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The nonlinearity of the constitutive relation for rocks becomes more prominent with a more complex physical-mechanical environment and mechanical behavior. The accurate establishment of the constitutive relation affects the determination of rock deformation and damage state from physical features. In this study, a novel statistical damage constitutive model for rocks is proposed based on quantified energy conversion. The novelty of the model is that the nature of rock damage before and after damage stress is considered. In the constitutive model, the evolution characteristics of energy conversion show a five-stage evolution with a 'spoon' form and correspond to the rock deformation and damage process, which can be fitted with the modified GaussAmp function; the damage variable is deduced by the Weibull distribution with energy conversion as the distribution variable, which presents a monotonic decrease caused by initial defects before the σ cd and shows a 'S' shape caused by nascent cracks after the σ cd. Furthermore, triaxial test data of three types of rocks under different confining pressures were used to verify the proposed model, and the results were in good agreement with the test data in most cases. The characteristics of the crack closure stage, peak stress, residual strength, and stress drop process are controlled by the model parameters, which can be determined using experimental data. As these parameters definitely have a physical meaning and a relation to the confining pressure, the proposed model has the potential to be used in rock engineering. [ABSTRACT FROM AUTHOR]

The hot deformation characteristics of deformed AZ81 magnesium alloy were studied by hot compression deformation on Gleeble-3800 thermal simulation test machine. The deformation temperatures were set at 300, 350, 400 and 450 °C, and the deformation rates were 0,01, 0,1 and 1s-1, respectively. Using the experimental data, the constitutive equation is obtained by friction correction and a series of formulas, and the constitutive equation is compared with the experimental data to verify its accuracy. [ABSTRACT FROM AUTHOR]

The small-strain stiffness of soil measured through dynamic tests can be utilized in the finite element method to simulate static conditions. Although numerous soil constitutive models incorporated the elastic law of the maximum shear modulus and normalized shear modulus degradation curves to simulate the small-strain behavior of soil, rare models can be calibrated using the normalized shear modulus degradation curves measured from the resonant column and torsional shear tests varying a wide range of mean effective stresses. The poor calibration of the elastic law in the soil constitutive model may result in uncertainties when simulating the initial stiffness of the foundation in finite element modeling. The current study developed a small-strain hypoelastic model based on normalized shear modulus degradation curves using four material parameters that provide greater flexibility in controlling the curvature shape of the degradation curves. The small-strain hypoelastic model was evaluated using an element test and applied to a settlement test on a shallow foundation, a laterally loaded test on a slender pile, and a series of laterally loaded tests on monopiles. The results indicated that the reference strain and curvature parameter in the empirical equations for the normalized shear modulus degradation curves should be related to the mean effective stress, and the curves should be carefully calibrated by using resonant column and torsional shear tests under low mean effective stresses. The calibrated hypoelastic model significantly improved the accuracy of predicting the nonlinear initial stiffness in finite element modeling. The suggested procedure of calibrating the small-strain hypoelastic model was proposed to provide guidance in various engineering practices. [ABSTRACT FROM AUTHOR]

