Stress-strain Behavior Research Articles

A Method for Determining Yield Stress of Unsaturated Soils from Lateral Pressure

Abstract Predicting the stress–strain behavior of unsaturated soils is essential for determining yield stress. This paper explores a new method for determining the yield stress of unsaturated soils from the lateral pressure curve. A series of earth pressure at rest (K0) ondometer tests were conducted on unsaturated Yangqin silt clay. Lateral stress was obtained under different saturations and compactness. The relationship curves between lateral and vertical net stress were drawn for each condition. An obvious turning point was observed in the curve, which can be used to determine the yield stress. The oedometer tests were conducted, and the Casagrande and the bilogarithmic methods were used for comparison purposes. The difference between the proposed and traditional methods was less than 17 %. The initial saturation and compactness influence on the yield stress was discussed. The yield stress increased with the decrease in saturation and increases in compactness, which is consistent with that of the classic method. The test results and comparison prove the rationality of the proposed method. No coordinate transformation is required in the proposed method, which is more convenient for data processing. It can be used to determine the yield stress of unsaturated soils from another perspective.

The axial compression mechanical performance of CFRP-confined fully replaced nonnatural coal gangue aggregate columns after freeze[sbnd]thaw cycles

With the continuous mining of coal worldwide, the accumulation of coal gangue, a byproduct of coal production, has increasingly posed severe environmental challenges. To mitigate the environmental pollution caused by coal gangue, this paper proposes the use of processed coal gangue as a replacement for coarse aggregates in concrete. Additionally, carbon fiber-reinforced polymers (CFRP) are employed to confine these square concrete columns, with the aim of expanding the application of nonnatural coal gangue concrete in freezethaw environments. Taking the number of CFRP layers, number of freezethaw cycles, and concrete strength grade as variables, a total of 54 samples were designed. Experimental and theoretical analyses were conducted to investigate the mechanical behavior of CFRP-confined fully replaced nonnatural coal gangue aggregate (FNCGA) columns. The specific conclusions are as follows: (1) Under a freezethaw environment, the stressstrain behavior of the CFRP-confined FNCGA columns undergoes three stages: an elastic ascending stage, a plastic descending stage, and a plastic ascending stage. (2) When the number of freezethaw cycles increases from 100 to 300, the Poisson's ratio of the elastic stage of the sample exhibiting an upward trend. (3) For the three-layer CFRP confined sample, the volumetric strain is positive (in compression), and the bearing capacity of the sample exceeds that of the unconfined concrete by approximately 10%. (4) Compared with existing models and experimental results, the bearing capacity and stressstrain model proposed in this study have greater accuracy, enabling better simulation of the mechanical performance of CFRP-confined FNCGA columns.

Regional Stiffness and Hardening Indices: New Indicators Derived from Multidimensional Dynamic CTA for Aneurysm Risk Assessment.

Two indices, indicating the regional average stiffness and the pace of strain hardening respectively, are derived from the nonlinear stress-strain behavior obtained from biomechanical analysis of aneurysm. A comprehensive method based on electrocardiographic-gated multidimensional dynamic computed tomography angiography (MD CTA) is developed for extracting these mechanical characteristics in vivo. The proposed indices are evaluated by 26 cases including 9 healthy, one aortosclerosis, and 16 abdominal aortic aneurysm cases. The difference of SSI and dSSI value between aneurysmal and healthy groups is up to orders in magnitude. Significant correlation of these indices with the clinical indicator of aneurysm diameter is found. Logistic models based on these indices are capable to sharply discriminate the healthy and the aneurysmal arteries with AUC>0.98. This work introduces new tools and new indices for aortic mechanical assessment which may shed light on understanding the mechanical condition, pathological state and eventually benefit clinical decision-making.

