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This research presents the results of laboratory experiments during the investigation of tensile strength–strain characteristics of Brisbane tuff disc specimens under static and diametral cyclic loading. Three different cyclic loading methods were used; namely, sinusoidal cyclic loading, type I and II increasing cyclic loading with various amplitude values. The first method applied the stress amplitude?cycle number (s–n) curve approach to the measurement of the indirect tensile strength (ITS) and fracture toughness (K IC) values of rocks for the first time in the literature. The type I and II methods investigated the effect of increasing cyclic loading on the ITS and K IC of rocks. For Brisbane tuff, the reduction in ITS was found to be 30 % under sinusoidal loading, whereas type I and II increasing cyclic loading caused a maximum reduction in ITS of 36 %. The maximum reduction of the static K IC of 46 % was obtained for the highest amplitude type I cyclic loading tested. For sinusoidal cyclic loading, a maximum reduction of the static K IC of 30 % was obtained. A continuous irreversible accumulation of damage was observed in dynamic cyclic tests conducted at different amplitudes and mean stress levels. Scanning electron microscope images showed that fatigue damage in Brisbane tuff is strongly influenced by the failure of the matrix because of both inter-granular fracturing and trans-granular fracturing. The main characteristic was grain breakage under cyclic loading, which probably starts at points of contact between grains and is accompanied by the production of very small fragments, probably due to frictional sliding within the weak matrix. 相似文献
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Investigating the Effect of Cyclic Loading on the Indirect Tensile Strength of Rocks 总被引：1，自引：1，他引：0
This paper presents the results of laboratory experiments during the investigation of the stress–strain characteristics of
Brisbane tuff disc specimens under diametral compressive cyclic loading. Two different cyclic loading methods were used: namely,
sinusoidal cyclic loading and cyclic loading with increasing mean level. The first method applied the S–N curve approach to the indirect tensile strength (ITS) of rock specimens for the first time in the literature, and the second
method investigated the effect of increasing cyclic loading on the ITS of rock specimens. The ITS of Brisbane tuff disc specimens
was measured using the Brazilian tensile strength test. The reduction in ITS was found to be 33% with sinusoidal loading tests,
whereas increasing cyclic loading caused a maximum reduction of 37%. It is believed that the fracturing under cyclic loading
starts at contact points between strong grains and weak matrices, and that contact points at grain boundaries are the regions
of stress concentration (i.e., indenters). Transgranular cracks emanate from these regions and intergranular cracks sometimes
pass through the contact points. Once cracking begins, there is a steady progression of damage and a general ‘loosening’ of
the rock, which is a precursor to the formation of intergranular cracks. 相似文献
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Mixed-Mode Fracturing of Rocks Under Static and Cyclic Loading 总被引：1，自引：1，他引：0
Static diametrical compression tests conducted on inclined cracked chevron notched Brazilian disc (CCNBD) Brisbane tuff specimens showed that the notched cracks at the centre of the specimens opened (Mode I) up to 30° crack inclination angle (β), whereas crack closure (Mode II) started for β > 33°, and closure became more pronounced at even higher β of 45° and 70°. Both the experimental and numerical results showed that the crack initiation angle (θ) was a function of the β. Scanning electron microscope (SEM) images showed that fatigue damage on cyclic loading of Brisbane tuff is strongly influenced by the failure of the matrix due to both intergranular and transgranular fracturing. 相似文献
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Experimental and Numerical Studies on Determination of Indirect Tensile Strength of Rocks 总被引：4，自引：2，他引：2
Nazife Erarslan Zheng Zhao Liang David John Williams 《Rock Mechanics and Rock Engineering》2012,45(5):739-751
Indirect tension tests using Brisbane tuff Brazilian disc specimens under standard Brazilian jaws and various loading arcs were performed. The standard Brazilian indirect tensile tests caused catastrophic, crushing failure of the disc specimens, rather than the expected tensile splitting failure initiated by a central crack. This led to an investigation of the fracturing of Brazilian disc specimens and the existing indirect tensile Brazilian test using steel loading arcs with different angles. The results showed that the ultimate failure load increased with increasing loading arc angles. With no international standard for determining indirect tensile strength of rocks under diametral load, numerical modelling and analytical solutions were undertaken. Numerical simulations using RFPA2D software were conducted with a heterogeneous material model. The results predicted tensile stress in the discs and visually reproduced the progressive fracture process. It was concluded that standard Brazilian jaws cause catastrophic, crushing failure of the disc specimens instead of producing a central splitting crack. The experimental and numerical results showed that 20° and 30° loading arcs result in diametral splitting fractures starting at the disc centre. Moreover, intrinsic material properties (e.g. fracture toughness) may be used to propose the best loading configuration to determine the indirect tensile strength of rocks. Here, by using numerical outcomes and empirical relationships between fracture toughness and tensile strength, the best loading geometry to obtain the most accurate indirect tensile strength of rocks was the 2α?=?30° loading arc. 相似文献
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The first combined mineralogical and geochemical investigation of coal ashes from the Northwest Thrace Coal Basin, Turkey, was performed as a case study. The coal ash samples were obtained at 525 °C (group I), 750 °C (group II), and 1000 °C (group III) ashing temperatures from coal samples from the basin and were studied in terms of their mineralogical and geochemical composition using XRD and ICP-MS methods. The determination of the mineralogical composition was done for all of the groups; the geochemical analysis was carried out only for group II. In accordance with the high SiO2, Fe2O3, CaO, and SO3 content of the ash, quartz (SiO2), hematite (Fe2O3), and anhydrite (CaSO4) are the major crystalline phases for all of the ash groups. The other minerals are muscovite, thenardite, tridymite, calcite, wollastonite, anorthite, cristobalite, gibbsite, ternesite, mullite, nahcolite, and nacrite. High-temperature phases such as mullite, wollastonite, and anorthite were observed at 750 and 1000 °C. According to the (Fe2O3 + CaO + MgO+ K2O+ Na2O)/(SiO2 + Al2O3+ TiO2) ratios varying from 0.19 to 5.65, the ashes are highly prone to slagging. Compared to average values of low-rank coal ashes, the contents of V, Cr, Co, Ni, Zn, As, Rb, Sr, Mo, Cs, W, and U of the ash are higher, whereas the total content of rare earth elements (REEs) (Σ 163.7 ppm) are lower. Based on upper continental crust normalization, As, Se, Th, and U are enriched in all of the samples. The higher trace element contents in the ashes might be considered as a possible health hazard. The correlation analyses indicated that Ca is associated with anhydrite and As with hematite. The correlation analyses also showed that newly formed Al and Ca silicates may contain the elements such as Ti, K, Na, Cr, Sn, and Pb. 相似文献
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In this research, experimental applications have been performed to reduce blast induced vibrations in open pit mines. For
this purpose, artificial discontinuity zones such as barrier holes and trench were opened in a dragline panel of Seyitomer
Lignite Enterprise, Kutahya, Turkey. Peak particle velocities in front of and behind them were measured by seismographs. In
this way, their effect against vibration was observed and compared. Barrier holes were opened 24 m deep through 3 parallel
lines and aligned at 1 m spacing. On the other hand, the trench had 8 m depth and 4 m width. During the research, 209 measurements
were taken belonging to 105 explosions. Twenty-eight explosions were carried out in the barrier holes experiments and 77 explosions
were carried out in the trench experiments. A decrease in vibration of 14.3–18.5% was obtained behind the barrier holes while
a decrease of 24.8–58.1% was provided by the trench. 相似文献
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