Abstract The influences of mode II loading on fracture process in Berea sandstone were investigated by comparing mode I and mixed-mode fractures that were created by center and eccentric notch beams under three-point bending. Fracture process was characterized by Acoustic Emission (AE) and related energy. Experimental results show mode II loading does not affect the length of fully-developed fracture process zone and maximum value of AE energy. However, it affects the zone from reaching fully-developed stage, i.e., mixed-mode fracture before or at peak load, and mode I after the peak. It also breaks the similarity and symmetry of AE events pattern.
Last. E. Di Battista(Polytechnic University of Turin)H-Index: 2
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Abstract An analysis of the Acoustic Emission (AE) activity and of the energy fields is carried out with reference to three-point bending (TPB) tests on concrete beams with different sizes. First, a cracking mode classification is performed on the basis of AE parameters like the average frequency and the rise angle of the waveforms. A compression test is also performed to verify if the identification of the fracture mode by means of the AE parameters is appropriate. Then, regarding the TPB tests...
Abstract Fracture tests were performed on sandstone specimens under three-point bending with a variety of notch positions to achieve KII/KI = 0–12%. At peak load, the maximum crack opening displacement measured by digital image correlation was 45 μm under mixed mode loading and 30 μm under mode I, and these values were used to determine the length of the cohesive zone: 10–12 mm for mixed mode and 5–7 mm for mode I. For mixed mode fracture, the displacement in the cohesive zone was identified to ...
#2Luigi Biolzi(Polytechnic University of Milan)H-Index: 26
Last. Joseph F. Labuz(UMN: University of Minnesota)H-Index: 32
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AbstractAn electronic speckle pattern interferometry (ESPI) system, which delivers high-resolution displacement data from fringes that are formed by the subtraction of laser speckle patterns, was constructed to study fracture initiation in a quasi-brittle material. Mode I opening and Mixed-Mode I and II fracture experiments were performed with a homogeneous, fine-grained (0.1–0.8 mm grain size) sandstone using the three-point bending test. Specimens were notched at various lengths and positions ...
The cohesive crack model has been widely accepted as the best compromise for the analysis of fracture of concrete and other quasibrittle materials. The softening stress-separation law of this model is now believed to be best described as a bilinear curve characterized by four parameters: the initial and total fracture energies Gf and GF, the tensile strength ft′, and the knee-point ordinate σ1. The classical work-of-fracture test of a notched beam of one size can deliver a clear result only for ...
Last. John Napier(University of the Witwatersrand)H-Index: 2
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The direct formulation of the complex variables boundary element method is generalized to allow for solving problems with constant body forces. The hypersingular integral equation for two-dimensional piecewise homogeneous medium is presented and the numerical solution is described. The technique can be used to solve a wide variety of problems in engineering. Several examples are presented to verify the approach and to demonstrate its key features. The results of calculations performed with the p...
#1Majid R. Ayatollahi(IUST: Iran University of Science and Technology)H-Index: 65
#2M.R.M. Aliha(IUST: Iran University of Science and Technology)H-Index: 50
Last. H. Saghafi(IUST: Iran University of Science and Technology)H-Index: 17
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An edge cracked semi-circular specimen subjected to asymmetric three-point bend loading was suggested for investigating mixed mode fracture in brittle materials. Using finite element analysis, the crack parameters were obtained for various crack lengths and different locations of loading points. It was shown that by selecting appropriate positions for the loading points, full mode mixities from pure mode I to pure mode II could be achieved. Then, a series of fracture tests were conducted on PMMA...
Acoustic emission (AE) energy, instead of amplitude, associated with each of the event is used to estimate the fracture process zone (FPZ) size. A steep increase in the cumulative AE energy of the events with respect to time is correlated with the formation of FPZ. Based on the AE energy released during these events and the locations of the events, FPZ size is obtained. The size-independent fracture energy is computed using the expressions given in the boundary effect model by least squares meth...
#1Qing Lin(UMN: University of Minnesota)H-Index: 11
#2Ali Fakhimi(New Mexico Institute of Mining and Technology)H-Index: 18
Last. Joseph F. Labuz(UMN: University of Minnesota)H-Index: 32
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Initiation of failure under three-point bending was observed in sandstone specimens with and without a stress concentrator. Acoustic emission (AE) and electronic speckle pattern interferometry (ESPI) were used to quantify the fracture phenomena through AE locations and ESPI images of an intrinsic damage zone. To investigate mixed mode fracture, beam tests with off-center notches were studied as well. Before about 95% of peak load, the locations of AE were somewhat random for beams with a smooth ...
#2R. Vidya Sagar(IISc: Indian Institute of Science)H-Index: 12
In this experimental study an acoustic emission (AE) technique was used on geometrically similar notched plain concrete three-point bend specimens of different sizes. This study aims to measure the acoustic emission energy released during fracture process of plain concrete beams and to investigate the relation between acoustic emission energy to fracture energy of plain concrete beams of different sizes. The technique of acoustic emission uses one or more sensors to listen to a wide range of eve...
