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Telmo G Santos

Universidade Nova de Lisboa, DEMI, Faculty Member

FCT / Universidade Nova de Lisboa, Departamento de Engenharia Mecânica e Industrial (DEMI), Faculty Member

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Telmo G. Santos, PhD in Mechanical Engineering, is an Associate Professor at the Department of Mechanical and Industrial Engineering (DEMI), NOVA School of Science and Technology of NOVA University of Lisbon (FCT NOVA) and a researcher at UNIDEMI. Author of about 50 publications with main expertise in Non-Destructive Testing (NDT) and Advanced Manufacturing (Additive manufacturing
Phone: 00351212948567
Address: Department of Mechanical and Industrial Engineering,
NOVA School of Science and Technology,
NOVA University Lisbon,
2829-516 Caparica,
Portugal.

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Papers by Telmo G Santos

Current Status and Perspectives on Wire and Arc Additive Manufacturing (WAAM)

Materials

Additive manufacturing has revolutionized the manufacturing paradigm in recent years due to the p... more Additive manufacturing has revolutionized the manufacturing paradigm in recent years due to the possibility of creating complex shaped three-dimensional parts which can be difficult or impossible to obtain by conventional manufacturing processes. Among the different additive manufacturing techniques, wire and arc additive manufacturing (WAAM) is suitable to produce large metallic parts owing to the high deposition rates achieved, which are significantly larger than powder-bed techniques, for example. The interest in WAAM is steadily increasing, and consequently, significant research efforts are underway. This review paper aims to provide an overview of the most significant achievements in WAAM, highlighting process developments and variants to control the microstructure, mechanical properties, and defect generation in the as-built parts; the most relevant engineering materials used; the main deposition strategies adopted to minimize residual stresses and the effect of post-processin...

Novel eddy current probes for pipes: application in austenitic round-in-square profiles of ITER

by Telmo G Santos and Miguel Machado

NDT & E International, 2017

Novel eddy current probes were developed to detect sub-millimetre defects with any orientation on... more 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.

Non-Destructive Testing Techniques for Detecting Imperfections in Friction Stir Welds of Aluminium Alloys

Aluminium Alloys, Theory and Applications, 2011

New method employing the electrical impedance for monitoring mechanical damage evolution in glass-reinforced: Applications to riveted joints

by Pamies Teixeira and Telmo G Santos

Materials and Design, 2012

and sharing with colleagues.

Developments in micro- and nano-defects detection using bacterial cells

by Luísa Quintino and Telmo G Santos

NDT & E International, 2016

This paper describes improvements to the NDT technique recently proposed, based on bacterial cell... more This paper describes improvements to the NDT technique recently proposed, based on bacterial cell suspensions to identify micro and nano surface defects. New bacterial strains were used with magnetic fields to improve bacteria mobility. Different materials and defect morphologies were tested, including nanoindentation defects, micro powder injection moulding components and micro laser welding. Nanoindentations with 0.6 μm depth and 5.3 μm side length were successfully detected. Bacterial cells allow identifying different topographic attributes of the surfaces, such as roughness. Cracks of about 0.5 μm wide and 10 μm depth in reference test block Type 1 were successfully detected.

Electrical conductivity field analysis of for evaluation of FSW joints in AA6013 and AA7075 alloys

by Telmo G Santos and Pedro Vilaça

Journal of Materials Processing Technology, 2011

To fully characterize Friction Stir Welding several techniques are required, mainly destructive, ... more To fully characterize Friction Stir Welding several techniques are required, mainly destructive, as hardness or metallographic testing. However, there is still a need for developing dedicated methods, preferably non-destructive. Electrical conductivity, based on a different physical principle, may constitute an alternative. The present study aims to characterize the electrical conductivity in friction stir welds and to investigate the correlation between this and the hardness observed in different regions of a weld. An eddy current planar probe was used for the measurements at different depths. For this, welded samples were machined in steps and in ramp and scans along orthogonal axis were performed. The results were correlated with the microstructural modifications. A close match between the electrical conductivity field and the microstructure was observed. A good correlation with hardness was noticed, suggesting that the non-destructive test has the potential to complement or substitute destructive methods as hardness tests.

