Stress Field Research Articles

Simulating a High-Resolution Tectonic Stress Field and Predicting the Fracture Distributions in Shale Reservoirs Based on a Heterogeneous Rock Mechanics Model with Adaptive Boundary Condition Constraints

Simulating a High-Resolution Tectonic Stress Field and Predicting the Fracture Distributions in Shale Reservoirs Based on a Heterogeneous Rock Mechanics Model with Adaptive Boundary Condition Constraints

FORMULATION OF A MODE I CRACK PROPAGATION MODEL BY ANALYZING THE STRESS FIELD AT THE CRACK TIP

One of the phases in the development of materials is knowledge of their possible degradation. At this stage, taking into account the influence of temperature variation remains essential for certain materials. The objective of this work is to take this aspect into account by formulating a mode I crack propagation model by studying the stress field in the vicinity of the crack tip. To do this, starting from Hookes law generalized in linear elasticity, we use the asymptotic expressions in displacements of the crack tip of Moes et Al. in order to obtain the stress field model. To validate the model, a comparison is made with data from the literature. The observations show a very high agreement of results. The advantage of this model is to take into account the role of temperature in the degradation of materials by analyzing crack propagation. It will be used in our future work.

Rock bolt and frame support of mine workings with a compound cross-section: Collective refuge chambers for mine workers

Purpose is to study the influence of mining and geological conditions on the time-dependent stability of the collective refuge chamber for mine workers with the adjacent mine workings and develop support schemes for different conditions of construction of such mine workings. Methods. Numerical modelling methods of the connected processes of elastoplastic deformation of gas-bearing rocks and gas filtration within the area disturbed during mining operations were used to study stability of mine workings with a compound cross-section, i.e. the collective refuge chambers and its adjacent extraction gallery. The model was based on fundamental principles of solid mechanics and filtration theory. The problem was solved using a finite element method. Findings. A classification of the conditions for locating collective refuge chambers for mine workers according to the relative strength of the enclosing rocks was developed. Support schemes for the chamber and its adjacent mine working were elaborated. The schemes include basic support and provide for its strengthening with rock bolts located in the roof of the mine working and chamber, or in their walls. The compliance of these support schemes with the developed classification of location conditions was determined. A numerical study of the time-dependent stability of the chamber and its adjacent mine working, while applying the recommended support scheme, was performed. It is shown that the strengthening of rock bolting schemes reduces the multicomponent stress field and the area of the zone of inelastic deformations, forms a rock-bolt overlap in the roof of the mine workings and chambers, which helps increase their stability under the complicated mining and geological conditions. Originality. Dependence of the changes within the area of a zone of inelastic deformations around the chamber with its adjacent mine working on the relative strength of the enclosing rocks was identified; time-dependent changes within the area of the zone of inelastic deformations, when using different support types, were specified. Practical implications. Support schemes for collective rescue chambers for mine workers in terms of different construction conditions were developed along with the procedure of their selection for specific mining and geological conditions. The results of the study provide theoretical substantiation and scientific guidelines for the selection of supports for collective refuge chambers adjacent to the mine working.

NEW APPROACHES TO JUSTIFICATION OF MATERIALS FOR GARMENTS USING THE EXAMPLE OF A MEN’S T-SHIRT

The possibility of using modern methods of virtual fitting of clothes on an avatar of the human body in the process of forming the quality of garments is shown. A general scheme for calculating the me-chanical processes developed in garments when fitting the human body in statics and dynamics is presented, as well as the main directions for automating the calculation process. Based on the chosen numerical method, the problem of selecting textile materials to ensure the required quality of the product was solved using the example of a men’s T-shirt. The mechanical properties of several samples of knitted fabrics for such products were determined. Based on the obtained values, the calculation of stress fields in the parts of a men’s T-shirt in various body avatar poses was carried out. An experimental verification of the modelling results was carried out. Regularities have been established between the mechanical properties of knitted fabric and the nature of stress in the structure of the product. The possibility of their use when choosing textile materials is shown from the point of view of ensuring the required quality of products at the design stage.

Relationship between stress field and apparent velocity and Poisson ratio fields

Relationship between stress field and apparent velocity and Poisson ratio fields

Influence of Interaction between Microcracks and Macrocracks on Crack Propagation of Asphalt Concrete.

