Search

The superplastic deformation behavior of 2 mm Ti60 sheet is studied, and the constitutive equation of superplastic deformation is established. The results show that when the strain rate is 5.00 × 10−3 s−1 and the temperature is 950 °C, the maximum superplastic elongation reaches 400%. Through the analysis of the true strain–true stress curve, it is found that the average apparent activation energy (Q) is 490.783 kJ mol−1 and the average strain rate sensitivity (m) is 0.49. Dynamic spheroidization (DG) promotes the transformation of lath α phase to equiaxed α phase. Dynamic recrystallization (DRX) promotes the generation of high‐angle grain boundaries (θ > 15°). After deformation, the strength of R‐type textures changes significantly. From the grip to the tip, the strength of R‐type texture gradually weakens, which is mainly caused by the rotation of grains during deformation. The deformation mechanism of Ti60 sheet is dominated by grain boundary sliding, and is coordinated by grain growth, DG, DRX, dislocation motion, and grain rotation. [ABSTRACT FROM AUTHOR]

Nickel-based powder metallurgy superalloys with high W and high γ’ content exhibit excellent high-temperature properties, but their high deformation resistance poses significant challenges for hot processing. In this study, the hot compression behaviour of an extruded nickel-based powder superalloy FGH4109 with high W (6.1%) and high γ’ phase contents (60%) was systematically investigated at temperatures ranging from 1060 ℃ ~ 1140 ℃, strain rates from 0.001 s−1 ~1 s−1, and maximum true strains of 0.7. Combined with the hot working map and the microstructure evolution in different hot working zones, the optimal hot working window for the alloy was determined to be in the temperature range of 1060 ℃ ~ 1140 ℃ and strain rates of 0.001 s−1 ~0.012 s−1, where the power dissipation efficiency η was greater than 0.5, and the dominant deformation mechanism was discontinuous dynamic recrystallisation. [ABSTRACT FROM AUTHOR]

In this study, we conducted a single-factor experiment where fine aggregates in each mixture were replaced with coal-fired slag at replacement rates in the range of 0–100%. We investigated the effect of slag substitution rate on the cubic compressive strength, splitting tensile strength, axial compressive strength, and static modulus of elasticity of slag concrete. Based on the experimental data, the stress–strain curve of the coal-fired slag concrete was divided into four phases: elastic, elasto-plastic, peak, and decline phases. A stress–strain constitutive equation was established to describe the coal-fired slag concrete. A replacement rate of 50% of the formulated coal-fired slag concrete meets the strength requirements of C60 structural applications, and the cubic compressive strength is the same as that of ordinary concrete. Coal-fired slag can be utilized in large quantities, improving the economic value of coal-fired slag and expanding the scope of application of slag concrete. [ABSTRACT FROM AUTHOR]

The present work deals with the hot deformation behavior of commercial Nb alloy C-103 and its microstructure evolution during uniaxial compression tests in the temperature range of 700-1100°C and the strain rate range of 0.001-0.4 s-1. Strain rate sensitivity, calculated from the compression tests data, was almost constant and showed a negative value in the temperature range of 700-900°C but increased significantly beyond 900°C. Dynamic strain aging was found to have a predominant effect up to 900°C, beyond which dynamic recovery and oxidation influenced the compressive properties. The microstructure of the deformed samples showed indications of dynamic recrystallization within the high strain rate sensitivity domain and features of flow instability in the regime of low strain rate sensitivity. The 950-1000°C temperature range and strain rate range of 0.001-0.1 s-1 were suggested as suitable hot deformation conditions. The constitutive equation was established to describe the alloy's flow behavior, and the average activation energy for plastic flow was calculated to be 267 kJ/mol. [ABSTRACT FROM AUTHOR]

The utilization of Titanium-clad steel plate (TCSP) spans various industries. Over time, there has been an increasing demand for enhanced mechanical properties, leading to the advancement of high-strength TCSP. As a result, self-produced high-strength TCSP was utilized to investigate the cooperative deformation behavior during isothermal axial thermal compression (TC) tests and to establish the constitutive equations and processing map. The results indicated that the TCSP did not deform cooperatively throughout the entire TC process. Initially, the titanium matrix deformed, and only when its strength matched that of the steel matrix did the TCSP deform cooperatively. The microstructure of the steel matrix revealed an increasing number of deformation grains, while the titanium matrix exhibited an increase in substructure grains with temperature. The primary orientation of the steel matrix was (101), while that of the titanium matrix was (01 1 ¯ 0) after TC. Furthermore, it was observed that the titanium matrix displayed a distinctive plate texture, while the steel matrix exhibited a mixed texture that became increasingly pronounced with temperature. The constitutive equation was derived using the Arrhenius model, and the material constants were represented by a fourth-order polynomial fit to the true strain. The established constitutive equation exhibited an accuracy of 96.27%. Finally, the process map constructed using the dynamic material model revealed the presence of four distinct zones. [ABSTRACT FROM AUTHOR]

