UC Davis

To examine the influence of residual stress on mechanical performance, specifically fatigue crack growth resistance, additively manufactured (AM) Type 304L stainless steel produced by directed energy deposition (DED) was evaluated and compared to conventional wrought Type 304/304L stainless steel. Increasing and decreasing alternating stress intensity factor (ΔK) tests were used to assess fatigue crack growth behavior over a range of crack growth rates in the near threshold regime (<10-8 m/cycle). Bulk residual stress and residual stress intensity factor (Kres) profiles of a fatigue specimen were measured using the incremental slitting method. Tensile residual stress at the edges of the DED materials led to positive values of Kres and faster fatigue crack growth rates in the DED material as compared to wrought material at the same applied ΔK. Correcting for the effects of Kres and crack closure in DED Type 304L and commercially available wrought Type 304/304L stainless steel shows that fatigue crack growth rates are similar at values of ΔK lower than 6 MPa·m0.5.