A new NDT technique based on bacterial cells to detect micro surface defects

by Telmo G Santos and Carla C C R de Carvalho

NDT & E International, 2014

This paper presents a new NDT technique based on bacterial cell suspensions to identify surface m... more This paper presents a new NDT technique based on bacterial cell suspensions to identify surface micro defects in a procedure similar to the one used in dye penetrant. Validation was performed using Rhodococcus erythropolis bacteria in aluminum, steel and copper samples, studying the penetration, liquid removal and revelation stages and the phenomena involved in each one, as well as, bacteria/material interaction. A detectability limit was estimated and this was seen to depend on the material. Under the tested conditions defects with a depth of 4.3, 2.9 and 6.8 µm were identified in Al, steel and Cu, respectively.

Innovative concept and application of EC probe for inspection of friction stir welds

International Journal of Microstructure and Materials Properties, 2014

This paper addresses a new non-destructive testing (NDT) system composed by a planar eddy curren... more This paper addresses a new non-destructive testing (NDT) system
composed by a planar eddy currents (EC) probe (ionic probe), electronic
devices for signal generation, conditioning and conversion, automated
mechanised scanning, and analysis software. The ionic probe allows a
3D-induced current in the material and an easy interpretation of the signal
based on a comprehensible perturbation of the signal. This provides enhanced
lift-off immunity and improved sensitivity. The ionic system was developed
focussing micro-defects detection on aluminium alloys processed by FSW. The
experimental results in AA2024 welded by FSW clearly show that this system
is able to detect imperfections around 50 μm, which contribute to increasing
the reliability on NDT of micro-imperfections. EC conventional probes are
also applied as material characterisation technique. Results are compared to
micro-structural analysis, and hardness measurements show that EC can map the different zones, providing a deeper understanding on precipitate dispersion
and grain shape and size.

Advances in NDT and materials characterization by eddy currents

Procedia CIRP, 2013

New materials and production technologies demand improved non-destructive techniques for inspecti... more New materials and production technologies demand improved non-destructive techniques for inspection and defect evaluation, especially when critical safety applications are involved. In this paper a new non-destructive testing (NDT) system is presented. The innovative system is composed by a new type of eddy currents probe, electronic devices for signal generation, conditioning and conversion, automated mechanized scanning and analysis software. This new probe provides enhanced lift-off immunity and improved sensitivity for defects detection. The IOnic system was developed mostly to be used for the defects detection on aluminum solid state processed alloys as Friction Stir Welding (FSW) and Friction Spot Welding (FSpW), however recent studies revealed IOnic probe good capacities on other applications. This study evaluates the capacity of the IOnic probe on detecting buried defects under the surface of Graphite and Stainless steel AISI 304 alloys extending the probe application to other materials and defect morphologies. In order to evaluate its performance results, a comparison with results from conventional EC probes is discussed.

A New Dual Driver Planar Eddy Current Probe With Dynamically Controlled Induction Pattern

by Telmo G Santos and Moises Piedade

NDT & E International, 2014

ABSTRACT A new planar eddy current probe design is presented. This new concept is capable of dyna... more ABSTRACT A new planar eddy current probe design is presented. This new concept is capable of dynamically modify the induced eddy currents pattern in accordance with the operational non-destructive testing parameters is presented. The probe is composed by two orthogonally positioned driver traces and a set of sensing coils on each quadrant between the traces. Eddy currents result from the magnetic field contribution of the two driver traces and can be modified by changing the relative amplitude and phase of the currents flowing in the driver traces. Finite Element Modeling was used to simulate the eddy currents patterns and to predict the probe response to defects with different orientations. Experimental validation was carried using a prototype of the probe and artificial defects showing very good agreement with the Finite Element Modeling.

