scispace - formally typeset
Search or ask a question

Showing papers on "Fracture (geology) published in 2020"


Journal ArticleDOI
TL;DR: A series of rock tests including Brazilian indirect tension test (BITT), three-point bending test (TPBT), modified shear test (MST), and uniaxial compression test (UCT) were conducted to investigate the acoustic emission (AE) characteristics and crack classification during rock fracture.

185 citations


Journal ArticleDOI
19 Jun 2020-Science
TL;DR: It is shown that improved fracture resistance in a steel with an ultrahigh yield strength of nearly 2 gigapascals can be achieved by activating delamination toughening coupled with transformation-induced plasticity.
Abstract: Developing ultrahigh-strength steels that are ductile, fracture resistant, and cost effective would be attractive for a variety of structural applications. We show that improved fracture resistance in a steel with an ultrahigh yield strength of nearly 2 gigapascals can be achieved by activating delamination toughening coupled with transformation-induced plasticity. Delamination toughening associated with intensive but controlled cracking at manganese-enriched prior-austenite grain boundaries normal to the primary fracture surface dramatically improves the overall fracture resistance. As a result, fracture under plane-strain conditions is automatically transformed into a series of fracture processes in "parallel" plane-stress conditions through the thickness. The present "high-strength induced multidelamination" strategy offers a different pathway to develop engineering materials with ultrahigh strength and superior toughness at economical materials cost.

162 citations


Journal ArticleDOI
TL;DR: In this paper, a dynamic procedure for describing reservoir features is proposed in order to enhance the conventional reservoir characterization methods, which utilizes the reported production data for a specific period of time in conjunction with rock and fluid properties to estimate drainage radius of the well and matrix block height, porosity and width of fracture in the estimated drainage radius.
Abstract: Estimation of fluid and rock properties of a hydrocarbon reservoir is always a challenging matter; especially, it is true for heterogeneous carbonate reservoirs. Petrophysical logs and laboratory activities are common methods for characterizing a hydrocarbon reservoir. This method in conjunction with geostatistical methods is applied to relatively homogeneous sandstone reservoirs or matrix media of dual-porosity heterogeneous carbonate reservoirs. To estimate properties of fracture system of a dual-media carbonate reservoir, outcrop properties, electrical borehole scans, fractal discrete fracture network and analogy with other reservoirs are common methods. Results which obtained from these methods describe the reservoir in a static way and could be relied on them for very small portion of the reservoir. In this paper, a dynamic procedure for describing reservoir features is proposed in order to enhance the conventional reservoir characterization methods. This method utilizes the reported production data for a specific period of time in conjunction with rock and fluid properties to estimate drainage radius of the well and matrix block height, porosity and width of fracture in the estimated drainage radius. The presented method is elaborated through its application in a real case. By this method, one can generate maps of matrix block size and fracture width and porosity throughout the reservoir. Also, it could be a powerful tool for estimation of effectiveness of acid/hydraulic fracturing activity.

135 citations


Journal ArticleDOI
TL;DR: Wang et al. as discussed by the authors developed and solved a hydraulic fracture height mathematical model aiming at high stress and multi-layered complex formations based on studying the effect of plastic region generated by stress concentration at fracture tip on the growth of fracture height.

99 citations


Journal ArticleDOI
TL;DR: In this article, the interaction behavior between vertical hydraulic fracture and bedding plane (BP) was discussed, and the results showed that due to the low bonding strength, the BPs could be easily activated even under high vertical stress difference coefficient.

98 citations


Journal ArticleDOI
TL;DR: In this paper, a time-series extraction method was proposed to represent coal and rock paroxysmal fractures, and the relationship between low-frequency EMR signals and coal fractures was analyzed theoretically.

94 citations


Journal ArticleDOI
Shumin Liu1, Xuelong Li1, Dengke Wang, Mingyang Wu1, Guangzhi Yin1, Minghui Li1 
TL;DR: In this article, the authors investigated the influence of temperature impact on the mechanical properties and acoustic emission (AE) characteristics of coal and found that temperature impact causes the development of pores and cracks in the coal, which reduces the strength of coal.
Abstract: Coal and rock mass constitute a type of porous medium. This study investigated the influence of temperature impact on the mechanical properties and acoustic emission (AE) characteristics of coal. A mechanism analysis was performed from the perspective of microstructure. The results show that the temperature impact causes the development of pores and cracks in the coal, which reduces the strength of coal. The elastic modulus of coal generally decreases with increasing temperature gradient. AE parameters increase with the increase in the load and reach the maximum value at the peak stress. AE parameters and cumulative parameters decrease with increasing temperature gradient. Not only does temperature impact change the fracture structure of the coal surface, but also the internal fracture structure of the coal is significantly affected. After temperature impact, the cracks expand and new cracks are initiated, and the fracture volume of the coal increases. Temperature impact causes the volume and specific surface area of small pores and meso-pores in coal to increase, and promotes the opening of the necking pores within the coal. The impact causes macro-pores to penetrate through to form cracks, which increases the transport of coal gas and significantly improves the permeability of coal. The thermal stress generated by coal under temperature impact is greater than its tensile strength, which promotes the cracking of coal, along with the initiation, widening, extension, and expansion of crack networks, which significantly change the fracture structure of coal. The research results lay a certain theoretical and experimental foundation for further study of mechanical properties of coal affected by liquid nitrogen.

