scholarly journals Mechanical Characteristics and Failure Mechanism of Siltstone with Different Joint Thickness

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Huigui Li ◽  
Zhengkai Yang ◽  
Huamin Li
Keyword(s):  
Elastic Modulus ◽  
Failure Mechanism ◽  
Uniaxial Compression ◽  
Compression Strength ◽  
Damage Model ◽  
Strain Curve ◽  
Compression Tests ◽  
Uniaxial Compression Strength ◽  
Stress Strain ◽  
Joint Thickness

The mechanics of rock mass is significantly affected by joints, but many existing studies of jointed rocks make simplifications that do not consider the joint thickness. To further study the influence of joint thickness on rock mechanics (mechanical properties, failure mechanism, damage model, etc.), we fabricated jointed siltstone specimens with different joint thickness (5, 10, 15, and 20 mm) and the specimens were subjected to uniaxial compression tests. The effects of joint thickness on the uniaxial compression strength (UCS), the strain at UCS, the elastic modulus, and the stress-strain curves were thus analyzed. For the stress-strain curve, with rising joint thickness, the upper concave in the initial compression stage intensified, the slope of the stress-strain in the elastic stage decreased, and the sudden stress drop after peak strength became more obvious. Both the peak compression strength and the elastic modulus gradually decreased with rising joint thickness, but a positive correlation was found between the strain at UCS and the joint thickness.

scholarly journals A Strain Rate-Dependent Damage Evolution Model for Concrete Based on Experimental Results

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Bin Xu ◽  
Xiaoyan Lei ◽  
P. Wang ◽  
Hui Song
Keyword(s):  
Strain Rate ◽  
Uniaxial Compression ◽  
Damage Evolution ◽  
Damage Model ◽  
Evolution Model ◽  
Experimental Results ◽  
Strain Rates ◽  
Compression Tests ◽  
Stress Strain ◽  
Actual Damage

There are various definitions of damage variables from the existing damage models. The calculated damage value by the current methods still could not well correspond to the actual damage value. Therefore, it is necessary to establish a damage evolution model corresponding to the actual damage evolution. In this paper, a strain rate-sensitive isotropic damage model for plain concrete is proposed to describe its nonlinear behavior. Cyclic uniaxial compression tests were conducted on concrete samples at three strain rates of 10−3s−1, 10−4s−1, and 10−5s−1, respectively, and ultrasonic wave measurements were made at specified strain values during the loading progress. A damage variable was defined using the secant and initial moduli, and concrete damage evolution was then studied using the experimental results of the cyclic uniaxial compression tests conducted at the different strain rates. A viscoelastic stress-strain relationship, which considered the proposed damage evolution model, was presented according to the principles of irreversible thermodynamics. The model results agreed well with the experiment and indicated that the proposed damage evolution model can accurately characterize the development of macroscopic mechanical weakening of concrete. A damage-coupled viscoelastic constitutive relationship of concrete was recommended. It was concluded that the model could not only characterize the stress-strain response of materials under one-dimensional compressive load but also truly reflect the degradation law of the macromechanical properties of materials. The proposed damage model will advance the understanding of the failure process of concrete materials.

scholarly journals Deterioration Characteristics and Energy Mechanism of Red-Bed Rocks Subjected to Drying-Wetting Cycles

2021 ◽  
Author(s):  
Kai Huang ◽  
Fusheng Zha ◽  
Bo Kang ◽  
Xianguo Sun ◽  
Yunfeng Li ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Failure Process ◽  
Microstructural Analysis ◽  
Strain Curve ◽  
Rock Failure ◽  
Dissipated Energy ◽  
Uniaxial Compression Strength ◽  
Stress Strain ◽  
Energy Mechanism ◽  
Red Bed

Abstract The red-bed rocks were chosen and studied by using uniaxial compressive experiment and scanning electron microscopy to investigate the effect of drying-wetting (D-W) cycles on the mechanical properties and microstructural characteristics of red-bed rock. Additionally, the energy mechanism of specimens subjected to drying-wetting cycles was also explained. Experimental results showed that, the stress-strain could be divided into four characteristic stages in the compression failure process. After subjecting to cycles of D-W, the stress-strain curve gradually changed from softening to hardening. At the same time, uniaxial compression strength (UCS) and elastic modulus dropped obviously, while Poisson’s ratio gradually raised. Microstructural analysis results indicated that the microstructure of the specimen surface was no longer dense and uniform, and the porosity of tested specimens significantly increased with D-W cycles increasing. As the porosity grew, UCS and elastic modulus gradually declined. According to the first law of thermodynamics, the process of rock failure was an event of energy transfer and conversion. As the number of D-W cycles increased, the energy density of specimens all present linear fell. From the perspective of the theory of energy dissipation, the dissipated energy was essential for rock failure, and closely related to the strength of the specimen. With D-W cycles increasing, the specimens were more prone to failure, and the dissipated energy required for failure decreased gradually.

