Selective laser melting has received a great deal of attention in recent years. Nevertheless, research has been mainly focused on the technical issues and their relationship with the final microstructure and monotonic properties. Fatigue behaviour has rarely been addressed, and the emphasis has been placed on high-cycle regimes. The aim of this paper is, therefore, to study, in a systematic manner, the cyclic plastic behaviour of AISI 18Ni300 maraging steel manufactured by selective laser melting. For this purpose, low-cycle fatigue tests, under fully-reversed strain-controlled conditions, with strain amplitudes ranging from 0.3% to 1.0%, were performed. After testing, fracture surfaces were examined by scanning electron microscopy to identify the main fatigue damage mechanisms. The analysis of results showed a non-Masing material, with a slight strain-softening behaviour, and non-linear response in both the elastic and plastic regimes. In addition, this steel exhibited a very low transition life of about 35 reversals, far below the values of conventional materials with equivalent monotonic mechanical properties, which can be attributed to the combination of high strength and low ductility. The total strain energy density, irrespective of strain amplitude, revealed itself to be a quite stable parameter throughout the lifetime. Finally, the SEM analysis showed for almost all the tested samples cracks initiated from the surface and inner defects which propagated through the rest of the cross section. A ductile/brittle fracture, with a predominance of brittle fracture, was observed in the samples, owing to the presence of defects which make it easier to spread the microcracks.

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Nanoparticle filling is a feasible way to increase the mechanical properties of polymer matrices. Abundant research work has been published in the last number of years concerning the enhancement of the mechanical properties of nanoparticle filled polymers, but only a reduced number of studies have been done focusing on the fatigue behaviour. This work analyses the influence of nanoclay reinforcement and water presence on the fatigue behaviour of epoxy matrices. The nanoparticles were dispersed into the epoxy resin using a direct mixing method. The dispersion and exfoliation of nanoparticles was characterised by X-ray Diffraction (XRD) and transmission electron microscopy (TEM). Fatigue strength decreased with the nanoclay incorporation into the matrix. Fatigue life of nanoclay filled composites was significantly reduced by the notch effect and by the immersion in water.

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Natural fibers combine technological, economic and ecological aspects. However, a major restriction on their successful use in long term composite applications is their high moisture absorption and poor dimensional stability. This paper is aimed at establishing a link between the mats grammage and the mechanical properties of the epoxy/jute fibers laminates. Composites reinforced by coarse, medium and fine (C, M and F) mats were processed by vacuum bagging. Some batches were immersed in water up to 60 days in order to study the hydro-degradation. Mechanical tests were performed to obtain the bending strength and impact response. The mechanical response to bending and impact loadings was conditioned not only by the percentage of fiber, but also by the thickness of the specimens, which leads to composites F having lower strength than composites C despite having a higher percentage of fiber. Immersion in water causes a marked loss of mechanical properties in the first days of immersion, especially for thinner fiber grammage composites. A strong influence of the mats grammage on the impact response was observed. Increasing mats grammage promotes a strong increase in peak load, restored energy and impact energy for perforation and also a marked reduction of the deformation.