Surface reinforcement of AA5083-H111 by friction stir processing assisted by electrical current

by Telmo G Santos, Miguel Machado, and Nuno Lopes

Surface reinforcement of AA5083-H111 by friction stir processing assisted by electrical current, 2014

ABSTRACT This paper presents a variant of friction stir processing (FSP) assisted by electric cur... more ABSTRACT This paper presents a variant of friction stir processing (FSP) assisted by electric current for the production of surface composites in aluminium, reinforced with alumina particles. The main objective was to improve the overall material surface reinforcing process by using this variant. Numerical simulations were performed to study the electrical current density and flow patterns in the FSP tool, and in the processed zone. The FSP tool was adapted to the specificities of the application. The concept was experimentally validated by pre-placing alumina particles with median sizes of 45 μm, over AA5083-H111 plates and friction stir process these. Tests were performed with and without an electrical current of about 500 A for comparison purposes. The pre-deposition of alumina produced an increase in surface hardness of around 40%. Using this electrical current variant, a higher extension and depth of reinforced layer were observed, with an increase of about 500% and 40% in depth and in width, respectively, while the surface substrate hardness dropped by 10%. The particles were more uniformly distributed and sparser.

A reconfigurable digital signal processing system for eddy currents non-destructive testing

by Telmo G Santos and Moises Piedade

2010 IEEE International Instrumentation and Measurement Technology Conference, I2MTC 2010 - Proceedings, 2010

This paper presents a digital signal processing system specially designed for eddy currents non-d... more This paper presents a digital signal processing system specially designed for eddy currents non-destructive testing. This new system has a field programmable gate array based processing core, communication interfaces, data conversion and analog devices to interface the probes. Communication with personal computers is ensured by Ethernet 10/100 and universal serial bus 2.0 high speed interfaces. The proposed architecture enables to set several combinations of peripherals cards to generate or acquire probe signals. Also, the new system allows the digital generation and analysis of the probe signals through multiple digital signal processing algorithms.

A Non-Conventional Technique for Evaluating Welded Joints Based on the Electrical Conductivity

Key Engineering Materials, 2014

Recent studies showed that electrical conductivity is a valuable technique to identify the differ... more Recent studies showed that electrical conductivity is a valuable technique to identify the different zones of solid-state welded joints with a good correlation with the microstructure and hardness. This is a relevant result since this technique is expedite and, in some cases, non destructive. The concept was applied to other welding processes as the ones involving fusion and to a wide range of materials. For this, a comprehensive study was performed using friction stir welding, tungsten inert gas (TIG) and gas metal arc (MAG) welding processes in either bead on plate or butt joints in: carbon steel, magnesium and titanium. Eddy current non-destructive testing (NDT) was used to measure the electrical conductivity at different depths in transverse sections of the processed materials. The obtained profiles were compared to the hardness profiles in the same sections. As a result, a good correlation was observed in most materials welded by solid state and by fusion processes. The variation of the electrical conductivity closely follows the one detected in the hardness. Another interesting conclusion is that, even for fusion welding of carbon steels, the technique has potential to complement the hardness measurements and microstructural observations, allowing to identify the distinct zones of welds in materials commonly used in industry.

Data fusion in non destructive testing using fuzzy logic to evaluate friction stir welding

Welding International, 2008

Application of Eddy Currents in Processed Materials Structural Evaluation

Materials Science Forum, 2012

Eddy currents are based on electromagnetic induction and analysis of electrical currents on condu... more Eddy currents are based on electromagnetic induction and analysis of electrical currents on conductive materials. This method is used for thickness measurements, corrosion and defects detection, electrical conductivity and magnetic permeability measurements. Recently, it has been exploited as a materials characterization technique, namely in solid state welding, since, compared to hardness, it is based in distinct physical phenomena. Electrical conductivity is controlled by electronic mobility, while hardness depends on crystal defects and thus a scale factor exists. This paper presents results of this characterization technique applied to multipass solid state friction stir processing (FSP) of AA1100 alloy. These results were compared to microstructural analysis and hardness measurements and show that eddy current is a feasibly, reliable and expedite technique to characterize processed materials. The electrical conductivity measured by eddy currents, maps more precisely structural features, while hardness does not. Measurement of electrical conductivity field suggests having potential to constitute an alternative and/or complement to hardness evaluation with the further advantage of being a non-destructive method.

Innovative Eddy Current Probe for Micro Defects

AIP Conference Proceedings 1211, 377 (2010), 2010

This paper reports the development of an innovative eddy current (EC) probe, and its application ... more This paper reports the development of an innovative eddy current (EC) probe, and its application to micro‐defects on the root of the Friction Stir Welding (FSW). The new EC probe presents innovative concept issues, allowing 3D induced current in the material, and a lift‐off independence. Validation experiments were performed on aluminium alloys processed by FSW. The results clearly show that the new EC probe is able to detect and sizing surface defects about 60 microns depth.

