Issue 53

C. Navarro et alii, Frattura ed Integrità Strutturale, 53 (2020) 337-344; DOI: 10.3221/IGF-ESIS.53.26 342 Figure 4: Details of initiation points on fracture surface of specimens: a) B1S4 Sup (as built, N f = 16214 cycles); b) B4S31 (laser shock peened, N f = 3099304 cycles) Figure 5: SEM images of two initial defects on fracture surface of specimens: a) B1S9Inf (shot peened, N f = 45992 cycles); b) B4S32 (laser shock peened, N f = 753603 cycles) Figure 6: Location of the crack initiation in each test where the fail initiated from an interior defect. Distances in mm. C ONCLUSIONS his paper shows the improvement of fatigue strength obtained with different treatments (shot peening, shot peening+CASE, laser peening, HIP) in Ti6Al4V specimens made using additive manufacturing. These treatments have mainly three effects: Surface roughness modification, compressive residual stresses and decreasing pore size (only HIP) [14-16]. The last treatment has little effect on fatigue life. The reason is that due to the stress gradient the cracks initiate from the surface and the surface roughness in the as built specimens and in the HIP specimens is similar. The shot peened specimens experiment a ten fold increase in fatigue life and most initiation points from the interior due to the residual stresses, but due to the high roughness and possible damage due to the treatment there is one crack starting T a) b)