The influence of Martensite Volume Fraction (MVF) on fracture mechanisms in a Dual Phase steel with two different grain sizes was studied in this work. Ferrite-Martensite microstructure was obtained by an intercritical heat treatment for both groups of grain sizes. The results show a direct relationship between a higher temperature during the intercritical heat treatment and the increase of the MVF. The fine microstructure with higher MVF presents a high tensile strength and a good ductility. Furthermore, in relation to the material behavior under impact conditions, grain refinement and higher values of MVF promote ductile fracture by typical microvoid coalescence. High values of impact energy refer to the presence of low-carbon martensite formed at higher temperatures, which is more ductile than high carbon martensite formed at lower temperatures. Additionally, fine-grained materials have a better ability to dissipate impact energy. It was shown that an increase of 10.0% in MVF allows fine grain microstructures to improve their capacity to dissipate impact energy by 11.4%. This behavior may be explained because of the low carbon content of the as-received material, and the mechanical properties of the martensite obtained by the intercritical heat treatment.

Crack growth resistance in dual-phase steel was studied. The dual phase steel microstructure was modified through heat treatments to increase the martensite volume fraction from 10% to 40%. The as-received and heat-treated samples were evaluated using a uniaxial tensile test, fatigue crack growth test, and fracture toughness test. Extended Finite Element Method (XFEM) was used to simulate the crack growth in compact tension test specimens. The results showed that an increase in martensite volume fraction is an effective way to increase the fracture resistance under different load conditions, quasistatics and dynamic, increasing the fracture toughness, tensile strength and fatigue resistance of the heat-treated material. Presence of a highest content of martensite results in formation of an important number of secondary cracks during the fatigue crack growth, which slow down the crack propagation. Moreover, martensite generates a crack closure over the crack tip, making the propagation difficult due to the irregularities caused by the crack growth on the martensite. Finally, the computational load-displacement curves are in good agreement with the experimental data.

This work analyses the effect of alkali treatment on the mechanical properties of banana fibre (Musa Paradisiaca). Fibres were extracted from the pseudostem by a defibring machine; they were mercerised and modified by 5% NaOH (w/v) alkali treatment. Morphological characterisation showed that treated fibres' surface was rougher than that of untreated fibres. Mechanical characterisation indicated that Young's modulus, ultimate tensile strength and strain became decreased by increasing both treated and untreated fibres' diameter.

The influence of Martensite Volume Fraction (MVF) on fracture mechanisms in a Dual Phase steel with two different grain sizes was studied in this work. Ferrite-Martensite microstructure was obtained by an intercritical heat treatment for both groups of grain sizes. The results show a direct relationship between a higher temperature during the intercritical heat treatment and the increase of the MVF. The fine microstructure with higher MVF presents a high tensile strength and a good ductility. Furthermore, in relation to the material behavior under impact conditions, grain refinement and higher values of MVF promote ductile fracture by typical microvoid coalescence. High values of impact energy refer to the presence of low-carbon martensite formed at higher temperatures, which is more ductile than high carbon martensite formed at lower temperatures. Additionally, fine-grained materials have a better ability to dissipate impact energy. It was shown that an increase of 10.0% in MVF allows fine grain microstructures to improve their capacity to dissipate impact energy by 11.4%. This behavior may be explained because of the low carbon content of the as-received material, and the mechanical properties of the martensite obtained by the intercritical heat treatment.

Las pruebas de impacto son una importante herramienta para la obtención de importantes propiedades, como la tenacidad al impacto y la temperatura de transición ductil-fragil, para la selección de un material en diseño mecánico. Se evaluó la tenacidad al impacto mediante pruebas de impacto Charpy en acero de fase doble (ferrita-perlita) de 10 mm de espesor a temperaturas que oscilan entre 90 ºC y -60 ºC. Las superficies de fractura fueron analizadas por microscopio óptico (MO). Debido a la alta dispersión, mostrada en los resultados, se emplaron numerosas pruebas en las mismas condiciones y el uso de métodos estadísticos para obtener un valor confiable. La temperatura de transición calculada (45 ºC) y la resistencia al impacto de Charpy se analizaron en función de la microestructura y el equivalente de carbono