Shear Strength Of Material Research Articles

The Effect of a Moving Boundary on the Shear Strength of Granular Materials in a Direct Shear Test

The boundary state significantly influences the soil shear strength. Therefore, it is necessary to overcome the limitations of existing indoor test instruments and determine the differences in the shear properties of granular materials to ensure the economic feasibility and mechanical integrity of engineering structures. In this study, the core formula for the direct shear test was derived from the static balancing analysis of the shear box, the external force on the specimen, and the internal force on the shear surface. Three loading methods were then developed by the staggered state of the upper and lower boxes: the upper box moving shear loading method (UM), the lower box moving shear loading method (LM), and the bidirectional moving shear loading method (BM). Finally, by manipulating the motion boundary, the discrete element method (DEM) was employed to simulate the shear test of granular materials. Among the three loading methods, the order of the peak shear stresses was as follows: UM > BM > LM. Moreover, the order of the sample post-peak stress uniformities was as follows: LM > BM > UM. A shear strength conversion formula was then proposed. The findings of this study promote the advancement of the shear mechanics theory of granular materials in direct shear testing and can serve as a scientific basis for the design and manufacture of shear equipment.

Shear strength of angular granular materials with size and shape polydispersity

Shear strength of angular granular materials with size and shape polydispersity

Study on Deterioration Characteristics of a Composite Crossarm Mandrel in a 10 kV Distribution Network Based on Multi-Factor Aging.

This paper presents a study that conducted 5000 h of multi-factor aging tests on 10 kV composite crossarms, considering the natural environment in coastal areas and actual power line operations. Various aging conditions, such as voltage, rain, temperature, humidity, salt fog, ultraviolet light, and mechanical stress, were applied during the tests. The research initially analyzed the influence of multi-factor aging on the bending and tensile properties of the full-size composite crossarm. Subsequently, a detailed investigation was carried out to assess the impact of aging on the mechanical properties, electrical insulation properties, and microscopic characteristics of the composite crossarm core bar. Results indicated that the tensile strength and bending strength of the full-size composite crossarm mandrel experienced minimal changes after aging, remaining well within operational requirements. However, the silicone rubber outer sheath's hydrophobicity decreased, leading to the appearance of cracks and holes on the surface, which provided pathways for moisture and salt infiltration into the mandrel. As a consequence, the bending strength and shear strength of the mandrel material were reduced by 16.5% and 37.7%, respectively. Moreover, the electrical performance test demonstrated a slight change in the mandrel's leakage current, while the electrical breakdown strength decreased by 22.8%. Microscopic analysis using SEM, three-dimensional CT, and TGA revealed that a small amount of resin matrix decomposed and microcracks appeared on the surface. Additionally, the fiber-matrix interface experienced debonding and cracking, leading to an increased moisture absorption rate of the mandrel material.

Strength and Deformation Behavior of Equestrian Riding Surfaces Improved with Recycled Geosynthetics

Abstract Recycled geosynthetic materials can be incorporated into sand-based soils to improve their shear characteristics and enhance surface response in different engineering applications. This paper summarizes research undertaken to explore the effect of recycled geosynthetic components added to silica sand, whose complex and engineered soil matrix is currently used in the equestrian riding industry. Approximately 120 direct shear tests were used to evaluate the shear strength and compressibility behavior of several riding surface mixtures blended with a combination of short polymer fibers and cut-up pieces of geotextile fabric along with other components such as crumb rubber and binding agents. As expected, results suggest that the shear characteristics of these surfaces are very sensitive to changes in material composition as geosynthetics are incorporated into the soil matrix. It was demonstrated that the addition of geosynthetics can significantly increase the shear strength of granular materials. Although these tests were initially performed for equestrian riding surface applications, the findings of this research could be used for other engineering applications (e.g., lightweight fills, temporary roadways, etc.).

Fluidity and Strength of Loess-Based Quick Consolidated Backfill Material with One High-Water Content.

