Abstract: A novel approach based on the equivalent homogenised material concept and the Theory of Critical Distances is formulated to perform static assessment of plain/notched objects of polylactide (PLA) when this polymer is additively manufactured with different infill levels. The key idea is that the internal net structure resulting from the 3D-printing process can be modelled by keeping treating the material as linear-elastic, continuum, homogeneous and isotropic, with the effect of the internal voids being taken into account in terms of change in mechanical/strength properties. This idea is initially used to assess the detrimental effect of the manufacturing voids on the static strength of the plain (i.e., un-notched) material. This is done by addressing this problem in a Kitagawa-Takahashi setting via the Theory of Critical Distances. Subsequently, this approach is extended to the static assessment of notched components of 3D-printed PLA, i.e., it is used to take into account simultaneously the effect of both manufacturing voids and macroscopic geometrical features. The accuracy and reliability of this design methodology was checked against a large number of experimental data generated by testing, under axial loading, plain specimens as well as notched samples (including open notches) of PLA. These specimens were manufactured by making the infill level vary in the range 10%-90%. This validation exercise allowed us to demonstrate that the proposed approach is highly accurate, returning estimates falling within an error interval of ±20%. This remarkable level of accuracy strongly supports the idea that static assessment of 3D-printed materials with complex geometries and manufactured with different infill levels can be performed by simply post-processing conventional linear-elastic Finite Element (FE) solid models, i.e., without the need for modelling explicitly the detrimental effect of the manufacturing voids.
Department of Civil and Structural Engineering, The University of Sheffield
Biography: Luca Susmel joined the University of Sheffield in 2011 as Professor of Structural Integrity. Since 1998 Luca has focused his attention mainly on problems related to the static, dynamic and fatigue assessment of engineering materials and components. In particular, by working both in Italy (University of Padova, University of Ferrara, University of Udine), in Ireland (Trinity College, Dublin), and in the UK (university of Sheffield), he has devised several novel engineering methods suitable for designing components (experiencing stress concentration phenomena of any kind) against static, dynamic and fatigue failures. According to his modus operandi, Luca has performed both theoretical and experimental investigations and all the design methods he has formalised so far have always been validated through a systematic experimental work. Luca has an outstanding and unique expertise in designing notched and welded components against constant and variable amplitude multiaxial fatigue.
The work done in the above research areas has led to more than 350 scientific papers in the period 1999-2022 (of which more than 135 articles in international peer-reviewed scientific journals) as well as to a book devoted to the multiaxial fatigue assessment (Susmel, L., Multiaxial Notch Fatigue: from nominal to local stress-strain quantities. Woodhead & CRC, Cambridge, UK, ISBN: 1 84569 582 8, March 2009). His scientific papers have attracted significant interest from the international scientific community, evidenced by an h-index of 38 with more than 5.65k citations in total according to Google Scholar. He is a member of the Editorial Boards of the two leading international journals in the fatigue and fracture field, namely “International Journal of Fatigue” and “Fatigue & Fracture of Engineering Materials & Structures”. Luca is the Editor-in-Chief of “Theoretical and Applied Fracture Mechanics” (published by Elsevier) which is one of the top journals in the fracture mechanics field (Impact Factor=3.021).
Luca has developed a software specifically designed to perform the fatigue assessment of plain/notched/welded components subjected to both constant and variable amplitude uniaxial/multiaxial fatigue loading (Copyright document N. 007849-D007048).
As to the transfer of his research’s outcomes into engineering practice, in recent years, and especially after the publication of his book, Luca’s expertise has been sought on many occasions by several structural engineering (working in both European and non-European companies) successfully using the approaches developed by Luca himself to design real components and structures.
Since the end of the 90s, Luca has been involved both as primary investigator and as co-investigator in a very large number of research projects funded by national public funding bodies, European Community, Trusts, and private companies.