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Santos, TG, Faria J, Vilaça P, Miranda RM.  2013.  Application of eddy currents in processed materials structural evaluation, 2013. 6th International Materials Symposium, Materiais 2011. 730-732:715-720., Guimaraes AbstractWebsite
Santos, TG, Miranda RM, Vilaça P.  2014.  Friction stir welding assisted by electrical joule effect to overcome lack of penetration in aluminium alloys, 2014. 17th Conference of the European Scientific Association on Material Forming, ESAFORM 2014. 611-612:763-772., Espoo: Trans Tech Publications 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
Santos, TG, Sorger G, Vilaça P, Miranda RM.  2014.  A non-conventional technique for evaluating welded joints based on the electrical conductivity, 2014. 17th Conference of the European Scientific Association on Material Forming, ESAFORM 2014. 611-612:671-676., Espoo: Trans Tech Publications Ltd AbstractWebsite
Santos, TG, Martins J, Mendes L, Miranda RM.  2014.  Process developments in FSW, 2014. 8th International Conference on Management Science and Engineering Management, ICMSEM 2014. 281:1015-1021.: Springer Verlag 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
Book Chapter
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.

Santos, TG, Oliveira JP, Machado MA.  2020.  Reliability and NDT Methods. Advanced Structured Materials. :265-295. Abstract

Composites are finding increased use in structural high demanding and high added value applications in advanced industries. A wide diversity exists in terms of matrix type, which can be either polymeric or metallic and type of reinforcements (ceramic, polymeric or metallic). Several technologies have been used to produce these composites; among them, additive manufacturing (AM) is currently being applied. In structural applications, the presence of defects due to fabrication is of major concern, since it affects the performance of a component with negative impact, which can affect, ultimately, human lives. Thus, the detection of defects is highly important, not only surface defects but also barely visible defects. This chapter describes the main types of defects expected in composites produced by AM. The fundamentals of different non-destructive testing (NDT) techniques are briefly discussed, as well as the state of the art of numerical simulation for several NDT techniques. A multiparametric and customized inspection system was developed based on the combination of innovative techniques in modelling and testing. Experimental validation with eddy currents, ultrasounds, X-ray and thermography is presented and analysed, as well as integration of distinctive techniques and 3D scanning characterization.

Conference Paper
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
Santos, T, Vilaça P, Reis L, Quintino L, De Freitas M.  2008.  Advances in NDT techniques for friction stir welding joints of AA2024, 2008. TMS 2008 Annual Meeting Supplemental: Materials Processing and Properties. 3:27-32., New Orleans, LA Abstract
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.

Santos, TG, Vilaça P, dos Santos J, Quintino L, Rosado L.  2010.  Innovative eddy current probe for micro defects, 2010. 36th Annual Review of Progress in Quantitative Nondestructive Evaluation, QNDE. 1211:377-384., Kingston, RI Abstract
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.

Rosado, L, Santos T, Piedade M, Ramos PM, Vilaça P.  2009.  New non-destructive test technique on metal inspection, 2009. 19th IMEKO World Congress 2009. 1:11-16., Lisbon Abstract
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
Rosado, LS, Ramos PM, Piedade M, Santos TG, Vilaça P.  2010.  A reconfigurable digital signal processing system for eddy currents non-destructive testing, 2010. 2010 IEEE International Instrumentation and Measurement Technology Conference, I2MTC 2010. :1284-1289., Austin, TX Abstract
Journal Article
Rosado, LS, Santos TG, Piedade M, Ramos PM, Vilaça P.  2010.  Advanced technique for non-destructive testing of friction stir welding of metals, 2010. Measurement: Journal of the International Measurement Confederation. 43(8):1021-1030. AbstractWebsite
Santos, TG, Fernandes FB, Bernardo G, Miranda RM.  2013.  Analyzing mechanical properties and nondestructive characteristics of brazed joints of NiTi shape memory alloys to carbon steel rods, 2013. International Journal of Advanced Manufacturing Technology. 66(5-8):787-793. AbstractWebsite
Santos, TG, Vilaça P, Quintino L, dos Santos J, Miranda RM.  2011.  Application of Eddy Current techniques to inspect friction spot welds in aluminium alloy AA2024 and a composite material, 2011. Welding in the World. 55(9-10):12-18. AbstractWebsite
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, 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
Santos, T, Vilaça P, Quintino L, dos Santos J.  2009.  Computational tools for modelling FSW and an improved tool for NDT, 2009. Welding in the World. 53(5-6):R99-R108. AbstractWebsite
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.

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