Stress Strain Research Articles

Comprehensive Study of Tolanene's Mechanical Properties: Effects of Temperature, Layering, Orientation, and Defects

This study explores the mechanical properties of both single-layered and multi-layered tolanene nanosheets via molecular dynamics (MD) simulations. The effects of critical parameters such as size, temperature, and defects on the mechanical behavior of armchair and zigzag configurations of single-layer Tolanene nanosheets are analyzed. Key mechanical properties, including Young's modulus, ultimate stress, fracture stress, and fracture strain, are evaluated based on the stress-strain curve. It is observed that the zigzag configuration exhibits a higher Young's modulus compared to the armchair configuration. However, the armchair structure shows greater ultimate stress than the zigzag configuration. An increase in temperature or the introduction of vacancy defects leads to a degradation of mechanical properties in both configurations. The sensitivity of Young's modulus to temperature is more pronounced in the zigzag configuration than in the armchair, even though the armchair configuration generally has a higher Young's modulus. Additionally, increasing the number of layers in the nanosheets results in an enhancement of Young's modulus, with the armchair configuration showing more significant improvement than the zigzag configuration. The variation in Young’s modulus with increasing layers is minimal for the zigzag configuration.

Dynamic Mechanical Properties and Constitutive Modeling of Polyurethane Microporous Elastomers.

The present study fabricated samples of polyurethane elastomers (PUEs) with three distinct densities and assessed their mechanical responses using split Hopkinson pressure bar (SHPB) tests. The findings reveal a significant increase in PUE stress with increasing strain rate and density. To further investigate the influence of strain rate sensitivity on PUEs, a strain rate sensitivity coefficient was employed to quantify the impact of strain rate on the mechanical properties of PUEs. Separate quantifications were performed for collapse stress, plateau stress, and densification strain as indicators of the strain rate sensitivity coefficient. The results demonstrate that the collapse stress sensitivity coefficient was notably affected by the applied strain rate. Additionally, both collapse and plateau stresses exhibited an increase with increasing density, which could be described by a power function relationship. Based on the theory of strain energy function, a constitutive model considering density and strain rate effects was developed to describe the stress-strain behavior of PUEs under various densities and strain rates. A comparison between this constitutive relationship and experimental results showed good agreement, highlighting its potential in describing dynamic mechanical behavior.

Crack tip stress intensification in strain-induced crystallized elastomer

Natural rubber (NR) exhibits strain-induced crystallization (SIC), enhancing tearing strength and crack resistance. However, the reinforcement mechanism along with nonuniform strain around a crack tip remains unclear. We reveal the nonuniform stress field around a crack tip using the DIC-based deformation field data and a hyperelasticity approach. A hyperelastic strain energy density function (W) is derived to be able to replicate stress-strain data across various deformations, encompassing equal and unequal biaxial, uniaxial, and pure shear stretching. These data cover the full range and magnitude of deformations around the crack tip. SIC significantly impacts the singular behaviors of strain and stress near the crack tip, causing a pronounced stress increase and strain decrease within the SIC zone that extends up to approximately 100 μm away from the crack tip. This results in a distinct crossover in singularity power-law index between the SIC zone and the fully amorphous zone. With increasing crack opening, the stress upturn intensifies, and the crossover shifts away from the crack tip due to SIC zone enlargement and local crystallinity increase. These findings deepen our understanding of the physics of SIC near crack tips and its reinforcement mechanism in strain-induced crystallizable soft solid materials.