Study on the uniaxial tensile mechanical behavior of two-dimensional single-crystal aluminum nitride

Abstract To investigate the tensile behavior and mechanical properties of single-crystal aluminum nitride (AlN) at the microscopic level, molecular dynamics simulations were used to study the effects of crystal orientation, strain rate, environmental temperature, and hole defect size on fracture strength, fracture mechanism, and potential energy during uniaxial tensile. The results show that the tensile strength of AlN in the [100] crystal direction is stronger. The anisotropic behavior characteristics of Al-N bonds fracture mechanism, crack growth rate, and cracking degree are significant when stretched along the [100], [010], and [110] crystal directions. Under high temperature condition, the lattice structure undergoes changes, causing grain boundaries to move and slip. This facilitates the breaking of bonds, leading to a decrease in tensile strength and a reduction in stored potential energy. Hole defects cause more lattice damage, reducing the energy required for Al-N bonds breakage and facilitating the propagation of microcracks. Additionally, it was found that the strain rate affects the stress-strain behavior of the model. An increase in strain rate leads to an increase in breaking stress, and the rapid deformation of AlN results in more energy being stored in the lattice in the form of potential energy. Therefore, the tensile strength and potential energy are improved.

Neuroevolution machine learning potential to study high temperature deformation of entropy-stabilized oxide MgNiCoCuZnO5

Entropy stabilized oxide of MgNiCoCuZnO5, also known as J14, is a material of active research interest due to a high degree of lattice distortion and tunability. Lattice distortion in J14 plays a crucial role in understanding the elastic constants and lattice thermal conductivity within the single-phase crystal. In this work, a neuroevolution machine learning potential (NEP) is developed for J14, and its accuracy has been compared to density functional theory calculations. The training errors for energy, force, and virial are 5.60 meV/atom, 97.90 meV/Å, and 45.67 meV/atom, respectively. Employing NEP potential, lattice distortion, and elastic constants is studied up to 900 K. In agreement with experimental findings, this study shows that the average lattice distortion of oxygen atoms is relatively higher than that of all transition metals in entropy-stabilized oxide. The observed distortion saturation in the J14 arises from the competing effects of minimum site distortion, which increases with increasing temperature due to enhanced thermal vibrations, and maximum site distortion, which decreases with increasing temperature. Furthermore, a series of molecular dynamics simulations up to 900 K are performed to study the stress–strain behavior. The elastic constants, bulk modulus, and ultimate tensile strength obtained from these simulations indicate a linear decrease in these properties with temperature, as J14 becomes softer owing to thermal effects. Finally, to gain some insight into thermal transport in these materials, with the so-developed NEP potential, and using non-equilibrium molecular dynamics simulations, we study the lattice thermal conductivity (κ) of the ternary compound MgNiO2 as a function of temperature. It is found that κ decreases from 4.25 W m−1 K−1 at room temperature to 3.5 W m−1 K−1 at 900 K. This suppression is attributed to the stronger scattering of low-frequency modes at higher temperatures.

Effect of current collector on the coupled electro-chemo-mechanical performance of graphite electrodes in LiBs.

The current collector, one of the main components in the manufacture of composite electrodes, is mainly used to enhance the mechanical stability and improve the performance and cycle performance of the electrodes. During the electrochemical reaction, the lithium diffusion can induce compressive stress and affect the mechanical performance, lifespan, and performance of batteries. Therefore, this study analyzed the influence of copper foil on the mechanical response and degradation performance of electrodes. In addition, a mathematical model was developed to analyze the effect of copper foil on the stress-strain behavior of the electrodes. The results indicated that the stress and modulus of the graphite electrodes have a non-linear increase with the lithiation process. Based on those findings, utilizing a thinner and more compliant current collector could effectively mitigate the in-plane strain and the stress within electrodes. Thus, developing a thinner and softer copper foil could simultaneously enhance the mechanical properties and specific density of composite electrodes for the next-generation LiBs.

Real-time Observation of Stress-strain Behavior beyond Necking in Martensitic Steel by <i>in-situ</i> Synchrotron X-ray Diffraction

Real-time Observation of Stress-strain Behavior beyond Necking in Martensitic Steel by <i>in-situ</i> Synchrotron X-ray Diffraction

Stress-Strain Behavior of Soft Soil Stabilized with Nickel Slag, Limestone, and Aluminum Hydroxide

Soil stabilization by combining several minerals is a form of material engineering aimed at increasing the bearing capacity of the soil to a higher level. The development of waste-based materials and the utilization of local potential are part of environmentally conscious construction. This study aims to analyses the mechanical behaviour of soil stabilized with several pozzolanic materials derived from nickel processing waste and limestone, which are local materials with very large deposits. ASTM standards were used in this study for both physical and mechanical testing. Unconfined compressive strength (UCS) tests were conducted to compare the mechanical behaviour of stabilized soil with that of natural soil. The test samples used were cylindrical with a diameter of 35 mm and a height of 70 mm. The binding materials consisted of nickel slag, aluminium hydroxide, and limestone, with the amount of each material based on the dry soil weight (γdry). The addition of lime in this study was varied at 2%, 4%, and 6%. The test results generally show that lime variations and curing time affect the increase in unconfined compressive strength (qu), with the highest value of 30.91 kg/cm² observed at 6% lime content after 28 days of curing.

