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Static and Dynamic Properties of Kuru Black Diorite and Grey Granite Using Full-Field Deformation Measurements
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0003-1345-0740
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0001-5218-396X
(English)Manuscript (preprint) (Other academic)
Keywords [en]
Rock Dynamic Fracture DIC SHPB
National Category
Other Mechanical Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-83908OAI: oai:DiVA.org:ltu-83908DiVA, id: diva2:1546989
Available from: 2021-04-23 Created: 2021-04-23 Last updated: 2021-10-15
In thesis
1. Towards Discrete Element Modelling of Rock Drilling
Open this publication in new window or tab >>Towards Discrete Element Modelling of Rock Drilling
2021 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The method of percussive rotary drilling is recognized as the most efficient method for hard rock drilling. Despite the clear advantages over conventional rotary meth-ods, there are still uncertainties associated with percussive rotary drilling. For geothermal applications, it is estimated that 50 % of the total cost per installed megawatt of energy is associated with drilling and well construction, with drill bit wear being a predominant cost factor. Numerical modelling and simulation of rock drilling, calibrated and validated towards rigorous experiments, can give insight into the rock drilling process. This thesis is focused on the prerequisites of numer-ical simulations of rock drilling, i.e. the development of a numerical model and experimental characterization of rock materials. A new approach for modelling brittle heterogeneous materials was developed in this work. The model is based on the Bonded Particle Method (BPM) for the Discrete Element Method (DEM), where heterogeneity is introduced in two ways. Firstly, the material grains are rep-resented by random, irregular ellipsoids that are distributed throughout the body. Secondly, these grains are constructed using the BPM-DEM approach with mi-cromechanical parameters governed by the Weibull distribution. The model was applied to the Brazilian Disc Test (BDT), where crack initiation, propagation, coalescence and branching could be investigated for different levels of heterogene-ity and intergranular cement strengths. The initiation and propagation of the cracks were found to be highly dependent on the level of heterogeneity and cement strengths. In the experimental study, the static and dynamic properties of two rock materials - Kuru grey granite and Kuru black diorite - were obtained from uniaxial compression and indirect tension tests. A Split-Hopkinson Pressure Bar was used to obtain the dynamic properties. Using high-speed photography with frame rate 663,000 fps, the crack initiation and propagation could be studied in de-tail, and the full-field exterior deformation fields of the samples were evaluated by using digital image correlation. From the high-speed images, the onset of unstable crack growth was detected. The crack-damage stresses, associated with unstable crack growth, was approx. 90 % of the peak strength in the dynamic compression tests, whereas the tensile crack-damage stress was approx 70 % of the tensile peak strength.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2021
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords
DEM Rock Dynamic Drilling
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-83911 (URN)978-91-7790-836-4 (ISBN)978-91-7790-837-1 (ISBN)
Presentation
2021-06-18, E632, 09:00 (English)
Opponent
Supervisors
Available from: 2021-04-23 Created: 2021-04-23 Last updated: 2023-09-05Bibliographically approved

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Wessling, AlbinKajberg, Jörgen

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