scholarly journals Experimental Study on Thermal Damage and Energy Evolution of Sandstone after High Temperature Treatment

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Rong-rong Zhang ◽  
Lai-wang Jing ◽  
Qin-yong Ma
Keyword(s):  
Strain Energy ◽  
Thermal Damage ◽  
Peak Stress ◽  
Temperature Treatment ◽  
P Wave ◽  
High Temperature Treatment ◽  
Energy Evolution ◽  
P Wave Velocity ◽  
Total Input ◽  
Evolution Characteristics

Thermal damage and energy evolution characteristics in process of impact failure of sandstone after high temperature treatment were studied by split Hopkinson pressure bar (SHPB) system. The ultrasonic P-wave velocity, density, porosity, peak stress, ET/E0, thermal damage, fracture, and energy evolution characteristics of sandstone with temperature during the experimental process were explored. Results show that, with the increase of temperature, the ultrasonic P-wave velocity and density decrease, while the porosity increases. It is found that the peak stress and ET/E0 decrease with the increase of temperature, and the decreasing trend is fitted with the simple cubic equation. Above 600°C, dynamic peak stress and ET/E0 decrease rapidly. The thermal damage of rock increases with the increase of temperature, which is in accordance with the logistic curve model. The thresholds of damage strain energy release rate are 200°C and 800°C in this research. Its total input strain energy decreases with the increase of processing temperature and decreases sharply when the temperature is over 600°C. The variation of total input strain energy has small change at the range from 400°C to 600°C.

scholarly journals Comparison of Mechanical Behavior and Acoustic Emission Characteristics of Three Thermally-Damaged Rocks

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2350 ◽  
Author(s):  
Jun Peng ◽  
Sheng-Qi Yang
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Mechanical Behavior ◽  
Thermal Damage ◽  
Strain Curve ◽  
Treatment Temperature ◽  
P Wave ◽  
High Temperature Treatment ◽  
High Porosity ◽  
Compression Tests

High temperature treatment has a significant influence on the mechanical behavior and the associated microcracking characteristic of rocks. A good understanding of the thermal damage effects on rock behavior is helpful for design and stability evaluation of engineering structures in the geothermal field. This paper studies the mechanical behavior and the acoustic emission (AE) characteristic of three typical rocks (i.e., sedimentary, metamorphic, and igneous), with an emphasis on how the difference in rock type (i.e., porosity and mineralogical composition) affects the rock behavior in response to thermal damage. Compression tests are carried out on rock specimens which are thermally damaged and AE monitoring is conducted during the compression tests. The mechanical properties including P-wave velocity, compressive strength, and Young’s modulus for the three rocks are found to generally show a decreasing trend as the temperature applied to the rock increases. However, these mechanical properties for quartz sandstone first increase to a certain extent and then decrease as the treatment temperature increases, which is mainly attributed to the high porosity of quartz sandstone. The results obtained from stress–strain curve, failure mode, and AE characteristic also show that the failure of quartz-rich rock (i.e., quartz sandstone and granite) is more brittle when compared with that of calcite-rich rock (i.e., marble). However, the ductility is enhanced to some extent as the treatment temperature increases for all the three examined rocks. Due to high brittleness of quartz sandstone and granite, more AE activities can be detected during loading and the recorded AE activities mostly accumulate when the stress approaches the peak strength, which is quite different from the results of marble.

scholarly journals The Effect of Confining Pressure and Water Content on Energy Evolution Characteristics of Sandstone under Stepwise Loading and Unloading

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Shuren Wang ◽  
Paul Hagan ◽  
Yanhai Zhao ◽  
Xu Chang ◽  
Ki-Il Song ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Water Content ◽  
Elastic Energy ◽  
Strain Energy ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Energy Evolution ◽  
Evolution Characteristics ◽  
Loading And Unloading ◽  
Stepwise Loading

To investigate the mechanical properties and energy evolution characteristics of sandstone depending on the water contents and confining pressure, the uniaxial and triaxial tests were conducted. The test results show that the strain energy was stored in the sandstone samples at the prepeak stage, and that is suddenly released when the failure occurred, and energy dissipation is sharply increased at the postpeak stage. The damage and energy dissipation characteristics of the samples are observed clearly under the stepwise loading and unloading process. The critical strain energy and energy dissipation show a clear exponential relationship. The critical elastic energy decreases linearly as the water content increases. As the confining pressure increases, the critical elastic energy of the samples transforms from linear to exponential. The concept of energy enhancement factor is proposed to characterize the strengthening effect induced by the confining pressure on the energy storage capacity of the rock samples. The energy evolution of the sandstone samples is more sensitive to the confining pressure than that of the water content.

scholarly journals Mechanical Properties of Cement Mortar after Dry–Wet Cycles and High Temperature

