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Статті в журналах з теми "True-triaxial loading"
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Yin, Jian-Hua, Chun-Man Cheng, Md Kumruzzaman, and Wan-Huan Zhou. "New mixed boundary, true triaxial loading device for testing three-dimensional stress–strain–strength behaviour of geomaterials." Canadian Geotechnical Journal 47, no. 1 (January 2010): 1–15. http://dx.doi.org/10.1139/t09-075.
Повний текст джерелаАнотація:
This paper presents a brief review of true triaxial apparatuses (TTAs) developed in the past and their advantages and limitations. Considering the limitations of previous designs, a new true triaxial loading device that provides mixed boundary conditions for a true triaxial apparatus (TTA) is introduced. This loading device consists of four sliding rigid plates and two flexible loading faces. The setup of the loading device together with the whole true triaxial system is described. Frictions between sliding plates and the soil membrane surfaces in the new loading device are examined. A three-dimensional finite element (FE) modelling study is carried out on the stress and strain distribution of a soil specimen subjected to loading from two different loading devices. It is found that stresses and strains of a soil specimen subjected to loading from the new sliding plates are far more uniform than those subjected to loading from nonsliding plates with preset gaps. Finally, the paper presents the applications of the present TTA with the new loading device for testing studies of a completely decomposed granite soil and a geofoam. Typical results are presented and discussed. It is found that the present mixed boundary loading device is very suitable for true triaxial testing on both soils and geofoam, especially under large strains or compression without corner contact problems.
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Shi, L., C. C. Li, X. Zhang, X. T. Feng, and G. Wang. "Strength characteristics of brittle rock subjected to multi-stage intermediate principal stress loading." Géotechnique Letters 12, no. 2 (June 1, 2022): 1–17. http://dx.doi.org/10.1680/jgele.21.00021.
Повний текст джерелаАнотація:
A series of single-stage true triaxial compression (TTC) tests and multi-stage intermediate principal stress (σ2) loading tests were carried out on three types of brittle rock specimens in this study to examine the influence of σ2 and the validity of obtaining strength parameters by multi-stage loading method under true triaxial stress conditions. There exists a critical σ2 at which the rock strength reaches its ultimate value under both loading conditions. Under the same σ3 level, the critical σ2 is much smaller under the multi-stage σ2 loading than under the single-stage TTC. The test results also show that the strength determined under multi-stage σ2 loading is much smaller than that determined under single-stage TTC. The strength difference can reach 39%. A lower strength is measured under multi-stage σ2 loading because the local fracture plane induced by true triaxial stress is parallel to the σ2, and the strength of the rock specimen containing this type of local fracture plane is not affected by σ2. On the other hand, rock damage accumulates during multiple loading and unloading cycles. The current testing results indicate the multi-stage loading test is not suitable for determining the strength envelope of brittle rock under true triaxial conditions.
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Shen, Wei, Guang-Jian Liu, Lin-Ming Dou, Si-Yuan Gong, and Hu He. "Influences of True Triaxial Loading-Unloading Stress Paths on Mechanical Properties and Wave Velocity of Coal Samples subject to Risk of Rock Burst." Shock and Vibration 2021 (September 14, 2021): 1–14. http://dx.doi.org/10.1155/2021/4074159.
Повний текст джерелаАнотація:
To study fracture evolution and peak stress in burst risk coal samples (BRCSs) under true triaxial loading and unloading conditions, experimental and numerical research was applied to BRCSs under true triaxial stress paths entailing “x-direction displacement fixed, y-direction loading, z-direction unloading.” Both the experimental and the numerical results demonstrated that the peak stress borne by the BRCSs was not only affected by the initial stress but also had a negative exponential relationship with the ratio of the unloading rate and the loading rate (RURLR); therefore, peak stress equations of BRCSs under true triaxial loading and unloading conditions were established. The triaxial stress-time curves obtained by experiments and simulations exhibited an “elasticity-yield-destruction” phase, and the characteristics of the yield phase were determined by the RURLR. A typical BRCS was selected for velocity tomographic imaging to analyze the fracture evolution characteristics under true triaxial loading and unloading. The results showed that when the BRCS was subjected to a triaxial state of stress, the high- and low-velocity regions existed alternately due to the presence of the crack; during the elastic phase, the crack closed during loading in the previous phase was reopened upon unloading, so that the velocity of the sample decreased and a wide range of low-velocity regions could be formed; when entering the yield phase, the original crack continued to expand into a hole-through crack, leading to wider extreme values and ranges of these low- and high-velocity regions; at the breaking phase, multiple microcracks were generated around the hole-through cracks, decreasing the overall velocity, and showing point distributions characteristics of high- and low-velocity regions. Overall, many low-velocity regions with similar normal directions to the unloading direction were formed; these correlated well with macrofractures (postfailure).
