Stress In Axial Direction Research Articles

Stress Regimes and Stress Fields Analysis Using Fault-Slip Data; Eastern Iran

In this paper direction of stress tensors and stress ellipsoids shape in Neogene, Paleogene, and older units were investigated. Moreover, relationship between shape of stress ellipsoid and exhumation of igneous units were determined using analysis of stress tensors. Analysis of relationships between stress regime and uplifting indicate that in the areas we observed the uplifting of the igneous units the shape of stress ellipsoid has been displaced locally from prolate to oblate which is due to local change of stress regime. Hence, local variation of stress regime in the eastern part of Shekarab Mountains caused boarder outcrops of igneous units. In the western part of study area shape of stress ellipsoid is prolate and it's due to existing reverse fault with strike-slip component. Comparison shape of stress ellipsoid in Eocene units indicate that shape of stress ellipsoid in the western, middle and eastern Shekarab Mountains is prolate, and as local there is oblate stress ellipsoid shape in eastern part. Results of this research indicate that direction of major stress axis had clockwise rotation from Cretaceous times to the present.

The Cause of the Earthquake (4.7 mb) and Recent Stress Regime Occurring in Al-Refaei Area, Mesopotamian plain, August 18th, 2017

Al-Refaei area is considered one of the highest seismically activity in the Mesopotamian Plain according to its seismic history. Depending on the International seismological Center, four seismic swarms were diagnosed in this area; these are: August 2004, January 2013, May-Jun 2017, and August 2017. Based on three focal mechanism solutions of magnitude greater than 4 mb, the stresses in the area were analysed. The results of focal mechanisms suggest that the faults movements in the study area show reverse movements, which is generated by compression force. To determine the directions of principal stress axes that affecting the faults in the area, the Rotational Optimization method were used. The directions of the three stress axes are: 02°/32°, 10°/302°, and 80°/136° for σ1, σ2, and σ3, respectively. The collision between the Arabian and Iranian plates is the main cause of seismic activity in Al-Refaei area. Therefore, Al-Refaei active fault is responsible for most the earthquakes in the area, and responsible for the earthquake that occurred in August 18th, 2017.

Stress dynamics associated with the Nyasa / Malawi rift: Implication for the present-day East African Rift System dynamics

The Nyasa/Malawi rift (NMR), known for its poor magma and notable seismic activity, has sparked a debate regarding its stress kinematics. It is on one hand viewed as a transform fault, while on other hand as a rift structure characterized by normal faulting. In order to address this controversy, we conducted paleostress analysis that involved collecting fault slip data along the central to southern region of the rift. We integrated our findings with published kinematic data on focal mechanisms in the rift. Our results reveal that the central part of the rift experiences radial or sub-radial extension, while the southern half is subject to oblique NNE-SSW transtensive tectonic forces. The minimum horizontal principal stress axis aligns with an orientation of 020°. As we move further south, the extension direction changes by approximately 25°, resulting in a predominantly north-south opening with a minimum horizontal stress axis direction of 175° (Shmin = 175°). The degree of structural penetration and intensity of faulting indicate that the north-south opening is more significant and pronounced in the southern region compared to the northern region. Additionally, we observed that faults dipping to the east and trending NW-SE exhibit sinistral (left-lateral) movement, while faults dipping to the southwestern side display dextral (right-lateral) movement. This suggests that, regionally, the NMR primarily experiences a normal faulting regime, albeit with a significant strike-slip component, which accounts for the oblique kinematics observed. The tectonic regimes identified through our fault slip data encompass the crust and upper mantle, spanning a lithospheric scale.

Influences of true 3D twin flaws on principal stress status and crack occurrence of brittle rock-like samples under uniaxial compression: Insights from experimental and DEM studies

