Hemihydrate phosphogypsum(HPG)-based filling materials have become a new low-cost green alternative for early strength filling materials.They also provide a promising solution for the large-scale utilization of phosph...Hemihydrate phosphogypsum(HPG)-based filling materials have become a new low-cost green alternative for early strength filling materials.They also provide a promising solution for the large-scale utilization of phosphogypsum.However,pipe plugging,which is caused by the poor workability of HPG-based filling materials,has become a major safety hazard in the filling process.Determining an economical and practicable method is urgently needed to improve the workability of HPG slurry work.First,this work found that grind-ing treatment was much more effective than increasing concentration(59wt%-65wt%)and adding tailings(20wt%-100wt%)in enhan-cing the workability of HPG slurry based on a comprehensive analysis of water retention,fluidity,and flow stability.Then,the combined effects of particle size,particle morphology,water film,and interparticle interactions on the workability of HPG slurry were quantitat-ively described through a microanalysis.Moreover,the first direct evidence for the transformation from robust embedded structures to soft stacking structures was presented.In practice,the filling materials should be prepared by grinding HPG for 20 min and mixing with 0-200wt%phosphorus tailings to achieve satisfactory workability and mechanical performance.The results of this study provide practic-al and feasible methods for addressing the stable transportation problem of HPG slurry.展开更多
Ultra-high performance fiber-reinforced concrete (UHPFRC) has received extensive attention from scholars and engineers due to its excellent mechanical properties and durability. However, there is a mutually restrictiv...Ultra-high performance fiber-reinforced concrete (UHPFRC) has received extensive attention from scholars and engineers due to its excellent mechanical properties and durability. However, there is a mutually restrictive relationship between the workability and mechanical properties of UHPFRC. Specifically, the addition of fibers will affect the workability of fresh UHPFRC, and the workability of fresh UHPFRC will also affect the dispersion and arrangement of fibers, thus significantly influencing the mechanical properties of hardened UHPFRC. This paper first analyzes the research status of UHPFRC and the relationship between its workability and mechanical properties. Subsequently, it outlines the test methods and indicators of UHPFRC workability, including fluidity, slump, V-funnel passing time, and rheology. Then, it reviews the impacts of metal fibers, synthetic fibers, hybrid fibers, and other fibers on the workability and mechanical properties of UHPFRC, and presents a reasonable range of fiber dosage for workability and mechanical properties. Key findings include: (1) Steel fibers within 1%–2% volume optimize workability-mechanical balance, while exceeding 2.5% reduces compressive strength by 7%–30%;(2) Hybrid steel-polypropylene fibers enhance toughness by 65%;(3) Fiber orientation control via rheology-modifying admixtures improves flexural strength by up to 64%. This review establishes a fiber factor (V·L/D) for predictive mix design, advancing beyond empirical approaches in prior studies.展开更多
Enhancing homogenization efficiency and hot-workability is the key issue for wrought superalloys in the industry.A novel approach for simultaneous accelerating the homogenization kinetics and improving hot-workability...Enhancing homogenization efficiency and hot-workability is the key issue for wrought superalloys in the industry.A novel approach for simultaneous accelerating the homogenization kinetics and improving hot-workability via a simple way of prior hot-deformation was proposed,which was not widely accepted for wrought superalloys.The homogenization efficiency is increased by 40%-70%via performing 10%-20%prior hot-deformation.Both theoretical and experimental analyses revealed that the increment in homogenization efficiency is mainly attributed to the decrease in interdendritic-segregation spacing,and thus the necessary diffusion distance,rather than that of dislocations.In addition,dynamic and static recrystallizations occurred during the prior hot-deformation and diffusion-annealing processes,and the grains were significantly refined even after the homogenization.Furthermore,the size of the precipitates was refined as well.These enhanced the hot-workability of the homogenized ingot for the subsequent cogging process.展开更多
This article investigated the factors and mechanisms that affected the workability and mechanical properties of cement paste incorporating nano-TiO_(2).The findings indicated that,for nano-TiO_(2)aqueous solution conc...This article investigated the factors and mechanisms that affected the workability and mechanical properties of cement paste incorporating nano-TiO_(2).The findings indicated that,for nano-TiO_(2)aqueous solution concentrations of 3%,6%,9%,and 12%,the optimal dispersion effect was achieved with an ultrasonic dispersion time of 20 minutes.Specifically,at a 6%nano-TiO_(2)content,both the workability and mechanical performance of the cement paste were enhanced.Furthermore,while nano-TiO_(2)did not alter the types of hydration products present in the cement paste,it did increase the amount of C-S-H gels.This enhancement was attributed to a higher number of nucleation sites for hydration products,which promoted hydration and reduced the porosity of the cement paste.展开更多
In this study, the effect of iron powder (Fe2O3) on the compressive strength, tensile strength, workability, and porosity of the binary blended concrete were experimentally investigated. For this purpose, Portland cem...In this study, the effect of iron powder (Fe2O3) on the compressive strength, tensile strength, workability, and porosity of the binary blended concrete were experimentally investigated. For this purpose, Portland cement was partially replaced by 1.5%, 2.5%, 3.5%, and 5% by weighing of iron powder. The amount of water-binder-ratio was considered constant. The workability of the fresh composite concrete was determined using cone Abrams method;mechanical properties were determined included compressive and tensile strengths at 7, 14, and 28 days and durability evaluated by water absorption and permeable porosity. It was observed that the compressive and tensile strengths change with the replacement of iron powder by up to 5%. However, the maximum improvement was gained at 2.5 wt% for compressive strength and 1.5 wt% for tensile strength. The workability of the fresh mixtures decreased when iron powder amount increased. It was observed that the porosity decreased respectively by 21.88% and 26.77% at 1.5 wt% and 2.5 wt% replacement. Moreover, this present study shows the importance and benefits to improve concrete properties by using micro-particles materials.展开更多
