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.
Highlights
The concept of embedding sensing elements into structural components has often been used for monitoring purposes, with recent examples of circular PZT (lead zirconate titanate (Pb[Zr(x)Ti(1-x)]O3 )) patches incorporated in concrete cylinders reported in [3]
This study proposes a comprehensive framework for monitoring the condition of joints in structures with composite members/components, by extending the methodology proposed for single slabs in [19]
With respect to previous relevant approaches, the key element of the current framework is that the structure is excited at a standard location irrespectively of the monitored joint
Summary
Other examples based on “off duty” inspection include [15] where a composite pick-up truck box involving adhesively bonded composite joints was diagnosed by means of pulsed thermography methodologies, and [16] with CFRP-epoxy adhesive single-lap joints inspected by means of eddy current pulse-compression thermography These are two examples of NDT and E techniques traditionally used for detecting defects in parts/components which have been adapted for monitoring of joints in structures. All joints should be monitored, even though only one of the slabs involved incorporates the 3D-printed sensing element For this reason, the contactless diagnosis principle in [19] (presented therein for a single slab) is upgraded with respect to data evaluation techniques.
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