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Almeida, G, Gonzalez J, Rosado L, Vilaça P, Santos TG.  2013.  Advances in NDT and materials characterization by eddy currents, 2013. 46th CIRP Conference on Manufacturing Systems, CIRP CMS 2013. 7:359-364., Setubal Abstract
Antin, K-N, Machado MA, Santos TG, Vilaça P.  2019.  Evaluation of Different Non-destructive Testing Methods to Detect Imperfections in Unidirectional Carbon Fiber Composite Ropes. Journal of Nondestructive Evaluation. 38(23) AbstractWebsite

Online monitoring of carbon fiber reinforced plastic (CFRP) ropes requires non-destructive testing (NDT) methods capable of detecting multiple damage types at high inspection speeds. Three NDT methods are evaluated on artificial and realistic imperfections in order to assess their suitability for online monitoring of CFRP ropes. To support testing, the microstructure and electrical conductivity of a carbon fiber rope is characterized. The compared methods are thermography via thermoelastic stress analysis, ultrasonic testing with commercial phased array transducers, and eddy current testing, supported by tailor-made probes. While thermoelastic stress analysis and ultrasonics proved to be accurate methods for detecting damage size and the shape of defects, they were found to be unsuitable for high-speed inspection of a CFRP rope. Instead, contactless inspection using eddy currents is a promising solution for real-time online monitoring of CFRP ropes at high inspection speeds.

Braz Fernandes, FM, Camacho E, Rodrigues PF, Inácio P, Santos TG, Schell N.  2019.  In Situ Structural Characterization of Functionally Graded Ni–Ti Shape Memory Alloy During Tensile Loading, dec. Shape Memory and Superelasticity. 5:457–467., Number 4 AbstractWebsite


Costa, FB, Machado MA, Bonfait GJ, Vieira P, Santos TG.  2021.  Continuous wave terahertz imaging for NDT: Fundamentals and experimental validation. Measurement. 172(108904) AbstractWebsite

Continuous wave terahertz (CW THz) imaging, is a variant of terahertz imaging that has been gaining scientific
and technological relevance in multiple areas. In this paper the fundamental phenomena of CW THz were
studied and a mathematical model was developed that successfully describes the Fabry–Perot interference for
such a system, opening the possibility for measurement of thicknesses and surface curvatures. The capabilities
of the system were tested using different types of defects, such as voids, water infiltrations and thin metallic
wires. The interactions between different materials, features and the radiation beam were numerically studied
using finite element method and the results agreed with the experiments. By comparing the results with other
Non-Destructive Testing methods, it was found that CW THz imaging is particularly interesting to image water
infiltrations and composite materials that incorporate conductive wires.

Dos Santos, TG, Silva BS, Dos Santos Vilaça P, Quintino L, Sousa JMC.  2008.  Data fusion in non destructive testing using fuzzy logic to evaluate friction stir welding, 2008. Welding International. 22(12):826-833.: Taylor and Francis Ltd. AbstractWebsite
Dos Santos, TG, Ramos PM, Dos Santos Vilaça P.  2008.  Non destructive testing of Friction Stir Welding: Comparison of planar eddy current probes, 2008. 16th IMEKO TC4 International Symposium on Exploring New Frontiers of Instrumentation and Methods for Electrical and Electronic Measurements; 13th International Workshop on ADC Modelling and Testing - IMEKO TC4 - TC21 Joint Session. :507-512., Florence Abstract
Duarte, VR, Rodrigues TA, Machado MA.  2021.  Benchmarking of Nondestructive Testing for Additive Manufacturing. 3D Printing and Additive Manufacturing. AbstractWebsite

Defect detection in additive manufacturing (AM) is of paramount importance to improve the reliability of products. Nondestructive testing is not yet widely used for defect detection. The main challenges are a lack of standards and methods, the types and location of defects, and the complex geometry of many parts. During selective laser melting (SLM), several types of defects can occur such as porosity, cracking, and lack of fusion. In this study, several nondestructive tests were conducted in a highly complex shaped part in AISI 316L stainless steel with real defects manufactured by SLM. Two additional artificial defects (one horizontal and one flat bottom hole) were produced and the defect detectability was evaluated. The techniques used were as follows: dye penetrant, infrared thermography, immersion ultrasonic, eddy current, and X-ray microcomputed tomography to assess different types of defects in the as-built part. We conclude that no single technique can detect every type of defect, although multiple techniques provide complementary and redundant information to critically evaluate the integrity of the parts. This approach is fundamental for improving the reliability of defect detection, which will help expand the potential for using AM to produce parts for critical structural applications.