Design and numerical investigation of the 3D reinforced re-entrant auxetic and hexagonal lattice structures for energy absorption properties

Lattice Structures (LS) are widely recognized for their light weight and excellent mechanical properties. In this study, strut reinforcement technique is applied to enhance the energy absorption properties of 3D re-entrant auxetic (Aux) and hexagonal (Hex) LS. Numerical investigation using finite element analysis (FEA) was carried out to understand the mechanical and energy absorption properties of the novel designs through quasi-static compression test. The uniaxial loading results of the reinforced designs were compared to the traditional 3D hexagonal and re-entrant auxetic LS. In order to numerically simulate the mechanical behaviour of 3D printed LS, mechanical properties of experimentally studied PA2200 matrix material (manufactured via additive manufacturing) was used. Study of the mechanical behaviour of the 3D printed LS parts is essential because additive manufacturing has the capacity to fabricate the complex LS compared to conventional manufacturing processes, and innovative LS design can provide high specific strength of parts. The stress–strain and energy absorption curve results indicate that the purposed new designs are excellent choice for energy absorption properties at large strain. The findings of this study contribute towards the novel design of 3D hexagonal and re-entrant auxetic LS for superior mechanical strength and specific energy absorption properties.

A multi-level Stress–Strain relationship and hydraulic characteristics for supporting grain-porous rock fracture system

Fracturing technology, essential for enhancing permeability within oil and gas reservoirs, relies on supported particles to maintain fracture conductivity. A comprehensive understanding of the stress-strain relationships and hydraulic properties of Supported Grain-Porous Media Fracture System (SG-PMFS) is crucial for optimizing hydrocarbon extraction and advancing geomechanical modeling. In this study, we introduced a multilevel spring compression deformation model that categorized SG-PMFS deformation into an equivalent tensile component in matrix pores of the far-field region, equivalent compressive components in matrix pores of the near-field region and fractures, and multilevel compressive components in supporting grains. We derived distributed uniaxial/triaxial stress-strain relationships to quantitatively characterize these multilevel deformation behaviors across distinct characteristic regions. Digital image correlation strain measurement was employed for experimental validation, confirming the model's accuracy. The experimental results identified five distinct characteristic regions within SG-PMFS, with the distribution factors of each deformation component decreasing with distance from the fracture. Self-supported grains significantly enhanced the correlation coefficient of experimental data, reducing the fracture-related bulk modulus from 11.99 MPa to 1 MPa. The degree of grain crushing was directly proportional to the bulk modulus of the corresponding multilevel compressive component. Furthermore, we established constitutive relationships between stress and key hydraulic properties: fracture aperture, compressibility, and porosity. The model predictions and experimental results consistently characterized the relationship between hydraulic properties and stress across different regions. The hydraulic behavior of SG-PMFS under stress was segmented into three stages: porous rock fracture-dominated deformation (0–2.2 MPa), first-level particle crushing (2.2–4.6 MPa), and second-level particle crushing (4.6–25 MPa). The contribution of grain crushing to porosity changes consistently exceeded 50%, making it the dominant factor in the porosity variation of SG-PMFS.

COMPUTER SIMULATION OF THE STRESS-STRAIN STATE OF BAR BLANKS MADE OF ALLOY 7075

The article presents a study of the characteristics and technological parameters of bar blanks made of aluminum alloy 7075, depending on the temperature and the forming process. The main goal is to determine the stress-strain state at various temperatures during the production of blanks, which contributes to understanding the mechanism of formation of the structure and properties of bar blanks. To do this, a computer simulation of the process based on the finite element method is used, using the Forge3D software environment. The results obtained confirm the uneven structure in the volume of workpieces, with a pronounced intensity of deformation in the surface layers. The formation of workpieces at different temperatures (200 and 250 °C) showed differences in stress intensity and strain rate, which is important for understanding the processes of formation of microstructure and material properties. Special attention is paid to the influence of temperature on the formation of stresses in the rods, as well as their distribution in thickness and length. The results obtained can be used to optimize the technological parameters of the aluminum alloy forming process in order to improve the quality of the final product and production efficiency. In general, the scientific conclusions of this study contribute to the further development of aluminum alloy processing technologies and their application in various industries. Keywords: computer modeling, finite element method, numerical model, processing technology, Forge3D, deformation characteristics, microstructure formation process.