Fracture structures commonly have negative impacts on the strength and safety of rock mass, and various combinations of 2D and 3D flaws make the destruction procedure becomes more complicated. Therefore, laboratory tests based on three types of flawed rocks (symmetric twin flaws with different 2D-3D occurrences) are finished to detect the mechanical, optical and acoustic characteristics of fractured rocks during the uniaxial compression test; PFC3D simulations are conducted for analyzing the deformation features, principal stress distributions, and detailed failure mechanism of the fractured rocks. The main results are as follows: 1) Different combinations of 2D & 3D preset flaws directly influence the results of deformation, stress distribution, and failure developments. 2) Rotation of the intermediate stress axes only appear near the flaw inclination boundary (when the monitoring position moves outwards), while the directions of intermediate principal stress axes remain stable near the flaw strike boundary. 3) Separating cracks by various occurrences helps to construct local failures along different directions, and make some local failures visible and clear; the traditional cracks (short line or thin oval shape) are induced by the uneven deformation in x-o-z planes, and the separated cracks (wide oval or standard disc shape) result from the uneven deformation in y-o-z planes. 4) Surrounding rocks at different positions suffer various modes of failures, the non-ignorable thickness of preset flaw leads to simultaneous Mode I and Mode II failure at the flaw tip, and the mixed Mode II&III failure only occurs in the rocks adjacent to the flaw strike boundary.

Experimental Study on Directional Shear of Q2 Remolded Loess Considering the Direction of Principal Stress

To investigate the strength and deformation characteristics of Q2 remodeled loess, soil samples from the Lishi area in Shanxi Province were adopted to examine the effects arising from the principal stress axis direction angle α and the medium principal stress ratio b on the shear and non-coaxial properties of remodeled loess based on the hollow cylindrical torsional shear system. As indicated by this study, when b was constant, the generalized shear stress ratio decreased with the increase in α at 0°–45°, while achieving the minimum value when α = 45°; α increased again with the increase in the principal stress axis direction angle at 45°–90°. When α was 0–45°, the generalized shear stress ratio tended to decrease with the increase in the intermediate principal stress ratio b. When α was 60°–90°, the shear strength ratios at different intermediate principal stress ratios were obtained as: strength at b = 0.5 > strength at b = 1 > strength at b = 0. Moreover, after the degree of strength volatility of this remodeled loess was defined to determine its breaking strain standard, it was found through a comparative analysis that when the generalized shear strain of this remodeled loess was 6.5%, the strength of this remodeled loess was over 90%. Thus, this study suggested the use of its generalized shear strain of 6.5% as its breaking strain standard. In addition, when α was at 0–45°, the direction angle of strain increment increased with the increase in the direction angle of the principal stress axis and reached the peak at 45°. When α was at 60°–90°, the direction angle of strain increment decreased with the increase in the direction angle of the principal stress axis, i.e., the non-coaxial characteristics of the remolded loess first increased, then decreased, and further tended to be coaxial.

Limitation analysis of the Hill48 yield model and establishment of its modified model for planar plastic anisotropy

In this paper, the limitations of the original Hill48 yield model in predicting uniaxial tensile yield stresses and r-values were analyzed in detail, and then the necessary and sufficient conditions for judging the applicability of the original Hill48 yield model were proposed. On this basis, the approximate satisfactions of the steel sheet DC04, DP980 and the aluminum alloy AA5754-O to the necessary and sufficient conditions were investigated. The results show that the necessary and sufficient conditions can be used to qualitatively analyze the predicted error of the original Hill48 model. Based on the inherent relationship of Hill48 yield function, the direction of principal stress axis was introduced into the anisotropic parameters, and a modified Hill48 model suitable for plane stress state was developed. According to the variation of the predicted error of the original Hill48 yield model in biaxial tensile stress, an exponential interpolation method including material parameter was proposed to correct the asymmetric biaxial stress between uniaxial stress state and symmetric biaxial stress state. The theoretical predicted results show that the modified model can accurately capture the directional yield stresses, r-values and yield locus. The main advantage of the modified model is that it still maintains a simple quadratic form in the stress tensor, and can significantly improve the predicted accuracy of anisotropic behavior of aluminum alloy and other materials from the use of associated flow rule.

Mechanical properties and failure mechanisms of composite laminates with classical fabric stacking patterns

In the design of composite materials, the properties and failure modes/mechanisms are always of the main concern. In this work, the mechanical properties and failure mechanisms of composite laminates with classical fabric stacking patterns ([(0, 90)]8 and [(0, 90)/(± 45)]4) were systematically investigated through mechanical experiments and FEM (finite element method) numerical simulations. The results show that the tensile modulus and bending modulus of the laminates were reduced by 22.2% and 37% after partially changing the stacking angle to ± 45°, but corresponding elongation and bending displacement were increased by 8.8% and 11.7%, respectively. Bending failure mode changes from complete fracture to partial fracture. Meanwhile, the delamination damage and tow peeling from the matrix increase significantly. FEM simulations on tensile and bending processes of the composites indicate that the ± 45° stacking angle leads to the change of the axial stress direction from SX (0°) to SY (± 45°), which is difficult to be observed from mechanical experiments. The FEM simulation provides a cost effective and efficient way for the structural visual optimization design and failure prediction of the actual composite materials.