Continuous extrusion is a very promising technique for forming Cu–Cr–Zr alloys which takes the upward continuous casted rods as raw materials. While the hot deformation behavior and constitutive equation of as-cast rods have never been reported. In the present study, the hot deformation behavior of as-cast Cu–Cr–Zr rods with columnar grains was investigated. The results showed that the flow stress at 500 °C is higher than that at 400 °C. The reason for that can be attributed to the dynamic precipitation process, which was confirmed by TEM observations. At this temperature, partial CDRX dominates the softening mechanism while at high temperatures DRV and DDRX play a critical role. The constitutive equation was then established and the deformation activation energy was determined to be 541.93 kJ/mol. The high activation energy was attributed to the large solidified columnar grains. At high strains, stable metal flows can be obtained at high strain rates and high temperatures according to the processing maps, which indicates that a high-speed deformation at a high temperature is favorable to the plastic forming of this material. This investigation thus provides valuable information on how to process the Cu–Cr–Zr rods by plastic deformation methods, for example, continuous extrusion. [ABSTRACT FROM AUTHOR]

Isothermal compression test is used to investigate the hot deformation behavior of spray co-deposited and extruded 10 vol% SiCP/Al–Cu–Mg–Ag composite. In this study, an accurate strain-compensated model based on Arrhenius constitutive equation is constructed with the corresponding R value of 0.9965 and AARE of 4.05%. The experimental results are in high agreement with the predicted flow stress. Hot deformation activation energy of the SiCP/Al composite (161.685 kJ/mol) is notably higher than that of Al–Cu–Mg–Ag alloy, which is attributed to the dislocations introduced by SiC reinforcement. The microstructure evolution of compressed specimens is characterized using EBSD and TEM. DRX, including CDRX and DDRX, is the main softening mechanism under the hot deformation conditions of high temperature, low strain rate and high strain. The transition of softening mechanism from DRV to DRX is due to the subgrains consuming dislocations and then transforming into DRX grains. Comparing the microstructure under different hot deformation parameters, the recrystallization degree is significantly influenced by temperature, followed by strain rate and strain. In addition, the recrystallization process is impeded by the primary Al2Cu phases, T phases and SiC particles in the composite through hindering the migration of dislocations.

Understanding the hot deformation behavior of steel and establishing corresponding hot processing maps are crucial methods for determining appropriate hot processing parameters. In this article, the hot deformation behavior of a high-nitrogen austenitic stainless steel was investigated in the temperature range of 900–1150 °C and the strain rate range of 0.01–10 s−1 on a Gleeble-3500 thermo-mechanical simulator. The results show that the flow stress of experimental steel increases with decreasing deformation temperature and increasing strain rate. Based on the Arrhenius model, a constitutive equation was developed for the experimental steel, with a hot deformation activation energy of 603.347 kJ/mol. The hot processing maps were created employing the dynamic material model to determine the optimum hot processing conditions for the experimental steel at different strain levels.

The present work deals with the hot deformation behavior of commercial Nb alloy C-103 and its microstructure evolution during uniaxial compression tests in the temperature range of 700-1100 °C and the strain rate range of 0.001-0.4 s-1. Strain rate sensitivity, calculated from the compression tests data, was almost constant and showed a negative value in the temperature range of 700-900 °C but increased significantly beyond 900 °C. Dynamic strain aging was found to have a predominant effect up to 900 °C, beyond which dynamic recovery and oxidation influenced the compressive properties. The microstructure of the deformed samples showed indications of dynamic recrystallization within the high strain rate sensitivity domain and features of flow instability in the regime of low strain rate sensitivity. The 950–1000 °C temperature range and strain rate range of 0.001-0.1 s-1 were suggested as suitable hot deformation conditions. The constitutive equation was established to describe the alloy's flow behavior, and the average activation energy for plastic flow was calculated to be 267 kJ/mol.

It is necessary to confirm the appropriate processing parameters for recycled-Be/2024Al composites before hot processing. Therefore, hot compression experiments were conducted on 40 and 50 vol% recycled-Be/2024Al composites prepared by pressure infiltration method. Meanwhile, the constitutive equations were established. The activation energy increased with the volume fraction of reinforcement, which means the increasing difficulty for composites to deform. However, different from ceramic reinforcements, Be is able to deform with matrix coordinately. This characteristic makes recycled-Be/2024Al composites more prone to deformation than ceramic reinforced Al composites with the same volume fraction of reinforcements. The processing maps of 40 and 50 vol% recycled-Be/2024Al composites have been drawn, and the appropriate processing parameters for 40 and 50 vol% recycled-Be/2024Al composites were determined as 495–525 °C,0.0006–0.0016 s−1 and 500–530 °C,0.016–0.04 s−1, respectively. The microstructures of samples hot compressed with various parameters were observed to identify the accuracy of processing maps.

Magnesium alloys have received a lot of attention in aerospace, automotive, electronic communications and other fields due to their low density, high specific strength and damping performance. However, magnesium alloy sheets prepared by conventional thermomechanical processing usually have a strong basal texture, resulting in poor formability. In this paper, Mg–Mn–Ce alloys with good plastic forming ability were prepared by studying and optimizing the annealing process. Under the low-temperature annealing condition, it can promote the static recrystallization and grain refinement of Mg–Mn–Ce alloy, and also eliminate the internal stress. With the increase of annealing temperature, a large amount of dispersed Mg12Ce as a stable second phase effectively hindered the grain boundary migration, while the nanoscale α-Mn forms a fine second phase to inhibit grain growth, and both of them together greatly stabilize the deformation structure of the alloy, and maintain a good grain organization under the condition of annealing temperature of 300 °C and holding time of 30 min. The present work also improves the Arrhenius constitutive equation for the Mg–Mn–Ce alloy with respect to the degree of deviation, which significantly improves the accuracy of the model in predicting the thermoforming behavior. Meanwhile, to address the shortcomings of the traditional forming method of magnesium alloy, the processing process of spreading the centrifugal casting tube flat is proposed, the forming process is simulated, and the location of easy breakage in the forming process is predicted. These findings provide microanalytical support for the improvement of forming properties of magnesium alloys by annealing.