A Methodologic Approach to Study Large and Complex Landslides: An Application in Central Apennines

The evaluation of landslide hazards in seismic areas is based on a deterministic analysis, which is unable to account for various uncertainties in the analysis process. This paper focuses on the probabilistic local seismic hazard analysis and extends the results to the landslide hazard analysis to consider both the uncertainties of the ground deformations and the strengths. The work studies the areas between Nibbiano and Sant’Erasmo hamlets in the Camerino municipality located in central Italy, where all constructions present evidence of damage caused by both the seismic sequence of 2016–2017 and the slope instability. An exhaustive geological and geophysical investigation has clarified the geological, geomorphological, and hydrogeological characteristics of the area, enabling a new characterization of material stress-strain behaviour. The study reveals that the low stiffness of the debris covers, and their fair degree of permeability contribute to potential instability scenarios triggered by both intense rainfall and the effects of strong earthquakes. The goal was to utilize the results to support local urban planning because in-depth knowledge of the possible evolutionary scenarios of the slopes is fundamental to the management of the degree of danger for structures, especially for people. Moreover, it was shown once again how a multi-source approach, with different investigation techniques, cannot be ignored for the study of the evolution of complex landslides.

Stress-Strain Behavior and Strength Development of High-Amount Phosphogypsum-Based Sustainable Cementitious Materials.

Phosphogypsum is a common industrial solid waste that faces the challenges of high stockpiling and low utilization rates. This study focuses on the mechanical properties and internal characteristics of cementitious materials with a high phosphogypsum content. Specifically, we examined the effects of varying amounts of ground granulated blast furnace slag (5-28%), fly ash (5-20%), and hydrated lime (0.5-2%) on the stress-strain curve, unconfined uniaxial compressive strength, and elastic modulus (E50) of these materials. The test results indicate that increasing the ground granulated blast furnace slag content can significantly enhance the mechanical properties of phosphogypsum-based cementitious materials. Additionally, increasing the fly ash content can have a similar beneficial effect with an appropriate amount of hydrated lime. Furthermore, microscopic analysis of the cementitious materials using a scanning electron microscope revealed that the high sulfate content in phosphogypsum leads to the formation of calcium aluminate as the main product. Concurrently, a continuous reaction of the raw materials contributes to the strength development of the cementitious materials over time. The results could provide a novel method for improving the reusing phosphogypsum amount in civil engineering materials.

Comparison of energy absorption characteristics of novel lattice structures inspired by Helleborus petticoat flower and fish scale pattern for different loading orientations

In the present work, arc-shaped, thin-strut-based structures were developed by taking inspiration from the cup shaped Helleborus petticoat flower and fish scale pattern. The designed structures have been additively manufactured with a fused deposition modeling process. In this work, one fish scale pattern inspired structure was developed and named FS structure, whereas two flower-inspired structures were developed and named FL4 and FL8 structures. The static compression tests were conducted to study stress-strain behavior of the proposed structures in two different orientations, viz. orientation:1 (along z-axis) and orientation:2 (along x-axis). Furthermore, the mechanical responses and energy absorption characteristics are comprehensively examined for the proposed structures in both orientations. The structures exhibited higher specific energy absorption (SEA) in orientation:1 compared to orientation:2. The increment in SEA is ∼29 % for FS, ∼298% for FL4, and ∼115% for FL8 structures in orientation:1 compared to orientation:2. Meanwhile, the proposed bio-inspired structures are capable of absorbing energies in the range of 0.06-0.47 MJ/m3, up to densification. Finally, SEA of proposed structures is compared with the SEA of other structures in the available literature.