Experiment and Failure Analysis of Rock‐Like Material Affected by Different Excavation Depths

In order to increase the understanding of the strength and failure mechanism of rock mass during tunnel excavation, a series of uniaxial compression tests were conducted on mortar specimen with cracks and holes by using a rock mechanics servo‐controlled testing system. And by monitoring the experimental process, the initiation, propagation, and coalescence process of cracks were observed and characterized. According to the experimental results, the influences of the excavation depth on the mechanical parameters and fracture characteristics of mortar specimens with single hole and the ones with single‐hole crack were analyzed in detail. In the specimens with single hole, the peak strength decreases with the increase of hole depth, but the peak strain and elastic modulus have no obvious linear correlation with the hole depth. And the position and angle of initial crack change differently with the increase of the hole depth. The position of initial crack moves from the side of the hole to the top of the hole. When the hole depth exceeds 50%, the crack initiation angle is no longer inclined to the axial stress direction, but parallel to the axial stress direction. In the specimens with single prefabricated crack, the wing‐shaped secondary cracks are generated at the tip of the precrack, and the antiwing‐shaped secondary cracks are generated at the tip when approaching the peak stress. However, in the specimens with single‐hole crack, no antiwing‐shaped crack appears. And when the hole depth reaches 80%, two wing‐shaped cracks appear at the precrack tip. One of the new wing‐shaped cracks appears in the direction of the extension line of the precrack.

GEOLOGICAL-AND-TECTONIC CONDITIONS OF FORMATION AND FOCAL MECHANISM OF TORAIGYR-SOGUETY EARTHQUAKE

The seismic characteristic of Toraigyr-Soguety earthquake is presented. The significant seismic events of the area are demonstrated including Chilik catastrophic earthquake. Geological-and-tectonic conditions of the epicentric areas of Chilik and Toraigyr-Soguety earthquakes are described. Kinematics of neotectonic faults is considered with respect to directions of main stress axes. Two models of focal mechanism of Toraigyr-Soguety earthquake compare with tectonic deformations of the area.

Paleostress regime reconstruction based on brittle structure analysis in the Shekarab Mountain, Eastern Iran

Eastern Iran, including the Sistan suture zone, comprises the boundary between Lut block and Afghan block. This research aims to reconstruct the stress regime evolution from the upper Cretaceous to Quaternary based on the brittle tectonic analysis. In this study, three episodic changes in stress regimes were recognized in the Shekarab Mountain using data inversion. In places where conglomerate outcrops are present, the Quaternary stress state is obtained using the youngest slickensides. The Quaternary stress state indicates that the direction of σHmax is close to N026°, which is compatible with the present-day Arabia-Eurasia convergence direction. Reconstruction of stress fields using age and sense of motion of faults shows that the stress regime during the Cretaceous was compressional, which caused the uplift of peridotites and ophiolites in the eastern part of the study area. The state of stress in the upper Eocene and Oligocene was transpressional; in the eastern part of the study area, there is a change from transpression to transtension. The exhumation of igneous rocks in the eastern part of the Shekarab Mountains is due to the local change of the stress regime. According to the results of this study, the first stage of stress state in the Shekarab Mountains was compressive and the average direction of maximum stress axis (σ1) was toward N337°. In Eocene, the tectonic regime was transpressional and the average direction of maximum stress axis (σ1) was toward N003°. In Quaternary, the tectonic regime is strike-slip and the average direction of maximum stress axis (σ1) is toward N026°. This implies that at least 49° clockwise rotation of σ1 happened in the Shekarab Mountain.

