Engenharia de Materiais
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/17
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7 resultados
Resultados da Pesquisa
- Reusing Surlyn® Ionomer Scraps in LDPE Blends: Mechanical and Thermal Properties(2023-01-05) BARBOSA, M. F.; Adriana Martinelli Catelli Souza© 2023 Universidade Federal de Sao Carlos. All rights reserved.This study aimed to evaluate the possibility of reusing industrial scraps of Surlyn® ionomer by obtaining blends with Low-Density Polyethylene (LDPE). Blends of LDPE and Surlyn® scraps were obtained by extrusion with compositions ranging from 25 to 75 wt% of the ionomer. Their melt flow index (MFI), morphology (SEM), mechanical (tensile, flexural, impact tests) and thermal properties (DSC, TGA, HDT tests) were analyzed. The morphology of the blends presented two phases, indicating the immiscibility of phases. Surlyn® incorporation promoted a decrease in the degree of crystallinity of LDPE and a slight increase in the thermal decomposition temperature. In addition, Surlyn® decreased the decomposition rate of LDPE. However, the decrease in the degree of crystallinity did not affect the mechanical properties of the blends. Incorporating ionomer in LDPE promoted an increase in tensile and flexural strength, tensile and flexural modulus and strain at break. Impact strength decreased with increasing ionomer concentration.
- Assessment of the Von Mises Stresses and Stress Triaxiality in Notches Using Modified Tensile Specimens(2023-05-26) PEREIRA, L. DOS S.; Gustavo Donato; MATTAR NETO, M.© 2023 Universidade Federal de Sao Carlos. All rights reserved.Complete understanding of the local stress triaxiality and stress concentration is essential to ensuring structural safety of several structures. A combination of mechanical tests with numerical simulations can be used to obtain this information. One way to study stress triaxiality is by modifying the standard tensile test geometry (ASTM E8) with a notch. Based on previous results from the literature, five notches were chosen: 10, 5, 3, 2, and 1 mm. These geometries were tested, and the results were numerically reproduced using the Abaqus/Explicit 2020 software. The models used were a non-linear model with the Gurson-Tvergaard-Needleman damage model to reproduce the failure. The numerical analyses allowed the assessment of the von Mises stress and stress triaxiality near the notch to compare with the standard smooth specimen. Two instants were considered as crack propagation onset; the instant of the maximum von Mises stress in the element at the center of the specimen, where the failure process begins; and the moment of maximum stress in the true stress x true strain curve. For the von Mises stress analysis, the difference between the curves was small. The stress triaxiality is a better variable to visualize the influences of the notch. When the strain is equal to a 0.07 (instant of the maximum force for the standard specimens), for the smaller notches (1 and 2 mm), there is a region where the effective plastic strain is zero. Consequently, the stress triaxiality is larger in this region than in the center. For the crack propagation onset instant, the plastic strain occurs along the whole transversal section. In this instant, the maximum value of stress triaxiality occurs in the center for all specimens. These results demonstrate that the stress triaxiality changes as the strain increases, i.e., varies with time.
- Polyamide 12 Filled with Cross-Linked Polyethylene Waste: Processing, Compatibilization, and Properties(2023-06-05) MORAES, W. G. B.; BONSE, B. C© 2023 Universidade Federal de Sao Carlos. All rights reserved.Cross-linked polyethylene (XLPE) is primarily used as a coating and insulator for electrical wires and cables. The cross-links render recycling through remelting unfeasible, and XLPE waste is usually incinerated or sent to landfills. Previous investigations showed that XLPE increased the impact strength of commodity thermoplastics. Hence, incorporating XLPE in polyamide 12, an engineering thermoplastic, was studied using maleic anhydride grafted polyethylene (PE-g-MA). Formulations were prepared using a co-rotating twin-screw extruder containing 20 wt% XLPE with 0, 2, 4, and 8 wt% compatibilizer. Test specimens were injection-molded. DSC results showed that adding XLPE and compatibilizer reduced PA12 crystallinity but affected little melt and crystallization temperatures. Morphological analyses revealed poor adhesion between polyamide 12 and XLPE, which improved when adding PE-g-MA. The lack of adhesion when XLPE is added strongly reduces the mechanical properties, except for impact strength, which increased by ca.120% compared to the formulation without XLPE; while using 4 wt% compatibilizer this increase was ca. 140%. When adding PE-g-MA as a compatibilizer, some recovery was achieved in tensile strength and strain at break, and impact strength increased furthermore. Flexure and HDT tests showed a decrease in stiffness after adding XLPE. Stiffness was further reduced in compositions containing compatibilizer.