The potential for using fly ash as a supplementary cementing material in concrete has been known almost since the beginning of the previous century. Fly ash was used as a supplementary cementing material (SCM) in the ...The potential for using fly ash as a supplementary cementing material in concrete has been known almost since the beginning of the previous century. Fly ash was used as a supplementary cementing material (SCM) in the production of Portland cement concrete. A supplementary cementing material, when used in conjunction with Portland cement, contributes to the properties of the hardened concrete through hydraulic or pozzolanic activity, or both. In this study, the fly ash and waste glass powder were used in concrete blocks to study the improvement of concrete in terms of workability and strength. Therefore, an experimental study will be conducted to measure the engineering properties of cured concrete. In this research, local raw material from Jaresh area was used.展开更多
Heavy components of low-alloy high-strength(LAHS) steels are generally formed by multi-pass forging. It is necessary to explore the flow characteristics and hot workability of LAHS steels during the multi-pass forging...Heavy components of low-alloy high-strength(LAHS) steels are generally formed by multi-pass forging. It is necessary to explore the flow characteristics and hot workability of LAHS steels during the multi-pass forging process, which is beneficial to the formulation of actual processing parameters. In the study, the multi-pass hot compression experiments of a typical LAHS steel are carried out at a wide range of deformation temperatures and strain rates. It is found that the work hardening rate of the experimental material depends on deformation parameters and deformation passes, which is ascribed to the impacts of static and dynamic softening behaviors. A new model is established to describe the flow characteristics at various deformation passes. Compared to the classical Arrhenius model and modified Zerilli and Armstrong model, the newly proposed model shows higher prediction accuracy with a confidence level of 0.98565. Furthermore, the connection between power dissipation efficiency(PDE) and deformation parameters is revealed by analyzing the microstructures. The PDE cannot be utilized to reflect the efficiency of energy dissipation for microstructure evolution during the entire deformation process, but only to assess the efficiency of energy dissipation for microstructure evolution in a specific deformation parameter state.As a result, an integrated processing map is proposed to better study the hot workability of the LAHS steel, which considers the effects of instability factor(IF), PDE, and distribution and size of grains. The optimized processing parameters for the multi-pass deformation process are the deformation parameters of 1223–1318 K and 0.01–0.08 s^(-1). Complete dynamic recrystallization occurs within the optimized processing parameters with an average grain size of 18.36–42.3 μm. This study will guide the optimization of the forging process of heavy components.展开更多
Hot deformation is a commonly employed processing technique to enhance the ductility and workability of Mg alloy.However,the hot deformation of Mg alloy is highly sensitive to factors such as temperature,strain rate,a...Hot deformation is a commonly employed processing technique to enhance the ductility and workability of Mg alloy.However,the hot deformation of Mg alloy is highly sensitive to factors such as temperature,strain rate,and strain,leading to complex flow behavior and an exceptionally narrow processing window for Mg alloy.To overcome the shortcomings of the conventional Arrhenius-type(AT)model,this study developed machine learning-based Arrhenius-type(ML-AT)models by combining the genetic algorithm(GA),particle swarm optimization(PSO),and artificial neural network(ANN).Results indicated that when describing the flow behavior of the AQ80 alloy,the PSO-ANN-AT model demonstrates the most prominent prediction accuracy and generalization ability among all ML-AT and AT models.Moreover,an activation energy-processing(AEP)map was established using the reconstructed flow stress and activation energy fields based on the PSO-ANN-AT model.Experimental validations revealed that this AEP map exhibits superior predictive capability for microstructure evolution compared to the one established by the traditional interpolation methods,ultimately contributing to the precise determination of the optimum processing window.These findings provide fresh insights into the accurate constitutive description and workability characterization of Mg alloy during hot deformation.展开更多
Water spewing and muck plugging often occur during earth pressure balance(EPB)shield machines tunnelling in water-rich sandy strata,even though the conventional foam has been employed to condition sandy soils.In this ...Water spewing and muck plugging often occur during earth pressure balance(EPB)shield machines tunnelling in water-rich sandy strata,even though the conventional foam has been employed to condition sandy soils.In this study,a novel thickened foaming agent suitable for EPB shield tunnelling in water-rich sandy strata is developed.In contrast to conventional foam-conditioned sands,the thickened foam-conditioned sand has a low permeability due to the consistent filling of soil pores with the thickened foam,and the initial permeability coefficient decreases by approximately two orders of magnitude.It also exhibits a suitable workability,which is attributed to the enhanced capability of the thickened foam to condition sandy soils.In addition,the effect of concentration on the stability of the foam is explained by the Gibbs-Marangoni effect,and conditioning mechanisms for the thickened foam on sands are discussed from the evolution of foam bubbles.展开更多
