Search

The development of an accurate and meticulously designed simulation model for heat distribution during welding has helped maintain the popularity of welding as a reliable approach for attaching components. A simulated heat source involves uneven heating, resulting in uneven deformation and stress. An ANSYS simulation is used to analyze the stress in a welded flat plate. The simulation models are created using SOLIDWORKS software. The model employs the temperature-dependent characteristics of alloy steel to function as a thermal model that evaluates stress and the distribution of heat within the structure. This study offers a comprehensive examination of welded joints through the utilization of THERMO-MECHANICAL Finite Element Analysis (FEA) tools, specifically ANSYS. The study focuses especially on the analysis of single U and unsymmetrical double U welding connections. The study examined the heat distribution, thermal loads, and impacts on fixtures associated with welding, specifically focusing on the design of the welding joint. The results indicate that the heat from welding caused a maximum deformation of 0.55 mm for the single U joint and 0.54 mm for the double U welding joints. Both joint configurations displayed significant thermal stress at a distance of 5 mm from the center of the weld. According to the ANSYS models, the heat-affected zone (HAZ) has a length of 45.4 mm for a single U joint and 53.6 mm for an unsymmetrical double U joint. The second aspect of this investigation involves assessing the comparative durability or thermal strains of various depositions in the previously mentioned joint. Moreover, it is essential to assess the expected heat distortion and stress when examining prospective welding materials for on-site use. This will enhance the implementation of the material. [ABSTRACT FROM AUTHOR]

Evaluating the filling soil strain and stress behaviors during offshore reclamation and consolidation processes is crucial in forming a stable marine engineering foundation. While, the one-dimensional stress-strain testing technology cannot reflect the three-dimensional (3D) characteristics of the large site, which poses a potential disaster to the uneven settlement of the site. In this study, we construct a platform for 3D testing of strain and stress state during soil consolidation process on the basis of the novel 3D strain rosette and 3D earth stress sensor. Subsequently, the platform was used in a consolidation model test of the Dalian Offshore Airport filling soil, which consists of red clay and stone powder in a mass ratio of 1:4. The results indicate that self-weight consolidation mainly involves an increase in isotropic spherical strain, while load consolidation results in significant shear strain. During soil consolidation process, stress increases first and then dissipates, while vertical compression occurs due to the self-weight of the soil. The evolution law of the principal strain is direction-independent, whereas that of the principal stress remains comparatively stable when the principal stress increases steadily. This study provides a reference for the consolidation deformation and soil strength evaluation of soil fill. [ABSTRACT FROM AUTHOR]

In this study, atomistic simulations were used to analyze the effects of nonglide stress and temperature on the mobility and structure of pyramidal-I (Pyr-I) and pyramidal-II (Pyr-II) 〈c + a〉 screw dislocations in single-crystal Mg. At a very low temperature (10 K), the pyramidal screw dislocations stably exist on Pyr-II planes and tend to glide on Pyr-I planes. The critical resolved shear stresses (CRSSes) of the pyramidal screw dislocations depend on the migration direction. Once a Pyr-II dislocation is transformed into a stuck core, a very high shear stress (243 and 391 MPa) is required to escape from the immobilized structure. Furthermore, their CRSSes increase with increasing compressive strain and decrease with increasing tensile strain normal to the slip planes. At the intermediate temperature range of 200 K ≤ T ≤ 400 K, the CRSSes of Pyr-I screw dislocations are weakly affected, whereas those of Pyr-II screw dislocations drastically decrease. Thus, both Pyr-I and Pyr-II screw dislocations have similar CRSS values at 400 K. At a higher temperature (500 K), Pyr-I screw dislocations frequently emit basal-〈a〉\langle a\rangle dislocation loops, and the remained dislocations are momentarily immobilized. The basal-〈a〉\langle a\rangle dislocation loops emitted from the 〈c + a〉 dislocations are quickly retracted, and the core structure is recovered as the shear deformation continues. This phenomenon can reduce the mobility of Pyr-I 〈c + a〉 screw dislocations at a higher temperature. The emission of basal-〈a〉\langle a\rangle dislocation loops is enhanced under compression.

The shear mechanical parameters of coal are important parameters for analyzing the deformation and stability of coal. In order to study the shear characteristics of straight joints of coal under different normal stress and shear rate conditions, the shear numerical simulation and laboratory test were carried out to study the influence of normal stress and shear rate on the shear characteristics of straight joints of coal. The results show that the shear strength of joints decreases with the increase of shear rate, and increases with the increase of normal stress. The higher the normal stress, the greater the influence of shear rate on the shear strength of joints. Shear stiffness is positively correlated with normal stress and negatively correlated with shear rate. When the shear rate reaches a certain value, the influence of shear stiffness is not obvious. The increase of shear rate makes the simulated joints more prone to shear slip, which is easy to cause coal and rock dynamic disasters. This phenomenon is more serious in high normal stress.

Metal fatigue is a problem in the use of metals in their applications, especially when they are exposed to cyclic or repetitive loads. This study analyzes the effect of round, rectangular and spherical cross-sections on fatigue failure of ST 60 steel. By providing a fatigue test load of 150 N and a rotating speed of 1500 rpm and a test specimen installation position with a distance of 70 cm, it was found that the round cross-section broke when experiencing 26,471 cycles, the rectangular cross-sectional shape broke when experiencing 115,515 cycles and the hollow round shape broke when experiencing 201,983 cycles. The largest shear stress is generated by a spherical cross-section with a value of 247.7 N/mm2 and the lowest is by a material with a hollow spherical cross-section with a value of 194.478 N/mm2. Normal stress and the highest shear stress are produced specimens with a spherical cross-sectional shape, this is because the spherical cross-section has a tendency to spread normal stress evenly over its surface.

