Strain gauge placement optimization methodology to measure multiaxial loads of complex structure

Abstract

The use of a strain gauge to measure loads is, in some respects, similar to its use in determining stress, but a different approach is required. In load measurement, it is necessary to compile a suitably selected configuration of strain gauges, which can be used to measure often very complex loads of the structure. For designing the engine mount instrumentation for the Flying Test Bed, an optimization tool has been developed. The algorithm and the theory behind the instrumentation design are described in detail. The basic principle is to find the strain gauge configuration that eliminates the measurement error due to the noise in the measured signal as much as possible. The input for optimization is the strain response of the structure to the applied loads analyzed using the FE model. In contrast to the common strategy using purely stochastic methods, this developed tool uses a hybrid approach based on a combination of a heuristic approach with repeated deterministic local optimization. The optimization is focused on the connection of a simple uni-axial strain gauge to a quarter-bridge and a T-rosette to a half-bridge that provides temperature compensation. Furthermore, an approach is proposed that takes into account the possibility of failure of some strain gauges. The instrumentation is thus robust and allows to obtain quality data even in the event of failure of some of the strain gauges.