Uncertainty reduction of damage growth properties using structural health monitoring

Structural health monitoring provides sensor data that can monitor fatigue-induced damage in service. This information may in turn be used to improve the characterization of material properties that govern damage growth for the structure being monitored. These properties are often widely distributed among nominally identical materials because of differences in manufacturing processes and due to aging effects. Improved accuracy in damage growth characteristics would allow more accurate prediction of the remaining useful life ofthe structural component. In this paper, a probabilistic approach using Bayesian inference is employed to progressively reduce the uncertainty in structure-specific damage growth parameters in spite of noise and bias in sensor measurements. Starting from an initial wide distribution of damage growth parameters that are obtained from coupon tests, the distribution is progressively narrowed using damage growth data between consecutive measurements. Detailed discussions on how to construct the likelihood function under the given noise of sensor data and how to update the distribution are presented. The approach is applied to simulated damage growth in fuselage panels due to cycles of pressurization. It is shown that the proposed method rapidly converges to the accurate damage growth parameters when the initial damage size is relatively large: e.g., 20 mm. Fairly accurate damage growth parameters are obtained even with measurement errors of 5 mm. Using the identified damage growth parameters, it is shown that the 95% conservative remaining useful life converges to the true remaining useful life from the conservative side. The proposed approach may have the potential of turning aircraft into flying fatigue laboratories.