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Karev, V. I., D. M. Kilmov, Yu F. Kovalenko, and K. B. Ustinov. "Experimental Study of Rock Creep under True Triaxial Loading." Mechanics of Solids 54, no. 8 (December 2019): 1151–56. http://dx.doi.org/10.3103/s0025654419080041.
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Reddy, Krishna R., and Surendra K. Saxena. "Liquefaction resistance of cemented sands under multidirectional cyclic loading." Canadian Geotechnical Journal 29, no. 6 (December 1, 1992): 989–93. http://dx.doi.org/10.1139/t92-108.
Повний текст джерелаАнотація:
This paper presents a methodology to predict liquefaction of uncemented and cemented sands under multidirectional cyclic loading conditions using solely conventional unidirectional cyclic test data. The method is found to be reasonably accurate based on the reported multidirectional cyclic test results using a true triaxial apparatus. Key words : sand, cementation, triaxial, experimental, theoretical, liquefaction.
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Shen, Wei, Lin-ming Dou, and Hu He. "Mechanical and Coal Burst Breeding Mechanism of Coal Samples under True Triaxial Loading and Unloading." Advances in Civil Engineering 2019 (November 11, 2019): 1–15. http://dx.doi.org/10.1155/2019/6050975.
Повний текст джерелаАнотація:
A true triaxial loading and unloading experiment entailing “y-direction stress loading, z-direction stress unloading, and x-direction displacement fixing” of coal samples was conducted. Through analysis of the stress characteristics, fracture characteristics, and energy evolution in coal samples, the mechanical and coal burst breeding mechanisms of coal samples under true triaxial loading and unloading were revealed. The experiment found that the yield stress and peak stress of coal samples were not only affected by the initial loading and unloading of lateral stress but also had a negative exponential relationship with the ratio of the unloading rate and the loading rate (RURLR), thereby establishing the stress equation of coal samples under a true triaxial loading and unloading. There was a yield turning point in the stress-time curve of coal samples, and the difference in triaxial stress and acoustic emission before, and after, yield was significant. It was found that a high unloading rate and high initial stress are precursors to coal sample bursting. During loading and unloading, the high-energy area expanded, but its location was always fixed to within a certain area. The energy in this area was rapidly released to form a burst source when the sample was subjected to high-speed unloading. The nonbursting coal samples and the burst coal samples showed characteristic slabbing and bursting behaviours, respectively: the former corresponding to the acoustic emission energy value being two orders of magnitude lower than the latter. The research results can provide a reference for the study of mechanical behaviours and coal burst criteria in the rock surrounding a coal roadway excavation.
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Wang, Shuai, Lianguo Wang, Jiansheng Tian, Hao Fan, Chongyang Jiang, and Ke Ding. "An Experimental Study on the Effects of True Triaxial Loading and Unloading Stress Paths on the Mechanical Properties of Red Sandstone." Minerals 12, no. 2 (February 5, 2022): 204. http://dx.doi.org/10.3390/min12020204.
Повний текст джерелаАнотація:
Loading and unloading stress paths play critical roles in investigating the deformation and failure of roadway excavation. In this study, tests under four different loading and unloading stress paths were conducted on red sandstone samples, with the aid of a self-developed true triaxial test system. Meanwhile, the deformation and failure characteristics of the samples were monitored during the tests. The following research conclusions were obtained: The octahedral shear stress is linearly correlated with the average effective stress, and the correlation coefficient R2 is 0.9825. The Mogi–Coulomb strength criterion is superior to the Drucker–Prager strength criterion in reflecting strength failure characteristics of red sandstone during loading and unloading. Shear failure tends to occur under uniaxial compression, whereas shear–tensile composite failure occurs under loading and unloading conditions. Compared with the true triaxial loading test, loading and unloading tests produce a larger strain in the unloading direction. Under loading and unloading stress paths, with the increase in intermediate principal stress (IPS), the strain in the direction of IPS gradually changes from expansion to compression, and the peak strength gradually increases. The state of IPS affects the failure strength of the sample and reflects the strengthening effect of IPS. This paper boasts a certain value and significance for research on the deformation and failure characteristics of sandstone in the actual in situ stress environment with triaxial dynamic changes.
