Low cycle fatigue behaviour of wire arc additively manufactured ER70S-6 steel

Wire arc additive manufacturing (WAAM) is a method of 3D printing that is well suited to the cost-sensitive construction industry. Fundamental test data on the mechanical properties of WAAM materials, especially under cyclic loading, are however lacking. To bridge this gap, an experimental study into the low cycle fatigue (LCF) behaviour of WAAM ER70S-6 steel has been conducted and is presented herein. Following quasi-static mechanical and geometric characterisation, a series of as-built and machined coupons was tested in different directions relative to the print layer orientation (θ = 0°, 45° and 90°) under constant amplitude LCF loading, covering a range of strain amplitudes from ±0.2% to ±2.0%. Fractographic analysis of the tested coupons was also performed to assess their failure mechanisms. On the basis of the experimental results, strain-life relationships and cyclic stress-strain curves were derived. The geometric undulations of the as-built coupons resulted in a weakening in the LCF properties, and the weakening effect increased with the loading angle θ and strain amplitude. The cyclic hardening/softening response of the WAAM material varied with the imposed strain amplitudes, while significant non-Masing behaviour was observed.