Experimental Study on the Uniaxial Compression Curves of Green High-Performance Fiber-Reinforced Cementitious Composites (GHPFRCC)

2014 ◽  
Vol 893 ◽  
pp. 201-204
Author(s):  
Xiu Ling Li ◽  
Juan Wang
Keyword(s):  
Uniaxial Compression ◽  
High Performance ◽  
Strain Curve ◽  
Cementitious Composites ◽  
Peak Strain ◽  
Fiber Reinforced ◽  
Compression Tests ◽  
Stress Strain ◽  
High Performance Fiber ◽  
Fiber Reinforced Cementitious Composites

Green high performance fiber reinforced cementitious composites (GHPFRCC) is the optimized mix proportion of engineered cementitious composites (ECC) with high volume of fly ash and polyvinyl alcohol (PVA) fiber. To study the compressive performance, the prism stress-strain relationship of GHPFRCC is the focus in this study. There are sixteen groups of GHPFRCC specimens with the size 40mm×40mm×160mm. The compressive stress-strain curves were obtained based on the uniaxial compression tests. Experimental results show that the uniaxial compression stress-strain curve belongs to the skewed unimodal curve. The peak strain can steadily reach more than 0.005, and it has put up a great plastic deformation capacity and post-peak ductility. It has still reserved some residual strength even when the strain is up to a bigger value. The research achievements can promote the application of GHPFRCC in the practical engineering.

A damage model for modeling the complete stress–strain relations of brittle rocks under uniaxial compression

2017 ◽  
Vol 27 (7) ◽  
pp. 1000-1019 ◽  
Author(s):  
Dongqiao Liu ◽  
Manchao He ◽  
Ming Cai
Keyword(s):  
Elastic Modulus ◽  
Uniaxial Compression ◽  
Test Data ◽  
Compression Test ◽  
Damage Model ◽  
Model Parameters ◽  
Uniaxial Compression Test ◽  
Mathematical Function ◽  
Stress Strain ◽  
Brittle Rocks

Based on the “elastic modulus method” derived from the hypothesis of strain equivalence and test data of complete stress–strain curves of marble, granite, and sandstone under uniaxial compression, a damage model in the form of Logistic equation is proposed to simulate the stress–strain relation of rocks. This model can describe the complete deformation process of rocks under uniaxial compression satisfactorily. The used mathematical function is simple with just four model parameters, and each parameter has distinct physical meaning. The validity of the model is demonstrated by a mathematical deduction analysis and the model is further verified using laboratory test data. In addition, this model provides a method for estimating the elastic modulus of undamaged rocks using uniaxial compression test results and it presents a reasonable explanation of the chaos phenomenon occurred in uniaxial compression test.

scholarly journals Effects of coupled static and dynamic strain rates on mechanical behaviors of rock-like specimens containing pre-existing fissures under uniaxial compression

2018 ◽  
Vol 55 (5) ◽  
pp. 640-652 ◽  
Author(s):  
Peng Feng ◽  
Feng Dai ◽  
Yi Liu ◽  
Nuwen Xu ◽  
Pengxian Fan
Keyword(s):  
Elastic Modulus ◽  
Strain Rate ◽  
Uniaxial Compression ◽  
Compression Strength ◽  
Elastic Energy ◽  
Dynamic Loads ◽  
Dynamic Strain ◽  
Strain Rates ◽  
Mechanical Behaviors ◽  
Uniaxial Compression Strength

Rocks containing pre-existing fissures in underground engineering are likely to be subjected to static pre-stress and dynamic loads simultaneously. Understanding the deformation and failure mechanism of fissured rocks under coupled static and dynamic strain rates is beneficial for the stability assessment of rock engineering structures. This study experimentally investigates the mechanical behaviors of fissured specimens under coupled static and dynamic loads with different loading parameters. Our experiments reveal that the coupled static–dynamic strain rates significantly affect the strength, deformation, energy characteristics, and failure mode of fissured specimens. For each dynamic strain rate, the strength and elastic modulus of specimens feature an increase first as the static pre-stress increases up to half of the uniaxial compression strength, and then a decrease. However, for each static pre-stress of coupled loads, the strength and elastic modulus increase noticeably with increasing dynamic strain rate. From the perspective of energy partition, for each static pre-stress, the higher dynamic strain rate induces greater energy dissipation of the specimens during the coupled loading, and more elastic energy is released at the end of loading. Moreover, for each dynamic strain rate, the pre-stress of half uniaxial compression strength induces the highest released elastic energy.