Dynamic fracture evolution of tight sandstone under uniaxial compression in high resolution 3D X-ray microscopy

Stress-induced fracture evolution in tight sandstone reservoir is of great significance in hydraulic fracturing treatment and borehole stability. The meso scale fracture mechanism needs to be well understood. In this work, the smaller-sized tight sandstone specimens (4 mm in diameter and 8 mm in height) from Bashijiqike formation were studied under uniaxial compression in high resolution three dimensional (3D) X-ray microscopy (XRM). Using high-resolution XRM, 2D slices and 3D digital cores with real pore structure characteristics were reconstructed at different stages of uniaxial compression. During the uniaxial loading process, porosity and diameter distribution of the voids were obtained to analyze the progressive deformation of rock, and then the complexity and heterogeneity of the cracks were quantified by applying fractal analysis. The results show that the fracture evolution of tight sandstone at meso scale could be divided into compaction stage, linear elastic behavior stage, non-linear deformation stage and residual deformation stage. The mineral composition and meso structure of tight sandstone have significant effects to its mechanical properties, fracture pattern and crack morphology under uniaxial compression. The propagation direction of secondary cracks tends to parallel to the direction of axial stress, revealed by higher resolution of region of interest (ROI) imaging.

RETRACTED ARTICLE: Numerical simulation of temperature field and temperature stress of thermal jet for water measurement

ABSTRACT Thermal-jet for water Measurement spallation is a rock removal process that utilizes induced thermal stress to fracture the rock into small fragments before melting of the rock occurs. Because of the low conductivity, thermal stress will be created on the rock surface. When the thermal stress exceeds the strength of the rock, cracks will form and expand. Eventually, rocks disintegrating into small fragments. The simulation result obtained by the Crank–Nicolson method of the temperature field and the distribution of thermal stress has been analyzed. The result indicates that during thermal spallation drilling, the temperature of the surface exposed to the thermal-jet for water Measurement rises rapidly and create temperature gradients in both radial and axial directions. Because of volume expansion, the heated part is subjected to compressive stress in radial direction and shear stress in axial direction, respectively. The result is very helpful to the field application.

Crustal anisotropy from shear-wave splitting of local earthquakes in the Garhwal Lesser Himalaya

SUMMARYCrustal anisotropy of the Garhwal Lesser Himalaya has been studied using local earthquake data from the Tehri seismic network. Earthquakes with magnitude (mL) up to 3, which occurred between January 2008 to December 2010, have been used for the shear wave splitting (SWS) analysis. SWS measurements have been done for steeply incident ray paths (ic ≤ 45°) to estimate the anisotropy fast axis orientation (ϕ) and the delay time (∂t). A total of 241 waveforms have been analysed, which yielded 209 splitting measurements, and 32 null results. The analysis reveals spatial and depth variation of ϕ and ∂t, suggesting complex anisotropic structure beneath the Garhwal Lesser Himalaya. The mean ∂t is estimated to be 0.07 ± 0.065 s with a mean depth normalized ∂t of 0.005 s km–1. We present the ϕ and Vs per cent anisotropy results by segregating these as a function of depth, for earthquakes originating above and below the Main Himalayan Thrust (MHT); and spatially, for stations located in the Outer Lesser Himalaya (OLH) and the Inner Lesser Himalaya (ILH). Earthquakes above the MHT sample only the Himalayan wedge, while those below the MHT sample both the underthrust Indian crust and the Himalayan wedge. Within the Himalayan wedge, for both OLH and ILH, the mean ϕ is oriented NE–SW, in the direction of maximum horizontal compressive stress axis (SHmax). This anisotropy is possibly due to stress-aligned microcracks controlled by the local stress pattern within the Himalayan wedge. The mean of normalized ∂t for all events originating within the Himalaya is 0.006 s km–1, which yields a Vs per cent anisotropy of ∼2.28 per cent. Assuming a homogeneous distribution of stress-aligned microcracks we compute a crack density of ∼0.0228 for the Garhwal Lesser Himalaya. At stations close to the regional fault systems, the mean ϕ is subparallel to the strike of the faults, and the anisotropy, locally, appears to be structure-related. For earthquakes originating below the MHT, in OLH, the mean ϕ orientation matches those from the Himalayan wedge and the normalized ∂t decreases with depth. This suggests depth localization of the anisotropy, primarily present within the Himalayan wedge. In the ILH, we observe large variations in the mean ϕ orientation and larger values of ∂t close to the regional fault/thrust systems. This is possibly a composite effect of the structure-related shallow crustal anisotropy and the frozen anisotropy of the underthrusting Indian crust. However, these cannot be segregated in this study.