Characterization of FSP by electrical conductivity

Surface Modification by Solid State Processing, 2014

This chapter presents a new technique for characterization of microstructures produced by solidst... more This chapter presents a new technique for characterization of microstructures produced by solidstate processing such as friction stir (FS), friction stir processing (FSP) or friction stir welding (FSW), based on electrical conductivity measurements. This characterization technique has been shown to be an expeditious method to assess the microstructural variations along the different material processing zones. The electrical conductivity can be correlated with the hardness with a good spatial resolution, and the two measuring techniques are complementary from the point of view of the phenomena and the area under analysis. In fact, electrical conductivity depends on the electron mobility, while hardness depends mostly on plastic deformation. On the other hand, hardness indentations can be of some micrometres, while the area under analysis is typically about 2 or 4 mm. The chapter also presents the fundamentals and the factors governing the electrical conductivity, the measuring approaches and some experimental results.

Application of Eddy Current Techniques to Inspect Friction Spot Welds In Aluminium Alloy AA2024 and a Composite Material

Welding in the World, 2011

New materials and production technologies demand improved non-destructive techniques for inspecti... more New materials and production technologies demand improved non-destructive techniques for inspection and defect evaluation, especially when critical safety applications are involved. In this paper two Non-destructive Testing (NDT) applications are presented: the inspection of Friction Spot Welding (FSpW) of AA2024-T351 with and without Alclad™ and a composite material GLAss-REinforced Fibre Metal Laminate (GLARE®) with artificial defects. The two applications were tested by Eddy Currents (EC), using both conventional planar spiral probes and a new EC probe developed by some of the authors, called lOnic probe. Four different FSpW conditions were produced and tested in 2 mm-thick plates of duraluminium with and without Alclad™. Three defects were introduced in GLARE® aiming to compare the reliability of the different NDT approaches. The experimental results show that the lOnic probe is able to identify different levels of FSpW quality regions by a distinctive perturbation on the output signal, whereas conventional probe cannot distinguish the different FSpW conditions. Regarding the GLARE® application, it was found that lOnic probe can detect the deeper defect easier than the conventional EC probe.

Developments in NDT for Detecting Imperfections in Friction Stir Welds in Aluminium Alloys

Welding in the World, 2008

Friction stir welding (FSW) has dramatically changed how aluminium alloys can be welded. The qual... more Friction stir welding (FSW) has dramatically changed how aluminium alloys can be welded. The quality of FS welds is usually excellent, but some imperfections periodically occur. The geometry, location, and microstructural nature of these imperfections bear no resemblance to the imperfections typically found in aluminium fusion welds. Consequently, it has been difficult to identify FS weld imperfections with common non-destructive testing (NDT) techniques. Therefore, further development of NDT techniques must be done to enable the detection of FS weld imperfections. This paper presents an integrated, on-line, NDT inspection system for FS welds, which employs a data fusion algorithm with fuzzy logic and fuzzy inference functions. It works by analyzing complementary and redundant data acquired from several NDT techniques (ultrasonic, Time of Flight Diffraction (ToFD), and eddy currents) to generate a synergistic effect that is used by the software to improve the confidence of detecting imperfections. The system was tested on friction stir welded AA5083-H111 specimens. The results indicate that by combining the output from various NDT processes, an improvement in finding imperfections can be obtained compared to using each NDT process individually. The methodology implemented in the QNDT_FSW system has given good results and improved reliability in the NDT of friction stir welds.

Computational Tools for Modelling FSW and an Improved Tool for NDT

Welding in the World, 2009

The good quality of Friction Stir Welding (FSW) joints enables the significant development of ind... more The good quality of Friction Stir Welding (FSW) joints enables the significant development of industrial applications of solid state welding technologies. This high quality standard is even more significant when FSW is compared to the fusion techniques. Nevertheless, in FSW joints some defects may arise which are very sensitive to small variations in some process parameters. Moreover, the results from computational modelling of the FSW are only valid for non-defective welds. Thus, in order for modelling of the process to contribute to the industrial consolidation of the FSW process, the experimental implementation results need to be supported by a reliable, Non-Destructive Testing (NDT) system. This work addresses an integrated scheme of two computational tools which enables the support of a faster establishment of process parameters, addressing the material flow analysis, with numerical coupling between fluid dynamics and solid mechanics; using the analytical iSTIR code; and a new, NDT, eddy currents probe, able to detect the typical FSW root imperfections.

