Paolo Ferro - Academia.edu (original) (raw)

Papers by Paolo Ferro

MATEC Web of Conferences

As a primary failure mechanism, fatigue failure of additively manufactured metallic parts has att... more As a primary failure mechanism, fatigue failure of additively manufactured metallic parts has attracted considerable attention in both aerospace and biomedical applications. According to some specific design requirements, the majority of engineering components and structures contain notches of different shapes. Due to the intensive stresses around the notches, they are prone to crack nucleation. In this research, LENS (Laser Engineered Net Shaping) technology is used to fabricate Ti-6Al-4V semi-circular notched specimens. The fatigue analyses were performed to contribute to the fundamental understanding of the mechanical/cracking behaviour of additively manufactured LENS Ti-6Al-4V specimens weakened by semi-circular notches and subject to fatigue loading.

Advances in Materials Science and Engineering

In the present study, distortion and residual stresses in the multipass welded joint were analyze... more In the present study, distortion and residual stresses in the multipass welded joint were analyzed with respect to heat input. The welded joint was produced using the gas tungsten arc welding (GTAW) process with dissimilar Ni-based filler of ERNiCrMo-3. This dissimilar joint is essential in power generating nuclear and thermal plants operating at elevated temperatures. The distortion and residual stress measurements were taken using the Vernier height gauge and XRD method. To evaluate the mechanical properties, tensile testing was carried out at room temperature. The welded joint qualified the tensile test with an average value of 593 MPa. In the weld metal, a significant variation of residual stresses is measured on the top surface of the weldment along with the thickness with peak magnitude of 145 MPa to 180 MPa at the fusion zone.

Advances in Materials Science and Engineering

Additive manufacturing is one of the fastest-growing fields in materials engineering. This is bec... more Additive manufacturing is one of the fastest-growing fields in materials engineering. This is because there is a new trend for custom, high-precision, and on-demand manufacturing. The undesired residual stress induced in the components during layer-by-layer melting and solidification of the metal powder is an important issue related to the selective laser melting (SLM) process that needs to be studied deeply. These stresses may impair mechanical performance and potentially result in premature failure. As a result, a thorough knowledge of residual stress is crucial for improved component dependability. By keeping constant process parameters, samples were produced with a difference in the scanning method. Results indicate that the defect-free parts are manufactured in all the four patterns used, and the self-balanced residual stresses are within the safe limits of yield strength.

Data for: Materials Selection in a Critical Raw Materials Perspective

Data in excel format used to create material maps

Caratterizzazione Multiscala DI Leghe ALSI9CU3(FE) Pressocolate Dopo Alligazione Con Cu, MG, ZN e SR

Influenza della diversa metodologia di produzione di leghe preziose (graniglia/piastrina) sulle proprietà di prodotti per protesi dentarie. Test di adesione materiale ceramico-lega preziosa

Materials, 2021

Approaches based on calculating Residual Notch Stress Intensity Factors (R-NSIFs) assume the weld... more Approaches based on calculating Residual Notch Stress Intensity Factors (R-NSIFs) assume the weld toe to be a sharp V-notch that gives rise to a residual singular stress distribution close to the weld toe. Once R-NSIFs are determined, they might be included in local fatigue criteria for the structural strength assessment of welded joints based on NSIFs due to external cyclic loading. However, the numerical calculation of R-NSIFs through finite element (FE) simulations of the welding process requires extremely refined meshes to properly capture the residual stress singularity. In this context, the Peak Stress Method (PSM) has recently been adopted to estimate R-NSIFs due to residual stresses by means of coarse meshes of 2D 4-node plane or 3D 8-node brick elements. The aim of this work is to investigate the applicability of the PSM to estimate R-NSIFs in a butt-welded joint using coarse meshes of 3D 10-node tetra elements. The R-NSIF distribution at the weld toe line is estimated by a...