Flexural toughness and stress-strain relationship of different types of steel fiber reinforced shotcrete in high geothermal environment

The shape of steel fiber plays a pivotal role in determining the mechanical properties of concrete. In this paper, the impacts of end-hooked, wavy and ultra-fine steel fibers (all with a doping amount of 1.0 %) on the compressive strength, flexural strength, flexural toughness, and strain-strain relationship of shotcrete under curing conditions of 20 ℃, 40 ℃, and 60 ℃ are studied. Furthermore, the flexural toughness of steel fiber shotcrete is evaluated using the energy absorption method, and a constitutive model for steel fiber shotcrete was established based on meso-damage mechanics theory. The results indicate that curing temperatures below 40 ℃ are conducive to enhancing the compressive strength, flexural strength, and flexural toughness of steel fiber shotcrete, while curing temperatures above 60 ℃ are unfavorable for the development of strength and toughness in steel fiber shotcrete. Regardless of the type of steel fiber, its incorporation can alleviate the negative impact of high-temperature curing on the strength and toughness of shotcrete. Under high-temperature curing conditions, the influence of end-hooked steel fibers on the strength of shotcrete is superior to that of corrugated and ultrafine steel fibers, while ultrafine steel fibers are beneficial for improving the flexural toughness of shotcrete. The slope, peak stress, and peak strain of the stress-strain curves of shotcrete cured at 40 ℃ and 60 ℃ with the addition of the three types of steel fibers are greater than those of concrete without steel fibers. Furthermore, the descending segment of the curve is wider and smoother, with a larger surrounding area, demonstrating good toughness, deformability, and ductility. The end-hooked steel fibers and ultrafine steel fibers exhibit superior performance in enhancing the toughness and ductility of shotcrete under high-temperature curing conditions compared to wavy steel fibers. Based on meso-damage theory, the impacts of curing temperature and steel fiber types on the constitutive model of shotcrete under axial compression were established, and the model parameters were discussed. The research results can provide theoretical support for the durability design of tunnel linings in high ground temperature environments.

Reliability of the Young's modulus of crab exoskeleton materials estimated from nanoindentation tests

The local and global mechanical properties of a mineralized biological material using the mud crab as a model material were investigated and compared. The stress–strain (s–s) curves for wet and dry conditions of the endocuticle were exactly examined by performing tensile tests with strain gauges. The local properties were examined through nanoindentation testing (NI) in a dry condition. The global Young's modulus, E, evaluated from the slope of the linear part of the s–s curve, did not vary with wet or dry specimen conditions; however, the stress and strain required to fracture depended on the conditions. The E was compared with the results of property mapping obtained from NI. Due to local differences in the grade of mineralization in the exoskeleton, the mapping indicated that nanoindentation tests should be performed for an extensive region of the cuticle. The results will provide useful information for future material development based on biomimetics.

Uniaxial compressive stress-strain behavior of steel fiber reinforced geopolymer concrete confined by stirrups: Experimental study and analytical model

The compressive stress-strain relationship of confined steel fiber reinforced geopolymer concrete (SFRGC) is a basis for its structural nonlinear analysis and engineering design. This paper presents an experimental study on the stress-strain behavior of stirrup confined-SFRGC under uniaxial compression, with emphasis on the effects of stirrup spacing, stirrup strength and steel fiber (SF) volume fraction. The failure modes, stress-strain curves, energy absorption capacity and post-peak ductility were analyzed. The results demonstrated that due to the stirrup constraint and SF fiber crack-bridging effects, the integrity of specimens was significantly improved, showing notable ductile failure mode. The stress-strain behavior of core SFRGC was notably affected by the constraint level of stirrups, however, the effect of SF was mainly reflected in post-peak stress-strain branches. Reducing the stirrup spacing, improving the stirrup strength, and increasing the SF content can effectively enhance the strength and deformation characteristics of confined-SFRGC, as well as ductility. Moreover, synergetic effect of SF and stirrups on improving the deformation capacity of SFRGC was observed, whereas the peak stress and corresponding strain changed insignificantly with the SF content. In addition, the stirrups can reach yield around the peak stress point. Based on the analysis of test results, formulae for characterizing the peak stress, peak strain, elastic modulus as well as stress-strain responses of confined-SFRGC were proposed, with the effective confinement index of stirrups and fiber reinforcing factor introduced. The model predicted curves were in great agreement with the test curves.

