Definition of a load adaptive baseline by inverse finite element method for structural damage identification

One principle limitation to the implementation of Structural Health Monitoring (SHM) systems in real structures is the influence of different operational conditions with respect to those adopted during SHM system design, potentially leading to damage misclassifications. To overcome this issue, this work proposes a methodology to perform Structural Health Monitoring leveraging on the inverse Finite Element Method (iFEM). The iFEM methodology, based on the minimisation of a weighted least-squares functional defined as a comparison between the experimental strains and the corresponding numerical ones, enables the reconstruction of the strain field of a structure by means of a number of strain sensors without requiring any a-priori knowledge of the boundary load conditions. This allows providing a load-adaptive baseline based on an anomaly index that highlights the actual health state of the structure by comparing the strain reconstructed by the iFEM at some test locations with the strain measured by a test sensor in the same position, independently from the applied load and without training requirements for load cancelling. When the analysed structure is in a “healthy” condition, the two values match, otherwise they do not. If multiple test positions are considered, the damage position can also be inferred. Though the formulation of the diagnostic problem is general for an arbitrary component geometry and damage type, the proposed method is numerically demonstrated by means of a clamped plate subjected to different loads in the presence of single and multiple fatigue crack damages.