Gomes, JF, Miranda RM, Santos TJ, Carvalho PA.  2014.  Emission of nanoparticles during friction stir welding (FSW) of aluminium alloys, 2014. Journal of Toxicology and Environmental Health - Part A: Current Issues. 77(14-16):924-930.: Taylor and Francis Inc. AbstractWebsite
Gomes, JF, Albuquerque PC, Miranda RM, Santos TG, Vieira MT.  2012.  Comparison of deposited surface area of airborne ultrafine particles generated from two welding processes, 2012. Inhalation Toxicology. 24(11):774-781. AbstractWebsite
Lopez, A, Bacelar R, Pires I, G.Santos T, PedroSousa J, Quintino L.  2018.  Non-destructive testing application of radiography and ultrasound for wire and arc additive manufacturing. Additive Manufacturing. 21:298-306. AbstractWebsite

The present work addressed the challenges of identifying applicable Non-Destructive Testing (NDT) techniques suitable for inspection and materials characterization techniques for Wire and Arc Additive Manufacturing (WAAM) parts. With the view of transferring WAAM to the industry and qualifying the manufacturing process for applications such as structural components, the quality of the produced parts needs to be assured. Thus, the main objective of this paper is to review the main NDT techniques and assess the capability of detecting WAAM defects, for inspection either in a monitoring, in-process or post-process scenario. Radiography and ultrasonic testing were experimentally tested on reference specimens in order to compare the techniques capabilities. Metallographic, hardness and electrical conductivity analysis were also applied to the same specimens for material characterization. Experimental outcomes prove that typical WAAM defects can be detected by the referred techniques. The electrical conductivity measurement may complement or substitute some destructive methods used in AM processing.

Machado, MA, Rosado L, Pedrosa N, Miranda RM, Piedade M, Santos TG.  2017.  Customized Eddy Current Probes for Pipe Inspection. Studies in Applied Electromagnetics and Mechanics. :283-290.: IOS Press Ebooks Abstract

A novel Eddy Current (EC) probe configurations were developed to detect millimeter defects with any orientation on inner or outer pipe surfaces. The probes were designed and experimentally validated in different materials where the defects tested were identified with a high sensitivity and good signal-to-noise ratio.

Machado, MA, Silva MI, Martins AP, Carvalho MS, Santos TG.  2021.  Double active transient thermography, nov. NDT & E International. :102566. AbstractWebsite


Machado, MA, Antin KN, Rosado LS, Vilaça P, Santos TG.  2019.  High speed inspection of UD CFRP composites. 58th Annual Conference of the British Institute of Non-Destructive Testing, NDT 2019. , Telford, UK Abstract

Online monitoring of carbon fibre reinforced polymer (CFRP) components requires a Non-Destructive Testing (NDT) method capable of contactless sensing of damage, while enabling high inspection speeds needed for monitoring large components. Eddy current testing (ECT) of CFRP components has great potential for two reasons. First, ECT probes are capable of operating without contact, although minimizing the lift-off is preferred. Second, impedance analysers with high sample rates make high-speed inspection possible. This research assesses the damage detection capabilities of eddy current probes on CFRP samples with artificial and realistic damage. To support the aptitude of the ECT method for these needs, the CFRP material is characterized and numerical simulations are performed in order to develop optimized and tailored ECT probes for the detection of defects with different morphologies, namely fibre breakage and delaminations, and to take into consideration the highly anisotropic electrical bulk resistivity of the CFRP material. Different ECT probes were designed, produced and experimentally validated. The experiments were performed at a high inspection speed (4 m/s) and the high sensitivity of the probes was demonstrated.

Machado, MA, Rosado LS, Mendes NM, Miranda RM, Santos TG.  2021.  Multisensor Inspection of Laser-Brazed Joints in the Automotive Industry, nov. Sensors. 21:7335., Number 21 AbstractWebsite

Automobile laser brazing remains a complex process whose results are affected by several process variables that may result in nonacceptable welds. A multisensory customized inspection system is proposed, with two distinct non-destructive techniques: the potential drop method and eddy current testing. New probes were designed, simulated, produced, and experimentally validated in automobile's laser-brazed weld beads with artificially introduced defects. The numerical simulations allowed the development of a new four-point probe configuration in a non-conventional orthogonal shape demonstrating a superior performance in both simulation and experimental validation. The dedicated inspection system allowed the detection of porosities, cracks, and lack of bonding defects, demonstrating the redundancy and complementarity these two techniques provide.

Machado, MA, Antin K-N, Rosado LS, Vilaça P, Santos TG.  2019.  Contactless high-speed eddy current inspection of unidirectional carbon fiber reinforced polymer. Composites Part B: Engineering. 168:226-235. AbstractWebsite

This paper presents the development and the results of a customized eddy current (EC) non-destructive testing (NDT) system for highly demanding online inspection conditions. Several planar eddy current array probes were designed, numerically simulated and experimentally compared for the inspection of low conductivity unidirectional carbon fibre reinforced polymer (CFRP) ropes. The inspections were performed using a dedicated scanner device at 4 m/s with 3 mm probe lift-off where defects under 1 mm were detected with an excellent SNR. Different defect morphologies and sizes, such as broken fibres and lateral cuts, were successful detected and compared to conventional probes.

