eprintid: 10203498 rev_number: 11 eprint_status: archive userid: 699 dir: disk0/10/20/34/98 datestamp: 2025-03-14 09:12:29 lastmod: 2025-03-14 09:12:29 status_changed: 2025-03-14 09:12:29 type: thesis metadata_visibility: show sword_depositor: 699 creators_name: Gruppelaar, Melle title: Fracture Toughness of Microarchitectured Lattices ispublished: unpub divisions: UCL divisions: B04 divisions: F45 keywords: Cellular solids, Buckling, T-stress, Fracture toughness, Lattice materials note: Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. abstract: Microarchitectured lattices possess exceptional mechanical properties, such as stiffness, strength, and toughness at low density, which have increasingly been explored by researchers and engineers. This thesis investigates the fracture toughness of microarchitectured lattices, failure mechanisms, crack-tip fields, and calculation methodologies, using a combination of numerical simulations and experimental techniques. First, the fracture of elastic-brittle lattices is analysed. The scaling of fracture toughness with relative density was studied for hexagonal, triangular, and kagome lattices, following a power-law relationship with exponents d=1, d=2, and d=0.9, respectively. Strut-buckling and crack-tip blunting significantly influenced the K1c scaling with relative density in triangular and kagome lattices. Results from different methodologies revealed discrepancies up to 30% in K1c predictions. A displacement field analysis demonstrated that standard fracture formulas inadequately capture the crack-tip fields in lattice materials, and that the T-stress has a negligible effect on K1c. An in-depth investigation into the role of strut-buckling on the fracture toughness of elastic-brittle triangular lattices complements the above observations. The buckling initiation occurred up to significantly high relative densities, e.g. 11%, and was governed by the cell-wall fracture strain. Post-buckling fracture toughness was significantly influenced by T-stress, causing a reduction in K1c up to 50%. Finally, the work examines the fracture toughness of elastoplastic triangular and hexagonal lattices with three choices of base material. The J1c scaling with relative density followed a power-law relationship, with coefficients dependent on base material and dominant deformation mechanism. Nodal geometry and local stress triaxiality significantly impacted the fracture toughness of hexagonal lattices. A load separation analysis indicated that SEN-B specimens may be most suitable for fracture toughness testing of elastoplastic lattices. Throughout the thesis, experimental investigations are presented that validate the numerical predictions. These experiments include the observation of the relationship between fracture toughness and relative density in elastic-brittle hexagonal lattices, the first practical observation of strut-buckling in triangular lattices and its effect on K1c, and one of the first experimental studies on the fracture toughness of planar elastoplastic lattices. date: 2025-01-28 date_type: published full_text_type: other thesis_class: doctoral_embargoed thesis_award: Ph.D language: eng verified: verified_manual elements_id: 2353293 lyricists_name: Gruppelaar, Melle lyricists_id: MJGRU55 actors_name: Gruppelaar, Melle actors_id: MJGRU55 actors_role: owner full_text_status: restricted pagerange: 1-295 pages: 295 institution: UCL (University College London) department: Mechanical Engineering thesis_type: Doctoral editors_name: Tan, PJ editors_name: Bele, Eral citation: Gruppelaar, Melle; (2025) Fracture Toughness of Microarchitectured Lattices. Doctoral thesis (Ph.D), UCL (University College London). document_url: https://discovery.ucl.ac.uk/id/eprint/10203498/7/Gruppelaar_10203498_Thesis.pdf