Browsing by Author "Batista, A. C."
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- Effect of bead characteristics on the fatigue life of shot peened Al 7475-T7351 specimensPublication . Ferreira, N.; Jesus, J. S.; Ferreira, J. A. M.; Capela, C.; Costa, J. M.; Batista, A. C.The present work aims to analyse the effect of shot peening processing parameters, material and size of beads on the fatigue behaviour of aluminium alloy AA7475-T7351. A systematic study was carried out on the roughness, surface hardening, residual stress profiles and fatigue life. Fatigue tests were carried out under both three points bending (3 PB) and tensile loadings. For 3 PB tests it was concluded that shot peening does not introduce significant improvement on fatigue life and that the use of low size glass beads is potentially beneficial, with roughness being as or more important than residual stresses. All tensile treated specimens presented an improvement of fatigue life in comparison to the untreated specimens, particularly when the crack initiated internally. Internal crack propagation generates a conical fracture surface until transition to mode I propagation.
- Evaluation of stress-strain behavior of surface treated steels by X-ray diffractionPublication . Coelho, Luís Manuel de Jesus; Batista, A. C.; Nobre, J. P.; Marques, M. J.X-ray diffraction assisted four-point bending method (XRDABM) enables to analyze the evolution of surface stress with the strain during bending of specimens. This experimental methodology was used to characterize the stressstrain behavior of two plasma nitriding steels, DIN 40 Cr Mn Mo 7 and DIN 32 Cr Mo V 13, with gradients of mechanical properties across the surface layers, allowing the characterization of the in-depth evolution of the local yield strength in the nitrided layer. The results show a significantly increase of the yield strength of the nitride layers and a good agreement between the in-depth evolution of the yield strength and the XRD peak breadth for the two nitrided steels.
- Two experimental methods to determining stress-strain behavior of work-hardened surface layers of metallic componentsPublication . Nobre, João P.; Batista, A. C.; Coelho, Luís Manuel de Jesus; Dias, A. M.Two experimental methods to characterize the mechanical behavior of work-hardened surface layers of metallic materials, induced by mechanical surface treatments, are described and discussed. The study was conducted using two steels with different mechanical properties, subjected to a similar shot-peening treatment. To characterize the elastic–plastic behavior of the surface layers affected by shot-peening, the X-ray diffraction assisted four-point bending method (XRDABM) and the normalized hardness variation method (NHVM) were applied. The results were compared and discussed taking into account the advantages and disadvantages of both methods. Similar yield strength values of the treated surfaces were found by both proposed methods. Taking into account their measuring characteristics, these can be considered complementary methods.