Luiz Carlos Rolim Lopes

Finite element analysis of the tube flow forming process

In this work, a numerical study is presented with to analyse the flow forming process as a function of the initial condition of the preform material, namely, in the as-received state and after quenching and tempering heat treatments. An industrial tube flow forming process is analysed with 2D plane-strain and 3D Finite Element (FE) models. The predictions indicate that the as-received condition gives slightly lower drawing forces in comparison to the quenching and tempering condition. Finally, the results determined with the 3D FE modelling show that the drawing forces strongly depend upon the element formulation adopted to describe the preform blank.

Effects of Heat Input Conditions on the Local Thermophysical Properties of Super Duplex Stainless Steels

The thermal properties of the super duplex stainless steels are strongly affected by the thermal history when welding procedure are applied leading to substantial changes on the mechanical properties of the welding region. The controlled dual phase microstructure (ferrite and austenite) guarantee excellent mechanical properties such as mechanical strength and corrosion resistance, in addition to small thermal expansion coefficient and high thermal conductivity. In this research a model able to predict the thermal history of the welding pieces coupled with local mechanical properties developed during welding procedure is developed. The model was verified by measured temperature profile and used to predict local properties such as grain size evolution, hardness and mechanical strength. An inverse method was implemented to obtain the parameters fitting for the grain growth evolution, hardness and yielding strength compatible with the final microstructure and grain size measured using SEM images and stereological techniques.

Correlation between Microstructure and Mechanical Properties of Austempered Ductile Irons

Austempered ductile cast irons (ADI) have received great attention in last years because their combined properties of good ductility, high strength and fracture toughness, good fatigue strength, good wear properties and low production cost. Such combination of properties can be reached because of their microstructures consist of a mixture acicular ferrite (bainite), residual austenite with a high carbon content and nodular graphite. In this work, the effect of austempering heat treatment on the microstructure of a commercial alloy to produce three different grades of ADI, with different strength level, is analyzed. Microstructure characterization has been performed using techniques of optical microscopy, scanning electron microscopy and x-ray diffraction. Mechanical properties were evaluated from tensile and impact tests at room temperature. In addition, the residual stress due to heat treatment was evaluated. The results of this study show that there is a strong relationship between austempering temperatures and mechanical properties. The highest tensile and yield strength obtained were 1599 and 1427 MPa, respectively, for the sample austempered at 280°C. The sample austempered at 320°C presented the highest Charpy absorption energy (99,90 J) and highest volume fraction of austenite (27%).

Study of the Effects of SiO2 Nanoparticles Concentration on the TiO2 Nanoparticles Suspensions Stabilization

TiO2 nanoparticles (NPTiO2) suspensions are in several ecosystems and residue treatment processes or disposal systems due to their large industrial use and handling. The interactions of the NPTiO2 with NPSiO2 have special interest due to their strong ability to maintain high TiO2 nanoparticles concentration in suspension and promote nanoparticles clustering. These characteristics are used either in cleaning systems or in production of nanoparticles solution for several applications in the food industry or medicine. In this study, suspensions of NPTiO2 and NPSiO2 are synthetized and their stabilizations are discussed. A base TiO2 nanoparticles suspension was synthetized and the initial concentrations of SiO2 nanoparticles (NPSiO2) were changed in order to determine the effects of presence of SiO2 nanoparticles on the stabilization and clustering size. Zeta potential and concentrations measurements were carried out throughout the time and correlated with the initial concentrations of the base suspensions. In this study, the concentrations, zeta potential and pH are measured to estimate the stability of the suspensions. The clustering size, obtained by nanoparticle tracking analysis (NTA), are also monitored and discussed. Results of column soil experiments are discussed and compared under similar conditions with literature data.

Modelamento numérico de um cilindro do tipo 2 para armazenamento de GNV

ISO 11439 standards considers 4 types of high-pressure cylinders to storing natural gas for vehicles applications. Among them the type 2, metal-lined hoop wrapped cylinder, is the aim of this work. It describes a numerical model built using ANSYS application to determine stress on the metal liner and on the composite material applied on the liner via filament winding process. Using design criterion for laminate composites, the total thickness of the composite layer has been evaluated to get an optimized value. Employing the element shell multilayer of ANSYS 8.1 and a model of the type 2 cylinder, the stress state in the metal liner and in each layer of the composite system of epoxy-glass fibre has been studied. The failure criterion of Hill-Tsai for composite laminates was used to analyse failure of each layer. The results are analysed considering the performance of the cylinder under test conditions of loading of 30 MPa.

Numerical Modelling of a High-Pressure Type 2 Cylinder for Storing Natural Gás for Vehicles

ISO 11439 standards considers 4 types of high-pressure cylinders to storing natural gas for vehicles applications. Among them the type 2, metal-lined hoop wrapped cylinder, is the aim of this work. It describes a numerical model built using ANSYS application to determine stress on the metal liner and on the composite material applied on the liner via filament winding process. Using design criterion for laminate composites, the total thickness of the composite layer has been evaluated to get an optimized value. Employing the element shell multilayer of ANSYS 8.1 and a model of the type 2 cylinder, the stress state in the metal liner and in each layer of the composite system of epoxy-glass fibre has been studied. The failure criterion of Hill-Tsai for composite laminates was used to analyse failure of each layer. The results are analysed considering the performance of the cylinder under test conditions of loading of 30 MPa.