Preliminary Results of a Structural Health Monitoring System Application for Real-Time Debonding Detection on a Full-Scale Composite Spar

Abstract

The present paper reports the outcomes of activities concerning a real-time SHM system for debonding flaw detection based on ground testing of an aircraft structural component as a basis for condition-based maintenance. In this application, a damage detection method unrelated to structural or load models is investigated. In the reported application, the system is applied for real-time detection of two flaws, kissing bond type, artificially deployed over a full-scale composite spar under the action of external bending loads. The proposed algorithm, local high-edge onset (LHEO), detects damage as an edge onset in both the space and time domains, correlating current strain levels to next strain levels within a sliding inner product proportional to the sensor step and the acquisition time interval, respectively. Real-time implementation can run on a consumer-grade computer. The SHM algorithm was written in Matlab and compiled as a Python module, then called from a multiprocess wrapper code with separate operations for data reception and data elaboration. The proposed SHM system is made of FBG arrays, an interrogator, an in-house SHM code, an original decoding software (SW) for real-time implementation of multiple SHM algorithms and a continuous interface with an external operator.

A Model-Assisted Probability of Detection Framework for Optical Fiber Sensors

“…Several studies have investigated debonding and delamination in stiffened composite panels for aerospace applications in a damage tolerance scenario with DOFSs [ 59 , 60 ] and FBGs [ 61 ], considering damage sizes in the 40–80 mm range. In this study, it is shown that in a DCB specimen, it is possible to achieve of 5.66 mm (see Table 2 ).…”

Laboratory Results of a Real-Time SHM Integrated System on a P180 Full-Scale Wing-Box Section

“…The SHM system provides recursive and continuous indications of the structural state, updating its output approximately each second, eventually accompanied by an acoustical signal if a discontinuity is detected. In synthesis, the main aims of this activity are: confirmation of the real-time functionality of the proposed SHM system already verified in [ 28 ]; confirmation of the capability of the developed SHM algorithm on a more complex structure, by referring to embedded and bonded optical fibers equipped with FBG arrays; confirmation of the capability of the SHM system to handle several algorithms, at the same time, being simultaneously fed with the same data; establishment of preliminary criteria for discerning the required sensor density for the specific selected sensor arrays, in terms of number of sensible devices per unit of length; this measure is expected to be strictly dependent on the irregularity size. …”

“…If cross-correlation magnitude at a pixel exceeds a threshold, a possible edge point is reposted. In detail, the cross-correlation of the strain gradient vector (dε) can be written [28] by using Equation (1) as follows:…”

“…It moves away from edge detection techniques that are usually utilized in digital image processing for identifying the boundary of different subjects [ 27 ]. After having preliminarily proven the feasibility of such a methodology on predominantly 1D structural elements, albeit with a complex architecture [ 28 , 29 ], the activity reported deals with an application on a full-scale wing-box section. Like the former study, the target of investigation is the real-time detection of skin–spar debonding.…”

“…The local high-edge onset (LHEO) algorithm considers structural damage as an edge discontinuity along the strain energy signature. The methodology logic diagram and other details can be found in [ 28 ].…”