Exploring the mechanical response of rock joint subjected to dynamic shear load is essential for revealing the mechanism of dynamic disasters in jointed rock masses. Using an impact-induced direct-shear method, a series of dynamic shear experiments were conducted on artificial granite joints with regularly undulating interface. The dynamic friction coefficient of joint was first obtained from planar jointed granite specimens before the dynamic shear strength and shear displacement of the regularly undulating joints were tested. During the test, the effects of normal stress and shear rate were both considered. The results show that when the shear velocity ranges from 1 to 9 m/s, the dynamic friction coefficient of the planar joint is negatively correlated with shear velocity, and decreases by at least 50% compared with that under quasi-static condition. The rate dependence of shear strength appears opposite for granite joints with undulating angles of 11.3° and 26.6°, respectively. A shear strength model for rock joint with an undulating angle of 11.3° is then suggested based on the test results. During impact shear sliding, the maximum shear displacement of the joint is linearly negatively related to the initial normal stress. While, non-driven sliding may occur under low normal stress and high impact velocity, which leads to a large magnitude of shear slip. Highlights: The shear strength and shear displacement of rock joints are tested with shear rate ranging from 1 to 9 m/s. The rate dependence of shear strength appears opposite for rock joints with sharp and gentle undulation and a shear strength model is suggested. Besides impact-driven sliding, the non-driven sliding may also occur in the joint under low normal stress and high impact velocity. [ABSTRACT FROM AUTHOR]

A model based on the Element Free Galerkin (EFG) method in the framework of linear elastic assumptions was developed to determine the distribution of interfacial stress in a concrete beam reinforced with FRP plates. In this model, the behavior of the adhesive layer between the surfaces is considered like a linear spring using its elastic properties, and MLS approximation functions are used to approximate the total displacement fields. In addition, the results were calculated and presented under the condition of complete adhesion between the surfaces. The results of the model were compared with the FEM model in Abaqus software for concrete beam and FRP panel. The results show that the EFG method has a good agreement with the outputs of the Abaqus model. To conclude this work, a parametric study was performed. It shows how the thickness of the adhesive layer and the FRP plate affect the shear and normal stress values of the adhesive. [ABSTRACT FROM AUTHOR]

The increasing use of geogrid in various geotechnical projects has made the evaluation of the shear behavior of soil reinforced with geogrid become particularly important. In this article, a series of large-scale direct shear tests have been performed on sand and gravel samples reinforced with geogrid. The purpose of the experiments was to investigate the impact of the geogrid mesh size and the relative density of the samples on the shear strength coefficient of the interface between soil and geogrid. In this study, 5 geogrids with different mesh sizes and one type of geotextile were used. According to the results, the average shear strength coefficient of sand and gravel samples reinforced with geogrid for different normal stresses and different relative densities was obtained between 0.72 and 0.94. As the relative density increases, the interface shear strength coefficient decreases, this means that the denser the sand, the more the shear strength of the sand/geogrid interface decreases. Based on the results, it was found that the contribution of particle interlocking in the shear resistance of the sand/geogrid interface is particularly important, so that the shear resistance coefficient of the interface increases with the increase in the size of the geogrid mesh.

Structural planes play an important role in controlling the stability of rock engineering, and the influence of structural planes should be considered in the design and construction process of rock engineering. In this paper, mechanical properties, constitutive theory, and numerical application of structural plane are studied by a combination method of laboratory tests, theoretical derivation, and program development. The test results reveal the change laws of various mechanical parameters under different roughness and normal stress. At the pre-peak stage, a non-stationary model of shear stiffness is established, and three-dimensional empirical prediction models for initial shear stiffness and residual stage roughness are proposed. The nonlinear constitutive models are established based on elasto-plastic mechanics, and the algorithms of the models are developed based on the return mapping algorithm. According to a large number of statistical analysis results, empirical prediction models are proposed for model parameters expressed by structural plane characteristic parameters. Finally, the discrete element method (DEM) is chosen to embed the constitutive models for practical application. The running programs of the constitutive models have been compiled into the discrete element model library. The comparison results between the proposed model and the Mohr-Coulomb slip model show that the proposed model can better describe nonlinear changes at different stages, and the predicted shear strength, peak strain and shear stiffness are closer to the test results. The research results of the paper are conducive to the accurate evaluation of structural plane in rock engineering.

Direct shear tests were conducted on sandstone specimens under different constant normal stresses to study the coalescence of cracks between non-persistent flaws and the shear sliding characteristics of the shear-formed fault. Digital image correlation and acoustic emission (AE) techniques were used to monitor the evolution of shear bands at the rock bridge area and microcracking behaviors. The experimental results revealed that the shear stresses corresponding to the peak and sub-peak in the stress-displacement curve are significantly affected by the normal stress. Strain localization bands emerged at both the tip of joints and the rock bridge, and their extension and interaction near the peak stress caused a surge in the AE hit rate and a significant decrease in the AE b value. Short and curvilinear strain bands were detected at low normal stress, while high normal stress generally led to more microcracking events and longer coplanar cracks at the rock bridge area. Furthermore, an increase in normal stress resulted in a higher AE count rate and more energetic AE events during friction sliding along the shear-formed fault. It was observed that the elastic energy released during the crack coalescence at the pre-peak stage was much greater than that released during friction sliding at the post-peak stage. More than 75% of AE events were located in the low-frequency band (0–100 kHz), and this proportion continued to rise with increasing normal stress. Moreover, more AE events of low AF value and high RA value were observed in specimens subjected to high normal stress, indicating that greater normal stress led to more microcracks of shear nature.

