Nabil Ben Fredj | Ensit : école nationale supérieure des ingénieurs de Tunis (original) (raw)

Papers by Nabil Ben Fredj

HAL (Le Centre pour la Communication Scientifique Directe), 2004

Thermally-cryogenically assisted machining (TCAM), also known as Hybrid machining, which consists... more Thermally-cryogenically assisted machining (TCAM), also known as Hybrid machining, which consists of a combination of hot machining and cryogenic machining processes is one of the attractive machining techniques for today's industry. Previous works attested that TCAM improves tool life and reduces cutting forces and chatter vibrations. However, in spite of its significant influence on in-service part performance and fatigue life, a little concern has been given to the TCAM induced residual stresses. This paper discusses the residual stress distribution on hardened D2 tool steel machined by TCAM and hard turning (HT) using PCBN cutting tools. The results showed that TCAM induces larger compressive area and larger maximum compressive stress levels below the machined surface comparatively to HT. When the cutting speed is increased, surface residual stresses tend to be tensile and the compressive residual stress depth is increased particularly in the case of TCAM.

Fatigue & Fracture of Engineering Materials & Structures, Sep 19, 2014

Residual Stress and Its Effects on Fatigue and Fracture

ABSTRACT In this investigation, ground surface integrity and fatigue behavior improvements of the... more ABSTRACT In this investigation, ground surface integrity and fatigue behavior improvements of the AISI 304 SS resulting from the application of wire brushing at ambient and low temperatures were investigated. It was found that the cold work hardening generated by the cryogenic brushing increases the levels of the compressive residual stresses comparatively to the dry brushing and therefore, results on higher nucleation fatigue lifetime of mechanical components having undergone this treatment. On the other hand the propagation fatigue lifetime of these components was found to be extended by plastic induced martensite formed at the tips of the nucleated fatigue cracks. The realized improvement rates expressed in terms of endurance limits at 2x106 cycles comparatively to the ground state are 47% for the dry brushing conditions and 72% for the cryogenic brushing.

International Review of Applied Sciences and Engineering, Mar 29, 2023

Fracture of Nano and Engineering Materials and Structures

Advances in Mechanical Engineering and Mechanics II, 2021

Ironmaking & Steelmaking

Design and Modeling of Mechanical Systems—III, 2017

In case of complex processes, the identification of out-of-control states, observed on control ch... more In case of complex processes, the identification of out-of-control states, observed on control charts, and their specific assignable causes are very complicated tasks. To overcome these difficulties artificial intelligence techniques have been used. Among these methods, the artificial neural networks can develop intelligence by using process data without need to expert opinion. This paper proposes an original method for process monitoring based on control chart exploration using artificial neural networks applicable for high batch size production requiring high sampling frequency. The developed approach helps to identify the out-of-control states and the corresponding process defects that lead to their occurrences. Attention is given to three most frequently observed cases in industrial practices: shifts, ascending and descending trends, and cyclic phenomena. The developed neural networks use back propagation algorithm and one hidden layer. A real industrial case of study was used to evaluate the recognition and identification performances of the developed artificial neural networks. Results have shown excellent recognition rates that reached percentages of identification of both process deviations and assignable causes higher than 90%.

Lecture Notes in Mechanical Engineering, 2020

This work focuses on the characterization of the tribological behavior of Hardox 500 steel in the... more This work focuses on the characterization of the tribological behavior of Hardox 500 steel in the ground state with different types of lubrication (dry and soluble oil), by using the technique of single cycle scratch testing. A CSM scratch testing machine equipped with a 50 µm radius Rockwell indenter was used for the experiments. The scratch length was set to 5 mm and different scratching loads (5 N, 10 N and 15 N) and speeds (10 mm/min, 50 mm/min and 100 mm/min) were considered. Results show that the friction coefficient and worn volume increase with the increase of the scratching load and speed and that samples ground using soluble oil have a martensitic microstructure characterized by very fine martensite laths that offers better wear resistance than sample ground under dry conditions. Thus, it could be conducted that the wear resistance of the Hardox 500 ground surfaces depends not only on the sliding speed and scratching normal load, but on the material microstructure also.

Advances in Mechanical Engineering and Mechanics, 2019

In this work, we investigate the effect of the grinding wheel morphology at grain scale on the st... more In this work, we investigate the effect of the grinding wheel morphology at grain scale on the stochastic aspects of the process. This morphology was controlled through dressing conditions in order to optimize the ground surface characteristics while minimizing their variance. It has been found that under the same grinding conditions, the surface characteristics and their dispersion vary significantly according to the dressing parameters. For the case of the grinding wheel (95A46M6V) dressed by a single-point diamond, a good choice of dressing conditions allows to reduce the roughness from 2 to 0.76 µm with a scatter less than 10% and to increase the hardening from 220Hv with a scattering of 40% to 382Hv with a dispersion of 23%.

