Abstract The present work develops cohesive zone models (CZM), i.e. cohesion-separation laws, for mode I fractures in different rank coals, including weakly caking coals, gas coals, fat coals, meager-lean coals and anthracite, through disk-shaped compact tension tests. Firstly, the experiments show that with the coal rank rising, the critical crack separation displacements and the degrees of the nonlinearity of the softening function decline gradually. By fitting the experimental data with the four commonly used cohesive zone models including the power law, the exponential law, the bilinear law and the linear law, the best-fitted model for each rank of coals was identified and the corresponding parameters were found. Secondly, to arrive at a general CZM formulation for the different rank coals, Karihaloo’s polynomial law was employed, which also gave better fit to the experimental data compared with the aforementioned four CZMs. After obtaining the CZM for coals, fracture energy was evaluated which is equal to the area under the softening curve. With the increase of the coal rank, the fracture energy reduces but its coefficient of variation increases. Thirdly, the geometric characteristics of fractures in different rank coals are studied. The lower rank coals have more tortuous crack propagation paths and larger roughness coefficients, whereas the higher rank coals possess wider average fracture apertures. Lastly, in order to further test the applicability of the obtained cohesion-separation laws, we implemented the Karihaloo’s polynomial CZM and the bilinear CZM into the cohesive elements of ABAQUS® using the user-subroutine VUMAT, and thereby simulated the crack propagation in single-edge notched beams made of weakly caking coals, fat coals, and meager-lean coals, respectively. It is found that the numerical results based on Karihaloo’s polynomial CZM have a better agreement with the experimental data than the bilinear CZM.
Abstract Fracture is one of the most commonly encountered failure modes of engineering materials and structures. Prevention of cracking-induced failure is, therefore, a major concern in structural designs. Computational modeling of fracture constitutes an indispensable tool not only to predict the failure of cracking structures but also to shed insights into understanding the fracture processes of many materials such as concrete, rock, ceramic, metals, and biological soft tissues. This chapter p...
Abstract To investigate the influence of geometric characteristics of deformable rough fractures under confining stresses on the behaviors of non-Darcy flow, four fractured sandstone specimens were used for hydraulic tests in the experiments. According to the experimental results of the relationships between the hydraulic gradient and the flow rate, it is demonstrated that the Forchheimer's equation can offer a good description of the non-Darcy flow in rough fractures. In addition, the coefficie...
#2Jian-Ying Wu(SCUT: South China University of Technology)H-Index: 21
Abstract Being able to seamlessly deal with complex crack patterns like branching, merging and even fragmentation, the phase-field model, amongst several alternatives, is promising in the computational modeling of dynamic fracture in solids. This paper presents an extension of our recently introduced phase-field cohesive zone model for static fracture to dynamic fracture in brittle and quasi-brittle solids. The model performance is tested with several benchmarks for dynamic brittle and cohesive ...
Abstract Being able to model complex nucleation, propagation, branching and merging of cracks in solids within a unified framework, the classical phase-field models for brittle fracture fail in predicting length scale independent global responses for a solid lacking elastic singularities (e.g., corners, notches, etc.). Motivated from Barenblatt’s approximation of Griffith’s brittle fracture with a vanishing Irwin’s internal length, this paper extends our recent work in quasi-brittle failure (Wu,...
#1Jianfeng Yang(TUT: Taiyuan University of Technology)H-Index: 6
#2Haojie Lian(TUT: Taiyuan University of Technology)H-Index: 13
Last. Yuedu Chen(TUT: Taiyuan University of Technology)H-Index: 5
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Abstract Effects of supercritical carbon dioxide (scCO 2 ) on fracture toughness of bituminous coals are studied. The semi-circular specimens under three-point bending (SCB) were adopted for conducting experiments on the coal samples after being immersed in scCO 2 for different soaking periods. To investigate the fracture toughness in different loading conditions, including pure mode I, pure mode II, and mixed mode I/II, the inclination angles of the prefabricated cracks in the coal SCB samples ...
#1Jian-Ying Wu(SCUT: South China University of Technology)H-Index: 21
Abstract Aiming to bridge the gap between damage and fracture mechanics for modeling localized failure in solids, this paper addresses a novel geometrically regularized gradient-damage model with energetic equivalence for cracking evolution. With the free energy potential defined as usual in terms of the local strain and damage fields, the constitutive relations are derived consistently from the standard framework of thermodynamics. Upon the sharp crack topology geometrically regularized by the ...
#1Yuedu Chen(TUT: Taiyuan University of Technology)H-Index: 5
#2Weiguo Liang(TUT: Taiyuan University of Technology)H-Index: 14
Last. Vinh Phu Nguyen(Monash University, Clayton campus)H-Index: 26
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Abstract The fracture geometric characteristics (FGC) have considerable influence on fluid flow in the fractured rock mass. The present work took experimental approaches to investigate the quantitative relationship between the FGC of a rough-walled fracture (RWF) and its hydraulic properties, particularly for the deformable fractures subjected to applied stresses. Taking into account the complexity of the FGC in realistic practice, the FGC studied in this work are comprised of three types: the s...