- Effect of aging heat treatment H950 and H1000 on mechanical and pitting corrosion properties of uns s46500 stainless steel(2018-01-05) BERALDO, C. H.; CALDERON-HERNANDEZ, J. W.; Rodrigo Magnabosco; ALONSO-FALLEIROS, N.© 2018 Universidade Federal de Sao Carlos. All rights reserved.The effect of aging temperature on mechanical and pitting corrosion properties of UNS S46500 was investigated. Tensile and Hardness tests were carried out and the microstructure was analyzed by optical microscopy, scanning electron microscopy and X-ray diffraction; Thermo-Calc simulations helped in the phase identification. Pitting corrosion properties were investigated in 0.6M NaCl electrolyte with sulfate additions by Potentiodynamic Polarization (PP). Hardness, tensile and yield strength of the UNS S46500 steel after lower aging temperature, 510ºC (H950), are higher than the ones found in the 538ºC (H1000) aged steel.This result is explained by microstructure, X-ray diffraction and Thermo-Calc analysis, which indicated the presence of austenite, chi phase and probably Ni3Ti precipitates finely and uniform distributed throughout the martensite matrix. Pitting corrosion resistance is equivalent in both aging temperatures. The sulfate inhibitor effect on UNS S46500 steel was enhanced for 538ºC condition when the electrolyte reaches 1Cl-:1SO4 2- ratio, which is explained by Ni sulfate adsorption and the amount of interfaces in the microstructure resulting in smaller amount of adsorption sites, such as coarsened Ni3Ti precipitates, smaller fraction of chi phase and recovery of dislocations in martensite structure.
- Comparison between stainless steels and Nickel alloys through pitting corrosion resistance electrochemical tests(2021-04-27) FRAZÃO, I.; Rodrigo Magnabosco; DELBLANC, A.© 2021 Universidade Federal de Sao Carlos. All rights reserved.Critical pitting temperature (CPT) is one of the most accepted criteria for alloy classification concerning pitting corrosion. The techniques used nowadays to determine CPT have different parameters for alloys of different material classes, preventing the comparison between stainless steels and nickel based alloys. This study aims to compare the corrosion resistance of nickel based alloys and stainless steels with high corrosion resistance through potentiostatic tests for CPT determination, using a 3M MgCl2 aqueous solution. CPT values were effectively determined for the stainless steels studied but the technique did not have the same efficiency for nickel based alloys due to the occurrence of crevice corrosion, even considering the higher PRE of nickel based alloys.
- Influence of the microstructure on the degree of sensitization of a duplex stainless steel UNS S31803 aged at 650°C(2013) De Melo E.B.; Magnabosco R.; De Moura Neto C.This work evaluates the phase transformations during aging of an UNS S31803 DSS at 650°C and its influence on the DOS. The material was solution treated at 1175°C and then aged at 650°C for times up to 360 h. SEM-BSC images indicate the formation of Cr2N, σ and ÷ phases in the samples aged at 650°C. The analysis of DL-EPR curves, obtained in a 1 M H2SO4 + 0.25 M NaCl + 0.01 M KSCN solution, shows an increase in DOS values for samples aged at 650°C. Probably, this increase observed in DOS values is mainly related to the presence of Cr-and/or Mo-depleted á, as a result of σ phase, ÷ phase and/or Cr2N formation at 650°C. Moreover, a possible healing up of Cr-and/ or Mo-depleted areas is observed between 1 h and 4 h of aging at 650°C.
- Kinetics of sigma phase formation in a duplex stainless steel(2009) Magnabosco R.This work determines the kinetics of sigma phase formation in UNS S31803 Duplex Stainless Steel (DSS), describing the phase transformations that occur in isothermal aging between 700 and 900 °C for time periods up to 1032 hours, allowing the determination of the Time-Temperature-Precipitation (TTP) diagram for sigma phase and proposing a model to predict the kinetics of sigma phase formation using a Johnson-Mehl-Avrami (JMA) type expression. The higher kinetics of sigma phase formation occurs at 850 °C. However, isothermal aging between 700 and 900 °C for time periods up to 1032 hours are not sufficient to the establishment of thermodynamic equilibrium. Activation energy for both nucleation and growth of sigma phase is determined (185 kJ.mol-1) and its value is equivalent to the activation energy for Cr diffusion in ferrite, indicating that diffusion of Cr is probably the major thermally activated process involved in sigma phase formation. The determined JMA type expression presents good fit with experimental data between 700 and 850 °C.