The stress-strain behavior of confined concrete under heating and residual conditions has been preliminarily addressed in previous research;however,its behavior at subsequent cooling temperatures after being heated to...The stress-strain behavior of confined concrete under heating and residual conditions has been preliminarily addressed in previous research;however,its behavior at subsequent cooling temperatures after being heated to peak temperature has yet to be thoroughly investigated.It is crucial for determining confined concrete structures’post-fire performance and burnout resistance.The paper presents the fundamental behavior of the confined concrete constitutive parameters and stress-strain curve at subsequent cooling temperatures after being heated to peak temperature.The study includes the stress-stress relationship of a 200 mm diameter cylinder with two distinct confinement spacings of 60 mm and 120 mm.The constitutive parameters for confined concrete were initially determined for a peak heating temperature of 750℃ and then modified to establish the stress-strain relationship for successive cooling temperatures of 500℃,250℃,and ambient temperature.The study results show that confinement has a considerable impact on compressive strength,stiffness,and ductility at ambient and fire conditions.After being heated to peak temperature,the confined concrete compressive strength recovers during successive cooling temperatures,with the recovery dependent on confinement spacing.The established stress-strain relationship can assist in better comprehending structural performance and capacity degradation for different tie spacings,and is useful for the analysis and design of confined RC(reinforced concrete)elements during and after a fire.展开更多
The ductile-to-brittle transition temperature(DBTT)of high strength steels can be optimized by tailoring microstructure and crystallographic orientation characteristics,where the start cooling temperature plays a key ...The ductile-to-brittle transition temperature(DBTT)of high strength steels can be optimized by tailoring microstructure and crystallographic orientation characteristics,where the start cooling temperature plays a key role.In this work,X70 steels with different start cooling temperatures were prepared through thermo-mechanical control process.The quasi-polygonal ferrite(QF),granular bainite(GB),bainitic ferrite(BF)and martensite-austenite constituents were formed at the start cooling temperatures of 780℃(C1),740℃(C2)and 700℃(C3).As start cooling temperature decreased,the amount of GB decreased,the microstructure of QF and BF increased.Microstructure characteristics of the three samples,such as high-angle grain boundaries(HAGBs),MA constituents and crystallographic orientation,also varied with the start cooling temperatures.C2 sample had the lowest DBTT value(−86℃)for its highest fraction of HAGBs,highest content of<110>oriented grains and lowest content of<001>oriented grains parallel to TD.The high density of{332}<113>and low density of rotated cube{001}<110>textures also contributed to the best impact toughness of C2 sample.In addition,a modified model was used in this paper to quantitatively predict the approximate DBTT value of steels.展开更多
For P91 steel weldment,performing post-weld heat treatment immediately after welding can enhance welding efficiency and reduce the risk of hydrogen-induced cracking.However,determining the post-weld cooling temperatur...For P91 steel weldment,performing post-weld heat treatment immediately after welding can enhance welding efficiency and reduce the risk of hydrogen-induced cracking.However,determining the post-weld cooling temperature(PWCT)is challenging due to potential impact on the mechanical properties of weldment after subsequent heat treatment.A systematic investigation is conducted to explore the effect of PWCT on the impact toughness of P91 steel welded joints.It has been demonstrated that the impact energy of the weld metal gradually increases from 40.2 to 49.5 J as the PWCT decreases from 300 to 100℃.Microstructural analysis reveals that PWCTs above 100℃ led to an increased dislocation density in the weld metal.Furthermore,in situ observations using a high-temperature confocal laser scanning microscope confirm that excessively high PWCTs result in the formation of untempered martensite after post-weld heat treatment.Such untempered martensites are identified as the primary cause of the reduced impact toughness in the weld metal.These findings underscore the importance of carefully controlling PWCT in welding procedures for P91 steel and similar grades.展开更多
The advancement of sophisticated smart windows exhibiting superior thermoregulation capabilities in both solar spectrum and long-wave infrared range maintains a prominent objective for researchers in this field.In thi...The advancement of sophisticated smart windows exhibiting superior thermoregulation capabilities in both solar spectrum and long-wave infrared range maintains a prominent objective for researchers in this field.In this study,a Janus window is proposed and prepared based on polymer-stabilized liquid-crystal films/thermochromic materials.It can achieve switchable front long-wave infrared emissivity(ε_(Front))and solar modulation ability(ΔT_(sol))through dynamic flipping,making it suitable for different seasonal energy-saving requirements.Outdoor experiments show that under daytime illumination,the indoor temperature decreases by 8℃,and the nighttime temperature drops by 5℃.MATLAB simulation calculations indicate that the daytime cooling power is 93 W m^(-2),while the nighttime cooling power reaches 142 W m^(-2).Interestingly,by modifying the conductive layer,it can effectively shield electromagnetic radiation(within the X-band frequency range(8.2-12.4)GHz).Energy simulation reveals the substantial superiority of this device in energy savings compared with single-layer polymer-stabilized liquid crystal,poly(N-isopropyl acrylamide),and normal glass when applied in different climate zones.This research presents a compelling opportunity for the development of sophisticated smart windows characterized by exceptional thermoregulation capabilities.展开更多