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Karev, V. I., D. M. Klimov, Yu F. Kovalenko, and K. B. Ustinov. "Erratum to: Experimental Study of Rock Creep under True Triaxial Loading." Mechanics of Solids 55, no. 1 (January 2020): 154. http://dx.doi.org/10.3103/s0025654420010240.
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Cambou, B., A. Dogui, K. Jafari, and F. Sidoroff. "On the equivalence between true triaxial and torsion shear loading paths." Computers and Geotechnics 2, no. 4 (January 1986): 207–17. http://dx.doi.org/10.1016/0266-352x(86)90018-2.
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Alexeev, A. D., V. N. Revva, N. A. Alyshev, and D. M. Zhitlyonok. "True triaxial loading apparatus and its application to coal outburst prediction." International Journal of Coal Geology 58, no. 4 (June 2004): 245–50. http://dx.doi.org/10.1016/j.coal.2003.09.007.
Повний текст джерелаДисертації з теми "True-triaxial loading"
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Akdag, Selahattin. "Experimental investigation of damage evolution during strain burst in brittle rocks for deep mines." Thesis, 2019. http://hdl.handle.net/2440/120726.
Повний текст джерелаАнотація:
The increasing demand for resources and depletion of near ground mineral resources caused deeper mining operations under high-stress and high-temperature rock mass conditions. As a results of this, strain burst, which is the sudden and violent release of stored strain energy during dynamic brittle failure of rocks, has become more prevalent and created considerable safety risks damaging underground infrastructures. This research focuses on the development of experimental methodologies to better understand the fundamental knowledge concerning the failure mechanism of strain burst and the influence of thermal damage, high confining pressure and various loading rate on the overall mechanical behaviour of highly brittle granitic rocks leading to strain burst. Strain burst is related to the elastic stored strain energy and how this stored energy is released during the unstable spontaneous failure. Therefore, it is significant to investigate the energy state during strain burst from the viewpoint of energy theory. In this sense, circumferential strain controlled quasi-static tests on Class II rocks over a wide range of confining pressures at different heat-treatment temperatures were conducted to capture the snap-back behaviour and calculate excess strain energy that is responsible for the spontaneous instability. A new energy calculation method associated with acoustic emission (AE) was developed to express the propensity of strain burst and investigate the post-peak energy distribution characteristics for brittle rocks under the coupling influence of confinement and temperature. In order to quantify the micro-crack density and reveal the micro-fracture characteristics of the brittle rocks exposed to various temperatures, scanning electron microscopy (SEM) analysis was also conducted. This is highly relevant to link the excess strain energy and the main failure mechanism triggering strain burst under high-temperature condition. The failure process of strain burst is the outcome of the unstable growth and coalescence of secondary micro-cracks. If the dissipative energy to grow pre-existing cracks and the secondary cracks is smaller than the elastic stored strain energy in rock masses, the residual strain energy will be released suddenly in the form of kinetic energy, resulting in ejecting high-velocity rock fragments. Therefore, understanding the crack initiation and propagation in rocks is of great concern for engineering stability and security. As an intrinsic property of rocks to resist crack initiation and propagation, the rock fracture toughness is the most significant material property in fracture mechanics. In this respect, the three-point bending method was applied using cracked chevron notched semi-circular bend (CCNSCB) granite specimens subjected to different temperatures under a wide range of loading rates in pure mode I. A suitable relation for the dimensionless stress intensity factor (𝑌∗) of SCB with chevron notch samples were presented based on the normalised crack length (𝛼) and half-distance between support rollers (𝑆/2). The minimum dimensionless stress intensity factor (𝑌𝑚𝑖𝑛∗) of CCNSCB specimens were determined using an analytical method, i.e., Bluhm’s slice synthesis method. In this study, the influence of thermal damage and loading rate on the quasi-static mode I fracture toughness and the energy-release rate using CCNSCB method was investigated. In the deep mining process, the rock mass is subjected to a dynamic disturbance caused by blasting, and mechanical drilling resulting in dynamic fractures in the forms of strain burst, slabbing, and spalling. The dynamic rock fracture parameters, including dynamic initiation