Initial Stress Field Research Articles

Effect of hydrostatic initial stress on a fiber-reinforced thermoelastic medium with fractional derivative heat transfer

Purpose – The purpose of this paper is to investigate the influences of fractional order, hydrostatic initial stress and gravity field on the plane waves in a linearly fiber-reinforced isotropic thermoelastic medium. Design/methodology/approach – The problem has been solved analytically and numerically by using the normal mode analysis. Findings – Numerical results for the temperature, the displacement components and the stress components are presented graphically and analyzed the results. The graphical results indicate that the effect of fractional order, hydrostatic initial stress and gravity field on the plane waves in the fiber-reinforced thermoelastic medium are very pronounced. Comparisons are made with the results in the absence and presence of hydrostatic initial stress and gravity field. Originality/value – In the present work, the authors shall formulate a fiber-reinforced two-dimensional problem under the effect of fractional order, hydrostatic initial stress, and gravity field. The normal mode analysis is used to obtain the exact expression for the temperature, displacement components, and stress components. A comparison is also made between the three theories in the absence and presence of gravity field. Such problems are very important in many dynamical systems.

Simulation Analysis on Tension and Deformation of Composite Soil Nailing

For studying the mechanism of the composite soil nailing, this paper applies FLAC-3D to simulate pure soil nailing, soil nailing-soil anchor, soil nailing-micro pile-soil anchor. The analytical results as follows: (1)Because of the anchoring of the anchor, the axial tension of soil nailing in each row is much smaller than the one in the pure soil nailing supporting, and the tension of soil nailing which are closed to soil anchor decreases obviously. (2)The extrusion action of prestressed anchor makes the potential slip surface backward shifts and the sliding radius increases, which is better for the stability of foundation pit side (3)Micro-pile increases the strength of the soil in a certain range and improves the initial stress field before the excavation. (4)The inner force of the whole soil nailing and the prestress anchor declines but the drop is not large after the establishment of the micro-pile support in advance. (5)Prestressed anchor and micropile play a very important role in controlling the deformation of foundation pit.

Welding Residual Stresses in Tubular Joints

In spite of an increased awareness of welding residual stress threat to structural integrity, the extent of its influence on fatigue especially under multiaxial loading is still unclear and is a matter of debate. One important reason for this lack of clarities is that the determination of the initial welding residual stress field in welded structures even at the fatigue crack initiation sites is difficult and requires complementary instruments. Since the fatigue crack initiation in sound welds almost always occurs on the surface, the determination of surface residual stresses could increase the awareness of the extent of their threat to the structural safety. In this paper the development of residual stresses in different TIG-welded tubular specimens out of S355J2H and S690QL steel is studied and compared. The mechanisms of the development of residual stresses based on heat input and cooling rate are discussed. The welding parameters and thus heat inputs are varied and the mechanisms leading to different residual stress states are investigated. X-ray method was used for residual stress state characterization.

<i>In Situ</i> Stress Measurement and Inversion in Deep Roadway

Jixi mine area is one of the early mined areas in China and it's a typical deep mine. Because of large deformation of underground roadway and dynamic disasters occurred frequently in this mine, five measurement points of in-situ stress in this mine was measured and then analyzed with inversion. Based on these in-situ stress measurement data, numerical model of 3D in-situ stress back analysis was established. According to different stress fields, related analytical samples of neural network were given with FLAC program. Through the determination of hidden layers, hidden nodes and the setting of parameters, the network was optimized and trained. Then according to field measurement of in-situ stress, back analysis of initial stress field was conducted. Compared with field measurement, with accuracy requirement satisfied, it shows that the in-situ stress of rock mass obtained is basically reasonable. Meanwhile, it proves that the measurement of in-situ stress can provide deep mines with effective and rapid means, and also provide reliable data to optimization of deep roadway layout and supporting design.