This paper aims to reveal the interaction relationship between microcracks and macrocracks and the influence of the interaction on the crack propagation behavior. A theoretical model of asphalt concrete was established for the interaction between microcracks with different crack densities and a macrocrack. And a meso-structure model of AC-13 dense-graded asphalt concrete was established by combining the Talyor medium method and the DEM (discrete element method). Macro and micro parameters, such as the stress-strain characteristics, crack evolution parameters, and crack tip stress field, were obtained through a semi-circular bend virtual test and used to study the characteristics of crack propagation under the interaction between microcracks and the macrocrack. The results indicate that the interaction has an effect throughout the process of asphalt concrete damage, and shows shielding and acceleration effects as the microcrack density changes. When the microcrack density is low (f3 ≤ 0.8), the crack propagation process, which is affected by the interaction effect, exhibits significant differences, and the interaction effect shows the shielding effect. When the microcrack density is high (f3 > 0.8), the fracture stage is mainly affected by the interaction effect, which shows the acceleration effect. The results provide a predictive theoretical and numerical model for low-temperature cracking of asphalt pavement, and theoretical support for the design, maintenance, and upkeep of long-life pavement.

Physiological and biochemical characteristics of milk thistle (Silybum marianum (L.) Gaertn) as affected by some plant growth regulators

AbstractMilk thistle (Silybum marianum (L.) Gaertn) is a globally and widely used medicinal plant that contains silymarin. This plant has antioxidant, antimicrobial, anticancer, hepatoprotective, cardiovascular‐protective, and neuroprotective effects. Plant quality, yield, and phytochemicals, especially silymarin content, change under various conditions like drought stress. Therefore, this research studied plant growth regulators (PGRs) like salicylic acid, spermidine, and brassinosteroid to increase plant tolerance to drought stress. Experimental treatments include different levels of irrigation (25%, 50%, 75%, and 90% field capacity), and foliar spraying including salicylic acid (75 and 150 mg/L), spermine (70 and 140 mg/L), and brassinosteroid (1 and 1.2 μM), separately, and water as a control and a secondary factor. The results revealed that the highest amount of leaf phenolic compounds was observed in the highest drought stress level (25%) and 75 mg/L salicylic acid application. Furthermore, brassinosteroid at different concentrations and salicylic acid (75 mg/L) increased leaf flavonoid content compared to other treatments. In 50% field capacity, foliar application of salicylic acid (150 mg/L) significantly increased seed yield by approximately 75% compared to control under the same stress level. Brassinosteroid application (1 μM) under 75% field capacity significantly increased the seed's taxifolin amount by 159%. Additionally, salicylic acid noticeably increased the silychristin concentration. The concentration of silydianin in the seed has also been increased under drought stress and foliar spraying with PGRs. Compared to the control, using spermidine below 75% field capacity caused an increase in its concentrations by over seven times. The highest silybin A amount was obtained in 50% field capacity and foliar150 mg/L salicylic acid. Taxifolin, silychristin, silydianin, silybinin B, iso‐silybinin A, and iso‐silybinin B compounds were identified in the seed extract. Generally, foliar spraying using plant growth regulators increased the number of silymarin compounds under drought stress conditions and field cultivation conditions.

Numerical Analysis of Temperature and Stress Field of Side Dam on the Twin‐Roll Strip Casting

Side sealing technology is crucial in the twin‐roll casting process. The performance of side dam materials directly determines twin‐roll casting (TRC) process stability and safety. An orthogonal test is conducted to study the effects of thermal conductivity, linear expansion coefficient, and elastic modulus on the maximum thermal stress of side dams. The elastic modulus and linear expansion coefficient are identified as key factors affecting the maximum thermal stress of the side dam. The fluctuation of maximum thermal stress under different elastic modulus and linear expansion coefficients is 79.7 and 75.8 MPa, respectively, whereas it is only 11.2 MPa under different thermal conductivity. A side dam with heterogeneous material along height and thickness gradient is designed. The results indicate that the maximum thermal stress in the contact area between the side dam and the molten metal decreases to 31.2 MPa, representing a reduction of more than 30 MPa compared to the homogeneous side dam with optimal performance. The results provide important guidance in improving the stability of the TRC process.

