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    Experimental Investigation of Fracture Process Zone in Rocks Damaged Under Cyclic Loadings
    (Springer, 2017) Ghamgosar, M.; Erarslan, N.; Williams, D. J.
    Compared with other materials, most rocks generally fail in a brittle fashion rather than exhibiting yielding or purely plastic deformation. However, the initiation and coalescence of micro-cracks in the nonlinear region, known as the 'fracture process zone' (FPZ), are the primary reason for fracture propagation in rocks. Different elasticity-related models proposed for determining the features of the FPZ have not achieved an adequate understanding of its various fracture patterns. Based on previous experiments and numerical models, micro-crack density has been shown to be a function of loading history and to vary depending on whether the loading is monotonic or cyclic. The aim of the study reported here was to examine the different patterns of the FPZ under various types of cyclic loading and to quantitatively define damage and fracture patterns through the grains or rock matrix. Considerable laboratory testing was conducted, and fractured samples were investigated by computerised tomography scanning, supported by thin-section analysis. In the study, two different types of cyclic loading were tested: stepped and continuous. A diametral compressive loading was applied at predetermined amplitude and frequency with the continuous cyclic loading. The applied cyclic diametral compressive load was returned to the original level after each step, and at the next step, the amplitude started from zero, with stepped cyclic loading (SCL). An average 30 % strength reduction was found due to the SCL and emergence of high micro-fracture density in the FPZ. We presume that hard rock breakage techniques will be improved, especially for rock-cutting technologies, such as drag bits and oscillating disc cutting, by understanding the effects of cyclic loading on rock strength.
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    Hertzian contact damage in a hollow circular cylinder
    (Crc Press-Balkema, 2016) Serati, M.; Williams, D. J.; Erarslan, N.
    This paper attempts to provide a theoretical framework for the determination of the stress state induced in a hollow cylinder (ring) under Hertzian compressions on its outer boundary. The solution is obtained using Airy stress functions, Michell-Fourier series expansions and Fourier-Bessel series expressions in polar coordinates. Parametric studies are also performed to investigate the influence of the loading angle and the geometrical aspect ratio of the ring on the induced stress tensor.
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    Micro-Mechanical and Micro-Structural Aspects of Strength Variation in Rocks under Various Loading Conditions
    (Tmmob Maden Muhendisleri Odasi, 2015) Erarslan, N.; Ghamgoshar, M.; Williams, D. J.
    This research focuses on the micro-mechanical and micro-structural aspects of strength variation in macro-scale rock structures, because final failure of rocks comes about through a process of interaction/coalescence among the many load-parallel or load-inclined tensile fractures that are generated by micro pre-existing cracks. Provide major contributions to the understanding of stress-induced micro-fracturing of rock under various loading conditions, static and dynamic, resulting in the degradation of macro-scale rock strength, or possibly strain-hardening, of rocks. The outcome of this research is expected to provide rock cutting, civil-geotechnical and mining design engineers with access to new, more accurate rock strength estimation methods, of high value for minimising the risks associated with rock strength uncertainty. A brittle rock type Brisbane tuff specimens were tested. Through the combined use of laboratory tests, Scanning Electron Microscope (SEM) techniques, and Computed Tomography (CT) scan technique, the damage mechanism of rocks under various loading conditions, including static and cyclic, were examined in nano-scale and the results were compared with each other for the first time in literature. Moreover, the sub-critical crack propagation phenomena, which is used to explain the premature failure of ceramics and metals and Fracture Process Zone (FPZ) phenomena, are explained in this research in terms of micro-mechanical strength reduction due to rock fatigue. Thus, modelling and understanding the crack propagation behaviour depending on different amplitude and frequencies are believed very important for the dynamic rock cutting researches and rock cutting machine manufacturers.