Percorrer por autor "Antunes, F. V."
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- Analysis of fatigue crack propagation in laser sintering metalPublication . Borrego, L. F. P.; Antunes, F. V.; Ferreira, J. A. M.; Costa, J. D.; Capela, C.Laser sintering metal has recently been used in the manufacture of components for different applications like aerospace or medicine. The approach to engineering design based on the cracks propagation assumption applying the concepts of linear elastic fracture mechanics (LEFM) is commonly used for aerospace engineering. However, fatigue crack propagation is linked to irreversible and non-linear mechanisms at the crack tip, therefore LEFM parameters can be successfully replaced by non-linear crack parameters, namely the plastic CTOD. A model linking da/dN with plastic CTOD is proposed here to characterize fatigue crack propagation. A comparison is made with other materials showing that for the same plastic CTOD the laser sintering material has a relatively large crack growth rate.
- Analysis of manufacturing parameters on the shear strength of aluminium adhesive single-lap jointsPublication . Pereira, A. M.; Ferreira, J. M.; Antunes, F. V.; Bártolo, P. J.An experimental and numerical investigation into the shear strength behaviour of aluminium alloy adhesive lap joints was carried out in order to understand the effect of geometrical and manufacturing parameters on the strength of adhesive bonding joints, with the aim of optimizing shear strength. The adherend material used for the experimental tests was an aluminium alloy in the form of thin sheets, and the adhesive used was a high strength epoxy. Five surface treatments were studied. The surface treatments process using sodium dichromate-sulphuric acid etch (CSA) and abrasive polishing (AP) resulted in improved joint shear strength when compared to acetone cleaning (SW), caustic etch (CE), and Tucker's reagent etch (TR). The decrease in surface roughness was found to increase the shear strength of single-lap joints. An increase in adherend thickness and overlap length was found to increase shear strength which means that an increase in joint rigidity increases its strength. A numerical analysis was developed to explain the effect of the geometrical parameters on rotation angle, stress and strain fields, and failure load. An increase in adherend thickness and overlap length decreases the joint rotation angle, reducing the plastic strain peak and therefore increasing the failure load.
- Assessment of the fatigue life of aluminium spot-welded and weld-bonded jointsPublication . Pereira, A. M.; Ferreira, J. A. M.; Antunes, F. V.; Bartolo, P.J.In modern machinery and automobile structures weight reduction and increased durability are the main issues in design. In these applications, lap welded and/or bonded joints are widely used; therefore, tools are needed to accurately predict their fatigue life. This paper is concerned with the fatigue strength of single lap joints formed with thin plates of 6082-T6 aluminium alloy using a high strength two-component epoxy adhesive (Araldite 420 A/B from Hunstman). Experimental S–N curves were obtained for resistance spot-welded and weld-bonded lap joints. The fatigue lives of weld-bonded joints were significantly higher than those of resistance spot-welding joints. In addition, fatigue lives were predicted with Morrow's modified Manson–Coffin (M/M–C) and the Smith–Watson–Topper (S–W–T) damage equations. Elastic–plastic numerical models were developed, replicating the experimental work, in order to obtain local stress and strain fields. An acceptable agreement was obtained between the numerical predictions and the experimental results. The M/M–C damage equation diverged from experimental results for relatively long fatigue lives, while the S–W–T equation gave good predictions for all fatigue lives.
- Multiaxial fatigue behaviour of maraging steel produced by selective laser meltingPublication . Branco, R.; Costa, J. D.; Martins Ferreira, J. A.; Capela, C.; Antunes, F. V.; Macek, W.This paper studies the multiaxial fatigue behaviour of maraging steel samples produced by selective laser melting. Hollow cylindrical specimens with transverse circular holes are subjected to different in-phase bending-torsion loading scenarios. Fatigue crack initiation sites and fatigue crack angles are predicted from the first principal stress field. Fatigue lifetime is computed using a straightforward approach, based on a one-parameter damage law, developed via uniaxial low-cycle fatigue tests. The cyclic plasticity at the notch-controlled process zone is accounted for by combining the equivalent strain energy density concept and the theory of critical distances within a linear-elastic framework. Regardless of the multiaxial loading scenario, experimental observations and predicted lives are very well correlated.