Under confining pressure, rocks transition from brittle failure to plastic failure, and residual strength exists after complete failure. However, in the process of establishing rock damage constitutive models, the strength criteria used usually do not consider residual stress. In cold region engineering, the freeze-thaw effect caused by temperature changes should be considered in the constitutive model, and strength criteria should also be introduced. Considering the failure characteristics of micro element when rock is subjected to freeze-thaw and load, and based on the impact of reducing the effective bearing area on each damage, the total damage variable and constitutive model of rock under freeze-thaw and load are established. Starting from the characteristics of the entire process of rock deformation, the revised Mohr-Coulomb (M-C) strength criterion of rock is established by considering freeze-thaw cycles and residual effects. The results show that: The theoretical curve and test curve of the constitutive model are not completely consistent, but the variance R2 between the two does not exceed 0.6, indicating that the theoretical curve is in good agreement with the test curve and can reflect the entire process of rock deformation and failure, verifying the rationality of the constitutive model and damage variable description. With the increasing of freeze-thaw cycles, the strength decreases and the deformation increases of rock. As the number of freeze-thaw cycles increases, the strength decreases and deformation increases. When the freeze-thaw cycle reaches 40 cycles, the strength decreases by more than 60%. With the increasing of confining pressure, the strength and deformation also increase. When the confining pressure increases from 0 to 6 MPa, the strength of red sandstone increases by more than 80% under the same freeze-thaw cycles, which is consistent with the actual situation. The revised M-C strength criterion data does not exceed the test data and is relatively close to the test data. The difference between the two is less than 25%, indicating that the established strength criteria can be safely used as a basis for rock elemental failure, verifying the rationality of the strength standard considering freeze-thaw and residual effects. This Revised M-C strength criterion introduces the influence of freeze-thaw cycles and residual stress factors, which not only characterizes the relationship between internal stress parameters in rock limit states under different freeze-thaw cycles, but also addresses the disadvantage of Drucker-Prager (D-P) criterion being more conservative. This method is based on the measured results of rock triaxial test, which makes it more flexible and the calculation results closer to reality. [ABSTRACT FROM AUTHOR]

The coagulation of fresh latex is one of the critical processes that impacts rubber quality during natural rubber processing. Constitutive relationships are the basis for the study of the mechanical properties of rubber materials and serve as a prerequisite for material simulation studies. However, studies on the effect of different coagulation methods on natural rubber constitutive relationships have yet to be carried out, and the current models used for natural rubber constitutive relationships need to be improved. In order to investigate the effects of different coagulation methods on the hyperelastic properties of natural rubber, the impact of natural coagulation, enzyme coagulation, acid coagulation, microbial coagulation, and enzyme-assisted microbial coagulation on the hyperelastic constitutive relationship of natural rubber were analyzed in detail based on tensile experiments and the Yeoh model. The results show that after introducing a strain rate-related factor, the Yeoh model can describe well the mechanical behavior of natural rubber carbon black composites in different deformation regions, and the rubber, studied with varying coagulation methods, exhibits different mechanical properties in different deformation regions. This study provides new evidence for the study of high-performance natural rubber and serves as a reference for process selection in the primary processing of natural rubber. [ABSTRACT FROM AUTHOR]

A thermal protection system is critical for ensuring the safe take-off and return of various aircraft. A key heat-resistant material within this system is the ceramic fiber insulation tile (CFIT), which is a porous three-dimensional network material with density ranges from 0.3 to 0.4 g/cm3 that exhibits complex mechanical behaviors. Due to the complexity of the service environment, experimental methods cannot accurately capture the mechanical behavior of a CFIT. Although simulation-based methods can provide insights, an accurate constitutive model for CFITs has yet to be established. To predict its complex mechanical behavior, an elastic–plastic damage constitutive model was established for CFITs. Based on the Hashin criteria and four fundamental assumptions, a yield rule was modified by introducing a damage factor in the TTT direction. The model was encoded into a user–material subroutine (UAMT) integrated within ABAQUS to capture the mechanical responses under four typical working conditions. The change trend of the simulation curve closely aligned with that of the experiment curve, better characterizing the stress–strain relationship of the CFIT under different working conditions such as compression, tension, and shear and the error was less than 18%. The proposed approach was validated by designing a millimeter-level indentation experiment. The results in this paper demonstrate that the maximum loading depths of the simulation and experiment were consistent, and the relative errors were within 12%, respectively. The research provides a reliable elastic–plastic damage constitutive model to predict the mechanical behavior of CFITs under complex working conditions. [ABSTRACT FROM AUTHOR]