Reducing the hot working temperature and high-temperature deformation resistance of titanium alloy to improve hot rolling and hot extrusion workability of products with thin walls and complex section shapes has always...Reducing the hot working temperature and high-temperature deformation resistance of titanium alloy to improve hot rolling and hot extrusion workability of products with thin walls and complex section shapes has always been an important topic in the field of titanium alloy processing.This paper proposed a strategy of adding Mo and Fe elements to simultaneously reduce the hot working temperature and high-temperature deformation resistance of Ti-6Al-4V alloy.The effects of Mo and Fe contents on the mi-crostructure,β transus temperature(Tp),and high-temperature flow stress(HFS)of Ti-6Al-4V-xMo-xFe(x=0-5)alloys were investigated.The results showed that adding Mo and Fe can substantially reduce the Tp and HFS of the alloy,and greatly improve its room-temperature strength.Compared with com-mercial Ti-6Al-4V samples,the T_(β) of Ti-6Al-4V-2Mo-2Fe and Ti-6Al-4V-3Mo-3Fe samples was decreased by 68-98 ℃,and the HFS at 800-900 ℃ was decreased by 37.8%-46.0%.Compared with hot-rolled Ti-6Al-4V samples,the room-temperature tensile strength of hot-rolled Ti-6Al-4V-2Mo-2Fe samples was increased by about 30%,while the elongation hardly decreased.The increased strength was mainly at-tributed to fine grain strengthening and solid solution strengthening.The hot workability and room-temperature strength of Ti-6Al-4V alloy can be significantly improved by adding 2-3 wt.%Mo and Fe simultaneously.展开更多
The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300...The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300 to 450 ℃ and the strain rate ranging from 0.0001 to 1 s 1. The strain rate sensitivity of the alloy was evaluated and used for establishing the power dissipation maps and instability maps on the basis of the flow stress data. The results show that the efficiency of power dissipation for the as-homogenized alloy is lower than that of the as-solution treated alloy. The deformation parameters of the dynamic recrystallization for the as-homogenized and as-solution treated alloy occur at 400 ℃, 0.01 s i and 450 ℃, 0.001 s-1, respectively. The flow instability region of the as-homogenized alloy is narrower than that of the as-solution treated alloy. These differences of the alloys with two different initial microstructures on the processing maps are mainly related to the dynamic precipitation characteristics.展开更多
This study describes the performance of concrete in fresh state, intended for sealing deep bore-holes in the host rock of radioactive repositories. Set of different paste volumes, combinations of water-to-powder ratio...This study describes the performance of concrete in fresh state, intended for sealing deep bore-holes in the host rock of radioactive repositories. Set of different paste volumes, combinations of water-to-powder ratios and fine aggregate contents have been performed within the frame of this study. The main objective was to search for tendencies, logical connections and phenomena that occur for different combination of materials regarding the fluidity and segregation and mainly the effect from the (paste) or fine aggregate content. It shall be pointed out that this investigation is a suggestion on how concrete can be optimized using two simple test methods based on changing the paste content. The results highlighted the importance of having sufficient amounts of filler and cement paste for separate and carry larger particles, which gives the concrete good workability and fluidity at casting. It was concluded that the slump behaviors can be optimized based on the adjustments of the superplastisizer dosage.展开更多
Due to their hexagonal crystal structure,magnesium alloys have relatively low workability at room temperature.In this study,the hot workability behavior of cast-extruded AZ31B magnesium alloy is studied through hot co...Due to their hexagonal crystal structure,magnesium alloys have relatively low workability at room temperature.In this study,the hot workability behavior of cast-extruded AZ31B magnesium alloy is studied through hot compression testing,numerical modeling and microstructural analyses.Hot deformation tests are performed at temperatures of 250℃ to 400℃ under strain rates of 0.01 to 1.0 s^(−1).Transmission electron microscopy is used to reveal the presence of dynamic recrystallization(DRX),dynamic recovery(DRY),cracks and shear bands.To predict plastic instabilities during hot compression tests of AZ31B magnesium alloy,the authors use Johnson–Cook damage model in a 3D finite element simulation.The optimal hot workability of magnesium alloy is found at a temperature(T)of 400℃ and strain rate(ε)of 0.01 s^(−1).Stability is found at a lower strain rate,and instability is found at a higher strain rate.展开更多
In this study,the workability of cement-based grouts containing n-TiO 2 nanoparticles and fly ash has been investigated experimentally.Several characteristic quantities(including,but not limited to,the marsh cone flow...In this study,the workability of cement-based grouts containing n-TiO 2 nanoparticles and fly ash has been investigated experimentally.Several characteristic quantities(including,but not limited to,the marsh cone flow time,the mini slump spreading diameter and the plate cohesion meter value)have been measured for different percentages of these additives.The use of fly ash as a mineral additive has been found to result in improvements in terms of workability behavior as expected.Moreover,if nano titanium oxide is also used,an improvement can be obtained regarding the bleeding values for the cement-based grout mixes.Using such experimental data,a multi-layer perceptron artificial neural network model has been developed(5 neurons in the hidden layer of the network model have been developed using a total of 42 experimental data).70%of the data employed in this model have been used for training,15%for validation and 15%for the test phase.The results demonstrate that the artificial neural network model can predict Marsh cone flow time,mini slump spreading diameter and plate cohesion meter values with an average error of 0.15%.展开更多
The hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy were investigated by compression tests in the temperature range of 250-450 ℃and the strain rate range of 0.001-10 s 1. The constituti...The hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy were investigated by compression tests in the temperature range of 250-450 ℃and the strain rate range of 0.001-10 s 1. The constitutive equation for the pre-extruded ZK60A alloy can be described by hyperbolic sine function. Processing maps were constructed from true strains of -0.2 to -0.8. The alloy experienced complete dynamic recrystallization （DRX） and showed good workability in the temperature range of 300-400 ℃ and the strain rate range of 0.01-0.001 s-Z, where hot working in pre-extruded ZK60A, such as forging, can be carried out. For large deformation to true strain of over -0.5, strain rates above 0.1 s-1 are not recommended at all temperatures, where flow instability such as local strain concentration, twinning deformation, abnormal grain growth, micro-cracks, and shear fracture were observed. Climb-controlled dislocation creep dominates both the plastic deformation and nucleation of DRX of the pre-extruded ZK60A magnesium alloy.展开更多