Towards sustainable construction: Harnessing potential of pumice powder for eco-friendly concrete, augmented by hybrid fiber integration to elevate concrete performance

This study investigates the innovative use of industrial waste pozzolana, specifically pumice powder (PP), as a partial replacement for cement, combined with hybrid fibers in concrete. Seven formulations varying PP content from 10 % to 35 % were tested, identifying 15 % PP as optimal. PP improved porosity due to its fineness, leading to better homogeneity, a refined microstructure, and an optimum compressive strength of 28.8 MPa with reduced permeability, enhancing durability. Hybrid fibers, including steel fibers (SF) from waste tires and polypropylene fibers (PF), improved toughness, ductility, and resistance to brittle failure. Tests on hybrid fiber-reinforced concrete (HyFRC) mixes with 1 % and 2 % hybrid fibers showed up to an 18.09 % increase in compressive, tensile, and flexural strengths. Energy dissipation in compressive response improved by 544.20 %, while flexural and splitting responses increased by up to 299.65 % and 208.57 %. Durability assessments in hydrochloric (HCl) and sulfuric acid (H2SO4) exposure revealed the synergy of fibers and PP enhanced resistance to chemical degradation, with high PF mixes losing as little as 0.04 % strength. Scanning electron microscopy (SEM) confirmed a dense, well-bonded matrix with reduced porosity. Analytical characterizations of mixtures such as energy dispersive x-ray spectroscopy (EDX) were studied. Regression models developed using Popovic’s and Mander’s models, accurately predicted HyFRC stress-strain behavior, closely aligning with experimental results. The integration of PP and hybrid fibers not only improved mechanical properties but also extended service life in harsh environments, offering a cost-effective, sustainable concrete solution.

Effect of particle size distribution and content of limestone powder on compressive response of high-early-strength cement mortars

This study examined the effect of particle size distribution and content of limestone powder on the compressive response of high-early-strength portland cement mortars cured either in water or under ambient conditions. Nineteen mortar mixtures were classified into three groups based on the particle size distribution of the pulverized limestone powders: L (blaine = 3467 cm2/g), M (blaine = 4710 cm2/g), and H (blaine = 5764 cm2/g). The design equations for the compressive strength gain rates and stress–strain relationship of ordinary portland cement (OPC) concrete were adapted for the present mortars. The test results revealed that the 28-d compressive strength (fc′) of the mortars tended to decrease with an increase in limestone powder content, even for mortars containing 5 % limestone powder with small particle sizes. This contrasts with the common trend of the positive effect of limestone powder on the compressive strength of OPC concrete up to a certain substitution level. Furthermore, mortars containing finer limestone powders exhibited a greater rate of decrease in fc′, regardless of the curing conditions. The modified equations show promise for reliably assessing both the compressive strength gain rates at different ages and the stress–strain behavior of high-early-strength portland cement mortars containing limestone powders.

Axial compression stress-strain relationship of lithium slag rubber concrete

Replacing cement with lithium slag and fine aggregate with rubber in concrete solves waste disposal, reduces material consumption, boosts sustainability, and enhances concrete performance. A set of prismatic concrete specimens with varying proportions were designed and experimentally tested in order to study the compressive stress-strain behavior of lithium slag rubber concrete (LSRC). The main factors affecting the specimens were lithium slag substitution ratio (SL=0%, 10%, 20%, 30%) and rubber substitution ratio (SR=0%, 5%, 10%, 15%). The results demonstrated that the LSRC exhibited good integrity during the damage. Furthermore, the incorporation of lithium slag (LS) was found to effectively compensate for the reduction in compressive strength due to the incorporation of rubber. When 10% of the fine aggregate was replaced with rubber and 20% of the cement was substituted with lithium slag, the axial compressive strength, elastic modulus, and peak strain of the tested specimens increased by 21.57%, 6.92%, and 17.26%, respectively. Compared with ordinary concrete, LSRC has good toughness, impact resistance and durability with minimal loss of strength, and has broad application prospects in engineering fields (such as airports, highways, housing expansion joints, concrete floors and railway concrete sleepers, etc.). Based on the experimental data, simplified modified equations to predict the compressive strength, elastic modulus, peak strain and axial stress-strain constitutive model of LSRC were proposed, so as to promote the development of LSRC.