Current Status and Perspectives on Wire and Arc Additive Manufacturing (WAAM)

Materials

Additive manufacturing has revolutionized the manufacturing paradigm in recent years due to the p... more Additive manufacturing has revolutionized the manufacturing paradigm in recent years due to the possibility of creating complex shaped three-dimensional parts which can be difficult or impossible to obtain by conventional manufacturing processes. Among the different additive manufacturing techniques, wire and arc additive manufacturing (WAAM) is suitable to produce large metallic parts owing to the high deposition rates achieved, which are significantly larger than powder-bed techniques, for example. The interest in WAAM is steadily increasing, and consequently, significant research efforts are underway. This review paper aims to provide an overview of the most significant achievements in WAAM, highlighting process developments and variants to control the microstructure, mechanical properties, and defect generation in the as-built parts; the most relevant engineering materials used; the main deposition strategies adopted to minimize residual stresses and the effect of post-processin...

Novel eddy current probes for pipes: application in austenitic round-in-square profiles of ITER

by Telmo G Santos and Miguel Machado

NDT & E International, 2017

Novel eddy current probes were developed to detect sub-millimetre defects with any orientation on... more 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.

Non-Destructive Testing Techniques for Detecting Imperfections in Friction Stir Welds of Aluminium Alloys

Aluminium Alloys, Theory and Applications, 2011

New method employing the electrical impedance for monitoring mechanical damage evolution in glass-reinforced: Applications to riveted joints

by Pamies Teixeira and Telmo G Santos

Materials and Design, 2012

and sharing with colleagues.

Developments in micro- and nano-defects detection using bacterial cells

by Luísa Quintino and Telmo G Santos

NDT & E International, 2016

This paper describes improvements to the NDT technique recently proposed, based on bacterial cell... more This paper describes improvements to the NDT technique recently proposed, based on bacterial cell suspensions to identify micro and nano surface defects. New bacterial strains were used with magnetic fields to improve bacteria mobility. Different materials and defect morphologies were tested, including nanoindentation defects, micro powder injection moulding components and micro laser welding. Nanoindentations with 0.6 μm depth and 5.3 μm side length were successfully detected. Bacterial cells allow identifying different topographic attributes of the surfaces, such as roughness. Cracks of about 0.5 μm wide and 10 μm depth in reference test block Type 1 were successfully detected.

Electrical conductivity field analysis of for evaluation of FSW joints in AA6013 and AA7075 alloys

by Telmo G Santos and Pedro Vilaça

Journal of Materials Processing Technology, 2011

To fully characterize Friction Stir Welding several techniques are required, mainly destructive, ... more To fully characterize Friction Stir Welding several techniques are required, mainly destructive, as hardness or metallographic testing. However, there is still a need for developing dedicated methods, preferably non-destructive. Electrical conductivity, based on a different physical principle, may constitute an alternative. The present study aims to characterize the electrical conductivity in friction stir welds and to investigate the correlation between this and the hardness observed in different regions of a weld. An eddy current planar probe was used for the measurements at different depths. For this, welded samples were machined in steps and in ramp and scans along orthogonal axis were performed. The results were correlated with the microstructural modifications. A close match between the electrical conductivity field and the microstructure was observed. A good correlation with hardness was noticed, suggesting that the non-destructive test has the potential to complement or substitute destructive methods as hardness tests.

A new NDT technique based on bacterial cells to detect micro surface defects

by Telmo G Santos and Carla C C R de Carvalho

NDT & E International, 2014

This paper presents a new NDT technique based on bacterial cell suspensions to identify surface m... more This paper presents a new NDT technique based on bacterial cell suspensions to identify surface micro defects in a procedure similar to the one used in dye penetrant. Validation was performed using Rhodococcus erythropolis bacteria in aluminum, steel and copper samples, studying the penetration, liquid removal and revelation stages and the phenomena involved in each one, as well as, bacteria/material interaction. A detectability limit was estimated and this was seen to depend on the material. Under the tested conditions defects with a depth of 4.3, 2.9 and 6.8 µm were identified in Al, steel and Cu, respectively.

