scholarly journals Unloading Mechanics and Energy Characteristics of Sandstone under Different Intermediate Principal Stress Conditions

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Yingjie Zhang ◽  
Jiangteng Li ◽  
Gang Ma ◽  
Shuangfei Liu
Keyword(s):  
Testing Machine ◽  
Strength Criterion ◽  
Intermediate Principal Stress ◽  
Loading Test ◽  
Energy Characteristics ◽  
True Triaxial ◽  
Triaxial Strength ◽  
Rock Testing ◽  
Cubic Polynomial ◽  
Loading And Unloading

The TRW-3000 true triaxial rock testing machine was used to conduct loading and unloading tests of sandstone under different σ 2 , and the true triaxial lateral unloading mechanics and energy characteristics of sandstone under different σ 2 were studied. The experimental results show the following: (1) compared with the results of the loading test, the peak strength of the sandstone under the unloading σ 3 path is reduced, the unloading direction has obvious expansion and deformation, and the amount of expansion increases significantly with the increase of σ 2 ; sudden brittle failure occurs at the end of unloading. E gradually decreases with the increase of H, and it performs well to use the cubic polynomial to fit the curve of E-H. (2) The Mogi–Coulomb strength criterion can accurately describe the true triaxial strength characteristics of sandstone under loading and unloading conditions. Compared with the results of the loading test, the values of c and φ obtained based on this criterion under the unloading σ 3 path are reduced. (3) Under the condition of unloading σ 3 , U, U e , and U d , when the specimen is broken, are all linearly positively correlated with σ 2 . U d increases nonlinearly with the increase of H, and as σ 2 increases, the slope of the U d -H curve becomes larger, and the specimen consumes more energy under the same unloading amount. Most of the energy absorbed by the specimen under the unloading σ 3 path is converted into U e , but as σ 2 increases, U d   / U increases, and the energy consumed when the specimen is broken is greater.

scholarly journals Research on Coal Mechanical Properties Based on True Triaxial Loading and Unloading Experiment

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Yanyan Peng ◽  
Haoxiang Deng ◽  
Minghong Xing ◽  
Pengfei Guo ◽  
Chun Zhu
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Principal Stress ◽  
Coal Mine ◽  
Test System ◽  
Intermediate Principal Stress ◽  
Mine Safety ◽  
Triaxial Loading ◽  
True Triaxial ◽  
Loading And Unloading

To study the safety issues caused by coal mine excavation, self-developed simulation of earth interior atmosphere and sound test system was used to perform true triaxial loading and unloading tests of coal. An acoustic emission detection system was used to record the damage evolution trend of coal under different intermediate principal stress states. The experimental results show that in the true triaxial unloading test, as the intermediate principal stress increases, the failure state of coal changes from shear failure to partial shear tension failure, finally leading to overall yield failure. In the stress-strain curves, with the increase in intermediate principal stress, the strain in the direction of intermediate principal stress gradually changes from compression to expansion, and typical expansion occurs. The Mogi–Coulomb strength criterion better reflects the strength failure characteristics of coal during unloading. The stress-acoustic emission diagrams show that the increase in intermediate principal stress causes the internal cracks of the coal to grow unsteadily and exponentially, and the increase in intermediate principal stress makes the coal lose its ability to continue to bear the load. Studying the influence of the intermediate principal stress on the mechanical properties of coal has practical significance for coal mine safety production.

scholarly journals Three dimensional statistical damage constitutive model of rock based on Griffith strength criterion

2021 ◽  
Author(s):  
Song Chen ◽  
Xiuling Cao ◽  
Zhao Yang
Keyword(s):  
Constitutive Model ◽  
Principal Stress ◽  
Damage Mechanics ◽  
Brittle Materials ◽  
Strength Criterion ◽  
Intermediate Principal Stress ◽  
True Triaxial ◽  
Damage Constitutive Model ◽  
Two Parameters ◽  
The Relationship

