Strength Criterion Research Articles

Investigation on directional rock fracture mechanism under instantaneous expansion from the perspective of damage mechanics: A 3-D simulation

With developments in geotechnical engineering, directional rock-breaking technology has been applied in large quantities. As a novel non-explosive rock-breaking technology, Instantaneous Expansion with a Single Crack (IESC) has been studied and applied to some extent in the past few years. IESC uses expansion gas to fracture rock mass in the predetermined direction by a special energy-gathering tube, which has the advantages of high safety, strong directional ability, and easy to operate. At present, there is a lack of in-depth investigation on the directional fracture mechanism of rock under the action of IESC. According to damage mechanics, the fundamental reason for rock fracture is due to the initiation, expansion, and penetration of internal cracks. In this study, a 3-D numerical model based on the theory of progressive failure is established to study the directional rock fracture mechanism of IESC, while a Conventional Expansion (CE) model without energy-gathering tube is established for comparative research. The maximum tensile stress criterion and unified strength criterion are used to identify damage failure of the element. The evolution processes of four key parameters are simulated, the types and degrees of tensile/compressive damage of the unit are analyzed, which aims to decipher the model's directional fracture mechanism under IESC loading. The established 3-D numerical models are validated by comparing with experimental results. The research results can contribute to further understanding the directional rock fracture mechanism of IESC and provide a theoretical basis for the application of IESC in the field.

Selection of drive system and chassis structure basic design and analysis for medium-sized urban electric bus

One of the alternative solutions to address environmental and energy challenges is the utilization of electric vehicles, particularly in the domain of public transportation. The focus was on the development of medium-sized electric buses to expand the reach of electric-powered public transport. The design process encompasses the selection of vehicle components, such as the drive system, and the configuration of a space frame chassis structure. The drive system was meticulously chosen and proved to exceed the design requirements, as it achieved a gradability of 12.44%, surpassing the targeted capability of 10% slope. Moreover, it boasts a maximum speed of 108 km/h, exceeding the design requirement of a maximum speed of 50 km/h, and can accelerate at a rate of 1-2 m/s². The chassis design adheres to regulations and standards and is grounded in the strength, stiffness, and natural frequency criteria. The initial chassis design did not meet the design requirement, however, through several iterations, a chassis structure was achieved with a vertical bending stiffness of 8.57 kN/mm and a torsional stiffness of 9.63 kNm/°. Based on the outcomes of this research, a drive system and chassis structure design that fully satisfies all the existing design requirements has been successfully attained.

Strength, durability, and toxicity characteristics of water treatment sludge based geopolymers for subgrade application

This study examined the strength, durability and toxicity characteristics of geopolymer made from water treatment sludge (WTS) using fly ash (FA) and ground granulated blast furnace slag (GGBS) as binding materials for the subgrade application. The mechanical properties of WTS-FA-GGBS geopolymers were assessed considering various parameters such as binder proportions, curing period, curing condition, Sodium silicate (SS) to Sodium hydroxide (SH) ratio (i.e. SS/SH), and Sodium hydroxide (NaOH) concentration. The results showed that increasing binder proportions, NaOH concentration, and curing period positively impacted the strength of the WTS-FA-GGBS geopolymer. The unconfined compressive strength (UCS) of the geopolymer samples with an SS/SH ratio of 2.5 showed higher compressive strength than those at an SS/SH ratio of 1. WTS-FA-GGBS geopolymers cured at 100°C showed increased UCS values after 1 to 3 days, but strength decreased after 7 days due to a faster geopolymerisation reaction, resulting in excessive moisture loss and microcracks in the geopolymerized samples. The study also found that all the geopolymer samples met the minimum strength criteria for cement-stabilized mix with a maximum mass loss of 8.17 % are well within the specified limits (<14 %) as per IRC:37–2018. The California Bearing Ratio (CBR) values of WTS-FA-GGBS geopolymers, which range from 41.11 % to 260.32 %, surpass the minimum criteria for cement stabilized subgrade or subbase material, as specified by IRC: SP:89–2010. Additionally, the changes during geopolymerization were confirmed by FESEM, EDS, and XRD analysis. The toxicity characteristic leaching procedure (TCLP) test results showed that the amounts of heavy metals in the geopolymer leachate were within the USEPA-mandated limits.