Effort of damage parameter in assessment of low cycle fatigue

A low-cycle fatigue (LCF) analysis is one of the main design stages for highly loaded structural elements used in various applications. For this analysis, it is necessary to determine the values of local stresses and deformations, taking into account both elastic and plastic regions in the zones of stress concentration. This study presents and assesses the engineering methods used for prediction of low-cycle fatigue in structural elements. For zones of stress (strain) concentration, the Neuber-Makhutov method for LCF, taking into account the type of material stress-strain diagrams, is employed. The concept of distributed damage, based on the main ideas of the continuum damage mechanics of Kachanov-Rabotnov, was used. An approach employing the damage parameter for assessment of damage accumulation in LCF in highly loaded areas of structural elements is presented.

Influence of Fiber Orientation on Mechanical Response of Jute Fiber-Reinforced Polymer Composites.

The influence of fiber orientation on the mechanical behavior of a polymer matrix composite reinforced with natural jute fibers is investigated in this study. Two fiber orientation configurations are examined: the first involves woven fibers aligned in the direction of testing, while the second considers a 45° orientation. The research involves manufacturing composite plates using jute fabric with the mentioned orientations, followed by cutting rectangular specimens for tensile testing to determine which orientation yields superior properties. Displacement fields are measured using a digital image correlation technique, synchronized with load data obtained from a universal testing machine equipped with a load cell to obtain stress-strain curves for each configuration. Results indicate that 0° specimens achieve higher stress but lower strain compared to 45° specimens. This research contributes to understanding the optimal fiber alignment for enhancing the mechanical performance of fiber-reinforced polymer composites.

Axial stress-strain behavior of pre-stressed CFRP confined concrete columns

Bonded carbon fiber reinforced polymer (CFRP) confined concrete presents issues such as stress hysteresis and easy detachment at the interface between CFRP and concrete. Applying prestress to CFRP can improve this situation. To investigate the stress-strain behavior of prestressed CFRP strengthened plain concrete columns (PC) under axial compression, a total of 1 unreinforced concrete column, 9 bonded CFRP strengthened concrete columns, and 27 prestressed CFRP strengthened concrete columns were designed. Including CFRP layers and the level of prestress were taken as the study factors, and axial compression tests were conducted on each specimen to analyze their axial compression performance. The test results indicated that applying prestress to CFRP results in the core concrete being constantly subjected to triaxial compression, with initial transverse compressive strain and longitudinal tensile strain, thereby increasing the initial stiffness of the core concrete. In contrast to bonded CFRP-strengthened columns, the ultimate axial stress, ultimate axial strain, and initial stiffness of prestressed CFRP-strengthened columns increased with the level of CFRP prestress, with a more pronounced improvement observed in columns wrapped with a higher number of layers of CFRP. For a 4-layer CFRP strengthened column prestressed at 0.3, the ultimate axial stress and ultimate axial strain increased by up to 13 % and 20 %, respectively, compared to bonded 4-layer CFRP strengthened columns, with the initial stiffness increasing by up to 30 %. On the other hand, applying prestress to CFRP can significantly enhance the effective utilization of CFRP, but it is negatively correlated with the number of CFRP layers. Compared to bonded 1-layer CFRP strengthened columns, the effective utilization rate increased from 0.63 to 0.91, a 44 % increase, when prestressing CFRP at 0.3. Finally, based on existing relevant research, a peak stress and strain model considering the ratio of confinement stiffness to strain ratio was proposed. Based on the fundamental assumptions of curve analysis, the design-oriented axial stress-strain model suitable for prestressed CFRP strengthened concrete columns was established, with good match between theoretical and experimental curves.