fracture toughness and fracture energy which are an important manifestation of dynamic rock failure (strain burst) in deep underground engineering and they are of great practical significance to assess the dynamic fracture behaviour of deep rock masses. Since deep rock engineering operations in high temperature and high pressure environment is prone to strain burst, the influence of thermally induced damage on the dynamic failure parameters of granite specimens was investigated. The damage evolution of granitic rocks were studied over a wide range of loading rates to reveal the rate dependency of strain burst. Dynamic fracture toughness tests were carried out on granite under different temperatures and impact loadings using a Split Hopkinson Pressure Bar (SHPB) apparatus at Monash University. With dynamic force balance achieved in the dynamic tests, the stable-unstable transition of the crack propagation crack was observed and the dynamic initiation fracture toughness was calculated from the dynamic peak load. The thermal damage influence on strain burst characteristics of brittle rocks under true-triaxial loading-unloading conditions was investigated using the AE and kinetic energy analyses. A unique strain burst testing system enabling to simulate the creation of excavation at the State Key Laboratory for Geomechanics and Deep Underground Engineering in Beijing (China) was used to replicate strain burst condition. Time-domain and frequency-domain responses AE waves related to strain burst were studied, and the damage evolution was quantified by b-values, cumulative AE energy and events rates that can be used as warning signals to rock failure. The ejection velocities of the rock fragments from the free face of the granite specimens were used to calculate kinetic energies which can be used as an indicator for quantitatively evaluating the intensity of strain burst. Based on the energy evolution characteristics of brittle rocks under uniaxial and triaxial compression, true-triaxial loading-unloading and three-point bending, new strain burst proneness indexes and strain burst criterion were proposed. The effects of temperature, confinement and loading rate on strain burst proneness were discussed. This study aims to advance the understanding on underlying processes that govern the macro-behaviour of brittle rocks during strain burst and make use of this insight to further advance our current predictive capabilities of strain burst with references to large-scale underground mining. Using the developed experimental methodologies in this study, fractures around an excavation to reduce the amount of excess strain energy leading to strain burst can be determined and ultimately incipient strain burst in deep mines can be predicted avoiding potential hazards. Using the methodology for forecasting of strain burst in this research can be used for enhanced understanding of the design of rock support in strain burst-prone areas in deep mining activities. The findings of this study will facilitate achieving a better and comprehensive understanding of the damage process during strain burst in deep mines. This study underpins the development of better and more efficient prediction methods for strain burst which will lead to better planning guidelines and ultimately safer deep underground working conditions.Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2019
Частини книг з теми "True-triaxial loading"
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Ingraham, Mathew D., Kathleen A. Issen, and David J. Holcomb. "Failure of Castlegate Sandstone Under True Triaxial Loading." In Advances in Bifurcation and Degradation in Geomaterials, 321–26. Dordrecht: Springer Netherlands, 2011. http://dx.doi.org/10.1007/978-94-007-1421-2_42.
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Karev, V. I., D. M. Klimov, and Yu F. Kovalenko. "Modeling Geomechanical Processes in Oil and Gas Reservoirs at the True Triaxial Loading Apparatus." In Springer Geology, 336–49. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-77788-7_35.
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Nikolai, Shevtsov, Zaitsev Alexey, and Panteleev Ivan. "Deformation and Destruction of Rocks on the True Triaxial Loading System with Continuous Acoustic Emission Registration." In Springer Proceedings in Earth and Environmental Sciences, 424–32. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-11533-3_42.
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"Energy conversion and damage evolution of rocks under cyclic loading conditions." In True Triaxial Testing of Rocks, 347–58. CRC Press, 2012. http://dx.doi.org/10.1201/b12705-33.
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"Numerical analysis of loading boundary effects in Mogi-type true triaxial tests." In True Triaxial Testing of Rocks, 35–50. CRC Press, 2012. http://dx.doi.org/10.1201/b12705-5.
