On the high cycle fatigue resistance of austenitic stainless steels with surface gradient microstructures: Effect of load ratio and associated residual stress modification

Modeling of the fatigue behavior of functionally graded materials: Study of the residual stresses induced by surface severe plastic deformation

“…This can be explained by the fact that only the austenite phase was considered in the modeling while a small amount of martensite can form in the sub-surface region of this 316 L stainless steel. 17 Moreover, it appears that the surface residual stress resulting from the simulation, +1150 MPa approximately for the stabilized gradient, is an intermediate value between the experimental ones measured at +875 and +1250 MPa in austenite and martensite, respectively. This good correspondence is due to the fact that, by fitting the local mechanical behavior from the micro-pillar compression results, the contribution of both phases was taken into consideration.…”

“…The material investigated here is the AISI 316 L stainless steel for which a full experimental fatigue behavior has been reported in a previous work. 17 The two types of prepared fatigue specimens, the initial and the SMAT treated ones, had a 9 mm diameter and a 12.5 mm gauge length. The initial specimens had a surface mirror polished state, and the SMAT ones were treated by USP using a SONATS peening device.…”

“…The specimens were placed at a distance of 20 mm of the Ti-6Al-4 V sonotrode, which was vibrating at a 20 kHz frequency and 60 μm amplitude. This set of parameters was chosen according to previous work 16,17,48 to allow comparison.…”

“…In addition to the 5, 20, 50, and 100 μm depth fitted from the literature, an intermediate value of 300 μm was extrapolated from these values by following the trend of the hardness gradient previously measured. 17 Table 2b summarizes the used material parameters in the current model in the core and in the SMAT affected layer. They were defined as a function of the depth below the surface considering that the core is reached bellow 600 μm and the core material parameters correspond to the ones identified for the initial material in the previous section.…”

“…[1][2][3][4][5][6][7][8] Among them, austenitic stainless steels have been widely studied. [9][10][11][12][13][14][15][16][17] However, conflicting results concerning the efficiency of these surface treatments to improve the fatigue life were observed and reported when specific treatment conditions were employed, [18][19][20][21] thus showing that the treatment parameters are sometimes critical and need to be wisely chosen in order to provide the desired enhancement in fatigue properties. Due to the importance of fatigue crack initiation in the fatigue life, such reduction of the fatigue limit is often attributed to the surface roughness and characteristic surface damage induced by the treatment.…”