Normal Stress Effects Research Articles

Calendering of non-isothermal viscoelastic sheets of finite thickness: A theoretical study

Abstract In this article, the sheeting of pseudoplastic material under non-isothermal conditions has been studied. It is an excellent forecasting instrument for sheeting, where the thickness of the sheet is relatively thin in relation to the roll size, according to theoretical study based on the lubrication theory. At the calendering process, the detachment point is determined by taking the material parameter’s impact into account. The governing equations are derived for the constitutive equation of the Carreau fluid with momentum and energy equations. Suitable non-dimensional parameters are used to develop the non-linear partial differential expressions into ordinary differential systems. The maximum pressure, roll separating force, normal stress effect, and power delivered to the fluid by rolls are among the engineering-relevant quantities that are determined. Moreover, a graphic analysis is conducted to examine the impact of different material parameters on the temperature profile, pressure gradient, velocity profile, and pressure distribution. The results specific mechanism is explained in depth.

Experimental and Numerical Study on Nonlinear Shear Behavior and Constitutive Model of Deep Shale Laminae Planes

The direct shear tests showed that the degradation of unevenness and waviness of the laminae plane is the primary reason for the dynamic decrease in shear strength. A shear constitutive model was proposed which considers the scale effect and the asperity geometry of the unevenness and waviness of the laminar plane. The evolution of the shear strength and stiffness with a normal stress and scale effect during the shearing of shale laminae planes was explored. The results show that high normal stress aggravates the stiffness hardening of laminae planes and forms larger peak shear stress and peak shear displacement. At the lab scale, the increase in the unevenness wavelength has a hardening effect on the shear stiffness and strength. The small-scale unevenness contributes most to the shear strength of shale laminae planes at the lab scale. At the field scale, the increase in the waviness wavelength has a softening effect on the shear stiffness and strength.

Mechanical behavior of en-echelon joints under cyclic shear loading conditions: Roles of joint persistence and loading conditions

Studying the mechanical response of en-echelon joints under cyclic shear loading conditions can provide novel insights into the instability of jointed rock masses under seismic conditions. To investigate the effects of joint persistence, normal stress, cyclic distance, and shear velocity on the cyclic shear behavior of en-echelon joints, a series of cyclic shear tests in the laboratory was performed. Findings revealed that the failure morphography of en-echelon joints manifested through brecciated shear zones and abraded rupture surfaces, resulting in notable reductions in shear strength and significant compressibility. The degradation factor of shear strength ranged from 0.363 to 0.708 after ten cycles. The shear strength degradation factor showed an inverse relationship with joint persistence and normal stress while exhibiting a direct correlation with cyclic distance over ten cycles. En-echelon joints characterized by moderate joint persistence, high normal stress, small cyclic distance, and low shear velocity demonstrated increased cyclic friction strength. Moreover, normal stress and joint persistence exerted a more significant influence on shear strength compared to cyclic distance and shear velocity. For en-echelon joints, shear stiffness increased during small shear displacements with cycle number while decreased during large shear displacements; shear stiffness was inversely proportional to the cyclic distance and joint persistence, and directly proportional to the normal stress. Compressibility of en-echelon joints correlated directly with joint persistence, normal stress, cyclic distance, and shear velocity. Compared to normal stress and cyclic distance, joint persistence and shear velocity exhibited less influence on compressibility

Global and Local Shear Behavior of the Frozen Soil–Concrete Interface: Effects of Temperature, Water Content, Normal Stress, and Shear Rate

The interface between soil and concrete in cold climates has a significant effect on the structural integrity of embedded structures, including piles, liners, and others. In this study, a novel temperature control system was employed to conduct direct shear tests on this interface. The test conditions included normal stress (25 to 100 kPa), temperature (ranging from 20 to −6 °C), water content (from 10 to 19%), and shear rates (0.1 to 1.2 mm/min). Simultaneously, the deformation process of the interface was continuously photographed using a modified visual shear box, and the non-uniform deformation mechanism of the interface was analyzed by combining digital image correlation (DIC) technology with the photographic data. The findings revealed that the shear stress–shear displacement curves did not exhibit a discernible peak strength at elevated temperatures, indicating deformation behavior characterized by strain hardening. In the frozen state, however, the deformation softened, and the interfacial ice bonding strength exhibited a positive correlation with decreasing temperature. When the initial water content was 16% and the normal stress was 100 kPa, the peak shear strength increased significantly from 99.9 kPa to 182.9 kPa as the test temperature dropped from 20 °C to −6 °C. Both shear rate and temperature were found to have a marked effect on the peak shear strength, with interface cohesion being the principal factor contributing to this phenomenon. At a shear rate of 0.1 mm/min, the curve showed hardening characteristics, but at other shear rates, the curves exhibited strain-softening behavior, with the softening becoming more pronounced as shear rates increased and temperatures decreased. Due to the refreezing of interfacial ice, the residual shear strength increased in proportion to the reduction in shear rate. On a mesoscopic level, it was evident that the displacement of soil particles near the interface exhibited more pronounced changes. At lower shear rates, the phenomenon of interfacial refreezing became apparent, as evidenced by the periodic changes in interfacial granular displacement at the interface.

