Eddy-current testing (ECT) offers a promising approach for non-destructive inspection of carbon fibre reinforced polymers (CFRPs), enabled by the electrical conductivity of the carbon fibres. However, due to their low and anisotropic bulk electrical conductivity, a complete understanding of how eddy-currents flow in these materials is missing, limiting accurate modelling and characterization of parts. This study investigates how induced current densities vary with changes in relative ply orientation between CFRP lamina, using a transmit-receive inductive measurement system. The relative angle between plies is systematically altered to examine the influence of relative ply orientation on eddy-current behaviour. The eddy-current density is deduced by changes in the magnetic flux measured by the receiver coil as a function of excitation frequency. Finite element models (FEM) of homogeneous anisotropic conductive CFRP layers predicts the samples with a (0/90)° ply orientation exhibit stronger eddy-current responses compared to (0/0)° samples. Experimental findings reveal that orthogonal orientations do not induce the strongest current densities, with peak eddy-current generation occurring at angular separations of 45-65° range with minimum occurring between 5-20°. The findings also indicate that larger coils show bigger regions of induced currents, and increasing frequency amplifies the non-monotonic trend. This suggests that frequency, stacking-sequence and symmetry of ply layers significantly influence eddy-current generation, suggesting the mechanism is governed by more complex physics than simple inter-ply, fibre contact interactions. This knowledge is crucial for improving ECT models, sensor designs and improving quality control of CFRP composites, enhancing their reliability and performance in engineering applications.

Keywords: Non-destructive Testing (NDT), Carbon fibre reinforced polymers (CFRPs), eddy currents testing (ECT), penetration depth, stacking sequence, ply orientation.

In lightweight structures, adhesive bonding provides a practical and efficient joining technique, especially for thin-walled structures and in joining dissimilar materials. Ensuring the reliability of these joints requires suitable monitoring techniques able to detect and quantify crack initiation and propagation within the adhesive layer.

This work presents an overview of several experimental investigations focused on the use of distributed optical fibre strain sensors for monitoring crack growth in adhesively bonded joints. Optical fibre sensors are lightweight, inert, and low profile, making them particularly suitable for integration into lightweight structures. Using Optical Backscatter Reflectometry (OBR) technology, the entire fibre length acts as a distributed strain sensor, providing strain measurements with a sub-millimetre spatial resolution over several meters of sensing length.

OBR sensors were applied on a range of adhesively bonded joint configurations subject to both static and fatigue loading conditions. The application of fibres both within the adhesive layer, and onto the backface of joints was explored. It is shown how joint geometry, loading conditions, and substrate material properties and morphology all influence the measured strain profile. Variations in the strain profile shape can be directly related to damage evolution. Results show that distributed fibre sensing enables accurate crack length monitoring across a variety of joint types and loading conditions, highlighting its potential for structural health monitoring of in-service bonded structures.

This study investigates the applicability of the magnetostrictive (magnetoelastic) method for stress evaluation in steel bridge members through numerical analysis. The magnetostrictive effect, where the magnetic permeability of ferromagnetic steel varies with applied stress, provides a potential basis for non-contact and non-destructive stress estimation.

Finite element simulations were conducted using COMSOL Multiphysics to analyze the magnetic flux density and field distribution of steel plate models subjected to different axial and bending stresses. The analysis focused on how stress magnitude, direction, and boundary configuration influence the magnetic field response. The correlation between magnetic field variation and internal stress was quantitatively examined to clarify the fundamental behavior of stress-dependent magnetic properties in steel members.

The results demonstrated that magnetic field changes computed from the finite element model can represent the influence of structural stress with reasonable consistency. These findings offer basic insights into the stress–magnetic field relationship in structural-scale components and serve as a preliminary step toward evaluating the potential of the magnetostrictive method for application to steel bridges.

Most commonly, heat exchangers are constructed of hundreds to thousands of tubes in parallel, encased in a metal shell. Heat exchangers operate continuously and are subject to several degradations and failures, such as erosion, corrosion, abrasion caused by support plates rubbing against the tubes, thermal shock, fouling etc. Conventional inspection methods are being used but they have their application limitations. The Eddy Current testing method, where a probe is physically pushed through each tube and pulled back, is one of the most well-known method of inspecting Heat Exchanger Tubes. The deposits in the tube interior can cause probe jamming and damage. Furthermore, Eddy Current Testing is heavily dependent on the tube material, which can be limited to non-ferromagnetic materials and requires “calibration standards” for any tube inspection. Eddy Current variations, such as Full/Partial Saturation Eddy Current, Remote Field Testing and Magnetic Flux Leakage Testing, though can be used for ferromagnetic materials, but have further drawbacks. Another method is ultrasonic Testing (IRIS), where a probe is invasively inserted in the tube. Although, IRIS is accurate but poses difficulties in the inspection procedure, where the need for good resolution dictates a narrow beam, which in turn entails a very slow pull rate so that the spiral scan of the tube provides full coverage. Filling the tubes with water, without air bubbles is messy and time consuming. IRIS also requires cleaning the tubes, which is another time-consuming and costly procedure that must take place before inspection even begins. A new acoustic (or sound) based inspection method is gaining popularity, to perform rapid, reliable, repeatable and comprehensive inspection method, Acoustic Pulse Reflectometry (APR). The technology can provide speed, accuracy and repeatability. The APR technology-based inspection system is not dependent on tube material or configuration. This report will demonstrate our effort in verifying the capability of Acoustic Pulse Reflectometry (APR) technology on Heat Exchanger Tube Inspection in terms of reliability, cost effectiveness and rapid inspection system.