Spatial and temporal variations of stress field in the Longmenshan Fault Zone after the 2008 Wenchuan, China earthquake

Summary We investigate the temporal and spatial patterns of the regional stress field along the Longmenshan Fault Zone (LFZ) following the 2008 Wenchuan Mw7.9 earthquake. Regional broadband seismic records are used to determine the focal mechanisms and centroid source depths of >400 aftershocks of magnitudes 3.3 ≤ Mw ≤ 5.9. The focal mechanisms are then used to invert for the temporal and spatial variations of the regional stress field. Results show clear spatial changes in the directions of principle stress axes as well as the faulting types along the LFZ. The regional stress field is in an overall thrust regime with nearly horizontal maximum compressional axis. In the southern section of the LFZ, in addition to the primarily thrust background with maximum compressional axis perpendicular to the main fault zone, strike-slip component is also present. In the middle section, the maximum compressional axis varies spatially, changing abruptly from perpendicular to parallel to the LFZ. In the northernmost section, the stress environment becomes primarily strike-slip. Our result suggests that the collision of Indian and Eurasian plates led to the first-order feature of the stress field in the study area. The geometry of blocks and faults, the lower crustal flow as well as the shallow crustal property difference are the major factors to controlling the local stress field. Temporal variations of stress field suggest that the mainshock caused a large stress disturbance at early stage in certain areas of LFZ, and the stress field variations with depth imply a different deformation pattern and different stress background in the shallow and lower crust.

Experimental Study on Reynolds Number Evolution of Gas-Filled Coal

The flow state of gas in coals is very complicated. We should pay attention to whether the permeability calculated by Darcy’s law is in accordance with the actual situation. We conducted an experiment on coal permeability and deformation under fixing confining pressure and increasing axial stress conditions. The objective is to investigate the variation of Reynolds number Re. In this study, the dynamic evolution of the Reynolds number is calculated under the relevant assumptions. The Reynolds number increases with an increase in the axial stress. In addition, the larger the value of initial Reynolds numbers, the greater the value of Re in the postpeak, and the possibility of nonlinear flow state is higher. Further, if the mass density (ρ) and fluid viscosity (μ) are constant, the decrease in the amplitudes of the flow rate is less than the increase in the equivalent diameter of the seepage path. Moreover, the tensile stress generated around the pores and fractures parallel or nearly parallel to the axial stress direction with increase in the axial stress results in an increase in the Reynolds numbers and equivalent diameter of the seepage path increase due to the development, expansion, and penetration of the cracks.

In-situ observation of crack initiation and propagation in Ni-based superalloy with film cooling holes during tensile test

The main aim of this work is to explore and analyze the crack initiation and propagation in nickel-based superalloy with film cooling holes (FCHs) during the in-situ tensile test. The stress value and position of crack initiation were determined by experiments and finite element analysis (FEA). Internal cracking of the metallic carbides (MC) composed by refractory elements has a greater impact on crack initiation and propagation. Both crack initiation and early expansion are Mode-I. The secondary crack spread in the opening type; however, the main crack spread in the form of slip separation. The material microstructure in crack tip plastic zone has a decisive effect on the crack propagation path. Finally, samples break along the {111} slip plane and perpendicular to the stress axis direction in the form of cross-cleavage.

Experimental Studies of Anisotropy on Borehole Breakouts in Mancos Shale

AbstractMeasuring the size and orientation of borehole breakouts is one of the primary methods for determining the orientation and magnitudes of the in situ stresses in the subsurface. To better understand the effects of anisotropy on borehole breakouts, experiments were conducted on Mancos Shale, a finely laminated mudrock. A novel testing configuration was developed to conduct borehole breakout experiments in a standard triaxial vessel and load frame. Samples were prepared at three different orientations and deformed under 6.9 to 20.7 MPa confining pressure. The results show a variation of peak strength and breakout geometry depending on the lamination orientation. Samples deformed parallel to laminations failed at a higher maximum compressive stress than samples deformed perpendicular to laminations, which were stronger than inclined samples. These relationships are quantified by a cosine‐based failure envelope. Observed breakout shapes in perpendicular samples are V‐shaped and symmetric around the borehole, which advance as a series of fractures of increasing size into the sidewalls. In inclined samples, fractures form along weaker laminations planes and grow in an en echelon pattern towards the axial stress direction. In parallel samples, long fractures grow from the wellbore towards the axial stress direction. The observed geometries highlight potential sources of error in calculating in situ stresses from borehole breakouts.

