High cycle fatigue life estimation of AlSi10Mg processed by laser powder bed fusion

Abstract

Abstract.Fatigue life is known to be dependent on the surface properties of the material. Surface roughness provokes local stress concentration and cause crack initiation even at minute cyclic loads. In laser powder bed fusion, the as-built surfaces show variable roughness depending on the orientation of the specimens with respect to the build plate. In order to analyse the effect of build angle on surface properties, flat tensile specimens were produced from an AlSi10Mg alloy in a Concept Laser M2 Cusing machine. Seven specimens were arranged from flat to perpendicular with respect to the build plate at 15° intervals. The as-built surface topography of each specimen was characterised by white light interferometry. Two methods for calculating the stress concentration factor for high cycle fatigue simulation were developed. The presence of subsurface porosity was a crucial factor in expanding the stress concentration as demonstrated by finite element analysis.

High cycle fatigue behavior and life prediction for additively manufactured 17-4 PH stainless steel: Effect of sub-surface porosity and surface roughness

“…In addition to such pores, the NS surface condition also contains deep valleys due to the surface roughness, which can introduce stress concentrations and negatively affect the fatigue performance of the material [10,17,26,43]. For the present material, the maximum valley depth measured on the polished sections was approximately 65 μm (see Figure 6a).…”

“…3.2), and semi-length on the surface around 350-450 μm. In one case, presence of a sub-surface pore with a diameter of 67 μm right below this outer layer has probably increased the detrimental effects of surface roughness [26,50] (see Figure 10b). The size and position of this pore is consistent with those detected via X-ray micro-CT scan (see Figure 5).…”

“…Three major approaches to consider the effects of net-shape surface condition are adopted in the literature: (i) the evaluation of the stress concentration induced by surface features [10,24,[26][27][28]; (ii) estimating a fictitious (i.e. equivalent initial flaw size approach) crack representing the 'as-built' condition [14,29], and (iii) measuring the dimensions of surface features for applying 'short crack' fracture mechanics concepts [10,14].…”

Very high cycle fatigue characterization of additively manufactured AlSi10Mg and AlSi7Mg aluminium alloys based on ultrasonic fatigue testing

“…The characteristics of the process such as laser power, layer height or metallic powder size used in the manufacturing as well as the post‐processing techniques employed to create more uniform crystal structures, reduce porosity, relieve stress concentrations and improve surface finish can have significant effects on fatigue life of parts produced using AM process 27 . Notably, the use of various heat treatment processes has been reported for making great improvements on fatigue characteristics of parts produced using AM 28,29 . Tridello et al 23 performed experimental investigations for effects of microstructure, residual stresses and building orientation of AM AlSi10Mg specimens fabricated by selective laser melting in VHCF regime.…”

“…27 Notably, the use of various heat treatment processes has been reported for making great improvements on fatigue characteristics of parts produced using AM. 28,29 Tridello et al 23 performed experimental investigations for effects of microstructure, residual stresses and building orientation of AM AlSi10Mg specimens fabricated by selective laser melting in VHCF regime. The authors reported that the defect size, microstructure and residual stresses could have significant effects on VHCF performance of AM AlSi10Mg alloy.…”