Mg-Gd-Zn based alloys have better creep resistance than other Mg alloys and attract more attention at elevated temperatures. However, the multiple alloying elements and various heat treatment conditions, combined with complex microstructural evolution during creep tests, bring great challenges in understanding and predicting creep behaviors. In this study, we proposed to predict the creep properties and reveal the creep mechanisms of Mg-Gd-Zn based alloys by machine learning. On the one hand, the minimum creep rates were effectively predicted by using a support vector regression model. The complex and nonmonotonic effects of test temperature, test stress, alloying elements, and heat treatment conditions on the creep properties were revealed. On the other hand, the creep stress exponents and creep activation energies were calculated by machine learning to analyze the variation of creep mechanisms, based on which the constitutive equations of Mg-Gd-Zn based alloys were obtained. This study introduces an efficient method to comprehend creep behaviors through machine learning, offering valuable insights for the future design and selection of Mg alloys.

Abstract Understanding the mechanical characteristics of rocks when subjected to direct tension is crucial for assessing the stability of rock formations. Within the scope of this research, a series of tests was conducted using Tage tuff to assess the deformation behavior and crack extension of rock under direct tension. The axial, lateral, and shear strain fields as well as crack propagation, localized deformation behavior, and failure mode of the rocks were analyzed using three-dimensional digital image correlation method. The results showed that the axial strain fields on the specimen surface were heterogeneous, with different locations and localization occurring in the pre-peak stage, which was similar to the evolution of shear strain, whereas the lateral strain only showed slight changes. The crack extension direction was inferred, indicating that both tensile and shear stress occurred in the tests. Furthermore, different stress–strain responses were observed for the inside and outside of the localized bands. Then, the surface patterns of specimen failure were scanned and analyzed to assess the failure mode and residual strength of the specimen under direct tensile stress. Finally, the results of direct tension, uniaxial compression, and Brazilian split tests for Tage tuff were compared, and the complete stress–strain curve of uniaxial tension (UT) was simulated using a nonlinear-variable-compliance constitutive equation. This study provides a deeper understanding into the damage behavior of rocks under direct tension.

Abstract In order to study the damage properties of red sandstone under combined action of temperature, water and stress, the uniaxial compression test was carried out for red sandstone after immersing in water for 0.5 h, 1 h and 3 h at 25 ℃, 55 ℃, 85 ℃ and 95 ℃, the mechanical properties, characteristic stress points, acoustic emission RA-AF parameters and failure forms of red sandstone were analyzed, the damage constitutive equation was established, and the damage properties of red sandstone were studied. The results showed: (1) temperature could significantly improve the saturated water content percentage of red sandstone. With the increase of temperature, the saturated water content percentage showed a trend of increase first and then decrease, and was the largest at 55 ℃; with the increase of temperature, the mechanical parameters (peak intensity, elasticity modulus, and stress at start point of expansion) decreased first and then increased, and was the smallest at 55 ℃; (2) the ratio of crack initiation stress to peak stress (σci/σf) initially increases and then decreases with rising temperatures for the same soaking duration. Conversely, it initially decreases and then increases with extended soaking time at the same temperature. The RA-AF acoustic emission signals predominantly occur in the tensile region at each stage account for a relatively large proportion, with the proportion of signals in the shear region significantly increasing as soaking time extends, corresponding well with the observed damage patterns. (3) By considering the damage due to temperature and water as Initial damage to red sandstone and the damage due to stress as load-induced damage, a damage variable based on the Weibull distribution function was established. The comprehensive damage constitutive equation derived from this can be applied to water-saturated red sandstone below 100 ℃. The findings provide theoretical reference for practical engineering applications.

In this paper, the flow behavior, constitutive model and microstructure evolution of solution-treated 2195 Al–Li alloy at temperatures from 123 K to 298 K and strain rates from 2000 s−1 to 5000 s−1 were studied. Experimental results show that the flow stress of the solution-treated 2195 Al–Li alloy is more sensitive to deformation temperature than strain rate. As the temperature declines from 298 K to 123 K, the flow stress at 2000 s−1 and 5000 s−1 increases by nearly 32.8% and 34.5%, respectively; whereas as the strain rate increases from 2000 s−1 to 5000 s−1, the flow stress at 298 K and 123 K only increases by 5.1% and 6.5%, respectively. The average strain hardening rate tends to decline with the increase in strain rate and temperature, and its value at 123 K and 2000 s−1 is about 1.5 times greater than that at 298 K and 5000 s−1. To overcome the very limited applicability of the conventional Arrhenius model with strain compensation, an Arrhenius-based model (c-Arrhenius model) is developed by coupling an independent strain term and then derived by using normalized flow stress and linear regression. To quantify the strain rate effect and temperature effect, a Johnson-Cook-based model (c-Johnson-Cook model) with exponential terms is developed. These two new constitutive models are validated via a comparative analysis, showing good predictability and accuracy. A further microstructure observation shows that the dislocation density is the highest at a strain rate of 5000 s−1 and cryogenic temperature of 123 K, which is beneficial for subsequent aging strengthening.