The Bayesian approach has been used as an effective framework in tracking the process mean and de... more The Bayesian approach has been used as an effective framework in tracking the process mean and detecting the random occasional jump on the control chart X̄, R. This approach make an estimation of the posterior distribution of the process mean based on its prior distribution and the set of past observations. In contrary to previous research, in this paper, we develop a Bayesian approach for tracking and updating the posterior distribution of the process mean where it is subject to random changes with dynamic prior probability of occurrence. To update this prior probability in each new observation, we used numerical integration based on the set of past observations. We assume a general model of process, where the observations are represented as a process mean plus a random error term. The performance of this model is investigated and compared to the performance of the posterior distribution chart [9] where the prior probability of the change’s occurrence is stable over time. The resul...

Lecture Notes in Mechanical Engineering, 2020

As one of severe plastic deformation (SPD) techniques, the deep rolling treatment was carried out... more As one of severe plastic deformation (SPD) techniques, the deep rolling treatment was carried out after machining to enhance the surface integrity (microstructure, grain size, residual stress, etc.) of many materials. Re-crystallized surface layers containing submicron-scaled grains could be produced during deep rolling process due to severe plastic deformation. These ultra-fine grained materials showed improved mechanical properties (fatigue, wear resistance, corrosion resistance, etc.). In this work, deep rolling process was performed to enhance the corrosion behavior of Stainless Steel type AISI 304 in severe environments like seawater. Findings of this study depicts that deep rolling generates an ultra-fine grain structure, multi-directional mechanical twins, strain-induced martensite in the surface layers. In addition, the application of deep rolling produced high and deep compressive residual stress distributions. As a matter of fact, the corrosion rate was reduced by 53% for deep rolled sample comparatively to machined one. Thus, the enhancement of AISI 304 corrosion behavior results from microstructural changes, deformation-induced martensite and compressive residual stresses.

The International Journal of Advanced Manufacturing Technology, 2021

The effects of deep rolling parameters; particularly, work speed and cooling conditions (dry and ... more The effects of deep rolling parameters; particularly, work speed and cooling conditions (dry and cryogenic) on the surface integrity of AISI 304L machined samples and their further impact on uniform and localized corrosion behavior in chloride environment were experimentally investigated in this work. The electrochemical behavior of machined and deep rolled samples was assessed using cyclic potentiodynamic polarization tests in synthetic seawater. Findings of this study exhibit that grain refinement generated in the surface layers leads to improved corrosion behavior of deep rolled specimens with regard to machining state. In addition, machined samples deep rolled at a speed of 25 m/min, without cooling, showed better corrosion resistance than those processed under cryogenic cooling. However, the application of cryogenic deep rolling at speeds of 75 m/min and 120 m/min significantly enhanced the electrochemical behavior of mechanically treated specimens. It was found that the corrosion behavior of AISI 304L deep rolled components is related to combined factors (surface roughness, strain-induced martensite, microhardness, residual stress). Despite of high amounts of strain-induced martensite that can deteriorate the electrochemical behavior, it was shown that deep rolled specimens under cryogenic cooling with low surface roughness depict better uniform and localized corrosion resistances.

The International Journal of Advanced Manufacturing Technology, 2017

The International Journal of Advanced Manufacturing Technology, 2018

In the current study, deep rolling treatment was applied to enhance low-cycle fatigue behavior of... more In the current study, deep rolling treatment was applied to enhance low-cycle fatigue behavior of the AISI 304 stainless steel. Desirability function approach was applied to determine the process parameters offering the optimal surface roughness and hardness as these surface characteristics are supposed to control the fatigue cracks initiation and growth. The enhancement of the low-cycle fatigue behavior was investigated using strain-controlled fatigue tests applied to machined and deep rolled specimens associated to experimental evaluation of surface topography, microhardness, and residual stress. Findings of this work show that an increase of the fatigue lifetime of the AISI 304 components can be achieved by the application of deep rolling to machined surfaces. Moreover, the application of an intermittent deep rolling leads to a significant extension of service life especially when it is performed at low strain amplitudes. The improvement of the residual lifetime of deep rolled components is explained based on evaluations of the surface texture changes, residual stresses, cold work hardening, and strain-induced martensite transformation.

