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Öğe Analysing mixed mode (I-II) fracturing of concrete discs including chevron and straight-through notch cracks(Pergamon-Elsevier Science Ltd, 2019) Erarslan, NazifePre-existing cracks in concrete material and discontinuities in concrete structures are seldom subjected to pure tensile loading (mode I); rather, they are subjected to compressive, shear (mode II) or mixed mode loading (mode I-II). Cracked Chevron Notched Brazilian Disc (CCNBD) and Semi-Circular Brazilian (SCB) specimens including chevron notch and straight-through cracks were used in this research to analyse mixed mode fracturing of concrete. Both the experimental and numerical results showed that the crack initiation angle (theta) was found dependent on the crack inclination angle (beta). Moreover, CCNBD specimens with chevron notch crack geometry was found more suitable than the SCB geometry with straight-through notch crack to analyse mixed mode fracturing behaviour of plain concrete. However, using CCNBD or SCB specimens straight-through notch cracks may be more useful for testing the fracturing properties of coarse-grained concrete as sharp chevron cracks reduce the possible Fracture Process Zone (FPZ) size in front of the notch crack tip. Further analyses showed that the critical crack length is found as 13 mm (dimensionless notch length (alpha) = 0.5). Thus, it is understood that the unstable crack propagation starts between the initial chevron notch crack and final chevron notch crack length and it shows all experiments were done accurately. This outcome would be useful for concrete researches to obtain the yield point by using the relative analysis for finding where the unstable crack propagation starts. (C) 2019 Elsevier Ltd. All rights reserved.Öğe Assessment of cerchar abrasivity test in anisotropic rocks(Techno-Press, 2019) Erarslan, NazifeThere have been developed a number of methods to assess the abrasivity of rock materials with the increased use of mechanized rock excavation. These methods range from determination of abrasive and hard mineral content using petrographic thin section analysis to weight loss or development of wear flat on a specified cutting tool. The Cerchar abrasivity index (CAI) test has been widely accepted for the assessment of rock abrasiveness. This test has been considered to provide a reliable indication of rock abrasiveness for isotropic rocks. However, a great amount of rocks in nature are anisotropic. Hence, viability assessment of Cerchar abrasivity test for the anisotropic rocks is investigated in this research. The relationship between CAI value and quartz content for the isotropic rocks is well known in literature. However, a correlation between EQ, F-Schimazek value, Rock Abrasivity Index (RAI) and CAI of anisotropic rocks such as phyllite was done first time in literature with this research. The results obtained with this research show F-Schimazek values and RAI values should be considered when determination of the abrasivity of anisotropic rocks instead of just using Cerchar scratch test.Öğe Effect of anisotropy on fracture toughness and fracturing of rocks(American Rock Mechanics Association (ARMA), 2015) Ghamgosar, Morteza; Williams, David J.; Erarslan, NazifeElastic parameters of rocks are typically used for design purposes in open pit and underground mining, underground spaces and rock-cutting projects. However, the ultimate strength of rocks is strongly influenced by their micro-fractures, preexisting cracks, and anisotropy due to inhomogeneity, discontinuities, and differing particle sizes or shapes and orientations. Since the fracture behaviour of rocks is important to geotechnical engineers concerned with the design of excavations and underground spaces, it is obvious that laboratory investigations of their anisotropic parameters are necessary for safe designs. The main objective of this paper is to investigate the effect of different orientations of the anisotropy of Brisbane sandstone specimens subjected to diametral compressive (indirect tensile) loading that influences their fracture toughness. To obtain the fracture toughness values of anisotropic Brisbane sandstone, Cracked Chevron Notch Brazilian Disc (CCNBD) specimens were prepared and tested according to International Society for Rock Mechanics (ISRM) standards. The fracture toughness of Brisbane sandstone was found to increase with increasing angle of anisotropy. Based on the experimental results, a statistical regression analysis was conducted to obtain the optimum orientation angle to obtain the highest strength under indirect tensile loading. Statistical analysis showed anisotropy orientations of 45° gave the highest fracture toughness value. Copyright 2015 ARMA, American Rock Mechanics Associa.Öğe Experimental and Numerical Studies on Tensile and Shear Fracturing of Brittle Materials(2017) Erarslan, NazifeKayalar ve beton gibi kırılgan malzemelerin ani ve şiddetli kırılmaları hala madencilik ve inşaat endüstrilerinde ölümcül olayların sebepleridir. Bu çalışmanın temel amacı ortak kırılma modu olan modeI-II, mod I (çekme kırılmaları) ve mod II (makaslama) kırılmalarından oluşan yenilmelerin, hazırlanmış CCNBD ismi verilen kaya ve beton numuneler ile incelenmesidir. Statik çapsal basma gerilmesi altında test edilen numunelerde, çatlak eğim açısı ?, 30? olana kadar çentik çatlağında Mod I kırılmaya neden olan açılmalar görülmüştür. Bunun yanında ? açısı 33?'den büyük olduğunda ise çentik çatlağında kapanma gözlenmiştir ve bu kapanma ? açısı 45? ve 70? olduğunda oldukça fazla ve belirgin olmuştur. Sonlu elemanlar yöntemi ile işleyen FRANC2D programı kullanarak sayısal modellemeler yapılmıştır ve gerilme dağılımı analizi, çatlaklanma modellemeleri