The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow inst...The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow instability regions at various temperatures, strain rates and strains, which exhibit intrinsic workability related to material itself. Finite element （FE） simulation can obtain the distribution of strain, strain rate, temperature and die filling status, which indicates state-of-stress （SOS） workability decided by die shape and different processing conditions. On the basis of this, a new material driven analysis method for hot deformation was put forward by the combination of FE simulation with 3D processing maps, which can demonstrate material workability of the entire hot deformation process including SOS workability and intrinsic workability. The hot forging process for hard-to-work metal magnesium alloy was studied, and the 3D thermomechanical FE simulation including 3D processing maps of complex hot forging spur bevel gear was first conducted. The hot forging experiments were carried out. The results show that the new method is reasonable and suitable to determine the aoorooriate nrocess narameters.展开更多
Growth of older population in United States requires multi-generational evaluation to characterize health measures for sustaining workability. Investigation of measures that working population would need and use with ...Growth of older population in United States requires multi-generational evaluation to characterize health measures for sustaining workability. Investigation of measures that working population would need and use with their work-life in an attempt to stay healthy and fit, could potentially reveal significant association that could extend workability and enhance work productivity such as performance, presenteeism, job satisfaction. Evaluation with selective longitudinal health profiling;employment prerequisites;socio-economic and psychological scales could characterize health measures significantly associated with work sustainability. Such health measures could potentially be employed by US working population early in their life and occupation to sustain and improve workability in their later epoch.展开更多
Little is known about the psychosocial work situation among staff working with people with cognitive restrictions, and research is needed. Aim: The aim of this study was to describe the symptom panorama and psychosoci...Little is known about the psychosocial work situation among staff working with people with cognitive restrictions, and research is needed. Aim: The aim of this study was to describe the symptom panorama and psychosocial work situation of staff working with people with cognitive restrictions and to identify predictors for their job satisfaction and workability. A cross sectional study was performed. Method: The Questionnaire Psycho Social Nordic (QPS-Nordic questionnaire) was used. Results: The results showed that the majority of the staff working with people with cognitive restrictions were satisfied with their job, but musculoskeletal symptoms were described by 40%. Decision demands at work were high compared to quantitative and learning demands. Musculoskeletal symptoms were related to low ability to master the work, low job control and high job demands. Symptoms from the neck region were correlated to stress. A low level of neck pain was related to a high level of job satisfaction. Predictors for workability were positive challenges in work and not being hindered by musculoskeletal symptoms in work. Predictors for job satisfaction were mastery, workability and not having pain during the last 7 days. Conclusion: Due to the relatively small sample the results should be interpreted with caution. The results indicated that positive challenges in work and not being hindered by musculoskeletal disorders predicted workability in this group and that mastery, workability and not having pain during the last 7 days predicted job satisfaction.展开更多
Despite the industrial significance of grain size for enhancing mechanical properties and formability,the in-depth deformation mechanisms at elevated temperature are still unclear.To investigate the functions of grain...Despite the industrial significance of grain size for enhancing mechanical properties and formability,the in-depth deformation mechanisms at elevated temperature are still unclear.To investigate the functions of grain size on hot workability and deformation mechanisms,three groups of Mg-1.2Zn-0.2Y alloy specimens with different grain sizes were hot compressed and then studied by combining constitutive model,processing map and microstructural observations.The results showed that the enhanced hot workability accompanying low deformation activation energy and small instability regime was obtained with refined grain size.During hot deformation,the decreased grain size in Mg1.2Zn-0.2Y alloy mainly improved the plastic deformation homogeneity,especially for the weakened local straining around grain boundaries.As a result,the dynamic recrystallization nucleation and texture development at lower strain level were influenced by the initial grain size.At higher strain magnitude,the growth and coarsening of dynamic recrystallized grains would further release strain localization and improve hot workability,while the texture was less impacted.Further,unlike the primary basal slip and deformation twinning in the specimen with coarse grain at low temperature,non-basal slips of dislocations were initiated with less deformation twins in the specimens with refined grain size.展开更多
The hot workability and dynamic recrystallization(DRX)mechanisms of pure nickel N6 were systematically investigated using hot compression tests.Based on hot compression data,the constitutive equation of N6 was develop...The hot workability and dynamic recrystallization(DRX)mechanisms of pure nickel N6 were systematically investigated using hot compression tests.Based on hot compression data,the constitutive equation of N6 was developed and its reliability was verified.Its hot processing map was constructed,and combined with microstructural observations,a semi-quantitative response relationship between hot deformation parameters and microstructure was established.The DRX process of N6 is a thermally activated process and particularly sensitive to the strain rate.The optimal hot processing parameters for N6 were determined to be 950−1050℃ and 0.1−1 s^(−1).Furthermore,it was proven that the dominant nucleation mechanism is discontinuous DRX characterized by grain boundary bulging and twins assisting nucleation,while the continuous DRX characterized by subgrains combined with rotation is an inactive nucleation mechanism.展开更多
基金financial support from the National Natural Science Foundation of China(No.52074137)the Yunnan Fundamental Research Projects,China(Nos.202301BE070001-054 and 202401CF070124)the Yunnan Major Scientific and Technological Projects,China(No.202403AA080001).
