Experimental Investigation of Sandstone under Cyclic Loading: Damage Assessment Using Ultrasonic Wave Velocities and Changes in Elastic Modulus

Yang, Shenglai; Zhang, Nong; Feng, Xiaowei; Kan, Jiaguang; Pan, Dongjiang; Qian, Deyu

doi:10.1155/2018/7845143

Cited by 14 publications

(9 citation statements)

References 45 publications

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“…The most basic task is selecting an appropriate damage variable to characterize the damage to the rock [21,22]. Based on the principles of residual strain [23], elastic modulus [24] and P-wave velocity [25], scholars have established expressions of damage variables. The attenuation of the elastic modulus and the accumulation of residual deformation are the external manifestations of damage; they cannot quantitatively reflect the degree of damage.…”

Section: Introductionmentioning

confidence: 99%

Energy Evolution and Damage Mechanism of Fractured Sandstone with Different Angles

Yao

Liu

et al. 2022

Energies

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To explore the influence of crack angle on the mechanical properties, energy evolution, and damage evolution of sandstone, uniaxial loading tests were conducted on sandstones with different crack angles. Through the stress–strain curve, the influence of the crack angle on the mechanical properties was analyzed. Based on energy theories and principles, the influence of crack angle on the energy conversion mechanism was analyzed. Based on crack angle and dissipated energy, a damage model considering the initial damage to the fractured sandstones was established. The following conclusions were drawn: (1) The strength and elastic modulus of sandstone decrease with an increase in crack angle, and Poisson’s ratio increases with an increase in crack angle; prefabricated cracks affect the crack initiation position, and accelerate the formation of fracture surfaces. (2) The stress–strain curve was divided into compaction stage, elastic stage, yield stage, and failure stage. The larger the crack angle, the longer the yield stage and the shorter the failure stage. (3) At the peak point, the elastic energy, dissipated energy, and input energy of fractured sandstone always decrease with an increase in crack angle; the energy consumption ratio increases with an increase in crack angle; and the energy storage ratio decreases with an increase in crack angle. (4) The damage variable shows a trend of slow accumulation–steady accumulation–rapid accumulation; the crack angle affects the initial damage of the specimen, and the dissipated energy affects the variation trend of the damage variable.

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Section: Introductionmentioning

confidence: 99%

Energy Evolution and Damage Mechanism of Fractured Sandstone with Different Angles

Yao

Liu

et al. 2022

Energies

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“…There are many definitions for the damage variable such as energy dissipation, maximum strain, residual strain, acoustic emission count, and ultrasonic wave velocity. − A rational damage variable should accurately describe the process of rock degradation, development of microfractures, and the process of microfractures converging into macrofractures. Most damage variables indicate that rock shows a classical three-stage behavior of damage evolution under CACMS. − The damage variable increases quickly in the first few cycles, which is due to the closure of microfractures in the rock specimen. Afterward, damage remains stable for a long cycling time and then increases sharply until the rock fails.…”

Section: Introductionmentioning

confidence: 99%

Influence of Increasing Mean Stress on Fatigue Properties of Shale during Pulsating Hydraulic Fracturing

