The safety of masonry structures following exposure to elevated temperatures depends on precise diagnostics regarding the residual integrity of their components. In this context, Ultrasonic Pulse Velocity (UPV) testing emerges as a viable Non-Destructive Evaluation (NDE) alternative, allowing for the agile inference of internal damage without compromising the remaining structural stability. This paper presents a systematic literature review on the application of UPV in structural masonry elements under high temperature conditions, aiming to consolidate the state-of-the-art and identify existing gaps. The methodology involved the selection and analysis of articles from scientific databases (such as Scopus and Web of Science), investigating the experimental protocols adopted, the elements analyzed, and the correlations between UPV and the thermal degradation of materials. The results reveal that, although UPV is sensitive to the physicochemical changes imposed by heat, scientific production on the subject remains scarce. Furthermore, a predominance of studies focusing on bedding mortars was observed, highlighting a data gap regarding masonry units and the behavior of the assembly. It is concluded that UPV is a promising tool for post-fire investigation; however, its practical consolidation requires the development of guidelines that account for the heterogeneity and interaction between the constituents of the constructive system.
In this paper a new fundamental information concept for ultrasonic NDE is introduced. It is demonstrated that differential wave fields with respect to a system parameter P contain structural information about this parameter and about how it affects the measured system response. This can be quantitatively formalized by introducing a balance equation for structural information in analogy to Poynting’s theorem for elastic energy. In the paper, we consider several aspects of the new information approach, such as information density, information flux vector, as well as information sources and sinks. We visualize how structural information in an ultrasonic field can be generated and annihilated and how it propagates to the sensors. We finally discuss possible potential impacts on NDE, SHM, numerical simulation, and machine learning.
Additive manufacturing has revolutionized high-performance industries by enabling the production of components with complex geometries and internal lattice structures that cannot be fabricated using conventional manufacturing methods. However, the layer-by-layer nature of this process makes the components prone to defects such as porosity, micro-cracks, and elevated surface roughness. Moreover, the presence of intricate internal features poses a serious challenge for ultrasonic inspection, as ultrasonic waves cannot effectively penetrate deep internal regions or obtain reliable reflections from internal surfaces. In this study, magnetorheological (MR) fluid is employed as a filling medium for these cavities to establish a continuous internal pathway that enables effective ultrasonic wave propagation and integrated inspection. MR fluids, whose rheological and acoustic properties change under applied magnetic fields, allow the tuning of sound velocity and acoustic impedance and can act as a conformable mold matching the component's geometry. This work investigates the variations in sound velocity and ultrasonic attenuation in MR fluid under magnetic fields and evaluates their role in acoustic-impedance matching and wave-transmission enhancement. Experimental test specimens are fabricated, and immersion ultrasonic testing is performed using MR fluid as the coupling medium. Signal-processing techniques are applied to mitigate noise caused by particle scattering. The result demonstrate that the proposed method improve ultrasonic penetration and signal quality, offering a novel and effective approach for the nondestructive inspection of additively manufactured components.
The paper presents the results of the comparative numerical and experimental studies of the propagation of low-frequency ultrasonic Lamb waves in flat polyethene boards. A non-contact ultrasonic technique was applied in the experiments. At the same time, numerical simulations were performed using the k- Wave MATLAB toolbox to simulate acoustic wave fields in the time domain. The studies focused on analysing the amplitudes of an antisymmetric (A0) Lamb wave mode. The subjects of the studies were homogeneous, isotropic polyethene boards in undamaged and damaged states. The three damaged states are delamination, a crack at the board's edge, and rupture in the middle part of the board. In the experiments, even minor defects of a few millimetres in size lead to 20% changes in the A0 Lamb wave amplitude. A qualitative agreement was observed between numerical simulations and experimental ultrasonic results. It was shown that the sensitivity of the experimentally measured Lamb-wave amplitudes was higher than that of the simulated amplitudes.
In the case of complex material structures, such as highly attenuative and anisotropic materials, multi-layer components or bonded structures, a swept-wave ultrasonic spectroscopy method, UltraSpec®, has proven to be useful where conventional techniques are inadequate. When coupled with specialized data analysis software, this produces a highly sensitive nondestructive inspection technique that can be employed for challenging inspection applications. UltraSpec uses a long-duration, swept-frequency excitation pulse in contrast to the short duration, large amplitude excitation pulses used in traditional ultrasonic methods. The technique offers substantial signal-to-noise improvement and can be efficiently tailored to application-specific frequency ranges to maximize sensitivity and fidelity. Spectral analysis, resonance characteristics and processed time reflections provide the user with more information to assess the structure being inspected. The system also allows for evaluations at different depths or interfaces within a complex stack-up. This is especially useful for bond inspections, porosity detection/quantification, identification of micro-cracking or impact damage in composite materials. The technique has been used to successfully produce material insights that cannot be provided by other methods. This paper will use results from challenging inspections to highlight these unique UltraSpec capabilities and advantages.
