Stress-strain Model Research Articles

Investigation of the rock mass state in the near-wall part of the quarry and its stability management

Introduction: The research is aimed to identify the vulnerable areas of quarry slopes through the creation of a stress-strain state model for the rock mass at the Vostochny quarry, East Saryoba field of the Zhi-landy Group of cupriferous sandstones, as well as their subsequent strengthening.Methods: The research is based on the development of a database containing information on mining-geological, geophysical, geodetic and aerospace surveys. The authors of the research use modern geodetic, aerospace and geophysical technologies for scientifically based predicting of technogenic disasters and the rock mass stress-strain state modeling to ensure safe and optimal mining of fields in difficult mining-geological conditions.Results: The results obtained show that the strengthening of weakened quarry slopes based on the rock mass stress-strain state modeling contributes to the scientific-practical profitability of field mining and provides safe mining in difficult mining-geological conditions.Discussion: Novelty is in the scientific substantiation of the method for strengthening quarry slopes, which is based on the rock mass stress-strain state modeling. The research is of great practical importance, as the rock mass stress-strain state modeling increases the reliability of predicting the rock mass state during its mining. Strengthening of quarry slopes using the proposed method reduces risks and increases safety and economic efficiency of mining the solid mineral deposits in difficult mining-geological conditions.

Mechanical characteristics and developing a compressive stress–strain model of geopolymer concrete

Mechanical characteristics and developing a compressive stress–strain model of geopolymer concrete

Identification of failure behaviors of underground structures under dynamic loading using machine learning

Understanding the dynamic responses of hard rocks is crucial during deep mining and tunneling activities and when constructing nuclear waste repositories. However, the response of deep massive rocks with openings of different shapes and orientations to dynamic loading is not well understood. Therefore, this study investigates the dynamic responses of hard rocks of deep underground excavation activities. Split Hopkins Pressure Bar (SHPB) tests on granite with holes of different shapes (rectangle, circle, vertical ellipse (elliptical short (ES) axis parallel to the impact load direction), and horizontal ellipse (elliptical long (EL) axis parallel to the impact load direction)) were carried out. The influence of hole shape and location on the dynamic responses was analyzed to reveal the rocks' dynamic strengths and cracking characteristics. We used the ResNet18 (convolutional neural network-based) network to recognize crack types using high-speed photographs. Moreover, a prediction model for the stress-strain response of rocks with different openings was established using Deep Neural Network (DNN). The results show that the dynamic strengths of the granite with EL and ES holes are the highest and lowest, respectively. The strength-weakening coefficient decreases first and then increases with an increase of thickness-span ratio (h/L). The weakening of the granite with ES holes is the most obvious. The ResNet18 network can improve the analyzing efficiency of the cracking mechanism, and the trained model's recognition accuracy reaches 99%. Finally, the dynamic stress-strain prediction model can predict the complete stress-strain curve well, with an accuracy above 85%.

Composite structures with embedded fiber optic sensors: A smart propellant tank for future spacecraft applications

Modern spacecraft and launch vehicle design is more oriented towards reducing system-level design and assembly complexities. In order to maintain high overall system performance while reducing these complexities, the use of smart materials and smart structural components is a well-known practice and is currently of rising interest to space systems' designers. The paper discusses a concept of smart space structures, in particular, a carbon fiber composites structure embedded with Optical Fiber Sensors (OFS) for spacecraft and launch vehicle applications. This study highlights the operational requirements for such tank and the smart features enabled by the optical fiber sensors. For the latter aspect, a quantitative comparison between Fiber Bragg Grating sensors (FBGs) and Distributed Optical Fiber Sensors (DOFS) based on Optical Frequency Domain Reflectometry (OFDR) is presented to state their core performance parameters, such as the sensitivity, sensing range, dynamic measurement capability, and spatial resolution. The increased performance and reliability in harsh environments associated with fiber optic sensors come with a reduction in size, mass, and power consumption compared to the conventional electronic sensors. Optical fiber sensors embedded in carbon fiber structures have proven their capability in providing accurate real-time measurements of temperature and monitoring structural integrity while detecting precisely possible points of rupture and failure as discussed and demonstrated in the literature review. The applications of fiber optic sensing in smart propellant tanks may extend to detecting fluid leakage, also providing increased precision in propellant gauging through temperature mapping, and can be used in on-ground qualification, pre-flight testing, as well as in-orbit operation, condition, and structural health monitoring. The article presents a statement for an optimal FOS embedding approach in composite pressure vessels and discusses the related placement and orientation method for the fiber optic sensors, coupled with a one component simplified analytical stress-strain transfer model deriving the stress component along the maximum principal direction (i.e., σMaxPrincipal). The novel approach is believed to serve the optimal employment of embedded FOS in composite structures, e.g., pressure vessels and light-weight structures in spacecraft, among other applications. The simplified model is believed to pave the way for effective data interpretation and processing, utilizing the available limited computational resources on-board the spacecraft.