Journal of Materials Engineering and Performance, 2016

HAL (Le Centre pour la Communication Scientifique Directe), 2004

Thermally-cryogenically assisted machining (TCAM), also known as Hybrid machining, which consists... more Thermally-cryogenically assisted machining (TCAM), also known as Hybrid machining, which consists of a combination of hot machining and cryogenic machining processes is one of the attractive machining techniques for today's industry. Previous works attested that TCAM improves tool life and reduces cutting forces and chatter vibrations. However, in spite of its significant influence on in-service part performance and fatigue life, a little concern has been given to the TCAM induced residual stresses. This paper discusses the residual stress distribution on hardened D2 tool steel machined by TCAM and hard turning (HT) using PCBN cutting tools. The results showed that TCAM induces larger compressive area and larger maximum compressive stress levels below the machined surface comparatively to HT. When the cutting speed is increased, surface residual stresses tend to be tensile and the compressive residual stress depth is increased particularly in the case of TCAM.

Fatigue & Fracture of Engineering Materials & Structures, Sep 19, 2014

Residual Stress and Its Effects on Fatigue and Fracture

ABSTRACT In this investigation, ground surface integrity and fatigue behavior improvements of the... more ABSTRACT In this investigation, ground surface integrity and fatigue behavior improvements of the AISI 304 SS resulting from the application of wire brushing at ambient and low temperatures were investigated. It was found that the cold work hardening generated by the cryogenic brushing increases the levels of the compressive residual stresses comparatively to the dry brushing and therefore, results on higher nucleation fatigue lifetime of mechanical components having undergone this treatment. On the other hand the propagation fatigue lifetime of these components was found to be extended by plastic induced martensite formed at the tips of the nucleated fatigue cracks. The realized improvement rates expressed in terms of endurance limits at 2x106 cycles comparatively to the ground state are 47% for the dry brushing conditions and 72% for the cryogenic brushing.

International Review of Applied Sciences and Engineering, Mar 29, 2023

Fracture of Nano and Engineering Materials and Structures

Advances in Mechanical Engineering and Mechanics II, 2021

Ironmaking & Steelmaking

Design and Modeling of Mechanical Systems—III, 2017

In case of complex processes, the identification of out-of-control states, observed on control ch... more In case of complex processes, the identification of out-of-control states, observed on control charts, and their specific assignable causes are very complicated tasks. To overcome these difficulties artificial intelligence techniques have been used. Among these methods, the artificial neural networks can develop intelligence by using process data without need to expert opinion. This paper proposes an original method for process monitoring based on control chart exploration using artificial neural networks applicable for high batch size production requiring high sampling frequency. The developed approach helps to identify the out-of-control states and the corresponding process defects that lead to their occurrences. Attention is given to three most frequently observed cases in industrial practices: shifts, ascending and descending trends, and cyclic phenomena. The developed neural networks use back propagation algorithm and one hidden layer. A real industrial case of study was used to evaluate the recognition and identification performances of the developed artificial neural networks. Results have shown excellent recognition rates that reached percentages of identification of both process deviations and assignable causes higher than 90%.

Lecture Notes in Mechanical Engineering, 2020

This work focuses on the characterization of the tribological behavior of Hardox 500 steel in the... more This work focuses on the characterization of the tribological behavior of Hardox 500 steel in the ground state with different types of lubrication (dry and soluble oil), by using the technique of single cycle scratch testing. A CSM scratch testing machine equipped with a 50 µm radius Rockwell indenter was used for the experiments. The scratch length was set to 5 mm and different scratching loads (5 N, 10 N and 15 N) and speeds (10 mm/min, 50 mm/min and 100 mm/min) were considered. Results show that the friction coefficient and worn volume increase with the increase of the scratching load and speed and that samples ground using soluble oil have a martensitic microstructure characterized by very fine martensite laths that offers better wear resistance than sample ground under dry conditions. Thus, it could be conducted that the wear resistance of the Hardox 500 ground surfaces depends not only on the sliding speed and scratching normal load, but on the material microstructure also.

Advances in Mechanical Engineering and Mechanics, 2019

In this work, we investigate the effect of the grinding wheel morphology at grain scale on the st... more In this work, we investigate the effect of the grinding wheel morphology at grain scale on the stochastic aspects of the process. This morphology was controlled through dressing conditions in order to optimize the ground surface characteristics while minimizing their variance. It has been found that under the same grinding conditions, the surface characteristics and their dispersion vary significantly according to the dressing parameters. For the case of the grinding wheel (95A46M6V) dressed by a single-point diamond, a good choice of dressing conditions allows to reduce the roughness from 2 to 0.76 µm with a scatter less than 10% and to increase the hardening from 220Hv with a scattering of 40% to 382Hv with a dispersion of 23%.

