Etude de l'intégrité de surfaces obtenues par usinage de haute précision d'un acier à roulement 100Cr6 (application à la tenue en fatigue de contact)

COMPIEGNE-BU (601592101) / SudocSudocFranceF

Investigation of Surface Integrity Induced by Various Finishing Processes of AISI 52100 Bearing Rings

Surface integrity induced by finishing processes significantly affects the functional performance of machined components. In this work, three kinds of finishing processes, i.e., precision hard turning, conventional grinding, and sequential grinding and honing, were used for the finish machining of AISI 52100 bearing steel rings. The surface integrity induced by these finishing processes was studied via SEM investigations and residual stress measurements. To investigate rolling contact fatigue performance, contact fatigue tests were performed on a twin-disc testing machine. As the main results, the SEM observations show that precision hard turning and grinding introduce microstructural alterations. Indeed, in precision hard turning, a fine white layer (<1 μm) is observed on the top surface, followed by a thermally affected zone in the subsurface, and in grinding only, a white layer with 5 μm thickness is observed. However, no microstructural changes are found after sequential grinding and honing processes. White layers induced by precision hard turning and grinding possess compressive residual stresses. Grinding and sequential grinding and honing processes generate similar residual stress distributions, which are maximum and compressive at the machined surface and tensile at the subsurface depth of 15 μm. Precision hard turning generates a “hook”-shaped residual stress profile with maximum compressive value at the subsurface depth and thus contributes as a prenominal factor to the obtainment of the longest fatigue life with respect to other finishing processes. Due to the high quality of surface roughness (Ra = 0.05 μm), honing post grinding improves the fatigue life of bearing rings by 2.6 times in comparison with grinding. Subsurface compressive residual stresses, as well as low surface roughness, are key parameters for extending bearing fatigue life

Sustainable High-Speed Milling of Magnesium Alloy AZ91D in Dry and Cryogenic Conditions

Magnesium alloy AZ91D is used extensively in the automotive industry because of its high strength-to-weight ratio. Typically, components produced using the alloy are required to have good surface finish and to contribute to high productivity but require long cutting times. Cryogenic cooling is an environmentally friendly technology which has been proven to improve cutting tool life and surface finish. This paper presents an investigation on the effects of dry and cryogenic cutting conditions at a high cutting speed regime for milling of magnesium alloy. This study focused on a high-speed regime due to the chips of magnesium alloy being highly combustible and an effective means of decreasing the temperature in the cutting zone was of great concern. The machining experiment was carried out using uncoated carbide end milling utilizing a full factorial design (L16) with cutting speeds of 900 m/min and 1300 m/min, feed rate of 0.02 mm/tooth and 0.05 mm/tooth, axial depth of cut at 0.2 mm and 0.3 mm, and radial depth of cut at 10 mm and 40 mm. For dry machining, the longest tool life at flank wear (VBmax) of 0.21 mm was at 30 min, which was obtained at cutting speeds of 1300 m/min, feed rate of 0.02 mm/tooth, axial depth of cut at 0.2 mm, and radial depth of cut at 40 mm. Using this cutting condition, a mirror-like surface of 0.106 µm was produced. For machining under cryogenic condition at VBmax of 0.2 mm, the maximum tool life of 1864 min was achieved at a cutting speed of 900 m/min, feed rate of 0.02 mm/tooth, axial depth of cut of 0.3 mm, and radial depth of cut of 40 mm. Under this cutting condition, a lower surface finish of 0.091 µm was obtained. It can be concluded that the application of liquid nitrogen (LN2) is very effective in enhancing the tool life and in obtaining a better-machined surface, especially at a lower cutting speed of 900 m/min. A longer tool life and high-quality machined parts will significantly improve the productivity and cost savings in the related industry

The Role of Orientation and Temperature on the Mechanical Properties of a 20 Years Old Wind Turbine Blade GFR Composite