Numerical Analysis on Minimal Safe Distance between Two Opposite Excavation Faces of Deep-Buried Tunnel

When the distance between two opposite excavation face is too small, the explosive load of one excavation face may causes rock failure of the other excavation face and result in engineering accidents. In this paper, the dynamic response of rock pillar between two opposite excavation faces during one explosive excavation cycle is investigated. An aftereffect function is adopted to reflect the viscoelastic properties of deep rock mass, and the explicit difference scheme of stress field is derived and then implemented by Matlab programs. The transient stress field of rock pillar is computed by coupling the initial stress field and the explosive waves. The analogies between the minimal safe distance and those influence factors such as explosive excavation load, rock mechanical properties, in-situ stresses, are fulfilled by this method. The back analysis results of a real case indicate that the results of presented method agree well with the actual situation.

Reflection of plane waves in an initially stressed perfectly conducting transversely isotropic solid half-space

Reflection of plane waves is studied at a free surface of a perfectly conducting transversely isotropic elastic solid half-space with initial stress. The governing equations are solved to obtain the velocity equation which indicates the existence of two quasi planar waves in the medium. Reflection coefficients and energy ratios for reflected qP and qSV waves are derived and computed numerically for a particular material. Effects of the initial stress and magnetic field are shown graphically on these reflection coefficients and energy ratios.

Propagation of P- and S-waves in initially stressed gravitating half space

The present paper contributes in studying the phase velocities of P- and S-waves in a half space subjected to a compressive initial stress and gravity field. The density and acceleration due to gravity vary quadratically along the depth. The dispersion equation is derived in a closed form. It is shown that the phase velocities depend not only on the initial stress, gravity, and direction of propagation but also on the inhomogeneity parameter associated with the density and acceleration due to gravity. Various particular cases are obtained, and the results match with the classical results. Numerical investigations on the phase velocities of P- and S-waves against the wave number are made for various sets of values of the material parameters, and the results are illustrated graphically. The graphical user interface model is developed to generalize the effect.

Regression analysis of initial stress field around faults based on fault throw by displacement discontinuity method

The back analysis of initial stress is usually based on measured stress values, but the measuring of initial stress demands substantial investment. Therefore, amounts of underground engineering have no measured initial stress data, such as tunneling engineering. Focusing on this problem, a new back analysis method which does not need measured initial stress data is developed. The fault is assumed to be caused by initial load, the displacement discontinuity method (DDM) which considered non-linear fault is adopted to establish a numerical model of the engineering site, and the multivariable regression analysis of the initial stress field around the faults is carried out based on the fault throw. The result shows that the initial stress field around the faults is disturbed significantly, stress concentration appears in the tip zone, the regressive fault throw matches the measured values well, and the regressive initial stress field is reliable.

Welding residual stress behavior under mechanical loading

For an accurate estimation of the fatigue performance of welded joints, not only the initial residual stress field but also its variation under load is decisive. The portion of residual stress which stays stable can shift the load stress range much the same way as the mean stresses do in fatigue loading. The relaxation of residual stresses during fatigue loading however reduces this hazard to the structural health. That is, before considering the influence of residual stresses in fatigue, the effect of fatigue on residual stresses should be understood. In this work, the influence of the quasi-static and cyclic loading on the relaxation of welding residual stresses in small specimens and large components out of different steels namely S235JRG2, S355J2G3, P460NL, S690QL, S960QL, and S1100QL has been investigated experimentally. X-ray diffraction analysis as a reliable method has been used for the determination of residual stress profiles in surface layers. For residual stress analysis in deeper layers, synchrotron and neutron diffraction techniques were applied as complementary methods. A clear recognition of the difference between initial welding residual stresses in small- and large-scale specimens was observed. Tensile residual stresses as high as the yield strength could appear in large-scale welded specimens. That was not the case for small-scale welds due to the low grade of restraint. Nevertheless, in both types of samples, the highest residual stresses were obtained in the weld centerline. At the weld toe which is critical regarding fatigue crack initiation, the magnitude of the residual stresses is lower. Beside of that, it was observed that in the case of relaxation, the first load cycles especially in components out of low-strength steels are decisive. The influence of loading conditions and local mechanical properties on the relaxation of welding residual stresses was investigated based on principles of solid mechanics. The von Mises failure criterion was able to describe the relaxation behavior.