文摘Hemihydrate phosphogypsum(HPG)-based filling materials have become a new low-cost green alternative for early strength filling materials.They also provide a promising solution for the large-scale utilization of phosphogypsum.However,pipe plugging,which is caused by the poor workability of HPG-based filling materials,has become a major safety hazard in the filling process.Determining an economical and practicable method is urgently needed to improve the workability of HPG slurry work.First,this work found that grind-ing treatment was much more effective than increasing concentration(59wt%-65wt%)and adding tailings(20wt%-100wt%)in enhan-cing the workability of HPG slurry based on a comprehensive analysis of water retention,fluidity,and flow stability.Then,the combined effects of particle size,particle morphology,water film,and interparticle interactions on the workability of HPG slurry were quantitat-ively described through a microanalysis.Moreover,the first direct evidence for the transformation from robust embedded structures to soft stacking structures was presented.In practice,the filling materials should be prepared by grinding HPG for 20 min and mixing with 0-200wt%phosphorus tailings to achieve satisfactory workability and mechanical performance.The results of this study provide practic-al and feasible methods for addressing the stable transportation problem of HPG slurry.
基金financed by Guangxi Transportation Science and Technology Achievement Promotion Project(GXJT-YFZX-2024-01-01):Intelligent Detection and Data Application R&D Center for Guangxi Transportation Industry.
文摘Ultra-high performance fiber-reinforced concrete (UHPFRC) has received extensive attention from scholars and engineers due to its excellent mechanical properties and durability. However, there is a mutually restrictive relationship between the workability and mechanical properties of UHPFRC. Specifically, the addition of fibers will affect the workability of fresh UHPFRC, and the workability of fresh UHPFRC will also affect the dispersion and arrangement of fibers, thus significantly influencing the mechanical properties of hardened UHPFRC. This paper first analyzes the research status of UHPFRC and the relationship between its workability and mechanical properties. Subsequently, it outlines the test methods and indicators of UHPFRC workability, including fluidity, slump, V-funnel passing time, and rheology. Then, it reviews the impacts of metal fibers, synthetic fibers, hybrid fibers, and other fibers on the workability and mechanical properties of UHPFRC, and presents a reasonable range of fiber dosage for workability and mechanical properties. Key findings include: (1) Steel fibers within 1%–2% volume optimize workability-mechanical balance, while exceeding 2.5% reduces compressive strength by 7%–30%;(2) Hybrid steel-polypropylene fibers enhance toughness by 65%;(3) Fiber orientation control via rheology-modifying admixtures improves flexural strength by up to 64%. This review establishes a fiber factor (V·L/D) for predictive mix design, advancing beyond empirical approaches in prior studies.
基金supported by the National Natural Science Foundation of China(No.51804232)Beijing Municipal Natural Science Foundation(No.2212041)+1 种基金supported by the Interdisciplinary Research Project for Young Teachers of USTB(Fundamental Research Funds for the Central Universities)(FRF-IDRY-20-020)GIMRT Program of the Institute for Materials Research,Tohoku University(202303-RDKGE-0518).
文摘Enhancing homogenization efficiency and hot-workability is the key issue for wrought superalloys in the industry.A novel approach for simultaneous accelerating the homogenization kinetics and improving hot-workability via a simple way of prior hot-deformation was proposed,which was not widely accepted for wrought superalloys.The homogenization efficiency is increased by 40%-70%via performing 10%-20%prior hot-deformation.Both theoretical and experimental analyses revealed that the increment in homogenization efficiency is mainly attributed to the decrease in interdendritic-segregation spacing,and thus the necessary diffusion distance,rather than that of dislocations.In addition,dynamic and static recrystallizations occurred during the prior hot-deformation and diffusion-annealing processes,and the grains were significantly refined even after the homogenization.Furthermore,the size of the precipitates was refined as well.These enhanced the hot-workability of the homogenized ingot for the subsequent cogging process.
基金Funded by National Natural Science Foundation of China(No.52108188)State Key Laboratory of Silicate Materials for Architectures(Wuhan University of Technology)(No.SYSJJ2024-15)+3 种基金State Key Laboratory of Mountain Bridge and Tunnel Engineering,Chongqing Jiaotong University(No.SKLBT-2301)Opening Project of State Key Laboratory of Green Building Materials(No.2022GBM10)Open Research Fund of Key Laboratory of Engineering Materials of Ministry of Water Resources,China Institute of Water Resources and Hydropower Research(No.EMF202407)General Project of Science and Technology Plan of Beijing Municipal Commission of Education(No.KM202110005018)。
文摘This article investigated the factors and mechanisms that affected the workability and mechanical properties of cement paste incorporating nano-TiO_(2).The findings indicated that,for nano-TiO_(2)aqueous solution concentrations of 3%,6%,9%,and 12%,the optimal dispersion effect was achieved with an ultrasonic dispersion time of 20 minutes.Specifically,at a 6%nano-TiO_(2)content,both the workability and mechanical performance of the cement paste were enhanced.Furthermore,while nano-TiO_(2)did not alter the types of hydration products present in the cement paste,it did increase the amount of C-S-H gels.This enhancement was attributed to a higher number of nucleation sites for hydration products,which promoted hydration and reduced the porosity of the cement paste.