EFFECTS IN DISCRETE AND CONTINUOUS STRENGTHENING OF MACHINES ELEMENTS

The work describes approaches to problem solving of operational and effective improvement of the technical and tactical characteristics of military and civilian machines: tanks, armored vehicles, diesel locomotives, turbo-expander power plants, autonomous power plants of strategic objects, etc. For this purpose, fundamentally new methods of strengthening of contacting machines elements are being developed. These methods combine the advantages of discrete and continuous strengthening methods, which have largely exhausted their capabilities by now. Qualitative features and advantages of proposed discrete-continuous strengthening methods require effective implementation. We are talking about the justification of progressive technical solutions based on the criteria of strength and durability. For this purpose, the methodology of multi-criteria synthesis in the expanded space of design and technological parameters will be improved. In addition, as a basis for substantiating advanced technological solutions, a set of related problems of analysis of the stress-strain state, friction and wear is formed. Therefore, based on the improved system approach, a much higher level of strength and durability of the reinforced structural parts is achieved than with traditional methods. The results of test problems solving are illustrated. In the result, micro-macromodels are generalized to determine the joint influence of structural and technological factors, microstructure, physical and mechanical properties of materials of reinforced layers on the contact interaction and stress-strain state of representative fragments of the system of discrete-continuous reinforced bodies. The results of analysis of combined influence of structural and technological factors, microstructure, physical and mechanical properties of materials reinforced layers have been established on the contact interaction and stress-strain state of test representative fragments of the system of discrete-continuously reinforced bodies. At the same time, a significant influence of reinforced layers properties was established on strength of contacting bodies.

Comparative study of multiple statistical damage mechanics models for rock behaviors under high temperature

Under the influence of external factors such as high temperature, chemical corrosion, and loading-unloading cycles, micro-cracks and pores may develop within rock structures. Continuum damage mechanics (CDM) characterizes these micro-defects arising within rocks, investigating the physico-mechanical behaviors of rocks in damaged states. This study, grounded in the theoretical framework of CDM and utilizing the Mohr-Coulomb failure criterion, integrates different probability distributions and damage coupling methods to develop three statistical damage models. The investigation primarily explores the effects of strength criteria, probability functions, and damage coupling mechanisms on the statistical damage models. In addressing the complex interplay between rock micro-defects and external stressors such as high temperatures and chemical corrosion, this study leverages the principles of CDM within the Mohr-Coulomb criterion framework. It advances the field by developing three innovative statistical damage models, enriched by diverse probability distributions and damage coupling methods. The research delineates the substantial impact of strength criteria, probability functions, and damage coupling mechanisms on the behavior of these models. Notably, it achieves a synthesis of theoretical constructs and experimental validation, demonstrating the models' capacity to reflect the nuanced behaviors of damaged rock accurately. Furthermore, this investigation contributes a methodological blueprint for statistical damage model construction, underscoring the critical selection of strength criteria and probability distributions. These efforts fortify the theoretical underpinnings necessary for the enhanced engineering application of statistics-driven damage analysis.

Viscoelastic plastic interaction of tunnel support and strain-softening rock mass considering longitudinal effect

A simplified two-stage method was employed to provide an explicit solution for the time-dependent tunnel-rock interaction, considering the generalized Zhang-Zhu strength criterion. Additionally, a simplified mechanical model of the yielding support structure was established. The tunnel excavation is simplified to a two-stage process: the first stage is affected by the longitudinal effect, while the second stage is affected by rheological behavior. Two cases are considered: one is that the rigid support is constructed during the first stage, and the other is that constructed at the second stage. Distinguished by the support timing at the seconde stage, different kinds of the “yield-resist combination” support method are divided into three categories: “yield before resist” support, “yield-resist” support, and “control-yield-resist” support. Results show that the support reaction of “control-yield-resist” is much higher than that of “yield before resist” if the initial geostress is not very high, but the effect is not obvious on controlling the surrounding rock deformation. So, the “yield before resist” support is much more economical and practical when the ground stress is not very high. However, under high geostress condition, through applying relatively high support reaction actively to surrounding rock at the first stage, the “control-yield-resist” support is superior in controlling the deformation rate of surrounding rock. Therefore, in the high geostress environment, it is recommended to construct prestressed yielding anchor immediately after excavation, and then construct rigid support after the surrounding rock deformation reaches the predetermined deformation.

