Failure Process and Stress-Strain Curve of Plane Strain Rock Specimen with Initially Random Material Imperfections

2007 ◽  
Vol 353-358 ◽  
pp. 1133-1136 ◽  
Author(s):  
X.B. Wang
Keyword(s):  
Rock Specimen ◽  
Failure Process ◽  
Shear Bands ◽  
Strain Curve ◽  
Peak Stress ◽  
Plastic Behavior ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Initial Imperfections ◽  
Ideal Plastic

The failure process of heterogeneous rock specimen with initially random material imperfections in uniaxial plane strain compression and the macroscopically mechanical response are numerically modeled by using FLAC (Fast Lagrangian Analysis of Continua). A FISH function is generated to prescribe the initial imperfections within the heterogeneous specimen by using Matlab. The imperfection is weaker than the intact rock. Beyond the failure of the imperfection, it undergoes ideal plastic behavior, while intact rock exhibits linear strain-softening behavior and then ideal plastic behavior once failure occurs. The specimen with smooth ends is loaded at a constant strain rate and is divided into 3200 elements. The maximum numbers of the initial imperfections in five schemes are 100, 300, 500, 700 and 900. The effects of the number of the imperfections on the fracture process, the final fracture pattern and the complete stress-strain curve are investigated. Prior to the peak stress, some imperfections extend in the axial direction and then a part of them coalesce to form inclined shear bands. Beyond the peak stress, shear bands progressively intersect the specimen; in the process the number of the yielded elements approximately remains a constant. With an increase of the number of the initial imperfections, the spacing of shear fractures decreases, the peak stress and corresponding axial strain decrease; the post-peak branch of stress-strain curve becomes steeper; much more elements fail in tension; the number of the yielded elements in tension in the vicinity of the two lateral edges of the specimen remarkably increases.

Stress-Strain Curves for Oxygen-Free High Conductivity Copper at Shear Strain Rates of up to 103s-1

1970 ◽  
Vol 185 (1) ◽  
pp. 1149-1158 ◽  
Author(s):  
K. Bitans ◽  
P. W. Whitton
Keyword(s):  
Shear Strain ◽  
Testing Machine ◽  
Shear Bands ◽  
Strain Curve ◽  
Strain Rates ◽  
Adiabatic Shear Bands ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
The Given ◽  
Tubular Specimens

Shear stress-shear strain curves for o.f.h.c. copper at room temperature have been obtained at constant shear strain rates in the range 1 to 103s-1, using thin walled tubular specimens in a flywheel type torsion testing machine. Results show that, for a given value of strain, the stress decreases when the rate of strain is increased. Moreover, the elastic portion of the stress-strain curve tends to disappear as the rate of strain is increased. It is postulated that these effects are due to the formation of adiabatic shear bands in the material when the given rate of strain is impressed rapidly enough. A special feature of the design of the testing machine used is the rapid application of the chosen strain rate.

scholarly journals Dynamic Characteristics of Sandstone under Coupled Static-Dynamic Loads after Freeze-Thaw Cycles

2020 ◽  
Vol 10 (10) ◽  
pp. 3351
Author(s):  
Bo Ke ◽  
Jian Zhang ◽  
Hongwei Deng ◽  
Xiangru Yang
Keyword(s):  
Energy Absorption ◽  
Dynamic Characteristics ◽  
Shear Failure ◽  
Strain Curve ◽  
Peak Stress ◽  
Peak Strain ◽  
Compression Stress ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Freeze Thaw

The effect of temperature fluctuation on rocks needs to be considered in many civil engineering applications. Up to date the dynamic characteristics of rock under freeze-thaw cycles are still not quite clearly understood. In this study, the dynamic mechanical properties of sandstone under pre-compression stress and freeze-thaw cycles were investigated. At the same number of freeze-thaw cycles, with increasing axial pre-compression stress, the dynamic Young’s modulus and peak stress first increase and then decrease, whereas the dynamic peak strain first decreases and then increases. At the same pre-compression stress, with increasing number of freeze-thaw cycles, the peak stress decreases while the peak strain increases, and the peak strain and peak stress show an inverse correlation before or after the pre-compression stress reaches the densification load of the static stress–strain curve. The peak stress and strain both increase under the static load near the yielding stage threshold of the static stress–strain curve. The failure mode is mainly shear failure, and with increasing axial pre-compression stress, the degree of shear failure increases, the energy absorption rate of the specimen increases first and then decreases. With increasing number of freeze-thaw cycles, the number of fragments increases and the size diminishes, and the energy absorption rates of the sandstone increase.

