Nondestructive Contactless Monitoring of Damage in Joints between Composite Structural Components Incorporating Sensing Elements via 3D-Printing

Abstract

A vibration-testing framework for detecting and identifying failing joints between composite structural members without dedicated equipment (accelerometers, amplifiers) or time-consuming system modeling methods is introduced. The sensing element is a 2826MB Metglas® magnetoelastic strip embedded in one of the members during its 3D-printing (layer-by-layer) fabrication process in fused deposition modeling mode. External dynamic loading of the structure causes changes to the strip’s magnetization, thus inducing voltage to a nearby placed coil in a contactless manner. The resulting signal depends on the structure’s behavior under loading (and therefore its condition), and may be recorded without amplification or filtering by conventional oscilloscopes. Its frequency analysis reveals patterns of shifted frequency and/or altered damping at specific modes attributed to failing joints. Apart from yielding results using less dedicated equipment than other vibration-testing methods, the current framework offers two additional benefits: (i) Excitation may be applied to the same structural point for all monitored joints; (ii) estimation of damping values for a given mode does not have to rely on empirical or system modelling techniques (both requiring dedicated expertise). Test runs with structures formed by two or three composite slabs joined in-series indicate promising results with successful detection and identification of failing joints.

Evaluating Contact-Less Sensing and Fault Diagnosis Characteristics in Vibrating Thin Cantilever Beams with a MetGlas® 2826MB Ribbon

“…Comparison of the two series of recorded voltage signals led to two conclusions. First, the time histories of both voltage series were almost identical, as expected for passive setups [18]. Second, the spectral characteristics of the voltage with the beam under excitation were different than those from the voltage recorded with the beam at rest.…”

“…Using a passive setup, fault diagnosis was achieved in polymer slabs with magnetoelastic ribbons integrated with 3D printing during slab manufacturing [17]. Fault diagnosis was also achieved for structures composed by bolting together such slabs, and specifically, for indicating loose connections between structural members [18]. Interestingly, this study demonstrated that although only one slab with integrated magnetoelastic material was used in the structure, more than one loose connection could be detected.…”

“…The sensing principle of the proposed passive setup was previously examined in [24] using a first series of tests with voltage recorded while the beam was at rest and a second one with the beam excited with a triangular force at 160 Hz. Triangular waveforms were used instead of pure sinusoids or pulses because they correspond better to real sources of vibrations such as those created by machine-reciprocating parts [18]. Comparison of the two series of recorded voltage signals led to two conclusions.…”

“…A final remark is related to these sensing and fault diagnosis results being obtained for a long, thin and flexible beam. The same basic setup with a model-based algorithmic framework was applied to shorter, thicker and quite more rigid polymer beams in the previous works [17] and (in part) [18], with similarly successful fault diagnosis results. Nonetheless, sensing properties were not comprehensively evaluated in these studies since they both aimed at obtaining fault diagnosis results.…”

“…Then, the vibrating magnetoelastic element produces magnetic flux, which is picked up by a reception coil in a contact-less manner. Analyzing the signal's spectral characteristics draws conclusions on the dynamics of the magnetoelastic part and, obviously, of the underlying mechanical structure [17][18][19][20][21]. This one-coil-only setup is referred to as the passive setup and was also reviewed in [5].…”