Automated detection and classification of concealed objects using infrared thermography and convolutional neural networks.

This paper presents a study on the effectiveness of a convolutional neural network (CNN) in classifying infrared images for security scanning. Infrared thermography was explored as a non-invasive security scanner for stand-off and walk-through concealed object detection. Heat generated by human subjects radiates off the clothing surface, allowing detection by an infrared camera.

Material-Enabled Impact Detection and Damage Localisation System Using Shape Memory Alloy Tufted Composites.

Shape memory alloy (SMA) tufted composites have shown a significant improvement of the mechanical strength, fracture toughness, and delamination resistance of structural joints. This paper investigated the self-sensing functionality of SMA tufted carbon/epoxy composite T-joints to enable in situ strain monitoring for the detection of low-velocity impacts. Indeed, large deformations in the tufted composite due to impacts caused abrupt changes in electrical resistance of SMA filaments, which were used to trigger the detection system.

3D rainbow phononic crystals for extended vibration attenuation bands.

We hereby report for the first time on the design, manufacturing and testing of a three-dimensional (3D) nearly-periodic, locally resonant phononic crystal (PnC). Most of the research effort on PnCs and metamaterials has been focused on the enhanced dynamic properties arising from their periodic design. Lately, additive manufacturing techniques have made a number of designs with intrinsically complex geometries feasible to produce.

Recent Advances in Active Infrared Thermography for Non-Destructive Testing of Aerospace Components.

Active infrared thermography is a fast and accurate non-destructive evaluation technique that is of particular relevance to the aerospace industry for the inspection of aircraft and helicopters' primary and secondary structures, aero-engine parts, spacecraft components and its subsystems. This review provides an exhaustive summary of most recent active thermographic methods used for aerospace applications according to their physical principle and thermal excitation sources. Besides traditional optically stimulated thermography, which uses external optical radiation such as flashes, heaters and laser systems, novel hybrid thermographic techniques are also investigated.

Phononic Crystal Waveguide Transducers for Nonlinear Elastic Wave Sensing.

Second harmonic generation is one of the most sensitive and reliable nonlinear elastic signatures for micro-damage assessment. However, its detection requires powerful amplification systems generating fictitious harmonics that are difficult to discern from pure nonlinear elastic effects. Current state-of-the-art nonlinear ultrasonic methods still involve impractical solutions such as cumbersome signal calibration processes and substantial modifications of the test component in order to create material-based tunable harmonic filters.

Nonlinear elastic multi-path reciprocal method for damage localisation in composite materials.

Nonlinear ultrasonic techniques rely on the measurement of nonlinear elastic effects caused by the interaction of ultrasonic waves with the material damage, and have shown high sensitivity to detect micro-cracks and defects in the early stages. This paper presents a nonlinear ultrasonic technique, here named nonlinear elastic multi-path reciprocal method, for the identification and localisation of micro-damage in composite laminates. In the proposed methodology, a sparse array of surface bonded ultrasonic transducers is used to measure the second harmonic elastic response associated with the material flaw.

On the generation of nonlinear damage resonance intermodulation for elastic wave spectroscopy.

Recent nonlinear elastic wave spectroscopy experiments have shown that the nonlinear ultrasonic response of damaged composite materials can be enhanced by higher vibrations at the local damage resonance. In this paper, the mathematical formulation for the generation of nonlinear wave effects associated with continuous periodic excitation and the concept of local defect resonance is provided. Under the assumption of both quadratic and cubic approximation, the existence of higher harmonics of the excitation frequency, superharmonics of the damage resonance frequency and nonlinear wave effects, here named as nonlinear damage resonance intermodulation, which correspond to the nonlinear intermodulation between the driving and the damage resonance frequencies, is proved.

Nonlinear elastic wave tomography for the imaging of corrosion damage.

This paper presents a nonlinear elastic wave tomography method, based on ultrasonic guided waves, for the image of nonlinear signatures in the dynamic response of a damaged isotropic structure. The proposed technique relies on a combination of high order statistics and a radial basis function approach. The bicoherence of ultrasonic waveforms originated by a harmonic excitation was used to characterise the second order nonlinear signature contained in the measured signals due to the presence of surface corrosion.

Modelling of multiscale nonlinear interaction of elastic waves with three-dimensional cracks.

This paper presents a nonlinear elastic material model able to simulate the nonlinear effects generated by the interaction of acoustic/ultrasonic waves with damage precursors and micro-cracks in a variety of materials. Such a constitutive model is implemented in an in-house finite element code and exhibits a multiscale nature where the macroscopic behavior of damaged structures can be represented through a contribution of a number of mesoscopic elements, which are composed by a statistical collection of microscopic units. By means of the semi-analytical Landau formulation and Preisach-Mayergoyz space representation, this multiscale model allows the description of the structural response under continuous harmonic excitation of micro-damaged materials showing both anharmonic and dissipative hysteretic effects.

Nonlinear elastic imaging using reciprocal time reversal and third order symmetry analysis.

This paper presents a nonlinear imaging method for the detection of the nonlinear signature due to impact damage in complex anisotropic solids with diffuse field conditions. The proposed technique, based on a combination of an inverse filtering approach with phase symmetry analysis and frequency modulated excitation signals, is applied to a number of waveforms containing the nonlinear impulse responses of the medium. Phase symmetry analysis was used to characterize the third order nonlinearity of the structure by exploiting its invariant properties with the phase angle of the input waveforms.

Acoustic emission localization in complex dissipative anisotropic structures using a one-channel reciprocal time reversal method.

This paper presents an imaging method for the localization of the impact point in complex anisotropic structures with diffuse field conditions, using only one passive transducer. The proposed technique is based on the reciprocal time reversal approach (inverse filtering) applied to a number of waveforms stored into a database containing the experimental Green's function of the structure. Unlike most acoustic emission monitoring systems, the present method exploits the benefits of multiple scattering, mode conversion, and boundaries reflections to achieve the focusing of the source with high resolution.

MR in the evaluation of new anterior cruciate ligament and tibial tunnel position: correlation with clinical and functional features.

Purpose: This study aimed to evaluate correlations between the position of the tibial tunnel, its alignment with the ligament-screw system, presence of intratunnel fluid, position of the tibial tunnel with respect to the Blumensaat line and clinical knee stability in patients who underwent arthroscopic reconstruction of the anterior cruciate ligament (ACL), by using magnetic resonance (MR) imaging.

Materials And Methods: Forty-eight patients (40 men, eight women; mean age, 31 years) underwent arthroscopic reconstruction of the ACL using double-strand semitendinosus and gracilis tendons. The new ACL was fixed to the tibial tunnel using Bio-Intrafix (Mitek).

Evaluation of magnetic resonance signal modification induced by hyaluronic acid therapy in chondromalacia patellae: a preliminary study.

Hyaluronic Acid (HA) is an alternative method for the treatment of osteoarthritis (OA), which acts on pain through a double action: anti-inflammatory and synovial fluid (SF) visco-supplementation. Magnetic Resonance Imaging (MRI), utilizing specific sequences, is a valid method for studying the initial phase of chondral damage. The analysis of the data, obtained through the intensity of values taken by positioning Region of Interest (ROIs) within the lesion, determining the differences before and after treatment with HA injected into the knee.