We derive explicit analytical expressions for the recurrence relations using the analytical matrix method for frequency response and the Bautista-Manero-Puig model for complex fluids. The BMP model is derived from the Extended Irreversible Thermodynamics formalism and has been shown to be useful in predicting the complex rheological behavior of self-associative systems. All harmonics of the alternating normal and shear stresses in oscillatory shear with various amplitude oscillatory regimes (AOS) can be calculated analytically, i.e., small amplitude oscillatory shear (SAOS), medium amplitude oscillatory shear (MAOS), and large amplitude oscillatory shear (LAOS). We show that incorporating the effects of the first and second normal stress differences for all AOS regimes leads to the emergence of higher harmonics. We establish the limits between the different AOS regimes based on criteria suggested by the analytical method. For some typical systems, such as CTAB-NaSal, we found a satisfactory quantitative agreement with the measured behavior of AOS. [ABSTRACT FROM AUTHOR]

A clear understanding of the dependence of the heat transfer process on the flow field in three‐dimensional (3D) rough fractures is crucial for many underground projects. In this study, 3D rough rock fractures with heterogeneous apertures and mechanical effects are established. Navier‐Stokes flow and local heat balance theory are used to simulate the seepage‐heat transfer coupling process. Five normal stresses and five flow velocities are set to quantify the influence of aperture variability on the flow field and heat transfer behavior of the fractures. The results show that the change in fracture aperture caused by normal stress is the direct cause of the nonlinear distribution of the flow field and temperature fluctuation. A quantitative parameter of temperature fluctuation degree in the fracture is proposed, which decreases exponentially with increasing fracture aperture and increases with greater flow velocity. An empirical model is established to describe the relationship between the heat transfer coefficient and the ratio of hydraulic aperture to mechanical aperture. The correctness of the model is verified by published seepage‐heat transfer coupling test results. The model is extended to establish the relationship between the heat transfer coefficient and the volume fraction of eddy. It is confirmed that the heat transfer coefficient increases with the augmentation of nonlinear flow, and the reason why the results of evaluating the heat transfer coefficient by roughness alone in related experiments are inconsistent is revealed. The results enhance the understanding of convective heat transfer characteristics in 3D rough rock fractures. [ABSTRACT FROM AUTHOR]

The shear stress–shear displacement relationship and shear strength parameters of the interface between the pipe and the surrounding soil are important for designing the jacking force. One most commonly used method to measure the shear strength of the pipe–soil interface is the direct shear test. This paper presents the results of a series of direct shear tests conducted in the laboratory on the pipe–soil interfaces for different moisture contents. Simultaneously, digital image correlation is used to supplement the research of the horizontal displacement field of the interface. The results show that the increase of normal stress will makes the interface more prone to strain hardening during the shearing process, and the influence of the change of specimen moisture content on the interface strain characteristics gradually weakens. The shearing process of the specimen mainly involved shearing contraction, and slight shear dilation occurs only when the moisture content is small. We proposed a unified model for describing the shear volumetric change caused by the combined action of moisture content and normal stress. The shear displacement field presents a layered distribution, which is related to the shear displacement corresponding to the shear stress. [ABSTRACT FROM AUTHOR]

In this scientific investigation, the impact of mechanical vibrations, precisely the vibration time (t), vibration amplitude (A), and external normal stress (σ), on the packing density (ρ) of wheat is thoroughly examined and analyzed. The findings reveal that both normal stress and vibration amplitude substantially affect wheat packing density, with increased normal stress and vibration amplitude resulting in higher packing density. Moreover, the utilization of normal stress accelerates the attainment of wheat's final stable bulk density and yields a higher value than freeloaded testing. The validity of the proposed approach, which employs normal stress and vibration amplitude as predictors for wheat packing density, was confirmed using an exponential model. This method holds considerable promise for optimizing wheat handling and storage operations, facilitating more accurate estimation of transportation expenses and storage needs, and minimizing wastage by ensuring optimal packing density during storage and transport. Moreover, the implications of this study have broader applicability to other granular materials, including pharmaceuticals, chemicals, and mining commodities, where packing density serves as a vital determinant of transport and storage efficiency, thereby underscoring the potential significance of the findings beyond the context of wheat. In summary, this study sheds light on the factors that influence wheat packing density, proposing a novel method for predicting packing density and providing insights into the potential applications of this method in agriculture and related industries. This study investigates the impact of mechanical vibrations, precisely the vibration time (t), vibration amplitude (A), and external normal stress (σ), on the packing density (ρ) of wheat particles. The findings demonstrate that both normal stress and vibration amplitude significantly influence wheat packing density, with higher stress and amplitude leading to increased density. Additionally, applying normal stress accelerates the attainment of stable bulk density in wheat, surpassing freeloaded testing. The study proposes an exponential model to predict wheat packing density based on vibration amplitude, offering promising prospects for optimizing wheat handling and storage operations. The implications extend to various granular materials in pharmaceuticals, chemicals, and mining industries, where packing density determines transport and storage efficiency. The investigation highlights the relevance of sensitivity analysis for precise data interpretation and paves the way for practical applications in agriculture and related sectors. [ABSTRACT FROM AUTHOR]

This study analyzes a concrete dam using Abaqus software at different water storage levels (60m, 70m, and 80m). The dam sections are designed based on these levels using approved equations by the United States Bureau of Reclamation. Static and dynamic forces, including seismic components, are calculated for worst-case scenarios. The analysis considers cases with and without galleries, varying the dam base width. Stresses (vertical, shear, and main) are calculated and presented as curves for comparison. The study examines the impact of reservoir water levels, additional base parts, and galleries on dam stability. Findings show that galleries significantly affect stress distribution, causing stress concentrations near openings. Normal stress is uniform except at the gallery, where it decreases. Maximum water storage leads to slight increases in normal stress. Without a gallery, normal stress increases until a certain distance, then decreases towards the pre-toe region, with maximum stress at the toe. The length of the additional base has a limited effect on normal stress. The presence of a gallery affects principal stress distribution, with higher values near the toe region for higher storage levels. The shear stress distribution is more uniform without a gallery. These findings demonstrate the complex interaction of factors in concrete dam stress behavior. Proper consideration of these factors is crucial for design, analysis, and maintenance to ensure structural integrity and performance. Further analysis considering material properties, loading conditions, and dam geometry would enhance understanding and facilitate precise design and safety assessments.