A finite element study on the irradiation-induced mechanical behaviors of aluminum-matrix radiation-shielding composites

Aluminum-matrix radiation-shielding composites play a crucial role in advanced nuclear energy systems and fuel containers owing to their shielding design flexibility and desired structural compatibility. After being irradiated by neutrons, the shielding composites undergo irradiation damage and exhibit irradiation-induced mechanical effects such as irradiation hardening and embrittlement, which directly threaten the industrial application of the material. In this study, a finite element method was used to investigate the irradiation-induced mechanical behavior of radiation-shielding B4CP-WP/Al composites. Using published data on the post-irradiation mechanical property evolutions of the matrix and shielding particles, and incorporating mechanisms of irradiation hardening and embrittlement, a finite element model was developed to describe the deformation of pristine and post-irradiation composites. Simulations of the post-irradiation mechanical properties of the aluminum-matrix radiation-shielding composites were conducted. The simulation results successfully reproduced the experimental findings for both the Al matrix and composites after irradiation. Furthermore, the stress-strain responses and deformation behaviors of the composites at different stages of irradiation damage are discussed. Finally, based on the simulation results, an artificial neural network was trained to efficiently predict the irradiation-induced mechanical behavior of the composites.

Design-oriented stress-strain model for short concrete columns wrapped with FRP sheets

Previous studies have presented models aimed at predicting the axial stress-strain behavior of circular concrete columns wrapped with carbon fiber reinforced polymer (CFRP). The majority of these models were developed based on normal strength concrete (NSC) with strengths below 50 MPa. Moreover, several of these models relied on a limited experimental database. In this study, a large collection of experimental data was gathered, including 310 concrete columns confined with CFRP wraps. This database comprised test results for unconfined concrete with a compressive strength ranging from 19.7 to 169.7 MPa, and a height-to-diameter (H/D) ratio of two. From these data, two new expressions were developed to estimate the ultimate compressive strength and the corresponding strain. To model the stress-strain behavior, new relationship was suggested. A comparison between the proposed model and the experimental results revealed good agreement, outperforming several existing models. Additionally, the expressions for ultimate strength and corresponding strain are simple and accurate, making them easy to apply in design. Furthermore, the proposed model demonstrates superior performance compared to other existing models.

Molecular dynamics study of mechanical stability of Ti4C3 MXene subjected to chirality, temperature, strain rate, and point-vacancy for Lithium-ion batteries

Two-dimensional Ti4C3 MXene has recently emerged as a promising electrode for Lithium-ion batteries (LIBs) because of its outstanding ion-transport abilities and high Li-absorbability. This study employed molecular dynamics simulation to explore the mechanical stability of Ti4C3 MXene subjected to various temperatures, strain rates, and vacancy concentrations. A slightly superior tensile strength and elasticity modulus have been observed along zigzag directions, measuring 148.14 GPa and 29.17 GPa, respectively. On the other hand, armchair-oriented Ti4C3 MXene shows a considerably greater fracture strain of 0.259 due to its strain-hardening tendency at lower temperatures. Elevated temperature decreases both fracture strength and fracture strain, which is opposite to the effect of strain rate. Armchair loading has been revealed to be more sensitive to strain rate than its counter direction. Unlike temperature and strain rate, point vacancy significantly deteriorates the elastic modulus of Ti4C3 MXene. Carbon vacancies are more probable than titanium vacancies, which have less formation energy. The atomistic deformation profile supports the predicted values of fracture strain from stress-strain behavior. This in-depth study offers a detailed understanding of the mechanical behavior of Ti4C3 MXene under diverse circumstances, which will aid further experimental study and be beneficial for adopting Ti4C3 as anode materials in LIBs.

Soft Soil Stabilization using Co-Pyrolytic Biochars from Sewage Sludge and Nymphaeale, an Invasive Plant Biomass