Examination of the stress-strain model for confined concrete considering the impact of corroded spiral bars

To examine the impact of corroded spiral bars on the confinement effect of concrete, a series of dry-wet cyclic accelerated corrosion tests and axial compression tests were performed on 36 RC (Reinforced Concrete) specimens. This study investigated the effects of various factors, including the degree of corrosion in spiral bars, the reinforcement configuration, and the concrete strength grade, on the axial compressive performance of confined concrete. The mechanical behavior of concrete, which was confined by corroded spiral bars, was analyzed by considering the corrosion characteristics, failure patterns, and load-carrying capacity of the specimens. A modified Mander model, which incorporates the influence of corroded spiral bars, was developed. The results indicate that increased corrosion accelerates specimen damage and reduces ductility. Stirrups show pull-off phenomena. A higher stirrup ratio enhances the bearing capacity and deformation capacity of specimen during destruction, while reducing longitudinal reinforcement buckling. Stronger concrete delays vertical cracking, increases bearing capacity, but reduces deformation capacity during destruction. The modified Mander model demonstrates high computational accuracy.

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.

Hemp Fiber-Reinforced Polymers Composite Jacketing Technique for Sustainable and Environment-Friendly Concrete.

This research suggested natural hemp fiber-reinforced ropes (FRR) polymer usage to reinforce recycled aggregate square concrete columns that contain fired-clay solid brick aggregates in order to reduce the high costs associated with synthetic fiber-reinforced polymers (FRPs). A total of 24 square columns of concrete were fabricated to conduct this study. The samples were tested under a monotonic axial compression load. The variables of interest were the strength of unconfined concrete and the number of FRR layers. According to the results, the strengthened specimens demonstrated an increased compressive strength and ductility. Notably, the specimens with the smallest unconfined strength demonstrated the largest improvement in compressive strength and ductility. Particularly, the compressive strength and strain were enhanced by up to 181% and 564%, respectively. In order to predict the ultimate confined compressive stress and strain, this study investigated a number of analytical stress-strain models. A comparison of experimental and theoretical findings deduced that only a limited number of strength models resulted in close predictions, whereas an even larger scatter was observed for strain prediction. Machine learning was employed by using neural networks to predict the compressive strength. A dataset comprising 142 specimens strengthened with hemp FRP was extracted from the literature. The neural network was trained on the extracted dataset, and its performance was evaluated for the experimental results of this study, which demonstrated a close agreement.

Mechanical properties and environmental implications of excess-sulfate cement concrete with phosphogypsum-based cold-bonded fine aggregates

Recycling waste phosphogypsum (PG) into phosphogypsum-based cold-bonded aggregates (PCBAs) for eco-concrete production has received extensive attention due to its sustainability for construction industry development. Currently, PCBAs mainly replace the coarse aggregates in concrete while the fine aggregates remain natural sand (NS). This study substitutes NS with phosphogypsum-based cold-bonded fine aggregates (PCBFAs) for the preparation of excess-sulfate cement concrete (ESCC), and the compressive strength, tensile splitting strength, flexural strength, and stress-strain curve were studied by considering replacement rations (0%, 25%, 50%, 75%, 100%). The results indicate that when the replacement ratio is 100%, the compressive strength, splitting tensile strength, and flexural strength of ESCC were reduced by 17.2%, 26.9%, and 29.2% respectively. The addition of PCBFAs will make the ascending segment of the stress-strain curve flatter and make the descending segment steeper. Based on the tested results, the prediction formulas of the mechanical properties and the uniaxial compressive stress-strain model of the concrete under different replacement ratios are proposed. Microstructure analysis indicates that the PCBFAs gradually integrate with the cement matrix, reducing the defects in the interface transition zone. Furthermore, ESCC effectively immobilizes impurities contained in PG. The research findings demonstrate the feasibility of using PCBFAs as a substitute for NS.