Abstract According to the damage mechanics theory and Lemaitre strain equivalence theory, because most rock materials are brittle materials, Griffith strength criterion has good applicability to describe the fracture failure of brittle materials from the perspective of energy. Using a new method to describe the rock micro-element strength based on Griffith strength criterion, and assuming the micro-element strength obeys the Weibull distribution, a true triaxial constitutive model of damage softening reflecting the whole process of rock failure is established. On this basis, the influence of the two parameters in the model on the curve of the constitutive model is analyzed, and the relationship between the two parameters and the intermediate principal stress in the model is established, and the model is revised reasonably. Finally, a true triaxial damage constitutive model of rock is established. The results are in good agreement with the experimental curve, which verifies its validity and rationality. At the same time, the relationship between the damage evolution and the strain and stress is discussed, and the influence of the size of the intermediate principal stress on the relationship is analyzed in detail.

scholarly journals An Extension Failure Criterion for Brittle Rock

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Aizhong Lu ◽  
Ning Zhang ◽  
Guisen Zeng
Keyword(s):  
Principal Stress ◽  
Poisson’S Ratio ◽  
Compressive Strain ◽  
Strength Criterion ◽  
Maximum Principal Stress ◽  
Intermediate Principal Stress ◽  
Brittle Rock ◽  
Poisson's Ratio ◽  
Triaxial Tests ◽  
True Triaxial

Under the triaxial compressive state, the compressive strain is supposed to happen in the direction of the maximum principal stress, but tensile strain happens in the direction of the minimum principal stress. Moreover, as the intermediate principal stress is not too high, the corresponding strain can also be tensile. If the brittle rock is assumed as linear elastic in the prefailure stage, a new strength criterion based on the sum of the two tensile strains was presented. The new criterion considers the differences in mechanical parameters (i.e., elastic modulus and Poisson’s ratio) under tension and compression. The parameters of the criterion only include Poisson’s ratio and uniaxial strength. And the effect of the intermediate principal stress σ 2 can be reflected. Certain featured failure phenomenon of rock material can be explained well by the proposed criterion. The results of conventional and true triaxial tests can verify the criterion well. Finally, the criterion is compared with the Mohr–Coulomb and Drucker–Prager criteria.

scholarly journals Bifurcation analysis of shear band in sand under true triaxial conditions with hypoplasticity

2021 ◽  
Author(s):  
Jun Liu ◽  
shun wang ◽  
Yang Wu ◽  
Wei Wu
Keyword(s):  
Shear Band ◽  
Principal Stress ◽  
Stress Ratio ◽  
Strength Criterion ◽  
Intermediate Principal Stress ◽  
True Triaxial ◽  
Acoustic Tensor ◽  
Strain Relationship ◽  
Bifurcation Behaviour ◽  
Hypoplastic Constitutive Model

Predicting the onset of shear band is of significance in understanding the failureof geomaterials. The prediction accuracy is dictated by the constitutive modelused for the description of the pre-bifurcation behaviour. In this study, we firstmodify a recently proposed hypoplastic constitutive model by incorporating ageneral strength criterion and a stiffness function. We proceed to consider theonset of shear band in sand under true triaxial conditions. We demonstrate thatour analyses capture the pre-bifurcation stress–strain relationship at differentvalues of intermediate principal stress and predict fairly well the onset ofshear band. The acoustic tensor criterion generally adopted in elastoplasticapproaches is inadequate for hypoplastic approaches. No special non-coaxialtreatment is required for the present approach to yield a reasonable variationtrend of bifurcation strain with intermediate principal stress ratio 𝑏.