According to different geological conditions and engineering disturbance, three dimensional numerical models of anchored jointed rock mass with two kinds of boundary conditions of constant normal load (CNL) and constant normal stiffness (CNS) were constructed considering the ductility damage of rockbolt, the stiffness degradation of grouting layer and the joint surface roughness. The effects of anchorage angle, joint surface morphology, and boundary conditions on the shear performance of anchorage system were analyzed, and the failure characteristics under different working conditions were revealed. Finally, the analytical solution of shear strength of anchored system was established. Results show that the larger the anchorage angle is, the more serious the necking phenomenon of rockbolt will be. The damage degree of the bonding layer and the horizontal displacement of the bedding rock mass decrease with the increase of the joint surface roughness. The CNL condition is to instantaneously apply high normal stress, and the CNS condition is to gradually form a high normal stress environment through the superposition of increment on the basis of the initial value, which can resist greater transverse load. This is equivalent to enhancing the ductility of the rockbolt. The shear strength of the system increases with the increase of normal stress and normal stiffness. Ignoring the normal stiffness will underestimate the shear strength.

As a new type of unconventional natural gas resource, shale gas plays a vital role in energy supply. In order to deeply understand the shale fracture seepage characteristics, filled and unfilled fracture seepage tests were carried out on shale samples with different fracture surface topography with the use of self-developed shale fracture seepage testing equipment. The fitting formula that the seepage discharge decreased as a negative exponential function with the increase in normal stress was obtained in the unfilled fracture seepage test; the fitting coefficient had a good logarithmic and exponential function relationship with joint roughness coefficient JRC and surface development interface area ratio Sdr. Meanwhile, the modified cubic law was obtained by adding the correction coefficient. The correction coefficient had an exponential relationship with the anisotropy value Ka. Compared with the unfilled one, the fracture surface topography had little effect on the seepage discharge when it was filled. The experimental results show the effects of water head difference, fracture surface topography, particle size, and thickness of filling sand on shale fracture seepage characteristics under different normal stress conditions, which have a certain significance for improving the efficiency of shale gas production. [ABSTRACT FROM AUTHOR]

Shear failure often occurs during the construction of the geotechnical engineering projects, especially under dynamic loading condition. To investigate the effect of loading rate and normal stress on the shear responses of rock materials, a bonded-particle model (BPM) was adopted to insight the failure process from a micro-mechanical perspective using the moment tensor. Firstly, we propose a novel calibration methodology for direct shear test, which provides a possibility to effectively derive microscopic parameters of PBM for obtaining the macroscopic properties of rocks considering loading rates under direct shear. Validation results show that the simulation demonstrated good agreement with the experimental results. Then, a series of simulated direct shear tests under different normal stresses ranging from 0 to 20 MPa and loading rate ranging from 10–3 to 10–1 mm/s were performed. The results demonstrate that both normal stress and loading rate have a positive influence on shear strength. However, normal stress has a greater impact on the shear strength compared to loading rate, and the effect of loading rate on shear strength weakens as the normal stress level increases. Increasing the loading rate and normal stress level led to a higher distribution of AE events in the nonlinear stage. At lower loading rates and normal stress, intense AE activity was concentrated around the peak stress point. In contrast, under higher situations, the nonlinear stage is prolonged, resulting in an increased number of AE events in the nonlinear and post-peak stages. Normal stress has a greater impact on the generation and propagation of micro-cracks compared to loading rate. With higher normal stress, the failure mode shifts from a shear-dominated to a mixed mode with tensile micro-cracks in a dominant role. Highlights: A numerical model was established using DEM to investigate the mechanical properties and failure mode evolution of rock specimens under shear loading, taking into account the influence of loading rate and normal stress factor. A novel calibration procedure was proposed for the direct shear model, and the results showed that it effectively improved the calibration efficiency compared with traditional methods, as validated by experimental data. The fracture behavior of the specimen under different strain rates and normal stress states was monitored using numerical simulation based on moment tensor theory of acoustic emission, which allowed for analysis of the shear failure process. [ABSTRACT FROM AUTHOR]

Heat transfer in jointed rock masses exhibits characteristics of discontinuous, heterogeneous, and anisotropic due to the effects of rock discontinuities. In this work, thermal contact resistance (TCR) evolution of granite joints under normal stress was investigated. A novel method was proposed for the measurement of TCR for rough rock joints. A numerical calculation program was established for the determination of contact area based on the initial morphology of the joint surfaces and the monitored joint closure during the experiment. An estimation model of TCR for granite joints based on the equivalent joint aperture was established. It is found that TCR of granite joints shows decreasing trend with normal stress. The decreasing rate is relatively large at the initial loading stage and gradually reduces with normal stress. The values of TCR eventually stabilize. TCR of granite joint has no obvious correlation with joint roughness coefficient. It is more significantly affected by the contact area. Plastic deformation and rupture of the micro-convex body on the joint surfaces occurred due to the application of normal stress, which improve the heat transfer efficiency and lead to the decrease in TCR. In general, predication results of the TCR estimation model show good consistency with the experimental data. The model is more suitable for the cases with small joint apertures. This study can provide knowledge to the better understanding of heat transfer in rock masses containing different kinds of discontinuities. Highlights: A novel method was proposed for the measurement of thermal contact resistance for rough rock joints. A numerical calculation program was established for the determination of contact area for rough rock joints. Evolution of thermal contact resistance with normal stress and joint contact area was obtained and analyzed. An estimation model of thermal contact resistance for granite joints based on the equivalent joint aperture was established. [ABSTRACT FROM AUTHOR]

In this analytical study, we are concerned about the influence of stresses produced due to a moving load on an elastic plate (which is not traveling with a moving load) under gravity lying over a semi-infinite water medium with hydrostatic stress. The elastic property of the plate is considered to be orthotropic. The water and elastic medium are bonded with an irregular interface. The type of irregularity is considered parabolic type. To discover the displacement field, the perturbation approach has been employed to solve the governing differential equations with variable coefficients. Due to moving load, closed-form normal and shear stresses are established for both elastic plate and semi-infinite water medium. The variation of non-dimensionalized shear and normal stresses with various parameters, such as gravitational coefficient, hydrostatic stress, and irregularity factor, is discussed through numerical computation and graphical demonstration. Moreover, some remarkable observations have been performed to study the influence of the frictional coefficient and depth factor on the shear and normal stresses of both mediums. Some particular cases also have been discussed for the validation of the problem. [ABSTRACT FROM AUTHOR]

