scholarly journals Influence of Water–Oil Saturation on the Fracture Process Zone: A Modified Dugdale–Barenblatt Model

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2882 ◽  
Author(s):  
Yuanxun Nie ◽  
Guangqing Zhang ◽  
Yuekun Xing ◽  
Shiyuan Li
Keyword(s):  
Hydraulic Fracturing ◽  
Capillary Pressure ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Rock Fracture ◽  
Peak Load ◽  
Image Correlation ◽  
Influence Of Water ◽  
Water Saturated

The wetting and nonwetting fluid saturations in porous reservoirs always change during long-term injection and production. The fracture process zone (FPZ) is a prominent feature in the rock fracture process. If the FPZ properties are influenced by pore fluids, the process of hydraulic fracturing will change greatly. The existing models do not consider the role of pore fluid when characterizing the FPZ. In this paper, a modified Dugdale–Barenblatt (D–B) model with capillary pressure is proposed. The model reflects the fact that the FPZ length decreases nonlinearly with the increase in capillary pressure, and it reveals the mechanism of capillary pressure on the equivalent fracture cohesion in the FPZ, which affects the FPZ length. Three-point bending tests were carried out on sandstone under various fluid saturations through digital image correlation (DIC), acoustic emission (AE), and scanning electron microscope (SEM). It was found that the FPZ length of the water–oil-saturated samples was 30–50% smaller than that of water-saturated/oil-saturated samples due to the capillary pressure effect, and the modified D–B model was well consistent with the experiments. The AE behaviors of different saturated samples were not the same: The cumulative AE signals changed abruptly at 90% of the peak load for the water–oil-saturated samples and at 50% of the peak load for water-saturated samples. This demonstrated that the effect of capillary pressure was more obvious than the weakening effect of microstructural damages. The significant influence of capillary pressure on FPZ requires continuous recognition in hydraulic fracturing design.

scholarly journals The crack opening displacement of rock fracture process zone

2019 ◽  
Vol 23 (3 Part A) ◽  
pp. 1479-1486
Author(s):  
Sheng Zhang ◽  
Yang Qiao ◽  
Hong-Bao Zhao
Keyword(s):  
Distribution Function ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Rock Fracture ◽  
Image Correlation ◽  
Crack Model ◽  
Opening Displacement ◽  
Growth Trend ◽  
Non Linear

The original displacement value of fracture process zone can be obtained by digital image correlation technology. According to the virtual crack model, the formula to obtain the opening displacement is given in the experiment. Basing on the damage Mechanics theory and the actual deformation characteristics of fracture process zone, the traditional opening displacement distribution function of fracture process zone is modified by defining the wave coefficient and the damage factor of the horizontal elastic modulus. The measured opening displacement is compared with the opening displacement of the traditional theoretical function and modified function, and the results show that the opening displacement is non-linear fluctuation characteristic distribution influenced by damage. The revise distribution function not only reflects the overall growth trend of the opening displacement, but also reflects the local fluctuation characteristics. It has an important theoretical significance for understanding the non-linear characteristics of rock fracture process.

Assessment of the fracture process zone in rocks using digital image correlation technique: The role of mode-mixity, size, geometry and material

2019 ◽  
Vol 29 (4) ◽  
pp. 646-666 ◽  
Author(s):  
M Moazzami ◽  
MR Ayatollahi ◽  
A Akhavan-Safar
Keyword(s):  
Digital Image Correlation ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Specimen Size ◽  
Image Correlation ◽  
Mode I ◽  
Mode Ii ◽  
Mode Mixity ◽  
Zone Length

This paper presents an experimental research on the length and shape of the fracture process zone of rocks under mode I, mixed mode (I + II) and mode II loading conditions for different geometries of cracked specimens made of two types of rocks, using the digital image correlation approach. Single edge notch bending (SENB) and semi-circular bend specimens are the two geometries considered. In order to investigate the effect of the specimen size on the fracture process zone length, rocks with three different sizes are produced and tested. To investigate the effect of the mode mixity on the fracture process zone length of marble and sandstone, the specimens are tested under different modes of loading. According to the experimental results, it is found that the fracture process zone length changes with mode ratio, specimen size, geometry and the material properties. The fracture process zone length increases when the mode of loading moves from mode I to mode II. Experimental results also show that fracture process zone becomes longer for specimens with larger sizes. The fracture process zone is also affected by the specimen geometry.