Argillaceous siltstone is prone to deformation and softening when exposed to water, which poses a great threat to practical engineering. There are significant differences in the degrees of damage to this type of rock caused by solutions with different water temperatures. This study aimed to better understand the effect of temperature on argillaceous siltstone by designing immersion tests at water temperatures of 5, 15, 25, and 35 °C, analyzing the mechanical properties and cation concentration shifts under each condition. A water temperature–force coupled geometric damage model for argillaceous siltstone was developed, incorporating a Weibull distribution function and composite damage factors to derive a statistical damage constitutive model. The findings reveal that, with increasing water temperature, the peak strength and elastic modulus of argillaceous siltstone display a concave trend, initially decreasing and then increasing, while the cation concentration follows a convex trend, first increasing and then decreasing. Between 15 and 25 °C, the stress–strain behavior transitions from a four-phase to a five-phase pattern, with pronounced plasticity. The model's theoretical curves align closely with experimental data, with the Weibull parameters m and λ effectively capturing the rock's strength and plastic characteristics. Changes in water temperature notably influence the damage variable D12 in the context of water temperature–peak stress coupling, with D12 initially increasing and then decreasing with higher temperatures. These research results can provide new methods for exploring the paths of soft rock disasters and provide guidance for designing defenses in geotechnical engineering. [ABSTRACT FROM AUTHOR]

The Laves phase NbCr2/Nb two-phase alloy has received significant research interest as a potential high-temperature structural material. Based on isothermal and constant strain rate compression experiments conducted on the alloy within a temperature range of 1000 -1200 °C and strain rate range of 0.001-0.1 s−1, the flow stress constitutive relationship of the alloy was established using the J-C model and BP artificial neural network model, respectively. It was found that the conventional J-C model fails to describe the flow stress softening behavior of the alloy. In contrast, the modified J-C model provides a better prediction of the flow stress softening phenomenon and accurately characterizes the flow stress behavior of the alloy, it exhibits high prediction accuracy as indicated by the correlation coefficient (R) of 0.9902, average absolute relative error (AARE) of 8.773% and mean relative error (MRE) of 7.389%. The flow stress behavior of the alloy can be more accurately characterized using the constitutive relationship built by the BP neural network model. The model exhibits higher prediction accuracy with R of 0.9998, AARE of 2.232% and MRE of 0.870%. The results demonstrate that the BP neural network model has superior capability in predicting the flow stress behavior of the alloy. The established flow stress constitutive relationship can provide more accurate and reliable fundamental data with respect to flow stress for finite element simulations of forging deformation process of the Laves phase NbCr2/Nb two-phase alloy. In addition, it serves as theoretical basis for rational design of forging process and accurate calculation of the deformation force of the alloy. [ABSTRACT FROM AUTHOR]

This paper introduces a novel technique for enhancing the joint strength in structural acrylic glass (polymethyl methacrylate, PMMA) under thermal cycling conditions. By employing bulk polymerization, the strength of PMMA joints was significantly reinforced. Tensile assessments from 20 °C to 140 °C were conducted to evaluate the mechanical properties of acrylic joints under varying temperature conditions. A constitutive model was established to correlate the strength of both the base material and the joints with temperature variations. The tensile test outcomes demonstrated that the innovative bulk polymerization method under thermal cycling conditions effectively increased the joint material strength to reach up to 90% of the base material's strength, and the post-thermal cycling tests demonstrate that post-thermal cycling has essentially no impact on the strength and modulus. This advancement in joint strength enhancement not only expands the potential applications of acrylic glass in architectural structures but also lays a substantial theoretical foundation for construction practices. [ABSTRACT FROM AUTHOR]