The constant strain rate compression experiment of powder metallurgy Mo–14Re alloys was carried out by Gleeble 1500 thermal simulation tester. The effects of deformation temperature (1100~1400 ℃) and strain rate (0.100~0.001 s−1) on the flow stress and microstructure evolution were analyzed. The constitutive equation of Mo–14Re alloys was established by hyperbolic sinusoidal Arrhenius model. The results show that, the flow stress of powder metallurgy Mo–14Re alloys decreases with the increase of deformation temperature or the decrease of strain rate during the thermal deformation, and the true stress-true strain curve shows the obvious work hardening and dynamic softening phenomenon. The dynamic softening behavior is mainly attributed to the dynamic recrystallization of Mo–14Re alloys at low strain rate (0.010 s−1 and 0.001 s−1) or high deformation temperature (>1200 ℃) during the thermal compression. The nucleation mode is grain boundary protruding nucleation. With the decrease of strain rate or the increase of temperature, the degree of recrystallization continues to increase, the grains continue to grow, and the Mo–14Re alloys are completely recrystallized at 1400 ℃ with the strain rate of 0.001 s−1.

In the geological disposal of radioactive waste, it is imperative to perform long-term assessments of the shielding efficacy and mechanical stability of the surrounding rock. Numerous investigations into the timedependent characteristics of various rock types have been undertaken to predict the long-term mechanical response of rocks. However, the time-dependent behaviors of diatomaceous earth, such as the strain-rate dependency of strength and creep behavior, remain unclear. In this study, constant-strain-rate and creep tests on diatomaceous earth specimens under undrained conditions and a confining pressure of 10 MPa, at both ambient (25 °C) and elevated (80 °C) temperatures were conducted. Although variations in strength (maximum differential stress) were observed between tests conducted at different temperatures, it is inconclusive as to whether the strength variations were primarily induced by temperature variations, as the unintentional deviation in water content between specimens used in the constant-strain-rate tests at 80 °C and 25 °C might have exerted some effects. The strain-rate dependency of strength and the creep behavior of diatomaceous earth were obtained, and a constitutive equation of the variable-compliance type, which accounts for the time-dependent behaviors of rocks, was applied to the obtained experimental results. Formulating an improved constitutive equation through further triaxial compression tests is an issue in the future.

Understanding the mechanical characteristics of rocks when subjected to direct tension is crucial for assessing the stability of rock formations. Within the scope of this research, a series of tests was conducted using Tage tuff to assess the deformation behavior and crack extension of rock under direct tension. The axial, lateral, and shear strain fields as well as crack propagation, localized deformation behavior, and failure mode of the rocks were analyzed using three-dimensional digital image correlation method. The results showed that the axial strain fields on the specimen surface were heterogeneous, with different locations and localization occurring in the pre-peak stage, which was similar to the evolution of shear strain, whereas the lateral strain only showed slight changes. The crack extension direction was inferred, indicating that both tensile and shear stress occurred in the tests. Furthermore, different stress–strain responses were observed for the inside and outside of the localized bands. Then, the surface patterns of specimen failure were scanned and analyzed to assess the failure mode and residual strength of the specimen under direct tensile stress. Finally, the results of direct tension, uniaxial compression, and Brazilian split tests for Tage tuff were compared, and the complete stress–strain curve of uniaxial tension (UT) was simulated using a nonlinear-variable-compliance constitutive equation. This study provides a deeper understanding into the damage behavior of rocks under direct tension. [ABSTRACT FROM AUTHOR]

Magnesium alloys show great promise in high-speed transport, aerospace, and military technology; however, their widespread adoption encounters challenges attributed to limitations such as poor plasticity and strength. This study examines the high-temperature deformation of semi-solid forged AZ91D magnesium alloy through a combination of experiments and simulations, with a focus on comprehending the influence of deformation conditions on dynamic recrystallization (DRX). The findings disclose that conspicuous signs of DRX manifest in the yield stress curve as strain increases. Additionally, decreasing the strain rate and temperature correlates with a reduction in both yield stress and peak strain, and the activation energy is 156.814 kJ/mol, while the critical strain and peak strain remain relatively consistent ( ε c = 0.66208 ε p ). Microstructural changes during high-temperature deformation and the onset of DRX are thoroughly examined through experimental methods. Moreover, a critical strain model for DRX and a predictive model for the volume fraction of DRX were formulated. These equations and models, validated through a combination of experiments and simulations, serve as invaluable tools for predicting the mechanical behavior and microstructural evolution, which also establishes a foundation for accurately predicting the deformation behavior of this alloy. By analyzing the hot deformation characteristics and dynamic compression mechanism of the newly developed semi-solid forging AZ91D magnesium alloy, a numerical simulation model can be effectively established. This model objectively reflects the changes and distributions of stress, strain, and rheological velocity, providing a scientific basis for selecting subsequent plastic deformation process parameters and designing mold structures. [ABSTRACT FROM AUTHOR]

Thermal simulation isothermal uniaxial compression experiments were carried out with Cube, Copper and S oriented aluminum single crystal(ASCs) at 25 〜300 °C and 0. 001 〜10 s-1. The true stress true strain curves of ASCs under different high temperature deformation conditions were obtained, and the strain compensation constitutive equation and thermal processing diagram were established. The results show that the degree of dynamic recrystallization(DRX) of ASCs with different crystal orientations is significantly different The DRX difficulty of ASCs with three orientations is as follows: Cube> CopperThe flow stress of ASCs during isothermal uniaxial compression decreases with the decrease of strain rate and the increase of deformation temperature. The maximum flow stress level of each orientation is Copper>S>Cube. The microstructure evolution energy dissipation of ASCs with different orientations during deformation is different, and the order of the power dissipation rate is Cube> Copper〉S. [ABSTRACT FROM AUTHOR]