2020 ◽  
Vol 6 (5) ◽  
pp. 1031-1038
Author(s):  
Xiong Liang-Xiao ◽  
Song Xiao-Gang
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
High Temperature ◽  
Cement Mortar ◽  
Peak Stress ◽  
Temperature Treatment ◽  
High Temperature Treatment ◽  
Factors Affecting ◽  
Temperature Exposure ◽  
Compressive Tests

The dry–wet cycle and high temperature exposure are important factors affecting the normal use and durability of concrete structures. The objective of this work is to investigate the mechanical properties of cement mortar specimens after combinations of dry–wet cycles and high temperature exposures, uniaxial compressive tests on cement mortar specimens were carried out under the following two sets of conditions: (1) high temperature treatment followed by a dry–wet cycle and (2) a dry–wet cycle followed by high temperature treatment. The results show that the compressive strength of specimens increases with the number of dry–wet cycles. After a dry–wet cycle and then a high temperature treatment procedure, the compressive strength of a specimen will first decrease and then increase with the number of dry–wet cycles. The strain at the peak stress of cement mortar decreases as the number of dry–wet cycles increases. At present, there are few research results about the mechanical properties of concrete first after combinations of dry–wet cycles and high temperature exposures. The work in this paper can enrich the results in this area.

Strain energy evolution characteristics and mechanisms of hard rocks under true triaxial compression

2019 ◽  
Vol 260 ◽  
pp. 105222 ◽  
Author(s):  
Yan Zhang ◽  
Xia-Ting Feng ◽  
Xiwei Zhang ◽  
Zhaofeng Wang ◽  
Mostafa Sharifzadeh ◽  
...  
Keyword(s):  
Strain Energy ◽  
Triaxial Compression ◽  
Energy Evolution ◽  
True Triaxial ◽  
Hard Rocks ◽  
Evolution Characteristics ◽  
True Triaxial Compression

scholarly journals The Ultrasonic P-Wave Velocity-Stress Relationship and Energy Evolution of Sandstone under Uniaxial Loading-Unloading Conditions

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Long Zhang ◽  
Zetian Zhang ◽  
Ru Zhang ◽  
Mingzhong Gao ◽  
Jing Xie
Keyword(s):  
Wave Velocity ◽  
Stress Level ◽  
Damage Accumulation ◽  
Uniaxial Loading ◽  
Acoustic Properties ◽  
P Wave ◽  
Energy Evolution ◽  
P Wave Velocity ◽  
Elastic Loading ◽  
Loading And Unloading

As shallow resources are exhausted, deep resources are gradually being exploited; consequently, mining disasters and accidents have increased significantly over time. During mining, a deep rock mass experiences complex mining-induced stress evolution, damage accumulation, and deformation failure processes, and the mechanical and acoustic properties of the rock constantly change. To better understand the variation in the mechanical and acoustic properties of rock under loading and unloading conditions, uniaxial loading-unloading experiments with real-time ultrasonic P-wave velocity monitoring were conducted on sandstone specimens drilled from a coal seam roof. The test results show that the axial stress level is directly related to the P-wave velocity. A logarithmic relationship exists between the ultrasonic P-wave velocity and stress in the tested sandstones. The wave velocity increase caused by the unit axial pressure increase is significantly lower than that at the initial loading stage after entering the higher stress level. The energy evolution of sandstone during loading and unloading is closely related to the stress loading history and reflects the damage accumulation in the rock. Under elastic loading, the energy accumulation is mainly reflected by an increase in elastic energy, and less energy is dissipated during the elastic loading period. Stress unloading causes high energy dissipation, resulting in irreversible strain and damage accumulation, which provides a good basis for using ultrasonic testing to preliminarily judge the failure of a specific rock and formulate corresponding engineering measures.

scholarly journals An Energy Preservation Index for Evaluating the Rockburst Potential Based on Energy Evolution

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3636
Author(s):  
Lin Gao ◽  
Feng Gao ◽  
Yan Xing ◽  
Zhizhen Zhang
Keyword(s):  
Elastic Strain ◽  
Strain Energy ◽  
Failure Modes ◽  
Elastic Strain Energy ◽  
Rock Deformation ◽  
Energy Evolution ◽  
Deformation And Failure ◽  
Rock Materials ◽  
Energy Preservation ◽  
Evolution Characteristics

The estimation of rockburst potential has attracted great attention in the field of rock mechanics and engineering. In this study, an original energy preservation index is proposed to evaluate the rockburst potential in view of the energy evolution characteristics of rock materials. To investigate the energy evolution during rock deformation and failure, a number of cyclic uniaxial compression experiments on five kinds of rocks were carried out. The results showed that the curves of energy evolution exhibited obvious stages and there were significantly different weakening degrees for different rock materials embodied by the decreasing degrees of the ratios of elastic strain energy to dissipated strain energy at the weakening stage. Then, the energy preservation index was further formulated based on the decreasing ratio. Furthermore, by analyzing the acoustic emission activities at the failure stage and failure modes of the five rock materials, the rockburst potential was analyzed according to the energy preservation index.