Advances in Materials Science and Engineering, 2021

Thermal and residual stress distributions induced by the gas tungsten arc welding (GTAW) process ... more Thermal and residual stress distributions induced by the gas tungsten arc welding (GTAW) process on Inconel 625 were studied using numerical simulation and experiments. A multi-pass welding model was developed that uses a volumetric heat source. Thermomechanical analysis is carried out to assess the Thermal and residual stress distributions. Experiments were carried out with 5 mm thick Inconel 625 plates. X-ray diffraction techniques were used to measure residual stresses, and IR thermometry was employed to capture the temperature values on the welded joints. Simulations were performed with ANSYS numerical code, and a close agreement was found between the predicted and experimentally measured residual stress. Thermal measurements were collected pass by pass from the analysis, and the agreement was 9.08%. The agreement between the measured and analysed residual stress was 11%.

International Journal of Physics Research and Applications, 2020

Circular Economy, Sustainability, Design for Environment are some of the keywords that identify n... more Circular Economy, Sustainability, Design for Environment are some of the keywords that identify new formidable challenges to be faced in the next years. Raw materials have a dominant role in reaching that goal. Green energy, electric vehicles, communication, etc. depends on raw materials labeled as critical because of their economic importance coupled with high supply risk. For this reason, mitigating actions need to be used in materials selection and design such as material substitution, improved materials effi ciency and recycling. In this technical communication, a method to implement raw materials criticality issues in materials selection is described according to the recent literature. The strategy is based on Ashby's approach and the defi nition of the alloy criticality index quantifying the criticality per unit of mass of the material.

Fatigue & Fracture of Engineering Materials & Structures, 2017

According to the recent literature, the intensity of linear elastic residual stress fields near t... more According to the recent literature, the intensity of linear elastic residual stress fields near the toe region of a welded joint can be quantified by the residual notch stress intensity factors (R-NSIFs). The computational effort required to compute the R-NSIFs implies strong limitations of applicability in practice, owing to the very refined meshes needed and to the non-linear transient nature of welding process simulations, especially in 3-dimensional numerical models of large structures. The peak stress method (PSM) is a design approach that takes care of the industrial needs of rapidity and ease of use. According to the PSM, it is possible to evaluate the R-NSIFs by using the peak stress calculated at the point of singularity with coarse finite element (FE) models. While the PSM was originally calibrated by using the Ansys FE code, in the present contribution, the PSM has been calibrated to rapidly estimate the R-NSIFs in the Sysweld FE environment.

International Journal of Metalcasting, 2018

Designers often need to know the mechanical properties of different zones of a casting. This is b... more Designers often need to know the mechanical properties of different zones of a casting. This is because such properties are often very different from those declared in the standard classification of the cast iron used or derived from separately cast specimens. At constant chemical composition, the mechanical properties of a casting will depend on the microstructure, which in turn is ruled by the cooling rate at each point of the component. In this work, a method developed to rapidly predict mechanical properties in each zone of a cast iron casting, which uses only results from moulding-solidification numerical simulation, is proposed. Such approach, applied to real cast irons components, was found to be in tune with experimental results.

Theoretical and Applied Fracture Mechanics, Jun 1, 2016

If a weld toe is modelled as a sharp V-notch angle, the stress distribution near the notch tip is... more If a weld toe is modelled as a sharp V-notch angle, the stress distribution near the notch tip is singular. Its intensity can then be quantified by means of Notch Stress Intensity Factors (NSIF), which have been proven to be capable of summarizing the high-cycle fatigue strength of welded joints having very different global and local geometries. When a singular residual stress field induced during solidification of the fusion zone near the weld toe, the local load ratio is modified making the fatigue strength sensitive to residual stresses in the high-cycle regime. However, for an accurate estimation of the fatigue performance of welded joints, it is necessary to consider not only the initial residual stress field but also its variation under load, as both of these may play an important role. In this work the effect of fatigue loading on the asymptotic residual stress redistribution near the weld toe of a butt-welded joint is studied by means of numerical simulations. A model is then proposed to estimate the influence of residual stresses on the fatigue strength of welded joints. Experimental results taken from the literature were found in good agreement with those predicted by the proposed model.

