scholarly journals Experimental Investigation on Crack Behavior and Stress Thresholds of Sandstone Containing a Square Inclusion under Uniaxial Compression

2020 ◽  
Vol 10 (21) ◽  
pp. 7621
Author(s):  
Quanqi Zhu ◽  
Diyuan Li
Keyword(s):  
Uniaxial Compression ◽  
Shear Failure ◽  
Shear Crack ◽  
Image Correlation ◽  
Interface Debonding ◽  
Compression Tests ◽  
Strain Behavior ◽  
Damage And Fracture ◽  
Crack Behavior ◽  
Strength And Stiffness

To study the effect of strength, stiffness and inclination angle of square inclusions on failure characteristics of rock, uniaxial compression tests were carried out on prismatic sandstone containing a square hole with different filling modes and hole angles using a servo-hydraulic loading system. Digital image correlation and acoustic emission techniques were jointly applied to analyze the damage and fracture process, and the crack stress thresholds were determined qualitatively and quantitatively by combining the stress–strain behavior. The results show that the mechanical properties and crack stress thresholds of pre-holed specimens increase with the increase of the strength and stiffness of inclusions, and are affected by the hole angle. Rock failure is mainly caused by secondary crack propagation and shear crack coalescence, eventually forming mixed tensile-shear failure. The crack behavior, especially the crack initiation position, is affected by the filling mode and the hole angle. Interface debonding tends to initiate at the vertical interface, while interface slipping tends to propagate along the inclined interface. Under identical loading conditions, the specimen with 45° hole is more susceptible to crack and damage than that with 0° hole. Notably, inclusions can inhibit the hole deformation and the fracture of rock matrix, especially the sidewall spalling of 0° hole.

scholarly journals Mechanical Response and Fracture Behavior of Brittle Rocks Containing Two Inverted U-Shaped Holes under Uniaxial Loading

2019 ◽  
Vol 9 (24) ◽  
pp. 5327
Author(s):  
Hao Wu ◽  
Guoyan Zhao ◽  
Weizhang Liang
Keyword(s):  
Fracture Behavior ◽  
Shear Failure ◽  
Mechanical Response ◽  
Numerical Study ◽  
Shear Crack ◽  
Image Correlation ◽  
Tensile Crack ◽  
Shear Cracks ◽  
Brittle Rocks ◽  
Hole Defects

Hole defects embedded in rocks have a crucial influence on their stability and failure mechanism. The purpose of this research is to explore the mechanical response and fracture behavior around inverted U-shaped openings in rocks under compressive stress. To begin with, a multitude of uniaxial compression experiments on prismatic sandstone samples with one single or two inverted U-shaped openings with different configurations were carried out. In the experiments, the advanced DIC (digital image correlation) and AE (acoustic emission) apparatus was combinedly utilized to monitor the crack growth and determine the threshold stresses involved in fracture behavior. After that, the stress distributions around the openings under unidirectional stress were simulated by a numerical study. Test results suggest that the presence of openings strongly degrades the strength and deformation parameters, and the reduction degree depends on the number and configuration of openings. During the fracture process, five sorts of cracks, namely the elementary tensile crack, posterior tensile crack, slabbing crack, shear crack and spalling crack, are formed around the openings. For the samples containing two openings, three categories of hole coalescence appear: slabbing coalescence, shear coalescence and tensile coalescence. The failure mode of the samples containing one single or two diagonal openings is dominated by shear cracks, while that of the other samples is tensile-shear failure. Stress analysis shows that the concentrated stresses at the peripheries of the openings can better explain the fracture behavior.

scholarly journals Uniaxial Experimental Study of the Deformation Behavior and Energy Evolution of Conjugate Jointed Rock Based on AE and DIC Methods

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Jiliang Pan ◽  
Xu Wu ◽  
Qifeng Guo ◽  
Xun Xi ◽  
Meifeng Cai
Keyword(s):  
Stress Field ◽  
Uniaxial Compression ◽  
Testing Machine ◽  
Peak Strength ◽  
Image Correlation ◽  
Compression Tests ◽  
Dissipation Energy ◽  
Included Angle ◽  
Natural Rock ◽  
Ae Counts

Conjugate joint is one of the most common joint forms in natural rock mass, which is produced by different tectonic movements. To better understand the preexisting flaws, it is necessary to investigate joint development and its effect on the deformation and strength of the rock. In this study, uniaxial compression tests of granite specimens with different conjugate joints distribution were performed using the GAW-2000 compression-testing machine system. The PCI-2 acoustic emission (AE) testing system was used to monitor the acoustic signal characteristics of the jointed specimens during the entire loading process. At the same time, a 3D digital image correlation (DIC) technique was used to study the evolution of stress field before the peak strength at different loading times. Based on the experimental results, the deformation and strength characteristics, AE parameters, damage evolution processes, and energy accumulation and dissipation properties of the conjugate jointed specimens were analyzed. It is considered that these changes were closely related to the angle between the primary and secondary joints. The results show that the AE counts can be used to characterize the damage and failure of the specimen during uniaxial compression. The local stress field evolution process obtained by the DIC can be used to analyze the crack initiation and propagation in the specimen. As the included angle increases from 0° to 90°, the elastic modulus first decreases and then increases, and the accumulative AE counts of the peak first increase and then decrease, while the peak strength does not change distinctly. The cumulative AE counts of the specimen with an included angle of 45° rise in a ladder-like manner, and the granite retains a certain degree of brittle failure characteristics under the axial loading. The total energy, elastic energy, and dissipation energy of the jointed specimens under uniaxial compression failure were significantly reduced. These findings can be regarded as a reference for future studies on the failure mechanism of granite with conjugate joints.

