PSI - Issue 68

Amy Milne et al. / Procedia Structural Integrity 68 (2025) 666–673 Milne et. al. / Structural Integrity Procedia 00 (2025) 000–000

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1. INTRODUCTION 316L stainless steel (SS) in its wrought form is used for high temperature applications, but there is currently limited literature on the performance of 316L SS components manufactured by laser powder bed fusion (LPBF) according to Sandmann et al. (2023, Williams et al. (2020a). 316L SS is known for its corrosion resistance, which makes it suitable for marine applications, as well as in chemical or nuclear plants with operating temperatures of up to approximately 650 °C as reported by Dryepondt et al. (2021). The layer-based nature of LPBF means that net-shaped components with complex geometries can be produced hence and LPBF offers benefits for component design. Current limitations of the LPBF technique include the development of multiaxial residual stresses (RS), porosity and microstructural and property inhomogenity as detailed in Sandmann et al. (2023, Williams et al. (2020b). Heat treatments may be used to relax RS, however the combination of high RS and high operating temperatures can cause accelerated creep crack growth (CCG), Pommier (2015). and so research into its high-temperature deformation and damage processes in 316L SS manufactured by LPBF is of great value. Recent work by Sandmann et al. (2023, Williams et al. (2020a) examined the uniaxial and multiaxial behaviour of 316L SS at 650 °C and 700 °C respectively. Itwas found that the creep strain rate varied by an order of magnitude for a given stress, depending on the sample’s orientation relative to the build direction, which was related to the grain structure. This work aims to understand the orientation-dependent anisotropic behaviour of CCG from a pre-existing defect through a series of tests on compact tension C(T) samples at 650 °C.

Nomenclature a crack length ̇ B B net

crack growth rate

fracture geometry thickness net sample thickness steady state creep parameter temperature dependent constant

C* D 0

stress intensity factor

K P W

applied load specimen width

Y geometry factor relating stress intensity factor to crack length ∅ power-law exponent 2. CREEP CRACK GROWTH AND FRACTURE MECHANICS THEORY

The stress ahead of a crack tip under linear elastic conditions is described by the stress intensity factor, K , given by Eqn [1], where the geometry dependency is described by the shape function Y(a/W) , which is determined numerically using finite element analysis (FEA). ! = √ ' ) [1] The shape function for C(T) specimens is described by Eqn [2]. #(%) = √ +16.7 − 104.7 ' ) + 369.9 ' ) ' − 573.8 ' ) ( + 360.5 ' ) ) 8 [2] For a side-grooved sample, the nominal stress applied to the sample is given by Eqn [3].