Passing-through I-plates-to-SHS moment resisting joints subjected to symmetric bending moments

When using hollow structural section (HSS) members in multi-storey buildings, beam-to-column moment resisting connections’ design raises critical questions to tackle. With conventional welded and bolted joints’ response being generally very flexible, the design resistance becomes governed by a deformation criterion rather than a strength criterion. This underscores the necessity for smart reinforcement techniques. A widespread solution is the diaphragm approach, in which the stiffeners usually protrude over the tubular column. The solution of plates passing through the HSS column is another stiffening option which was studied recently for CHS, yet, SHS columns have not been subject to comparable scrutiny. The objective of this paper is to study experimentally, numerically, and analytically the mechanical behaviour of I-beam-to-SHS column moment resisting joints using passing through I-plates under symmetric bending moments. The testing of two full-scale specimens corroborates previous findings with CHS columns in the elastic regime. However, significant deviations were observed in the post-peak response, revealing new insights into the behaviour of SHS columns. Failure was due to progressive buckling of passing through plates and yielding of tube-wall in transverse compression. A finite element model using solid and contact elements is developed and validated against experimental data. This model underscores how loads are redistributed between the tube wall and passing plates. A simplified version of the FE model is used to perform a thorough parametric numerical analysis on 101 configurations expanding upon the experimental test database by varying geometrical parameters such as passing plate thickness, tube, and beam dimensions. Finally, an analytical model integrating the different components of the joint is proposed to evaluate the initial rotational stiffness and the bending resistance.

Damage ratio strength criterion for asphalt mixtures and its application in rutting prediction

The current damage ratio strength theory is employed to predict the multiaxial strength of asphalt mixtures at various temperatures. Based on the dimensionless triaxial strength of asphalt mixtures, the values of six empirical parameters are recommended to establish the corresponding dimensionless strength criterion. The multiaxial strength data of diverse asphalt mixtures, including OGFC-13, AC-13, AC-20, AC-25, SMA-13, and SUP12.5 at different temperatures, are employed to validate the proposed criterion, which is then compared with other criteria. The results indicate that the suggested dimensionless strength criterion with uniform parameter values can accurately predict the true triaxial, confining triaxial, and biaxial strength values of asphalt mixtures across various temperatures. Furthermore, the proposed criterion is employed to elucidate the mechanical mechanism of rutting, offering a valuable insight for predicting flow rutting of pavement under loads.

Assessing the Reliability of Rock Slopes Based on the Nonlinear Strength Criterion

Assessing the Reliability of Rock Slopes Based on the Nonlinear Strength Criterion

Gravity dam displacement monitoring using in situ strain and deep learning

AbstractRecent studies in dam displacement monitoring primarily focus on single‐response monitoring or model updating using advanced techniques. Few studies involve the combination analysis of displacement with other synchronized responses utilizing their monitoring characteristics. In situ strain data provide a strength‐safety perspective for dam displacement monitoring. The challenge lies in that estimating displacement directly using limited discrete strain data may be misleading. This paper analyzes the relationship between displacement and global, and multipoint local strains from the perspective of the differences in load effects of gravity dams, and indicates that introducing appropriate state factors improves the estimation. A displacement estimation model driven by strain data and state factors is developed using stacked convolutional neural network, and the variable relationships within the model are interpretated via accumulated local effects. Incorporating specific strength criteria, a novel displacement monitoring indicator based on the tensile safety of the dam heel is proposed. A case study of a gravity dam showcases the effectiveness of the proposed approach in comparison with the solely strain‐based model and the traditional hydrostatic‐seasonal‐time factors‐based model.

Interaction between yielding tunnel support and strain-softening rock mass based on the three-dimensional strength criterion

Interaction between yielding tunnel support and strain-softening rock mass based on the three-dimensional strength criterion

To justification of concrete strength criterion at biaxial compression

Introduction. Numerous experimental data from Russian and foreign researchers indicate that the classical plasticity hypotheses do not take into account the different resistance to uniaxial tension and compression, the influence of the spherical tensor. At the same time, experiments show that the ultimate resistance depends on the type of stress state, and hydrostatic pressure increases the strength and plasticity of solids. Aim. To establish the dependence of the influence of the second component of stresses during biaxial compression of concrete on the parameters of the complete diagrams of deformation of the material σbR and εbR it is necessary to describe these diagrams, and to construct a closed curve on the plane of the main stresses (concrete strength criterion). Materials and methods. Based on the experimental materials of foreign and domestic researchers, including the experiments of the authors of the article, methods of mechanics of deformed solids, limit curves and a closed curve on the plane of the main stresses in the form of a chain line forming the smallest area strength surface in the form of a catenoid are proposed. Results. The article provides an analysis of the known strength criteria from the point of view of their geometric interpretation in the stress space. It is shown that these studies relate mainly to metals and metal structures, and for the design of reinforced concrete and steel-concrete structures in a complex stress state, it is necessary to develop an appropriate criterion for the strength of concrete. Conclusions. As a result, the proposed limit curves and the surface (material strength criterion) on the plane of main stresses in the form of a catenoid accurately reflect the behavior of concrete under conditions of uniform and uneven flat stress state, and the equation of the surface in the form of a catenoid is a generalization of the equations of limit curves for each of the three types of flat stress state. At the same time, there is no overestimation of strength in the "compression – compression" area in this case.