To study the flow and strength characteristics of loess-based backfill materials, orthogonal tests were used to design a cemented backfill material combining loess, high-water content materials, cement, and fly ash. By using the range, analysis of variance, and multi-variate regression analysis, influences of four key factors on the initial setting time, diffusivity, compressive strength, and shear strength of the backfill material were investigated. These four factors included the mass concentration of loess water (A), the content of high-water content materials (B), cement content (C), and content of fly ash (D). The results showed that the initial setting time, diffusivity, compressive strength, and shear strength of the backfill material were 13~33 min, 400~580 mm, 0.917-3.605 MPa, and 0.360-0.722 MPa, respectively, all distributed in wide ranges. For the initial setting time, the four factors were listed in descending order as A > D > B > C according to their influences; for diffusivity, the four factors were listed as A > B > C > D; for the compressive strength, the four factors were ranked as A > C > D > B; for the shear strength, the four factors were ranked such that A > C > D > B. With regard to the comprehensive index, the four factors were such that A > B > D > C. That is, the factors were listed in descending order as the mass concentration of loess water, cement content, the content of fly ash, and content of high-water content materials according to their significance in influencing characteristics of the loess-based backfill material. Comprehensive analysis indicated that the fluidity of the material was mainly influenced by the mass concentration of loess water, and the two were negatively correlated. The hydro-consolidation effect of materials with high-water contents accelerated material solidification. The strength of the backfill material was mainly influenced by the cement content while only slightly affected by contents of other materials. In this way, a prediction model for characteristic parameters, namely, fluidity and strength, of the loess-based backfill material under the action of various factors was established.

Thermodynamic constitutive model for granular soils considering particle shape distribution

Particle shape has a significant effect on the shear strength and shear dilatancy properties of granular materials. This study presents a granular thermodynamic theory investigate the effects of particle shape and distribution on the mechanical properties and behavior of granular materials. The theory model outcomes closely resemble experimental results, effectively capturing the impact of particle shape on the mechanical properties and shear dilation of granular materials. The paper analyzes the relationship between a granular system's plastic behavior and granular temperature and explores the influence of irregularly shaped granular on the system's strength and kinetic energy activity. The granular temperature behavior during external loading is studied, showing that granular temperatures increase to a maximum value before gradually decreasing to a more stable state. Simulation results based on the proposed model also indicate obvious effects of nonuniform particle-shape distribution on the mechanical properties of granular materials, providing a comprehensive insight into the underlying mechanisms of the particle-shape effects from the perspective of thermodynamics.

Experimental Study on the Reciprocating Shear Characteristics and Strength Deterioration of Argillaceous Siltstone Rockfill Materials

The reciprocating shear mechanical properties and strength deterioration mechanisms of rockfill materials are of great research significance for high-fill slope stability analysis. To study the shear strength characteristics of argillaceous siltstone rockfill materials with different fabric characteristics under reciprocating shear loading, we analyzed the shear strength, hysteresis loop area, damping ratio, shear strength parameter, and shear stiffness of coarse-grained soils with different coarse grain contents using a coarse-grained soil direct shear testing machine capable of reciprocating shear and revealed their strength deterioration mechanism. The test results show that the shear strength of argillaceous siltstone rockfill materials is significantly affected by the coarse grain content and the number of reciprocating shears. Specifically, the shear strength increases with the coarse grain content and decreases with the number of reciprocating shears. The hysteresis loop area is positively correlated with the coarse grain content and negatively correlated with the number of reciprocating shears. The damping ratio is not related to the coarse grain content but tends to decrease with the number of reciprocating shears. Soil cohesion and the internal friction angle increase with the coarse grain content and decrease with the number of reciprocating shears. The soil failure shear stiffness is linearly correlated with the coarse grain content, and the normalized shear stiffness is logarithmically related to the number of reciprocating shears. According to these relationships, an empirical formula for the shear stiffness of argillaceous siltstone rockfill materials under different coarse grain contents and different numbers of reciprocating shears can be established to provide a basis for analyzing rockfill stability.

Effects of irregular pores on the shear properties of the plane

Through section analysis and optical microscope observation of thick-section composite materials, it is found that there are significant differences in pore micro-characteristics of samples with different thicknesses. It is pointed out that the difference in pore micro-characteristics in the composite matrix is one of the reasons for the change in the interlaminar shear strength of composite materials. In this paper, irregular pore profiles are obtained through image processing, and the parameters to quantitatively characterize the microscopic characteristics are proposed. A randomly generated three-dimensional representative volume element (RVE) model including fiber, matrix, fiber/matrix interface, and pores. The effect of irregular pores with different sizes and distributions on the interlaminar shear strength of composite materials is given. The RVE numerical analysis results show that the interface failure between the fiber and the matrix near the pore causes damage. At the same porosity, the shear strength decreases with the increase of the maximum pore size. At the same time, the porosity concentration also has a significant effect on the interlaminar shear strength of thick section composite. The numerical results verify that the influence of pores on the interlaminar shear properties of thick-section composites is related to the microscopic characteristic parameters of pores.