Quantitative analyses on geometric shape effect of microdefect on fatigue accumulation in 316L stainless steel

Engineering Fracture Mechanics

Tuning lamellar structure distribution around elliptical notch in Ti-6Al-4V for fatigue performance

Procedia Structural Integrity

Acta Metallurgica Slovaca, 2021

It is well known that pitting corrosion resistance of duplex and superduplex stainless steels str... more It is well known that pitting corrosion resistance of duplex and superduplex stainless steels strongly depends on microstructural characteristics such as ferrite/austenite proportion, presence of intermetallic phases and elemental partitioning between the austenite and ferrite phases. In particular, during the welding operation, very fine chromium nitrides may precipitate within ferrite grains of the heat affected zone drastically reducing the corrosion resistance of welded joints of duplex and super duplex stainless steels. However, due to their small size and low distribution, analyzing the chemical composition and crystallography of chromium nitrides is quite difficult and only a restricted number of advanced techniques of investigation may discriminate their signal from the surrounding matrix. This work is aimed at supporting the microstructural characterization of a welded joint of a superduplex stainless steel by means of a field-emission gun scanning electron microscope. Sub-...

High Density AlSi10Mg Aluminium Alloy Specimens Obtained by Selective Laser Melting

Lecture Notes in Mechanical Engineering, 2019

Additive manufacturing technology offers new design possibilities compared to traditional casting... more Additive manufacturing technology offers new design possibilities compared to traditional casting processes applied to metallic materials. Not only there are no limits in shape, but a higher microstructure control is allowed compared to traditional processes. Irrespective of the sample dimensions, the solidification defects induced by SLM process depend only on process parameters and do not vary from zone to zone of the component like in a casting component: the higher the casting dimensions and thickness variations, the lower the microstructure homogeneity resulting from different cooling conditions inside the casting itself.

L’applicazione delle vibrazioni meccaniche a uno stampo durante la fase di solidificazione e cert... more L’applicazione delle vibrazioni meccaniche a uno stampo durante la fase di solidificazione e certamente uno strumento per il controllo della microstruttura e quindi delle caratteristiche finali di un getto. Nel presente lavoro, viene descritta l’evoluzione microstrutturale di una lega AlSi9Cu3 rafforzata con il 10vol.% di SiCp e solidificata in presenza di vibrazioni meccaniche indotte su uno stampo metallico. Il materiale e stato colato in presenza di vibrazioni nell’intervallo di accelerazione compreso tra 0 e 41 volte l’accelerazione di gravita. L’applicazione delle vibrazioni meccaniche ha provocato una dispersione delle particelle di SiC ragionevolmente omogenea su scala macroscopica. Tale miglioramento nella distribuzione del rinforzo e risultato osservabile fino a valori di accelerazione di 10g. Con accelerazione superiori, si sono rilevati fenomeni di segregazione e la formazione di grosse cavita interne ai getti colati. Su scala microscopica, le tecniche di analisi d’immagi...

Solderability in tunnel furnace of Silver alloys parts and influence on subsequent remelting

Materials, 2020

Hybrid Metal Extrusion and Bonding (HYB) is a novel solid-state welding method for metals and all... more Hybrid Metal Extrusion and Bonding (HYB) is a novel solid-state welding method for metals and alloys that utilises continuous extrusion as a technique to enable aluminium filler metal additions. In the present study, a new semi-analytical model for the heat generation during aluminium butt welding is presented. As a starting point, the classical Rosenthal thin plate solution for the pseudo-steady-state temperature distribution around a fully penetrating line source is invoked. Then, the associated heat generation is calculated by considering the individual contributions from the tip of the rotating pin, the pin shoulder, and the filler metal additions on the net power input. In a calibrated form, the model yields thermal efficiency factors that are in close agreement with those obtained from more sophisticated finite element analyses but with considerably less computational effort.

Materials, 2021

An analytical model is proposed to rapidly capture the thermal and residual stresses values induc... more An analytical model is proposed to rapidly capture the thermal and residual stresses values induced by the hybrid metal extrusion and bonding (HYB) process on dissimilar-metal butt-welded joints. The power input for two welding velocities is first assessed using a thermal–mechanical model solved by a heat generation routine written in MATLAB code. Subsequently, the obtained temperature history is used as input to solve the equilibrium and compatibility equations formulated to calculate the thermal and residual stresses. To verify the soundness of the analytical approach, a Finite Element numerical model of the entire process is carried out and results are compared with those coming from the proposed rapid method. It is found that the degree of accuracy reached by the analytical model is excellent, especially considering the tremendous time reduction when compared to that characterizing the standard numerical approach.