The Bayesian approach has been used as an effective framework in tracking the process mean and de... more The Bayesian approach has been used as an effective framework in tracking the process mean and detecting the random occasional jump on the control chart X̄, R. This approach make an estimation of the posterior distribution of the process mean based on its prior distribution and the set of past observations. In contrary to previous research, in this paper, we develop a Bayesian approach for tracking and updating the posterior distribution of the process mean where it is subject to random changes with dynamic prior probability of occurrence. To update this prior probability in each new observation, we used numerical integration based on the set of past observations. We assume a general model of process, where the observations are represented as a process mean plus a random error term. The performance of this model is investigated and compared to the performance of the posterior distribution chart [9] where the prior probability of the change’s occurrence is stable over time. The resul...

Lecture Notes in Mechanical Engineering, 2020

As one of severe plastic deformation (SPD) techniques, the deep rolling treatment was carried out... more As one of severe plastic deformation (SPD) techniques, the deep rolling treatment was carried out after machining to enhance the surface integrity (microstructure, grain size, residual stress, etc.) of many materials. Re-crystallized surface layers containing submicron-scaled grains could be produced during deep rolling process due to severe plastic deformation. These ultra-fine grained materials showed improved mechanical properties (fatigue, wear resistance, corrosion resistance, etc.). In this work, deep rolling process was performed to enhance the corrosion behavior of Stainless Steel type AISI 304 in severe environments like seawater. Findings of this study depicts that deep rolling generates an ultra-fine grain structure, multi-directional mechanical twins, strain-induced martensite in the surface layers. In addition, the application of deep rolling produced high and deep compressive residual stress distributions. As a matter of fact, the corrosion rate was reduced by 53% for deep rolled sample comparatively to machined one. Thus, the enhancement of AISI 304 corrosion behavior results from microstructural changes, deformation-induced martensite and compressive residual stresses.

The International Journal of Advanced Manufacturing Technology, 2021

The effects of deep rolling parameters; particularly, work speed and cooling conditions (dry and ... more The effects of deep rolling parameters; particularly, work speed and cooling conditions (dry and cryogenic) on the surface integrity of AISI 304L machined samples and their further impact on uniform and localized corrosion behavior in chloride environment were experimentally investigated in this work. The electrochemical behavior of machined and deep rolled samples was assessed using cyclic potentiodynamic polarization tests in synthetic seawater. Findings of this study exhibit that grain refinement generated in the surface layers leads to improved corrosion behavior of deep rolled specimens with regard to machining state. In addition, machined samples deep rolled at a speed of 25 m/min, without cooling, showed better corrosion resistance than those processed under cryogenic cooling. However, the application of cryogenic deep rolling at speeds of 75 m/min and 120 m/min significantly enhanced the electrochemical behavior of mechanically treated specimens. It was found that the corrosion behavior of AISI 304L deep rolled components is related to combined factors (surface roughness, strain-induced martensite, microhardness, residual stress). Despite of high amounts of strain-induced martensite that can deteriorate the electrochemical behavior, it was shown that deep rolled specimens under cryogenic cooling with low surface roughness depict better uniform and localized corrosion resistances.

The International Journal of Advanced Manufacturing Technology, 2017

The International Journal of Advanced Manufacturing Technology, 2018

In the current study, deep rolling treatment was applied to enhance low-cycle fatigue behavior of... more In the current study, deep rolling treatment was applied to enhance low-cycle fatigue behavior of the AISI 304 stainless steel. Desirability function approach was applied to determine the process parameters offering the optimal surface roughness and hardness as these surface characteristics are supposed to control the fatigue cracks initiation and growth. The enhancement of the low-cycle fatigue behavior was investigated using strain-controlled fatigue tests applied to machined and deep rolled specimens associated to experimental evaluation of surface topography, microhardness, and residual stress. Findings of this work show that an increase of the fatigue lifetime of the AISI 304 components can be achieved by the application of deep rolling to machined surfaces. Moreover, the application of an intermittent deep rolling leads to a significant extension of service life especially when it is performed at low strain amplitudes. The improvement of the residual lifetime of deep rolled components is explained based on evaluations of the surface texture changes, residual stresses, cold work hardening, and strain-induced martensite transformation.

Journal of Materials Engineering and Performance, 2016