well as the damping mechanism. Therefore, in order to make accurate modal parameter measurements, the damping mechanism at play must be known to be either viscous or hysteretic a priori. Here, comparisons between the evaluated frequency values are used to glean this information. The damping mechanism of an experimental system (consisting of resilient layer and mass plate) is then determined using two simple modal parameter estimators and applying statistical methods.

Improving the accuracy of the n-dB method for determining damping of non-lightly damped systems

“…This result has been reported using a numerical model in [3]. As with a viscous-damped system, there is a maximum value of damping that can be measured depending on the value of r. Comparing jG h x ð0Þj and jG h x ðxÞj, both from (5), leads to the inequality…”

“…However, if the quadrature parts are available then the real part of the response could simply be used. This determines exact damping for both viscous and hysteretic damping [3]. This, therefore, reduces the motivation to use the imaginary part as a basis for accurately determining damping for non-lightly damped systems.…”

“…A dual damping SDOF model has previously been described by the authors [3]. The equation of motion in displacement, x, with applied harmonic force, F o , is…”

“…The authors have previously shown that using the real spectral part the system natural frequency can be determined using any response parameter, and that the damping can be determined accurately for non-lightly damped systems with either viscous or hysteretic damping [3]. Such measurements are sensitive to phase offset errors, although techniques exist to correct for them [4].…”

Accuracy and robustness of four basic single degree of freedom methods for determining the modal parameters of non-lightly damped systems

“…However, in many cases the damping mechanism is not known or readily identifiable. The present authors have previously used comparisons between exact and non-exact strategies to indicate the damping mechanism at play [1]. Here, this technique is extended to all response parameters, and three additional methods are considered.…”