94 citations


Journal ArticleDOI
TL;DR: In this article, a 3D thermal-hydraulic coupled numerical model is proposed to describe the interaction of fluid flow and heat transfer, and the effect of multiple hydraulic fractures on geothermal energy extraction performance.

90 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of the strain rate on the acoustic emission (AE) characteristics with strain rate, uniaxial compression tests at different loading rates and impact loading tests were conducted on granite using a MTS322 rock mechanical test system and split Hopkinson pressure bar (SHPB) system, respectively.

89 citations


Journal ArticleDOI
TL;DR: The failure characteristics and the various induced fractures of shale are investigated in this paper, where different loading rates were applied for different inclination angles of the weak planes of shale (θ ǫ = 0, 15, 30, 45, 60, 75, 90°).
Abstract: The failure characteristics and the various induced fractures of shale are investigated in this paper. Brazilian tests were conducted for different inclination angles of the weak planes of shale (θ = 0, 15, 30, 45, 60, 75, 90°). Different loading rates were applied (V = 0.005 kN/s, 0.02 kN/s, 0.1 kN/s, and 0.5 kN/s). The results show that there is an increase in the Brazilian split strength (BSS) with the increase in the inclination angle from 0° to 90°, with possibly a local dip for 45°. When θ = 45°, both the split modulus (Es) and the absorbed energy (U) had the minimum values, whereas the fracture maximum deviation distance (L′max) had the maximum value. The geometrical trajectory of the fracture in shale samples can be classified into three types, namely the through fracture, the non-through fracture, and the multiple fracture. The BSS, Es, and U of shale gradually increased with the increase in loading rate. Additionally, the fracture is more close to the center. This is because, as the loading rate increases, the time for the propagation and evolution of internal damage of shale decreases.

89 citations


Journal ArticleDOI
01 Jul 2020
TL;DR: In this article, a machine learning approach was proposed to predict fracture processes connecting molecular simulation into a physics-based data-driven multiscale model, based on atomistic modeling and a novel image-processing approach.
Abstract: Summary Fracture is a catastrophic process whose understanding is critical for evaluating the integrity and sustainability of engineering materials. Here, we present a machine-learning approach to predict fracture processes connecting molecular simulation into a physics-based data-driven multiscale model. Based on atomistic modeling and a novel image-processing approach, we compile a comprehensive training dataset featuring fracture patterns and toughness values for different crystal orientations. Assessments of the predictive power of the machine-learning model shows excellent agreement not only regarding the computed fracture patterns but also the fracture toughness values and is examined for both mode I and mode II loading conditions. We further examine the ability of predicting fracture patterns in bicrystalline materials and material with gradients of microstructural crystal orientation. These results further underscore the excellent predictive power of our model. Potential applications of this model could be widely applied in material design.

Journal ArticleDOI
Gan Feng1, Gan Feng2, Xiaochuan Wang1, Man Wang, Yong Kang1 
TL;DR: In this paper, the fracture characteristics of fine-grained granite were examined for a potential geothermal-energy reservoir, and the results indicated that thermal cycling leads to decreased fracture toughness (Keff), absorbed energy (U), longitudinal wave velocity (Pv), and increased permeability (K).

Journal ArticleDOI
TL;DR: In this article, the authors proposed an external driving force for the evolution of the phase field to model the strength of the material, which implicitly accounts for the presence of the inherent microscopic defects in the material.
Abstract: Twenty years in since their introduction, it is now plain that the regularized formulations dubbed as phase-field of the variational theory of brittle fracture of Francfort and Marigo (1998) provide a powerful macroscopic theory to describe and predict the propagation of cracks in linear elastic brittle materials under arbitrary quasistatic loading conditions. Over the past ten years, the ability of the phase-field approach to also possibly describe and predict crack nucleation has been under intense investigation. The first of two objectives of this paper is to establish that the existing phase-field approach to fracture at large — irrespectively of its particular version — cannot possibly model crack nucleation. This is so because it lacks one essential ingredient: the strength of the material. The second objective is to amend the phase-field theory in a manner such that it can model crack nucleation, be it from large pre-existing cracks, small pre-existing cracks, smooth and non-smooth boundary points, or within the bulk of structures subjected to arbitrary quasistatic loadings, while keeping undisturbed the ability of the standard phase-field formulation to model crack propagation. The central idea is to implicitly account for the presence of the inherent microscopic defects in the material — whose defining macroscopic manifestation is precisely the strength of the material — through the addition of an external driving force in the equation governing the evolution of the phase field. To illustrate the descriptive and predictive capabilities of the proposed theory, the last part of this paper presents sample simulations of experiments spanning the full range of fracture nucleation settings.

