Determination of Stress Histories in Structures by Natural Input Modal Analysis

In this paper it is shown that stress histories can be estimated with high accuracy by integrating measured accelerations to obtain displacement and then performing a modal decomposition of the so estimated displacements. The relation between the modal coordinate and the stress in an arbitrary point is established by a finite element model. It is shown, that when performing the modal decomposition, either experimental mode shapes or numerically estimated mode shapes can be used. However, it is important to verify that the numerical modes correspond reasonably well to the experimental modes. It is shown that the so estimated stress histories can replace strain gauge measurements in many cases, and it allows for an accurate estimation of fatigue damage.In this paper it is shown that stress histories can be estimated with high accuracy by integrating measured accelerations to obtain displacement and then performing a modal decomposition of the so estimated displacements. The relation between the modal coordinate and the stress in an arbitrary point is established by a finite element model. It is shown, that when performing the modal decomposition, either experimental mode shapes or numerically estimated mode shapes can be used. However, it is important to verify that the numerical modes correspond reasonably well to the experimental modes. It is shown that the so estimated stress histories can replace strain gauge measurements in many cases, and it allows for an accurate estimation of fatigue damage.