This study systematically investigates the mechanical properties of plain concrete (PC) and 2% steel fiber reinforced concrete (SFRC) under both static and dynamic loading conditions, utilizing advanced mechanical testing equipment and dynamic impact testing methods. The strain rate range studied spans from 10−4 s−1 to 483.12 s−1. Under static loading conditions, the maximum bearing capacity and energy absorption capacity of 2% SFRC are 2.16 times and 3.83 times greater than those of PC, respectively, indicating a significant enhancement in toughness and resistance to failure. Under dynamic loading conditions, the energy absorption capacity of SFRC increases to 6.36 times that of PC. The impact failure behavior of SFRC was analyzed using the split-Hopkinson pressure bar—digital image correlation (SHPB-DIC) method, revealing that the failure was primarily driven by splitting tension. The failure process was subsequently categorized into four distinct stages. At high strain rates, the dynamic enhancement factor, peak stress, and peak strain of SFRC exhibit a linear increase with strain rate, whereas the energy absorption capacity increases in a nonlinear manner. This study presents a simplified viscoelastic constitutive model with four parameters and develops a damage-based viscoelastic constitutive model with seven parameters, demonstrating its broad applicability. The findings offer both theoretical insights and experimental evidence to support the use of SFRC under high strain rate conditions. [ABSTRACT FROM AUTHOR]

Shear behaviour of soil–structure interfaces greatly affects the performance of geotechnical structures. The soil–structure interfaces in geothermal structures (e.g., energy pile and energy wall) are often subjected to varying temperature and suction conditions. However, there is no constitutive model to simulate the coupled effects of suction and temperature on the shear behaviour of soil–structure interfaces. In this study, a thermo-mechanical model was newly developed based on the bounding surface plasticity framework to predict the thermo-mechanical behaviour of saturated and unsaturated interfaces. A power function was used to calculate the degree of saturation at the interface and improve the evaluation of suction effects on interface shear strength. A linear relationship between temperature and interface critical state friction angle was proposed to incorporate thermal effects. New equations were also proposed to describe the critical state lines (CSLs) in the void ratio versus stress plane (e- ln σ n * ) and to model the shearing-induced deformation at various temperatures and suctions. The experimental data from different interfaces in the literature were used to evaluate the model capability. Comparisons between measured and computed results suggest that this model can well capture the coupled effects of temperature, suction, and net normal stress on the shear behaviour of interfaces. [ABSTRACT FROM AUTHOR]

The world has abundant marine resources, and the use of seawater, sea sand, and coral instead of seawater, river sand, and gravel can compensate for the lack of traditional building materials for marine engineering construction. Additionally, glass fiber–reinforced polymers (GFRPs) have excellent corrosion resistance and can effectively solve the corrosion problem of steel reinforcement in harsh environments. The bond performance between GFRP bars and sea sand–coral concrete (SSCC) is an important factor in deciding whether this approach can be applied in actual projects such as RC. In this study, the effects of the SSCC strength grade, diameter, bond length, and rib height on the bond performance between GFRP bars and SSCC were investigated using direct pullout tests. The bond performance between GFRP bars and SSCC was compared with that between GFRP bars and ordinary concrete (OC). Furthermore, the microstructure and damage characteristics of the GFRP bars and SSCC were observed using scanning electron microscopy (SEM). The test results show that the main failure modes of the specimens include GFRP bar pullout failure and SSCC splitting failure. The rib height has a greater effect on the bond performance, and in specimens with a strength grade of SSCC25, diameter of 12 mm, and bond length of 5d , the bond strength between a deep-ribbed GFRP bar and the SSCC was 75.6% greater than that of specimens with a shallow-ribbed GFRP bar. The bond strength between the GFRP bars and SSCC decreased with increasing diameter and bond length, but the bond stiffness was almost the same. When the diameter increased from 8 to 14 mm, the bond length increased from 3d to 7d , and the bond strength decreased by 57.3% and 36.9% respectively. The bond strength and bond stiffness increased with increasing strength grade of the SSCC. Moreover, SEM showed that the surface damage of GFRP bars with pullout failure was severe, whereas the surface integrity of GFRP bars with splitting failure specimens was better. Based on the experimental results, the bond–slip constitutive model of the GFRP bar with SSCC yielded satisfactory results. [ABSTRACT FROM AUTHOR]