MATEC Web of Conferences

As a primary failure mechanism, fatigue failure of additively manufactured metallic parts has att... more As a primary failure mechanism, fatigue failure of additively manufactured metallic parts has attracted considerable attention in both aerospace and biomedical applications. According to some specific design requirements, the majority of engineering components and structures contain notches of different shapes. Due to the intensive stresses around the notches, they are prone to crack nucleation. In this research, LENS (Laser Engineered Net Shaping) technology is used to fabricate Ti-6Al-4V semi-circular notched specimens. The fatigue analyses were performed to contribute to the fundamental understanding of the mechanical/cracking behaviour of additively manufactured LENS Ti-6Al-4V specimens weakened by semi-circular notches and subject to fatigue loading.

Advances in Materials Science and Engineering

In the present study, distortion and residual stresses in the multipass welded joint were analyze... more In the present study, distortion and residual stresses in the multipass welded joint were analyzed with respect to heat input. The welded joint was produced using the gas tungsten arc welding (GTAW) process with dissimilar Ni-based filler of ERNiCrMo-3. This dissimilar joint is essential in power generating nuclear and thermal plants operating at elevated temperatures. The distortion and residual stress measurements were taken using the Vernier height gauge and XRD method. To evaluate the mechanical properties, tensile testing was carried out at room temperature. The welded joint qualified the tensile test with an average value of 593 MPa. In the weld metal, a significant variation of residual stresses is measured on the top surface of the weldment along with the thickness with peak magnitude of 145 MPa to 180 MPa at the fusion zone.

Advances in Materials Science and Engineering

Additive manufacturing is one of the fastest-growing fields in materials engineering. This is bec... more Additive manufacturing is one of the fastest-growing fields in materials engineering. This is because there is a new trend for custom, high-precision, and on-demand manufacturing. The undesired residual stress induced in the components during layer-by-layer melting and solidification of the metal powder is an important issue related to the selective laser melting (SLM) process that needs to be studied deeply. These stresses may impair mechanical performance and potentially result in premature failure. As a result, a thorough knowledge of residual stress is crucial for improved component dependability. By keeping constant process parameters, samples were produced with a difference in the scanning method. Results indicate that the defect-free parts are manufactured in all the four patterns used, and the self-balanced residual stresses are within the safe limits of yield strength.

Data for: Materials Selection in a Critical Raw Materials Perspective

Data in excel format used to create material maps

Caratterizzazione Multiscala DI Leghe ALSI9CU3(FE) Pressocolate Dopo Alligazione Con Cu, MG, ZN e SR

Influenza della diversa metodologia di produzione di leghe preziose (graniglia/piastrina) sulle proprietà di prodotti per protesi dentarie. Test di adesione materiale ceramico-lega preziosa

Materials, 2021

Approaches based on calculating Residual Notch Stress Intensity Factors (R-NSIFs) assume the weld... more Approaches based on calculating Residual Notch Stress Intensity Factors (R-NSIFs) assume the weld toe to be a sharp V-notch that gives rise to a residual singular stress distribution close to the weld toe. Once R-NSIFs are determined, they might be included in local fatigue criteria for the structural strength assessment of welded joints based on NSIFs due to external cyclic loading. However, the numerical calculation of R-NSIFs through finite element (FE) simulations of the welding process requires extremely refined meshes to properly capture the residual stress singularity. In this context, the Peak Stress Method (PSM) has recently been adopted to estimate R-NSIFs due to residual stresses by means of coarse meshes of 2D 4-node plane or 3D 8-node brick elements. The aim of this work is to investigate the applicability of the PSM to estimate R-NSIFs in a butt-welded joint using coarse meshes of 3D 10-node tetra elements. The R-NSIF distribution at the weld toe line is estimated by a...