Post-fire behavior of double-sided stainless-clad bimetallic steels

This paper presents an experimental investigation of the post-fire behavior of double-sided stainless-clad bimetallic steels (DSSCBS), which is a new type of high-efficiency material and is promising to be used in cold-formed structures. A total of 48 tensile coupon specimens were extracted from two types of DSSCBS plates, with 316L stainless steel as the cladding material and Q235 or Q345 carbon steel as the substrate material. The specimens were heated up to various temperatures up to 1000 °C and subsequently cooled down to ambient temperature via air-cooling or water-cooling methods, to evaluate the effect of different cooling approaches. Additionally, the influence of in-fire stresses, which reflects the load ratios of structural members in fire hazards, was also examined. Stress-strain curves as well as key mechanical properties including the elastic modulus, yield strength, ultimate strength, ultimate strain and fracture strain were obtained and fully reported. Moreover, the measured post-fire retention factors were compared with existing prediction equations for carbon steel and stainless steel, as well as the prediction curves for single-sided stainless-clad bimetallic steel to assess their applicability to this novel material. New predictive rules for retention factors of DSSCBS in post-fire conditions were proposed with stress-strain models advanced to offer a reference for future numerical simulation and assessment of the post-fire behavior of members and structures of DSSCBS.

A multiaxial multiscale compressive thermo-mechanical damage model for Fiber Reinforced Cementitious Composites (FRCC)

In the current study, a multiaxial multiscale compressive stress-strain model for Fiber Reinforced Cementitious Composites (FRCC) was innovatively developed. The proposed model was on the basis of the theory of thermodynamics, multiscale theory and internal variable theory. The free energy function and dissipation function were established to characterize the elastic and plastic deformation of FRCC, respectively. The multiscale behaviors of FRCC in meso-scale and macro-scale was taken into account. In meso-scale, the energy dissipation functions of fiber in tension and bond-slip deformation in the interface transition zone (ITZ) were established. The resistance to cracking of cementitious matrix through the fiber bond stress were taken into account. In macro-scale, the thermo-mechanical coupling contributions of plastic damage, thermal damage, yield surface and hardening evolution were creatively considered in the potential function within thermodynamics framework. The influence of types and volume fractions of fibers on the reinforcement mechanism was discussed. When the temperature is higher than the melting point of fiber, the fiber influence coefficients was employed. The sensitivity of yield surface was discussed. The numerical predictions of this developed model were carried out for validation. The nonlinear stress-strain responses of concrete were accurately captured at temperatures ranges from 20 °C to 800 °C compared with the experimental data, which indicates the accuracy and applicability of the proposed model.

Numerical simulation of steel-concrete composite beams and slabs at elevated temperatures

Steel-concrete composite beams with shear studs providing composite action between the concrete slabs and steel beams are widely used in modern steel-framed building construction. Three-dimensional finite element modelling has been a viable option for investigating the fire behaviour of composite beams. Although many finite element models are available in the open literature, most of them are simplified models verified by limited test data. Meanwhile, early test data often did not have all the required information for finite element simulation, and some assumptions need to be made. But more detailed test data are now available in the open literature for steel-concrete composite beams, which can be used to develop a generalised finite element model. In addition, National Institute of Standards and Technology has proposed new stress-strain models for steels at elevated temperatures, which can be compared with the more widely adopted Eurocode 4 steel material models in simulating composite beams. Accordingly, this paper selected 22 specimens, including two reinforced concrete slabs, 12 composite beams with reinforced concrete slabs, two composite slabs with profiled steel sheeting, two steel-concrete composite push test specimens with profiled steel sheeting, and four composite beams with profiled steel sheeting, from nine references to verify the developed finite element model. The proposed finite element model can capture different failure modes of composite beams, such as steel yielding/local buckling, concrete cracking/crushing, debonding of profiled steel sheeting, and stud fracture, which is crucial to comprehend the composite beam behaviour at elevated temperatures.