In this paper, a new micromechanical hysteresis loop constitutive model of C/SiC composites with different interphases was developed considering the probabilistic‐statistical matrix fragmentation process. The lengths of matrix fragmentation were divided into three types, that is, long matrix fragments (LMFs), medium matrix fragments (MMFs), and short matrix fragments (SMFs). The distributions of the LMFs, MMFs, and SMFs with increasing tensile stress were determined using the probabilistic‐stochastic model by assuming the two‐parameter matrix strength distribution. The micro stress field of the LMFs, MMFs, and SMFs upon unloading and reloading was obtained and adopted to determine the corresponding stress‐strain relations. The interaction of matrix fragmentation lengths, especially for the LMFs with large debonding energy (LDE) and SMFs, was considered in the closed‐form constitutive model and hysteresis‐based inverse tangent modulus (ITMs) damage parameter. Synergistic effects of the fiber volumes, peak stresses, and interface debonding energy on the interface damage state, mechanical hysteresis loops, and related ITMs with small debonding energy and LDE were also analyzed. Comparisons of the mechanical hysteresis loops using the new hysteresis models considering matrix stochastic fragmentation and hysteresis models considering constant matrix fragmentation were also discussed. Experimental cyclic tensile hysteresis loops and unloading/reloading ITMs of C/(PyC)/SiC and C/(PyC+SiC)/SiC composites with different interphase thickness (i.e., t = 300, 600, 1000, and 2000 nm) were predicted using the developed constitutive model. Evolution of the unloading/reloading interface slip ratio was analyzed for different tensile peak stresses. [ABSTRACT FROM AUTHOR]

The finite element modeling method has been widely applied in the modeling of the cutting process to characterize the instantaneous and microscale deformation mechanism that was difficult to obtain using physical experiments. The lubrication and cooling conditions, such as minimum quantity lubrication and cryogenic liquid nitrogen, affect the thermo-mechanical behaviors and machined surface integrity in the cutting process. In this work, a grain-size-dependent constitutive model was used to model orthogonal cutting for Ti-6Al-4V alloy with MQL and LN2 conditions. The cutting forces and chip morphologies that were measured in the cutting experiments of Ti-6Al-4V alloy were used to validate the simulated forces. The relative errors between the measured and simulated principal forces were less than 8%, while the relative errors of thrust forces were less than 19%. The predicted chip morphologies and surface grain refinement agreed well with the experimental results under the conditions with different uncut chip thicknesses and edge radii. Additionally, the relationship between the plastic displacement and grain refinement, as well as the microhardness and residual stresses under MQL and cryogenic conditions, were discussed. This work provides an effective modeling method for the orthogonal cutting of Ti-6Al-4V alloy to understand the mechanism of the plastic deformation and machined surface integrity under the MQL and LN2 conditions. [ABSTRACT FROM AUTHOR]

The metallic materials used to manufacture turbine components can potentially be replaced with ceramics such as Si3N4, but the stress on turbine discs is difficult to determine experimentally, which hinders the development and optimization of ceramics. The finite element method solves this problem, but it requires an accurate constitutive model and parameters. Existing methods for determining model parameters lack versatility and do not consider the internal pores of ceramics. This work proposes a method for determining the parameters of the high-temperature rapid fracture constitutive model of ceramics with internal pores based on the results of industrial computed tomography (CT) and high-temperature fracture toughness experiments. The constitutive model for a ceramic with internal pores was selected based on the typical service conditions of turbine discs. Industrial CT was used to measure pore information. A finite element preprocessor was developed to create simulated specimens with pores. The high-temperature fracture toughness of the ceramics was measured. Pore insensitivity was the parameter obtained from the high-temperature constitutive model of ceramics with pores using this method. The maximum relative error between the predicted and experimental flexural strengths was 6.8%. It provides a new idea for determining the parameters of constitutive models for materials with pores. [ABSTRACT FROM AUTHOR]