Atomistic simulation of hardening in bcc iron-based alloys caused by nanoprecipitates

The paper presents results of atomistic simulations of hardening in model bcc iron-based alloys due to secondary phase precipitates formation. The simulations are based on shear stress relaxation technique and experimental data on morphology of precipitates. Atomistic methods were developed to reproduce the shear strength of bcc iron-based materials. The large-scale atomistic simulations were carried out for model binary alloys: Fe–Cr imitating low-carbon ferritic and ferritic–martensitic steels and Fe–Cu imitating low-carbon bainitic steel. A representative set of atomic structures is compiled with account for the chemical composition and concentration and size of secondary phase, comparable with those in steels of the considered classes and available experimental data on radiation and thermal induced precipitation. Obtained results on hardening were verified against experimental data and the dispersed barrier hardening model.

Breakage in quasi-static discrete element simulations of ice rubble

Breakage of particles plays a key role in force transmission in granular materials. Discrete element method (DEM) simulations are often used to model granular materials, but modeling particle breakage in them remains a challenge. Models for breakage of non-spherical particles are scarce and often the existing models are computationally heavy to be used in simulations with large numbers of particles. To address this, the present study develops a particle breakage model for quasi-static DEM simulations of non-spherical particles that fail due to shear. The model is novel, since it is based on experimental observations and high resolution modeling. Breakage models based on experimental evidence are rare as it is often virtually impossible to gain detailed data on the mechanisms related to breakage. The developed particle breakage model was integrated into a DEM code and direct shear box experiments on ice rubble, a granular material consisting of ice particles, were then simulated. Accounting for particle breakage in DEM simulations improved their accuracy: simulations were compared to experiments and the results were found to be in better agreement when particle breakage was taken into account. The effect of particle breakage on the shear strength of a granular material was found to be independent of particle size, decreasing fast with increasing particle strength. The combined effect of shear box length and breakage was also studied. The results showed that the strength of a granular material may be determined reasonably well with a shear box that has a box to particle length ratio greater than 60.

Research on the Model for the Friction Coefficient of Resin-Based Friction Material and Its Experimental Verification

Resin-based friction materials have been widely used in the friction braking of automobiles and power machinery. Based on experiments for the variation law of friction and wear morphology, a new model for the friction coefficient of resin-based friction materials was proposed, which includes the effects of both the micro convex body on the surface of the friction material and the frictional film generated during the friction process. This quantitative model of friction coefficient materials was established for the modelling of shear strength, compressive strength, shear strength of the frictional film, contact load and wear morphology. The shear strength, compressive strength and wear morphology of the friction material were adjusted by changing the content of basalt fibers and flaky potassium magnesium titanate. Finally, the accuracy of this quantitative model of friction coefficient was verified through experiments on friction samples with different formulations and by changing the frictional contact load. The results show that the predicted friction coefficient of the model is in good agreement with the experimental friction coefficient, the difference between the upper and lower limits of the forecast is only 5.03% and 2.30%, respectively. Meanwhile, the influence of the ratio of shear strength to compressive strength on the friction coefficient is greater than the proportion of wear morphology. The proposed friction model provides a reference value for the study of new resin-based friction materials.

Experimental investigation of surface roughness changes of an underground structure's material during its driving into the ground

The mechanical interaction between dispersed soils and the surface of underground structures is fundamental in generating their load-bearing capacity. The technical and economic efficiency of piles and supporting structures depends on the friction forces that appear on the contact of their material with the soil. One of the main factors which has a significant influence on friction forces is the roughness of the material surface. Installation of underground structures, such as pile driving or vibro-driven sheet piling, is accompanied by long periods of material contact with dispersed soils: some structural segments can slip on the soil for tens of metres. As a result, it is likely that the surface properties of the underground structure material will change during this process. Although there is a considerable amount of tribological research, the methodology of such experiments does not fully represent the pile driving process in the soil mass. This means that it is not possible to accurately estimate the change in the surface properties of underground structure materials as they are driven into the soil using the results of these studies. The present paper describes a simulation of an underground structure made of three different materials: steel, fibreglass and fluoroplastic; in fine medium sand. The roughness of the materials was monitored while they were moving in the sand. It was found that with increasing diving depth the roughness of each material becomes less. And the value of this change is influenced by such material properties as material density, shear strength and hardness.