Mechanical testing of colloidal solids with millipascal stress and single-particle strain resolution.

We introduce a technique, traction rheoscopy, to carry out mechanical testing of colloidal solids. A confocal microscope is used to directly measure stress and strain during externally applied deformation. The stress is measured, with single-mPa resolution, by determining the strain in a compliant polymer gel in mechanical contact with the colloidal solid. Simultaneously, the confocal microscope is used to measure structural change in the colloidal solid with single particle resolution during the deformation. To demonstrate the utility and sensitivity of this technique, we deform a hard-sphere colloidal glass in simple shear, and from the macroscopic shear strain and measured stress determine the stress-strain curve. Using the stress-strain curve and measured shear modulus, we decompose the macroscopic shear strain into an elastic and a plastic component. We also determine a local strain tensor for each particle using the changes in its nearest-neighbor distances. These local strains are spatially heterogeneous throughout the sample, but, when averaged, match the macroscopic strain. A microscopic yield criterion is used to split the local strains into subyield and yielded partitions; averages over these partitions complement the macroscopic elastic-plastic decomposition obtained from the stress-strain curve. By combining mechanical testing with single-particle structural measurements, traction rheoscopy is a unique tool for the study of deformation mechanisms in a diverse range of soft materials.

Stress wave effects and their mechanisms on stress-strain curves in the elastic phase of SHPB tests

In Split Hopkinson Pressure Bar (SHPB) tests, the stress wave effects during the elastic phase of the stress-strain curve and their influence mechanisms are crucial. Due to the extremely short duration of the elastic deformation phase, the stress wave effects on the specimen during this stage cannot be ignored. This leads to significant errors in the obtained elastic stress-strain curves. However, the dynamic compressive elastic stress-strain relationship forms the basis for studying the viscoelastic behavior of materials. Accurate determination of elastic yield stress and yield strain is also essential for deriving accurate plastic stress-strain relationships. Quantitative research on the stress wave effects during the elastic compression phase of SHPB tests is fundamental for decoupling and obtaining accurate material elastic curves. This paper conducts a quantitative theoretical analysis of the structural effects caused by stress wave evolution during the elastic compression phase, based on the assumption of plane waves. It studies the deviation characteristics and main factors of the phenomenological engineering stress-strain curves of the specimen compared to the actual material stress-strain curves under different conditions, revealing the influence rules and mechanisms of this deviation. The maximum stress deviation value and its corresponding dimensionless time, as well as the variation trend of the maximum stress deviation value within different fluctuation intervals, are calculated. Additionally, the study investigates the cases where the incident wave is arc-shaped or a combination of arc and linear waves. The findings provide theoretical references for the precise design and accurate data processing of SHPB tests.

Axial compressive behavior of short columns of BFRP strip-PVC tube composite reinforced fiber recycled concrete

In this paper, axial compression tests were performed on recycled fiber concrete short columns reinforced by BFRP strips and PVC tube. The main variables investigated were the type of reinforcement (BFRP strip reinforcement or BFRP strip-PVC tube composite reinforcement) and the volumetric configuration rate of BFRP (One or three different number of strips layers and 25 mm/37.5 mm/50 mm with different strip spacing). A set of specimens was selected for each experimental group and simulated through ABAQUS to be used to assess the accuracy of the test. The investigation results show that BFRP strip-PVC tube composite reinforcement not only improves the ultimate bearing capacity of the specimen, but also improves the damage morphology of the fiber-recycled concrete short columns. The reinforcement method's effect on the specimen's stiffness is more significant during the nonlinear strengthening phase of the stress-strain curve. The specimen’s peak stress and ultimate strain of the specimens increased significantly with higher volumetric configuration rate of BFRP. Based on the analysis of the experimental results, the stress-strain calculation model with a softened section is also of better applicability. The study’ results provide a theoretical basis and reference for the future application of fiber recycled concrete.

