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.

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.

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.

A Comparison of Cohesive Crack Model and Crack Band Model in Concrete Fracture

2012 ◽  
Vol 170-173 ◽  
pp. 3375-3380
Author(s):  
Liang Wu ◽  
Ze Li ◽  
Shang Huang
Keyword(s):  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Crack Opening ◽  
Cohesive Crack ◽  
Band Model ◽  
Crack Model ◽  
Concrete Fracture ◽  
Cohesive Crack Model ◽  
Crack Band

The cohesive crack model and the crack band model are two convenient approaches in concrete fracture analysis. They can describe in full the fracture process by the different manner: The entire fracture process zone is lumped into the crack line and is characterized in the form of a stress-displacement law which exhibits softening; or the inelastic deformations in the fracture process zone are smeared over a band of a certain width, imagined to exist in front of the main crack. The correlation of the two models is developed based on a characteristic width of crack band. The analysis shows that they can yield about the same results if the crack opening displacement in the cohesive crack model is taken as the fracturing strain that is accumulated over the width of the crack band model. Some basic problems are also discussed in finite element analysis.

Fracture Parameters of Alkali-Activated Aluminosilicate Composites with Ceramic Precursor

2020 ◽  
Vol 309 ◽  
pp. 73-79
Author(s):  
Hana Šimonová ◽  
Ivana Kumpová ◽  
Iva Rozsypalová ◽  
Patrik Bayer ◽  
Petr Frantik ◽  
...  
Keyword(s):  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Crack Model ◽  
Mechanical Fracture ◽  
Ceramic Precursor ◽  
Fracture Parameters ◽  
Alkali Activated

This paper deals with selected alkali-activated aluminosilicate composites with a ceramic precursor in terms of their characterization using mechanical fracture parameters. Three composites were studied. They were manufactured using brick powder as a precursor and an alkaline activator with a dimensionless silicate modulus of Ms = 1.0, 1.2 and 1.4. The test specimens were nominally 40 × 40 × 160 mm in size and had a central edge notch with a depth of 1/3 of the specimen’s height. At least 6 specimens made of each composite were tested at the age of 28 days. The specimens were subjected to three-point bending tests, during which diagrams showing force vs. deflection at midspan (F–d diagrams) and force vs. crack mouth opening displacement (F–CMOD diagrams) were recorded. After the processing of these diagrams, values were determined for the static modulus of elasticity, effective fracture toughness (including its initiation component from the analysis of the first part of the F–CMOD diagrams), effective toughness and specific fracture energy using the effective crack model, Work-of-Fracture method, and Double-K fracture model. After the fracture experiments had been performed, compressive strength values were determined for informational purposes from one part of each specimen that remained after testing. In order to obtain visual information about the internal structure of the composites before and after the mechanical testing, the selected specimen was examined via X-ray microtomography. Tomographic measurements and image processing were performed for the qualitative and quantitative evaluation of internal structural changes with an emphasis on the calculation of porosimetry parameters as well as the visualization of the fracture process zone. The fractal dimension of the fracture surface and fracture process zone was determined. The porosity and microstructure images of selected samples taken from specimens were assessed.

scholarly journals CHARACTERIZATIONS ON FRACTURE PROCESS ZONE OF PLAIN CONCRETE

2019 ◽  
Vol 25 (8) ◽  
pp. 819-830
Author(s):  
Yuxiang Tang ◽  
Hongniao Chen
Keyword(s):  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Speckle Pattern ◽  
Plain Concrete ◽  
Cohesive Crack ◽  
Electronic Speckle Pattern Interferometry ◽  
Crack Model ◽  
Fe Model ◽  
Durability Analysis

The fracture property of concrete is essential for the safety and durability analysis of concrete structures. Investigating the characteristics of the fracture process zone (FPZ) is of great significance to clarify the nonlinear fracture behaviour of concrete. Experimental and numerical investigations on the FPZ of plain concrete in pre-notched beams subjected to three-point bending were carried out. Electronic speckle pattern interferometry (ESPI) technique was used to observe crack evolution and measure the full-field deformation of the beams. The development of the FPZ were evaluated qualitatively and quantitatively based on the in-plane strain contours and displacement field measured by ESPI, respectively. By integrating the cohesive crack model and finite element (FE) model, various tension softening curves (TSCs) were employed to simulate the fracture response of concrete beams. By comparing the deformation obtained by FE simulation and experiments, the TSCs of plain concrete were evaluated and most suitable TSCs of concrete were recommended.

scholarly journals Finite Element Computation of Crown Deflection of Cracked Concrete Gravity Dam under Effect of Creep in Fracture Process Zone

2020 ◽  
Vol 9 (12) ◽  
pp. 97-102
Keyword(s):  
Finite Element ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Concrete Gravity Dam ◽  
Strain Behavior ◽  
Micro Cracks ◽  
Non Linear ◽  
Element Computation ◽  
Dam Stability

The concrete dams contain micro-cracks and flaws, developed during the hardening of concrete. Under the influence of static and dynamic loads, tensile stress at the crack's end causes the crack to grow, leading to structural failure. In the present study, a Finite Element (FE) computation is present to account for an effect of creep and non-linear stress-strain behavior in the fracture process zone (FPZ) for analyzing the horizontal deflection of the crown of a dam. The model test was perform for an old existing concrete dam for deflection of the dam's crown for a single crack and the results were compare with field data. The present model successfully simulates the effects of non-linear stress and creep in FPZ on the horizontal dam-crown deflection. It concludes that the analysis of dam stability in conventional methods must include the stress field behavior in FPZ.

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.

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