Complete Deformation Process Research Articles

Technique for studying in high resolution poromechanical deformation of a rocklike medium.

Pressurized fluid injection into underground rocks occurs in applications like carbon sequestration, hydraulic fracturing, and wastewater disposal and may lead to human-induced earthquakes and surface uplift. The fluid injection raises the pore pressure within the porous rocks, while deforming them, yet this coupling is rarely captured by experiments. Moreover, experimental studies of rocks are usually limited to postmortem inspection and cannot capture the complete deformation process in time and space. In this Letter we will present a unique experimental system that can capture the spatial distribution of poromechanical effects in real time by using an artificial rocklike transparent medium mimicking the deformation of sandstone. We will demonstrate the system abilities through a fluid injection experiment, showing the nonuniform poroelastic expansion of the medium and the corresponding poroelastic model that captures completely the results without any fitting parameters. Moreover, our results demonstrate and validate the underlying assumptions of the poroelastic theory for fluid injection in rocklike materials, which are relevant for understanding human-induced earthquakes and injection induced surface uplift.

A numerical study on rotational stiffness characteristics of the disk lock joint

Rotational stiffness characteristics of the disk lock joint have a significant effect on the load bearing capacity and stability of disk lock scaffolds. However, experimental researches on scaffold joints are usually expensive and time consuming, especially when different joint connection configurations and loading modes are involved. This paper explores the feasibility and effectiveness of the 3D nonlinear finite element analysis method for studying the rotational stiffness characteristics of the disk lock joint. Detailed geometric models of the disk lock joints are established and the geometric models are meshed with finite elements. The elastoplastic constitutive model based on the isotropic hardening law and the associated flow rule is used to describe the complete deformation process of the material, and the penalty stiffness method is applied to accurately simulate the interaction between different components. Thus the complete finite element models of the disk lock joints are established. Firstly, the loading processes of the one-way disk lock joint are simulated and verified by experiments. To further demonstrate the robustness and effectiveness of the finite element method, the loading processes of disk lock joints under different connection configurations and loading modes are simulated. The influences of connection configurations and loading modes on joint rotational stiffness are also investigated to reveal the load bearing mechanism of the disk lock joint, and thereby contribute to better predictions of the load bearing capacity of the disk lock scaffolds.

ФІЗИЧНІ ПЕРЕДУМОВИ МОДЕЛЮВАННЯ ГАЗОВОЇ ПРОНИКНОСТІ ПІДРОБЛЕНОГО ВУГЛЕПОРОДНОГО МАСИВУ

Purpose. Justification of the gas collectors formation physical model on the basis of research of conformity of permeability of rock mass to the full diagram of rock sample deformation. Methodology consists in sequential analysis of the stages of the complete deformation diagram of the rock specimen under “hard” loading, comparing them with the stages of formation of the high stress zone in front of the lava bottom and statistical analysis of laboratory test results. Results. Based on the rock’s deformation properties analysis and their comparison with the rock sample full deformation diagram, the physical model of formation of gas reservoirs during the development of gas-saturated coal seam is substantiated. Within the solved problem framework, four stages of the complete deformation process are analyzed, namely: elastic, at the limit of strength, out-of-bounds stage and equivoluminal flow zone. The gas collector boundaries, which are the characteristic points of the rock sample deformation diagram in specified deformations mode (the limit of elastic strength and the limit of final strength) are determined. It is proved that the structural and textural features of the coal mass in connection with the course of gas-dynamic processes are manifested in the change in the pores and cracks volume contained in it, which together make the filtration space. Knowledge regarding the transfer of the permeability changes established regularities and free methane accumulation zones formation to the real rock mass, if the process of its forgery is considered as a consistent change of geomechanical states of rocks, is obtained. Scientific novelty lies in the first substantiated possibility of modeling the stress state before the longwall face by equivalent stages of the rock sample destruction in the given deformations mode. Gradual comparative analysis of the internal mechanism of rock samples deformation along the complete deformation diagram allowed establishing causal relationships between geomechanical and gas-dynamic processes in coal mass, and qualitatively characterizing general trends in permeability and volumetric expansion in changes of these samples. Practical value of the work lies in the justification of the principle of construction of a digital geomechanical model for the detection of man-made gas collectors in a mined coal mass.