文摘In this study, the effect of iron powder (Fe2O3) on the compressive strength, tensile strength, workability, and porosity of the binary blended concrete were experimentally investigated. For this purpose, Portland cement was partially replaced by 1.5%, 2.5%, 3.5%, and 5% by weighing of iron powder. The amount of water-binder-ratio was considered constant. The workability of the fresh composite concrete was determined using cone Abrams method;mechanical properties were determined included compressive and tensile strengths at 7, 14, and 28 days and durability evaluated by water absorption and permeable porosity. It was observed that the compressive and tensile strengths change with the replacement of iron powder by up to 5%. However, the maximum improvement was gained at 2.5 wt% for compressive strength and 1.5 wt% for tensile strength. The workability of the fresh mixtures decreased when iron powder amount increased. It was observed that the porosity decreased respectively by 21.88% and 26.77% at 1.5 wt% and 2.5 wt% replacement. Moreover, this present study shows the importance and benefits to improve concrete properties by using micro-particles materials.
文摘The potential for using fly ash as a supplementary cementing material in concrete has been known almost since the beginning of the previous century. Fly ash was used as a supplementary cementing material (SCM) in the production of Portland cement concrete. A supplementary cementing material, when used in conjunction with Portland cement, contributes to the properties of the hardened concrete through hydraulic or pozzolanic activity, or both. In this study, the fly ash and waste glass powder were used in concrete blocks to study the improvement of concrete in terms of workability and strength. Therefore, an experimental study will be conducted to measure the engineering properties of cured concrete. In this research, local raw material from Jaresh area was used.
基金National Natural Science Foundation of China(No.52305373)Jiangxi Provincial Natural Science Foundation(No.20232BAB214053)+2 种基金Science and Technology Major Project of Jiangxi,China(No.20194ABC28001)Fund of Jiangxi Key Laboratory of Forming and Joining Technology for Aerospace Components,Nanchang Hangkong University(No.EL202303299)PhD Starting Foundation of Nanchang Hangkong University(No,EA202303235).
文摘Heavy components of low-alloy high-strength(LAHS) steels are generally formed by multi-pass forging. It is necessary to explore the flow characteristics and hot workability of LAHS steels during the multi-pass forging process, which is beneficial to the formulation of actual processing parameters. In the study, the multi-pass hot compression experiments of a typical LAHS steel are carried out at a wide range of deformation temperatures and strain rates. It is found that the work hardening rate of the experimental material depends on deformation parameters and deformation passes, which is ascribed to the impacts of static and dynamic softening behaviors. A new model is established to describe the flow characteristics at various deformation passes. Compared to the classical Arrhenius model and modified Zerilli and Armstrong model, the newly proposed model shows higher prediction accuracy with a confidence level of 0.98565. Furthermore, the connection between power dissipation efficiency(PDE) and deformation parameters is revealed by analyzing the microstructures. The PDE cannot be utilized to reflect the efficiency of energy dissipation for microstructure evolution during the entire deformation process, but only to assess the efficiency of energy dissipation for microstructure evolution in a specific deformation parameter state.As a result, an integrated processing map is proposed to better study the hot workability of the LAHS steel, which considers the effects of instability factor(IF), PDE, and distribution and size of grains. The optimized processing parameters for the multi-pass deformation process are the deformation parameters of 1223–1318 K and 0.01–0.08 s^(-1). Complete dynamic recrystallization occurs within the optimized processing parameters with an average grain size of 18.36–42.3 μm. This study will guide the optimization of the forging process of heavy components.
基金supported by the National Natural Science Foundation of China(Grant Nos.52305361,51775194,52090043)China Postdoctoral Science Foundation(2023M741245)the National Key Research and Development Program of China(2022YFB3706903).
文摘Hot deformation is a commonly employed processing technique to enhance the ductility and workability of Mg alloy.However,the hot deformation of Mg alloy is highly sensitive to factors such as temperature,strain rate,and strain,leading to complex flow behavior and an exceptionally narrow processing window for Mg alloy.To overcome the shortcomings of the conventional Arrhenius-type(AT)model,this study developed machine learning-based Arrhenius-type(ML-AT)models by combining the genetic algorithm(GA),particle swarm optimization(PSO),and artificial neural network(ANN).Results indicated that when describing the flow behavior of the AQ80 alloy,the PSO-ANN-AT model demonstrates the most prominent prediction accuracy and generalization ability among all ML-AT and AT models.Moreover,an activation energy-processing(AEP)map was established using the reconstructed flow stress and activation energy fields based on the PSO-ANN-AT model.Experimental validations revealed that this AEP map exhibits superior predictive capability for microstructure evolution compared to the one established by the traditional interpolation methods,ultimately contributing to the precise determination of the optimum processing window.These findings provide fresh insights into the accurate constitutive description and workability characterization of Mg alloy during hot deformation.
基金The financial support from the National Natural Science Foundation of China(Grant No.52022112)the Fundamental Research Funds for the Central South University(Grant No.2023ZZTS0366)are acknowledged and appreciated.The authors are also grateful for the help from Dr.Ji Zhao of China University of Mining and Technology.
文摘Water spewing and muck plugging often occur during earth pressure balance(EPB)shield machines tunnelling in water-rich sandy strata,even though the conventional foam has been employed to condition sandy soils.In this study,a novel thickened foaming agent suitable for EPB shield tunnelling in water-rich sandy strata is developed.In contrast to conventional foam-conditioned sands,the thickened foam-conditioned sand has a low permeability due to the consistent filling of soil pores with the thickened foam,and the initial permeability coefficient decreases by approximately two orders of magnitude.It also exhibits a suitable workability,which is attributed to the enhanced capability of the thickened foam to condition sandy soils.In addition,the effect of concentration on the stability of the foam is explained by the Gibbs-Marangoni effect,and conditioning mechanisms for the thickened foam on sands are discussed from the evolution of foam bubbles.