Joint Inclination Effect on Strength, Stress-Strain Curve and Strain Localization of Rock in Plane Strain Compression

2005 ◽  
Vol 495-497 ◽  
pp. 69-76 ◽  
Author(s):  
X.B. Wang
Keyword(s):  
Plane Strain ◽  
Strain Softening ◽  
Strain Curve ◽  
Plane Strain Compression ◽  
Peak Strength ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Softening Behavior ◽  
Ideal Plastic ◽  
Joint Inclination

Peak strength, mechanical behavior, and shear band (SB) of anisotropic jointed rock (JR) were modeled by Fast Lagrangian Analysis of Continua (FLAC). The failure criterion of rock was a composite Mohr-Coulomb criterion with tension cut-off and the post-peak constitutive relation was linear strain-softening. An inclined joint was treated as square elements of ideal plastic material beyond the peak strength. A FISH function was written to find automatically elements in the joint. For the lower or higher joint inclination (JI), the higher peak strength and more apparent strain-softening behavior are observed; the failure of JR is due to the slip along the joint and the new generated SBs initiated at joint’s two ends. For the lower JI, the slope of softening branch of stress-strain curve is not concerned with JI since the new and longer SBs’s inclination is not dependent on JI, as can be qualitatively explained by previous analytical solution of post-peak slope of stress-strain curve for rock specimen subjected to shear failure in uniaxial compression based on gradient-dependent plasticity. For the higher JI, the post-peak stress-strain curve becomes steeper as JI increases since the contribution of the new SBs undergoing strain-softening behavior to axial strain of JR increases with JI. For the moderate JI, the lower strength and ideal plastic behavior beyond the elastic stage are found, reflecting that the inclined joint governs the deformation of JR. The present numerical prediction on anisotropic peak strength in plane strain compression qualitatively agrees with triaxial experimental tests of many kinds of rocks. Comparison of the present numerical prediction on JI corresponding to the minimum peak strength of JR and the oversimplified theoretical result by Jaeger shows that Jaeger’s formula has overestimated the value of JI.

scholarly journals A Stress-Strain Model for Brick Prism under Uniaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Keun-Hyeok Yang ◽  
Yongjei Lee ◽  
Yong-Ha Hwang
Keyword(s):  
Strain Curve ◽  
Peak Stress ◽  
Test Results ◽  
Compression Tests ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Proposed Model ◽  
Relationship Model ◽  
Strain Relationship ◽  
Strain Model

This study proposes a simple and rational stress-strain relationship model applicable to brick masonry under compression. The brick prism compression tests were conducted with different mortar strengths and with constant brick strength. From the observation of the test results, shape of the stress-strain curve is assumed to be parabola. In developing the stress-strain model, the modulus of elasticity, the strain at peak stress, and the strain at 50% of the peak stress on the descending branch were formulated from regression analysis using test data. Numerical and statistical analyses were then performed to derive equations for the key parameter to determine the slopes at the ascending and descending branches of the stress-strain curve shape. The reliability of the proposed model was examined by comparisons with actual stress-strain curves obtained from the tests and the existing model. The proposed model in this study turned out to be more accurate and easier to handle than previous models so that it is expected to contribute towards the mathematical simplicity of analytical modeling.

scholarly journals Stress–Strain Curve and Carbonation Resistance of Recycled Aggregate Concrete after Using Different RCA Treatment Techniques

2021 ◽  
Vol 11 (9) ◽  
pp. 4283
Author(s):  
Long Li ◽  
Dongxing Xuan ◽  
Chisun Poon
Keyword(s):  
Elastic Modulus ◽  
Strain Curve ◽  
Peak Stress ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Aggregate Concrete ◽  
Treatment Techniques ◽  
Carbonation Resistance

Five recycled coarse aggregate (RCA) treatment techniques including flow-through carbonation, pressurized carbonation, wet carbonation, nano silica (NS) pre-spraying and combined pressurized carbonation with NS pre-spraying, were utilized to improve the performance of recycled aggregate concrete (RAC). The characteristics of the stress–strain curves of RACs including peak stress, peak strain, elastic modulus, ultimate strain and toughness were evaluated after using the above RCA treatment techniques. A theoretical model for natural aggregate concrete was used to analyse the stress–strain curve of RAC. Additionally, the carbonation resistance of RAC after using different RCA treatment techniques were investigated. The results showed that the calculated stress–strain curve of RAC based on the theoretical model matched well with the experimental results. Among the three types of carbonation techniques, pressurized carbonation caused the highest improvement in peak stress and elastic modulus of RAC, followed by flow-through carbonation, the last was wet carbonation. The NS pre-spraying method contributed to even higher improvement in peak stress and elastic modulus of RAC than the pressurized carbonation method. The combined pressurized carbonation with NS pre-spraying exhibited the highest enhancement of RAC because both the RCA and the new interface transition zone (ITZ) were improved. The carbonation resistance of RAC was improved after using all the studied RCA treatment techniques.