• A machine learning model was established to accurately predict the minimum creep rate of Mg-Gd-Zn based alloys. • The effects of alloying elements and heat treatment conditions on the creep properties of Mg-Gd-Zn based alloys were revealed. • Variations of creep mechanism in Mg-Gd-Zn based alloys were analyzed based on the predicted creep stress exponents and creep activation energies. • Creep constitutive equations of Mg-Gd-Zn based alloys were established for future design and selection of Mg alloys served at high temperatures. Mg-Gd-Zn based alloys have better creep resistance than other Mg alloys and attract more attention at elevated temperatures. However, the multiple alloying elements and various heat treatment conditions, combined with complex microstructural evolution during creep tests, bring great challenges in understanding and predicting creep behaviors. In this study, we proposed to predict the creep properties and reveal the creep mechanisms of Mg-Gd-Zn based alloys by machine learning. On the one hand, the minimum creep rates were effectively predicted by using a support vector regression model. The complex and nonmonotonic effects of test temperature, test stress, alloying elements, and heat treatment conditions on the creep properties were revealed. On the other hand, the creep stress exponents and creep activation energies were calculated by machine learning to analyze the variation of creep mechanisms, based on which the constitutive equations of Mg-Gd-Zn based alloys were obtained. This study introduces an efficient method to comprehend creep behaviors through machine learning, offering valuable insights for the future design and selection of Mg alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

The prediction accuracy of the deformation behavior of materials by finite element (FE) simulation depends on the parameters in selected material models. Although the parameters are conventionally identified from standard material tests (e.g., uniaxial tensile and multiaxial material tests) to characterize the deformation behavior, the identification process requires a large number of experiments. We develop a novel inverse methodology for estimating the material model parameters by combining digital image correlation (DIC) measurement and FE simulation coupled with an ensemble-based four-dimensional variational method (En4DVar). En4DVar incorporates the experimental data obtained from a material test into the FE simulation that reproduces the test and inversely estimates the parameters such that the simulation results follow the experimental data, allowing for the reduction of experimental effort. We use the proposed method to estimate the parameters of a strainhardening law and anisotropic yield function from the results of uniaxial tensile test of a round bar of aluminum alloy. DIC measurement is conducted to obtain experimental data of the three-dimensional displacement and strain field over the surface of the specimen, including the post-necking range. The results demonstrate that En4DVar is a promising method for inversely estimating the parameters and characterizing the deformation behavior of a material from the results of a small number of tests. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study the damage properties of red sandstone under combined action of temperature, water and stress, the uniaxial compression test was carried out for red sandstone after immersing in water for 0.5 h, 1 h and 3 h at 25 ℃, 55 ℃, 85 ℃ and 95 ℃, the mechanical properties, characteristic stress points, acoustic emission RA-AF parameters and failure forms of red sandstone were analyzed, the damage constitutive equation was established, and the damage properties of red sandstone were studied. The results showed: (1) temperature could significantly improve the saturated water content percentage of red sandstone. With the increase of temperature, the saturated water content percentage showed a trend of increase first and then decrease, and was the largest at 55 ℃; with the increase of temperature, the mechanical parameters (peak intensity, elasticity modulus, and stress at start point of expansion) decreased first and then increased, and was the smallest at 55 ℃; (2) the ratio of crack initiation stress to peak stress (σci/σf) initially increases and then decreases with rising temperatures for the same soaking duration. Conversely, it initially decreases and then increases with extended soaking time at the same temperature. The RA-AF acoustic emission signals predominantly occur in the tensile region at each stage account for a relatively large proportion, with the proportion of signals in the shear region significantly increasing as soaking time extends, corresponding well with the observed damage patterns. (3) By considering the damage due to temperature and water as Initial damage to red sandstone and the damage due to stress as load-induced damage, a damage variable based on the Weibull distribution function was established. The comprehensive damage constitutive equation derived from this can be applied to water-saturated red sandstone below 100 ℃. The findings provide theoretical reference for practical engineering applications. [ABSTRACT FROM AUTHOR]

The hot compression test of CrFeCoNiAl0.1 high entropy alloy at temperature range of 950-1100 °C and strain rates range of 0.001–1 s−1 was carried out by Gleeble−3500 thermal compression simulator. The characteristics of microstructure evolution of the studied alloy during hot deformation were studied by means of OM and EBSD. The Arrhenius-type constitutive equation was constructed, and the hot deformation activation energy was calculated to be 307.77 K J mol−1. The proportion of low angle grain boundaries is 10.2% at the condition of 1050 °C/0.01 s−1, and the complete dynamic recrystallization (DRX) occurs. The characteristic parameters are determined according to the relationship between the work hardening rate and the true stress, and the mathematical relationship between the critical conditions for DRX and Z parameters is obtained. The critical stress for DRX decreases with increasing temperatures and decreasing strain rates. The kinetic model of DRX is constructed by the Avrami equation. Higher temperature and lower strain rate were beneficial to the occurrence of DRX. Based on microstructure evolution, the DRX volume fraction model of CrFeCoNiAl0.1 high entropy alloy was verified, and the experimental results are close to the predicted results. The DRX volume fraction model can correctly predict the DRX behavior of CrFeCoNiAl0.1 high entropy alloy. [ABSTRACT FROM AUTHOR]