Experimental study on the failure characteristics and mechanism between spalling failure and rockburst

To reveal the differences in the failure characteristics and mechanisms between rockburst and spalling failure, the comparison experiment between spalling failure and rockburst occurred in a circular cavity were carried out. Experiment results reveal that rockburst is accompanied by the intense ejection of fragments, whereas spalling failure features with the slow detachment of fragments. Additionally, besides the plate and flaky fragment, the rockburst fragment exhibits more pronounced blocky features. In terms of strength and deformation characteristics, the peak stress for rockburst is 1.04 times that of spalling failure, whereas the plastic deformation of spalling failure is 1.75 times that of rockburst. Furthermore, considering the micro failure and energy evolution process, three interpretations were proposed to elucidate the distinct mechanisms between rockburst and spalling failure, including: (i) The swift invasion of shear cracks triggers the buckling failure of pre-existing plate-like fractures, causing the fragment ejection observed in rockburst. When shear cracks not substantially contribute to the evolutionary process, the continuous penetrating of the pre-existing tensile cracks will culminate in the gradual delamination and spalling failure of the sidewall. (ii) The energy dissipating behavior determines the distinct mechanisms of rockburst and spalling failure. Almost all of the energy input preceding rockburst is converted into the elastic strain energy of rock units, whereas the energy input preceding spalling failure results in greater energy dissipation (about 1.85 times that of rockburst). (iii) under the framework of Mohr-Coulomb strength criterion, it has been revealed that the rock units of spalling failure adhere to the minimum failure energy criterion. However, the energy accumulated by the rock units prior to rockburst surpasses the minimum energy necessary for failure. This residual energy provides the fractured rock mass with kinetic energy, ultimately leading to a violent ejection phenomenon of rockburst.

A Novel Mohr–Coulomb–Matsuoka–Nakai Strength Criterion for Rocks Considering Brittle–Ductile Domain

A Novel Mohr–Coulomb–Matsuoka–Nakai Strength Criterion for Rocks Considering Brittle–Ductile Domain

DEM-based study on mechanical behavior and strength criterion in layered slate under triaxial compression

DEM-based study on mechanical behavior and strength criterion in layered slate under triaxial compression

A numerical strain-softening solution of a circular opening in nonlinear yield rock masses

Strain-softening behavior occurs when the surrounding rock reaches its peak load, complicating the prediction of stress and displacement. The linear Mohr-Coulomb yield criterion and semi-linear Hoek-Brown yield criterion are widely used in elastoplastic analysis. However, the established criteria struggle to universally describe the nonlinear behavior of various rock types. This study aims to overcome the difficulty and propose the solution of surrounding rock in a circular tunnel following any nonlinear yield criterion and plastic potential function. The derivation of the equivalent cohesive strength and frictional angle for an arbitrary nonlinear yield criterion in the form of σ1=fσ3 using the secant method, along with the determination of the equivalent dilatancy angle for any nonlinear plastic potential functions, was conducted. Concerning the elastoplastic solution of a thick-cylinder, a numerical strain-softening solution for a circular tunnel in nonlinear yield rock masses was derived. Verification of the proposed solution was performed against the established analytical and/or numerical elasto-(brittle-)plastic and strain-softening solutions in rock masses following the Mohr-Coulomb, (generalized) Hoek-Brown, and unified strength criteria. The impact of critical plastic shear strain on displacement, plastic radius, and residual radius was further analyzed. The predictions of displacement and residual region for the Jinping II project also meet the field test results.

Mechanical properties and constitutive model of artificial frozen sandy soils under true triaxial stress state conditions

Triaxial compression tests were conducted on frozen sandy soils under a constant minimum principal stress (σ3 = 1.6 MPa) and various intermediate principal stresses (σ2 = 1.6, 3.4, 5.2, 7.0, 8.8, 9.8 MPa). The purpose of the research was to investigate the influence of intermediate principal stress on mechanical properties of frozen soil, and to establish a constitutive model to predict the stress-strain relationship of frozen soil under complex stress state. The test results obtained demonstrated that the crack damage stress and failure stress initially increase and then decrease with an increase in the intermediate principal stress. However, the crack initiation stress exhibits an initial increase up to a specific value, after which it stabilizes. From the perspective of crack propagation, the influence mechanism of intermediate principal stress on the strength was discussed. With the variation of stress state, the difference between intermediate principal strain and minimum principal strain gradually increases. The deformation difference was revealed using the stress superposition principle and Poisson's effect. Finally, the constitutive model based on the Weibull distribution and Drucker-Prager strength criterion can accurately represent the stress-strain relationships of frozen sandy soils under true triaxial stress states.