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"Triaxial loading system as a tool for solving geotechnical problems of oil and gas production." In True Triaxial Testing of Rocks, 317–26. CRC Press, 2012. http://dx.doi.org/10.1201/b12705-29.
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"The hollow cylinder test as an alternative to true triaxial loading of prismatic rock specimens." In True Triaxial Testing of Rocks, 89–98. CRC Press, 2012. http://dx.doi.org/10.1201/b12705-9.
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Ma, Xiaodong, Bezalel C. Haimson, and John W. Rudnicki. "True triaxial failure stress and failure plane of two porous sandstones subjected to two distinct loading paths." In Porous Rock Fracture Mechanics, 285–307. Elsevier, 2017. http://dx.doi.org/10.1016/b978-0-08-100781-5.00013-0.
Повний текст джерелаТези доповідей конференцій з теми "True-triaxial loading"
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Zhu, X., M. Serati, E. Mutaz, and Z. Chen. "True Triaxial Testing of Anisotropic Solids." In 56th U.S. Rock Mechanics/Geomechanics Symposium. ARMA, 2022. http://dx.doi.org/10.56952/arma-2022-2125.
Повний текст джерелаАнотація:
ABSTRACT: Accurate determination of rock mechanical properties (particularly sedimentary shales, mica and schists with foliation and bedding planes) is critical to the safe design and excavation of underground mines and tunnels. Traditional techniques to calculate rock elastic properties often involve testing cylindrical or disc-shaped specimens under uniaxial compression or diametrical loading. But, these stress conditions may not represent the actual stress state under which rock is subjected at depth. A true triaxial testing technique on cubed specimens are, therefore, preferred as it better represents field stress conditions. This paper introduces and verifies a modified step-compression true-triaxial based technique to measure the elastic constants in fibre-reinforced epoxy samples, selected as a low-porosity anisotropic solid. The elastic constants obtained from the proposed method (even under higher stress levels) are found to be in good agreement with results from the benchmark tests with uniaxial compression but in the meanwhile offers other anisotropic parameters, which cannot be obtained from conventional measurements. 1. INTRODUCTION Accurate determination of rock directional elastic properties has always been a hot topic in rock mechanics with immediate applications in most geotechnical and mining engineering (Eberli et al., 2003). While rock is frequently treated as a CHILE (continuous, homogeneous, isotropic, and linearly elastic) medium, this assumption provides only limited insight into the true rock mass deformations (Chou & Chen, 2008; Serati, Alehossein, & Williams, 2016). A more practical rock behavior is therefore the consideration of rock anisotropy, since many rocks exposed near the Earth’s surface show various levels of directionally dependent properties due to bedding, stratification, foliation, fissuring, schistosity, jointing, and faulting (Amadei, 1996). In the stress-strain relationship study for a loaded rock sample, rock behavior can be generally classified into four categories: isotropic, transversely isotropic, orthotropic, and anisotropic. The number of elastic constants to represent the stress-strain relation of a complete anisotropic rock is 21. However, due to the elastic symmetry of three isotropic planes, the number of stiffness constants of an orthotropic material can be reduced to nine (9) constants only. It can be further reduced to five elastic parameters for a transversely isotropic material (E1, E2, ν1, ν2, and G2) and two (namely the Poisson’s ratio and Young’s modulus) for a perfectly isotropic material, where the subscripts "1" and "2" refer to in-plane and out-of-plane directions in transversely isotropic materials (Ding et al., 2006).
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Akdag, Selahattin, Murat Karakus, Giang Nguyen, and Abbas Taheri. "Influence of specimen dimensions on bursting behaviour of rocks under true triaxial loading condition." In Eighth International Conference on Deep and High Stress Mining. Australian Centre for Geomechanics, Perth, 2017. http://dx.doi.org/10.36487/acg_rep/1704_32_akdag.
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Li, Jiaying, Chunyan Qi, Ye Gu, Yu Ye, and Jie Zhao. "Experiment on Mechanical Properties and Seepage Capability of Deep Tight Sandstone Under True-Triaxial Stresses Environment." In Abu Dhabi International Petroleum Exhibition & Conference. SPE, 2021. http://dx.doi.org/10.2118/208082-ms.