The mechanism of low strain rate and moderate principal stress effects in triaxial prestressed marble under lateral impulsive load

Stress waves have a significant impact on the strength and deformation characteristics of deep rock masses at a certain distance from the epicenter or explosion source. In order to study the dynamic responses of deep-buried marble under the disturbance condition, the true triaxial compression test (TTC), the true triaxial disturbed compression test with lateral impulsive load (TTDC) and the synchronous acoustic emission monitoring on the marble were respectively conducted to simulate the influencing process of the seismic wave. The test results show that under lateral impulsive load, a ‘short-range plateau’ phenomenon occurs in the stress-strain curves of the marble samples. With the increase of intermediate principal stress σ2, the ‘short-range plateau’ of ε2 and ε3 curves gradually shrinks and even disappears, and the anisotropy of sample deformation becomes more obvious. The σ2 significantly affects the microfracture activity and the evolution of energy inside the samples under the impulsive load in the whole process of true triaxial disturbed compression. The lateral impulsive load weakens the marble strength which shows an obvious low strain-rate disturbance effect. The marble samples under the impulsive load have a high sensitivity to axial load and are liable to form local brittle fracture. This fracture induced by local stress concentration and strain energy release becomes more pronounced when the axial load is further applied to the samples. By contrast, the impulsive load in σ2 direction has a protective effect on limiting the lateral deformation of the samples and improving its axial deformation capacity, which greatly changes the action mechanism of σ2 on the sample lateral deformation. The variation of marble mechanical properties under lateral impulsive load is the result of the interaction between the low strain-rate disturbance and the intermediate principal stress effect.

Compressive performance of underwater concrete piers reinforced with prefabricated FRP shells

A novel underwater spliceable basalt fiber-reinforced polymer (BFRP) shell-confined concrete structure was proposed that rapidly reinforces underwater piers by lapping the FRP shell with adhesive underwater combined with nondispersive mortar (NDM) filling. Thirty-six prefabricated BFRP shells combined with nondispersive mortar reinforced concrete columns (PFRCs) were made for axial compression testing. The effects of the BFRP layer number, lap length and pouring environment on the specimen performance were compared, and different damage patterns and stressstrain relationship curves were obtained. The test results reveal that the PFRCs exhibited two failure modes: BFRP fracture failure in nonlapped segments and BFRP bond adhesive peeling failure in lap segments, and the specimens with more BFRP layers and shorter lap lengths were prone to BFRP bond adhesive peeling failure. From 2 to 4 layers, the ultimate stress and ultimate strain values increased by 1.18–1.91 times and 5.18–10.32 times, respectively, demonstrating increasing the number of BFRP layers is a more effective means to improve the structural performance. The ultimate strength of the underwater reinforced specimens reached more than 70 % of that of the corresponding specimens on land, which demonstrated the feasibility of using prefabricated FRP-molded shell reinforcing technology for submerged piers. Finally, the calculation model of an FRP-confined concrete column is evaluated, and the full stressstrain curves of the PFRCs are proposed.

Experimental study on the mechanical characteristics of weakly cemented mudstone under different loading rates