scholarly journals Effect of Layer Thickness on the Physical and Mechanical Properties of Sand Powder 3D Printing Specimens

2021 ◽  
Vol 9 ◽  
Author(s):  
Qing Xu ◽  
Lishuai Jiang ◽  
Changqing Ma ◽  
Qingjia Niu ◽  
Xinzhe Wang
Keyword(s):  
Mechanical Properties ◽  
3D Printing ◽  
Layer Thickness ◽  
Uniaxial Compression ◽  
Strain Curve ◽  
Physical And Mechanical Properties ◽  
Image Correlation ◽  
Ductile Material ◽  
Compression Tests ◽  
Failure Patterns

The application of sand powder three-dimensional (3D) printing technology in the field of rock mechanics and mining engineering has tremendous potential, but it is still in the preliminary exploration stage. This study investigated the effect of printing layer thickness on the physical and mechanical properties of rock-like specimens with sand powder 3D printing. Quartz sand powder was used as the printing material, and the specimens were prepared with three different layer thicknesses of 0.2, 0.3, and 0.4 mm. Uniaxial compression tests with a combination of digital image correlation (DIC), acoustic emission (AE) and 3D microscope observations were performed to analyze the mechanical properties and failure patterns of the specimens during loading. Experimental findings showed that increasing the layer thickness from 0.2 to 0.4 mm would result in a decrease in the weight, density, uniaxial compression strength, and elastic modulus of the specimens. The stress-strain curve, deformation and failure patterns, crack growth process, and AE characteristics of the specimens with a layer thickness of 0.2 mm are similar to the AE characteristics of rock-like material, whereas the specimens with layer thicknesses of 0.3 and 0.4 mm deform like a ductile material, which is not appropriate for simulation of coal or rock mass. In future studies, rock-like specimens should be prepared with a small layer thickness.

Effect Of Elevated Temperatures On Complete Concrete Deformation Diagrams

2019 ◽  
pp. 9-14
Keyword(s):  
Experimental Data ◽  
Elastic Modulus ◽  
Elevated Temperatures ◽  
Peak Load ◽  
Relative Deformation ◽  
Deformation Characteristics ◽  
Compression Tests ◽  
Strain Behavior ◽  
Different Temperatures ◽  
Deformation Diagrams

The analysis of the previous results of the study on concrete stress-strain behavior at elevated temperatures has been carried out. Based on the analysis, the main reasons for strength retrogression and elastic modulus reduction of concrete have been identified. Despite a significant amount of research in this area, there is a large spread in experimental data received, both as a result of compression and tension. In addition, the deformation characteristics of concrete are insufficiently studied: the coefficient of transverse deformation, the limiting relative compression deformation corresponding to the peak load and the almost complete absence of studies of complete deformation diagrams at elevated temperatures. The two testing chambers provided creating the necessary temperature conditions for conducting studies under bending compression and tension have been developed. On the basis of the obtained experimental data of physical and mechanical characteristics of concrete at different temperatures under conditions of axial compression and tensile bending, conclusions about the nature of changes in strength and deformation characteristics have been drawn. Compression tests conducted following the method of concrete deformation complete curves provided obtaining diagrams not only at normal temperature, but also at elevated temperature. Based on the experimental results, dependences of changes in prism strength and elastic modulus as well as an equation for determining the relative deformation and stresses at elevated temperatures at all stages of concrete deterioration have been suggested.

scholarly journals Confinement effects for rubberised concrete in tubular steel cross-sections under combined loading

2021 ◽  
Vol 21 (2) ◽  
Author(s):  
A. Mujdeci ◽  
D. V. Bompa ◽  
A. Y. Elghazouli
Keyword(s):  
Axial Compression ◽  
Cross Section ◽  
Cross Sections ◽  
Image Correlation ◽  
Combined Loading ◽  
Test Results ◽  
Compression Tests ◽  
Confinement Effects ◽  
Rubber Content ◽  
Dependent Modification

AbstractThis paper describes an experimental investigation into confinement effects provided by circular tubular sections to rubberised concrete materials under combined loading. The tests include specimens with 0%, 30% and 60% rubber replacement of mineral aggregates by volume. After describing the experimental arrangements and specimen details, the results of bending and eccentric compression tests are presented, together with complementary axial compression tests on stub-column samples. Tests on hollow steel specimens are also included for comparison purposes. Particular focus is given to assessing the confinement effects in the infill concrete as well as their influence on the axial–bending cross-section strength interaction. The results show that whilst the capacity is reduced with the increase in the rubber replacement ratio, an enhanced confinement action is obtained for high rubber content concrete compared with conventional materials. Test measurements by means of digital image correlation techniques show that the confinement in axial compression and the neutral axis position under combined loading depend on the rubber content. Analytical procedures for determining the capacity of rubberised concrete infilled cross-sections are also considered based on the test results as well as those from a collated database and then compared with available recommendations. Rubber content-dependent modification factors are proposed to provide more realistic representations of the axial and flexural cross-section capacities. The test results and observations are used, in conjunction with a number of analytical assessments, to highlight the main parameters influencing the behaviour and to propose simplified expressions for determining the cross-section strength under combined compression and bending.