Повний текст джерелаАнотація:
Abstract The characteristics of seepage capability and rock strain during reservoir depletion are important for reservoir recovery, which would significantly influence production strategy optimization. The Cretaceous deep natural gas reservoirs in Keshen Gasfield in Tarim Basin are mainly buried over 5000 m, featuring with ultra-low permeability, developed natural fractures and complex in-situ stress states. However, there is no comprehensive study on the variation of mechanical properties and seepage capability of this gas reservoir under in-situ stress conditions and most studies on stress-sensitivity are conducted under conventional triaxial or uniaxial stress conditions, which cannot truly represent in-situ stress environment. In this work, Cretaceous tight sandstone in Keshen Gasfield was tested under true-triaxial stresses conditions by an advanced geophysical imaging true-triaxial testing system to study the stress-sensitivity and anisotropy of rock stress-strain behavior, porosity and permeability. Four groups of sandstone samples are prepared as the size of 80mm×80mm×80mm, three of which are artificially fractured with different angle (0°,15°，30°) to simulate hydraulic fracturing. The test results corresponding to different samples are compared to further reveal the influence of the fracture angle on rock mechanical properties and seepage capability. The samples are in elastic strain during reservoir depletion, showing an apparent correlation with fracture angles. The porosity decreases linearly with stress loading, where the decrease rate of effective porosity of fracture samples is significantly higher than that of intact samples. The permeabilities decrease exponentially and show significant anisotropy in different principal stress directions, especially in σH direction. The mechanical properties and seepage capability of deep tight sandstone are successfully tested under true-triaxial stresses conditions in this work, which reveals the stress-sensitivity of anisotropic permeability, porosity and stress-strain behavior during gas production. The testing results proposed in this paper provides an innovative method to analyse rock mechanical and petrophysical properties and has profound significance on exploration and development of tight gas reservoir.
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Silva, C. H. C., F. O. Porras Ortiz, D. Fratta, and E. J. Macari. "Mechanical Response of Unsaturated Particulate Materials: A Stiffness Assessment Study Under Controlled Matric Suction." In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-39366.
Повний текст джерелаАнотація:
This paper describes issues related to stiffness of unsaturated particulate materials including the effects of time-varying processes during the formation and disruption of the menisci during loading and their effect in the matric suction. The phenomena are studied using a true triaxial device with matric suction control and equipped with bender elements for shear-wave velocity measurements. Evidence shows that the low-strain and high-strain stiffness of the particulate media are stress- and suction-controlled. However at high strains the stiffness that results from the effect of matric suction is lost and its re-stiffening rate depends on the moisture content.
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Chen, Yufei, Changbao Jiang, Guangzhi Yin, Andrew K. Wojtanowicz, and Dongming Zhang. "Triaxial Testing of Gas Shale Permeability Dependence on Heterogeneous Stress With Respect to Bedding." In ASME 2019 38th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/omae2019-96707.
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Abstract Shale gas has recently become the most promising source of unconventional hydrocarbon energy. Shale gas well deliverability and economics depend on extremely low permeability that is not only dependent on the rock bedding trend but is also controlled by in-situ stresses. Thus, prediction of well’s deliverability requires understanding permeability of a dipping shale with natural bedding under conditions of unequal stresses in-situ. The purpose of this study was to determine relative contributions of normal and tangential stresses with respect to the rock bedding plane on permeability evolution of Longmaxi shale in the Sichuan Basin, southwest China. The study involved an analysis of the rock bedding structure, followed with triaxial testing of rock samples and theoretical modeling. We used SEM observation to identify existence of microfractures and numerous inter-particle pores along the shale bedding planes that provide dominant pathways for gas flow depending upon closing stress value. Stress-dependent permeability was tested with a newly-developed multi-functional true triaxial geophysical (TTG) apparatus providing for a steady state gas flow through the rock sample under conditions of normal stress and two unequal tangential stresses. Also simulated were the effects of stress-bedding and load cycling. The results showed shale permeability reduction during the stress loading process and its gradual recovery during the unloading process for both normal and tangential stress loading cycles. A hysteresis of the permeability response to cyclic loading was the largest when normal stress cycling was dominant. Moreover, permeability change was more pronounced in response to normal stress but some effects of the tangential stresses were also observed — particularly when the tangential stresses were dominant. A theoretical model was derived to describe permeability change with effective stress in the presence of normal and tangential stresses. The model was empirically matched with the experimental results. Assessment of relative contributions of normal and tangential stresses was quantified with the analysis of variance (ANOVA). The analysis revealed significance levels of normal stress, and two tangential stresses σt1 and σt2 on shale permeability as 81%, 5% and 14%, respectively, showing dominant effect of normal stress with clear contribution of tangential stresses. An almost 20-percent contribution of tangential stress loading to permeability response indicates a need for improvement in computing effective stress in permeability predictions of the Longmaxi shale. It also warrants testing other gas shales to specifically determine the effect.