Properties of Hard Rubber. XIX. Effect of Temperature on Cross-Breaking Strength and Elongation

1947 ◽  
Vol 20 (2) ◽  
pp. 525-526
Author(s):  
W. H. Willott
Keyword(s):  
Breaking Strength ◽  
Testing Machine ◽  
Effect Of Temperature ◽  
Loading Test ◽  
Standard Size ◽  
Test Pieces ◽  
The Cross ◽  
Hot Weather ◽  
Electric Radiator ◽  
Usual Order

Abstract In a series of cross-breaking tests carried out on hard rubber during hot weather, the values of the breaking elongation were higher than was expected, although the cross-breaking strength was of the usual order. It was thought that the high temperature might account for these results by making the hard rubber more plastic. The following experiments were, therefore, performed to investigate the effect of small changes of temperature, such as are encountered at different times of the year, on the cross-breaking strength and elongation. Test-pieces of standard size (75 × 25 × 5 mm.) were cut from a sheet of hard rubber of the composition: 68 per cent rubber, 32 per cent sulfur, which had been vulcanized for 5 hours at 155° C. They were immersed in a beaker of water and kept at the required temperature for about 15 minutes, when they were judged to have attained a steady temperature. The tests were carried out on an Avery fabric-testing machine fitted with special clamps to give a three-point loading test, the distance between the supporting knife-edges being 50.4 mm. (2 in.). These clamps were heated to the temperature of the specimens by means of an electric radiator. The specimens were tested as soon as possible after they had been removed from the water, so that the change of temperature during the test was reduced as far as possible. The standard conditions already laid down, were observed.

Reasonable Strength Criterion Research of High Arch Dam Based on Brittle Failure Constitutive Relation

2014 ◽  
Vol 578-579 ◽  
pp. 964-967
Author(s):  
Zhi Qiang Wang ◽  
Wen Biao Liu
Keyword(s):  
Constitutive Relation ◽  
Brittle Failure ◽  
Concrete Strength ◽  
Safety Evaluation ◽  
Strength Criterion ◽  
Arch Dam ◽  
Dam Failure ◽  
Dam Safety ◽  
High Arch Dam ◽  
Triaxial Strength

The brittle failure finite element method is widely used in arch dam safety evaluation, but it also has some problems, the concrete strength criterion is different, the dam failure range is different. This article first introduces brittle failure constitutive relation and three strength criterions, then takes a high arch dam as an example to compute, obtains some conclusions that the relative failure range of foundation plane corresponds to blaxial strength criterion is slightly bigger than the result of uniaxial strength criterion, is almost the same as the result of triaxial strength criterion. Because the influence of the third principal stress is compressed stress to the dam crack is taken into account under multiaxial strength criterion, therefore using multiaxial strength criterion is more reasonable.

Crack mode and life of Ti-6Al-4V under multiaxial low cycle fatigue

2015 ◽  
Author(s):  
Takamoto Itoh ◽  
Masao Sakane ◽  
Takahiro Morishita ◽  
Hiroshi Nakamura ◽  
Masahiro Takanashi
Keyword(s):  
Hollow Cylinder ◽  
Stress Ratio ◽  
Biaxial Loading ◽  
Fatigue Testing ◽  
Low Cycle Fatigue ◽  
Testing Machine ◽  
Multiaxial Fatigue ◽  
Cycle Fatigue ◽  
Loading Test ◽  
Failure Life

This paper studies multiaxial low cycle fatigue crack mode and failure life of Ti-6Al-4V. Stress controlled fatigue tests were carried out using a hollow cylinder specimen under multiaxial loadings of ?=0, 0.4, 0.5 and 1 of which stress ratio R=0 at room temperature. ? is a principal stress ratio and is defined as ?=sigmaII/sigmaI, where sigmaI and sigmaII are principal stresses of which absolute values take the largest and middle ones, respectively. Here, the test at ?=0 is a uniaxial loading test and that at ?=1 an equi-biaxial loading test. A testing machine employed is a newly developed multiaxial fatigue testing machine which can apply push-pull and reversed torsion loadings with inner pressure onto the hollow cylinder specimen. Based on the obtained results, this study discusses evaluation of the biaxial low cycle fatigue life and crack mode. Failure life is reduced with increasing ? induced by cyclic ratcheting. The crack mode is affected by the surface condition of cut-machining and the failure life depends on the crack mode in the multiaxial loading largely.

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