基金National Natural Science Foundation of China(No.52090041).
文摘Reducing the hot working temperature and high-temperature deformation resistance of titanium alloy to improve hot rolling and hot extrusion workability of products with thin walls and complex section shapes has always been an important topic in the field of titanium alloy processing.This paper proposed a strategy of adding Mo and Fe elements to simultaneously reduce the hot working temperature and high-temperature deformation resistance of Ti-6Al-4V alloy.The effects of Mo and Fe contents on the mi-crostructure,β transus temperature(Tp),and high-temperature flow stress(HFS)of Ti-6Al-4V-xMo-xFe(x=0-5)alloys were investigated.The results showed that adding Mo and Fe can substantially reduce the Tp and HFS of the alloy,and greatly improve its room-temperature strength.Compared with com-mercial Ti-6Al-4V samples,the T_(β) of Ti-6Al-4V-2Mo-2Fe and Ti-6Al-4V-3Mo-3Fe samples was decreased by 68-98 ℃,and the HFS at 800-900 ℃ was decreased by 37.8%-46.0%.Compared with hot-rolled Ti-6Al-4V samples,the room-temperature tensile strength of hot-rolled Ti-6Al-4V-2Mo-2Fe samples was increased by about 30%,while the elongation hardly decreased.The increased strength was mainly at-tributed to fine grain strengthening and solid solution strengthening.The hot workability and room-temperature strength of Ti-6Al-4V alloy can be significantly improved by adding 2-3 wt.%Mo and Fe simultaneously.
基金Projects(2010CB731701,2012CB619502) supported by the National Basic Research Program of ChinaProject(CX2012B043) supported by Hunan Provincial Innovation Foundation for Postgraduate,ChinaProject(51021063) supported by Creative Research Group of National Natural Science Foundation of China
文摘The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300 to 450 ℃ and the strain rate ranging from 0.0001 to 1 s 1. The strain rate sensitivity of the alloy was evaluated and used for establishing the power dissipation maps and instability maps on the basis of the flow stress data. The results show that the efficiency of power dissipation for the as-homogenized alloy is lower than that of the as-solution treated alloy. The deformation parameters of the dynamic recrystallization for the as-homogenized and as-solution treated alloy occur at 400 ℃, 0.01 s i and 450 ℃, 0.001 s-1, respectively. The flow instability region of the as-homogenized alloy is narrower than that of the as-solution treated alloy. These differences of the alloys with two different initial microstructures on the processing maps are mainly related to the dynamic precipitation characteristics.
文摘This study describes the performance of concrete in fresh state, intended for sealing deep bore-holes in the host rock of radioactive repositories. Set of different paste volumes, combinations of water-to-powder ratios and fine aggregate contents have been performed within the frame of this study. The main objective was to search for tendencies, logical connections and phenomena that occur for different combination of materials regarding the fluidity and segregation and mainly the effect from the (paste) or fine aggregate content. It shall be pointed out that this investigation is a suggestion on how concrete can be optimized using two simple test methods based on changing the paste content. The results highlighted the importance of having sufficient amounts of filler and cement paste for separate and carry larger particles, which gives the concrete good workability and fluidity at casting. It was concluded that the slump behaviors can be optimized based on the adjustments of the superplastisizer dosage.
文摘Due to their hexagonal crystal structure,magnesium alloys have relatively low workability at room temperature.In this study,the hot workability behavior of cast-extruded AZ31B magnesium alloy is studied through hot compression testing,numerical modeling and microstructural analyses.Hot deformation tests are performed at temperatures of 250℃ to 400℃ under strain rates of 0.01 to 1.0 s^(−1).Transmission electron microscopy is used to reveal the presence of dynamic recrystallization(DRX),dynamic recovery(DRY),cracks and shear bands.To predict plastic instabilities during hot compression tests of AZ31B magnesium alloy,the authors use Johnson–Cook damage model in a 3D finite element simulation.The optimal hot workability of magnesium alloy is found at a temperature(T)of 400℃ and strain rate(ε)of 0.01 s^(−1).Stability is found at a lower strain rate,and instability is found at a higher strain rate.
基金funded by The Scientific and Technological Research Council of Turkey-TUBITAK[Grant No.219M522].
文摘In this study,the workability of cement-based grouts containing n-TiO 2 nanoparticles and fly ash has been investigated experimentally.Several characteristic quantities(including,but not limited to,the marsh cone flow time,the mini slump spreading diameter and the plate cohesion meter value)have been measured for different percentages of these additives.The use of fly ash as a mineral additive has been found to result in improvements in terms of workability behavior as expected.Moreover,if nano titanium oxide is also used,an improvement can be obtained regarding the bleeding values for the cement-based grout mixes.Using such experimental data,a multi-layer perceptron artificial neural network model has been developed(5 neurons in the hidden layer of the network model have been developed using a total of 42 experimental data).70%of the data employed in this model have been used for training,15%for validation and 15%for the test phase.The results demonstrate that the artificial neural network model can predict Marsh cone flow time,mini slump spreading diameter and plate cohesion meter values with an average error of 0.15%.
基金Projects(51171113,51301107) supported by the National Natural Science Foundation of China
文摘The hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy were investigated by compression tests in the temperature range of 250-450 ℃and the strain rate range of 0.001-10 s 1. The constitutive equation for the pre-extruded ZK60A alloy can be described by hyperbolic sine function. Processing maps were constructed from true strains of -0.2 to -0.8. The alloy experienced complete dynamic recrystallization （DRX） and showed good workability in the temperature range of 300-400 ℃ and the strain rate range of 0.01-0.001 s-Z, where hot working in pre-extruded ZK60A, such as forging, can be carried out. For large deformation to true strain of over -0.5, strain rates above 0.1 s-1 are not recommended at all temperatures, where flow instability such as local strain concentration, twinning deformation, abnormal grain growth, micro-cracks, and shear fracture were observed. Climb-controlled dislocation creep dominates both the plastic deformation and nucleation of DRX of the pre-extruded ZK60A magnesium alloy.