scholarly journals Investigation of Microcrack Propagation and Energy Evolution in Brittle Rocks Based on the Voronoi Model

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2108
Author(s):  
Guanlin Liu ◽  
Youliang Chen ◽  
Xi Du ◽  
Peng Xiao ◽  
Shaoming Liao ◽  
...  
Keyword(s):  
Uniaxial Compression ◽  
Damage Evolution ◽  
Rock Sample ◽  
Rock Fracture ◽  
Damage Threshold ◽  
Crack Development ◽  
Energy Evolution ◽  
Shear Cracks ◽  
Compression Tests ◽  
Microcrack Propagation

The cracking of rock mass under compression is the main factor causing structural failure. Therefore, it is very crucial to establish a rock damage evolution model to investigate the crack development process and reveal the failure and instability mechanism of rock under load. In this study, four different strength types of rock samples from hard to weak were selected, and the Voronoi method was used to perform and analyze uniaxial compression tests and the fracture process. The change characteristics of the number, angle, and length of cracks in the process of rock failure and instability were obtained. Three laws of crack development, damage evolution, and energy evolution were analyzed. The main conclusions are as follows. (1) The rock’s initial damage is mainly caused by tensile cracks, and the rapid growth of shear cracks after exceeding the damage threshold indicates that the rock is about to be a failure. The development of micro-cracks is mainly concentrated on the diagonal of the rock sample and gradually expands to the middle along the two ends of the diagonal. (2) The identification point of failure precursor information in Acoustic Emission (AE) can effectively provide a safety warning for the development of rock fracture. (3) The uniaxial compression damage constitutive equation of the rock sample with the crack length as the parameter is established, which can better reflect the damage evolution characteristics of the rock sample. (4) Tensile crack requires low energy consumption and energy dispersion is not concentrated. The damage is not apparent. Shear cracks are concentrated and consume a large amount of energy, resulting in strong damage and making it easy to form macro-cracks.

scholarly journals Compression and Strain Predictive Models in Non-Structural Recycled Concretes Made from Construction and Demolition Wastes

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3177
Author(s):  
Evelio Teijón-López-Zuazo ◽  
Jorge López-Rebollo ◽  
Luis Javier Sánchez-Aparicio ◽  
Roberto Garcia-Martín ◽  
Diego Gonzalez-Aguilera
Keyword(s):  
Compressive Strength ◽  
Predictive Models ◽  
Unconfined Compressive Strength ◽  
Image Correlation ◽  
Peak Strain ◽  
Compression Tests ◽  
Maximum Peak ◽  
3D Digital Image Correlation ◽  
Granulometric Analysis ◽  
Physical And Chemical

This work aims to investigate different predictive models for estimating the unconfined compressive strength and the maximum peak strain of non-structural recycled concretes made up by ceramic and concrete wastes. The extensive experimental campaign carried out during this research includes granulometric analysis, physical and chemical analysis, and compression tests along with the use of the 3D digital image correlation as a method to estimate the maximum peak strain. The results obtained show that it is possible to accurately estimate the unconfined compressive strength for both types of concretes, as well as the maximum peak strain of concretes made up by ceramic waste. The peak strain for mixtures with concrete waste shows lower correlation values.

MECHANICAL CHARACTERIZATION OF MATERIALS AND DIAGNOSIS OF STRUCTURES BY INVERSE ANALYSES: SOME INNOVATIVE PROCEDURES AND APPLICATIONS

2014 ◽  
Vol 11 (03) ◽  
pp. 1343002 ◽  
Author(s):  
GIULIO MAIER ◽  
VLADIMIR BULJAK ◽  
TOMASZ GARBOWSKI ◽  
GIUSEPPE COCCHETTI ◽  
GIORGIO NOVATI
Keyword(s):  
Structural Analysis ◽  
Digital Image Correlation ◽  
Residual Stresses ◽  
Mechanical Characterization ◽  
Image Correlation ◽  
Alkali Silica Reaction ◽  
Compression Tests ◽  
Material Models ◽  
Characterization Of Materials

A survey is presented herein of some recent research contributions to the methodology of inverse structural analysis based on statical tests for diagnosis of possibly damaged structures and for mechanical characterization of materials in diverse industrial environments. The following issues are briefly considered: identifications of parameters in material models and of residual stresses on the basis of indentation experiments; mechanical characterization of free-foils and laminates by cruciform and compression tests and digital image correlation measurements; diagnosis, both superficially and in depth, of concrete dams, possibly affected by alkali-silica-reaction or otherwise damaged.

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