Abstract Polymeric composite materials, presenting a practical solution for sealing non-metallic expansion joints under extreme conditions such as high temperatures and harsh chemical and physical abrasion, were investigated in this scientific study to discern the impact of welding parameters on their degradation and properties. The study entailed the bonding of polymeric composite blankets through hot plate pressing with a PTFE film, encompassing variations in temperature, duration, and load application. The findings elucidated that lower temperatures and shorter processing times failed to achieve optimal blanket adhesion, while higher temperatures led to material degradation, subsequently diminishing the mechanical strength of the welded joint. In contrast, extended processing times and the application of load during welding demonstrated a positive correlation, enhancing the mechanical strength of the joint by ameliorating interfacial adhesion. This research underscores the critical significance of carefully selecting welding parameters to ensure the peak performance and durability of polymeric composite structures.

Resumo Simulações pelo método dos elementos finitos (MEF) foram realizadas para entender os efeitos das taxas de aquecimento/resfriamento na distribuição de tensões residuais. Dois parâmetros de material dos trilhos foram usados, enquanto as condições de contorno permaneceram constantes: tamanho da zona afetada pelo calor, temperatura máxima e taxa de extração de aquecimento. Para complementar a análise, foi realizada uma solda de topo por centelhamento de um trilho Premium com parâmetros de soldagem ajustado para obter uma baixa extensão de zona afetada pelo calor, sem resfriamento forçado, para examinar a microestrutura formada nas regiões críticas na alma e no extremo do patim. Os resultados mostraram que houve concentração de tensões residuais verticais na região da alma, enquanto a presença de tensão residual de compressão no sentido horizontal foi predominantemente superficial na região do trilho superior. Ao usar dois parâmetros de simulação de materiais semelhantes (trilhos), os resultados foram substancialmente diferentes. Os exames metalográficos mostraram que não havia presença de microconstituintes aciculares (martensita/bainita). Além disso, foi observada ferrita pro-eutetóide na região central, cementita em contorno de grão austenítico prévio na região próxima a AC3 e esferoidização quase completa na região de sítio de esferoidização máxima da alma. Em contrapartida, na região do extremo do patim, apresentou microestrutura completamente perlítica na região central e próxima a AC3 e menor volume de esferoidização na região de máxima esferoidização, provavelmente devido à maior taxa de resfriamento nesta região.

Abstract Simulations using the finite element method (FEM) were done to understand the effects of heating/cooling rates on the distribution of residual stresses. Two material parameters from rails were used while the boundary conditions remained constant: heat-affected zone size, maximum temperature and heating extraction rate. To complement the analysis, a flash-butt weld of a Premium rail was done with welding parameters adjusted to obtain a narrow HAZ, without forced cooling, to examine the microstructure formed in the critical regions in the web and the edge of the rail foot. The results showed that there was a concentration of vertical residual stresses in the web region, while the presence of horizontal compression residual stresses was mostly superficial in the rail head region. The main result from the simulation sets was that when using two simulation parameters with similar materials (rails) substantially different results were obtained. Metallographic examinations showed that there was no presence of acicular microconstituents (martensite/bainite). In the rail web, proeutectoid ferrite was observed in the central region, cementite in a previous austenitic grain boundary, in the region that reached temperatures close to AC3, and almost complete spheroidization in the region of maximum spheroidization. In contrast, in the rail foot edge region, there was a completely pearlitic microstructure, in the central region and in the zone that reached temperatures close to AC3, and a lower volume of spheroidization in the region where maximum spheroidization is typically observed, probably due to the higher cooling rate in this region.

Abstract This study analysed the integrity of welded joints of a UNS S32205 duplex stainless steel, using different welding energies: 0.5 kJ.mm-1, 1.0 kJ.mm-1, and 3.5 kJ.mm-1. Microstructural characterisation, tensile testing, intergranular attack susceptibility testing (ASTM A262 practice A) and pitting/crevice corrosion resistance tests (critical pitting temperature test, ASTM G48 practice C) were performed in these welded joints. The results showed that the tensile properties of the welded joints did not vary significantly with the welding energy. The microstructure's ferrite content in the molten zone (MZ) was proportional to the welding energy: the ferrite concentration in the 0.5 kJ.mm-1 weldings was approximately 75%. When the welding energy increased to 3.5 kJ.mm-1, the amount of ferrite dropped to 54%. The 3.5 kJ.mm-1 welded joint featured a comparatively higher proportion of coarser austenite grains. The HAZ of the 3.5 kJ.mm-1 welded joint was comparatively more susceptible to the intergranular attack along the α/γ interfaces, while in the base metal and the other two welded joints, the intergranular attack along the α/γ interfaces was not prominent. Additionally, the pitting corrosion took place preferentially in the ferrite phase of the HAZ for all welding conditions.

Resumo: Ao analisar a norma ABNT NBR 8800-2008, foi constatado que não há consideração sobre a tensão ou compressão exercida nas regiões soldadas por filetes. O cálculo para dimensionamento de perna só leva em referência o cisalhamento da seção. Utilizando recursos como a simulação e o ensaio mecânico de tração, foi possível comparar as dimensões mínimas das pernas com a estipulada pela norma NBR. Realizou-se o processo de soldagem com eletrodo revestido, utilizando o aço estrutural ASTM A36, e para realização da soldagem foi empregado o eletrodo AWS A5.1 E7018. As soldagens focaram com tamanho de filetes com perna entre 3,5 mm e 7 mm que posteriormente estas juntas soldadas foram submetidas a ensaios de tração. Para a comparação dos resultados, foi empregado simulação numérica estática em tração pelo método dos elementos finitos com auxílio do software Abaqus®. Assim com os dados gerados através da simulação e o ensaio mecânico de tração pode-se legitimar as especificações da norma em relação ao tamanho mínimo de perna em relação à espessura da chapa.

Abstract: It was found that there is no consideration of the tensile or compression stresses applied in the regions of fillet weld when analyzing the ABNT NBR 8800-2008 standard. The calculation for dimensioning the leg only takes into account the section shear. Using resources such as simulation and mechanical traction test, it was possible to compare the minimum dimensions of the legs with that stipulated by the NBR standard. The welding process was carried out with a coated electrode, using structural steel ASTM A36, and the welding was performed using the AWS A5.1 E7018 electrode. Tensile testing were performed on fillet welding samples with lengths between 4 mm and 8 mm. It was used a numerical simulation in traction by the finite element method was used with the aid of the Abaqus® software. Thus, with the data generated through the simulation and the mechanical tensile test, the specifications of the standard can be assured in relation to the minimum leg size in relation to the plate thickness.

Abstract Stress corrosion cracking (SCC) of UNS S31603 austenitic stainless steel (ASS), UNS S32205 duplex stainless steel (DSS) and UNS S32750 super duplex stainless steel (SDSS) was investigated. SCC tests were carried out at 110 ºC for 500 h under drops of synthetic seawater (DET, drop evaporation test). Two loading conditions were investigated: 50 % and 100 % of the experimental yield strength of each steel. DSS and SDSS specimens showed no susceptibility to SCC under loading of 50 % of their yield strength, contrary to ASS, but all steels fractured at the highest load. SCC nucleated under the salt deposit formed on the surface of all specimens. SCC propagation was mainly transgranular, but SCC propagation of DSS also featured crack ramification in the austenite phase. In addition, SDSS also presented crack propagation along the ferrite/austenite interfaces. Transgranular cleavage fracture was also observed in all fractured specimens, but DSS also presented ferrite/austenite interfacial brittle fracture, while SDSS also featured intergranular brittle fracture.