The Intraplate Stress Field of West Africa

AbstractWest Africa continues to host a growing number of low and intermediate‐magnitude earthquakes (M2‐5) along its passive margins, and its continental interior. Earthquake activity in these regions raises the need to comprehend the causes and the tectonic controls of the seismicity. Unfortunately, such studies are rare. Here, we apply single‐station inversion techniques to constrain fourteen focal mechanisms, computed after compiling a set of high‐quality waveforms. We describe the connection between seismicity, the contemporary stress field, anthropogenic activity and Holocene fault scarps in the region. Our results indicate transpressive stresses acting on the inherited brittle structures in the passive margins. We also observe a compressive regime in the intracontinental failed rifts. We attribute the seismicity to the reactivation of “weak” faults in the Neoproterozoic and Mesozoic failed rifts, the passive transform structures, and the intracratonic Precambrian brittle shear zones.

Dislocation loop and irradiation-induced synergistic-competitive mechanism in Cu-rich precipitates: a phase-field study

Both irradiation and dislocations have been proposed as routes to rationally manipulate spatial distribution and micromorphology of precipitate. An interesting effect emerges in Fe–10at.%Cu–3at.%Mn–1.5at.%Ni–1.5at.%Al alloy due to the synergistic-competitive roles of dislocation loop and irradiation. Base on cascade mixing, vacancy-interstitial atoms and dislocation stress field model, we examine nucleation and growth dynamics of Cu-rich precipitates, where both dislocation loop and irradiation act in conjunction. Analytical treatments identify regimes, where the distribution of elements and point defects due to irradiation and dislocations are specific to the Cu-rich precipitates. Simulation results reveal that density, size and distribution of Cu-rich precipitates are a manifestation of the competing effects of the dislocation loop and the irradiation rate. More specifically, the dislocation loop preferentially assists the formation of precipitates and new dislocations at lower irradiation rates. Only the irradiation induces the formation of Cu-rich precipitates with the irradiation rate continues to increase. Equipped with molecular dynamics, where reproduces major interaction features of the solutes with point defects under displacement cascade, can verify multi-component morphologies of Cu-rich precipitates. This modeling framework provides an avenue to explore the role of dislocation loop and irradiation on the microstructural evolution of Cu-rich precipitates.

Characteristics of Penetration Strength and Fracture Features under Nonuniform Stress Field around Borehole Surrounding Rock.

In the process of mining coal energy, the excavation of roadways and drilling causes the formation of a nonuniform stress field around the penetration holes, which will lead to a significant concentration of stress around the penetration hole. It even leads to the destruction of the surrounding rock of the penetration hole, affecting the integrity of the surrounding rock of the penetration hole. It has an effect on the strength of the rock obtained by the borehole penetration methods. Based on Abaqus software, the numerical model of borehole penetration was constructed by embedding cohesion elements between solid elements. After analyzing the simulation results obtained under different stress boundaries and penetration directions, the following findings are obtained. (1) Using the occurrence of cracks in the borehole surrounding rock as the criterion, the rock is categorized into either an elastic stress state or a plastic stress state after applying different stress boundary conditions. (2) When the borehole surrounding rock is in the elastic (plastic) stress state, the penetration strength increases (decreases) with the increase of lateral pressure coefficient. (3) In the elastic stress state, borehole surrounding rock's fracture area and crack penetration depth increase (decrease) with the increase of lateral pressure coefficient when the penetration direction is parallel (perpendicular) to the maximum principal stress. In the plastic stress state, the fracture area increases, while crack penetration depth decreases with higher lateral pressure coefficient.