Introduction. There are many destructions of earth dams in the world due to the loss of seepage strength of soils of the dam body or foundation. The seepage stability of soils is directly related to the phenomenon of hydraulic fracturing (HF), so prevention of conditions causing hydraulic fracturing is a very important task in the design and operation of earth dams. Hydraulic fracturing is closely related to uneven settlement of the dam soils and building structures. In earth dams, the phenomenon of uneven settlement often occurs in the areas between the dam soil and the side masses of the dam site, the dam soil and concrete structures, such as culverts and spillways, foundation structural elements, the impervious core of the dam and adjacent soil zones. The article is devoted to the study of the seepage stability of soil dams in the area of round-shaped culvert spillway.Materials and methods. The study was carried out with the help of numerical modelling using Plaxis software package. The Bung Bung earth dam (Vietnam) was taken as an object of study.Results. The results of the studies showed that the normal stress around the culvert was reduced to a level much lower than the water pressure in the seepage flow with a high probability of hydraulic fracturing in the volume of soil below the spillway. Thus, hydraulic fracturing can occur in these areas. The article proposes two structural approaches to prevent hydraulic fracturing: to change the cross-sectional shape of the culvert and to install a clay jacket around the spillway. Both approaches were tested numerically. The calculations demostrated that the application of both methods reduces the conditions for the occurrence of hydraulic fracturing near the culvert.Conclusions. Dam failure due to hydraulic fracturing can cause serious damage. The implementation of methods to prevent hydraulic fracturing is important to ensure the safe dam conditions.

Investigating the shear strength characteristics of sliding zone soil is crucial for evaluating slope safety and stability. This paper discusses the shear strength characteristics of Lishi loess and N2 laterite in the sliding zone under different influencing factors based on in-suit multiple shear tests, and the shear strength characteristics of Lishi loess were contrasted and analyzed based on field and laboratory tests. The results indicated a favorable correlation between the shear strength of soil samples and normal stress. The shear strength attenuation of clay-rich N2 laterite was much larger than that of sand-rich Lishi loess with the increase of the shear stage. Importantly, the mutation points of the shear rate corresponding to the peak stress of soil samples were obtained, which can be used as a symbol to judge the transfixion of the shear plane. Moreover, the stress-strain characteristics of Lishi loess under the same normal load were diverse as a result of the different experimental methods, and the residual strength characteristics for the two tests also varied substantially. Notably, the Lishi loess in the field test has a more stable residual strength than the laboratory direct shear test conducted. The findings can aid in the comprehension of the mechanical behavior of loess and laterite on the Loess Plateau. [ABSTRACT FROM AUTHOR]

It is of great significance to study the fracture closure process and contact area under normal stress to quantitatively study the stress and strain of engineering rock surfaces. A mechanical analysis model of the relationship between the mesoscopic mechanical aperture and the normal deformation of fractured media under elastic conditions is established based on the finite element method. The change in the contact area of the fracture surfaces under normal stress at different levels is studied. The distribution of the contact stress, the distribution of the fracture closure, and the change in the asperity at each contact point are described in detail. The results show that the normal stress and normal deformation of the fracture exhibit a nonlinear relationship, and the normal stiffness decreases with increasing stress. The local deformation of fractures also follows this rule. Under different levels of stress, the aperture always maintains a Gaussian distribution, and as the normal stress increases, the increased contact area reduces the standard deviation of the aperture distribution. The theoretically calculated results are validated, demonstrating the accuracy and predictability of the model. Highlights: A contact model was proposed to show fracture mesoscopic deformation characteristics. The lateral distribution of the contact stress was proposed for the first time. The accuracy of the macroscopic mechanical analysis was improved. [ABSTRACT FROM AUTHOR]

In the drilling and stimulation operations of deep/ultra-deep oil and gas wells, high in situ stress conditions may increase the occurrence probability of rock shear failures. According to Mole-Coulomb laws, the friction coefficient becomes more significant in evaluating borehole instability, faults/natural fractures activation and hydraulic-natural fractures intersection scenarios. This paper proposes a multiscale model to calculate the rock friction coefficients based on the surface properties at different scales. The key parameters of surface properties are obtained from three-dimensional laser scan of friction planes, and the results are verified by the direct shearing and triaxial compression strength tests. For the flat or new-cutting surfaces, the computed basic friction coefficients range of 0.231–0.509, fitting well with the tested values of 0.303–0.437. It also shows that the basic friction coefficients grow in the order of shale, carbonate and tight sandstone, positively associated with the size of the rock sedimentary particles. For the roughness surfaces, the coefficients are computed based on the former basic friction values and the surface asperity dip angles distribution, and the values located in a wide range of 0.541–1.113, also matched well with the measured friction coefficients via direct shearing tests. When the normal stress increase, the rock friction coefficients generally decline, and the values of some shale and dolomite samples can decrease to 0.2, due to the existence of beddings or fracture fillings. The above outcomes may provide useful insights for wellbore instability assessment and hydraulic fracturing optimization. [ABSTRACT FROM AUTHOR]

The behavior of composite materials under tensile and bending loading differs, and material designs optimized for tensile loading may not be suitable for applications subjected to bending loading. In this study, the bending behavior of two different composite materials, namely glass and carbon fiber-reinforced composites, was analyzed under a three-point bending load. The output from the analysis of these two materials was compared, revealing that, in addition to longitudinal direction strength, transverse and through-thickness directional strength, as well as shear strength in all planes of the composite, are essential to minimize deformations, normal stress, and shear stress. In the study, under the same loading and boundary conditions, the carbon epoxy composite exhibited 84% more deformation than the FR-4 composite at the maximum load considered for the study. Furthermore, the strength of the FR-4 composite in the loading direction was 2.4 times greater than that of the carbon epoxy composite. The present work is used for the effective design of the composite material under bending loading.

