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Fracture of laser-based powder bed fusion produced Ti6Al4V
Louw, D. F. 2025. Fracture of laser-based powder bed fusion produced Ti6Al4V. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/961bff00-ca87-4973-8bb3-2f4c7dac059b
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613966901968896 |
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| access_status_str | Open Access |
| author | Louw, Daniel Francois |
| author2 | Becker, Thorsten Hermann |
| author_browse | Becker, Thorsten Hermann Louw, Daniel Francois |
| author_facet | Becker, Thorsten Hermann Louw, Daniel Francois |
| author_sort | Louw, Daniel Francois |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Louw, D. F. 2025. Fracture of laser-based powder bed fusion produced Ti6Al4V. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/961bff00-ca87-4973-8bb3-2f4c7dac059b |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/132233 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:44:33.029Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/132233 Fracture of laser-based powder bed fusion produced Ti6Al4V Louw, Daniel Francois Becker, Thorsten Hermann Neaves, Melody Stellenbosch University. Faculty of Engineering. Dept. of Mechanical & Mechatronic Engineering. Additive manufacturing Metal powders Computer-aided design Fracture mechanics UCTD Louw, D. F. 2025. Fracture of laser-based powder bed fusion produced Ti6Al4V. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/961bff00-ca87-4973-8bb3-2f4c7dac059b Thesis (PhD)--Stellenbosch University, 2025. ENGLISH ABSTRACT: This project seeks to provide insights that enable the design of damage-tolerant, high-performance components produced out of Ti6Al4V by laser-based powder bed fusion (LPBF). By investigating the relationship between fracture toughness, microstructural characteristics, and residual stresses, progress is made to produce more damage-tolerant components. Finally, the capabilities of predicting support breakage, delamination, and in-situ cracking with finite element modeling (FEM) of the process, are evaluated. This capability has the potential to significantly reduce the number of trial-and-error iterations needed to successfully manufacture a component free from such issues. The project starts by establishing a link between the material’s micro- and mesostructure and its fracture toughness. The fracture toughness was measured in various orientations to gain additional insight into the toughening mechanism. It was found that variations in post-process heat treatment can cause fracture toughness to vary between 42 and 95 MPa√m. The differences in fracture toughness are largely due to differences in ductility, which is linked to how the heat treatment affects the hierarchical lath structure. Anisotropy in fracture toughness is attributed to elongated prior-𝛽 grains, whereby low fracture toughness arises if the crack propagation direction aligns with the elongated boundaries. A heat treatment step above the 𝛽-transus temperature (𝑇𝛽) removes the anisotropy. The second contribution of this project lies in quantifying the influence of residual stress, a well-known process attribute, on fracture toughness. Fracture toughness in the as-built condition was measured in two orientations with a range between 24 and 37 MPa√m obtained. In each orientation, the residual stress distribution before fatigue pre-cracking in the compact tension specimen on the crack plane was measured with the contour method. Thereafter, the stress intensity factor due to residual stress after fatigue pre-cracking was determined by finite element modeling (FEM). It was found that fracture toughness in the as-built condition is reduced by up to 36 % by residual stresses. This quantitative result cannot be generalized to all fracture toughness measurements performed on as-built material because it is a function of how the specimen is cut from the as-fabricated block. Still, it indicates the importance of residual stress when interpreting fracture toughness. The final contribution of this project lies in evaluating the capability of a FEM of the process. It was found that a FEM based on the inherent strain method can be combined with a criterion based on the stress intensity factor or the volume strain energy density to predict the height at which in-situ cracking occurs accurately to within 12 %. AFRIKAANSE OPSOMMING: Hierdie projek beoog om insig te genereer wat die vervaardiging van komponente uit Ti6Al4V, wat bestand is teen skade in hoë las toepassings, met behulp van laser gebaseerde laagvervaardiging toelaat. Deur die verwantskap tussen mikrostruktuur, resspaning en breuktaaiheid te ondersoek word vordering gemaak om skade-bestande komponente te ontwikkel. Uiteindelik word die vermoë om, ondersteunstrukture wat breuk, delaminasie en die vorming van krake tydens die bouproses te voorspel, met behulp van eindige element modellering van die proses geëvalueer. Hierdie vermoë het die potensiaal om kostes en tyd te spaar deurdat minder pogings nodig gaan wees om ‘n komponent suksesvol te genereer. Die projek begin deur die verwantskap tussen die breuktaaiheid en meso- of mikrostruktuur van die material te ondersoek. Die breuktaaiheid is gemeet in verskillende oriëntasies om insig te verkry in meganismes wat taaiheid beïnvloed. Daar is bevind dat verskillende hittebehandeling die breuktaaiheid kan laat varieer tussen 42 en 95 MPa√m. Die verskille in breuktaaiheid is toegeskryf aan verskille in smeebaarheid wat afhang van die hiërargiese langwerpige korrels se reaksie op hittebehandeling. Die breuktaaiheid is rigtingafhanklik deurdat swak breuktaaheid waargeneem word wanneer die kraakgroeirigting oplyn met die verlengde voorafgaande 𝛽 korrels. Deur ‘n hittebehandelingsstap bo die 𝛽 oorgangstemperatuur te doen, word die rigtingafhanklikheid verwyder. Die tweede bydrae van hierdie projek is deurdat die invloed van resspanning op breuktaaiheid gekwantifiseer is. Daar is gevind dat die breuktaaiheid van die material voor hittebehandeling rigtingafhanklik is met ‘n variasie tussen 24 en 37 MPa√m. In elke orientasie is die resspanningsverspreiding voor die groei van die vermoeidheidskraak in die toetstuk gemeet met die kontoer metode. Daarna is die spanningsintensiteitsfaktor as gevolg van resspanning bepaal met behulp van eindige element analises. Daar is bevind dat die breuktaaiheid voor hittebehandeling met soveel as 36 % deur resspanning verlaag word. Hierdie resultaat kan beïnvloed word deur die posisie van die toetstuk ten opsigte van die blok waaruit dit gesny word, maar dit is ‘n aanduiding van die belangrike rol wat resspanning speel. Die finale bydrae van hierdie projek is om die vermoë van eindige element modellering van die vervaardigingsproses te evalueer. Daar is gevind dat eindige element modellering, gebaseer op die inherente vervormingstegniek, en ‘n kriterium gebaseer op die spanningsintensiteitsfaktor, of die volume energie digtheid, die hoogte waarby krake vorm tydens die proses akkuraat tot binne 12 % kan voorspel. Doctoral 2025-05-30T10:24:18Z 2025-05-30T10:24:18Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/132233 en Stellenbosch University xvii, 104 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Additive manufacturing Metal powders Computer-aided design Fracture mechanics UCTD Louw, Daniel Francois Fracture of laser-based powder bed fusion produced Ti6Al4V |
| title | Fracture of laser-based powder bed fusion produced Ti6Al4V |
| title_full | Fracture of laser-based powder bed fusion produced Ti6Al4V |
| title_fullStr | Fracture of laser-based powder bed fusion produced Ti6Al4V |
| title_full_unstemmed | Fracture of laser-based powder bed fusion produced Ti6Al4V |
| title_short | Fracture of laser-based powder bed fusion produced Ti6Al4V |
| title_sort | fracture of laser based powder bed fusion produced ti6al4v |
| topic | Additive manufacturing Metal powders Computer-aided design Fracture mechanics UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/132233 |
| work_keys_str_mv | AT louwdanielfrancois fractureoflaserbasedpowderbedfusionproducedti6al4v |