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Percorrer por autor "Costa, J.D.M."

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  • Analysis of the initial delamination size on the mode I interlaminar fracture of carbon/epoxy composites
    Publication . Reis, P.N.B.; Ferreira, J.A.M.; Antunes, F.V.; Costa, J.D.M.; Capela, C.; Capela, Carlos;
    This paper describes an experimental study of the initial delamination length effects on the mode I fracture toughness using DCB tests. Delamination failure was also predicted using exponential cohesive model and a quite good agreement with experimental results was obtained. Numerical predictions showed a significant influence of initial delamination length on the force-displacement curves.
    2009Atas de conferência Acesso aberto Ver mais
  • Assessment of the fatigue performance of heat-treated addictive manufactured TiAl6V4 specimens
    Publication . Borrego, L.P.; Jesus, J. de; Ferreira, J.A.M.; Costa, J.D.M.; Capela, C.; Capela, C.
    Titanium Ti6Al4V alloy has excellent mechanical properties and corrosion resistance combined with low specific weight, and is commonly used in biomedical applications, automotive and aerospace components, involving fatigue loadings. Current work studies the fatigue behavior under strain amplitude control of titanium TiAl6V4 specimens, intending to characterize fatigue strength from low to high life range after different heat treatments. Fatigue tests were carried out at room temperature, using round dog bone specimens produced by selective laser melting (SLM), where laser powder deposition occurred in layers perpendicular to the loading direction. Two batches of specimens were tested: one subjected to a stress relieve treatment and a second one treated by the hot isostatic pressing process (HIP). The material was characterized in terms of the tensile mechanical properties, cycle curve, Basquin and Coffin equations. Additional analysis of the hardness and scanning electron microscopy was carried out to complement the discussion of the results. The obtained dada showed that the stress relieved specimens exhibits significantly cyclic softening, increasing with applied strain, while HIP specimens show a practically stable cyclic behavior in relation to the monotonic curve. Material response for both treatments is well fitted by Basquin and Coffin-Manson formulations. The transition life was 187 reversals and 326 reversals, for stress relieved and HIP specimens, respectively. Fatigue life for a given strain is governed by the strain value, independently of the post manufacturing heat treatment.
    2019Artigo científico Acesso aberto Ver mais
  • Fatigue behaviour of nanoclay reinforced epoxy resin composites
    Publication . Ferreira, J.A.M.; Borrego, L.P.; Costa, J.D.M.; Capela, C.
    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.
    2013-09Artigo científico Acesso restrito Ver mais
  • Impact response of nano reinforced mat glass/epoxy laminates
    Publication . Ferreira, J.A.M.; Santos, D.S.C.; Capela, C.; Costa, J.D.M.
    The present work intends to characterize the effect that nanoclay and carbon nanotubes matrix reinforcements have on low velocity impact response of epoxy/glass fiber composites. The composite matrix used was the epoxy resin Biresin® CR120 combined with the hardener CH120-3 and the fiberglass triaxial mats ETXT 450. The results of the present paper are discussed in terms of load-time, load-displacement, energy-time diagrams and damage. The incorporation of nanoparticles produces only small improvement of the impact response in terms of the peak load and specific recovery energy. Peak load decreases slightly with increasing percentage of nanoparticles reaching a maximum decrease of 6 % for 3 wt% of nanoclays. Specific recovery energy increases in comparison with control formulation, around 14–18 % for 0.5 wt% addition of nanotubes and 7–15 % for 1 wt% of nanoclays, respectively. Specific recovery energy tends to decrease for higher percentages of nanoparticles in consequence of its poor distribution. Damaged area apparent shows a small reduction with nanoparticle content.
    2015-03-04Artigo científico Acesso restrito Ver mais