Papers by Author: José Divo Bressan

Abstract: The fretting is responsible for many failures of components in the industry. It is present in assemblies like rivet and screw fixture, dovetailjoint, shaft and hub with key, and all connections of two bodies with a contact force and a small induced relative displacement. Topic of studies for decades, the researchers perform experimental tests with some simplification in order to accelerate the phenomenon, some times using standard devices or creating dedicated machines for better representing the behavior of the desired components. There are a few studies with thin sheets, in which the fretting fatigue has more impact because a small reduction of the cross section due to the wear of crack results in a significant increase of stress and rate of crack propatation, decresing the number of cycles until failure. In this work, it wasbuild a device to generate the fretting fatigue with two different shape of contact pad. The specimen is a stainless steel sheet thickness 0.152mm, which fractures and surfaces were analyzed using the SEM and white light interferometer to understand the fractures.

Abstract: This study aims to assess the evolution of surface roughness and waviness parameters with plastic strain in Interstitial Free – IF steel sheet. For the achievement of this study, it was considered various roughness and waviness profile parameters such as: arithmetic average roughness (Ra), maximum distance peak-valley (Rt), average waviness (Wa) and waviness of the total height peak-valley (Wt). Tensile test specimens of IF steel at 0º, 45º and 90º to the direction of rolling were fabricated. After preparing the sheet proof specimens, it was performed simple tensile tests and measurements of roughness and waviness of the specimen surface at various strain stages resulting in a large quantity of data. During the tensile test, it has been measured the following plastic strain to indicate the incremental step: (e1) longitudinal strain and (e2) transverse strain. From these data, it was possible to obtain points needed to plot the curves of roughness and waviness parameters versus strain and to determine the material behavior using equations of the equivalent strain. From the curves drawn it was possible to see how the material roughness and waviness behaves during the straining in the uniaxial tensile state, with the possibility to predict the influence of plastic strain on roughness and waviness parameters and the onset of local necking of IF steel sheet. The waviness parameters Wt is the best for characterizing the onset of local necking.

Abstract: Hot extrusion is a metal forming process with a huge importance in the manufacturing of long metallic bars with complex shapes, and because of this, academics and industries are especially interested in better understanding how metal flows during the process. In order to have a reliable computational tool that can help to solve and to obtain material internal flow, experimental tests and numerical simulation with the finite element method were carried out to obtain results of the velocity fields generated in hot direct extrusion of aluminum billets (aluminum alloy 6351). The experimental results of the velocity field will be used to validate a computational code based on the finite volume method.

Abstract: The aim of this study was to evaluate the influence of the amount and distribution of inclusions of titanium carbonitride and manganese sulfide on the machinability and polishability of Villares VP100 steel which is used in manufacturing polymer injection molds. By means of materials metallography, captured images were processed with image analysis software to characterize the inclusions. Tool life tests were performed in an open cavity in order to approach the real processes situation found in the toolmaking industry. The flank wear and chip formation were evaluated periodically. The cutting forces were also evaluated under the same conditions applied to the tool life test. The polishing tests were performed in a polishing equipment specially developed for this purpose, which allows adjustable rotation speed and pressure load. In the polishing process, abrasives with particle size of 1mm are applied and surface roughnesses of the samples were evaluated according to the polishing time. The results show that the amount of titanium and size of titanium carbonitride hard inclusions are fundamental for good machinability, while the soft sulfides of manganese do not take any effect in the presence of these hard particles. The polishability is worsened by the presence of large inclusions of manganese sulfides, forming pin holes.

Abstract: The aim of this study was to evaluate the influence of tool flank wear on polishability and wear resistance of mold steel. Two surfaces of Villares VP20ISO steel were machined, one was roughed with worn tools (VB>0.3 mm) and another one with new tools (0.05 mm<VB<0.1 mm), followed by the finishing process of both surfaces by machining with new tools. The surface residual stresses were then measured using the X-ray diffraction method. Surfaces were etched down to different depths in order to monitor the residual stresses in the total affected depth of workpiece deformed layer. The results show that the cutting and passive forces provided the major differences between two machining conditions. The micro-hardness in the cross section did not show significant differences. Moreover, the residual stress measurements showed that after the finishing process, the surface roughed with new tools exhibited 100 MPa compressive stresses at 35 mm below the surface, while the surface roughed with worn tools provided a valley of tensile stress from the surface. Tests conducted on a pin-on-disk tribometer showed that the wear rates of the surface roughed with new tools were lower than the one roughed with worn tools and, after the polishing process, that the surface finishing of the surface roughed with new tools was better.