scholarly journals Mixed-Mode I-II Fracture Process Zone Characteristic of the Four-Point Shearing Concrete Beam

Materials ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3203
Author(s):  
Guodong Li ◽  
Zhengyi Ren ◽  
Jiangjiang Yu
Keyword(s):  
Specific Surface ◽  
Mixed Mode ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Concrete Beam ◽  
Coarse Aggregate ◽  
Process Zone ◽  
Image Correlation ◽  
Mode I ◽  
Surface Areas

The size of the fracture process zone (FPZ) has significance for studying the fracture mechanism and fracture characteristics of concrete. This paper presents the method of assessing the FPZ of Mixed-Mode I-II for quasi-static four-point shearing concrete beams with pre-notched by Lagrangian strain profiles from digital image correlation (DIC). Additionally, it explores the influences of volume rates of the coarse aggregate of 0%, 28%, 48%, and 68%, and the specific surface areas of 0.12 m2/kg, 0.15 m2/kg, and 0.26 m2/kg on the size of the FPZ. It shows that the size of FPZ in four-point shearing concrete beam can be characterized by the displacement field and strain field using DIC. The size of FPZ conforms to linear positive correlation with the volume rate of coarse aggregate, and linear negative correlation with the specific surface area of coarse aggregate. It presents that the crack initiation of the four-point shearing beam with the pre notch is dominated by mode I load, and the propagation and fracture of Mixed-Mode I-II cracks are caused by the combined effect of Mode I and Mode II loading.

scholarly journals Experimental Study on the Fracture Process Zone Characteristics in Concrete Utilizing DIC and AE Methods

2019 ◽  
Vol 9 (7) ◽  
pp. 1346 ◽  
Author(s):  
Shuhong Dai ◽  
Xiaoli Liu ◽  
Kumar Nawnit
Keyword(s):  
Crack Extension ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Surface Deformation ◽  
Process Zone ◽  
Image Correlation ◽  
Displacement Fields ◽  
Ae Signal ◽  
Tip Position ◽  
Extension Length

The present work focuses on investigating the characteristics of the fracture process zone (FPZ) in concrete. The Single-edge notched (SEN) concrete beams under three-points bending are employed for conducting mode I fracture propagation. The displacement fields on the specimen surface and the internal AE signal of specimen are obtained simultaneously in real time by digital image correlation (DIC) and acoustic emission (AE) techniques. The experimental and analytical results indicated that the crack tip position, the crack extension length and the stress intensity factors (SIF) are obtained dynamically and quantitatively by DIC technique, and the length of FPZ is identified, respectively, by DIC and AE techniques in the crack extension process. The distribution of internal AE events is consistent with that of FPZ identified from surface deformation of specimens.

scholarly journals Crack Propagation and Fracture Process Zone (FPZ) of Wood in the Longitudinal Direction Determined Using Digital Image Correlation (DIC) Technique

2019 ◽  
Vol 11 (13) ◽  
pp. 1562 ◽  
Author(s):  
Ying Yu ◽  
Weihang Zeng ◽  
Wen Liu ◽  
He Zhang ◽  
Xiaohong Wang
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Strain Field ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Longitudinal Direction ◽  
Image Correlation ◽  
Elastic Crack ◽  
Dic Technique

As a state-of-the-art method, the digital image correlation (DIC) technique is used to capture the fracture properties of wood along the longitudinal direction, such as the crack propagation, the strain field, and the fracture process zone (FPZ). Single-edge notched (SEN) specimens made of Douglas fir (Pseudotsuga menziesii) from Canada with different notch-to-depth ratios are tested by three-point-bending (3-p-b) experiment. The crack mouth opening displacements (CMOD) measured by the clip gauge and DIC technique agree well with each other, verifying the applicability of the DIC technique. Then, the quasi-brittle fracture process of wood is analyzed by combing the load-CMOD curve and the strain field in front of the preformed crack. Additionally, the equivalent elastic crack length is calculated using the linear superposition hypothesis. The comparison between the FPZ evolution and the equivalent elastic crack shows that specimens with higher notch-to-depth ratios have better cohesive effect and higher cracking resistance.

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