Research on stress field inversion and large deformation level determination of super deep buried soft rock tunnel

Understanding the characteristics and distribution patterns of the initial geo-stress field in tunnels is of great significance for studying the problem of large deformation of tunnels under high geo-stress conditions. This article proposes a ground stress field inversion method and large deformation level determination based on the GS-XGBoost algorithm and the Haba Snow Mountain Tunnel of the Lixiang Railway. Firstly, the hydraulic fracturing method is used to conduct on-site testing of tunnel ground stress and obtain tunnel ground stress data. Then, a three-dimensional model of the Haba Snow Mountain Tunnel will be established, and it will be combined with the GS-XGBoost regression algorithm model to obtain the optimal boundary conditions of the model. Finally, the optimal boundary condition parameters are substituted into the three-dimensional finite-difference calculation model for stress calculation, and the distribution of the in-situ stress field of the entire calculation model is obtained. Finally, the level of large deformation of the Haba Snow Mountain Tunnel will be determined. The results show that the ground stress of the tunnel increases with the increase of burial depth, with the maximum horizontal principal stress of 38.03 MPa and the minimum horizontal principal stress of 26.07 MPa. The Haba Snow Mountain Tunnel has large deformation problems of levels I, II, III, and IV. Level III and IV large deformations are generally accompanied by higher ground stress (above 28 MPa) and smaller surrounding rock strength. The distribution of surrounding rock strength along the tunnel axis shows a clear "W" shape, opposite to the surface elevation "M" shape. It is inferred that the mountain may be affected by geological structures on both sides of the north and south, causing more severe compression of the tunnel surrounding rock at the peak.

Influence of double-side symmetric oblique laser shock peening on shape deviation, surface integrity, and fatigue properties of the blades in small-sized blisk

Double-sided symmetric oblique laser shock peening (DSOLSP) was adopted to experiment on a small-sized blisk with restricted space. The influences of different laser energies on the shape deviation, surface roughness, microhardness, and residual stress of the blades were studied. The optimum process parameters were selected based on the shape deviation results of the blades and the microstructural evolution of the surface layers was investigated. The strengthening effect of DSOLSP treatment on notched blades was evaluated by vibration fatigue tests. It was found that DSOLSP can effectively cover the fatigue vulnerable regions without interference. Two-way bending deformation was formed after DSOLSP, and the shape deviation of the blades could be controlled within ±0.02 mm. With the increase of laser energy, the surface roughness and the depth of work-hardened layer increased. The full-thickness compressive residual stress (CRS) field was induced. A gradient microstructure was generated on the surface of the blade, and the size of average nanograins on the topmost surface is approximately 36.5 nm. The fatigue strength of the DSOLSP treated blades with notches was increased by 25.9 %. The enhancement can be attributed to the synergistic strengthening of CRS and gradient microstructure.

Plastic zone characteristics and rapid stability evaluation indexes of circular tunnels subjected to non-hydrostatic stress: A novel complex variable solution incorporating 3D rock mass strength

The morphological characteristics and distribution range of the plastic zone around tunnels, influenced by the true three-dimensional high geostress environment in deep engineering, constitute fundamental reference data for both tunnel design and the control of surrounding rock stability. Based on the GZZ three-dimensional rock mass strength criteria and the complex variable method, a novel semi-analytical method for solving the plastic zone of a circular tunnel subjected to non-hydrostatic stress is presented. The conformal mapping is employed to intricately transform the complex boundaries of plastic zones characterized by diverse shapes onto the unit circle boundary within the image plane. This framework proves invaluable for the precise analytical process of the complex plastic zone morphology and the plastic influence range within the surrounding rock under complex stress conditions. In contrast to traditional analytical methods, the efficacy and versatility of our proposed approach are substantiated. Notably, it demonstrates unique advantages, particularly in the context of non-hydrostatic stress fields and varied rock mass parameters, with respect to predicting both surrounding rock stability and plastic zone morphology. Through the analysis of numerous cases, the study reveals the systematic patterns of influence that in-situ stress and surrounding rock characteristic parameters have on the shape and maximum depth of the plastic zone. The results indicate that (1) there are notable disparities in the morphology and extent of the plastic zone between the GZZ and GHB criteria; (2) the transition of the plastic zone in surrounding rock from U-shaped to V-shaped is significantly influenced by the geostress-to-strength ratio Kσ; (3) there is a notable linear correlation observed between the maximum plastic zone thickness rmax and both Kσ and the stress concentration factor KSCF, importantly, this correlation is independent of far-field stress and the brittleness characteristics of the surrounding rock. These findings provide a novel discriminative method for the rapid analysis of surrounding rock stability in deep circular tunnels.