Innovative concept and application of EC probe for inspection of friction stir welds

International Journal of Microstructure and Materials Properties, 2014

This paper addresses a new non-destructive testing (NDT) system composed by a planar eddy curren... more This paper addresses a new non-destructive testing (NDT) system
composed by a planar eddy currents (EC) probe (ionic probe), electronic
devices for signal generation, conditioning and conversion, automated
mechanised scanning, and analysis software. The ionic probe allows a
3D-induced current in the material and an easy interpretation of the signal
based on a comprehensible perturbation of the signal. This provides enhanced
lift-off immunity and improved sensitivity. The ionic system was developed
focussing micro-defects detection on aluminium alloys processed by FSW. The
experimental results in AA2024 welded by FSW clearly show that this system
is able to detect imperfections around 50 μm, which contribute to increasing
the reliability on NDT of micro-imperfections. EC conventional probes are
also applied as material characterisation technique. Results are compared to
micro-structural analysis, and hardness measurements show that EC can map the different zones, providing a deeper understanding on precipitate dispersion
and grain shape and size.

Advances in NDT and materials characterization by eddy currents

Procedia CIRP, 2013

New materials and production technologies demand improved non-destructive techniques for inspecti... more New materials and production technologies demand improved non-destructive techniques for inspection and defect evaluation, especially when critical safety applications are involved. In this paper a new non-destructive testing (NDT) system is presented. The innovative system is composed by a new type of eddy currents probe, electronic devices for signal generation, conditioning and conversion, automated mechanized scanning and analysis software. This new probe provides enhanced lift-off immunity and improved sensitivity for defects detection. The IOnic system was developed mostly to be used for the defects detection on aluminum solid state processed alloys as Friction Stir Welding (FSW) and Friction Spot Welding (FSpW), however recent studies revealed IOnic probe good capacities on other applications. This study evaluates the capacity of the IOnic probe on detecting buried defects under the surface of Graphite and Stainless steel AISI 304 alloys extending the probe application to other materials and defect morphologies. In order to evaluate its performance results, a comparison with results from conventional EC probes is discussed.

A New Dual Driver Planar Eddy Current Probe With Dynamically Controlled Induction Pattern

by Telmo G Santos and Moises Piedade

NDT & E International, 2014

ABSTRACT A new planar eddy current probe design is presented. This new concept is capable of dyna... more ABSTRACT A new planar eddy current probe design is presented. This new concept is capable of dynamically modify the induced eddy currents pattern in accordance with the operational non-destructive testing parameters is presented. The probe is composed by two orthogonally positioned driver traces and a set of sensing coils on each quadrant between the traces. Eddy currents result from the magnetic field contribution of the two driver traces and can be modified by changing the relative amplitude and phase of the currents flowing in the driver traces. Finite Element Modeling was used to simulate the eddy currents patterns and to predict the probe response to defects with different orientations. Experimental validation was carried using a prototype of the probe and artificial defects showing very good agreement with the Finite Element Modeling.

Surface reinforcement of AA5083-H111 by friction stir processing assisted by electrical current

by Telmo G Santos, Miguel Machado, and Nuno Lopes

Surface reinforcement of AA5083-H111 by friction stir processing assisted by electrical current, 2014

ABSTRACT This paper presents a variant of friction stir processing (FSP) assisted by electric cur... more ABSTRACT This paper presents a variant of friction stir processing (FSP) assisted by electric current for the production of surface composites in aluminium, reinforced with alumina particles. The main objective was to improve the overall material surface reinforcing process by using this variant. Numerical simulations were performed to study the electrical current density and flow patterns in the FSP tool, and in the processed zone. The FSP tool was adapted to the specificities of the application. The concept was experimentally validated by pre-placing alumina particles with median sizes of 45 μm, over AA5083-H111 plates and friction stir process these. Tests were performed with and without an electrical current of about 500 A for comparison purposes. The pre-deposition of alumina produced an increase in surface hardness of around 40%. Using this electrical current variant, a higher extension and depth of reinforced layer were observed, with an increase of about 500% and 40% in depth and in width, respectively, while the surface substrate hardness dropped by 10%. The particles were more uniformly distributed and sparser.