With the gradual shift of coal mining to the western coal mining region of China, floor heave in weakly cemented mudstone roadways has become an issue affecting the safety and efficiency of coal mine production. Additionally, different mining rates can lead to fluctuating support stresses on the roof and floor of weakly cemented mudstone roadways. Therefore, obtaining a comprehensive understanding of the mechanical properties of weakly cemented mudstone at different loading rates is conducive to improving the issue of floor heave in such roadways and provides a theoretical basis for further study. In this context, a series of uniaxial mechanical tests with concurrent acoustic emission monitoring were conducted on specimens of weakly cemented mudstone under various loading rates (0.005, 0.01, 0.05, and 0.1 mm/s). The stress‒strain and acoustic emission response curves were obtained to effectively characterize the strength, deformation, damage, macroscale instability, and crack propagation characteristics of the mudstone under the influence of loading rate effects. The research results support the following findings: (1) With increasing loading rate, the peak strength and elastic modulus of weakly cemented mudstone significantly increase, while the peak axial strain and peak radial deformation significantly decrease. (2) With increasing loading rate, the stress required to trigger the expansion of weakly cemented mudstone gradually increases, and a significant power-law relationship arises between the strain of the mudstone at the start of expansion and the loading rate. (3) With increasing loading rate, the acoustic emission ringing count of weakly cemented mudstone increases: The failure of weakly cemented mudstone changes from small-range progressive failure to sudden failure, and the failure mode transitions from shear failure to tensile‒shear composite failure. (4) The studied mudstone damage variables increase with increasing loading rate, following an approximate exponential function. The conclusions obtained in this work can provide a theoretical basis for the evolution mechanism and control of floor heave in deep roadway mining.

Unified stress–strain calculation model for UHPC-filled stainless-steel tubular columns with various cross-sectional shapes under axial compression

Different cross-sectional shapes of ultrahigh-performance concrete (UHPC)-filled stainless-steel tubular (UHPCFSST) columns result in their stress-strain curves exhibiting softening or hardening stages, and currently, there is no unified calculation model available that can effectively simulate these variations. Based on experimental data, models for predicting peak stress, peak strain, ultimate stress, and ultimate strain of UHPCFSSTs with high accuracy has been provided. Comparative analysis reveals that the stress transfer capability and stability of UHPCFSSTs with the different cross-sectional shapes from highest to lowest are as follows: circular, square, and rectangular. Building upon Wei et al.'s general stress-strain calculation model, a high correlation pattern between parameter b and hoop confinement coefficient (ξs) has been obtained through correlation analysis, elucidating the post-peak behavior of stress-strain curves of UHPCFSSTs. By modeling parameter b, Wei et al.'s model has been extended to accommodate the stress-strain relationship under axial compression for UHPCFSSTs with different cross-sectional shapes. This establishes a unified stress-strain calculation model for UHPCFSSTs with different cross-sectional shapes under axial compression. Comparative analysis indicates that the proposed unified calculation model for axial compression stress-strain behavior of UHPCFSSTs can effectively quantify the influence of cross-sectional shape on stress-strain curves, demonstrating high predictive accuracy and generality.

Fusion of finite element and machine learning methods to predict rock shear strength parameters

Abstract The trial-and-error method for calibrating rock mechanics parameters has the disadvantages of complexity, being time-consuming, and difficulty in ensuring accuracy. Harnessing the repeatability and scalability intrinsic to numerical simulation calculations and amalgamating them with the data-driven attributes of machine learning methods, this study uses the finite element analysis software RS2 to establish 252 sets of sandstone sample data. The recursive feature elimination and cross-validation method is employed for feature selection. The shear strength parameters of sandstone are predicted using machine learning models optimized by the particle swarm optimization (PSO) algorithm, including the backpropagation neural network, Bayesian ridge regression, support vector regression (SVR), and light gradient boosting machine. The predicted value of cohesion is proposed as the input feature to predict the friction angle. The results indicate that the optimal input characteristics for predicting cohesion are elastic modulus, Poisson's ratio, peak stress, and peak strain, while the optimal input characteristics for predicting friction angle are peak stress and cohesion. The PSO-SVR model demonstrates the best performance. The maximum error between the predicted values of cohesion and friction angle and the calculated results of RSData program are 3.5% and 4.31%, respectively. The finite element calculation is in good agreement with the stress–strain curve obtained in the laboratory. The sensitivity analysis indicates that SVR's prediction performance for cohesion and friction angle tends to be stable when the sample size is >25. These results offer a valuable reference for accurately predicting rock mechanics parameters.