Journal ArticleDOI
TL;DR: In this paper, the feasibility of the inter-fracture injection and production (IFIP) method to increase oil production rates of horizontal wells is investigated, and the suggested well completion scheme for the IFIP methods is presented.
Abstract: Well production rates decline quickly in the tight reservoirs, and enhanced oil recovery (EOR) is needed to increase productivity. Conventional flooding from adjacent wells is inefficient in the tight formations, and Huff-n-Puff also fails to achieve the expected productivity. This paper investigates the feasibility of the inter-fracture injection and production (IFIP) method to increase oil production rates of horizontal wells. Three multi-fractured horizontal wells (MFHWs) are included in a cluster well. The fractures with even and odd indexes are assigned to be injection fractures (IFs) and recovery fractures (RFs). The injection/production schedule includes synchronous inter-fracture injection and production (s-IFIP) and asynchronous inter-fracture injection and production (a-IFIP). The production performances of three MFHWs are compared by using four different recovery approaches based on numerical simulation. Although the number of RFs is reduced by about 50% for s-IFIP and a-IFIP, they achieve much higher oil rates than depletion and CO2 Huff-n-Puff. The sensitivity analysis is performed to investigate the impact of parameters on IFIP. The spacing between IFs and RFs, CO2 injection rates, and connectivity of fracture networks affect oil production significantly, followed by the length of RFs, well spacing among MFHWs, and the length of IFs. The suggested well completion scheme for the IFIP methods is presented. This work discusses the ability of the IFIP method in enhancing the oil production of MFHWs.

Journal ArticleDOI
TL;DR: In this article, a two-phase flow model of water-sediment inrush in coal mining was established and verified by a laboratory-scale test, which showed that with increases sediment particle diameter, volume fraction and initial water phase velocity, the resistance of sediment particles grows gradually.
Abstract: To investigate the mechanism of water–sediment inrush during coal mining, the characteristics of water–sediment flow in rock fractures were quantitatively analyzed by computational fluid dynamics (CFD). Based on the two-phase flow theory, a resistance model of water–sediment flow in fractures was established and verified by a laboratory-scale test. The results showed that: (1) With increases sediment particle diameter, volume fraction, and initial water phase velocity, the resistance of sediment particles grows gradually. (2) The drag force of sediment particles is mainly generated from the collision of the water phase and fracture wall. The velocity distribution of sediment particles can be divided into three stages, i.e., continuous increase, rapid decrease, and slow fluctuation. (3) The numerical model was shown to have high predictive accuracy by comparison with the test results. The model’s predictive accuracy decreases with increased water phase velocity and decreases of the sediment particle diameter and volume fraction. (4) The smaller the fracture width, the larger the inclination and bending angles, and the greater the resistance of the two-phase flow in the fracture. Collisions between the particles and fracture wall cause velocity attenuation of the sediment particles. We propose water–sediment inrush prevention and control technology based on the numerical analysis results.


Journal ArticleDOI
TL;DR: In this paper, the strength of a 3D non-persistent jointed specimen is characterized by three stages as the joint inclination angle (θ) increases from 0° to 90°.

Journal ArticleDOI
TL;DR: In this article, the authors present a wealth of laboratory data and suggest tools, widely used in geotechnics but adapted here to better suit volcanic rocks, to upscale these values to the scale of a volcanic rock mass.