Mechanical behavior and particle crushing of irregular granular material under high pressure using discrete element method

This study investigated the influence of stress levels on the mechanical behavior and particle crushing of irregular granular materials. Granular materials with irregular sides were modelled using the discrete element method. A new method of using a shear fracture zone to characterize the deformation of irregular granular materials under high pressure was proposed. The crushing energy is analysed based on the first law of thermodynamics. The shear strength of irregular granular materials shows significantly nonlinear behavior due to particle crushing. The deformation behavior can be characterized with the help of particle rotation under low confining pressure, and can be characterized with the help of particle breakage under high confining pressure. Granular materials easily break into many single fine particles under high confining pressure. The breakage degree can be represented by the value of crushing energy. Irregular granular materials have a large breakage degree under high confining pressures. It weakens the stability of engineered structures constructed from granular materials.

Grain size distribution does not affect the residual shear strength of granular materials: An experimental proof.

Granular materials are used in several fields and in a wide variety of processes. An important feature of these materials is the diversity of grain sizes, commonly referred to as polydispersity. When granular materials are sheared, they exhibit a predominant small elastic range. Then, the material yields, with or without a peak shear strength depending on the initial density. Finally, the material reaches a stationary state, in which it deforms at a constant shear stress, which can be linked to the residual friction angle ϕ_{r}. However, the role of polydispersity on the shear strength of granular materials is still a matter of debate. In particular, a series of investigations have proved, using numerical simulations, that ϕ_{r} is independent of polydispersity. This counterintuitive observation remains elusive to experimentalists, and especially for some technical communities that use ϕ_{r} as a design parameter (e.g., the soil mechanics community). In this Letter, we studied experimentally the effects of polydispersity on ϕ_{r}. In order to do so, we built samples of ceramic beads and then sheared these samples in a triaxial apparatus. We varied polydispersity, building monodisperse, bidisperse, and polydisperse granular samples; this allowed us to study the effects of grain size, size span, and grain size distribution on ϕ_{r}. We find that ϕ_{r} is indeed independent of polydispersity, confirming the previous findings achieved through numerical simulations. Our work fairly closes the gap of knowledge between experiments and simulations.

Deformation of trenched multilayer pipelines during large lateral displacement due to subsea geohazards

Large lateral displacement of trenched multilayer pipelines may be induced by ground movement, landslides, ice gouging, etc. The significant difference between the shear strength of the backfill material and the native soil may affect the pipeline-backfill-trench interaction, the failure mechanisms, and consequently the lateral soil resistance. However, this challenging and less-explored aspect has not been covered thoroughly in design codes, even for rigid pipes. This paper investigates the influences of multilayer pipeline-backfill-trench interaction on the deformation of pipe section, soil failure mechanism, resultant lateral soil resistance, and soil pressure on the pipe by large deformation finite element analyses. A decoupled model consisting a Coupled Eulerian-Lagrangian (CEL) approach with a rigid pipe in ABAQUS was created along with a finite element (FE) model of multilayer flexible pipe in ANSYS to assess their relative merits for this problem. A parametric study was conducted to investigate the influences of key factors, including the trench geometry, stiffness of backfill material, native seabed soil properties, burial depth, and intensity of pipeline-trench bed interaction. The study showed that the ignorance of the pipeline-backfill-trench interaction by using uniform soil might result in underestimation and overestimation of the lateral soil resistance at different displacement amplitudes.

Influence of different solid particles in friction modifier on wheel-rail adhesion and damage behaviours

Friction modifier (FM) is widely used in the curve section to suppress the damage and noise between the wheel and rail. This paper compared typical third body materials, including water, oil and FM to explore their influencing mechanism on wheel-rail adhesion and damage. Furthermore, FM samples containing different solid particles were prepared. The tribological performance of these FM samples, water and oil were tested with a twin-disc testing apparatus and a hand-push tribometer. The results indicated that the shear strength of the third body material plays a vital role in the friction. The hardness of solid particles in FM greatly influences the friction control performance of FM. The change in the hardness of the solid particles makes the FM exhibit either “lack of lubrication” or “over lubrication”, that both are detrimental to the wheel and rail interface. For FM material, it is necessary to select solid particles according to the adhesion and damage comprehensively. The most suitable particle in this paper was kaolin.