Estimation of residual stresses developed in SS 304L / Zr-2.5%Nb joints

Joints between stainless steel (SS) and zirconium based alloys have various applications in nuclear technology [1]. Since mechanical integrity of these joints under reactor operating conditions for the reactor life time viz. 40-50 years is vital, the qualification criterion for these joints should be very critical. The large difference in thermal coefficient of expansion of Zr-based alloys and SS leads to generation of residual stresses at the joint interface, which can have deteriorating effect on the bond integrity and mechanical properties of the joint [2]. Therefore, a proper estimation of these stresses is essential for its qualification. One of the accepted ways of mitigating such high residual stresses is by using suitable ductile interlayers between the joining materials. In the present work, the magnitude, nature and distribution of the residual stresses have been estimated using finite element method (FEM). Simulations were performed using axisymmetric model to evaluate the residual stress field generated while cooling SS304L/Zr-2.5%Nb joint from 1273 K to ambient temperature. The stress fields were calculated assuming elasto-plastic behaviour of the joining materials. The SS part of the joint was found to experience a maximum radial tensile stress of about 260 MPa, and a maximum shear stress of 55 MPa at the SS/Zr-2.5%Nb interfacial region. The maximum compressive stress in axial direction was found to be 92 MPa. Similar simulations were also performed by introducing Ni and Ti interlayers of thickness 200 μm each between SS304L and Zr-2.5%Nb. The maximum radial tensile stress on the SS side was found to be 243 MPa and a maximum shear stress of about 74 MPa near SS/Ni interface, while the maximum compressive stress in axial direction was 55 MPa. Therefore, it can be seen that a reduction in residual stress levels can be achieved upon incorporation of Ti and Ni interlayers.

Construction of beam elements considering von Kármán nonlinear strains using B-spline wavelet on the interval

• Beam elements by incorporating von Kármán nonlinear strains using B-spline wavelet on the interval are formulated. • Both Euler–Bernoulli beam theory and Timoshenko beam theory based elements are constructed. • A background integration cell based Gauss quadrature is used for numerical integration. • Numerical locking issues of proposed formulations are addressed. The current paper proposes the formulation of beam elements using B-spline wavelet on the interval based wavelet finite element method by incorporating von Kármán nonlinear strains. Formulation is proposed for both Euler–Bernoulli beam theory and Timoshenko beam theory. A background cell based Gauss quadrature is proposed for numerical integration. Numerical examples are solved for transverse deflections and stresses in axial direction, and are compared with the existing converged results from finite element method. The issues of membrane and shear locking for the proposed elements are examined and solution techniques are suggested to overcome the issues.

Deformation and CO2 gas permeability response of sandstone to mean and deviatoric stress variations under true triaxial stress conditions

The magnitude and direction of geo-stress undergoes complex changes following disturbance by artificial excavation in underground engineering. Tests were conducted using the self-made multi-functional true triaxial geophysical apparatus to investigate the influence of stress Lode angle on deformation, deformation modulus, and permeability of sandstone under true triaxial stress conditions (σ1> σ2 > σ3). The results indicate that principal, volumetric, and deviatoric strains, as well as permeability varied with the stress Lode angle, and eventually increased/decreased at different levels. For constant deviatoric stress and variable mean stress, the plastic strain decreased with increasing M (ratio of deviatoric stress q to mean stress p), whereas the permeability increased. For constant mean stress and variable deviatoric stress, the principal, volumetric, and deviatoric strains, as well as the permeability decreased first and then increased with the increase in M; the rock generated fracture surface when M was relatively large. The gas flow and stress axis directions significantly influence the value and changing trend of the permeability. With increasing stress Lode angle, the permeability increased first and then decreased. In our stress condition testing, the permeability value and variation range were maximum when the gas flow direction was parallel to σ1; when it was parallel to σ3, the permeability demonstrated an upward trend, but with a smaller increase range. Conversely, when it was parallel to σ2, the permeability decreased and the variation range was minimized. Finally, based on the analysis of the experimental results, we developed a permeability model that is expressed by both volumetric and deviatoric strains.