A crystal plasticity approach to understand fatigue response with respect to pores in additive manufactured aluminium alloys. (August 2022)

• Record Type: Journal Article
• Authors: Cao, Mengzhen; Liu, Yang; Dunne, Fionn P.E.
• Is Part Of: International journal of fatigue. Volume 161(2022)
• Publication Date: 2022-08
• Subjects: Fatigue crack nucleation -- Pore -- Fatigue life prediction -- Crystal Plasticity -- Additive manufacturing; Materials -- Fatigue -- Periodicals; Materials -- Fatigue; Periodicals; 620.1122
• DOI: 10.1016/j.ijfatigue.2022.106917
• Languages: English
• ISSNs: 0142-1123

Abstract

Graphical abstract: Highlights: Established model microstructures of SLM AlSi10Mg containing differing pore types in additive manufacturing. Mechanistic explanations for the high sensitivity of fatigue cracks to pores. Shift of critical sites from gas/keyhole pore to microstructural inhomogeneities at high cyclic stress. Fatigue crack nucleation lives predicted based on the stored energy density criterion. Abstract: A crystal plasticity finite element modelling method integrated with a stored energy density criterion is utilized to comparatively investigate fatigue crack nucleation behaviour and quantify fatigue life with respect to different pore types in AlSi10Mg fabricated by selective laser melting. Representative microstructural models show that fatigue crack nucleation exhibits high sensitivity to both gas/keyhole and lack of fusion pores, but particularly the latter, which leads to much lower fatigue life at high stress levels. Multi-intragranular slip system activations occurring at the sharp corners of lack of fusion pores contribute to substantial increase in local geometrically necessary dislocation density. Together with the rapid accumulation of slip, these drive high local stored energy density at the tips of lack of fusion pores. For gas/keyhole pores, high stresses lead to pore-induced shear band formation which shifts the origin of crack nucleation away from the pore to other microstructural features. At low stresses, fatigue life for lack of fusion and gas/keyhole pores tend to converge but remain shorter than for pore-free microstructures.