Browsing by Author "Santos, L.M.S."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Assessment of the fatigue life on functional hybrid laser sintering steel componentsPublication . Ferreira, J.A.M.; Santos, L.M.S.; Silva, J. da; Costa, J.M.; Capela, C.The construction of hybrid parts: comprised of two different materials or obtained by two distinct technological processes is one of the main advantages of laser sintering metal. Various important aspects strongly affect the mechanical properties of sintering metal components: porosity, surface roughness, scan speed, layer thickness, and residual stresses. A major drawback is the occurrence of pores originating from initial powder contaminations, evaporation or local voids after powder-layer deposition, once these pores can act as stress concentrators leading to failure, especially under fatigue loading. The purpose of present work was to study the effect scan speed on the porosity and mechanical properties. Also the performance of two different material parts was studied. The sintering laser parts were manufactured in maraging steel AISI 18Ni300, while the substrates of hybrid specimens were produced alternatively in two materials: the steel for hot work tools AISI H13 and the stainless steel AISI 420. The results showed that a very high scan speed (400 or 600 mm/s) causes the appearance of high porosity percentages and consequent drastic reduction of tensile strength and stiffness. Tensile properties of sintered specimens and two different material parts was similar. However, the fatigue strength of two different material parts tends to decrease, for long lives, when compared with single sintered specimens. © 2015 The Authors.
- Fatigue behaviour of selective laser melting steel componentsPublication . Santos, L.M.S.; Ferreira, J.A.M.; Jesus, J.S.; Costa, J.M.; C. CapelaSelective laser melting (SLM) is a laser based rapid manufacturing technology that builds metal parts layer-by-layer using metal powders and a computer controlled laser. Various important aspects strongly affect the mechanical properties of sintered metal components, such as: porosity, surface roughness, scan speed, layer thickness, and residual stresses. Therefore, properties of SLM manufactured parts must be carefully analysed, particularly under fatigue conditions. The purpose of this work was to study the effect of scan speed, porosity and microstructure on the mechanical properties and fatigue strength of sintered laser samples. Sintered laser parts were manufactured in maraging steel AISI 18Ni300. Fatigue behaviour is related to process parameters, such as: surface residual stresses, microstructure and porosity. The results showed that a very high scan speed (400 or 600 mm/s) causes the appearance of high percentages of porosity and a consequent drastic reduction of tensile strength and stiffness. Fatigue behaviour was assessed in terms of the traditional S-N curves and of the da/dN–DK crack propagation curves. Fatigue life predictions based on Hartman and Schijve’s equation underestimated significantly fatigue lives, particularly for low stress levels. The results of the tests performed at variable amplitude loading were well fitted by Miner’s law.
- Fatigue Performance of Hybrid Steel Samples with Laser Sintered ImplantsPublication . Santos, L.M.S.; Ferreira, J.A.M.; Costa, J.D.; C. CapelaLaser sintering metal has recently been used in the manufacture of metallic structural hybrid components comprising two different materials obtained by two distinct technological processes. This process allows to obtain productivity gains reducing sintering time and hence the cost. In current study it was used a machined substrate in which it is built by sintering the remaining part. The purpose of present work was to study the effect of the substrate material and interface microstructure on the fatigue performance under constant and variable block loadings. The sintering laser parts were manufactured in maraging steel AISI 18Ni300, while the substrates of hybrid specimens were produced alternatively in two materials: the steel for hot work tools AISI H13 and the stainless steel AISI 420. Fatigue strength will be quantified in terms of S - N curves. The results show that tensile properties of sintered specimens and of the hybrid parts was similar. Fatigue strength for short lives, of the sintered specimens and hybrid parts was quite similar. However, the fatigue strength of hybrid parts tends to decrease, for long lives, when compared with single sintered specimens. The fatigue tests under block loadings leads to indicate that the application of Miner’s law is adequate to predate fatigue life in hybrid components with sintered implants, despite having been observed a tendency to be conservative for long life.