Towards Automatic Crack Size Estimation with iFEM for Structural Health Monitoring

Abstract

The inverse finite element method (iFEM) is a model-based technique to compute the displacement (and then the strain) field of a structure from strain measurements and a geometrical discretization of the same. Different literature works exploit the error between the numerically reconstructed strains and the experimental measurements to perform damage identification in a structural health monitoring framework. However, only damage detection and localization are performed, without attempting a proper damage size estimation. The latter could be based on machine learning techniques; however, an a priori definition of the damage conditions would be required. To overcome these limitations, the present work proposes a new approach in which the damage is systematically introduced in the iFEM model to minimize its discrepancy with respect to the physical structure. This is performed with a maximum likelihood estimation framework, where the most accurate damage scenario is selected among a series of different models. The proposed approach was experimentally verified on an aluminum plate subjected to fatigue crack propagation, which enables the creation of a digital twin of the structure itself. The strain field fed to the iFEM routine was experimentally measured with an optical backscatter reflectometry fiber and the methodology was validated with independent observations of lasers and the digital image correlation.

Numerical Analysis Results of Debonding Damage Effects for an SHM System Application on a Typical Composite Beam

“…In this sense, strain gauges are optimal options for this target, being classically employed during laboratory and flight experiments, providing the verification and validation of the structure, and permitting to carry out numerical experimental correlation and assessment of the developed theoretical models, mostly finite element-based ones [16,17]. Indeed, strain-based techniques for deformation reconstruction methods are highly diffused in literature and include, for example, the inverse finite element method (iFEM), the use of the so-called iQS4 elements for deformation data reconstruction, and finding applications for damage diagnosis and crack monitoring-as reported for instance in [18][19][20]-among many other works. In the first paper herein mentioned, the same authors who originally developed the iFEM method [21] also introduced the iQS4, a four-node quadrilateral inverse element.…”

Delamination Detection and Localization in Vibrating Composite Plates and Shells Using the Inverse Finite Element Method

“…In this regard, Kefal et al [ 54 ] incorporated the peridynamic theory within the iFEM and proposed a robust real-time crack prognosis system. In another study, Oboe et al [ 55 ] introduced a “Gaussian likelihood index” for estimating the size of the crack under mode I failure. To this end, several iFEM models associated with different damage scenarios were developed, and through calculating the likelihood index, the length of the crack can be approximated.…”

On the Detection of Thickness Loss in Ship Hull Structures Through Strain Sensing

“…On account of their prevalence and importance to structural safety, fatigue cracks have been a focal point of SHM research [6] with works dealing with all different levels of the SHM hierarchy proposed by Rytter [7]; namely, damage detection [8,9,10], localization [11,12,13], quantification [14,15,16] and prognosis [17,18,19]. Naturally, the prognostic aspect of SHM is of particular interest when it comes to fatigue crack growth [20,21], as its focus is to obtain probabilistic predictions of the evolution of structural deterioration.…”