3D limit analysis of rock slopes based on equivalent linear failure criterion with tension cut-off

Hoek-Brown (HB) failure criterion is widely used to predict the strength of intact or heavily jointed rock mass. For stability analysis of rock slopes governed by the HB failure criterion, the equivalent linearity to Mohr-Coulomb (MC) criterion is often adopted, leading to the well-known equivalent Mohr-Coulomb method (EMCM). Existing studies on EMCM analysis mainly consider the shear strength of rock material, while consideration of the tensile strength is rare. This contradicts the fact that the underlying tensile strength of rock mass has considerable impact on the rock slope stability in real world. In this regard, this paper proposes a limit analysis-based approach that can account for tension in the three-dimensional (3D) stability analysis of HB rock slope. This approach is established on the equivalent linearity of the HB criterion with consideration of tensile strength, known as the equivalent tension cut-off MC method (ETMCM), and using a horn-like 3D mechanism of limit analysis. The safety factor solutions given by the proposed approach are validated by previous studies and numerical results. Parametric studies are conducted to investigate the effect of rock tensile strength on slope stability. Results show that the consideration of tension leads to a more conservative safety factor and a sharper curvature of the failure surface, and these impacts tend to be more obvious with the increases in slope inclination and slope width. Finally, the stability of the HB rock slope under seepage conditions is studied using the proposed approach. The results indicate that the effect of tensile strength is highly remarkable in seepage circumstances.

Prediction of the Elastic Properties of Ultra High Molecular Weight Polyethylene Reinforced Polypropylene Composites Using a Numerical Homogenisation Approach

The elastic properties of polypropylene (PP) and ultra-high molecular weight polyethylene (UHMWPE) textile composites were predicted using finite element analysis (FEA). A three-dimensional (3D) model of composites was generated by introducing a cloth made from UHMWPE fibers into a PP matrix. Regarding the weaving type, the reinforcement was fabricated by replicating plain and twill-woven materials. Additionally, the elastic properties of the composites were compared and evaluated by varying the volume fraction of UHMWPE in the composites from 45% to 75%. The elastic modulus of the composites containing textiles prepared using the plain weaving method was greater than that of the composites containing textiles prepared using the twill weaving method. Along the axial direction, the shear modulus calculation results for the plain-woven reinforcement textiles were distinct. However, the shear moduli in both directions were similar in the twill-woven reinforcement materials. Moreover, the future development of composites should quantify the simulation by measuring the tensile strength and shear strength of real materials.

Shear creep behaviour of soil–structure interfaces under thermal cyclic loading

The coupling effect of initial shear stress and thermal cycles on the thermomechanical behaviour of clay concrete and sand–concrete interfaces has been studied. A set of drained monotonic direct shear tests was conducted at the soil–concrete interface level. Samples were initially sheared to half of the material's shear strength and then they were subjected to five heating/cooling cycles before being sheared to failure. The test results showed that the effect of thermal cycles on the shear strength of the materials was negligible, yet shear displacement occurred during application of thermal cycles without an increase in shear stress, confirming the coupling between the shear stress and temperature. In addition, a slight increase of stiffness due to the coupling was observed which diminished with further shearing.

Investigation of shear properties of axial flow fan blade material with partial woven jute reinforcements

Axial flow fan blades are often made from glass-fibre reinforced polymers (GFRP), which are increasingly used in making composites. These non-biodegradable composite reinforcements, on the other hand, pose significant environmental and human health risks, especially at the end of its service life. Until now, companies have hustled to use GFRP without regard to disposal. Glass fibres recycling is expensive and unjustifiable. On the other hand, natural fibres are gaining popularity due to their sustainability. So, they're suitable for polymer composites. To improve the biodegradability of GFRP composites after service life, it must be determined to what extent natural fibres can be reinforced in them without significantly affecting mechanical properties. In this work, the material C1 is an 18-ft axial flow fan blade material made of GFRP. The materials C2 to C6 were made by substituting one layer of C1 with woven jute and changing the location of the jute in C1. All the materials are tested for shear strength as per IS 1998-62. The shear strength results were validated by using the finite element software ANSYS R19.2. The woven jute fibre composite has higher shear properties when jute is placed in the second position (C2). C2 preserves the shear strength of the blade material and also improves biodegradability after service life.