PSI - Issue 13

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

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The fatigue data shows that the fatigue strength at 2 × 10 6 cycles for the unnotched specimens was 26.0% of UTS, and further reduced to 18.3% and 12.6% for semi-circular and v-shaped notch respectively. The slope and scatter of the two different notch geometries are similar, while the fatigue data for the unnotched geometry is less steep and has a larger scatter. Table 3. Normalized fatigue strength at 2 × 10 6 , elastic stress concentration factor, fatigue notch factor and fatigue notch sensitivity factor for each geometry. Specimen geometry Δσ/σ UTS k t k f q Unnotched 0.260 1.07 - - Semi-circular 0.183 1.31 1.42 1.35 V-shaped notch 0.126 2.43 2.06 0.74 In the case of notched fatigue data reported by Razavi et al. (2017a, 2017b) the notch sensitivity for as-build Ti 6Al-4V was 0.45 for semi-circular geometry and 0.54 for v-shaped notch geometry when referring to the net cross section area when describing the elastic stress concentration factor. The notched fatigue data reported on Inconel 718 by Chen et al. (1999) shows a notch sensitivity of 0.16 with an elastic stress concentration factor of 5.67 referring to the net cross section in the notched region. The high notch sensitivity obtained for the semi-circular notch specimens can indicate that the notch alone is not the only driving mechanisms for fatigue. The fact that the semi-circular specimens were built with higher overhang angle than the v-shaped notch, and the v-shaped notch shows a notch sensitivity below 1, could indicate that there might be some dependency between the overhang angle of printing and The fatigue data show less scatter and steeper trend lines for notched specimens then for unnotched specimens. High values of fatigue notch sensitivity was obtained for notch geometries. The semi-circular specimens showed a notch sensitivity higher than full notch sensitivity, while the v-shaped notch displayed a notch sensitivity below full notch sensitivity. Both notch geometries was printed with overhang in the notched region, as the specimens were built without support structure. A possible dependency between the building angle and the fatigue behaviour of the specimens will be further elaborated. The stress fields of the different geometries has been analysed both by use of FE and analytical models, the analytical model was able to describe the stress field in the geometries well in region close to the notch tip. In the region far away from the notch tip, there is some error in the model, this could be due to the fact that the stress field models are developed for notches in large plates and not double notched specimens, as proposed by Lazzarin and Filippi (2006). 2006 References Berto, F., Lazzarin, P., 2009. A review of the volume-based strain energy density approach applied to V-notches and welded structures, Theoretical and Applied Fracture Mechanics, Volume 52, Issue 3, 183-194. Berto, F., Lazzarin, P., 2014. Recent developments in brittle and quasi-brittle failure assessment of engineering materials by means of local approaches, Materials Science and Engineering: R: Reports, Volume 75, 1-48. Chen, Q., Kawagoishi, N., and Nisitani, H., 1999. Evaluation of notched fatigue strength at elevated temperature by linear notch mechanics. International Journal of Fatigue, 21(9):925 - 931. Lazzarin, P., and Filippi, S., 2006. A generalized stress intensity factor to be applied to rounded v-shaped notches. International Journal of Solids and Structures, 43(9):2461 – 2478. Lazzarin, P., and Tovo, R., 1996. A unifed approach to the evaluation of linear elastic stress fields in the neighborhood of cracks and notches. International Journal of Fracture, 78:3-19. Razavi, S.-M.-J., Ferro, P., Berto, F., 2017a. Fatigue Assessment of Ti–6Al–4V Circular Notched Specimens Produced by Selective Laser Melting. Metals, 7, 291. Razavi, S.M.J., Ferro, P., Berto, F., Torgersen, J., 2017b. Fatigue strength of blunt V-notched specimens produced by selective laser melting of Ti 6Al-4V, Theoretical and Applied Fracture Mechanics. the fatigue life. 6. Conclusions