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Rohrman, A. K., and C. L. Ho. "Laboratory Evaluation of Naturally Abraded Ballast Behavior and Properties." In 2018 Joint Rail Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/jrc2018-6206.
Повний текст джерелаАнотація:
Laboratory tests are commonly used to investigate the performance and behavior of ballast in various conditions. In large part, these investigations use freshly quarried rock prepared to meet gradation requirements of AREMA or similar organizations as the ballast material. When worn ballast is desired, some studies run the fresh ballast through an apparatus, such as the one used in LA Abrasion, to create an artificially worn ballast. Past investigations of the effects of angularity on the strength properties of granular materials provide mixed results. There is a clear need for further understanding of the behavior of abraded ballast. In this investigation, a naturally abraded ballast, sourced from an active rail, is used in laboratory testing to assess its mechanical properties and behavior. Based on gradation testing, this material was most likely an AREMA #4 graded material when it was first placed into the track bed. However, particle breakage that occurred during the time that it was used in track led to a broader gradation that included smaller ballast pieces. Triaxial testing was performed to determine the strength properties, stress-strain behavior, and volumetric strain behavior of clean ballast in varying moisture conditions. Box testing was used to investigate the settlement of the ballast under dynamic loading. The ballast in the box test was prepared to the same density as the triaxial tests so that the results are analogous. The results of the triaxial tests exhibited typical behavior, with the samples undergoing initial contraction followed by dilation. However, the results showed that the deformations were larger than might be expected from a similar angular ballast. Additionally, strengths do not appear to be significantly reduced compared to angular ballast. The box tests also showed typical results, though less total settlement occurred than might be expected. The unexpected results from these tests could be explained by the broader gradation of the abraded ballast. It has been shown that a wider range of particle sizes in a granular material increases the strength. It is likely that this holds true for this particular ballast, despite the increased level of abrasion. However, the more rounded particles are still less likely to interlock, resulting in the high deformations exhibited in the triaxial tests. The introduction of water to the tests does not have hugely negative effects on the strength, likely because the lack of fouling prevents large amounts of water from being held by the ballast. Abraded ballast appears to achieve the desired strengths needed for support railroad loads, however the increased deformability of the material makes it less than ideal for use in track.
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Baxter, Carl, Andrew Sherry, David O’Gara, and David Beardsmore. "Strain Limits for High Strength Riser Materials." In ASME 2004 23rd International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2004. http://dx.doi.org/10.1115/omae2004-51332.
Повний текст джерелаАнотація:
High strength materials are being used to increase the capability of dynamic risers to withstand deep water and high pressure flows. Design codes generally require that these materials operate well within their ultimate capability in the main body of the riser, but components of the riser such as screwed connectors and flanges often experience high localized or secondary stresses above yield. These stresses are allowable because they are self-limiting or in strain controlled situations. In addition the main body of the riser may also exceed yield in survival conditions when the riser may be allowed to undergo permanent distortion, but not fracture. However, high strength materials often exhibit lower ductility than traditional steels and as a result, there is a need to understand how these materials behave under high multiaxial stress conditions in order to quantify the true margin of safety in the component. The work reported in this paper focuses on titanium Grade 29, which has been used for tapered stress joints on steel catenary risers, and is now being considered for use in the riser touch down zone on several deepwater projects. The work on burst testing was also part of the validation of Dn V-RP-201, “Design of Titanium Risers”. This paper explores two approaches to determining a material model for failure. The first method used the Rice and Tracy void fraction model but this was found to be geometry dependent for this material and not ideal for failure prediction. A method was developed for determining strain limits under triaxial loading conditions using diffuse necking theory. The theory was applied to burst tests of high-pressure cylinders and gave a good prediction of the burst pressure and strain at failure.