Research on the residual compressive properties of concrete with preload after sustained high temperatures

The containment vessel of nuclear power plants, concrete structures near the furnaces and roller lines, and chimneys, are exposed to high temperatures (120 °C to 350 °C) for long term. Research on the compressive properties of concrete after short-term high temperatures (usually within 3 h) has been widely conducted, while that of concrete after sustained high temperatures is scarce. In this research, the effects of temperature (120 °C to 350 °C), heating duration (3 h to 32 h) and initial stress level (0.2 to 0.6, ratio of initial applied stress to compressive strength at room temperature) on the failure mode, compressive strength, peak strain and stress-strain relationship of concrete after sustained high temperatures were studied. The results show that with increasing temperature and heating duration, concrete compressive strength gradually decreases, while concrete peak strain gradually increases. At heating duration of 24 h, the properties of concrete have basically stabilised. Preloading helps the concrete to resist the adverse effects of high temperatures by inhibiting the dehydration of cement matrix and the cracking of interfacial transition zone. For concrete with preload, transient thermal strain and short-term creep at high temperatures could not be recovered after cooling, which causes a significant increase in the peak strain of concrete. A compressive stress-strain model for concrete with preload after sustained high temperatures was developed, which consists of pre-creep ascending segment, creep segment, post-creep ascending segment and descending segment. Comparison of the prediction results with the test results proves that the model has high accuracy.

Eccentric compression behavior of partially CFRP wrapped seawater sea-sand concrete columns reinforced with epoxy-coated rebars

The combined use of seawater sea-sand concrete (SSC), epoxy-coated rebar (ECR) and fiber-reinforced polymer (FRP) can achieve significant economic and environmental benefits in coastal infrastructure constructions. Thus, this paper first presents an experimental and analytical study on the eccentric compression behavior of partially carbon FRP (CFRP) wrapped SSC columns reinforced with ECR. The effects of load eccentricities, thickness of CFRP strips, clear spacing ratios, and slenderness ratios were comprehensively analyzed. Test results show that as the eccentricity increased from 60 mm to 120 mm, the increment of load capacity of partially CFRP wrapped columns reduced by 27.6 % to 17.1 %. Moreover, a larger lateral deflection was detected for the specimens with a relatively high slenderness ratio, which results in an obvious second-order effect and further aggravates the nonlinearity of axial load-bending curves, especially for the specimens under a small eccentricity. In addition, an eccentricity-dependent stress-strain model for concrete was developed under FRP strip-steel hoop composite confinement, and the lateral deflection formula of eccentrically loaded columns was also derived based on force equilibrium analysis. Finally, a new theoretical formula incorporating the effect of the slenderness ratio was also presented for the determination of load and moment capacity of the partially CFRP wrapped columns based on section analysis. By comparing with the test results, the developed model exhibits satisfactory accuracy.

Compressive stress-strain model for concrete-filled filament-wound FRP tubes with arbitrary fiber orientation: An analytical approach

An analytical model is proposed to predict the non-linear hoop stress- strain response of multi-laminated fiber reinforced polymer (FRP) tube when subjected to internal pressure. This model incorporates the arbitrary stacking of fiber direction and thickness of individual lamina in FRP tube to effectively calculate confinement pressure exerted by FRP tube on solid concrete columns under uniaxial compression. Next, the model is augmented with Jiang and Teng’s analysis-oriented model to predict the axial behavior of concrete filled FRP tube solid columns with fibers oriented in any arbitrary direction. The predictions by the proposed model are then compared with numerous experimental axial stress-strain/load-strain response of FRP-confined concrete columns collected from the literature. It is found that the present model can closely predicts with the experimental outcomes, outperforming several existing analytical models.

Finite Element Simulation of Stress Distribution and Strain Model Optimization for Strain-Inducing SOI Wafers with Highly Stressed SiN Films

Finite Element Simulation of Stress Distribution and Strain Model Optimization for Strain-Inducing SOI Wafers with Highly Stressed SiN Films

Confinement mechanism and modeling of basalt TRM confined concrete: Effect of mortar matrix grade

Textile reinforced mortar (TRM) confinement significantly enhances the compressive strength and ultimate axial strain of concrete. This study mainly investigated the influence of mortar strength on the stress-strain behavior of TRM-confined concrete to advance understanding of its confinement mechanism. We conducted 48 compression tests on concrete columns, comparing those without jackets to those confined in basalt TRM (BTRM). Variables included the number of textile layers (0 to 4) and mortar matrix strengths (from low-grade ‘M1′ to high-grade ‘M3′). Results indicated that a critical confinement stiffness ratio of 0.024 is essential for strain hardening behavior with marked strain capacity enhancement. Low-grade mortar diminished the effective confinement stiffness of BTRM jackets, manifesting as either a steeper descending plateau in the strain-softening stress-strain curve or a more gradual ascending plateau in the strain-hardening curve. High-strength mortar significantly reduced both the hoop rupture strain of BTRM jackets and the ultimate axial strain of the confined concrete. This study integrated the identified BTRM confinement mechanism into an existing stress-strain model for FRP-confined concrete, enhancing its predictive accuracy for BTRM-confined concrete. Specially, a coefficient, termed km, was introduced to quantify the mortar grade's impact on confinement stiffness in the confining pressure equation. Predictive results closely matched experimental data, especially in replicating plateau characteristics of the stress-strain curve.