Advances in Materials Science and Engineering, 2021

Thermal and residual stress distributions induced by the gas tungsten arc welding (GTAW) process ... more Thermal and residual stress distributions induced by the gas tungsten arc welding (GTAW) process on Inconel 625 were studied using numerical simulation and experiments. A multi-pass welding model was developed that uses a volumetric heat source. Thermomechanical analysis is carried out to assess the Thermal and residual stress distributions. Experiments were carried out with 5 mm thick Inconel 625 plates. X-ray diffraction techniques were used to measure residual stresses, and IR thermometry was employed to capture the temperature values on the welded joints. Simulations were performed with ANSYS numerical code, and a close agreement was found between the predicted and experimentally measured residual stress. Thermal measurements were collected pass by pass from the analysis, and the agreement was 9.08%. The agreement between the measured and analysed residual stress was 11%.

International Journal of Physics Research and Applications, 2020

Circular Economy, Sustainability, Design for Environment are some of the keywords that identify n... more Circular Economy, Sustainability, Design for Environment are some of the keywords that identify new formidable challenges to be faced in the next years. Raw materials have a dominant role in reaching that goal. Green energy, electric vehicles, communication, etc. depends on raw materials labeled as critical because of their economic importance coupled with high supply risk. For this reason, mitigating actions need to be used in materials selection and design such as material substitution, improved materials effi ciency and recycling. In this technical communication, a method to implement raw materials criticality issues in materials selection is described according to the recent literature. The strategy is based on Ashby's approach and the defi nition of the alloy criticality index quantifying the criticality per unit of mass of the material.

Fatigue & Fracture of Engineering Materials & Structures, 2017

According to the recent literature, the intensity of linear elastic residual stress fields near t... more According to the recent literature, the intensity of linear elastic residual stress fields near the toe region of a welded joint can be quantified by the residual notch stress intensity factors (R-NSIFs). The computational effort required to compute the R-NSIFs implies strong limitations of applicability in practice, owing to the very refined meshes needed and to the non-linear transient nature of welding process simulations, especially in 3-dimensional numerical models of large structures. The peak stress method (PSM) is a design approach that takes care of the industrial needs of rapidity and ease of use. According to the PSM, it is possible to evaluate the R-NSIFs by using the peak stress calculated at the point of singularity with coarse finite element (FE) models. While the PSM was originally calibrated by using the Ansys FE code, in the present contribution, the PSM has been calibrated to rapidly estimate the R-NSIFs in the Sysweld FE environment.

International Journal of Metalcasting, 2018

Designers often need to know the mechanical properties of different zones of a casting. This is b... more Designers often need to know the mechanical properties of different zones of a casting. This is because such properties are often very different from those declared in the standard classification of the cast iron used or derived from separately cast specimens. At constant chemical composition, the mechanical properties of a casting will depend on the microstructure, which in turn is ruled by the cooling rate at each point of the component. In this work, a method developed to rapidly predict mechanical properties in each zone of a cast iron casting, which uses only results from moulding-solidification numerical simulation, is proposed. Such approach, applied to real cast irons components, was found to be in tune with experimental results.

Theoretical and Applied Fracture Mechanics, Jun 1, 2016

If a weld toe is modelled as a sharp V-notch angle, the stress distribution near the notch tip is... more If a weld toe is modelled as a sharp V-notch angle, the stress distribution near the notch tip is singular. Its intensity can then be quantified by means of Notch Stress Intensity Factors (NSIF), which have been proven to be capable of summarizing the high-cycle fatigue strength of welded joints having very different global and local geometries. When a singular residual stress field induced during solidification of the fusion zone near the weld toe, the local load ratio is modified making the fatigue strength sensitive to residual stresses in the high-cycle regime. However, for an accurate estimation of the fatigue performance of welded joints, it is necessary to consider not only the initial residual stress field but also its variation under load, as both of these may play an important role. In this work the effect of fatigue loading on the asymptotic residual stress redistribution near the weld toe of a butt-welded joint is studied by means of numerical simulations. A model is then proposed to estimate the influence of residual stresses on the fatigue strength of welded joints. Experimental results taken from the literature were found in good agreement with those predicted by the proposed model.

