Fatigue Assessment of Ti–6Al–4V Circular Notched Specimens Produced by Selective Laser Melting

Abstract

Additive manufacturing (AM) offers the potential to economically produce customized components with complex geometries in a shorter design-to-manufacture cycle. However, the basic understanding of the fatigue behavior of these materials must be substantially improved at all scale levels before the unique features of this rapidly developing technology can be used in critical load bearing applications. This work aims to assess the fatigue strength of Ti-6Al-4V smooth and circular notched samples produced by selective laser melting (SLM). Scanning Electron Microscopy (SEM) was used to investigate the fracture surface of the broken samples in order to identify crack initiation points and fracture mechanisms. Despite the observed fatigue strength reduction induced by circular notched specimens compared to smooth specimens, notched samples showed a very low notch sensitivity attributed both to hexagonal crystal lattice characteristics of tempered alpha prime grains and to surface defects induced by the SLM process itself.

Low-Cycle Fatigue Behaviour of AISI 18Ni300 Maraging Steel Produced by Selective Laser Melting

“…1.00E+01 Regarding components having complex geometries, no specific design criteria have been presented so far to consider stress concentration phenomena arising from geometrical discontinuities [14,15]. Hence, the same methodology can be examined in future for the notched specimens produced by additive manufacturing.…”

The Formation of Strong {100} Texture by Dynamic Strain-Induced Boundary Migration in Hot Compressed Ti-5Al-5Mo-5V-1Cr-1Fe Alloy

“…The microstructure and mechanical properties of titanium alloys are sensitive to processing parameters such as deformation temperature and strain rate [1,2]. The hard processing characterization of titanium alloy is also a problem during industrial manufacture [3]. Many titanium alloys are hot processed in the β single region to obtain a homogeneous microstructure.…”

Effect of corrosion and fatigue on the remaining life of structures and its implication to additive manufacturing

“…The sentence used in [37] was: "The surface roughness is the single most severe factor for fatigue for additive manufactured materials". The importance of characterizing the material discontinuities, including surface roughness, associated with AM materials is also stressed in [33,32,42]. Indeed, [42] suggested that, as we have seen in the previous section, the surface roughness of the material can be treated in the same way as short cracks.…”

“…This is particularly true for cracks in aircraft applications where, as detailed in MIL-STD 1530 [32], the design and certification approval require analytical tools that are capable of capturing crack growth and the role of testing is to validate or correct the damage tolerance analysis. Berto et al [33][34][35][36], Kahlin, Ansell and Moverare [37,38], Greitemeier et al [39], Chan [40] and Leuders et al [41] each revealed that the rough surfaces associated with as additively manufactured parts significantly degrade the fatigue performance of AM structures. The sentence used in [37] was: "The surface roughness is the single most severe factor for fatigue for additive manufactured materials".…”