An extended mesoscaled M-K model for predicting discrete ultimate strains and evaluating the effect of normal stress on forming limits

Due to the size effect, the formability of metal sheets diminishes and the ultimate strain points exhibit a more discrete distribution. This poses a huge challenge to the process design and manufacture of microparts. This paper presents a modified mesoscopic scale forming limit model based on the M-K model. The model extends the forming limit curve (FLC) into forming limit bands to predict the discrete nature of the ultimate strain. In addition, a method for applying normal stresses to increase the forming limit of thin metal sheets is proposed. The effects of normal stresses on surface roughening and flow stresses in thin metal sheets were evaluated and quantified by uniaxial tensile experiments under normal stresses. The results show that the normal stress suppresses the increase of surface roughness and improves the work hardening rate. The effect of normal stresses on forming limits was obtained using a constructed model. The results show that the predictions of the proposed model are able to include almost all the ultimate strain points. The forming limit bands are more inclusive and safer than the single forming limit curve. In addition, the forming limits of thin plates under normal stresses are significantly increased, which is attributed to the suppression of surface roughening and the increase of strain hardening index. The forming limit bands proposed in this paper provide a more reliable form of forming limit assessment for thin metal plates. The proposed method of applying normal stresses provides a robust and inexpensive process route to address the challenge of poor formability of thin metal sheets.

Effects of Particle Size and Normal Stress on the Frictional Stability and Healing of Simulated Basalt Gouges: Implications for Lunar Seismicity

Effects of Particle Size and Normal Stress on the Frictional Stability and Healing of Simulated Basalt Gouges: Implications for Lunar Seismicity

Thermoelastic analysis of FG-CNTRC cylindrical shells with various boundary conditions and temperature-dependent characteristics using quasi-3D higher-order shear deformation theory

Abstract. This study focuses on performing static analysis of FG-CNTRC cylinder shells with various boundary restrictions, including thermomechanical responses. The governing equations are developed by taking into account the temperature-dependent material features, the quasi-3D high-order shear deformation hypothesis, and the normal transverse stress effect. The temperature gradient inside the thickness is expected to fluctuate, and the distribution pattern is derived by using the heat transfer equation and considering the temperature boundary limitations. A singular trigonometric series and the Laplace transform are used in an analytics solution to address basic equations. This study primarily examines the stress levels at the border region. The findings indicate that it is crucial to take into account the abrupt rise in stress at the boundary area, particularly when the shell’s relative length is small. The reciprocal impact of pressure and temperature load is also emphasized. Significant findings indicate that thermal load may either augment or diminish stress levels, contingent upon the orientation of the pressure and thermal load effect. The results of the study of this issue serve as the foundation for the calculation and design of relevant structures in practical applications. Furthermore, this serves as a foundation for the creation of more intricate issues in the forthcoming.

Experimental studies on the interfacial shear characteristics between joint concrete and foamed polymer in cross-river shield tunnel