The hot compression test of as-cast P91 alloy steel was carried out by Gleeble3500 multi-functional thermal simulation test machine under the deformation conditions of temperature of 900 ~ 1 100 °Cand strain rate of 0, 1~5 s-1. The high temperature flow behavior of as-cast P91 alloy steel was studied. The effects of strain rate and deformation temperature on the two-phase relationship of as-cast P91 alloy steel were analyzed. The strain rate compensation factor Z was introduced, and the Arrhenius constitutive model equation was established. The results show that the theoretical value of the peak stress calculated by the constitutive model is in good agreement with the experimental results, and the correlation is 96, 8 %, which verifies the feasibility of the model. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Iron Steel Vanadium Titanium is the property of Iron Steel Vanadium Titanium Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The material constitutive equation of 25CrMo4 steel was established through an isothermal compression experiment. First, a thermal compression experiment was carried out with a Gleeble-3500 thermal simulator to study the thermoplastic deformation behaviour of 25CrMo4 steel at various temperatures (850, 950, 1050, and 1150 °C) and strain rates (0.01, 0.1, 1.0, and 10 s−1). The measured true stress–strain curve showed that when the temperature is constant, the flow stress increases with the strain rate, whereas when the strain rate is constant, the flow stress decreases with the temperature. Then, the constitutive model of peak stress of 25CrMo4 was established after analyzing the stress and strain statistics. The model parameters were optimized. The accuracy of the flow stress constitutive model was verified by comparing the flow stress prediction model with the experimental results. The hot forging process of the inner core wheel was numerically simulated based on DEFORM-3D v11 software, and the parameters of this process were formulated by analyzing the metal flow rate and equivalent stress and strain fields. [ABSTRACT FROM AUTHOR]

The finite element method combined with the experiment analyzed the evolution mechanism of the plastic strain state and warping deformation of the TA2/Q345R composite plate during heat treatment. Then, the factors influencing plastic strain state and shape warping in the composite plate were discussed. The results show that during the heat treatment process, the composite plate’s internal strain state and macroscopic shape state are impacted by the thermal strain and bending strain between the heterogeneous metal layers, and both are in a continuous dynamic variation state. Therefore, the ultimate deformation behaviour of the composite plate depends on the accumulation and inheritance of plastic deformation during heat treatment. There is a critical value of the composite ratio and the total thickness of the composite plate, respectively, which determines the direction of the warpage after heat treatment. [ABSTRACT FROM AUTHOR]

A constitutive equation was established using finite element method (FEM) combined with neural network optimization and dimensionless model to uniformly describe the nanoindentation behavior of different crystal planes of sapphire crystal. The surface micromechanical behavior of four typical crystal planes (C, A, R, M) of the sapphire crystal was studied using nanoindentation method. The comparison between the calculated results of the constitutive equation and the measured results show that: the loading and unloading curves can be expressed by quadratic functions of the indentation depth h; the loading curve is a function of the elastic modulus E, yield stress Y, and work hardening index n of the intrusion surface, while the unloading curve is also related to the unloading position (the maximum depth) hmax in addition to these three factors; for the same crystal plane, the residual depth hr is proportional to hmax, and the plastic work Wp is proportional to the third power of hmax. The results also indicate that, for super hard and brittle materials such as sapphire crystal, which are difficult to apply conventional mechanical performance testing methods, the combination of the constitutive equation and nanoindentation testing can effectively obtain their basic mechanical property. [ABSTRACT FROM AUTHOR]

In the geological disposal of radioactive waste, it is imperative to perform long-term assessments of the shielding efficacy and mechanical stability of the surrounding rock. Numerous investigations into the timedependent characteristics of various rock types have been undertaken to predict the long-term mechanical response of rocks. However, the time-dependent behaviors of diatomaceous earth, such as the strain-rate dependency of strength and creep behavior, remain unclear. In this study, constant-strain-rate and creep tests on diatomaceous earth specimens under undrained conditions and a confining pressure of 10 MPa, at both ambient (25 °C) and elevated (80 °C) temperatures were conducted. Although variations in strength (maximum differential stress) were observed between tests conducted at different temperatures, it is inconclusive as to whether the strength variations were primarily induced by temperature variations, as the unintentional deviation in water content between specimens used in the constant-strain-rate tests at 80 °C and 25 °C might have exerted some effects. The strain-rate dependency of strength and the creep behavior of diatomaceous earth were obtained, and a constitutive equation of the variable-compliance type, which accounts for the time-dependent behaviors of rocks, was applied to the obtained experimental results. Formulating an improved constitutive equation through further triaxial compression tests is an issue in the future. [ABSTRACT FROM AUTHOR]

CoCrFeNiZr0.3 is a two-phase coexisting (Laves + FCC) high-entropy alloy with high strength, excellent corrosion resistance, and thermal stability. However, the inhomogeneous distribution of the eutectic structure among the dendrites has a detrimental effect on the coordinated deformation of the material. The current study shows that the grain size, weave structure, and second phase distribution of high-entropy alloys can be significantly changed by thermal deformation, which affects the mechanical and physical properties, as well as the chemical stability of the alloys. In this study, the thermal deformation behavior of CoCrFeNiZr0.3 biphasic hypoeutectic high-entropy alloy was investigated using a Gleeble-3500 thermal simulation tester under the conditions of deformation temperature of 950–1100 °C and deformation rate of 0.001–1 s−1. The results show that CoCrFeNiZr0.3 high-entropy alloy has higher deformation activation energy, which means its deformation resistance is larger. In addition, the microstructure with finer grain size and uniform distribution of Laves phase can be obtained by EBSD analysis after compression at 1000 °C and 0.01 s−1. [ABSTRACT FROM AUTHOR]