Shear tests on sandstone containing non-connected joints under the unloading normal stress but fixed shear stress conditions were conducted with various initial normal stress and unloading rate. During the unloading process, continuous shear dilation could be observed. For initial normal stress = 5–20 MPa, the sliding initiation normal displacement decreased by 17.14–66.32 % but the sliding initiation shear displacement increased by 21.91–98.19 %. The sliding initiation normal stress declined by 7.18–15.57 % for unloading rate = 0.002–0.01 MPa/s but increased by a factor of 3.18–3.53 with the initial normal stress. Shear sliding of the jointed samples was more prone to occur at a smaller initial normal stress with a larger unloading rate. From the numerical simulation results via PFC2D, during the unloading process, cracking was first initiated from central part of the rock bridge and propagated gradually to coalesce with cracks developed from the joint tips. The penetrating fracture surfaces led to shear sliding of the jointed samples, and shear wear occurred on the fractures as shear displacement continued increasing. For unloading rate = 0.002–20 MPa/s, quantity of cracks corresponding to shear displacement of 1.2 mm decreased by 12.18–36.34 %. Cracking degree was more serious for the samples at a low unloading rate due to progressively developed cracks near the main failure planes before shear sliding and more accumulated cracks in the shearing wear stage for fractures under a larger normal stress.

Copyright of Geology & Resources is the property of Geology & Resources Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Scale effects on the mechanical behavior of rock joints have been extensively studied in rocks and rock-like materials. However, limited attention has been paid to understanding scale effects on the shear strength of rock joints in relation to normal stress σn applied to rock samples under direct shear tests. In this research, a two-dimensional particle flow code (PFC2D) is adopted to build a synthetic sandstone rock model with a standard joint roughness coefficient (JRC) profile. The manufactured rock model, which is adjusted by the experiment data and tested by the empirical Barton's shear strength criterion, is then used to research scale effects on the shear strength of rock joints caused by normal stresses. It is found that the failure type can be affected by JRC and σn. Therefore, a scale effect index (SEI) that is equal to JRC plus two times σn (MPa) is proposed to identify the types of shear failure. Overall, shearing off asperities is the main failure mechanism for rock samples with SEI > 14, which leads to negative scale effects. It is also found that the degree of scale effects on the shear strength of rock joints is more obvious at low normal stress conditions, where σn < 2 MPa. [ABSTRACT FROM AUTHOR]

When geosynthetics are used in various types of reinforced soil projects, the main problems are the stability, safety and long-term service performance of the reinforced structures. The friction characteristics of the reinforced soil interface have a direct impact on the stability and safety of the reinforced structures. However, there are many researches on clay and sand, and there are few reports on the interface interaction between gravel soil mixture and geogrid. In this study the reconstruction and extension project of Lanzhou-Haikou expressway from Nanning to Fangchenggang in Guangxi is taken as the background, the indoor large direct shear test of the gravel-soil mixture and geogrid interface shear characteristics are studied, and the effects of the different shear rate, degree of compaction and normal stress on the interaction characteristics of direct shear interface are discussed. The test results show that when the normal stress σv ≤30 kPa, the peak value of the interfacial shear stress presents a linear growth trend with the increasing compaction degree. With the further increase of normal stress, the growth trend changes from linear growth to polygonal growth. With the increasing shear rate, the shear stress at the interface between the reinforcement and soil is maximum at the shear rate v =1.5 mm/min. The interfacial cohesion increases with the increasing compaction degree, and the interfacial friction angle is just the opposite. Under different shear rates, the interfacial cohesion and friction angle fluctuate within a certain range of 38.725 kPa to 50.495kPa and 25.873° to 29.683°, respectively. The direct shear curve of the reinforced-soil direct shear interface is characterized by strain hardening, and the shear displacement corresponding to the inflection point under different influencing factors is mostly concentrated between 0.83% and 1.83% of the shear area length. The results can provide design parameters and theoretical reference for reinforced engineering construction with gravel - soil mixture as filler.

The quality of yarn is largely determined by the properties of the fibers from which it is produced. There is a certain correlation between the properties of the fibers and the yarn. Toothed feeding cylinders with elastic casings act on the fiber tape according to the laws of mechanics. Thin shells are widely used in the design of elements in many branches of modern technology, particularly in mechanical engineering. In this feeding cylinder thin shells are installed, which helps to obtain high-quality yarn on rotor spinning machines. The calculated results of the feed cylinder with elastic casings in the feed area of rotor spinning machines are given. Each parameter is conditionally discussed according to the laws of dynamics and resistance of materials. [ABSTRACT FROM AUTHOR]

Investigation of granular materials' geomechanical and geological characteristics could provide invaluable information to researchers working in petroleum and civil engineering, geoscience, and petrophysics. In this study, the effects of normal stress and sand grain size on the petrophysical and geomechanical characteristics of artificial samples (made of a wide range of sand grains and cement) were investigated, while the chemical composition and mineralogy of all the samples were kept identical. The results showed that the rock porosity and permeability, the main criteria for evaluating rock storativity and transmissibility, respectively, were adversely affected by applying normal stress and the increase of grain size. Based on the results, there is a critical range of grain size (i.e., 0.1–0.2 mm) above which rock permeability decreases sharply with an increase in normal stress. The geomechanical outcomes revealed that improving the cementation process by applying compaction force, and thus, increasing the degree of hydration has a greater effect on ameliorating rock strength than reducing rock porosity. Besides, the uniaxial compressive strength (UCS) and Brazilian test results indicated that fine-grained samples fail at lower normal stress (i.e., at 38% and 66% of the coarse samples, respectively) compared with coarse-grained samples because of the large number of grain-to-grain boundaries. The fracture patterns showed a straight line for very fine and fine-grained samples, while an irregular shape appeared for medium and coarse-grained samples. In the end, a comparison of distinct petrophysical and geomechanical rock properties, such as X-ray fluorescence analysis, UCS, porosity, and permeability, between artificial and natural samples has been made to analyze the difference between them. [ABSTRACT FROM AUTHOR]