This research addresses a significant gap in current literature by proposing an alternative to traditional carbon positive soil stabilizers by utilizing sewage sludge in conjugation with Nymphaeale, an invasive plant biomass derived co-pyrolytic biochars to stabilize the soft soil, with a focus on understanding strength gaining mechanism. Various combinations of sewage sludge and Nymphaeale biomass underwent thermogravimetric analysis in a nitrogen environment, suggesting 450⁰C as pyrolysis temperature for biochar synthesis. Soft soil, which is considered problematic for construction, was blended with five distinct dosages (0%, 5%, 7.5%, 10%, and 12.5%) of biochars (BC75:25, BC50:50, BC25:75) by weight and unconfined compressive strength values were examined over curing periods of 1, 7, 14, and 28 days. The stress-strain and failure behaviour of soil-biochar mixes varied depending on the type of biochar used. SBC25:75 mixes exhibited ductile behaviour, whereas SBC75:25 mixes showed brittle failure. Furthermore, unconfined compressive strength values of soil-biochar mixes increased 4-5 times with maximum strength achieved at 10% dosage of BC50:50. Biochar dosages led to a reduction in moisture content and an increase in alkalinity and conductivity of the mixes, facilitating the initiation of pozzolanic reactions. The combined findings from the various analysis suggested that the presence of free oxides of calcium in biochars disrupted the laminated structure of the soil and reacted with silica and other aluminum silicates, resulting in the densification of the structure and the formation of cementing mineral phases in the mixes. Overall, the research-work emphasizes the idea of creating novel environmentally friendly binders for soil stabilization through the utilization of waste materials.

Concurrent experimental testing and computational micromechanical modeling of a UD NCF GFRP composite ply

The current research work presents a detailed and thoroughly validated computational micromechanical modeling methodology to study the damage initiation and propagation in a uni-directional (UD) glass fiber-reinforced non-crimp fabric (NCF) composite ply. Under the applied transverse tension and compression loads, the effect of various microscale material and geometrical parameters on the ply level stress–strain behavior is studied. To this end, along with the distinctly modeled individual microscale constituents of the UD NCF composite ply (axial fibers, backing fibers, and matrix), the generated RVE (Representative Volume Element) model consists of manufacturing-induced defects and variabilities such as voids as well as the backing fiber’s out-of-plane waviness. The fiber/matrix interface failure behavior in the generated RVE model is simulated using cohesive zone formulations that follow bi-linear traction-separation law. Whereas the hydrostatic pressure-dependent non-linear stress–strain response followed by the fracture of the epoxy matrix is captured using the linear Drucker-Prager plasticity model coupled with the stress triaxiality-based failure criterion. The backing fibers stress–strain and failure behavior is modeled using the linear elastic and isotropic material model in conjunction with the maximum stress criterion.The proposed numerical methodology is thoroughly validated both qualitatively and quantitatively by conducting detailed experiments on a neat epoxy as well as at the composites laminate level. Upon comparing the experimental and computational results, the observed knee or slope change in the bi-linear stress–strain response of the UD NCF composite ply under transverse tension is attributed to the loss of the load-carrying ability of the axial fiber bundle due to fiber/matrix interface debonding followed by the ply splitting. Under the application of transverse compression load, the composite ply failure behavior is governed by the formation of a dominant matrix plastic shear band in the axial fiber bundles, which is in turn triggered by the fiber/matrix interface failure. Under the applied loads in the matrix-dominated direction, the presented research work provides a detailed insight into the microscale damage initiation and propagation in a UD NCF composite ply and its consequent influence on the macroscale stress–strain response.

Undrained shear mechanical behaviors of dense gassy sand

Shallow gas can cause many disasters, and it is reported in many marine engineering constructions. For this, it is imperative to understand the impact of gas on the mechanical behaviors of soil. This study investigated the influence of undrained triaxial compression tests on dense gassy sand commonly encountered in coastal areas. Triaxial tests were performed on specimens with saturations of 100%, 99.8%, 95.9%, and 92.7% under confining pressures of 50 kPa and 200 kPa by a self-developed multi-purpose integrated triaxial apparatus (MITA) for gassy soil. The results are presented in terms of monotonic stress‒strain behavior, volumetric behavior, shear strength, and excess pore water pressure (EPWP). The occurrence of gas bubbles has different effects on loose and dense sands, augmenting the undrained shear strength of loose sand while concurrently diminishing that of dense sand. The deviatoric stress of dense sand increases during shear shrinkage, which is similar to the characteristics of loose sand under the influence of gas bubbles. However, following sand dilation, the effect of gas bubbles on deviatoric stress manifests in an antithetical manner. With elevated gas content, the shear strength of dense sand decreases, accompanied by a deceleration in the development of EPWP and a notable increase in volumetric changes. To this end, a microscopic explanation concerning the deformation and evolution of gas bubbles within sand during the shear process was presented to reveal the macroscopic laws governing the undrained shear attributes of dense gassy sand.