A reconfigurable digital signal processing system for eddy currents non-destructive testing

by Telmo G Santos and Moises Piedade

2010 IEEE International Instrumentation and Measurement Technology Conference, I2MTC 2010 - Proceedings, 2010

This paper presents a digital signal processing system specially designed for eddy currents non-d... more This paper presents a digital signal processing system specially designed for eddy currents non-destructive testing. This new system has a field programmable gate array based processing core, communication interfaces, data conversion and analog devices to interface the probes. Communication with personal computers is ensured by Ethernet 10/100 and universal serial bus 2.0 high speed interfaces. The proposed architecture enables to set several combinations of peripherals cards to generate or acquire probe signals. Also, the new system allows the digital generation and analysis of the probe signals through multiple digital signal processing algorithms.

A Non-Conventional Technique for Evaluating Welded Joints Based on the Electrical Conductivity

Key Engineering Materials, 2014

Recent studies showed that electrical conductivity is a valuable technique to identify the differ... more Recent studies showed that electrical conductivity is a valuable technique to identify the different zones of solid-state welded joints with a good correlation with the microstructure and hardness. This is a relevant result since this technique is expedite and, in some cases, non destructive. The concept was applied to other welding processes as the ones involving fusion and to a wide range of materials. For this, a comprehensive study was performed using friction stir welding, tungsten inert gas (TIG) and gas metal arc (MAG) welding processes in either bead on plate or butt joints in: carbon steel, magnesium and titanium. Eddy current non-destructive testing (NDT) was used to measure the electrical conductivity at different depths in transverse sections of the processed materials. The obtained profiles were compared to the hardness profiles in the same sections. As a result, a good correlation was observed in most materials welded by solid state and by fusion processes. The variation of the electrical conductivity closely follows the one detected in the hardness. Another interesting conclusion is that, even for fusion welding of carbon steels, the technique has potential to complement the hardness measurements and microstructural observations, allowing to identify the distinct zones of welds in materials commonly used in industry.

Data fusion in non destructive testing using fuzzy logic to evaluate friction stir welding

Welding International, 2008

Application of Eddy Currents in Processed Materials Structural Evaluation

Materials Science Forum, 2012

Eddy currents are based on electromagnetic induction and analysis of electrical currents on condu... more Eddy currents are based on electromagnetic induction and analysis of electrical currents on conductive materials. This method is used for thickness measurements, corrosion and defects detection, electrical conductivity and magnetic permeability measurements. Recently, it has been exploited as a materials characterization technique, namely in solid state welding, since, compared to hardness, it is based in distinct physical phenomena. Electrical conductivity is controlled by electronic mobility, while hardness depends on crystal defects and thus a scale factor exists. This paper presents results of this characterization technique applied to multipass solid state friction stir processing (FSP) of AA1100 alloy. These results were compared to microstructural analysis and hardness measurements and show that eddy current is a feasibly, reliable and expedite technique to characterize processed materials. The electrical conductivity measured by eddy currents, maps more precisely structural features, while hardness does not. Measurement of electrical conductivity field suggests having potential to constitute an alternative and/or complement to hardness evaluation with the further advantage of being a non-destructive method.

Innovative Eddy Current Probe for Micro Defects

AIP Conference Proceedings 1211, 377 (2010), 2010

This paper reports the development of an innovative eddy current (EC) probe, and its application ... more This paper reports the development of an innovative eddy current (EC) probe, and its application to micro‐defects on the root of the Friction Stir Welding (FSW). The new EC probe presents innovative concept issues, allowing 3D induced current in the material, and a lift‐off independence. Validation experiments were performed on aluminium alloys processed by FSW. The results clearly show that the new EC probe is able to detect and sizing surface defects about 60 microns depth.