Hybrid equilibrium formulation with adaptive element side orientation for cohesive crack prediction

AbstractThe present article proposes an hybrid equilibrium element (HEE) formulation for the prediction of cohesive fracture formation and propagation with the crack modelled by extrinsic interface embedded at element sides. The hybrid equilibrium element formulation can model high order (quadratic, cubic and quartic) stress fields which strongly satisfy homogeneous equilibrium equations, inter‐element and boundary equilibrium equations. The HEE can implicitly model both the initially rigid behaviour of an extrinsic interface and its debonding condition with separation displacement and softening. The extrinsic interface is embedded at the element sides and its behaviour is governed by means of the same degrees of freedom of HEE (generalized stresses), without any additional degree of freedom. The proposed extrinsic cohesive model is developed in the thermodynamic framework of damage mechanics. The proposed crack propagation criterion states that crack grows when the maximum principal stress reaches the tensile strength value, in a direction orthogonal to the principal stress direction. The crack is embedded at an element side and the mesh around crack tip is adapted, by rotation of the element sides, in order to have the interface aligned to the crack growth direction. Three classic two‐dimensional problems of fracture propagation are numerically reproduced and the results compared to the experimental data or to the other numerical results.

Structural Analysis of Deck Reinforcement on Composite Yacht for Crane Installation

The crane installation on the deck of a yacht redistributes the stress field and affects the local structural integrity and performance. The safe operation of the yacht is associated with the optimal placement of the crane on the deck and the proper local structural reinforcement. Here, the structural analysis of the bow part of a yacht made of composite materials is studied, considering the retrofit installation of a crane, in three different cases of reinforcing the deck: (a) without any reinforcement, (b) with a T-type reinforcement, and finally, (c) with a longitudinal beam. The T-type connects the longitudinal bulkhead and the deck, reinforced locally with overlamination skin and adhesive-filler. The longitudinal beam works as a local longitudinal stiffener attached to the deck and connects the second, third, and fourth transverse frames. The structural analysis is performed using the finite element method following the classification societies’ rules. The local reinforcements are made from the same composite materials as the unreinforced deck. The maximum deformations, the principal stresses, and the safety factors following Tsai-Wu and Hashin criteria are calculated and compared for the three different cases. The T-type and longitudinal reinforcements reduce deck stresses by 33%, with longitudinal reinforcement reducing deck deformation by 17%. Composite failure analysis shows the structure was near failure, and the reinforcements enhance safety; T-type is better for multiaxial loads (Tsai-Wu), and longitudinal is superior for micromechanical failure (Hashin). By considering the structural performance and safety aspects, designers and engineers can make optimal decisions regarding yacht crane installation and proper reinforcement, leading to safer and more efficient structures.

Gradient anisotropic design of Voronoi porous structures

Gradient and anisotropic design have proved to be two effective approaches for customizing lightweight porous parts in recent years due to their outstanding performances comparing to the uniform porous ones, such as high specific strength, specific surface areas and high energy and shock absorption capacities, etc. However, it is still challenging to integrate both gradient and anisotropy into a same porous part, while making it profile adaptable simultaneously. In this paper, a novel gradient anisotropic design method of Voronoi porous structures for parts customization is proposed driven by the stress field of a part in a specific application scenario. Firstly, the stress field is decomposed into a stress scalar field and a stress direction field. The former is mapped into the Voronoi site distribution by a weighted random sampling algorithm that globally controls the gradient of the mechanical properties, while the latter is applied to adjust the shapes and orientations of the Voronoi cells for tailoring the anisotropy locally. Then, a lightweight gradient anisotropic Voronoi porous (GAVP) part is customized based on a Voronoi cell growth strategy with preferred directions, making the porous part highly profile adaptable. Finally, the influences of the design parameters on the mechanical properties of the GAVP parts are analyzed in detail, and the proposed design method is further validated experimentally and numerically. The results show that the integration of gradient and anisotropy significantly enhances the mechanical properties of a GAVP part compared to the corresponding gradient porous or anisotropic porous ones, because our GAVP structure modeling method realize a more optimal allocation of material locally, which makes the stress distribution much more even.

