Percorrer por autor "Jesus, Joel de"
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- Fatigue Behavior of Hybrid Components Containing Maraging Steel Parts Produced by Laser Powder Bed FusionPublication . Santos, Luís; Jesus, Joel de; Borrego, Luís; Ferreira, José A. M.; Fernandes, Rui F.; Costa, José D. M. da; Capela, CarlosThis investigation concerns about of fatigue behavior under controlled loading and under strain control for hybrid specimens with parts produced with conventional processes in steel AISI H13 and the stainless steel AISI 420 and the rest part produced by laser powder bed fusion in AISI 18Ni300 steel. The controlled loading tests were performed in constant and variable amplitude. Fatigue failure of hybrid samples occurs mostly in laser-melted parts, initiated around the surface, in many cases with multi-nucleation and propagated predominantly between the deposited layers. Fatigue strength of hybrid parts, tested under displacement control is similar, but for specimens tested under load control the fatigue strength the fatigue strength of hybrid specimens is progressively lesser than laser powder bed fusion samples. Despite a tendency to obtain conservative predictions, Miner’s law predicts reasonably the fatigue lives under block loadings. The interface between materials presented an excellent joining and fatigue strength because the fatigue failure of hybrid samples occurred mostly in laser melted parts out of the interface.
- Fatigue crack propagation along interfaces of selective laser melting steel hybrid partsPublication . Lima Santos, Luís; Ferreira, José A.M.; Borrego, Luis P.; Costa, Jose D.; Jesus, Joel de; Capela, CarlosSelective laser melting (SLM) is an emerging additive manufacturing technology, capable of producing complex geometry components. The current work studied both the effect of substrate material and mean stress on the fatigue crack growth behaviour along interfaces of bi‐material specimens, substrate, and part by SLM. Fatigue tests were carried out in agreement with ASTM E647 standard, using 6‐mm‐thick compact specimens. The substrate steel has only a negligible effect both on the fatigue crack propagation rate and on the crack path. The failure occurs in the material additively manufactured by SLM, near the interface. The mean stress produced only a reduced influence on the fatigue crack propagation rate in the Paris regime. For larger values of ΔK, where Kmax approaches KIc, a significant influence of the mean stress was observed. In spite of nondetection of crack closure, the application of overloads promoted significant fatigue crack retardation, quite similar for both substrate materials, probably due to the crack bifurcation during the overload.
- Fatigue Failure from Inner Surfaces of Additive Manufactured Ti-6Al-4V ComponentsPublication . Jesus, Joel de; Ferreira, José António Martins; Borrego, Luís; Costa, José D.; Capela, CarlosSelective laser melting (SLM) is an additive manufacturing process for producing metallic components with complex geometries. A drawback of this process is the process-inherent poor surface finish, which is highly detrimental in materials submitted to fatigue loading situations. The goal of this work is to analyze the fatigue behavior of Ti-6Al-4V specimens with internal axial channels under the following different conditions: hole drilled, hole as manufactured, and hole threaded M4 × 0.7. All the cases studied showed a lower fatigue performance as compared with solid samples due to the surface roughness and geometry effect that produced a surface stress concentration leading to a reduction in fatigue strength. The fractography revealed that crack initiation occurred from the internal surface in all specimens with internal channel mostly from defects as unfused particles and lack of fusion zones, while for the solid specimens crack initiation was observed from the external surface due to insufficient fusion defect. The application of the Smith-Watson-Topper energy-based parameter was revealed to be a good tool for fatigue life prediction of the different series studied.
- Influence of Local Properties on Fatigue Crack Growth of Laser Butt Welds in Thin Plates of High-Strength Low-Alloy SteelPublication . Riofrío, Patricio G.; Jesus, Joel de; Ferreira, José A. M.; Capela, CarlosIn this work, local properties such as hardness and fatigue crack grow rate in the heat‐affected zone of four laser‐welded butt joints in thin high‐strength low‐alloy steel were ex-amined, so as to explain and predict fatigue lives at high stress levels through the fracture mechanics approach. The different welded series presented a similar fatigue crack growth rate in the heat‐affected and fusion zones, but lower than base metal due to the higher hardness of the bainitic–martensitic microstructure verified in the welded series. The results showed that at high stress levels in the as‐welded condition, the fatigue initiation stage can be neglected and assume some types of cracks, with an initial crack of 0.07 mm and appropriate fatigue crack growth rates, estimates of fatigue life close to the experimental results were obtained.
- A Novel Specimen Produced by Additive Manufacturing for Pure Plane Strain Fatigue Crack Growth StudiesPublication . Jesus, Joel de; Borges, Micael; Antunes, Fernando; Ferreira, José; Reis, Luis; Capela, CarlosFatigue crack growth is usually studied using C(T) or M(T) specimens with through-thickness cracks. The objective of the present study is to propose a cylindrical specimen with central crack, produced by additive manufacturing. This geometry allows to have pure plane strain state along the whole crack front, avoiding the complexities associated with corner points, crack shape, and variation of crack closure along crack front. Additionally, this geometry may be used to develop studies in vacuum, avoiding expensive vacuum equipment, since the air is not in contact with the crack front. Cylindrical specimens of Ti6Al4V titanium alloy were produced by Selective Laser Melting and tested at a stress ratio R = 0. Marking with overloads was the solution adopted to measure the length of the internal cracks. The fracture surfaces presented circular crack fronts and the da/dN-DK curves showed a great influence of atmosphere on fatigue crack growth. An average difference of 50% was found between the results in air and vacuum. Therefore, this geometry with internal crack is an interesting alternative to through-thickness geometries.