https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Mon, 15 Jun 2026 15:07:42 GMT 2026-06-15T15:07:42Z http://hdl.handle.net/10985/8778 Assessment of low cycle fatigue improvement of machined AISI 316 stainless steel by brush hammering SIDHOM, Naziha; MAKHLOUF, Kamel; KHLIFI, Ammar; SIDHOM, Habib; BRAHAM, Chedly The effects of wire brush hammering on low cycle fatigue behaviour of AISI 316 austenitic stainless steel has been investigated on turned samples through an experimental study combining strain controlled fatigue tests, scanning electron microscope examination and X-ray diffraction analysis. An increase in fatigue life by 266% was reported at an imposed strain amplitude of Δεt/2 = 0.2%. This improvement is limited to Δεt/2 ≤ 0.5%. It is found that wire brush hammering produces a surface texture that favours, under cyclic loading, nucleation of randomly dispersed short cracks of the order of 50 μm in length stabilized by a compressive residual stress field. In contrast, turned surface showed much longer unstable cracks of the order of 200 μm in length nucleated in the machining groves and propagated under the effect of a tensile residual stress field. It has also been established that wire brush hammering can be used as intermittent treatment to improve the residual fatigue life of components subjected to cyclic loading. The treatment is very efficient if it is performed at a fraction of service lifetime ni/Nr lower than 0.5. Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/8778 2014-01-01T00:00:00Z SIDHOM, Naziha MAKHLOUF, Kamel KHLIFI, Ammar SIDHOM, Habib BRAHAM, Chedly The effects of wire brush hammering on low cycle fatigue behaviour of AISI 316 austenitic stainless steel has been investigated on turned samples through an experimental study combining strain controlled fatigue tests, scanning electron microscope examination and X-ray diffraction analysis. An increase in fatigue life by 266% was reported at an imposed strain amplitude of Δεt/2 = 0.2%. This improvement is limited to Δεt/2 ≤ 0.5%. It is found that wire brush hammering produces a surface texture that favours, under cyclic loading, nucleation of randomly dispersed short cracks of the order of 50 μm in length stabilized by a compressive residual stress field. In contrast, turned surface showed much longer unstable cracks of the order of 200 μm in length nucleated in the machining groves and propagated under the effect of a tensile residual stress field. It has also been established that wire brush hammering can be used as intermittent treatment to improve the residual fatigue life of components subjected to cyclic loading. The treatment is very efficient if it is performed at a fraction of service lifetime ni/Nr lower than 0.5. http://hdl.handle.net/10985/8136 Low cycle fatigue life improvement of AISI 304 by initial and intermittent wire brush hammering MAKHLOUF, Kamel; SIDHOM, Naziha; KHLIFI, Ammar; SIDHOM, Habib; BRAHAM, Chedly The effects of hammering by wire brush as a method of improving low cycle fatigue life of highly ductile austenitic stainless steel AISI 304 have been investigated through an experimental study combining imposed strain fatigue tests and assessment of surface characteristic changes under cyclic loading by SEM examinations and XRD analysis. It has been shown that the fatigue life of wire brush hammered surface was increased by 307% at an imposed strain rate of 0.2% and only 17% at an imposed strain rate of 0.5%, comparatively to the turned surface. This increase in fatigue life is explained in terms of fatigue damage that is related to crack networks characteristics and stability which are generated during fatigue on both turned and wire brush hammered surfaces. The improvement of brushed surface is attributed to the role of the surface topography, the near surface stabilized compressive residual stresses and superfi-cial cold work hardening on the fatigue crack network nucleation and growth. It is found that wire brush hammering produces a surface texture that favors, under cyclic loading, nucleation of randomly dispersed short cracks of the order of 40 lm in length stabilized by the compressive residual stress field that reached a value of r0 = 749 MPa. In contrast, turned surface showed much longer unstable cracks of the order of 200 lm in length nucleated in the machining groves with high tendency to propagate under the effect of tensile residual stress field that reached value of r0 = 476 MPa. This improvement is limited to strain rates lower than 0.5%. At higher strain rates, a cyclic plastic deformation induced martensitic phase alters furthermore the fatigue behavior by producing high cyclic strengthening of the bulk mate-rial. This phenomenon lead to a reduction in strain imposed fatigue life. It has also been established that wire brush hammering can be used as an onsite surface treatment to improve the residual fatigue life of components subjected to cyclic loading. The efficiency of this treatment is demonstrated if it is performed at a fraction of service lifetime Ni/Nr lower than 0.5. Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10985/8136 2013-01-01T00:00:00Z MAKHLOUF, Kamel SIDHOM, Naziha KHLIFI, Ammar SIDHOM, Habib BRAHAM, Chedly The effects of hammering by wire brush as a method of improving low cycle fatigue life of highly ductile austenitic stainless steel AISI 304 have been investigated through an experimental study combining imposed strain fatigue tests and assessment of surface characteristic changes under cyclic loading by SEM examinations and XRD analysis. It has been shown that the fatigue life of wire brush hammered surface was increased by 307% at an imposed strain rate of 0.2% and only 17% at an imposed strain rate of 0.5%, comparatively to the turned surface. This increase in fatigue life is explained in terms of fatigue damage that is related to crack networks characteristics and stability which are generated during fatigue on both turned and wire brush hammered surfaces. The improvement of brushed surface is attributed to the role of the surface topography, the near surface stabilized compressive residual stresses and superfi-cial cold work hardening on the fatigue crack network nucleation and growth. It is found that wire brush hammering produces a surface texture that favors, under cyclic loading, nucleation of randomly dispersed short cracks of the order of 40 lm in length stabilized by the compressive residual stress field that reached a value of r0 = 749 MPa. In contrast, turned surface showed much longer unstable cracks of the order of 200 lm in length nucleated in the machining groves with high tendency to propagate under the effect of tensile residual stress field that reached value of r0 = 476 MPa. This improvement is limited to strain rates lower than 0.5%. At higher strain rates, a cyclic plastic deformation induced martensitic phase alters furthermore the fatigue behavior by producing high cyclic strengthening of the bulk mate-rial. This phenomenon lead to a reduction in strain imposed fatigue life. It has also been established that wire brush hammering can be used as an onsite surface treatment to improve the residual fatigue life of components subjected to cyclic loading. The efficiency of this treatment is demonstrated if it is performed at a fraction of service lifetime Ni/Nr lower than 0.5. http://hdl.handle.net/10985/8135 Evaluation of residual stress relaxation and its effect on fatigue strength of AISI 316L stainless steel ground surfaces: Experimental and numerical approaches LAAMOURI, Adnen; SIDHOM, Habib; BRAHAM, Chedly This paper is aimed at evaluating the residual stress relaxation and its effect on the fatigue strength of AISI 316L steel ground surfaces in comparison to electro-polished surfaces. An experimental evaluation was performed using 3-point and 4-point bending fatigue tests at Rr = 0.1 on two sets of notched spec-imens finished by electro-polishing and grinding. The residual stress fields were measured at the notch root of specimens, before and after fatigue tests, by means of the X-ray diffraction technique. It was found a degradation of about 35% for the 4-point bending fatigue limit at 2 106 cycles of the ground spec-imens in comparison to the electro-polished ones. This degradation is associated with a slight relaxation of the grinding residual stresses which remain significant tensile stresses at the stabilized state. While under the 3-point bending test, these residual stresses relax completely and provoke a noticeable increase of the fatigue limit estimated at about 50% in comparison to the 4-point bending fatigue test. The numerical evaluation of residual stress relaxation was carried out by FE analyses of the cyclic hard-ening behaviour of the ground layer. The isotropic and nonlinear kinematic model proposed by Chaboche was used and calibrated for the base material and the ground layer. The results show that residual stres-ses relax to a stabilized state characterized by elastic-shakedown response. This stabilization is occurred after the first cycle of the 4-point bending test corresponding to the higher stress concentration (Kt- 4p = 1.66), while it requires many cycles under the 3-point bending test corresponding to the lower stress concentration (Kt-3p = 1.54). The incorporation of stabilized residual stress values into the Dang Van’s cri-terion has permitted to predict with an acceptable accuracy the fatigue limits under both bending modes. Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10985/8135 2013-01-01T00:00:00Z LAAMOURI, Adnen SIDHOM, Habib BRAHAM, Chedly This paper is aimed at evaluating the residual stress relaxation and its effect on the fatigue strength of AISI 316L steel ground surfaces in comparison to electro-polished surfaces. An experimental evaluation was performed using 3-point and 4-point bending fatigue tests at Rr = 0.1 on two sets of notched spec-imens finished by electro-polishing and grinding. The residual stress fields were measured at the notch root of specimens, before and after fatigue tests, by means of the X-ray diffraction technique. It was found a degradation of about 35% for the 4-point bending fatigue limit at 2 106 cycles of the ground spec-imens in comparison to the electro-polished ones. This degradation is associated with a slight relaxation of the grinding residual stresses which remain significant tensile stresses at the stabilized state. While under the 3-point bending test, these residual stresses relax completely and provoke a noticeable increase of the fatigue limit estimated at about 50% in comparison to the 4-point bending fatigue test. The numerical evaluation of residual stress relaxation was carried out by FE analyses of the cyclic hard-ening behaviour of the ground layer. The isotropic and nonlinear kinematic model proposed by Chaboche was used and calibrated for the base material and the ground layer. The results show that residual stres-ses relax to a stabilized state characterized by elastic-shakedown response. This stabilization is occurred after the first cycle of the 4-point bending test corresponding to the higher stress concentration (Kt- 4p = 1.66), while it requires many cycles under the 3-point bending test corresponding to the lower stress concentration (Kt-3p = 1.54). The incorporation of stabilized residual stress values into the Dang Van’s cri-terion has permitted to predict with an acceptable accuracy the fatigue limits under both bending modes. http://hdl.handle.net/10985/12176 Correlation between microstructure and intergranular corrosion behavior of low delta-ferrite content AISI 316L aged in the range 550e700 C BEN RHOUMA, A; AMADOU, Tidiane; SIDHOM, Habib; BRAHAM, Chedly The microstructure and the phase identification of austenitic stainless steel AISI 316L with low δ-ferrite content (δ ≤ 1%) and aged for up to 80 000 h at temperatures ranging from 550 to 700 °C were investigated by using an optical microscope (OM), a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Local changes of chromium content, resulting from nucleation and growth of chromium-rich phases during aging, were quantitatively assessed by energy dispersive X-ray spectroscopy (EDX) in the scanning transmission electron microscope (STEM). The intergranular corrosion behavior (IGC) of annealed and aged specimens was evaluated using the double loop electrochemical potentiokinetic reactivation (DL-EPR) and completed by IGC morphologies according to the ASTM A262 practice A standard. The results showed that δ-ferrite decomposed gradually into M23C6 at 550 °C and decomposed totally into intermetallic phases (σ, η, χ, and R) and into secondary austenite (γr) at temperatures equal to or higher than 650 °C. Similarly γ-austenite decomposed into M23C6 carbide at 550 °C and into intermetallic phases such as η and σ in addition to carbide, at higher temperatures. The time-temperature-sensitization diagram (TTS) was established and used to calculate the critical cooling rate (CCR) that prevents IGC sensitization. The analysis of IGC results leads to the conclusion that sensitization-desensitization is still controlled by the characteristics of chromium-depleted area surrounding austenite grain boundary regions. No significant effect of remained δ-ferrite and derived components on the corrosion behavior of AISI 316 L containing 1% of δ-ferrite. Sun, 01 