Experimental study and numerical simulation of uniaxial compression on artificial rock samples with Z-shaped fractures

2021 ◽  
Author(s):  
Tao Zhou ◽  
Haijun Chen ◽  
Liangxiao Xiong ◽  
Zhongyuan Xu ◽  
Jie Yang ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Crack Length ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Failure Surface ◽  
Peak Strength ◽  
Particle Flow Code ◽  
Compression Tests ◽  
Failure Characteristics ◽  
Change Trend

Abstract To study the influence of the inclination and length of Z-shaped fissures on the mechanical properties and failure characteristics of the rock mass, this study conducts a series of uniaxial compression tests on rock-like materials with prefabricated Z-shaped fractures. In addition, two-dimensional Particle Flow Code software is used to perform uniaxial compression numerical simulations. The results show that when the specified inclination angle γ (γ = 0°, 30° or 45°) of the parallel cracks on both sides remains unchanged, the peak strength and elastic modulus of the sample show an M-shaped change trend with an increase in the inclination angle β of the middle connection crack. When γ = 60° or 90°, however, the peak strength and elastic modulus of the sample show a trend of decreasing, increasing, and then decreasing as β increases. In addition, the peak strength and elastic modulus of the sample decrease with an increase in the crack length. The influence of crack length on the elastic modulus is less than that of compressive strength. Further, the main failure mode of specimens with Z-shaped cracks is determined to be tension–shear mixed failure manifested by crack propagation from the tip of the prefabricated crack to the upper and lower boundaries of the sample. As a result, a through failure surface is formed with the prefabricated crack, which destroys the sample.

scholarly journals Constant Strain-Rate Tensile Testing of Natural Snow

1980 ◽  
Vol 26 (94) ◽  
pp. 519 ◽  
Author(s):  
H. Singh ◽  
F.W. Smith
Keyword(s):  
Strain Rate ◽  
Strain Gage ◽  
Constant Strain Rate ◽  
Strain Curve ◽  
Strain Rates ◽  
Strain Gages ◽  
Compression Tests ◽  
Snow Sample ◽  
Stress Strain ◽  
Natural Snow

Abstract In conducting tension and compression tests on snow samples, strains and strain-rates are usually determined from the displacements of the ends of the samples. In this work, a strain-gage which mounts directly onto the snow sample during testing, was developed and was found to give accurate and direct measurements of strain and strain-rates. A commercially available 0-28 pF variable capacitor was modified to perform the required strain measurements. It is a polished metallic plunger sliding inside a metal-coated glass tube. The plunger and tube were each soldered to the end of a spring-steel wire arm. To the other end of these arms were soldered to 10 mm square pads made of thin brass shim stock. The whole device weighs 2.5 g and the low coefficient of friction in the capacitor resulted in a very low actuation force. To mount the strain gage, the pads are wetted and frozen onto the snow sample. A high degree of sensitivity was achieved through the use of “phase-lock-loop” electronic circuitry. The capacitance change caused by the strain in the sample, changes the frequency of output signal from an oscillator and thus causes the change in output from the system. In the locked state, to which the system is constantly driven by a feed-back loop, the system output is almost ripple free. The strain gages were calibrated in the field in order to take into account the effects of very low field temperatures. The calibration curves were almost linear over the travel of 15 mm, the maximum limit. The sensitivity of the system is 4 mV per strain unit, but this could be increased by an order of magnitude by minor adjustments in the circuit. Constant strain-rate tensile tests were performed on natural snow at Berthoud Pass, Colorado, U.S.A., in the density range of 140-290 kg m-3. Four strain gages were mounted onto the samples to sense any non-uniform deformation which otherwise would have gone unnoticed or caused scatter in the data. The average indication of these gages was used to construct stress—strain curves for various types of snow at different strain-rates. The effect of strain-rate on the behavior of snow was studied. “Ratcheting” in the stress-strain curve in the region where the snow becomes plastic was observed first by Kinosita in his compression tests. A similar phenomenon was observed in these tension tests. It was found that directly measured strain is quite different from that which would be calculated from sample end movement. Strain softening was not observed in these tests up to total strains of 8%. The strain-rate effects found were comparable to the results of other investigators.

Experimental Research on Mechanical Properties of Recycled Aggregate Concrete under Uniaxial Loading

2013 ◽  
Vol 671-674 ◽  
pp. 1736-1740
Author(s):  
Xue Yong Zhao ◽  
Mei Ling Duan
Keyword(s):  
Elastic Modulus ◽  
Coarse Aggregate ◽  
Strain Curve ◽  
Recycled Concrete ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Peak Strain ◽  
Stress Strain ◽  
Aggregate Concrete ◽  
Recycled Coarse Aggregate

The complete stress-strain curves of recycled aggregate concrete with different recycled coarse aggregate replacement percentages were tested and investigated. An analysis was made of the influence of varying recycled coarse aggregate contents on the complete stress-strain curve, peak stress, peak strain and elastic modulus etc. The elastic modulus of RC is lower than natural concrete (NC), and with the recycled coarse aggregate contents increase, it reduces. While with the increase of water-cement ratio (W/C), recycled concrete compressive strength and elastic modulus improve significantly. In addition, put forward a new equation on the relationship between Ec and fcu of the RC.

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