yapılarak Mod I ve II tıkızlık değerleri olan KIc and KIIc değerleri bulunmuştur. Sayısal analiz sonuçlarına göre, çapsal basma gerilmesi altında test edilen CCNBD numunelerde salt Mod I veya salt Mod II kırılmaların mümkün olmadığı bulunmuştur. Ayrıca sayısal analiz sonuçları, çatlaklanmanın başlamasında mode I tıkızlık değeri olan KIC'nin Mod II tıkızlık değeri KIIC'den daha baskın olduğu ve oluşmuş çatlağın ilerlemesinde ise tam tersi olduğunu göstermiştirÖğe Investigation the effect of cyclic loading on fracture propagation in rocks by using Computed Tomography (CT) techniques(American Rock Mechanics Association (ARMA), 2015) Ghamgosar, Morteza; Stewart, Penny; Erarslan, NazifeIn Brazilian test, applied diametrical compression stress induces indirect tensile stresses normal to the vertical plane crossing through the rock disc and the ultimate failure occurs at the place where the maximum tensile stress is concentrated. The mechanical behaviour of rock with pre-existing cracks under static loading has been studied widely. In this study, the fracturing behaviour of Brisbane Tuff, under static and cyclic loading has been analysed applying an ISRM standard Cracked Chevron Notched Brazilian Disc (CCNBD) geometry. Specifically, X-ray Computed Tomography (CT) techniques have been used to investigate the fracturing behaviour of rocks under static and cyclic loading. The fracturing behaviour of rocks technically depends on the nature of loading, strength of mineral and text of rocks. Laboratory observations demonstrated that there is a distinct difference in fracturing between the static and cyclic loading. It was found that the cyclic loading had an important effect on micro-fracture propagation through the Fracture Propagation Zone (FPZ). Copyright 2015 ARMA, American Rock Mechanics Association.Öğe Microstructural investigation of subcritical crack propagation and Fracture Process Zone (FPZ) by the reduction of rock fracture toughness under cyclic loading(Elsevier Science Bv, 2016) Erarslan, NazifeThis study presents the results of laboratory diametrical compression tests performed on Brisbane tuff disc specimens to develop much-needed understanding of the micro-mechanical and micro-structural dynamics of sub critical crack propagation. The strength variation in rocks under mechanical loading without corrosive chemical environment was investigated by investigating the mode-I (tensile) fracture toughness (K-IC) response to static and cyclic loading. In some cases, cracks can grow at a lower load level compared to the static case. This phenomenon is called subcritical crack propagation and depends on,the behaviour of the Fracture Process Zone (FPZ). The K-IC response to cyclic loading was found to be different from that under static loading in terms of the ultimate load and the damage mechanisms in front of the chevron crack. A maximum reduction of the static K-IC of 43% was obtained for the highest amplitude increasing cyclic loading test. Detailed Scanning Electron Microscope (SEM) examinations were performed on the surfaces of the tips of the chevron notch cracks, revealing that both loading methods cause fatigue in the disc rock specimens. When compared with static rupture, the main difference with the cyclically loaded specimens was that intergranular cracks were formed due to particle failure under cyclic loading, while smooth and bright cracks along cleavage planes were formed under static loading. It is believed in this study that the rock texture characteristics such as interlocked and cemented grains, cement volume, cement mineralogy play very important role on damage behaviour of rocks and development of FPZ and subcritical cracking. (C) 2016 Elsevier B.V. All rights reserved.Öğe Progressive damages in hard rock by utilising an oscillating undercut technology(CRC Press/Balkema, 2018) Ghamgosar, Morteza; Duffield, Stephen; Erarslan, NazifeRock cutting is a complex phenomenon that requires advanced and sophisticated techniques to predict fracture initiation and propagation under applied or induced mechanical forces. While conventional cutters apply compressive or impact forces to break a rock body, the idea of applying cyclic forces to rock has led to a novel system to break rocks under tension and fatigue mechanisms. Experimental and numerical models have shown that the oscillating disc cutter (ODC), as a new technology in rock cutting industries, can potentially enable more than 30% increase damage in hard rocks, which offers a profitable, safer and cheaper method to underground rock cutting operations. The various physical properties of the rock influence fracturing behaviour in the cutting process, including water content, dry density, porosity and temperature. In addition to the environmental and physical effects, the roles of microfractures and micro-damaging are deterministic, such as structural anisotropy, grain sizes, different mineral compositions, crack size, amplitude and frequency. A noticeable difference in the fracturing behaviour of monzonite specimens was observed under static and cyclic loading. Symmetrical fracture surfaces were seen under static failure, while excessive dust and crushed particles with no evidence of symmetrical fractures were determined under cyclic test. As the main mechanism in ODC is cyclic action at the cutter disc, therefore; this paper discusses laboratory and numerical results of microfractures propagation in Fracture Process Zone (FPZ) under the cyclic loading in order to utilise and optimise for the ODC technology. © 2018 Taylor & Francis Group, London.Öğe The Brazilian Disc Test Under a Non-Uniform Contact Pressure Along Its Thickness(Springer Wien, 2016) Serati, Mehdi; Alehossein, Habib; Erarslan, Nazife[Abstract Not Available]