Jan 2017 00:00:00 GMT http://hdl.handle.net/10985/12176 2017-01-01T00:00:00Z BEN RHOUMA, A AMADOU, Tidiane SIDHOM, Habib BRAHAM, Chedly The microstructure and the phase identification of austenitic stainless steel AISI 316L with low δ-ferrite content (δ ≤ 1%) and aged for up to 80 000 h at temperatures ranging from 550 to 700 °C were investigated by using an optical microscope (OM), a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Local changes of chromium content, resulting from nucleation and growth of chromium-rich phases during aging, were quantitatively assessed by energy dispersive X-ray spectroscopy (EDX) in the scanning transmission electron microscope (STEM). The intergranular corrosion behavior (IGC) of annealed and aged specimens was evaluated using the double loop electrochemical potentiokinetic reactivation (DL-EPR) and completed by IGC morphologies according to the ASTM A262 practice A standard. The results showed that δ-ferrite decomposed gradually into M23C6 at 550 °C and decomposed totally into intermetallic phases (σ, η, χ, and R) and into secondary austenite (γr) at temperatures equal to or higher than 650 °C. Similarly γ-austenite decomposed into M23C6 carbide at 550 °C and into intermetallic phases such as η and σ in addition to carbide, at higher temperatures. The time-temperature-sensitization diagram (TTS) was established and used to calculate the critical cooling rate (CCR) that prevents IGC sensitization. The analysis of IGC results leads to the conclusion that sensitization-desensitization is still controlled by the characteristics of chromium-depleted area surrounding austenite grain boundary regions. No significant effect of remained δ-ferrite and derived components on the corrosion behavior of AISI 316 L containing 1% of δ-ferrite. http://hdl.handle.net/10985/14077 A multireflection and multiwavelength residual stress determination method using energy dispersive diffraction MARCISZKO, Marianna; WAWSZCZAK, Roman; SIDHOM, Habib; WROBEL, Mirosław; WRONSKI, Sebastian; OPONOWICZ, Adrian; GENZEL, Christoph; KLAUS, Manuela; BACZMANSKI, Andrzej; BRAHAM, Chedly The main focus of the presented work was the investigation of structure and residual stress gradients in the near-surface region of materials studied by X-ray diffraction. The multireflection method was used to measure depth-dependent stress variation in near-surface layers of a Ti sample (grade 2) subjected to different mechanical treatments. First, the multireflection grazing incidence diffraction method was applied on a classical diffractometer with Cu Kα radiation. The applicability of the method was then extended by using a white synchrotron beam during an energy dispersive (ED) diffraction experiment. An advantage of this method was the possibility of using not only more than one reflection but also different wavelengths of radiation. This approach was successfully applied to analysis of data obtained in the ED experiment. There was good agreement between the measurements performed using synchrotron radiation and those with Cu Kα radiation on the classical diffractometer. A great advantage of high-energy synchrotron radiation was the possibility to measure stresses as well as the a0 parameter and c0/α0 ratio for much larger depths in comparison with laboratory X-rays. © 2018 International Union of Crystallography. Mon, 01 Jan 2018 00:00:00 GMT http://hdl.handle.net/10985/14077 2018-01-01T00:00:00Z MARCISZKO, Marianna WAWSZCZAK, Roman SIDHOM, Habib WROBEL, Mirosław WRONSKI, Sebastian OPONOWICZ, Adrian GENZEL, Christoph KLAUS, Manuela BACZMANSKI, Andrzej BRAHAM, Chedly The main focus of the presented work was the investigation of structure and residual stress gradients in the near-surface region of materials studied by X-ray diffraction. The multireflection method was used to measure depth-dependent stress variation in near-surface layers of a Ti sample (grade 2) subjected to different mechanical treatments. First, the multireflection grazing incidence diffraction method was applied on a classical diffractometer with Cu Kα radiation. The applicability of the method was then extended by using a white synchrotron beam during an energy dispersive (ED) diffraction experiment. An advantage of this method was the possibility of using not only more than one reflection but also different wavelengths of radiation. This approach was successfully applied to analysis of data obtained in the ED experiment. There was good