Damage detections in nonlinear vibrating thermally loaded plates

In this work, geometrically nonlinear vibrations of fully clamped rectangular plates subjected to thermal changesare used to study the sensitivity of some vibration response parameters to the presence of damage and elevated temperature. The geometrically nonlinear version of the Mindlin plate theory is used to model the plate behaviour.Damage is represented as a stiffness reduction in a small area of the plate. The plates are subjected to harmonicloading leading to large amplitude vibrations and temperature changes. The plate vibration response is obtained by a pseudo-load mode superposition method. The main results are focussed on establishing the influence of damage on the vibration response of the heated and the unheated plates and the change in the time-history diagrams and the Poincaré maps caused by damage and elevated temperature. The damage criterion formulated earlier for nonheated plates, based on analyzing the points in the Poincaré sections of the damaged and healthy plate, is modified and tested for the case of plates additionally subjected to elevated temperatures. The importance of taking into account the actual temperature in the process of damage detection is shown

Modelling of sprayer boom dynamics by means of maximum likelihood identification techniques, Part 1: A comparison of input-output and output-only modal testing

It is a well-known fact that the linear dynamic behaviour of mechanical structures can be studied by modelling the relation between force(s) [input(s)], acting on the structure, and their resulting structural vibration response(s) [output(s)]. For industrial structures, in their real in-operation conditions, it often becomes hard (or impossible) to experimentally measure the excitation. For this reason, attention has been paid to the development of system identification techniques that work on a basis of response data only. The use of such techniques allows the identification of modal models for structures excited by unknown ambient noise and vibration. In this contribution, controlled vibration experiments were conducted on a sprayer boom that was mounted on a tractor. A comparison was made between the results of a classic input-output and output-only modal analysis based on maximum likelihood system identification techniques. Due to the interaction between the dynamic artificial excitation device and the test structure, the output-only approach modelled the excitation device together with the test structure. The identified output-only modal parameters were validated by direct comparison to the identification results obtained on a classic input-output transfer function data set between the generator input signal and the structural responses. (C) 2003 Silsoe Research Institute. All rights reserved Published by Elsevier Science Ltd.status: publishe