Abstract Crack initiation and propagation in rock involve the development of a nonlinear zone around the crack tip called fracture process zone. The existence of fracture process zone influences the fracture behavior and therefore it must be carefully investigated. This zone is normally idealized as a cohesive zone whose mechanical properties are difficult to measure. In this study, a relatively simple approach is proposed to identify the properties of the cohesive zone and the length of the cohesionless crack in a sandstone specimen under three-point bending. Two types of specimens were tested: beams with center notch and with smooth boundary. The digital image correlation (DIC) was utilized to obtain the opening displacement around the position where the fracture initiated. For a small length of a horizontal section around the specimen center, the material is considered to be in the state of uniaxial tension and its behavior is interpreted by the cohesive zone model. The proposed approach discusses three types of opening displacement distribution patterns (I), (II), (III). Pattern (I) is related to tensile loading of the material, pattern (II) suggests the development of material softening within the cohesive zone and pattern (III) indicates the development of the cohesionless crack. These displacement patterns together with the appropriate reference loadings are used to identify the length of the cohesionless crack. For example, observation of pattern (III) is consistent with the development of the cohesionless crack when the reference loading is the beginning of experiment. Further, the proposed method is useful for measuring the critical crack opening displacement and the fracture energy.
#2Qing Lin(China University of Petroleum)H-Index: 11
Last. Joseph F. Labuz(UMN: University of Minnesota)H-Index: 32
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Abstract Rock fracture and the induced displacement field are investigated through physical and numerical experiments. A Berea sandstone specimen with a central notch was tested in three-point bending. Digital image correlation (DIC) was used to obtain the displacement patterns as the fracture initiated and propagated. The DIC results clearly show the development of a damage zone and displacement discontinuity along the center line of the beam at peak load. It is suggested that a traction-free o...
Last. Shiyuan Li(China University of Petroleum)H-Index: 2
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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-de...
Abstract A three point bending fracture test was performed on a typical quasi-brittle material (Berea sandstone). The loading was continued into the post-peak region where crack growth was visible along the center line of the beam. Subsequent inspection of a portion of the specimen showed that part of the fracture offered no resistance to loading – a cohesionless crack existed. Digital image correlation was used to study the nature of the displacement discontinuity associated with the cohesionle...
Tensile cracking in asphalt pavements due to vehicular and thermal loads has become an experimental and numerical research focus in the asphalt materials community. Previous studies have used the discrete element method (DEM) to study asphalt concrete fracture. These studies used trial-and-error to obtain local fracture properties such that the DEM models approximate the experimental load-crack mouth opening displacement response. In the current study, we identify the cohesive fracture propertie...
#1Wei-Wei Ji(CAS: Chinese Academy of Sciences)H-Index: 4
#2Peng-Zhi Pan(CAS: Chinese Academy of Sciences)H-Index: 19
Last. Meng-Ping Du(CAS: Chinese Academy of Sciences)H-Index: 1
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•Digital image correlation is used to determine the fracture mode of rock.•Pure mode II fracture cannot be created by so-called mode II loading without confinements.•CCBD specimens generate a mix-mode fracture and SCB specimens generate a mode I fracture.
#1Ali Fakhimi(New Mexico Institute of Mining and Technology)H-Index: 18
#2Fang Wan(New Mexico Institute of Mining and Technology)H-Index: 1
Abstract The bonded particle discrete element method is used to study the fracture process zone in three point bending tests of notched beams. Five different specimen sizes and different material ductility are studied. To capture the damaged contacts around the induced macro-crack (fully softened and detached contacts in front of the notch), a contact bond model with softening is implemented. Material ductility is modified by changing the post-peak slope of the load-displacement curve of the con...
Digital Image Correlation (DIC) is an important and widely used non-contact technique for measuring material deformation. Considerable progress has been made in recent decades in both developing new experimental DIC techniques and in enhancing the performance of the relevant computational algorithms. Despite this progress, there is a distinct lack of a freely available, high-quality, flexible DIC software. This paper documents a new DIC software package Ncorr that is meant to fill that crucial g...
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 ...
Abstract Evaluation of mode I fracture characteristics, such as critical opening displacement and process-zone length, is fundamental for the analysis and prediction of crack growth. To identify deformation with micron-scale resolution, experiments were performed using digital image correlation, where displacement is determined through a comparison of a pair of digital images by matching a small area from the image before deformation to the image after deformation. The matching process uses a cr...