Finite Element Simulation and Analysis of Initial Residual Stress Field for Titanium Alloy Monolithic Component Blank

In this paper, the initial residual stress field for titanium alloy monolithic component blank is simulated and analyzed by applying a sequentially coupled thermal and mechanical procedure based on finite element method. The control equation of heat conduction of annealing process is studied, and the boundary condition and fundamental equations of simulation are given. The research results show that the initial residual stress field for titanium alloy monolithic component blank radiates from the center region to outside, the center region being the maximum value, then decreases gradually, until a minimum value is attained at the corner.

The Dynamic Construction Numerical Analysis of Large-Span Section, Long and Deep-Depth Tunnel

Using finite element principle, the numerical simulation analysis model of the tunnels with large-span, long and deep-depth was established. The killed cells excavated in part as, while supporting part as a unit was reactivated among the simulation analysis. The changing characteristics of the initial stress field, the circular soil excavation and supporting, the core soil excavation, as well as the down step excavation and supporting was simulated analysis during dynamic construction of the tunnel. Those will be provided a scientific basis for the safe construction.

Plane contact problem for a prestressed incompressible elastic layer clamped along the base

The problem of a rigid punch penetration into the upper face of a layer is considered in the case of a homogeneous field of initial stresses. The model of isotropic incompressible nonlinearly elastic material determined by the Mooney potential is used. The case of rigid clamping of the layer along its lower face is considered under the assumption that the additional stresses caused by the penetrating punch are small compared with the initial ones. This assumption allows one to linearize the problem of determining the additional stresses. This problem is then reduced to solving an integral equations of the first kind with a difference kernel which allows one to determine the pressure in the contact region. An asymptotic solution is constructed for large values of the parameter characterizing the relative thickness of the layer. Amodified Multhopp-Kalandiyamethod is also used to obtain a solution for a wider range of the parameter.

Grain boundary modeling using an elasto-plastic theory of dislocation and disclination fields

Using a recent elasto-plastic theory of dislocation and disclination fields, a continuous representation of grain boundaries is introduced. Periodic arrays of wedge disclination dipoles, including those defined in the Disclination Structural Unit Model, are set-up as initial configurations in a dynamic model for symmetric tilt boundaries. These configurations are found to be unstable when the transport of disclinations is allowed. Driven by their self couple-stress field, the motion of disclinations leads to relaxation of the initial elastic curvature and stress fields and to nucleation and transport of relaxation dislocations, until an equilibrium configuration of lower energy is reached. Most of the residual elastic energy of grain boundaries is localized in a non-singular nanometric layer. This energy arises from alternative dilatation and contraction of the lattice around disclinations, and from lattice curvature and shear between disclination dipoles. By virtue of its continuous and dynamic character, the present theory allows modeling absolute misorientations and leads to energy density levels comparable to molecular statics findings.

Analysis on Earthquake Damage Forms and Affecting Factors of Underground Cavern

According to the information about underground damage in earthquake all over the world, it is summarized that earthquake damage is caused by mountain slope failure, the collapse of cavern’s export, dislocation damage of cavern’s cross-section, great displacement along the fault intersection, spalling of surrounding rock, disturbance or deformation of the support and lining system, et. The earthquake damage factors of underground cavern were analyzed by using numerical simulation techniques. It is shown that when the earthquake intensity value is high, or the initial stress field is small, or lining stiffness is high, the underground will more easily be destroyed by earthquake. Compared with the square tunnel and horseshoe-shaped tunnel, dynamic stability of circular tunnel is better. The export of cavern is vulnerable to earthquake damage.

Propagation of Rayleigh waves in a rotating orthotropic material elastic half-space under initial stress and gravity

This paper aims to investigate the influence of rotation, initial stress and gravity field on the propagation of Rayleigh waves in a homogeneous orthotropic elastic medium. The government equations and Lame’s potentials are used to obtain the frequency equation which determines the velocity of Rayleigh waves, including rotation, initial stress and gravity field, in a homogeneous, orthotropic elastic medium has been investigated. The numerical results analyzing the frequency equation are discussed and presented graphically. It is important to note that the Rayleigh wave velocity in an orthotropic elastic medium increases a considerable amount in comparison to the Rayleigh wave velocity in an isotropic material. The results indicate that the effects of rotation, initial stress and gravity field on Rayleigh wave velocity are very pronounced.