Extrusion of Al-Si alloy compacts under conventional conditions and in the semi-solid state

.In this research work the results of hot extrusion process of aluminium alloy compacts conducted at the temperature of conventional hot extrusion as well as at the temperature range corresponding to the semi-solid state were presented. Initial material was prepared by uniaxial pressing of Al17Si5Fe3Cu1.1Mg0.6Zr alloy powder. The extrusion process was carried out under isothermal conditions, and the temperature stability was strictly controlled. The changes of extrusion force in relation to punch displacement were recorded during hot deformation to demonstrate the effects associated with the appearance of the liquid phase in the volume of the processed material. After extrusion the samples were cooled in water as well as at room temperature. The influence of temperature of extrusion and the resulting fraction of the liquid phase in the processed material on its microstructure and chosen mechanical properties were determined. Mechanical properties of the examined alloy after deformation were carried out by measuring the hardness and in uniaxial compression tests. Additionally, one of the compacts was remelted and cast, what made possible comparison of the microstructure and chosen properties of the obtained products. In the result of the investigations it has been proved, that extrusion in semi-sold state results in reduction of forces necessary to complete deformation process and leads to obtaining the material with good mechanical properties and fine-grained, favourable microstructure.

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

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.

Coupling between the statistical damage model and permeability variation in reservoir sandstone: Theoretical analysis and verification

Reservoir sandstone contains pre-existing weaknesses, and its fluid flow properties may be altered when subjected to mechanical loading. Simulation of the complete deformation process of reservoir sandstone and its fluid transportation is important in the fields of rock mechanics and gas production. Based on the statistical damage theory with consideration of void volume changes and fluid pressure, a new constitutive model was developed to describe the mechanical characteristics of saturated porous media in geo-materials. On the basis of the Weibull distribution for rock micro-strength, the damage variable was defined and a semi-analytical permeability variation model was established. Experimental results demonstrated that the theoretical model was in good agreement with the test data during rock deformation, and the permeability variation is a function of the stress-induced damage. Furthermore, the applicability of the rock failure criterion based on the Drucker-Prager criterion and the energy release principle is discussed. Visible influences of void volume change and fluid pressure in the damage variable calculation were also detected.

Mechanical behavior and permeability evolution of gas infiltrated coals during protective layer mining

This study investigated the stress–strain–permeability relationship of a Chongqing coal under the stress path during the mining process. The abutment stress was first measured at the longwall (LW) face 3211 of Songzao Mine in Chongqing, China. The field monitoring results revealed that the concentration coefficient of the abutment stress was approximately 1.5–2.0 during protective layer mining. Then, triaxial compression tests for the gas-infiltrated coals were conducted under the above stress path and different gas pressures. These tests, with the simultaneous actions of unloading confining stress and loading axial stress, are called SUL tests. The triaxial compression tests revealed that the peak deviatoric stress and the corresponding strain of coal under SUL tests were lower than those under conventional triaxial compression (CTC) tests. Poisson's ratio was higher, but the elastic modulus was lower in SUL tests. The permeability evolution of coal under the SUL tests underwent four distinct stages: the increasing stage in the process of SUL, decreasing stage, slowly increasing stage beyond the yield point, and sharply increasing stage after the peak stress. With the increased gas pressure, the peak deviatoric stress and corresponding axial strain decreased, Poisson's ratio increased, and elastic modulus decreased. Further, the permeability of coal increased with increasing gas pressure in the complete deformation process.

Behavior of Sway Two-Bay, Two-Story Composite Steel Frames in Fire

The experimental results of three full-scale two-story, two-bay, composite steel frames under furnace loading are described briefly. During tests, the composite beams and steel columns were exposed to fire, and only the beam-to-column connections of the tested frames were protected. The furnace temperature, composite steel beam temperature, steel column temperature, horizontal displacements of the columns, and vertical deflections of the composite beams as well as the complete deformation process of the test frames observed during the heating phase and the cooling phase are given. By introducing the slope-deflection equations and joint equilibrium conditions at each joint, the critical temperatures of the buckling of two-story, two-bay, composite steel frames are determined for different furnace scenarios; therefore, this method can consider the effect of the axial force at different levels. The calculated critical temperatures agree well with the experimental results.

A Constitutive Model of Rocks under Uniaxial Tension

A constitutive model is proposed to simulate the completely deformation process of rocks under uniaxial tension. Based on the revised elastic modulus method derived from the hypothesis of strain equivalence, we analyzed the relationship between the damage variable and the strain. It is found that the relation can be modeled using a sigmoid curve. This model can describe the complete deformation process of rocks under uniaxial tension satisfactorily. In particular, the nonlinearity near the peak in the pre-peak region is accurately captured by the proposed constitutive model. The rapid decrease of rock strength after peak load can also be captured satisfactorily. The used mathematical function is simple and the damage evolution process is clear. The validity of the model is verified using laboratory test data.