agreement between the measurements performed using synchrotron radiation and those with Cu Kα radiation on the classical diffractometer. A great advantage of high-energy synchrotron radiation was the possibility to measure stresses as well as the a0 parameter and c0/α0 ratio for much larger depths in comparison with laboratory X-rays. © 2018 International Union of Crystallography. http://hdl.handle.net/10985/18458 Influences of up-milling and down-milling on surface integrity and fatigue strength of X160CrMoV12 steel LAAMOURI, Adnen; GHANEM, Farhat; SIDHOM, Habib; BRAHAM, Chedly This paper aims to compare the influences of the two peripheral milling modes, up-milling and down-milling, on surface integrity and fatigue strength of X160CrMoV12 high-alloy steel. The experimental investigations showed an important difference between integrity of both milled surfaces. The down-milled surface is lowly work-hardened and well finished (lower roughness), but subjected to tensile residual stresses and severely damaged by folds of metal and short micro-cracks. The up-milled surface is highly work-hardened and subjected to compressive residual stresses, but poorly finished (higher roughness) and damaged by a density of micro-cavities due to carbide extraction. The results of 3-point bending fatigue tests revealed that the fatigue limit at 2 × 106 cycles of the up-milled state is largely higher of about 26% in comparison with the down-milled state. The effects of surface integrity induced by each milling mode on fatigue strength were evaluated using a HCF behaviour predictive approach based on Dang Van’s multiaxial criterion. The predictive results estimated that the pre-existing micro-cracks play a dominant role in the fatigue strength degradation of the down-milled surface while the other surface effects seem to be lower. On the contrary, the fatigue strength of the up-milled surface is less affected by the pre-existing micro-cavities. The detrimental roughness effect (stress concentration effect) is significantly reduced by the beneficial effects of superficial hardening and compressive residual stresses. So, this study revealed that up-milling is the more appropriate mode for a better surface integrity towards fatigue strength of X160CrMoV12 steel than the down-milling mode. Tue, 01 Jan 2019 00:00:00 GMT http://hdl.handle.net/10985/18458 2019-01-01T00:00:00Z LAAMOURI, Adnen GHANEM, Farhat SIDHOM, Habib BRAHAM, Chedly This paper aims to compare the influences of the two peripheral milling modes, up-milling and down-milling, on surface integrity and fatigue strength of X160CrMoV12 high-alloy steel. The experimental investigations showed an important difference between integrity of both milled surfaces. The down-milled surface is lowly work-hardened and well finished (lower roughness), but subjected to tensile residual stresses and severely damaged by folds of metal and short micro-cracks. The up-milled surface is highly work-hardened and subjected to compressive residual stresses, but poorly finished (higher roughness) and damaged by a density of micro-cavities due to carbide extraction. The results of 3-point bending fatigue tests revealed that the fatigue limit at 2 × 106 cycles of the up-milled state is largely higher of about 26% in comparison with the down-milled state. The effects of surface integrity induced by each milling mode on fatigue strength were evaluated using a HCF behaviour predictive approach based on Dang Van’s multiaxial criterion. The predictive results estimated that the pre-existing micro-cracks play a dominant role in the fatigue strength degradation of the down-milled surface while the other surface effects seem to be lower. On the contrary, the fatigue strength of the up-milled surface is less affected by the pre-existing micro-cavities. The detrimental roughness effect (stress concentration effect) is significantly reduced by the beneficial effects of superficial hardening and compressive residual stresses. So, this study revealed that up-milling is the more appropriate mode for a better surface integrity towards fatigue strength of X160CrMoV12 steel than the down-milling mode. http://hdl.handle.net/10985/18403 Experimental and numerical multi-scale approach for Sheet-Molding-Compound composites fatigue prediction based on fiber-matrix interface cyclic damage TAMBOURA, Sahbi; AYARI, Houssem; SHIRINBAYAN, Mohammadali; LARIBI, Mohamad-Amine; BENDALY, Hachmi; SIDHOM, Habib; TCHARKHTCHI, Abbas; FITOUSSI, Joseph