Stress-Strain Model for Confined Concrete in Cross-Shaped Columns

2012 ◽  
Vol 450-451 ◽  
pp. 822-826
Author(s):  
Lin Zhu Sun ◽  
Tie Cheng Wang ◽  
Fang Yang
Keyword(s):  
Strain Curve ◽  
Peak Stress ◽  
Confined Concrete ◽  
Peak Strain ◽  
Test Results ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
The Cross ◽  
Strain Model ◽  
Variation Rule

To establish complete stress-strain curve equations for confined concrete in cross-shaped columns, we designed 7 test specimens corresponding to the usable eigenvalue range of stirrup of the cross-shaped columns. We obtained the test results of the reinforced concrete cross-shaped columns through axial compression test, got the system parameters of a stress-strain model through statistical analysis of the test data, and then established stress-strain curves for confined concrete in the cross-shaped columns. This model reflects the variation rule of the stress-strain curve of confined concrete in cross-shaped columns. Compared with the stress-strain model for confined concrete in square columns, the confined concrete in cross-shaped columns has smaller peak stress, larger peak strain, and relatively steeper descending part of curve. The research results provide theorotical basis for nonlinear analysis of cross-shaped columns.

scholarly journals Proposed Constitutive Law of Uniaxial Compression for Concrete under Deterioration Effects

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2048 ◽  
Author(s):  
Yiwei Gao ◽  
Xuhua Ren ◽  
Jixun Zhang ◽  
Lingwei Zhong ◽  
Shuyang Yu ◽  
...  
Keyword(s):  
Uniaxial Compression ◽  
Failure Process ◽  
Strain Curve ◽  
Ductile Deformation ◽  
Deformation Capacity ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
New Model ◽  
Freeze Thaw ◽  
Prediction Curve

In order to study the ductile deformation characteristics and failure process of plain concrete under uniaxial compression, this paper proposes a new constitutive model. The new model was used to fit and analyze the constitutive curve of concrete under uniaxial compressive under various degradation forms and was compared with the traditional constitutive models. Finally, the new model was used to quantitatively analyze and predict the stress–strain curve of concrete in different degradation periods of a set of freeze–thaw measured data. The results show that, compared with the traditional constitutive model, the new model is simple in form and has few parameters, and the numerical value of the parameter can reflect the ductile deformation capacity of concrete. The fitting curve of the new model has the highest fitting degree with the measured stress–strain curve of concrete, and the goodness of fit (R2) is also the largest. The new model is suitable for fitting the stress–strain curve of concrete under uniaxial compression under various deteriorating forms, and the degree of fit between the constitutive prediction curve and the measured curve is high. It can be seen from the fitting results of the new model parameters that the ductile deformation capacity of concrete decreases first and then increases slightly, which is inconsistent with the law of gradual deterioration of strength. There is a minimum moment of ductility deformation capacity of concrete (MDC). The MDC of O-C40 concrete is about 114 freeze–thaw cycles, and the MDC of O-C50 concrete is about 116 freeze–thaw cycles; the degree of fit between the constitutive prediction curve and the measured curve is high. We hope that the improvement mentioned offers valid reference to the study of ductile deformation characteristics and failure process of compressed concrete under different deterioration forms.

Evaluation of Damage for Alumina/Graphite Refractory Using Apparent Sonic Velocity Measurement

2007 ◽  
Vol 352 ◽  
pp. 31-34
Author(s):  
Ryoichi Furushima ◽  
Yohtaro Matsuo ◽  
Tadashi Shiota ◽  
Kouichi Yasuda
Keyword(s):  
Ultrasonic Method ◽  
Compressive Loading ◽  
Strain Curve ◽  
Damage Mechanism ◽  
Plastic Behavior ◽  
Sonic Velocity ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Loading Process ◽  
Apparent Sonic Velocity

Damage evaluation for alumina/graphite refractory was conducted under uni-axial compressive loading. Apparent sonic velocity during a loading-unloading cycle was measured by ultrasonic method. Quasi-elastic-plastic behavior was observed in the stress-strain curve for each cycle. However, it is difficult to detect damage from the stress-strain curve during each loading- unloading cycle. On the other hand, using the result of change in apparent sonic velocity during a loading-unloading cycle, it is possible to estimate damage to some extent. The apparent sonic velocity kept approximately constant during the first loading process, but it decreased remarkably during the first unloading one. In the subsequent loading-unloading cycles, it increased in the loading process and decreased in the unloading one. Consequently, it is concluded that damage mechanism during the first loading-unloading cycle is different from that during the subsequent loading- unloading cycles for alumina/graphite refractory.

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