#1Qianbing Zhang(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 25
#2Jian Zhao(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 63
We present a detailed experimental procedure for the quantitative determination of mechanical properties and full-field strain measurement of rock material under dynamic loads. Three kinds of testing methods, i.e., notched semi-circular bending, Brazilian disc, and uniaxial compression, were conducted using a split Hopkinson pressure bar (SHPB) system. Experimental setup, data acquisition and interpretation were described in detail. The digital image correlation (DIC) technique in conjunction wi...
Fracturing in rocks results in the formation of an inelastic region surrounding the crack tip called the fracture process zone (FPZ), which is often characterized using the Linear Cohesive Zone Model (LCZM). Various numerical studies have shown that the prediction of the FPZ characteristics is significantly influenced by variability in the input parameters of LCZM, such as crack tip opening displacement and tensile strength. In this study, an integrated approach was used for evaluating the LCZM ...
#1Qing Lin(China University of Petroleum)H-Index: 11
#2Xin Bian(China University of Petroleum)H-Index: 1
Last. Yunhu Lu(China University of Petroleum)H-Index: 11
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Abstract Fracture criterion of local symmetry has been widely used to predict the fracture kink and simulate the fracture trajectory in rocks under the mixed-mode loading. Although its prediction is a tension dominated fracture, under small scale yielding the criterion must include two aspects: the local mode I stress intensity factor (SIF) kI is maximum and the local mode II SIF kII is zero. Two aspects are not identical when fracture just initiates, but they will be equivalent after the crack ...
Abstract In order to investigate the development characteristics and size effect of rock fracture process zone (FPZ), the GCTS RTX-3000 rock mechanics testing machine was used to carry out on semi-circular bend (SCB) sandstone specimens with diameters of 50 mm, 100 mm, 150 mm and 200 mm, respectively. Combined with the digital image correlation (DIC) method, the variations of the displacement field at the crack tip of specimens with different sizes were analyzed. The results show that the crack ...
Last. Ashutosh Trivedi(DCE: Delhi Technological University)H-Index: 10
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The transportation system has drawn attention due to the growing threats of cracks to the roads and bridges. To accurately detect cracks was made possible by the introduction of deep learning. In this paper, we propose the modified LeNet 5 model for detecting cracks in roads and bridges. We summarize our work in the following points: - 1. We worked on the three datasets, i.e., Automated Bridge Crack Detection Dataset, Concrete Crack Images for Classification Dataset, and Asphalt Crack Dataset. 2...
#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...
Last. Luming Shen(USYD: University of Sydney)H-Index: 24
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Abstract Bimrocks feature stiff blocks randomly distributed in a soft matrix. Despite their wide distribution in nature, their significant effects on the failure of rock structures such as slopes, mines and tunnels have not been fully understood. Bimrocks behave differently as compared with other rock types since they contain mix of blocks of different strength, size and volume distribution and a matrix of different physical and mechanical characteristics. The purpose of this study is to investi...
Abstract To investigate the energy storage and dissipation characteristics during rock flexure fracturing, a series of single cyclic loading–unloading flexural fracture tests was conducted on rectangular rock beams using the three-point loading technique. The results show that under different experimental unloading levels, the elastic and dissipation energies increase linearly as the input energy increases. On this basis, the linear energy storage and dissipation laws were obtained, which were i...
Abstract Experiments on sandstone specimens are conducted to investigate the mechanical, energy conversion and frictional heating characteristics of locking sections in two types of large-scale rockslides. The flaw geometry of the conceptual model is a combination of two preexisting flaws and a locking section. A deep insight into the failure mechanism of locking sections is gained by using digital image correlation (DIC) technology, thermal imaging technology, and thermodynamics theory. Two dif...
#1Tubing Yin(CSU: Central South University)H-Index: 6
#1Tubing Yin(CSU: Central South University)H-Index: 14
Last. Bingqiang Wu(CSU: Central South University)H-Index: 2
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Abstract The safety of cracked rock structures after thermal treatment is the concern of many existing engineering programs. To obtain a deep understanding of rock fracture process, mode I fracture tests are carried out on thermally treated granite (from 25 °C to 800 °C) using notched semi-circular bending (NSCB) specimens in this paper. An acoustic emission (AE) technique is employed to monitor the real-time AE activities during the whole deformation process. The double-K parameters extracted f...