Hou¹,

Peng

Chen

et al. 2022

Energy Fuels

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During pulsating hydraulic fracturing (PHF), reservoir rock can be subjected to constant amplitude, constant mean stress (CACMS) cyclic loading or constant amplitude, increasing mean stress (CAIMS) cyclic loading. The influence of increasing mean stress on rock fatigue strength, fatigue lifetime, fatigue damage, and energy evolution of shale is rarely investigated, and which type of cyclic loading is more efficient for PHF has not been determined and demonstrated. In this Article, a series of uniaxial compression tests under these two types of cyclic loading are first conducted. A fatigue lifetime model for CAIMS is established. The shale strength and fatigue lifetime for CACMS and CAIMS are then compared. Their differences are explained by their dissipated energy density evolution and damage evolution. Finally, a nonlinear damage accumulation model to predict damage evolution for CAIMS cyclic loading is proposed. It is suggested that CAIMS is a better cyclic loading type when its amplitude is higher than 30% UCS (uniaxial compressive strength) of rock. This provides a meaningful amplitude threshold for CAIMS parameter optimization in the PHF construction. In this case, compared with CACMS cyclic loading, CAIMS cyclic loading significantly decreases the shale strength by up to 20% UCS and the fatigue lifetime from over 500 to 9. Different from an inverted-S-shaped damage evolution for CACMS cyclic loading, damage evolution for CAIMS cyclic loading exhibits a monotonic increasing trend. The damage variable growth rates of CACMS and CAIMS both show a three-stage trend: (1) their growth rates both decrease; (2) the growth rate for CACMS remains stable, while for CAIMS its growth rate slowly increases; and (3) their growth rates both increase sharply. Correspondingly, the dissipated energy density evolutions for CACMS and CAIMS show a similar three-stage trend. It can be concluded that during the second stage, for CAIMS microfractures and plastic deformation inside specimens are developed and accumulated more and faster than those for CACMS cyclic loading. This explains the phenomenon that the fatigue lifetime and strength of CAIMS cyclic loading are less than those of CACMS. The nonlinear damage accumulation model proposed in this Article can well fit experimental results. This model can be used for accurately describing reservoir rock mechanical property degradation during hydraulic fracture simulation induced by PHF.

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“…In the low-stress region, Hsieh et al [6] concluded that the stiffness of the rock will first increase due to the crack closure and then decrease when crack growth occurs after repeated loading. Yang et al [7] used the P-and S-wave velocities based on the ultrasonic wave velocity method to reflect the sandstone behaviour (i.e. elastic modulus and the shear modulus) under cyclic loading condition and found that rock specimens stiffen during loading and soften during unloading.…”

Section: Introductionmentioning

confidence: 99%

Experimental and numerical investigation of the fatigue behaviour and crack evolution mechanism of granite under ultra-high-frequency loading

et al. 2020

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Assisted ultrasonic vibration technology has received great interest in the past few years for petroleum and mining engineering related to hard rock breaking. Understanding the fatigue behaviour and damage characteristics of rock subject to ultra-high-frequency loading is vital for its application. In this research, we conducted ultrasonic vibration breaking rock experiments combined with an ultra-dynamic data receiver and strain gauges to monitor the development of strain in real time. The experimental results show that the strain curve is U-shaped, and it can be divided into three stages: the strain first decreases, then remains steady (with light fluctuations) and finally increases. The sample first underwent compressive deformation, and no rupture occurred. As the vibration continued, the compressive deformation decreased with the initiation and propagation of cracks, and fragmentation occurred. To elucidate the crack evolution mechanism of the granite specimens, numerical simulations were performed using particle flow code in two dimensions (PFC2D), and an improved fatigue damage model based on the flat-joint contact model was proposed. The numerical results indicate that this model can effectively reproduce the fatigue characteristics of hard brittle rocks under ultrasonic vibration. By analysing the stress and strain fields and cracking process, the crack evolution mechanism in the brittle hard rock under ultra-high-frequency loading is revealed. These experimental and numerical results are expected to improve the understanding of the fragmentation mechanism of rock under assisted ultrasonic vibration.

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Experimental Investigation of Sandstone under Cyclic Loading: Damage Assessment Using Ultrasonic Wave Velocities and Changes in Elastic Modulus

Cited by 14 publications

References 45 publications

Energy Evolution and Damage Mechanism of Fractured Sandstone with Different Angles

Energy Evolution and Damage Mechanism of Fractured Sandstone with Different Angles

Influence of Increasing Mean Stress on Fatigue Properties of Shale during Pulsating Hydraulic Fracturing

Experimental and numerical investigation of the fatigue behaviour and crack evolution mechanism of granite under ultra-high-frequency loading

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