基金Project(2011ZX04014-051)supported by the Key Scientific and Technical Project of ChinaProjects(51375306,50905110)supported by the National Natural Science Foundation of China
文摘The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow instability regions at various temperatures, strain rates and strains, which exhibit intrinsic workability related to material itself. Finite element （FE） simulation can obtain the distribution of strain, strain rate, temperature and die filling status, which indicates state-of-stress （SOS） workability decided by die shape and different processing conditions. On the basis of this, a new material driven analysis method for hot deformation was put forward by the combination of FE simulation with 3D processing maps, which can demonstrate material workability of the entire hot deformation process including SOS workability and intrinsic workability. The hot forging process for hard-to-work metal magnesium alloy was studied, and the 3D thermomechanical FE simulation including 3D processing maps of complex hot forging spur bevel gear was first conducted. The hot forging experiments were carried out. The results show that the new method is reasonable and suitable to determine the aoorooriate nrocess narameters.
文摘Growth of older population in United States requires multi-generational evaluation to characterize health measures for sustaining workability. Investigation of measures that working population would need and use with their work-life in an attempt to stay healthy and fit, could potentially reveal significant association that could extend workability and enhance work productivity such as performance, presenteeism, job satisfaction. Evaluation with selective longitudinal health profiling;employment prerequisites;socio-economic and psychological scales could characterize health measures significantly associated with work sustainability. Such health measures could potentially be employed by US working population early in their life and occupation to sustain and improve workability in their later epoch.
文摘Little is known about the psychosocial work situation among staff working with people with cognitive restrictions, and research is needed. Aim: The aim of this study was to describe the symptom panorama and psychosocial work situation of staff working with people with cognitive restrictions and to identify predictors for their job satisfaction and workability. A cross sectional study was performed. Method: The Questionnaire Psycho Social Nordic (QPS-Nordic questionnaire) was used. Results: The results showed that the majority of the staff working with people with cognitive restrictions were satisfied with their job, but musculoskeletal symptoms were described by 40%. Decision demands at work were high compared to quantitative and learning demands. Musculoskeletal symptoms were related to low ability to master the work, low job control and high job demands. Symptoms from the neck region were correlated to stress. A low level of neck pain was related to a high level of job satisfaction. Predictors for workability were positive challenges in work and not being hindered by musculoskeletal symptoms in work. Predictors for job satisfaction were mastery, workability and not having pain during the last 7 days. Conclusion: Due to the relatively small sample the results should be interpreted with caution. The results indicated that positive challenges in work and not being hindered by musculoskeletal disorders predicted workability in this group and that mastery, workability and not having pain during the last 7 days predicted job satisfaction.
基金supported by the National Natural Science Foundation of China(51774124,52074114)Hunan Provincial Natural Science Foundation of China(2019JJ40017,2020JJ5062)+1 种基金Key Technologies R&D in Strategic Emerging Industries and Transformation in High-tech Achievements Program of Hunan Province(2019GK4045)Graduate Training and Innovation Practice Base of Hunan Province.
文摘Despite the industrial significance of grain size for enhancing mechanical properties and formability,the in-depth deformation mechanisms at elevated temperature are still unclear.To investigate the functions of grain size on hot workability and deformation mechanisms,three groups of Mg-1.2Zn-0.2Y alloy specimens with different grain sizes were hot compressed and then studied by combining constitutive model,processing map and microstructural observations.The results showed that the enhanced hot workability accompanying low deformation activation energy and small instability regime was obtained with refined grain size.During hot deformation,the decreased grain size in Mg1.2Zn-0.2Y alloy mainly improved the plastic deformation homogeneity,especially for the weakened local straining around grain boundaries.As a result,the dynamic recrystallization nucleation and texture development at lower strain level were influenced by the initial grain size.At higher strain magnitude,the growth and coarsening of dynamic recrystallized grains would further release strain localization and improve hot workability,while the texture was less impacted.Further,unlike the primary basal slip and deformation twinning in the specimen with coarse grain at low temperature,non-basal slips of dislocations were initiated with less deformation twins in the specimens with refined grain size.
基金supported by the Science Foundation for Distinguished Young Scholars of Gansu Province,China(No.18JR3RA134)Lanzhou University of Technology Support Plan for Excellent Young Scholars,China(No.CGZH001)the National Nature Science Foundation of China(No.51665032).
文摘The hot workability and dynamic recrystallization(DRX)mechanisms of pure nickel N6 were systematically investigated using hot compression tests.Based on hot compression data,the constitutive equation of N6 was developed and its reliability was verified.Its hot processing map was constructed,and combined with microstructural observations,a semi-quantitative response relationship between hot deformation parameters and microstructure was established.The DRX process of N6 is a thermally activated process and particularly sensitive to the strain rate.The optimal hot processing parameters for N6 were determined to be 950−1050℃ and 0.1−1 s^(−1).Furthermore,it was proven that the dominant nucleation mechanism is discontinuous DRX characterized by grain boundary bulging and twins assisting nucleation,while the continuous DRX characterized by subgrains combined with rotation is an inactive nucleation mechanism.