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Dawson, Jane, Martin Bluck, Ian Fisher, and Jeff Sutherland. "Holistic Data Approach and Results: How the Latest Enhancements in ILI Technology Benefit Engineering Criticality Assessments." In 2010 8th International Pipeline Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ipc2010-31284.
Повний текст джерелаАнотація:
Recent enhancements in the Magnetic Flux Leakage (MFL) in-line inspection (ILI) technology has enabled more reliable detection and more accurate reporting of a greater range of anomaly types than ever before, though the true value rests with what the integrity engineering specialists are able to do with the enhanced information to translate it into an actionable Integrity Management Plan. This paper describes how the enhanced information can be used in engineering criticality assessments and the benefits this brings to the operator in the form of integrity management decision-making with higher confidence, reduced investigation and repair costs and less operational disruption from ILI activity. This paper demonstrates how the new holistic data approach brings a seamless transition from raw inspection data to an actionable integrity report, with more advanced assessment of metal loss and mechanical damage data. Engineering criticality assessments are used to illustrate how the enhanced ILI information is used and how the results benefit integrity management decision-making. For example: • Fitness for Service corrosion assessment determines the immediate and future integrity needs by evaluating the criticality of corrosion anomalies identified during an ILI. Taking account of the reduced ILI uncertainty associated with the new MFL technology, the immediate and short-term response schedules can be developed with higher confidence than before and long term remediation activities and re-inspection intervals can be truly optimized. • For re-inspections, the focus is on the determination of accurate corrosion growth rates. Using signal-matching techniques, active corrosion sites can be identified and the corrosion growth rates estimated with high confidence. This provides the basis for optimizing the long-term remediation activities and re-inspection intervals. • The ability to account for coincidental anomalies and loading conditions, e.g., the occurrence of bending strains resulting from loss of ground support coincident with girth weld anomalies, circumferential corrosion or denting/buckling are important integrity considerations that influence how the anomalies are assessed. • Improved Caliper sensor resolution enables the dent profile to be visualized more accurately leading to improvements in the way dents are assessed, i.e. using strain-based methods. Reliable detection of gouging within dents is an essential component for establishing the cause and assessing the severity of dents and has always been challenging for conventional MFL ILI tools. This enhanced MFL technology enables metal loss within dents to be detected and viewed via a Triaxial magnetic sensor system, providing more information of the nature of the metal loss within the dent.
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Donato, Gustavo Henrique B., and Grace Kelly Q. Ganharul. "Methodology for the Experimental Assessment of True Stress-Strain Curves After Necking Employing Cylindrical Tensile Specimens: Experiments and Parameters Calibration." In ASME 2013 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/pvp2013-97993.
Повний текст джерелаАнотація:
Simulations and structural integrity evaluations including severe plasticity have undergone significant expansion during recent years (e.g. fracture mechanics FE models including ductile tearing and/or generalized yielding), which demand accurate true stress-strain data until fracture. This is a consequence of the use of high toughness ductile materials subjected to severe loadings and high levels of operational efficiency and optimization. However, tensile tests present one inconvenience when providing such data, since the occurrence of plastic instability (necking) complicates the direct assessment of true stress-strain curves until final fracture. Two main difficulties can be pointed out: i) the nonuniform geometry assumed by the cross sections along its length and; ii) the imposition of a complex triaxial stress state. The first occurrence can only be overcome by real-time physical measurements. The second occurrence demands a correction model to provide an equivalent stress including triaxial effects. Current authors recently demonstrated that even the well-known Bridgman’s correction presents limitations, particularly for strains greater than ∼ 0.50–0.60, which motivated proposals to better describe the geometrical evolution of necking minimizing the need for real-time physical measurements [1]. As a new step in this direction, this work presents three key contributions: i) first, experiments regarding the geometrical evolution of necking were largely extended incorporating 10 materials to corroborate the validity of the recently proposed model (including Carbon, stainless steels and copper); ii) second, and for the same materials, the necking region was investigated in more details to verify to which extent an osculating circle well describes the high deformation region. A new model could be proposed to better support future solid mechanics analyses regarding equilibrium and stress/strain fields; iii) finally, a modified Bridgman’s model is proposed, followed by recommended practices for testing. The results provide further support to σ-ε assessment considering severe plasticity and demanding less physical measurements.