As the weak structure of geotechnical engineering, frozen rock joints determine the stability of geotechnical engineering in frozen region. To study the influencing factors of the peak shear displacement of frozen rock joints, three groups of tuff coupling joints (upper and lower joints completely coincide) are selected in Jiangluling Tunnel, Qinghai Province, China. The joint surface morphology is obtained by three-dimensional scanning technology. The joints are frozen at – 35 ℃ for 12 h before direct shear test. The test results show that there are three main shear failure patterns of frozen rock joints, which are mainly determined by the opening degree of joints. The peak shear displacement decreases with the increase in joints surface roughness and opening degree, and increases with the increase in normal stress. By analyzing the characteristics of peak shear displacement under different opening degrees and normal stress, the influencing factors of peak shear displacement and shear strength of frozen rock joints are discussed. On this basis, the expression of peak shear displacement of frozen rock joints is proposed. It provides a theoretical basis for quantitative study on shear deformation of frozen rock joints. The study provides technical support for geotechnical engineering construction and rock slope instability prevention in frozen region. [ABSTRACT FROM AUTHOR]

As a new type of unconventional natural gas resource, shale gas plays a vital role in energy supply. In order to deeply understand the shale fracture seepage characteristics, filled and unfilled fracture seepage tests were carried out on shale samples with different fracture surface topography with the use of self-developed shale fracture seepage testing equipment. The fitting formula that the seepage discharge decreased as a negative exponential function with the increase in normal stress was obtained in the unfilled fracture seepage test; the fitting coefficient had a good logarithmic and exponential function relationship with joint roughness coefficient JRC and surface development interface area ratio Sdr. Meanwhile, the modified cubic law was obtained by adding the correction coefficient. The correction coefficient had an exponential relationship with the anisotropy value Ka. Compared with the unfilled one, the fracture surface topography had little effect on the seepage discharge when it was filled. The experimental results show the effects of water head difference, fracture surface topography, particle size, and thickness of filling sand on shale fracture seepage characteristics under different normal stress conditions, which have a certain significance for improving the efficiency of shale gas production.

The shear strength of a structural plane is a critical parameter in the analysis of engineering rock stability. Significant differences exist due to the various normal stresses in the structural plane. Therefore, evaluating the rock deformation to effectively determine the influence of normal stresses at different scales on the shear strength of structural planes is of great significance. This study discusses the effects of normal stress and structural plane size on shear strength through numerical simulations and regression analysis. The results showed that the shear strength of the structural plane increases linearly with increasing normal stress. The shear strength of the structural plane decreases with increasing size, and the corresponding curve is exponential. The characteristic size and shear strength increase linearly with increasing normal stress. This paper presents the concrete form of these relationships, which can be used to calculate and predict the shear strength, which has significance in guiding engineering.

Normal stress on dikes is one of the most critical parameters for a sound dike design. With more rapidly rising sea levels due to global warming, dikes are seriously threatened by overtopping induced by the combination of wave and storm surge. Compared with wave overtopping on positive freeboard, the curling breaking wave on dikes induced by the combined wave and surge overtopping may destroy the weakly protected dike crest and landward slope. Thus, in order to prevent severe damage to dikes, it is necessary to fully understand the normal stress induced by the combined wave and surge overtopping. In this paper, physical model tests were carried out to study the normal stress on dike induced by the combined wave and surge overtopping. Two characteristics of normal stress on dike were observed. The spatial distribution of normal stress on dike was also analyzed. It was found that the Weibull distribution can be used to effectively describe the statistical distribution of peak normal stresses. Furthermore, by curve fitting of the laboratory measured data, the Weibull factors on the part of the crest and the upper part of the landward slope were obtained.

In this paper, the effect of temperature on rheological properties of magnetorheological (MR) gel is investigated under rotational steady shear and oscillatory dynamic shear. A kind of fluid-like MR gel (MRG) was firstly synthesized by mixing carbonyl iron powder (CIP) with polymer matrix. Then, the relationship between yield stress, normal stress of MRG and shear rate under six temperatures and four magnetic field strengths were studied by rotational shear experiments. The results demonstrate that the dependence of shear stress on temperature displays an opposite tendency in comparison with that of normal stress on temperature. Moreover, maximum yield stress, one of the most important parameter of MR materials, decreases with the increment of temperature. Under oscillatory dynamic shear test, storage and loss moduli and normal stress of MRG all increase with temperature when a magnetic field is applied, which presents a contrary trend in the absence of a magnetic field. Related mechanisms about the alternation of microstructures of MRG were proposed to explain the above-mentioned phenomena. This paper is helpful in fabricating semi-active engineering devices using MR materials as a medium. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the increasing scale and depth of underground engineering, the geological environment that engineering is faced with is becoming more complex. As the weak position of rock mass, the structural surface has a particularly great influence on the mechanical characteristics of the rock mass. In order to obtain the shear strength characteristic of the structural plane and analyze the influence of morphological parameters such as the undulating angle and bulge degree on shearing, taking medium-low permeability tight sandstone as the research object, four kinds of structural plane samples with different undulating angles (10, 20, 30 and 40°) were prepared with a Python and high-precision engraving machine. Direct shear tests under different normal stresses (2, 4, 6 and 8 MPa) and shear rates (0.6, 1.2 and 2.4 mm/min) were performed, and the shear mechanical properties were analyzed. The structural surfaces before and after shearing were scanned using a high-precision three-dimensional scanner, so as to evaluate the roughness of the structural surface and determine the influence from various factors on the shear characteristics. The test results showed that for the structural plane with the same undulating angle, the peak shear stress increased approximately linearly with an increase in normal stress at a 0.6 mm/min shear rate and an increment speed of approximately 0.82, while the peak shear stress negatively correlated with the shear rate at a value of 4 MPa for normal stress. The larger the undulating angle was, the greater the influence of the shear rate (the shear stress decreased by 2.31 MPa at a 40° angle). When the normal stress and the shear rate were fixed, the peak shear stress corresponding to the structural surface gradually increased with the increase in the undulating angle, and the maximum increment was 5.04 MPa at 4 MPa normal stress and a 0.6 mm/min shear rate. An analysis of the morphological characteristics of the structural plane showed that when the undulating angle (40°) and the normal stress (6 and 8 MPa) were larger, the damage of the structural plane became more obvious, the shear point was closer to the tooth valley position, and the mechanical bite force and friction force of the structural plane were better utilized. When the shear rate was lower (0.6 mm/min), the friction characteristics of the shear surface were more visible, the shear was increasingly sufficient, and the corresponding shear strength was also greater. [ABSTRACT FROM AUTHOR]

