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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.

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This work examines the effect of weld strength mismatch on fracture toughness measurements defined by J and CTOD fracture parameters using single edge notch bend (SE(B)) specimens. A central objective of the present study is to enlarge on previous developments of J and CTOD estimation procedures for welded bend specimens based upon plastic eta factors (η) and plastic rotational factors (r p ). Very detailed non-linear finite element analyses for planestrain models of standard SE(B) fracture specimens with a notch located at the center of square groove welds and in the heat affected zone provide the evolution of load with increased crack mouth opening displacement required for the estimation procedure. One key result emerging from the analyses is that levels of weld strength mismatch within the range ±20% mismatch do not affect significantly J and CTOD estimation expressions applicable to homogeneous materials, particularly for deeply cracked fracture specimens with relatively large weld grooves. The present study provides additional understanding on the effect of weld strength mismatch on J and CTOD toughness measurements while, at the same time, adding a fairly extensive body of results to determine parameters J and CTOD for different materials using bend specimens with varying geometries and mismatch levels.

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The mechanical behavior of polypropylene (PP) and 30 wt% coir fiber reinforced PP composites, with and without compatibilizer, were assessed through monotonic (tensile and bending) and cyclic (fatigue) tests. Fatigue load controlled tests were conducted under tension loads at a frequency of 6 Hz. The fracture mechanism was accompanied by surface fracture analyses using both optical microscopy and scanning electron microscopy. The compatibilizer used was the PP grafted with maleic anhydride. The compatibilized composites exhibited longer fatigue life times. It was also concluded that the presence of coir fibers changed the preferential fatigue mechanism, because the fracture mechanism in PP was mainly caused by heat generated by viscous effects during solicitation (thermal fatigue), whereas in the compatibilized and noncompatibilized PP/coir composites the predominant fracture mechanism was mechanical fatigue.