Entwicklung und Validierung einer Prüfmethodik zur Charakterisierung des dynamischen Verhaltens von geschraubten Fügestellen

Research output: ThesisMaster's Thesis

Organisational units

Abstract

Damping is a significant parameter in dynamic systems. Energy dissipation limits the vibration amplitudes, stresses, deformations or acoustic emissions towards a tolerable level. Therefore, a sophisticated construction requires the consideration of damping. Due to the current lack of understanding and difficulties with the correct implementation of damping in the simulation, experimental methods are mainly used to investigate the mechanisms of damping and to derive damping characteristics as input for the numerical simulation. Damping in mechanical joints, particularly in bolted joints, causes most of the energy dissipation in systems, hence it is attributed a special importance in part design. In this master thesis an innovative testing methodology is presented which enables the characterization of the dynamic behaviour of bolted joints. A structure-dynamically optimised design of the test bench is constructed by modal analysis, whereby a wide variation of the load condition in the joint can be studied. Experiments with an electrodynamic shaker are carried out to validate the vibration behaviour of the test bench, to identify suitable test parameters for recording a non-linear system behaviour, and to investigate the effects of a bolted joint on the dynamics of a system. The basic idea of the testing methodology is to compare the frequency response of a split, bolted specimen with a monolithic specimen of identical geometry and mass as reference. In this work, two representative specimen designs A and B were examined. The maximum vibration amplitudes of the bolted specimen A decreased by more than half compared to the monolithic specimen A, and the damping ratio increased by approximately 17 %. Furthermore, a strongly non-linear response was observed, which can be explained by micro and macro slip in the joint and the clamping of the specimen. The experiments with the specimen design B showed that the decrease of the maximum gain was only 10 % off and the non-linear behaviour was less pronounced. A reduction of the tightening torque of the bolts from 10 Nm to 2 Nm resulted in a maximum vibration amplitude near the resonance point declining by approximately two thirds and a rising damping ratio (+51 %). The lower surface pressure leads to increased freedom in the relative movement of the joining parts (micro and macro slip) and thus to an enhanced energy dissipation and more damped transfer behaviour.

Details

Translated title of the contributionDevelopment and validation of a testing methodology to characterize the dynamic behaviour of bolted joints
Original languageGerman
QualificationDipl.-Ing.
Awarding Institution
Supervisors/Advisors
Award date28 Jun 2019
Publication statusPublished - 2019