Prediction of Full Field Dynamic Stress/Strain from Limited Sets of Measured Data

Abstract

Transient events may cause degradation of a structure’s useful life. Often these events have an unknown effect on the structure. Some examples are helicopter hard landing, strong wind gusts on large turbine blades, and other similar occasional events. In many cases, only a handful of sensors are available for the evaluation of these rare, short-term events. This limited data does not always provide the detail necessary in order to determine the effects of the events that occur; this is very important especially in terms of the overall fatigue usage for the system. While a finite element model may be available, use of this limited data does not lend itself to easily integrate into the identification of the dynamic stress and dynamic strain. Often times, estimates of the forcing function can be approximated and used to identify the response. But these techniques are very approximate. A newly developed real time operating data expansion technique has been successfully used for the identification of more detailed information from limited sets of data. This expansion has mainly been used to augment the limited data acquired and allows for better overall visualization of these transient types of events. This technique has mainly been used for general response characteristics for structures. In this work, expansion techniques are developed in conjunction with the finite element mass and stiffness matrices to provide information at all of the finite element degrees of freedom from these limited sets of measured data points. With this approach, dynamic stress and dynamic strain can be identified from measured transient events thereby enabling estimation of fatigue accumulation or usage. Several cases are described to illustrate the overall process and results that are obtained from the expansion technique; these are compared to full reference solution results to verify the accuracy of the technique.