Dynamic mechanical characteristic testing at low temperatures was conducted for the typical porphyry and sandstone specimens of Yulong Copper Mine in Tibet, China. The stress and strain characteristics of the specimens at different temperatures were analyzed. A dynamic constitutive model was developed by considering the initial damage. Furthermore, microscopic damage characteristics during the water-saturated rock freezing process were investigated using the PFC3D software, revealing the mechanisms of frost heave damage to rocks. The results indicated that the water-ice phase transition either enhanced or deteriorated the specimen strength at low temperatures. Specifically, freezing at −10°C and −20°C enhanced the strength of sandstone. However, freezing at −10°C enhanced the porphyry specimens, and freezing at −20°C caused significant frost swelling injury. The new constitutive equation effectively fitted the dynamic stress and strain curves for both specimens, highlighting their differences. The maximum contact force and particle contact in the frozen rock PFC3D model were affected by rock and water particle deformations. The frost swelling deformation of water particles had a more pronounced impact on specimen damage and was related to the temperature. A specific freezing temperature existed at which the increase in saturated rock strength corresponded to the maximum specimen strength at that temperature.

In this paper, the hot deformation behavior of Ti65 alloy was investigated over the temperature range of 930–1110 °C with the strain rate of 0.001–1 s−1. According to the stress-strain curves, the constitutive equation was developed to describe the flow behavior of Ti65 alloy. The processing maps were constructed based on the dynastic materials model (DMM) and the perfect formability zone of Ti65 alloy is found under the temperature of 970–1020 °C and the strain rate of 0.001–0.1 s−1. In addition, a three-dimensional nonlinear transient thermo-mechanically coupled finite element model of the multi-dimensional forging (MDF) process of Ti65 alloy was developed. The effects of the forging temperature and forging speed, on the temperature rise, residual stress, and grain refinement were predicted. By analyzing the temperature and stress distribution, the optimum forging temperature and speed for Ti65 alloys were determined to be 1000 °C and 10 mm/s, respectively. Increasing the forging temperature or reducing the forging speed reduces the temperature rise and the maximum tensile stress, thus reducing the risk of cracking. Additionally, the equivalent strain increases as forging speed decreases. Simultaneously, the accumulated strain is more significant for the inside of the forgings. The results of this research are instructive for the optimization of the MDF process.

Magnesium-manganese series alloys, as materials with very low-density value, have excellent mechanical properties and corrosion resistance, and have broad prospects in automotive, aerospace, biomedical and other fields. In this work, the thermal deformation behavior and microstructural evolution of Mg–Mn–Ce alloys were investigated through uniaxial hot stretching experiments on Mg–Mn–Ce alloy plates under different deformation conditions, with the main focus on the plastic deformation mechanism of Mg–Mn–Ce alloys under different forming conditions. The unified viscoplastic constitutive equation for coupled damage is developed and compared with different types of constitutive equation models. Remarkably, the decrease in peak stress with increasing temperature or decreasing strain rate in Mg–Mn–Ce alloys is due to the fact that the internal slip system of the material is more easily activated with increasing temperature. As the temperature increases, the dislocations within the material decrease, which is due to the fact that the temperature increase makes the DRX action progressively stronger than the dislocation action, and the DRX leads to a significant coarsening of the grains at 573 K. In addition, the fracture behavior of the alloy under different deformation conditions has also been investigated, and the fracture pattern of Mg–Mn–Ce alloys transitions from pronounced cleavage fracture to the appearance of dimples and finally to ductile fracture with a large number of dimples as the temperature increases.

To investigate the hot deformation characteristics, workability, and interfacial microstructure of the titanium/steel bimetallic composite, hot compression simulations were carried out on the TA1/SUS430 composite within the temperatures of 750 °C–1050 °C, accompanied by strain rates spanning from 0.01 s⁻1–10 s⁻1. The hyperbolic sine Arrhenius constitutive equation and back-propagation artificial neural network (BP-ANN) model for flow stresses of this bimetallic composite were developed. 2D and 3D hot processing maps were established to study processability. The results revealed the calculated average activation energy (Q) was 277.9671 kJ/mol. The BP-ANN model demonstrated higher prediction accuracy than the Arrhenius model, with a correlation coefficient (R2) of 0.99947. As the strain increases, the area of the unstable region in the processing map expands, and the failure mode is characterized by the formation of microcracks at the bonded interface. Interfacial exfoliation manifested under elevated temperature and high strain rate deformation conditions. High power dissipation (η) values were observed within the processing parameters of 875°C–950 °C/0.01 s−1-0.03 s−1. The bimetal exhibited superior deformation coordination at low strain rates. TiC predominantly constituted the interface products at lower temperatures, while at higher temperatures, phases containing both Fe and Ti dominated. Furthermore, the deformed steel stratum manifested a pronounced cubic orientation //CD and a less dominant recrystallized γ orientation. This γ texture attenuated progressively with increased deformation temperatures, while the strain rate has less impact.

