title: Effects of strain rate and surface cracks on the mechanical behaviour of Balmoral Red granite.
abstract: This work presents a systematic study on the effects of strain rate and surface cracks on the mechanical properties and behaviour of Balmoral Red granite. The tensile behaviour of the rock was studied at low and high strain rates using Brazilian disc samples. Heat shocks were used to produce samples with different amounts of surface cracks. The surface crack patterns were analysed using optical microscopy, and the complexity of the patterns was quantified by calculating the fractal dimensions of the patterns. The strength of the rock clearly drops as a function of increasing fractal dimensions in the studied strain rate range. However, the dynamic strength of the rock drops significantly faster than the quasi-static strength, and, because of this, also the strain rate sensitivity of the rock decreases with increasing fractal dimensions. This can be explained by the fracture behaviour and fragmentation during the dynamic loading, which is more strongly affected by the heat shock than the fragmentation at low strain rates.This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.
authors.affiliation: Department of Material Science, Tampere University of Technology, POB 589, 33101, Tampere, Finland ahmad.mardoukhi@tut.fi.
authors.forename: Ahmad
authors.identifier: http://orcid.org/0000-0003-1673-7755
authors.initials: A
authors.lastname: Mardoukhi
authors.affiliation: University of Potsdam, Institute of Physics and Astronomy, 14476, Potsdam, Golm, Germany.
authors.forename: Yousof
authors.identifier: http://orcid.org/0000-0002-8459-1332
authors.initials: Y
authors.lastname: Mardoukhi
authors.affiliation: Department of Material Science, Tampere University of Technology, POB 589, 33101, Tampere, Finland.
authors.forename: Mikko
authors.identifier: http://orcid.org/0000-0002-3793-2720
authors.initials: M
authors.lastname: Hokka
authors.affiliation: Department of Material Science, Tampere University of Technology, POB 589, 33101, Tampere, Finland.
authors.forename: Veli-Tapani
authors.initials: VT
authors.lastname: Kuokkala
keywords: dynamic loading; fractal dimension; granite; rock; split Hopkinson pressure bar; surface cracks