Multiscale modeling of diffuse damage and localized cracking in quasi-brittle materials under compression with a quadratic friction law

The diffuse damage and localized cracking of quasi-brittle materials (i.e., rocks and concretes) under compression can be delineated by a matrix-microcrack system, wherein a solid matrix phase is weakened by a large number of randomly oriented and distributed microcracks, and the macroscopic cracking is formed by a progressive evolution of microcracks. Several homogenization-based multiscale models have been proposed to describe this matrix-microcrack system, but most of them are based on a linear friction law on the microcrack surface, rendering a linear strength criterion. In this paper, we propose a new quadratic friction law within the local multiscale friction-damage (LMFD) model to capture the plastic distortion due to frictional sliding along the rough microcrack surface. Following that, a macroscopic Ottosen-type nonlinear strength criterion is rationally derived with up-scaling friction-damage coupling analysis. An enhanced semi-implicit return mapping (ESRM) algorithm with a substepping scheme is then developed to integrate the complex nonlinear constitutive model. The performance of LMFD model is evaluated compared to a wide range of experimental data on plain concretes, and the robustness of ESRM algorithm is assessed through a series of numerical tests. Subsequently, to effectively describe the localized cracking process, a regularization scheme is proposed by combining the phase-field model with the established LMFD model, and the discretization independent crack localization is numerically verified.

Study on physical and mechanical properties of high-grade highway subgrade slate in permafrost region under freeze–thaw cycles

The subgrade crushed-rocks of Gonghe-Yushu (Gongyu) Expressway in Qinghai Province are seriously weathered, resulting in a series of pavement diseases. Among the weathered crushed-rocks, the weathering degree of slate is particularly serious, and its physical and mechanical properties, weathering resistance and applicability are not clear. Therefore, this paper takes the slate in the subgrade crushed-rocks of Gongyu Expressway as the research object, and drills the core of the slate rock block to make a cylindrical standard sample, and uniaxial and triaxial compression tests, nuclear magnetic resonance tests, and electron probe micro-analysis tests were performed on it within 50 freeze–thaw cycles (FTC) under saturated conditions. According to the test results, the mass, longitudinal wave velocity, and strength of the slate specimens all decrease with the increase of the number of FTC, the cohesion (C)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$({\ ext{C}})$$\\end{document} increases first and then decreases, and the change trend of internal friction angle (φ) is completely opposite to the cohesion. The FTC has an expansion effect on the pores of the slate specimens, and the microstructure of the rock particles on the specimen’s surface is removed and becomes smooth. The results of mechanical tests are used in the Hoek–Brown (H-B) strength criterion, and a unified expression of the H-B criterion suitable for slate in permafrost regions is established. The above conclusions can provide some construction reference and maintenance of high-grade highways in cold regions.

Stress-dependent instantaneous cohesion and friction angle for the Mohr–Coulomb criterion

The strength criterion of rock is essential for stability control and safety design of geotechnical engineering constructions. Due to its widespread adoption, the Mohr–Coulomb (M-C) criterion is prominent among strength criteria. However, the M-C criterion is constrained by three significant limitations: it fails to capture the nonlinear strength response, overlooks the critical state, and disregards σ2. This study introduces a novel Stress-dependent Instantaneous Friction angle and Cohesion (SIFC) model for the M-C criterion to represent the convex strength envelope of intact rock, covering the spectrum from non-critical to critical states. In pursuit of this objective, an innovative approach for calculating these instantaneous shear parameters at each corresponding σ3 is initially introduced. By examining the confining pressure dependency of the instantaneous friction angle and cohesion, the SIFC model is derived and introduced to the M-C criterion. The SIFC-enhanced M-C criterion, utilizing parameters obtained from triaxial tests under lower σ3, delineates the complete non-linear strength envelope in (σ1, σ3) space, covering brittle to ductile behavior. This criterion is then extended to polyaxial stress conditions. Validation through triaxial test data confirms that the SIFC-enhanced M-C criterion accurately reflects the strength characteristics of the tested rocks.