The hot deformation behavior of the solutionized Cu–15Ni–8Sn alloy is investigated by hot compression tests at temperatures of 750–900 °C and strain rates of 0.001–1.0 s−1. The flow stress curves of the alloy are analyzed, and the constitutive equations are developed to predict the flow behavior of the alloy. In addition, the optimal deformation conditions are proposed through the constructed hot processing map and microstructure analysis, revealing the impact of the deformation mechanism under different deformation parameters on the microstructure evolution. The results show that temperature and strain rate have a great influence on the hot deformation of the alloy. The strain-compensated constitutive equation can well predict the peak flow stress of the alloy, with a correlation coefficient of 0.993 between experimental and predicted values. The high power consumption region is mainly caused by dynamic recovery and partial dynamic recrystallization, while flow localization is the main reason for the appearance of the unstable region. The optimum hot processing conditions for the alloy are at a temperature range of 750–780 °C and the strain rate is 0.001–0.0025 s−1.

The hot deformation behavior and mechanism of Ti65 alloy with a bimodal microstructure were investigated by isothermal compression experiments conducted on the Thermecmastor-Z simulator equipment at temperatures ranging from 950 to 1110 °C and strain rates ranging from 0.01 to 10.0 s−1. The Arrhenius constitutive model, based on strain compensation, and Grey Wolf optimization-neural network with back propagation model (GWO–BP), were both established. The differences between the experimental and predicted value of flow stress were compared and analyzed using the two models. The results show that the prediction accuracy of GWO–BP in the two-phase region is higher than that of Arrhenius model. In the single-phase region, both methods demonstrated high prediction accuracy. Compared to the single-phase region, the flow stress of Ti65 alloy shows a higher degree of softening in the two-phase region. During deformation in the two-phase region, the initial lamellar α phase transformed from a kinked and elongated morphology to a globularized topography as the strain rate decreased. Boundary-splitting was the primary mechanism leading to the spheroidization process. The degree of recrystallization increased with the increase in strain rate during the deformation in the single-phase region, while dynamic recovery and strain-induced grain boundary migration were the main deformation mechanisms at a lower strain rate. Discontinuous dynamic recrystallization may be the dominant recrystallization mechanism under a high strain rate of 10 s−1. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Xinjiang University (Natural Science Edition) is the property of Xinjiang University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The deteriorated plasticity arising from the insoluble precipitates may lead to cracks during the rolling of FeCrAl alloys. The microstructure evolution and hot deformation behavior of an FeCrAl alloy were investigated in the temperature range of 750–1200 °C and strain rate range of 0.01–10 s−1. The flow stress of the FeCrAl alloy decreased with an increasing deformation temperature and decreased strain rate during hot working. The thermal deformation activation energy was determined to be 329.49 kJ/mol based on the compression test. Then, the optimal hot working range was given based on the established hot processing maps. The hot processing map revealed four small instability zones. The optimal working range for the material was identified as follows: at a true strain of 0.69, the deformation temperature should be 1050–1200 °C, and the strain rate should be 0.01–0.4 s−1. The observation of key samples of thermally simulated compression showed that discontinuous dynamic recrystallization started to occur with the temperate above 1000 °C, leading to bended grain boundaries. When the temperature was increased to 1150 °C, the dynamic recrystallization resulted in a microstructure composed of fine and equiaxed grains. [ABSTRACT FROM AUTHOR]

In the present work, the hot deformation behavior and microstructural evolution of a TiB2/Al-Zn-Mg-Cu-Zr composite were studied. Hot compression tests were conducted within a temperature range of 370 °C to 490 °C and a strain rate of 0.001 s−1 to 10 s−1. We established the Arrhenius constitutive equation with Zener–Hollomon parameters and processing maps and discussed the microstructural evolution during hot deformation. The results indicated that the safe processing parameter region falls within 370 °C–490 °C and 0.001 s−1–0.025 s−1. The influence of the strain rate on the safe processing range is more dominant than that of deformation temperature, which is primarily attributed to TiB2. Dynamic softening is primarily governed by dynamic recovery (DRV). Small particles (η, Al3Zr) can pin dislocations, promoting the rearrangement and annihilation of dislocations and facilitating DRV. Higher temperatures and lower strain rates facilitated dynamic recrystallization (DRX). Continuous dynamic recrystallization (CDRX) occurs near high-angle grain boundaries induced by strain-induced boundary migration (SIBM). TiB2 and large second-phase particles generate high-density geometrically necessary dislocations (GNBs) during hot deformation, which serve as nucleation sites for discontinuous dynamic recrystallization (DDRX). This enhances dynamic softening and improves formability. [ABSTRACT FROM AUTHOR]

The high temperature compression experiments of 2209 duplex stainless steel were carried out by using Glee-ble3800 thermal simulator, the rate was 0,01~10 s-1, and the deformation temperature was 950~1 100°C. The strain rate and deformation temperature were analyzed and the effect of strain rate and deformation temperature were analyzed. The high-temperature rheological behavior of 2209 duplex stainless steel was investigated, and the effects of strain rate and deformation temperature on the two-phase relationship of 2209 duplex stainless steel were analyzed, the strain rate compensation factor Z was introduced, and the Arrhenius eigenmodel equation was established. The results show that the theoretical value of peak stress calculated numerically by this constitutive model fits well with the experimental results, and the correlation is 97,3 %, which verifies the feasibility of the model. [ABSTRACT FROM AUTHOR]