A constitutive equation and generalized Gassmann modulus for multimineral porous media

Geophysics ◽  
2005 ◽  
Vol 70 (2) ◽  
pp. N17-N26 ◽  
Author(s):  
José M. Carcione ◽  
Hans B. Helle ◽  
Juan E. Santos ◽  
Claudia L. Ravazzoli
Keyword(s):  
Porous Medium ◽  
Porous Media ◽  
Strain Energy ◽  
Saturated Porous Medium ◽  
Low Frequency ◽  
P Wave ◽  
Stress Strain Relation ◽  
P Wave Velocity ◽  
Two Phases ◽  
The Time Domain

We derive the time-domain stress-strain relation for a porous medium composed of n − 1 solid frames and a saturating fluid. The relation holds for nonuniform porosity and can be used for numerical simulation of wave propagation. The strain-energy density can be expressed in such a way that the two phases (solid and fluid) can be mathematically equivalent. From this simplified expression of strain energy, we analogize two-, three-, and n-phase porous media and obtain the corresponding coefficients (stiffnesses). Moreover, we obtain an approximation for the generalized Gassmann modulus. The Gassmann modulus is the bulk modulus of a saturated porous medium whose matrix (frame) is homogeneous. That is, the medium consists of two homogeneous constituents: a mineral composing the frame and a fluid. Gassmann's modulus is obtained at the low-frequency limit of Biot's theory of poroelasticity. Here, we assume that all constituents move in phase, a condition similar to the dynamic compatibility condition used by Biot, by which the P-wave velocity is equal to Gassmann's velocity at all frequencies. Our results are compared with those of the Berryman-Milton (BM) model, which provides an exact generalization of Gassmann's modulus to the three-phase case. The model is then compared to the wet-rock moduli obtained by static finite-element simulations on digitized images of microstructure and is used to fit experimental data for shaly sandstones. Finally, an example of a multimineral rock (n > 3) saturated with different fluids is given.

scholarly journals Experimental Investigation of the Relationship between the P-Wave Velocity and the Mechanical Properties of Damaged Sandstone

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Qi-Le Ding ◽  
Shuai-Bing Song
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Young’S Modulus ◽  
Wave Velocity ◽  
Young's Modulus ◽  
P Wave ◽  
Rock Properties ◽  
High Temperature Treatment ◽  
P Wave Velocity ◽  
The Relationship

To obtain an improved and more accurate understanding of the relationship between the P-wave velocity and the mechanical properties of damaged sandstone, uniaxial compression tests were performed on sandstone subjected to different high-temperature treatments or freeze-thaw (F-T) cycles. After high-temperature treatment, the tests showed a generally positive relationship between the P-wave velocity and mechanical characteristics, although there were many exceptions. The mechanical properties showed significant differences for a given P-wave velocity. Based on the mechanical tests after the F-T cycles, the mechanical properties and P-wave velocities exhibited different trends. The UCS and Young’s modulus values slightly decreased after 30, 40, and 50 cycles, whereas both an increase and a decrease occurred in the P-wave velocity. The UCS, Young’s modulus, and P-wave velocity represent different macrobehaviors of rock properties. A statistical relationship exists between the P-wave velocity and mechanical properties, such as the UCS and Young’s modulus, but no mechanical relationship exists. Further attention should be given to using the P-wave velocity to estimate and predict the mechanical properties of rock.

scholarly journals Effect of thermal cycling on mechanical properties and energy evolution of sandstone

2020 ◽  
Vol 24 (6 Part B) ◽  
pp. 4001-4009
Author(s):  
Peng Hou ◽  
Lin Gao ◽  
Yan Xing ◽  
Zhao-Peng Zhang
Keyword(s):  
Mechanical Properties ◽  
Thermal Cycling ◽  
Thermal Cycle ◽  
P Wave ◽  
Reservoir Rock ◽  
Temperature Cycle ◽  
Energy Evolution ◽  
Compression Tests ◽  
Evolution Law ◽  
P Wave Velocity

In geothermal energy exploration, the reservoir rock is always subjected to thermal cycles and its physical properties will be seriously affected. In this paper, the changes of the internal structure of the sandstone after the thermal cycle are firstly evaluated by ultrasonic tests. Then, uniaxial compression tests are conducted on the treated specimens. The effects of the thermal cycling on mechanical properties and energy evolution law of the sandstone are analyzed. The results show that the density, P-wave velocity and mechanical properties of the sandstone reduced with the increase in the thermal cycle, especially in the high temperature cycle. The increase of the temperature in the thermal cycle can increase the influence of the thermal cycle on the energy evolution law.

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