Vibration-based Estimation of Tension and Boundary Stiffness in Bolts and Bolted Structures Using Added Mass Mary Brons, October 2023

Vibration-based Estimation of Tension and Boundary Stiffness in Bolts and Bolted Structures Using Added Mass

Mary Brøns

Denmark Technical University

October 17, 2023

Abstract:

Can we use measured vibration responses to estimate unknown parameters in bolts and bolted structures? That is the pivot of this seminar.

In the first part, we will discuss a method for estimating bolt tension from transverse vibrations, thus, how to evaluate the pretension just by giving a bolt a knock with a hammer. The principle is simple: by hitting the bolt twice. By the second time, a small known mass is added to the end of the bolt, e.g., an extra nut. By doing so, an independent measurement is obtained without introducing more unknown parameters. Combining the two measurements and using classical parameter estimation techniques can provide very accurate pretension estimates. A tool like this is especially of interest to the wind turbine industry. A single turbine tower is held together by tens of thousands of bolts, and it is a considerable issue how to control and ensure the correct bolt tension in a swift, cost-efficient, and accurate manner. Turbine bolts are also extremely large and non-slender, which introduces additional challenges we will address during the seminar.

In the second part, we build on the added mass principle and consider how to expand the concept of estimating joint parameters in a more general sense. When two parts are connected, the connection is rarely rigid. This connection can sometimes be represented by a set of flexible springs. As for the bolts, we will discuss the potential in estimating joint spring stiffness using added mass, but this time by considering a bolted structure as a set of substructures and introducing frequency-based substructuring.