#1Soo-Ho Chang(SNU: Seoul National University)H-Index: 10
#2Chung-In Lee(SNU: Seoul National University)H-Index: 12
Last. Seokwon Jeon(SNU: Seoul National University)H-Index: 15
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Rock fracture mechanics has been widely applied to blasting, hydraulic fracturing, mechanical fragmentation, rock slope analysis, geophysics, earthquake mechanics, hot dry rock geothermal energy extraction and many other practical problems. But a standard method to accurately determine fracture toughness of rocks, one of the most important parameters in fracture mechanics as an intrinsic property of rock, has not been yet well established. To obtain rock fracture toughness, disc-type specimens w...
#2Zhizhang Wang(China University of Petroleum)H-Index: 1
Last. Wanchun Zhao(Northeast Petroleum University)H-Index: 1
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Rock brittleness is an essential factor affecting underground engineering disasters and energy extraction. A large number of cracks are generated during rock destruction, and many acoustic emission (AE) signals are accompanied. The propagation speed and modes of cracks in different brittle rocks differ during failure, and their AE signals also show differing characteristics. In this study, uniaxial compression experiments cooperating with AE monitoring on rock-like materials with different britt...
#1Qindong Lin(CAS: Chinese Academy of Sciences)H-Index: 1
#2Shihai Li(CAS: Chinese Academy of Sciences)H-Index: 5
Last. Xinquan Wang(CAS: Chinese Academy of Sciences)H-Index: 1
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Abstract With the aim of modelling the energy dissipation phenomenon during the initiation and propagation of cracks, a novel cohesive fracture model is proposed in this study based on the multi-scale model of rocks and the Lennard-Jones potential between non-bonding molecules. The proposed model establishes the corresponding relationship of deformation in the multi-scale model of rocks and suggests that the fracture energy is essentially the manifestation of the transformation of deformation en...
Abstract An in-depth understanding of the thermomechanical properties of rocks is fundamentally important in many fields of geotechnical engineering. However, the microcracking mechanisms of thermally-treated granite under mode I loading are very complex. To investigate the effect of thermal treatment on the microcracking behavior, we perform mode I three-point bending tests on a set of pre-notched semi-circular specimens. The specimens are pre-heated to different target temperatures (i.e. 50 °C...
#1Qing Lin(China University of Petroleum)H-Index: 11
#2Siqi Wang(China University of Petroleum)H-Index: 4
Last. Yunhu Lu(China University of Petroleum)H-Index: 11
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Abstract Influence of the fracture process zone (FPZ) poses a challenge to accurately determine the FPZ and traction-free crack during the fracture process in a rock structure. In this study, an engineering approach based on concepts of the cohesive zone model, is proposed to identify them in a sandstone beam under three-point bending. Two types of specimens were tested, including center notch and smooth boundary beams. Acoustic emission (AE) and digital image correlation (DIC) were used to moni...
#1Qing Lin(China University of Petroleum)H-Index: 11
#2Siqi Wang(China University of Petroleum)H-Index: 4
Last. Yunhu Lu(China University of Petroleum)H-Index: 11
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Abstract Mode II fracture, as one basic fracture mode, remains an interesting topic in fracture mechanics. However, its realization is a challenge in the laboratory, especially for quasi-brittle materials. In this study, two types of specimens were tested: the angled edge crack semi-circular specimen under three-point bending (SCB) and double edge notched compression (DENC) specimen. Digital image correlation (DIC) was used to measure the displacements surrounding the notch tip, which helps to i...
Last. Yaohui Gao(CAS: Chinese Academy of Sciences)H-Index: 3
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Abstract In this study, servo-controlled biaxial compression tests were conducted on marble specimens to investigate their failure characteristics and fracturing process. The complete stress-strain curves were obtained, and the three-dimensional (3D) features of the failure surfaces were acquired by 3D laser scanning. Acoustic emission (AE) monitoring and moment tensor (MT) analysis were used in combination to better understand the fracturing mechanism of marble under biaxial compression. It was...
#1Min Zhang(CUMT: China University of Mining and Technology)H-Index: 2
#2Linming Dou(CUMT: China University of Mining and Technology)H-Index: 1
Last. Shan Huang(Freiberg University of Mining and Technology)H-Index: 1
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Abstract This paper documents investigations of the fatigue behaviour of strong burst-prone coal in terms of energy dissipation, hysteresis and micro-seismicity. The energy dissipation characteristics of the coal subjected to multi-level-frequency cyclic loading were studied. Two hysteresis indexes were proposed according to the stress-strain relation during cyclic loading. These two indexes are effective as twin precursors to predict the fatigue failure of coal samples. The effect of frequency ...
Abstract Concrete is an important engineering material whose tensile property plays an important role in structural safety. Thus, the effect of strain rate on crack evolution in concrete during ten...