Machado, MA, Rosado L, Pedrosa N, Vostner A, Miranda RM, Piedade M, Santos TG.  2017.  Novel eddy current probes for pipes: Application in austenitic round-in-square profiles of ITER. NDT&E International. 87:111-118. AbstractWebsite

Novel eddy current probes were developed to detect sub-millimetre defects with any orientation on the inner surface of pipes. Five different probes were designed, produced and experimentally validated. These probes include arrays of planar trapezoidal coils in a flexible substrate used alone or together with different winded drive coils. Numerical simulations with Finite Element Method were used to predict the probe response to defects with any orientation. Experimental results in austenitic steel jackets used in ITER revealed that the new probes have an improved reliability compared to conventional toroidal bobbin probes, allowing a higher sensitivity to circumferential defects.

Machado, MA, Inácio PL, Santos RA, Gomes AF, Martins AP, Carvalho MS, Santos TG.  2019.  Inspection of composite parts produced by additive manufacturing: Air-coupled ultrasound and thermography. 58th Annual Conference of the British Institute of Non-Destructive Testing, NDT 2019. , Telford, UK Abstract

Polymeric parts produced by Fused Deposition Modelling (FDM) Additive Manufacturing (AM) has no special safety requirements, and therefore, NDT is not required. However, the use of AM to produce Fibre Reinforcement Thermoplastics (FRTP) parts means that structural applications with safety requirements are envisaged, demanding reliable NDT methods. This paper presents experimental results and numerical simulation by Finite Element Method (FEM) of the NDT inspection of different parts of polymeric and RFTP composite materials. The parts were produced by FDM Additive Manufacturing and different delamination defects were introduced at different positions and with different dimensions and morphologies. Two different NDT techniques were used, exploiting different inspection parameters: air-coupled ultrasound, using frequencies between 50 and 400 kHz and active transient thermography, in both reflection and transition modes. The influence of the curvature of the parts was analysed, from the experimental point of view, and the results were compared with different numerical simulation strategies. It was shown that, both NDT techniques can detect the defects, with good spatial resolution, being the thermography reflection mode the fastest and expedite for curvature parts. The numerical simulation corroborates the experimental results allowing a deeper insight on the physical phenomena involved.

Machado, MA, Antin K-N, Rosado LS, Vilaça P, Santos TG.  2021.  High-speed inspection of delamination defects in unidirectional CFRP by non-contact eddy current testing, nov. Composites Part B: Engineering. 224:109167. AbstractWebsite


Machado, MA, Rosado LFSG, Mendes NAM, Miranda RMM, dos Santos TJG.  2021.  New directions for inline inspection of automobile laser welds using non-destructive testing, sep. The International Journal of Advanced Manufacturing Technology. AbstractWebsite

An innovative pilot installation and eddy current testing (ECT) inspection system for laser-brazed joints is presented. The proposed system detects both surface and sub-surface welding defects operating autonomously and integrated with a robotized arm. Customized eddy current probes were designed and experimentally validated detecting pore defects with 0.13 mm diameter and sub-surface defects buried 1 mm deep. The integration of the system and the manufacturing process towards an Industry 4.0 quality control paradigm is also discussed.

Matos Filipe, L, Santos TG, Valtchev S, Pamies Teixeira J, Miranda RM.  2012.  New method employing the electrical impedance for monitoring mechanical damage evolution in glass-reinforced: Applications to riveted joints, 2012. Materials and Design. 42:25-31. AbstractWebsite
Miranda, RM, Santos TG, Gandra J, Lopes N, Silva RJC.  2013.  Reinforcement strategies for producing functionally graded materials by friction stir processing in aluminium alloys, 2013. Journal of Materials Processing Technology. 213(9):1609-1615. AbstractWebsite
Miranda, RM, Gandra JP, Vilaca P, Quintino L, Santos TG.  2014.  Surface modification by solid state processing, 2014. Surface Modification by Solid State Processing. :1-183.: Elsevier Ltd. AbstractWebsite
Moreira, PMGP, Santos T, Tavares SMO, Richter-Trummer V, Vilaça P, de Castro PMST.  2008.  Mechanical characterization of friction stir welds of two dissimilar aluminium alloys of the 6xxx series, 2008. Advanced Materials Forum IV - Selected, peer reviewed papers from the 4th International Materials Symposium Materiais 2007 and 8th Encontro da Sociedade Portuguesa de Materiais - SPM. 587-588:430-434., Porto AbstractWebsite
Moreira, PMGP, Santos T, Tavares SMO, Richter-Trummer V, Vilaça P, de Castro PMST.  2009.  Mechanical and metallurgical characterization of friction stir welding joints of AA6061-T6 with AA6082-T6, 2009. Materials and Design. 30(1):180-187. AbstractWebsite
Nascimento, F, Santos T, Vilaça P, Miranda RM, Quintino L.  2009.  Microstructural modification and ductility enhancement of surfaces modified by FSP in aluminium alloys, 2009. Materials Science and Engineering A. 506(1-2):16-22. AbstractWebsite