Journal ArticleDOI
TL;DR: The computation of the steady state fracture toughness as a function of the cohesive strength shows that cleavage fracture can be predicted in otherwise ductile metals using sensible values for the material parameters and the hydrogen concentration.
Abstract: We present a gradient-based theoretical framework for predicting hydrogen assisted fracture in elastic-plastic solids. The novelty of the model lies in the combination of: (i) stress-assisted diffusion of solute species, (ii) strain gradient plasticity, and (iii) a hydrogen-sensitive phase field fracture formulation, inspired by first principles calculations. The theoretical model is numerically implemented using a mixed finite element formulation and several boundary value problems are addressed to gain physical insight and showcase model predictions. The results reveal the critical role of plastic strain gradients in rationalising decohesion-based arguments and capturing the transition to brittle fracture observed in hydrogen-rich environments. Large crack tip stresses are predicted, which in turn raise the hydrogen concentration and reduce the fracture energy. The computation of the steady state fracture toughness as a function of the cohesive strength shows that cleavage fracture can be predicted in otherwise ductile metals using sensible values for the material parameters and the hydrogen concentration. In addition, we compute crack growth resistance curves in a wide variety of scenarios and demonstrate that the model can appropriately capture the sensitivity to: the plastic length scales, the fracture length scale, the loading rate and the hydrogen concentration. Model predictions are also compared with fracture experiments on a modern ultra-high strength steel, AerMet100. A promising agreement is observed with experimental measurements of threshold stress intensity factor Kth over a wide range of applied potentials.

Journal ArticleDOI
TL;DR: In this paper, a grouting device was developed for preparing standard grouting samples, and shear tests and confined seepage tests were conducted on single-fracture chlorite schist with and without grouting.

Journal ArticleDOI
TL;DR: In this paper, the influence of fiber, temperature and loading rate on the fracture toughness of asphalt concrete was investigated experimentally on the End Notch Disc Bend (ENDB) specimen.

Journal ArticleDOI
TL;DR: In this paper, an isotropic neural network based fracture initiation model is proposed, trained and validated to describe the onset of fracture across the range of stress states, strain rates and temperatures considered.

Journal ArticleDOI
TL;DR: Fracture mechanics analyses demonstrate that the hybrid toughening mechanisms of crack twisting and crack bridging mode arising from DFB architecture enable excellent fracture resistance with crack orientation insensitivity.
Abstract: Bioinspired architectural design for composites with much higher fracture resistance than that of individual constituent remains a major challenge for engineers and scientists Inspired by the survival war between the mantis shrimps and abalones, we design a discontinuous fibrous Bouligand (DFB) architecture, a combination of Bouligand and nacreous staggered structures Systematic bending experiments for 3D-printed single-edge notched specimens with such architecture indicate that total energy dissipations are insensitive to initial crack orientations and show optimized values at critical pitch angles Fracture mechanics analyses demonstrate that the hybrid toughening mechanisms of crack twisting and crack bridging mode arising from DFB architecture enable excellent fracture resistance with crack orientation insensitivity The compromise in competition of energy dissipations between crack twisting and crack bridging is identified as the origin of maximum fracture energy at a critical pitch angle We further illustrate that the optimized fracture energy can be achieved by tuning fracture energy of crack bridging, pitch angles, fiber lengths, and twist angles distribution in DFB composites

Journal ArticleDOI
TL;DR: In this article, a split Hopkinson pressure bar experimental system (SHPB-GAS) was built, using which dynamic impact experiments of gas-bearing coal were performed, and the results indicated that samples presented axial tension fracture under the combination loading (axial static load, confining pressure, gas pressure, and impact load).

Journal ArticleDOI
TL;DR: In this paper, an innovative technique called digital image correlation (DIC) was used to trace the fracture process, and important fracture parameters, such as the FPZ size and critical opening displacement, were measured by full-field displacement and strain measurement.

Journal ArticleDOI
28 Apr 2020-Fractals
TL;DR: In this paper, a significantly large number of electromagnetic signals are generated as a result of fracture appearance and crack expansion during coal and rock loading, and the generation of electromagnetic signal is studied.
Abstract: During coal and rock loading, a significantly large number of electromagnetic signals are generated as a result of fracture appearance and crack expansion. The generation of electromagnetic signal ...

Journal ArticleDOI
Yiyu Lu1, Li Wang1, Zhaolong Ge1, Zhe Zhou1, Kai Deng1, Shaojie Zuo1 
01 Jan 2020-Fuel
TL;DR: In this paper, a series of in-situ compression experiments under continuous injection liquid conditions and dynamically monitored the samples using nuclear magnetic resonance methods were performed to better understand the evolution of the fracture and pore structure of coals that contain macro-fractures during hydraulic fracturing.

Journal ArticleDOI
TL;DR: In this article, the authors present a comprehensive workflow to model hydraulic fracture by accounting for interactions with numerous crosscutting natural fracture or joint sets, as well as the effect of temporary plugging in opened fractures.

Journal ArticleDOI
TL;DR: In this article, the effect of in-plane raster orientation on the tensile and fracture strengths of poly-lactic acid (PLA) samples made by fused deposition modeling technique was investigated.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the fracture toughness of sandstone specimens with different crack inclinations (0°, 5°, 15°, 30°, 45° and 54°) and showed that cyclic F-T treatments can lead to degradation in fracture toughness values.