Issue 55

F.K. Fiorentin et al, Frattura ed Integrità Strutturale, 55 (2021) 119-135; DOI: 10.3221/IGF-ESIS.55.09

Based on the S-N curve presented in Fig. 3, it was possible to insert the equivalent stress computed at each selected potential critical point for an applied load of 34155 N (R=  1) . Fig. 17 presents the fatigue results for the Orientation 1. The group of points called “No Residual Stress” are the ones where only the cyclic load is present, and since the load ratio on this study is -1, they result on a null mean stress, therefore are located exactly on the S-N curve. Accounting the effect of the residual stress, it can be noticed that it has a detrimental effect on fatigue behavior for all points. The tensile residual stress obtained from AM simulation process for the purpose locations and taking into account the referred orientation have led to a reduction on the estimated number of cycles. Consequently, it can be stated that for the present orientation the residual stress due to manufacturing process will reduce the fatigue life of the component, from 1.1  10 5 cycles to 2.0  10 4 cycles as can be observed in the Fig. 17.

500

No Residual Stress With Residual Stress (AM)

400

300

σ a

200

Alternating Stress [MPa]

100

1E+04

1E+05

1E+06

1E+07

1E+08

1E+09

Number of Cycles

Figure 17: SN curve considering the alternating stress points and the mean stresses for build orientation 1.

For the second studied building orientation, the results are presented in Fig. 18. This manufacturing orientation presented an interesting and promising effect. Ignoring the residual stresses, the most critical point for fatigue was the point 2 (the same as in orientation 1). However, this point presented compressive residual stresses, which are beneficial for fatigue. Hence, taking into account the residual stresses, the fatigue behaviour of this region was improved. Due to the residual stress originated by the AM, the overall fatigue life of the component was improved, increasing from 1.1  10 5 cycles to 5.0  10 5 cycles. In addition, the region of failure was no longer around point 2, moving to the point 1.

500

No Residual Stress With Residual Stress (AM)

200 300

100

σ a

9

Alternating Stress [MPa]

1E+04 1E+05 1E+06 1E+07 1E+08 1E+09 1E+10 1E+11 1E+12 1E+13 1E+14 1E+15 1E+16 1E+17 1E+18

Number of Cycles

Figure 18: SN curve considering the alternating stress points and the mean stresses for build orientation 2.

132

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