Ultimate Conditions Prediction and Stress–Strain Model for FRP-Confined Concrete Using Machine Learning

Ultimate Conditions Prediction and Stress–Strain Model for FRP-Confined Concrete Using Machine Learning

Experimental study on dynamic direct tensile performances of steel fiber-reinforced RPC at high strain rates

Reactive power concrete (RPC) exhibits excellent mechanical properties, makes it great potential for applications. RPC has gained increasing attention in academic and engineering areas and has been used in fields such as anti-explosion engineering. The insufficient tensile strength of RPC is one of the critical reasons for its structural failure. Existing studies revealed that the strain rate effect of concrete under dynamic tension is stronger than that under dynamic compression. The existing research focuses either on dynamic splitting and spalling tests, or dynamic uniaxial tensile properties with a strain rate of 0–100/s, neither of which are representative of the effect of RPC subject to explosion. In addition, the study of the dynamic uniaxial tensile constitutive model of RPC has not been reported in the existing research. To solve the existing limitations, this study conducted dynamic direct tension tests on steel fiber-reinforced RPC with a predefined strain rate higher than 100 s−1 using a Split Hopkinson Tension Bar (SHTB) apparatus. RPC dumbbell-shaped samples, including plain RPC and steel fiber-reinforced RPC (SFRPC) with 1 % and 2 % fiber volumetric fractions, were tested at high strain rates of 98–528 s−1. Based on the test results of this study and those derived from existing publications, the relationship between dynamic direct tensile properties, steel fiber fraction, and strain rate was quantitatively analyzed, and corresponding empirical formulae were proposed. To meet the demand for numerical analysis on RPC structures subjected to explosive forces, a dynamic tensile stress-strain model for steel fiber-reinforced RPC considering steel fiber, strain rate, and dynamic toughness, was established.

Experimental Assessment of Mechanical Properties of Corroded Low–Alloy Structural Steel

This study investigates the mechanical properties of corroded Q355B structural steel subjected to a simulated marine atmosphere and an industrial atmosphere. The micro-morphology of corroded steel in two different environments was analyzed by SEM (scanning electron microscopy). Tension tests were performed to determine the degradation laws of the mechanical properties of corroded steel, including its yield strength, ultimate strength, elastic modulus, ultimate strain and elongation after fracture. The test results indicate that the elongation after fracture of the steel is the most severely deteriorated property after corrosion. The recommended empirical formula for limiting the maximum corrosion rate is established. It is found that when the initial elongation is 30%, the maximum allowable corrosion rate is 19.2%. Based on the achieved results, a simplified time-dependent stress–strain model of Q355B structural steel is established considering the coupling effects of corrosive environments and applied stress, which is also evaluated using relevant research. In addition, axial compression tests were conducted on corroded square stud columns to verify the effectiveness of the established model. It is indicated that the model can be used for fitness-for-purpose analyses in structural integrity assessments.

Elevated-temperature material properties and fracture behavior of fire-resistant steel FR355

Fire-resistant steel (FRS) has been increasingly used in engineering structures due to their advantages of excellent earthquake and fire resistance properties. Accurately characterization of material properties and limit states of steel material is very important for structural-safety design and finite element (FE) simulation. This paper presents the results of experimental and numerical investigations on the elevated-temperature performance of FRS in terms of material properties, full-range true stress-strain curve, ductile fracture behavior, which has not yet been reported. The experimental part of the present paper includes the steady-state tensile testing of conventional structural steel (CSS) and FRS at temperatures up to 800 °C. Hollomon law and weighted average method were adopted to derive full-range true stress-strain behavior of the investigated steels at elevated temperatures, which is required for ductile fracture simulation in ABAQUS. Ductile fracture of tensile coupon specimens was modelled using the stress-modified critical strain model (SMCS). To verify the accuracy and application of the proposed true stress-strain and fracture models, finite element (FE) simulations of tensile coupon tests were performed using ABAQUS/explicit. It shows that the FE simulation incorporating proposed material plastic behavior and ductile fracture model provides accurate predictions for fracture response of the tensile coupons.