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 potential application of the magnetostrictive method for evaluating stress states in steel bridge members by numerical analysis. A numerical study was conducted using COMSOL Multiphysics to examine the magnetic field response of steel plate specimens under different stress states. A model incorporating magnetic saturation behavior was introduced, and the results show that the induced coil voltage increases with stress difference, exhibiting a nonlinear response with reduced sensitivity at higher stress levels. Based on this model, a parametric analysis focusing on sensing conditions was carried out, with particular attention to the influence of lift-off distance on measurement stability and sensitivity. These findings suggest that the proposed model can capture, to a certain extent, the influence of stress difference on magnetic response, indicating the potential feasibility of stress evaluation using magnetic measurements. Ongoing work focuses on the influence of input parameters (such as excitation frequency, current amplitude, and material properties), as well as the magnetic field behavior under more complex stress states, and aims to develop a more realistic model for structural members, thereby providing a basis for optimizing measurement conditions and improving existing magnetostrictive measurement approaches.

Remote acoustic inspection using a string-shooter impact device offers a practical and safe alternative for evaluating tiled and concrete surfaces located in high or inaccessible areas. The method enables suspended wall inspection, allowing the device to be lowered along building façades, as well as ground-based inspection of tunnel ceilings without scaffolding or direct access. Furthermore, the compactness and simplicity of the mechanism make it a strong candidate for integration with unmanned aerial vehicles, providing a pathway toward fully remote tapping inspection at elevated locations.
In this study, we successfully developed a downsized and lightweight string shooter designed specifically for suspended deployment. The reduction in size was achieved without sacrificing impact performance, ensuring sufficient acoustic excitation for detecting debonding in tiled surfaces. A major technical advancement in this work is the improvement of the roller mechanism, which has historically been a critical durability bottleneck. The redesigned roller significantly increases operational life and reliability during repeated high-speed string release and retrieval cycles.
Experimental results and preliminary field evaluations demonstrate that the enhanced system provides stable impact energy, improved durability, and consistent acoustic responses suitable for defect identification. These improvements collectively contribute to a more practical and field-ready inspection tool. The proposed technology offers a promising path toward safer, more efficient, and more scalable high-elevation acoustic inspection, and it broadens the potential applications of remotely operated NDT systems for infrastructure maintenance.