Elastoplastic model for discontinuous shear deformation of deep rock mass

Deep rock mass possesses some unusual properties due to high earth stress, which further result in new problems that have not been well understood and explained up to date. In order to investigate the deformation mechanism, the complete deformation process of deep rock mass, with a great emphasis on local shear deformation stage, was analyzed in detail. The quasi continuous shear deformation of the deep rock mass is described by a combination of smooth functions: the averaged distribution of the original deformation field, and the local discontinuities along the slip lines. Hence, an elasto-plastic model is established for the shear deformation process, in which the rotational displacement is taken into account as well as the translational component. Numerical analysis method was developed for case study. Deformation process of a tunnel under high earth stress was investigated for verification.

Nonlinear elastic-perfect plastic constitutive model of soil-structure interface under high stress

Briefly introduced the simple shear apparatus under high stress that was developed from RMT. A series simple shear tests under high stress show that the relation curve between shear stress and tangential displacement under high normal stress is different from the hyperbolic curve in direct shear tests, and the complete deformation process of interface under high stress can be described as nonlinear elastic-perfect plastic(NEPP). According to some characteristics of the fitting curve, the deficiency of the NEPP was pointed out. The mathematic “half value index” was used to illustrate that Weibull distribution with three parameters (WNEPP) can overcome the mathematical deficiencies of the NEPP. The advantage of the WNEPP is that the fitting curve of WNEPP more accurately coincided with the testing data was testified by further comparison.

Experimental Study on the Behavior of Full-Scale Composite Steel Frames under Furnace Loading

In current design codes, structural fire behavior is evaluated by conducting experiments on isolated structural elements in a standard fire condition. In such tests involving single isolated elements, many aspects of structural behavior that occur due to the interaction between adjacent members as well as the role of connections cannot be studied. Performance of real structures subject to fires is often much better than that predicted from standard tests due to structural continuity and the interaction between members. In addition, tests performed under the current design codes subject the structural element to a heat up phase only and do not consider the cool-down phase during which local/global failure of the structure may occur. This paper describes the results of a furnace test conducted on two full-scale composite steel frames. In one frame the beam-to-column connections were protected while in the second frame the columns as well as the beam-to-column connections were protected. A special test furnace was built in which full-scale frames could be tested under load. The structural frame was subjected to a heat up phase followed by a cool-down phase. During the test, the furnace temperature, steel and concrete temperatures as well as the horizontal and vertical deflections were recorded. The complete deformation process of the test frame observed during the heating phase and the cooling phase, including failure of the frame is described in this paper. A comparison of the data obtained from the two tests indicates that the fire resistance of a composite beam is significantly better than that of a steel column. Finally, experimental data on fire resistance of composite frames with conventional floor slab construction was compared with data from slim floor slab construction. Results indicate that the fire resistance rating of frames constructed with slim floor slabs is at least as good as that of frames with conventional floor slab construction. It is proposed that in certain engineering design scenarios, the composite beam may not have to be protected due to its higher fire resistance rating, while the steel column should be protected from fire heating.

Numerical simulation of rock fracturing under uniaxial compression using virtual internal bond model

A multi-scale virtual internal bond (VIB) model for the isotropic materials has been recently proposed to describe the material deformation and fracturing. During the simulation process of material fracturing using VIB, the fracture criterion is directly built into the constitutive formulation of the material using the cohesive force law. Enlightened by the similarity of the damage constitutive model of rock under uniaxial compression and the cohesive force law of VIB, a VIB density function of rock under uniaxial compression is suggested. The elastic modulus tensor is formulated on the basis of the density function. Thus the complete deformation process of rock under the uniaxial compression is simulated.