Quantitative analyses on geometric shape effect of microdefect on fatigue accumulation in 316L stainless steel

Engineering Fracture Mechanics

Tuning lamellar structure distribution around elliptical notch in Ti-6Al-4V for fatigue performance

Procedia Structural Integrity

Acta Metallurgica Slovaca, 2021

It is well known that pitting corrosion resistance of duplex and superduplex stainless steels str... more It is well known that pitting corrosion resistance of duplex and superduplex stainless steels strongly depends on microstructural characteristics such as ferrite/austenite proportion, presence of intermetallic phases and elemental partitioning between the austenite and ferrite phases. In particular, during the welding operation, very fine chromium nitrides may precipitate within ferrite grains of the heat affected zone drastically reducing the corrosion resistance of welded joints of duplex and super duplex stainless steels. However, due to their small size and low distribution, analyzing the chemical composition and crystallography of chromium nitrides is quite difficult and only a restricted number of advanced techniques of investigation may discriminate their signal from the surrounding matrix. This work is aimed at supporting the microstructural characterization of a welded joint of a superduplex stainless steel by means of a field-emission gun scanning electron microscope. Sub-...

High Density AlSi10Mg Aluminium Alloy Specimens Obtained by Selective Laser Melting

Lecture Notes in Mechanical Engineering, 2019

Additive manufacturing technology offers new design possibilities compared to traditional casting... more Additive manufacturing technology offers new design possibilities compared to traditional casting processes applied to metallic materials. Not only there are no limits in shape, but a higher microstructure control is allowed compared to traditional processes. Irrespective of the sample dimensions, the solidification defects induced by SLM process depend only on process parameters and do not vary from zone to zone of the component like in a casting component: the higher the casting dimensions and thickness variations, the lower the microstructure homogeneity resulting from different cooling conditions inside the casting itself.

L’applicazione delle vibrazioni meccaniche a uno stampo durante la fase di solidificazione e cert... more L’applicazione delle vibrazioni meccaniche a uno stampo durante la fase di solidificazione e certamente uno strumento per il controllo della microstruttura e quindi delle caratteristiche finali di un getto. Nel presente lavoro, viene descritta l’evoluzione microstrutturale di una lega AlSi9Cu3 rafforzata con il 10vol.% di SiCp e solidificata in presenza di vibrazioni meccaniche indotte su uno stampo metallico. Il materiale e stato colato in presenza di vibrazioni nell’intervallo di accelerazione compreso tra 0 e 41 volte l’accelerazione di gravita. L’applicazione delle vibrazioni meccaniche ha provocato una dispersione delle particelle di SiC ragionevolmente omogenea su scala macroscopica. Tale miglioramento nella distribuzione del rinforzo e risultato osservabile fino a valori di accelerazione di 10g. Con accelerazione superiori, si sono rilevati fenomeni di segregazione e la formazione di grosse cavita interne ai getti colati. Su scala microscopica, le tecniche di analisi d’immagi...

Solderability in tunnel furnace of Silver alloys parts and influence on subsequent remelting

Materials, 2020

Hybrid Metal Extrusion and Bonding (HYB) is a novel solid-state welding method for metals and all... more Hybrid Metal Extrusion and Bonding (HYB) is a novel solid-state welding method for metals and alloys that utilises continuous extrusion as a technique to enable aluminium filler metal additions. In the present study, a new semi-analytical model for the heat generation during aluminium butt welding is presented. As a starting point, the classical Rosenthal thin plate solution for the pseudo-steady-state temperature distribution around a fully penetrating line source is invoked. Then, the associated heat generation is calculated by considering the individual contributions from the tip of the rotating pin, the pin shoulder, and the filler metal additions on the net power input. In a calibrated form, the model yields thermal efficiency factors that are in close agreement with those obtained from more sophisticated finite element analyses but with considerably less computational effort.

Materials, 2021

An analytical model is proposed to rapidly capture the thermal and residual stresses values induc... more An analytical model is proposed to rapidly capture the thermal and residual stresses values induced by the hybrid metal extrusion and bonding (HYB) process on dissimilar-metal butt-welded joints. The power input for two welding velocities is first assessed using a thermal–mechanical model solved by a heat generation routine written in MATLAB code. Subsequently, the obtained temperature history is used as input to solve the equilibrium and compatibility equations formulated to calculate the thermal and residual stresses. To verify the soundness of the analytical approach, a Finite Element numerical model of the entire process is carried out and results are compared with those coming from the proposed rapid method. It is found that the degree of accuracy reached by the analytical model is excellent, especially considering the tremendous time reduction when compared to that characterizing the standard numerical approach.