The inadequate grouting performance in cross-river shield tunnels is primarily due to the insufficient bonding strength between the grouting material and the tunnel segments. In this study, a series of tests were conducted to compare foamed polymer and common grouting materials, focusing on the tangential bonding performance of the interface with tunnel segment concrete under varying humidity conditions. The applicability of polymer for treating leaks in cross-river shield tunnels was explored. The effects of polymer density, interfacial humidity, interfacial roughness, and normal stress on the shear strength of the polymer-concrete interface were investigated. A mathematical model reflecting the interface shear characteristics between polymer and concrete was established and validated. The test results have shown that, due to the fast reaction speed and high expansion rate, foamed polymer was found to be a feasible solution for addressing leakage in cross-river shield tunnels. Compared with common grouting materials, the density of foamed polymer is controllable, and the shear strength between foamed polymer and concrete segments is less affected by humid conditions. The minimum shear strength of the interface between foamed polymer and concrete is 1.2 MPa, while the maximum is 2.0 MPa. Foamed polymer can meet the needs of leakage treatment of cross-river shield tunnel. The interfacial shear strength between foamed polymer and concrete segments is directly proportional to the polymer density, interfacial roughness, and normal stress, and inversely proportional to the level of humid in the tunnel. The influence of various factors on interfacial strength is ranked as follows: polymer density > interfacial humidity > normal pressure > interfacial roughness. The residual error of linear regression mathematical model for the shear strength of interface between foamed polymer and segment concrete follows a normal distribution. The fitting results were proven to be accurate, allowing for the intuitive prediction of the quantitative relationship between shear strength and multiple influencing factors.

Effects of Mean Normal Stress and Microstructural Properties on Deformation Properties of Ultrahigh-Strength TRIP-Aided Steels with Bainitic Ferrite and/or Martensite Matrix Structure.

The effects of mean normal stress on the deformation properties such as the strain-hardening, strain-induced martensite transformation, and micro-void initiation behaviors of low-carbon ultrahigh-strength TRIP-aided bainitic ferrite (TBF), bainitic ferrite/martensite (TBM), and martensite (TM) steels were investigated to evaluate the various cold formabilities. In addition, the deformation properties were related to the microstructural properties such as the matrix structure, retained austenite characteristics, and second-phase properties. Positive mean normal stress considerably promoted strain-induced martensite transformation and micro-void initiation, with an increased strain-hardening rate in an early strain range in all steels. In TM steel, the primary martensite matrix structure suppressed the micro-void initiation through high uniformity of a primary martensite matrix structure and a low strength ratio, although the strain-induced transformation was promoted, and a large amount of martensite/austenite constituent or phase was contained. A mixed matrix structure of bainitic ferrite/primary martensite in TBM steel also suppressed the micro-void initiation because of the refined microstructure and relatively stable retained austenite. Promoted micro-void initiation of TBF steel was mainly promoted by a high strength ratio.

Measurement of 3D joint surface morphology and estimation for shear mechanical behavior: A theoretical model and experimental investigation

The majority of rock engineering instabilities are primarily due to shear slips and failures on the joint surfaces, and the measurement of joint surface morphology is crucial for shear strength evaluation. In this study, the high-precision 3D laser scanner was first used to characterize and digitally reconstruct the surface morphology of various joints. The evaluation method of joint surface roughness was modified according to the 2D profile data and shear direction. Then, the effects of normal stress and initial joint roughness coefficient on the shear mechanical behavior were investigated by experimental method. The damage evolution characteristics and failure mechanism of the joint surface are analyzed by acoustic emission monitoring and image binarization calculations. The research results indicate that as the normal stress and initial joint roughness coefficient increase, the peak shear stress and shear displacement, residual strength, and cumulative AE counts of rock joints display an increasing trend. Based on the evolution of mechanical parameters, a new mechanical model of rock joints to predict shear strength and deformation was developed, which was validated by comparing the theoretical prediction curves with test results. A good concordance was achieved between the shear test and theoretical results, indicating that the developed model can effectively predict the shear strength and deformation of joint surfaces under different normal stress and roughness. This research results are expected to provide a valuable guidance for early warning and evaluation of geological disasters.

Experimental study on the shear behavior of saw-toothed ice-rich debris–rock interface: effects of undulation, ice content, normal stress, and temperature

Experimental study on the shear behavior of saw-toothed ice-rich debris–rock interface: effects of undulation, ice content, normal stress, and temperature

A comparative study of progressive failure of granite and marble rock bridges under direct shearing

Shear failure of rock bridges is an important process in geological phenomena, including landslides and earthquakes. However, the progressive failure of natural rock bridges has not yet been fully understood. In this work, we carried out direct shearing experiments on both granite and marble rock bridges, and applied acoustic emission (AE) monitoring throughout the experiments. With the mechanical curves and the evolution of AE activity (including AE energy rate and b value), the failure of rock bridges can be divided into three pre-failure phases and one ultimate failure phases. We analyzed the effects of normal stress and lithology on the pre-failure phases. We noted that with the increasing of normal stress, the length of stable cracking phase decreases and the length of unstable cracking phase slightly increases, except for marble rock bridges at high normal stress, which maintains a great proportion of stable cracking phase that possibly results from the great off-fault damage. Increasing normal stress also suppresses the dilation of granite rock bridges, but has a different effect on marble rock bridges, which also suggests the effect of lithology on failure modes.