Investigation of geometric and material effects on the fatigue performance of composite and steel adhesive joints

This study experimentally investigates the combined effect of several parameters on the fatigue behaviour of adhesive bonded single lap joints, including: substrate material (steel, glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP)); adhesive material (epoxy and methacrylate); as well as joint geometry (overlap length and adhesive thickness).Results showed that despite the lower bulk strength of the ductile methacrylate adhesive, in terms of the ratio of fatigue load to ultimate failure load, joints bonded by this adhesive had a higher fatigue performance when compared to joints bonded by the epoxy one, with differences in fatigue life of up to 20 times for the same load ratio. In a similar substrate configuration, flexible GFRP substrates reduced the fatigue life of the joints bonded by the methacrylate adhesive more than 10 times when compared to steel joints for the same load. However, in a dissimilar configuration, an increase in fatigue life was observed which, based on a finite element analysis, was attributed to the ductility of the adhesive and its effects on the stress field. In CFRP joints bonded by the epoxy adhesive, a deterioration in fatigue performance was observed due to the occurrence of interfacial failure.Regarding the geometrical factors, increasing overlap length led to a decrease of the fatigue life for the same nominal shear stress. Similar trend was obtained for adhesive thickness. A parametric analysis revealed that overlap length is the parameter that affects more the fatigue performance of the joints.

Deep Learning Approaches for Water Stress Forecasting in Arboriculture Using Time Series of Remote Sensing Images: Comparative Study between ConvLSTM and CNN-LSTM Models

Irrigation is crucial for crop cultivation and productivity. However, traditional methods often waste water and energy due to neglecting soil and crop variations, leading to inefficient water distribution and potential crop water stress. The crop water stress index (CWSI) has become a widely accepted index for assessing plant water status. However, it is necessary to forecast the plant water stress to estimate the quantity of water to irrigate. Deep learning (DL) models for water stress forecasting have gained prominence in irrigation management to address these needs. In this paper, we present a comparative study between two deep learning models, ConvLSTM and CNN-LSTM, for water stress forecasting using remote sensing data. While these DL architectures have been previously proposed and studied in various applications, our novelty lies in studying their effectiveness in the field of water stress forecasting using time series of remote sensing images. The proposed methodology involves meticulous preparation of time series data, where we calculate the crop water stress index (CWSI) using Landsat 8 satellite imagery through Google Earth Engine. Subsequently, we implemented and fine-tuned the hyperparameters of the ConvLSTM and CNN-LSTM models. The same processes of model compilation, optimization of hyperparameters, and model training were applied for the two architectures. A citrus farm in Morocco was chosen as a case study. The analysis of the results reveals that the CNN-LSTM model excels over the ConvLSTM model for long sequences (nine images) with an RMSE of 0.119 and 0.123, respectively, while ConvLSTM provides better results for short sequences (three images) than CNN-LSTM with an RMSE of 0.153 and 0.187, respectively.

Surface effect on the partial-slip contact of a nano-sized flat indenter

The partial-slip contact at nano-scale is always influenced by a surface effect. A new model based on the Gurtin-Murdoch (G-M) surface elasticity theory is proposed in this paper to study the partial-slip contact behavior of a rigid flat nano-indenter on an elastic half-space. The surface effect in the partial-slip contact is characterized via a non-classical boundary condition involving a surface-induced normal traction related to the residual surface stress and a surface-induced tangential traction related to the surface elasticity, the influences of which on stress and displacement fields and the stick-slip state at the contact surface are investigated. It is found that, with the increase of residual surface stress, both the normal pressure and vertical and horizontal displacements in the contact zone decrease, the relative slip between indenter and substrate reduces and the stick region is enlarged. Such effects are basically attributed to the action of the surface-induced normal traction opposite to the externally applied compression. However, the increase of surface elastic constants is conductive to the relative slip and results in a shrinkage of the stick region, which is attributed to the action of the surface-induced tangential traction opposite to the frictional stress. An interesting phenomenon is further unveiled that, when the frictional coefficient increases, the dominant role in affecting the stick-slip state changes from the surface-induced tangential traction to the normal one, thus inspiring a feasible route to manipulate the surface effect by tuning the frictional coefficient of substrate. The present research enables one to better understand the partial-slip contact behavior of nano-indenters, which is of guiding value for anti-wear designs in nano-mechanical devices.