Constitutive and life modelling of a laser powder bed fusion IN718 component for hypersonic flight

Additively manufactured (AM) IN718, created by use of laser-powder bed fusion (L-PBF), is one of several candidate materials being pursued for introduction as components into flight hardware. In an attempt to certify an AM IN718 component for flight worthiness, a Qualified Metallurgical Plan, substantially similar to NASA’s MSFC-SPEC-3717[1](#fn-0002), was implemented to create materials and components exhibiting both inter-build and intra-build consistencies. As a function of this work, specimens were created and tested in monotonic loading, strain-controlled low cycle fatigue, and force-controlled low cycle fatigue. Data was created by use of specimens in both machined and as-built conditions and at temperatures up to 400°C. Additionally, test results from specimens having prismatic gage sections were compared to those having a sharp notch (Kt=3). The test data was subsequently used to create non-linear combined kinematic and isotropic constitutive models to aid in the prediction of material deformation response resulting from hypersonic flight loading conditions (generally thermo-mechanical fatigue and/or creep-fatigue). Furthermore, a physics-based life model originally created for single crystal nickel-based superalloys experiencing thermo-mechanical fatigue was calibrated for the additively manufactured IN718 material studied here. Validation and verification tests of specimens experiencing multiple variations of typical “low-speed” hypersonic flight loading conditions and boundary conditions indicate that the calibrated life model predicts the effects of surface finish (machined versus as-built), geometric discontinuities, varying temperatures, and varying loads well. The constitutive models were then combined with a finite element solid model in ABAQUS to aid in the life prediction of flight hardware created as part of this work.