This work evaluates the mechanical properties of the glass fiber reinforced polymer (GFRP) material taken from an out of service 100 KW power wind turbine blade which has been in service life of 20 years old. Investigated samples were taken from two positions of undamaged regions at 1.6 m and 5.4 m from the rotor hub, respectively. Microstructure investigation and lay-up analysis were carried out. Fiber weight fraction of the investigated samples was ranging between 0.55–0.60. Tensile and compression tests were carried out at the temperature range from −10 °C to +50 °C on specimens which were machined so as to be loaded in the blade length direction LD, transverse to the blade length TD and off axis; 45° to the blade length. Tensile elastic modulus of the investigated GFRP was determined in the three direction tested. The number of fiber fabric layers found to be decreasing along the blade length away from the root and the density of the fibers along the length is the highest (858 gm/mm2) and in the transverse direction is the lowest (83 gm/mm2). The microstructure of the GFRP composite showed good wetting for the fiber by the polymer with some features of lack of penetration at the high density fiber bundles and some production porosity in the matrix. The tensile Properties at room temperature (RT) and high temperature are almost similar with the highest properties for the samples aligned with the blade length. The compressive strength is highest at the transverse direction samples and lowest at the blade length direction and decreasing with the increase of the test temperature. The bending properties are significantly affected by the fiber orientation with the highest properties for samples aligned with the blade length and the lowest for the samples with the transverse direction

Dissimilar Friction Stir Welding of AA2024 and AISI 1018: Microstructure and Mechanical Properties

This study investigated the effect of the friction stir welding rotation rate and welding speed on the quality and properties of the dissimilar joints between aluminum and carbon steel. Plates of 4 mm thickness from both AA2024 and AISI 1018 were successfully friction stir butt welded at rotation speeds of 200, 250, and 300 rpm and welding speeds of 25, 50, and 75 mm/min. The joint quality was investigated along the top surface and the transverse cross-sections. Further investigation using scanning electron microscopy was conducted to assess the intermetallic layers and the grain refining in the stir zone. The mechanical properties were investigated using tensile testing for two samples for each weld that wire cut perpendicular to the welding direction and the hardness profiles were obtained along the transverse cross-section. Both the top surface and the transverse cross-section macrographs indicated defect free joints at a rotation rate of 250 rpm with the different welding speeds. The intermetallic compounds (IMCs) formation was significantly affected by the heat input, where there is no formation of IMCs at the Al/steel interfaces when higher traverse speed (75 mm/min) or lower rotation speed (200 rpm) were used, which gave the maximum tensile strength of about 230 MPa at the low rotation speed (200 rpm) along with 3.2% elongation. This is attributed to the low amount of heat input (22.32 J/mm) experienced. At the low traverse speed (25 mm/min and 250 rpm), a continuous layer of Al-rich IMCs FeAl3 is formed at the joint interface due to the high heat input experienced (79.5 J/mm). The formation of the IMCs facilitates fracture and reduced the tensile strength of the joint to about 98 MPa. The fracture mechanism was found to be of mixed mode and characterized by a cleavage pattern and dimples. The hardness profiles indicated a reduction in the hardness at the aluminum side and an increase at the steel side

Bobbin Tool Friction Stir Welding of Aluminum Using Different Tool Pin Geometries: Mathematical Models for the Heat Generation

In this work, three mathematical models for the heat generation during bobbin tool friction stir welding (BT-FSW) of aluminum using three tool pin geometries have been proposed. The models have utilized and updated the available models for the heat generation during the conventional tool friction stir welding (CT-FSW). For the validation of the models, BT-FSW experiments have been carried out for aluminum alloy AA1050 using three different pin geometries (cylindrical, square, and triangular), at different welding speeds of 200, 400, 600, 800, and 1000 mm/min and a constant tool rotation speed of 600 rpm. The welding temperatures during BT-FSW have been measured to be compared with that calculated from the models at the same parameters. It has been found that the calculated welding temperatures from the models and that measured during BT-FSW are in good agreement at all the investigated welding speeds especially in case of the square and cylindrical pins, proving the validity of the developed models for the predication of the heat generation as well as the welding temperatures. This will allow proper designing of the BT-FSW parameters and avoiding the conditions that can deteriorate the joint quality and properties