In this paper, a multi-scale approach is proposed to predict the stiffness reduction of a Sheet-Molding-Compound (SMC) composite submitted to low cycle fatigue (until 2.105 cycles). Strain-controlled tensile fatigue tests (R = 0.1) are carried out at various strain ranges. Damage is investigated at both macroscopic and microscopic scales through the evolutions of Young's modulus and SEM observations, after interrupted fatigue tests at different lifetime periods. The results show that the fatigue degradation of the composite is mainly controlled by fiber-matrix interface debonding. A quantitative analysis allows determining the threshold and kinetics of the fiber-matrix interface damage during cyclic loading as a function of the orientation of fibers. Moreover, a fiber-matrix interface damage criterion, taking into account the local cyclic normal and shear stresses at the interface, is introduced in the Mori and Tanaka approach in order to predict the loss of stiffness. The parameters of this local criterion are identified by reverse engineering on the basis of the experimental results described above. Finally, the predicted loss of stiffness is very consistent with the experimental results Wed, 01 Jan 2020 00:00:00 GMT http://hdl.handle.net/10985/18403 2020-01-01T00:00:00Z TAMBOURA, Sahbi AYARI, Houssem SHIRINBAYAN, Mohammadali LARIBI, Mohamad-Amine BENDALY, Hachmi SIDHOM, Habib TCHARKHTCHI, Abbas FITOUSSI, Joseph In this paper, a multi-scale approach is proposed to predict the stiffness reduction of a Sheet-Molding-Compound (SMC) composite submitted to low cycle fatigue (until 2.105 cycles). Strain-controlled tensile fatigue tests (R = 0.1) are carried out at various strain ranges. Damage is investigated at both macroscopic and microscopic scales through the evolutions of Young's modulus and SEM observations, after interrupted fatigue tests at different lifetime periods. The results show that the fatigue degradation of the composite is mainly controlled by fiber-matrix interface debonding. A quantitative analysis allows determining the threshold and kinetics of the fiber-matrix interface damage during cyclic loading as a function of the orientation of fibers. Moreover, a fiber-matrix interface damage criterion, taking into account the local cyclic normal and shear stresses at the interface, is introduced in the Mori and Tanaka approach in order to predict the loss of stiffness. The parameters of this local criterion are identified by reverse engineering on the basis of the experimental results described above. Finally, the predicted loss of stiffness is very consistent with the experimental results http://hdl.handle.net/10985/17523 Numerical and experimental analysis of residual stress and plastic strain distributions in machined stainless steel BEN MOUSSA, Naoufel; SIDHOM, Habib; BRAHAM, Chedly In this study, a numerical approach has been developed to predict the near surface residual stresses and plastic strain resulting from turning in orthogonal cutting configuration. This approach is based on the Arbitrary Lagrangian-Eulerian (ALE) formulation using the commercial finite element code Abaqus-Explicit. The coefficients of the used material behavior law and friction model required for the simulation are identified experimentally in this study. The simulated results are validated by experiments carried out on AISI 316L stainless steel. Using this method, the effect of the depth of cut (Doc) and the cutting speed (Vc) on the surface properties has been established. The simulated residual stress gradient resulting from machining has been experimentally validated by X-ray diffraction measurements. The simulated plastic strain gradient has been validated by an experimental microhardness-strain relationship established in this study. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10985/17523 2012-01-01T00:00:00Z BEN MOUSSA, Naoufel SIDHOM, Habib BRAHAM, Chedly In this study, a numerical approach has been developed to predict the near surface residual stresses and plastic strain resulting from turning in orthogonal cutting configuration. This approach is based on the Arbitrary Lagrangian-Eulerian (ALE) formulation using the commercial finite element code Abaqus-Explicit. The coefficients of the used material behavior law and friction model required for the simulation are identified experimentally in this study. The simulated results are validated by experiments carried out on AISI 316L stainless steel. Using this method, the effect of the depth of cut (Doc) and the cutting speed (Vc) on the surface properties has been established. The simulated residual stress gradient resulting from machining has been experimentally validated by X-ray diffraction measurements. The simulated plastic strain gradient has been validated by an experimental microhardness-strain relationship established in this study. http://hdl.handle.net/10985/15979 Evaluation by the double loop electrochemical potentiokinetic reactivation test of aged ferritic stainless steel intergranular corrosion susceptibility SIDHOM, Habib; AMADOU, Tidiane; BRAHAM, Chedly An experimental design method was used to determine the effect of factors that significantly affect the response of the double loop-electrochemical potentiokinetic reactivation (DL-EPR) test in controlling the susceptibility to intergranular corrosion (IGC) of UNS S43000 (AISI 430) ferritic stainless steel. The test response is expressed in terms of the reactivation/activation current ratio (I r /I a pct). Test results analysed by the analysis of variance (ANOVA) method show that the molarity of the H 2SO4 electrolyte and the potential scanning rate have a more significant effect on the DL-EPR test response than the temperature and the depassivator agent concentration. On the basis of these results, a study was conducted in order to determine the optimal operating conditions of the test as a nondestructive technique for evaluating IGC resistance of ferritic stainless steel components. Three different heat treatments are considered in this study: solution annealing (nonsensitized), aging during 3 hours at 773 K (500 °C) (slightly sensitized), and aging during 2 hours at 873 K (600 °C) (highly sensitized). The aim is to find the operating conditions that simultaneously ensure the selectivity of the attack (intergranular and chromium depleted zone) and are able to detect the effect of low dechromization. It is found that a potential scanning rate of 2.5 mV/s in an electrolyte composed of H 2SO4 3 M solution without depassivator, at a temperature around 293 K (20 °C), is the optimal operating condition for the DL-EPR test. Using this condition, it is possible to assess the degree of sensitization (DOS) to the IGC of products manufactured in ferritic stainless steels rapidly, reliably, and quantitatively. A time-temperature-start of sensitization (TTS) diagram for the UNS S43000 (France Inox, Villepinte, France) stainless steel was obtained with acceptable accuracy by this method when the IGC sensitization criterion was set to I r /I a > 1 pct. This diagram is in good agreement with the time-temperature-start of precipitation (TTP) diagram that delineates the domain of low dechromization consecutive to chromium carbide precipitation. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/10985/15979 2010-01-01T00:00:00Z SIDHOM, Habib AMADOU, Tidiane BRAHAM, Chedly An experimental design method was used to determine the effect of factors that significantly affect the response of the double loop-electrochemical potentiokinetic reactivation (DL-EPR) test in controlling the susceptibility to intergranular corrosion (IGC) of UNS S43000 (AISI 430) ferritic stainless steel. The test response is expressed in terms of the reactivation/activation current ratio (I r /I a pct). Test results analysed by the analysis of variance (ANOVA) method show that the molarity of the H 2SO4 electrolyte and the potential scanning rate have a more significant effect on the DL-EPR test response than the temperature and the depassivator agent concentration. On the basis of these results, a study was conducted in order to determine the optimal operating conditions of the test as a nondestructive technique for evaluating IGC resistance of ferritic stainless steel components. Three different heat treatments are considered in this study: solution annealing (nonsensitized), aging during 3 hours at 773 K (500 °C) (slightly sensitized), and aging during 2 hours at 873 K (600 °C) (highly sensitized). The aim is to find the operating conditions that simultaneously ensure the selectivity of the attack (intergranular and chromium depleted zone) and are able to detect the effect of low dechromization. It is found that a potential scanning rate of 2.5 mV/s in an electrolyte composed of H 2SO4 3 M solution without depassivator, at a temperature around 293 K (20 °C), is the optimal