For simulating the actual working conditions, a series of gradient ratio tests of geotextile filtering clay are completed by using an improved gradient ratio permeameter that can apply vertical load. The tests are carried out under the condition of the critical hydraulic gradient (1.0) and hydraulic gradient equal to 2.0, respectively, with the 4th layer of clay soil in Shanghai and the short fiber needle punched non-woven geotextile. The variation of the filtration performance of geotextile with hydraulic gradient and normal stress is studied by changing the vertical load. The results show that the hydraulic gradient and normal stress are the important factors affecting the clogging characteristics and the permeability of geotextile filter. The gradient ratio of the geotextile filter clay increases with the increase of the vertical load, but there is no impermissible clogging when it is stable. Under a certain load, the coefficient of permeability decreases with time and then tend to stabilize. The stabilized coefficient of permeability decreases with the increase of the vertical load. The hydraulic gradient from 1.0 to 2.0 also causes the increase of the gradient ratio and the decrease of the permeability. The test results better reflect the filtration effect of the geotextile filter under the actual working conditions, which can provide references for similar engineering design.

This research article represents the recompacted dense sand sample behaviour and stress distribution in the direct shear box. In Lithuania, sand is quite common on a construction site, in general about 32%. To reduce the influence of the shear box design on the experimentally determined values of the soil strength parameters, it is necessary to know the regularities of the change of the normal load acting in the shear plane. Three different normal stresses of 50, 100, and 200 kPa were applied to the dense sand in the direct shear boxes during experimental and numerical simulation. The results showed an obvious evidence of non-uniformity of stress for standard and raised specimens. The numerical analysis exhibited that when the sample is loaded only with a vertical load, approximately 75% of that load is transferred to the sample bottom, 84% to the shear plane, and 95% to the top. At the end of the shear test, the vertical force in the shear plane reaches maximum, the normal stress is higher by 13.5% than applied on the sample top. The shear strength of sandy soils were influenced by box size and sample height too. The improved shear box apparatus allows to estimate the vertical load at shear plane.

• Normal stress increases work-hardening rate and delays necking of pure titanium thin sheet. • Normal stresses increase the activity of most slip systems. • A large number of FCC lamellas and twins are formed under normal stresses. • Both twins and FCC lamellas are beneficial for improving ductility. • Normal stress facilitates surface grain deformation and inhibits surface roughening. Improving the formability of sheet metal is a constant challenge in microforming. In this study, applying normal stresses to the specimen surface is found to be an effective method for improving the ductility of pure titanium sheets. This case only occurs when the normal stress is higher than a critical value. By characterizing the microstructure, it is found that the normal stress induces a change in the deformation mechanism, which improves the work-hardening rate and the capacity for homogeneous deformation. The plastic deformation mechanism of pure titanium thin sheets undergoes a transformation from exclusively slip-based to a multi-mechanistic mode that couples slip, twinning, and FCC phase transformation. Normal stress exacerbate the deformation of surface grains and inhibit surface roughening. Moreover, normal stress activates deformation twins and FCC phase transformation by increasing the Schmid factor of the associated twin/slip systems. FCC phases and deformation twins contribute to enhancing the work-hardening rate through mechanisms such as the dynamic Hall-Petch effect, reorientation texture hardening, and dislocation substructure strengthening. Moreover, they enhance the material's ductility by providing additional deformation modes to accommodate strain. By virtue of the coordinated action of various deformation mechanisms, a more uniform distribution of thickness strain is achieved. It delays onset of plastic instability and enhances the formability of thin sheets. Considering the changes in dislocation density induced by different microstructures, a modified model is constructed. Based on the dislocation density and the surface layer model, this model predicts the flow stress size effect, as well as changes in flow stress and work hardening rate induced by normal stress due to microstructure transformation. This work provides a complete understanding of the mechanical property response and microstructure evolution under normal stress. It also gives a feasible solution for improving the formability of titanium thin sheet in microforming. [ABSTRACT FROM AUTHOR]

Two-component particle image velocimetry was employed to measure the influence of surface roughness on a Mach 2 boundary layer. Three surface conditions were examined: a smooth wall, patterned diamond-shaped roughness, and an approximately random realistic roughness. The response of the boundary layer was characterized in ensemble-averaged measurements of the mean velocity and Reynolds stresses. The streamwise development of the mechanical distortions introduced by the diamond-shaped roughness was also explored through observation of roughness-generated shock waves and changes in the boundary-layer profile. Measurements acquired at three streamwise locations are consistent with the trends observed in other studies when scaled by the roughness friction velocity. Ensemble-averaged outer-scaled streamwise velocity profiles showed a velocity deficit in the near-wall region. Inner-scaled boundary-layer profiles showed a downward vertical shift in the scaled velocities of 4.5 and 3 for the diamond roughness and nonuniform/realistic roughness topologies, respectively. These values show similar responses to the results seen in the literature for similar test conditions. The roughness effects were shown to increase in magnitude along the streamwise distance. [ABSTRACT FROM AUTHOR]

The purpose of the NASA Juncture Flow experiment was to acquire high-quality flowfield details deep in the corner of a wing-body junction specifically for the purpose of computational fluid dynamics (CFD) validation. A truncated DLR F6 wing was used along with a flat-sided fuselage with windows that allowed both laser Doppler velocimetry and particle image velocimetry measurements to be made very close to the corner. This paper describes the experiment and its results. It also makes comparisons between the wind-tunnel data and Reynolds-averaged Navier-Stokes CFD results using a new version of a quadratic constitutive relation that was recently developed to improve separated corner-flow predictions. This validation experiment provides useful flowfield data that can be used to test the ability of CFD methods and models to accurately represent separated juncture flow physics. [ABSTRACT FROM AUTHOR]