Structural rigidity optimization with an initial design dependent stress field. Application to thermo-elastic stress loads

This paper presents a compliance optimization methodology considering an initial stress field. Assuming a local dependency of the initial stress with the optimization parameters, the obtained numerical procedure is composed of finite element stress calculations and local minimization problems that are solved analytically or using a simple bisection procedure. This optimization algorithm is then found to be numerically very efficient. Two optimization problems that fall in the scope of the proposed methodology are considered: topology optimization of the isotropic mixture of two isotropic linear elastic materials (one of the material possibly being void) and orientational optimization (i.e. distribution of anisotropy) with an orthotropic linear elastic material. Numerical examples illustrating the optimization methodology in the case of thermo-elastic stress loads are presented.

Effects of large historical earthquakes, viscous relaxation, and tectonic loading on the 2008 Wenchuan earthquake

The 2008 Wenchuan earthquake (M7.9) occurred on the Longmenshan Fault in Sichuan, China. Both the seismicity and slip rate of the fault are lower than those of other faults in the region. By incorporating large earthquakes in the region during the past 222 years into our investigation, the effects of historical earthquakes, viscous relaxation, and tectonic loading on the Wenchuan earthquake were studied, using a quasi‐static, finite element model. In this model, we first simulated an initial stress field constrained by fault slip rates obtained by GPS and geologic observations in the region. We then simulated earthquakes by fault softening. The results show that tectonic loading has the most significant effect on the Longmenshan Fault, whereas viscous relaxation of the lower crust and upper mantle has the least effect. The effects of the historical earthquakes are variable; some promote the earthquake potential and others retard the earthquake potential.

Propagation of Rayleigh waves in magneto-thermo-elastic half-space of a homogeneous orthotropic material under the effect of rotation, initial stress and gravity field

The propagation of magneto-thermoelastic plane waves in an initially stressed, homogeneous orthotropic, conducting half-space under a magnetic field, rotation and gravity field have been investigated. The generalized theory of thermoelasticity is employed, by assuming the mechanical behavior as dynamic, to study the problem. The Lame’s potential is used to obtain the frequency equation that determines the velocity of Rayleigh waves that obtained as a real part and the attenuation coefficient as an imaginary part under the rotation, magnetic field, initial stress and gravity field. Numerical results have been given and illustrated graphically for each case considered. Dispersion curves of wave propagation are represented graphically in different theories of thermoelasticity. The results indicate that the effect of rotation, initial stress and gravity field are very pronounced. Comparison is made with the results predicted by the theory of thermoelasticity in the absence of rotation, initial stress and gravity field.

On the problem of radial vibrations in non-homogeneity isotropic cylinder under influence of initial stress and magnetic field

In the present work, the effects of initial stress, magnetic field and non-homogeneity on wave propagation of free harmonic waves in isotropic material are discussed. The one-dimensional equation of elastodynamic is solved in terms of radial displacement and different cases of the boundary conditions for the hollow cylinder are considered. The determination is concerned with the eigenvalues of the natural frequencies of the radial vibrations for different boundary conditions in the case of harmonic vibrations. Numerical results are given and illustrated graphically for each case considered. Comparisons are made with the results in the absence of initial stress, magnetic field and non-homogeneity.

Back-Analysis on Initial Ground Stress of Underground Workshop Region of Shenzhen Pumped Storage Power Station

Abstract. This article based on the underground workshop region of the Shenzhen pumped storage power station, carrying on back-analysis for the initial geostress field of the region of station with method of this article, and then we can obtained the actual initial ground stress.This article based on the measured ground stress data, a 3D non-linear finite element back analysis numerical model for ground stress is set up and the landforms is simulated. This thesis has used ANSYS to do finite element calculation for rocks and soils, the corresponding sample of neural network have been gained. By setting the parameters, the neural network is optimized, then the network is trained with the optimized result. Finally, the initial ground stress field is back-analyzed with in-situ measured stress values. The result is compared with measured value, which meets the requirement for accuracy, showing the reasonabilily of the rock ground stress field obtained.