Investigation on mechanical behaviors and energy characteristics of deep-buried marble in a hydraulic tunnel in Southwest China

Shear behavior of rock is of great significance to the stability of deep-buried rock in transportation geotechnical engineering. A series of direct shear tests are carried out on deep-buried marble with different size and shape to focused on the mechanical properties and size shape effects of deeply buried marble, which have been less studied previously. The results show that the size and shape of the specimen have a relatively small impact on the trend of shear stress-shear displacement curve. The failure morphology at the front and rear surfaces shows a significant normal stress effect. Some properties of specimens with different sizes and shapes increase with increasing normal stress, but the dilation angle generally decreases with the increasing normal stress. With the increase of the shear plane size of intact specimen, the cohesion decreases gradually while the internal friction angle increases steadily. The difference value in peak strain between axial compression and direct shear tests is relatively small while it is huge for the peak compression and peak shear strength. The results in this study are beneficial for further understanding the shear mechanics, energy evolution process and size effects of deep-buried rock in transportation geotechnical engineering.

Viscoelastic wetting: Cox–Voinov theory with normal stress effects

Viscoelastic wetting: Cox–Voinov theory with normal stress effects

PHÂN TÍCH TĨNH VỎ TRỤ FG-CNTRC CHỊU TẢI TRỌNG CƠ NHIỆT VỚI TÍNH CHẤT VẬT LIỆU PHỤ THUỘC VÀO NHIỆT ĐỘ

This article presents a thermo-elastic static analysis of the FG-CNTRC cylinderical shell subjected to a thermo-mechanical load. The temperature is assumed to vary through the thickness, and the temperature distribution is derived from the heat transfer formula. The gorvening equations of thermoelastic analysis are established by using the higher-order shear deformation theory, including the transverse normal stress effect. The material properties of FG-CNTRC are temperature-dependent. Using an analytical solution that used the single trigonometric series and the Laplace transformation to solve these equations of shell with the different boundary conditions. The present approach is validated by comparing the results with published results. The effects of different boundary conditions and temperatures on the displacement and stresses of the FG-CNTRC cylindrical shells are investigated. The results show the jumping variation of the stress components at the boundary position. Besides, when the temperature increases, the maximum absolute value of the axial stress increases while that of the circumferential stress decreases.

Bonded particle model for dilated polyhedron considering fracture modes and its application to lateral resistance of ballast bed in cold regions

Considering the spatial arrangement characteristics of bonded irregular particle systems, this paper first constructs irregular dilated polyhedron elements based on the Voronoi cutting algorithm and Minkowski Sum theory. Subsequently, by extending the traditional sphere-based BPM (Bonded Particle Model) to irregular particle elements, a novel dilated polyhedron bonding-breaking model considering different fracture modes is developed under arbitrary contact modes. A collision example between two bonded square particles and a rigid plate is adopted to verify the stability of the model. Later, the difference between the tensile-shear fracture mode and the mixed fracture mode with damage process for contact bond is compared by the discrete element simulations of the tension-fracture behavior between two bonded square particles and the uniaxial compression simulation of frozen ballast aggregate. Finally, the influence of section size on the lateral resistance of the ballast bed structure at low temperatures is discussed using the dilated polyhedron BPM. The results showed that the developed dilated polyhedron BPM considering different fracture modes can realize mechanical behaviours between bonded irregular particles. Compared with the tensile-shear fracture mode, the mixed fracture mode not only considers the combined effect of normal and tangential stress on the bond but also realizes the damage deformation and stiffness attenuation of the bond, which can achieve the “delayed” fracture effect. Meanwhile, the model also shows good reliability in analyzing large-scale engineering problems, such as the mechanical performance of low-temperature ballast beds. The research effectively develops the bonding and breaking model of irregular elements and provides a new perspective for the contact-bond-fracture behavior simulation of irregular granular materials.