Behavior of Full-scale Frames with Slim Floor Slab Construction under Exposure in a Fire Resistance Furnace

In recent years, there has been increasing interest in developing and designing slim floor systems in steel-framed buildings. This article describes the results of a furnace test conducted on two full-scale composite steel frames with slim floor slab construction to understand their performance under fire loading. In one frame, the beam-to-column connections were protected, while in the second frame, the columns as well as the beam-to-column connections were protected. During the test, the furnace temperature, the steel and concrete temperature, as well as the horizontal and vertical displacements were recorded. The complete deformation process of the test frame observed during the heating phase and the cooling phase, including failure of the frame, is described in this article. A comparison of the data obtained from the two tests indicates that the fire resistance of a composite beam is significantly better than that of a steel column. Fire resistance of composite frames with slim floor slabs is compared with data on a conventional floor slab. Results indicate that the fire resistance rating of frames constructed with slim floor slabs is at least as good as that of frames with conventional floor slab construction.

Thermal and structural response of two-storey two-bay composite steel frames under furnace loading

The collapse of the World Trade Center Towers and other recent fires in tall buildings has motivated this study to understand the performance of structural frames under fire loading. Three two-storey, two-bay composite steel frames were constructed and subjected to dead loads by applying weight blocks, and to thermal load by placing the frame in a furnace. The furnace was specially designed to allow for controlled heating of the structural elements that formed the four compartments of the test frame. This paper describes the experimental results of furnace test conducted on the three full-scale composite frames. The three tests differed from each other in the number and location of compartments that were heated by the furnace. For each test, the structural elements were subjected to a heating-up phase followed by a cooling-down phase. The furnace temperatures and the steel and concrete temperatures recorded during the test are presented. The thermally induced horizontal displacements of the columns and vertical deflections of the composite beams are discussed. Observations on local buckling of the steel beam, cracking of the concrete slab and failure of the beam-to-column connections are tabulated. Experimental results of the three tests are compared with each other by studying the complete deformation process of the test frames over time. Results indicate that the deformation process of the test frames was highly dependent on the number and location of compartments that were subjected to thermal loading.

Thermal and structural response of a two-story, two bay composite steel frame under fire loading

The collapse of the World Trade Center Towers and other recent fires in tall buildings has motivated a study to understand the performance of structural frames under fire loading. A two-storey, two-bay composite steel frame was constructed and was subjected to dead loads using load blocks, and to thermal load by placing the frame in a furnace. The furnace was specially designed to allow for controlled heating of the structural elements that form the various compartments of the test frame. This paper describes the experimental results of a furnace test conducted on three full-scale composite frames. The three tests differed from each other in the number of compartments that were heated by the furnace and in the relative location of the heated compartments. For each test, the structural elements were subjected to a heat-up phase followed by a cool-down phase. The furnace temperatures as well as the steel and the concrete temperatures recorded during the test are discussed. The thermally induced horizontal displacements and vertical deflections of the various structural elements are presented. Observations on local buckling of the steel beam, cracking of the concrete slab and failure of the beam-to-column connection are tabulated. Experimental results of the three tests are compared and contrasted by studying the complete deformation process of the test frames over time. Results indicate that the deformation process and time to failure of a structure is highly dependent on the number of compartments that are heated and the relative location of the compartments that are subjected to fire loading.

Finite-element analysis of indentation experiments in surface-coated materials

There are only a few methods suitable for a quantitative characterization of the mechanical properties of surface-coated materials; indentation testing is one of those methods. Within the last decade, a great deal of effort has been made to improve the indentation test and to gather information on the complete deformation process from experimental and numerical investigations. Following this line, this contribution concentrates on the numerical calculation of the elastic-plastic field of deformation in the specimen during the indentation process and the corresponding load-depth of indentation curves in dependence on the dominating parameters. The basic idea is to determine the influence of geometrical imperfections of the indenter on the—experimentally obtained—mechanical properties such as hardness and to provide methods which enable one to distinguish between properties of the system used for testing and the material investigated. Results obtained for uncoated and coated materials are compared.

Cylindrical bending of metal strips

AbstractCopper, brass, and mild steel strips were deformed under elastic-plastic bending in cylindrical dies by matched cylindrical punches, without the use of any lubrication, to study the history of the enforced deformation. Separation between the punch and the strip, the punch load-displacement relationship, and the elastic springback are described. The deformation model is found to be dominated by the parameter (Y/E) (l/h), where Y is the material yield stress, E its Young's modulus, h the strip thickness, and I the strip length. When the value of this parameter is small, the strip is described as ‘stiff‘, and when it is large, ‘slender‘. The complete deformation process may be divided into several stages, each associated with a number of loading points. The phenomena of multi-point loading and the effects of largest punch load have been successfully incorporated into an explanation of the non-uniformity in final curvature of the strip after springback.