This paper revisits the problem of computational modelling of a fluid-driven fracture propagating in a permeable porous medium using zero-thickness flow cohesive interface elements. Both cases of continuous and discontinuous pressure field across the fractures are implemented in a unified formulation. The paper provides computational aspects of hydraulic fracture modelling such as mesh generation, execution time, convergence and numerical integration issues. We show that Newton-Cotes quadrature ...
#1Yixin Zhao(CUMT: China University of Mining and Technology)H-Index: 65
#2Shuang Gong(CUMT: China University of Mining and Technology)H-Index: 2
Last. Yaodong Jiang(CUMT: China University of Mining and Technology)H-Index: 17
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Abstract In order to study the influence of bedding angle and loading rate on the initiation fracture toughness (IFT) of coal, notched semi-circular bending (NSCB) specimens were made by using a split Hopkinson pressure bar (SHPB) system. The dynamic IFT of NSCB coal specimens with various bedding angles and crack lengths under different loading rates were analyzed and discussed. A high-speed high-resolution digital camera was used to record the processes of cracking initiation and propagation i...
Last. Amin Heidarpour(Monash University, Clayton campus)H-Index: 23
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Interfacial cracking occurs in many engineering problems such as delamination in composite laminates, matrix/interface debonding in fibre reinforced composites etc. Computational modelling of these interfacial cracks usually employs compatible or matching cohesive interface elements. In this paper, incompatible or non-matching cohesive interface elements are proposed for interfacial fracture mechanics problems. They allow non-matching finite element discretisations of the opposite crack faces th...
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 ...
Abstract A field-enriched finite element method is proposed in this paper to simulate the failure process of rocks. According to the different types of defects, the proposed method can select the appropriate failure criteria for voids and cracks. Field variables are used to characterize the crack location and to realize the influence of cracks on the physical field of the numerical model. The main features and the capability of the field-enriched finite element method to efficiently simulate the...
#1Liu Zhenghe(TUT: Taiyuan University of Technology)H-Index: 1
#2Shaohua Wang(TUT: Taiyuan University of Technology)
Last. Yang Dong(TUT: Taiyuan University of Technology)
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Directional hydraulic fracturing by prefabricating longitudinal (axial) cracks on the sides of boreholes is an effective technique to control hard roof and ensure mining safety. In the present work, a true triaxial hydraulic fracturing experimental device was used to study the influence of prefabricated crack (pre-crack) parameters (including inclination angle and crack length), fracturing fluid viscosity, and mechanical characteristics of rocks on directional hydraulic fracturing with axial pre...
Last. Katriona Edlmann(Edin.: University of Edinburgh)H-Index: 12
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Soft cyclic hydraulic fracturing has become an effective technology used in subsurface energy extraction which utilises cyclic hydraulic flow pressure to fracture rock. This new technique induces fatigue of rock to reduce the breakdown pressure and potentially the associated risk of seismicity. To control the fracturing process and achieve desirable fracture networks for enhanced permeability, the rock response under cyclic hydraulic stimulation needs to be understood. However, the mechanism for...
Abstract The present work studies the Park–Paulino–Roesler (PPR) model, a unified potential-based cohesive zone model (CZM), for mixed mode I/II fractures in different ranked coals, including weakly caking coals, fat coals and anthracite, by using disk-shaped compact tension (DC(T)) tests and punch-through shear (PTS) tests. The PTS experiments showed that with the increase in coal rank, the initial shear stiffness and shear peak loads grow and the maximum tangential crack opening displacement (...
Abstract The present paper investigates the effects of CO2-saturation and confining pressures on the fracture toughness of carbon dioxide saturated bituminous coals. Three-point bending experiments were performed with semi-circular coal specimens (SCB) after they were immersed in different CO2 pressures. The experimental results show that the pure modes I and II fracture toughnesses of coal samples gradually decrease with the growth of CO2-saturation pressure. Additionally, the fracture toughnes...
The present work conducted laboratory experiments of fracturing in fat coals, anthracites, and mudstones. Three different fluids were selected as the fracturing fluids, including water, liquid CO2 (L-CO2), and supercritical CO2 (Sc-CO2). The resulting fracture morphologies and fracture apertures of the coal specimens were investigated using 3D morphological scanning, and the permeabilities of the samples were measured before and after fracturing. The experimental results showed that the breakdow...
Last. Haojie Lian(TUT: Taiyuan University of Technology)H-Index: 13
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The influence of water content on mode I fracture toughness (KIc) of mudstones has been studied using semi-circular bend (SCB) specimens subject to three-point bendings. And the mudstone SCB specimens are divided into three types, including Type-A, Type-B and Type-C, corresponding to the three configurations of the bedding planes, including divider direction, arrester direction, and transverse direction, respectively. The test results show that the values of KIc for the three types of specimens ...