operating condition for the DL-EPR test. Using this condition, it is possible to assess the degree of sensitization (DOS) to the IGC of products manufactured in ferritic stainless steels rapidly, reliably, and quantitatively. A time-temperature-start of sensitization (TTS) diagram for the UNS S43000 (France Inox, Villepinte, France) stainless steel was obtained with acceptable accuracy by this method when the IGC sensitization criterion was set to I r /I a > 1 pct. This diagram is in good agreement with the time-temperature-start of precipitation (TTP) diagram that delineates the domain of low dechromization consecutive to chromium carbide precipitation. http://hdl.handle.net/10985/17903 Effects of finishing processes on the fatigue life improvements of electro-machined surfaces of tool steel GHANEM, Farhat; FREDJ, Nabil Ben; SIDHOM, Habib; BRAHAM, Chedly Machining the EN X160CrMoV12 tool steel by electro-discharge machining (EDM) process generates significant modifications of microgeometrical, microstructural and mechanical properties of the upper layers of the machined components. In this paper, the role of these modifications in controlling the stability, under cyclic loading, of the propagation of the crack networks generated by EDM is discussed. High cycle fatigue tests (2×106 cycles) show that the presence of these cracks in brittle layers, i.e. white layer, quenched the martensitic layer, and a field of tensile residual stresses (+750 MPa) results in a loss of 34% of endurance limit comparatively with the endurance evaluated for the milled state that generates crack-free surfaces. It is shown, in this work, that the detrimental effect of these crack networks can be controlled by putting in compression the upper layers of the EDM surfaces. Indeed the application of wire brushing to EDM surfaces generates compressive residual stresses (≈-100 MPa) that stabilise the crack networks propagation and therefore restores to the EDM surfaces their endurance limit value corresponding to the milled state. Moreover, removing the crack networks by polishing generates a stabilised residual stress value of ≈-130 MPa. This results in an improvement rate of about 70% of the endurance limit comparatively with the EDM state and of 26% in comparison to the milled state. These rates could be further increased by the application of the wire brushing process to the polished surfaces that reached 75% and 30% comparatively to the EDM and milling states respectively. In this case, a stabilised surface residual stress of about ≈-150 MPa was measured on the specimen surfaces. Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/10985/17903 2011-01-01T00:00:00Z GHANEM, Farhat FREDJ, Nabil Ben SIDHOM, Habib BRAHAM, Chedly Machining the EN X160CrMoV12 tool steel by electro-discharge machining (EDM) process generates significant modifications of microgeometrical, microstructural and mechanical properties of the upper layers of the machined components. In this paper, the role of these modifications in controlling the stability, under cyclic loading, of the propagation of the crack networks generated by EDM is discussed. High cycle fatigue tests (2×106 cycles) show that the presence of these cracks in brittle layers, i.e. white layer, quenched the martensitic layer, and a field of tensile residual stresses (+750 MPa) results in a loss of 34% of endurance limit comparatively with the endurance evaluated for the milled state that generates crack-free surfaces. It is shown, in this work, that the detrimental effect of these crack networks can be controlled by putting in compression the upper layers of the EDM surfaces. Indeed the application of wire brushing to EDM surfaces generates compressive residual stresses (≈-100 MPa) that stabilise the crack networks propagation and therefore restores to the EDM surfaces their endurance limit value corresponding to the milled state. Moreover, removing the crack networks by polishing generates a stabilised residual stress value of ≈-130 MPa. This results in an improvement rate of about 70% of the endurance limit comparatively with the EDM state and of 26% in comparison to the milled state. These rates could be further increased by the application of the wire brushing process to the polished surfaces that reached 75% and 30% comparatively to the EDM and milling states respectively. In this case, a stabilised surface residual stress of about ≈-150 MPa was measured on the specimen surfaces.