Aline Emanuelle Albuquerque Chemin

Este artigo utiliza diversos modelos de previsão de vida à fadiga implementados no programa NASGRO para prever o comportamento de trincas sob carregamento de amplitude constante e variável. Os dados experimentais consistem em uma liga de alumínio aeronáutico SAE-AMS 7475-T7351. Corpos de prova compactos C(T) foram utilizados para amplitude de carregamento constante (CAL), enquanto corpos de prova M(T) foram selecionados para amplitude de carregamento variável (VAL). Com relação aos dados de amplitude constante, as taxas de crescimento da fadiga e, consequentemente, os parâmetros da equação de Paris e os valores de KIC foram obtidos a partir das simulações. Dessa forma, os valores obtidos foram satisfatórios, com boas correlações. Em relação à VAL, os parâmetros de calibração para cada modelo de interação foram obtidos para cada espectro de carga neste trabalho: os espectros TWIST e FALLSTAFF e suas versões mini. O programa NASGRO 4.0 apresentou, de modo geral, bons resultados de previsão.

This study investigates the effects of different post-weld heat treatments (PWHT) on the mechanical properties and microstructure of ASTM 335 Gr P91 martensitic steel, commonly used in boiler applications. Mechanical tests were conducted at room temperature, 300°C, and 600°C. Two PWHT conditions were applied: (i) PWHT-1, involving a 300°C isothermal treatment followed by heating to 770°C, and (ii) PWHT-2, following the same profile but without cooling to room temperature after the initial isothermal step. The resulting microstructure exhibited martensitic features, with a gradient of prior austenite grain boundaries in the heat-affected zone (HAZ) and δ-ferrite formation in the fusion zone (FZ), reducing toughness. Ultimate tensile strength decreased with increasing temperature, ranging from 675–750 MPa (RT), 525–615 MPa (300°C), and 375–440 MPa (600°C). Elongation was highest at 600°C (BM: 25–30%, FZ: 8–20%), decreasing at room temperature (BM: 20–25%, FZ: 2–12%). Toughness tests showed crack propagation across BM, HAZ, and FZ, with the lowest energy absorption in FZ (0.05–0.4 mm, 12–50 J). At 600°C, toughness decreased in BM and HAZ but increased in FZ, suggesting a change in deformation mechanisms at elevated temperatures.