Characterization of FSP by electrical conductivity

Surface Modification by Solid State Processing, 2014

This chapter presents a new technique for characterization of microstructures produced by solidst... more This chapter presents a new technique for characterization of microstructures produced by solidstate processing such as friction stir (FS), friction stir processing (FSP) or friction stir welding (FSW), based on electrical conductivity measurements. This characterization technique has been shown to be an expeditious method to assess the microstructural variations along the different material processing zones. The electrical conductivity can be correlated with the hardness with a good spatial resolution, and the two measuring techniques are complementary from the point of view of the phenomena and the area under analysis. In fact, electrical conductivity depends on the electron mobility, while hardness depends mostly on plastic deformation. On the other hand, hardness indentations can be of some micrometres, while the area under analysis is typically about 2 or 4 mm. The chapter also presents the fundamentals and the factors governing the electrical conductivity, the measuring approaches and some experimental results.

Application of Eddy Current Techniques to Inspect Friction Spot Welds In Aluminium Alloy AA2024 and a Composite Material

Welding in the World, 2011

New materials and production technologies demand improved non-destructive techniques for inspecti... more New materials and production technologies demand improved non-destructive techniques for inspection and defect evaluation, especially when critical safety applications are involved. In this paper two Non-destructive Testing (NDT) applications are presented: the inspection of Friction Spot Welding (FSpW) of AA2024-T351 with and without Alclad™ and a composite material GLAss-REinforced Fibre Metal Laminate (GLARE®) with artificial defects. The two applications were tested by Eddy Currents (EC), using both conventional planar spiral probes and a new EC probe developed by some of the authors, called lOnic probe. Four different FSpW conditions were produced and tested in 2 mm-thick plates of duraluminium with and without Alclad™. Three defects were introduced in GLARE® aiming to compare the reliability of the different NDT approaches. The experimental results show that the lOnic probe is able to identify different levels of FSpW quality regions by a distinctive perturbation on the output signal, whereas conventional probe cannot distinguish the different FSpW conditions. Regarding the GLARE® application, it was found that lOnic probe can detect the deeper defect easier than the conventional EC probe.

Developments in NDT for Detecting Imperfections in Friction Stir Welds in Aluminium Alloys

Welding in the World, 2008

Friction stir welding (FSW) has dramatically changed how aluminium alloys can be welded. The qual... more Friction stir welding (FSW) has dramatically changed how aluminium alloys can be welded. The quality of FS welds is usually excellent, but some imperfections periodically occur. The geometry, location, and microstructural nature of these imperfections bear no resemblance to the imperfections typically found in aluminium fusion welds. Consequently, it has been difficult to identify FS weld imperfections with common non-destructive testing (NDT) techniques. Therefore, further development of NDT techniques must be done to enable the detection of FS weld imperfections. This paper presents an integrated, on-line, NDT inspection system for FS welds, which employs a data fusion algorithm with fuzzy logic and fuzzy inference functions. It works by analyzing complementary and redundant data acquired from several NDT techniques (ultrasonic, Time of Flight Diffraction (ToFD), and eddy currents) to generate a synergistic effect that is used by the software to improve the confidence of detecting imperfections. The system was tested on friction stir welded AA5083-H111 specimens. The results indicate that by combining the output from various NDT processes, an improvement in finding imperfections can be obtained compared to using each NDT process individually. The methodology implemented in the QNDT_FSW system has given good results and improved reliability in the NDT of friction stir welds.

Computational Tools for Modelling FSW and an Improved Tool for NDT

Welding in the World, 2009

The good quality of Friction Stir Welding (FSW) joints enables the significant development of ind... more The good quality of Friction Stir Welding (FSW) joints enables the significant development of industrial applications of solid state welding technologies. This high quality standard is even more significant when FSW is compared to the fusion techniques. Nevertheless, in FSW joints some defects may arise which are very sensitive to small variations in some process parameters. Moreover, the results from computational modelling of the FSW are only valid for non-defective welds. Thus, in order for modelling of the process to contribute to the industrial consolidation of the FSW process, the experimental implementation results need to be supported by a reliable, Non-Destructive Testing (NDT) system. This work addresses an integrated scheme of two computational tools which enables the support of a faster establishment of process parameters, addressing the material flow analysis, with numerical coupling between fluid dynamics and solid mechanics; using the analytical iSTIR code; and a new, NDT, eddy currents probe, able to detect the typical FSW root imperfections.