PSI - Issue 13

K. Solberg et al. / Procedia Structural Integrity 13 (2018) 1762–1767 K. Solberg / Structural Integrity Procedia 00 (2018) 000–000

1763

2

This new possibility of geometrical complexity allows for creating unprecedented topologies not possible to obtain by conventional manufacturing processes, however, components are often containing highly notched regions, which can strongly affect the fatigue life. Despite the importance of this research area for future applications, fatigue and especially the geometrical induced failure of AM Inconel 718 is underexplored. Chen et al. (1999) previously studied notched fatigue behaviour of Inconel 718 under rotary bending at both room and elevated temperature, obtaining results showing low fatigue notch sensitivity. Razavi et al. (2017a, 2017b) has studied notched fatigue behaviour of as-build Selective Laser Melted Ti-6Al-4V specimens, both v-shaped notch and semi-circular notch, and investigated the possibility of using the energy based method strain energy density in order to predict fatigue life of AM components. One of the main advantages of using strain energy density is that it is mesh independent as reported by Berto et al. (2009, 2014) while this is not the case for similar methods based on stress such as critical distance theory. 2. Material, geometries and experimental procedure The material used is AM Inconel 718 produced by use of SLM without any post processing. Three different test specimens were considered, one unnotched geometry and two double notched geometries, one blunt v-shaped notch and one semi-circular shaped notch. The three different geometries are shown in Fig. 1, and the dimensions are given in Table 1. The specimens were built to a solid in a layer-by-layer fashion with a layer height of 50 µm. They were produced standing such that the anticipated loading direction is normal to the manufactured layers. The specimens were printed without support structure. This way, the upper part of the notch region was printed with overhang, while the lower part was not.

Fig. 1. Geometry of different test specimens. From left unnotched, semi-circular notch and v-shaped notch.

Table 1. Specimen dimensions Specimen geometry

t [mm]

w 1 [mm]

w 2 [mm]

l [m] 80.0 80.0 80.0

ρ [mm]

2α [°]

Unnotched

5.0 5.0 5.0

15.0 15.0 15.0

7.0 5.0 5.8

30.31

- -

Semi-circular V-shaped notch

5.00 1.00

90

The fatigue test of the specimens was done on a MTS Landmark Servohydraulic Test System with load controlled sinusoidal loading, loading ratio R = σ min / σ max = 0 and frequency of 10 Hz. A minimum and a maximum load was defined for each case, where the minimum load level was 0 kN for all cases. The specimens were tested at different load levels resulting in different fatigue life, the data is presented in S – N diagrams describing the fatigue behavior of the different notch geometries. Specimens that did not fail at 2 × 10 6 cycles were considered as runout.