Shear Mechanical Properties of Bolt-Grout Interface under Different Bolt Surface Profiles

The shear behavior of the Bolt-Grout interface has a significant effect on the stability of a bolting system. In this paper, a series of shear tests were conducted on Bolt-Grout interfaces, and the effects of rib spacing, rib angles, and normal stress on the shear characteristics and failure modes of the Bolt-Grout interface were investigated. The results showed that the shear strength varied nonlinearly with an increase in rib spacing and angle, and also that it increased linearly with an increase in normal stress. With smaller rib spacings, the effect of rib spacing on peak shear strength was more apparent. The failure modes of the interface can be categorized as shear-slip failure, shear-break failure, and composite failure. The proportion of shear-slip failure and shear-break failure mainly depends on the rib spacing, rib face angle and normal stress.

Mechanical resistance behind fiber-reinforced polymer pile: Role of clay minerals

Due to the geotechnical design requirements of the fiber-reinforced polymer (FRP) pile embedded in clay, interface friction evolution between the FRP pile and clay plays a crucial role in determining the pile shaft resistance. It is observed from the experimental evaluation that the earth pressure and shear rate affect the pile-soil interface behavior. In this study, a cross-linked epoxy resin is created to contact a siloxane surface of kaolinite in the molecular dynamic simulation. The interfacial accommodation between kaolinite and epoxy resin is studied. In order to investigate the effect of normal stress and sliding velocity on nanoscale friction characteristics, the steered molecular dynamics is utilized to simulate the sliding of the kaolinite model on the surface of the epoxy resin. Simulation results show that the calculated peak interface shear coefficient decreases nonlinearly as the normal stress increases, which follows a logarithmic relationship consistent with the FRP-soil interface shear test. On the other hand, it is observed that two distinct velocity regions, slow pulling mode (5–200 m/s) and fast pulling modes (300–800 m/s), are well fitted by extended Bell theory. The stick–slip motion is only found in slow sliding velocity mode. This increasing tendency of the energy barrier with the normal stresses indicates that higher pulling forces are required for the FRP to slide along the soil at higher normal stress. The present work provides a fundamental understanding of the friction mechanisms between kaolinite and epoxy resin.

Experimental investigation on shear strength deterioration at the interface between different rock types under cyclic loading

The shear strength deterioration of bedding planes between different rock types induced by cyclic loading is vital to reasonably evaluate the stability of soft and hard interbedded bedding rock slopes under earthquake; however, rare work has been devoted to this subject due to lack of attention. In this study, experimental investigations on shear strength weakening of discontinuities with different joint wall material (DDJM) under cyclic loading were conducted by taking the interface between siltstone and mudstone in the Shaba slope of Yunnan Province, China as research objects. A total of 99 pairs of similar material samples of DDJM (81 pairs) and discontinuities with identical joint wall material (DIJM) (18 pairs) were fabricated by inserting plates, engraved with typical surface morphology obtained by performing three-dimensional laser scanning on natural DDJMs sampled from field, into mold boxes. Cyclic shear tests were conducted on these samples to study their shear strength changes with the cyclic number considering the effects of normal stress, joint surface morphology, shear displacement amplitude and shear rate. The results indicate that the shear stress vs. shear displacement curves under each shear cycle and the peak shear strength vs. cyclic number curves of the studied DDJMs are between those of DIJMs with siltstone and mudstone, while closer to those of DIJMs with mudstone. The peak shear strengths of DDJMs exhibit an initial rapid decline followed by a gradual decrease with the cyclic number and the decrease rate varies from 6% to 55.9% for samples with varied surface morphology under different testing conditions. The normal stress, joint surface morphology, shear displacement amplitude and shear rate collectively influence the shear strength deterioration of DDJM under cyclic shear loading, with the degree of influence being greater for larger normal stress, rougher surface morphology, larger shear displacement amplitude and faster shear rate.

Effects of Mean Normal Stress on Strain-Hardening, Strain-Induced Martensite Transformation, and Void-Formation Behaviors in High-Strength TRIP-Aided Steels

To analyze various types of cold formability in TRIP-aided polygonal ferrite (TPF), annealed martensite (TAM), and bainitic ferrite (TBF) steels, the effects of the mean normal stress on the strain-hardening, strain-induced martensite transformation, and void-formation behaviors were investigated. The strain-hardening behavior was influenced by positive mean normal stress and was hardly influenced by zero and negative mean normal stresses in all steels. Positive mean normal stress promoted the strain-induced martensitic transformation behavior, especially in TBF steel due to the high mechanical stability of the retained austenite. The void-formation behavior was also promoted by positive mean normal stress, especially in TPF steel. These behaviors were also related to the microstructural properties, such as the matrix structure, retained austenite characteristics, and second phase.