Phase Change Material(PCM)-based cold energy storage system(CESS)can effectively utilize the peak and valley power resources to reduce the excessive dependence on the power grid.In this study,a PCM-based CESS was desi...Phase Change Material(PCM)-based cold energy storage system(CESS)can effectively utilize the peak and valley power resources to reduce the excessive dependence on the power grid.In this study,a PCM-based CESS was designed for cold storage applications.The optimal number of PCM plates was determined through numerical simulations to meet the required cold storage temperature and control time.Additionally,the air temperature field,flow field,and melting characteristics of the PCMplates during the cooling release process were analyzed.The effects of plate positioning and thickness on the cooling release performance were further investigated.The results indicated that when 64PCMplateswere used,the duration formaintaining temperatures below−18℃increased from0.6 h to approximately 16.94 h.During the cooling release process,the temperature field in the cold storage exhibited stratification,and the melting of the PCM plates was non-uniform.Placing the PCM plates at the top or within the interlayers without cargo above proved more effective,with their cooling release power being approximately twice that of the PCM plates placed in the interlayers with cargo above.Furthermore,reducing the thickness of the PCMplates from15 to 7.5mmresulted in a 3.6-h increase in the time below−18℃and a 4.5-h reduction in the time required to reach 80%liquid phase fraction.展开更多
In order to meet the growing global energy demand and fulfill energy conservation and emission reduction goals, the efficient utilization of solar energy is becoming increasingly critical. However, the effects of high...In order to meet the growing global energy demand and fulfill energy conservation and emission reduction goals, the efficient utilization of solar energy is becoming increasingly critical. However, the effects of high temperatures on solar absorption are rarely considered in practical research. Therefore, this study presents a porous zinc and silver sulfide solar absorber with high-temperature radiative cooling capabilities. The solar absorption rate and radiative cooling efficiency in the high-temperature range(636 K–1060 K) are computed using the finite-difference time-domain method. Furthermore, the impact of parameters such as characteristic length, porosity, incident angle, and pore shape factor on both the absorption rate and efficiency of the solar absorber is analyzed. The mechanism is further examined from the perspective of microscopic thermal radiation. The results show that, in the high-temperature range, the solar absorption rate increases with higher porosity and incident angles, reaching its peak when the characteristic length is 1 μm. These findings highlight the significant potential of the solar absorber for efficient solar energy harvesting in photo-thermal conversion applications within a specific high-temperature range.展开更多
In liquid rocket engines,regenerative cooling technology is essential for preserving structural integrity under extreme thermal loads.However,non-uniform coolant flow distribution within the cooling channels often lea...In liquid rocket engines,regenerative cooling technology is essential for preserving structural integrity under extreme thermal loads.However,non-uniform coolant flow distribution within the cooling channels often leads to localized overheating,posing serious risks to engine reliability and operational lifespan.This study employs a three-dimensional fluid–thermal coupled numerical model to systematically investigate the influence of geometric parameters-specifically the number of inlets,the number of channels,and inlet manifold configurations-on flow uniformity and thermal distribution in non-pyrolysis zones.Key findings reveal that increasing the number of inlets from one to three significantly enhances flow uniformity,reducing mass flow rate deviation from 1.2%to below 0.3%.However,further increasing the inlets to five yields only marginal improvements indicating diminishing(<0.1%),returns beyond three inlets.Additionally,temperature non-uniformity at the combustion chamber throat decreases by 37%-from 3050 K with 18 channels to 1915 K with 30 channels-highlighting the critical role of channel density in effective thermal regulation.Notably,while higher channel counts improve cooling efficiency,they also result in increased pressure losses of approximately 18%–22%,emphasizing the need to balance thermal performance against hydraulic resistance.An optimal configuration comprising 24 channels and three inlets was identified,providing minimal temperature gradients while maintaining acceptable pressure losses.The inlet manifold structure also plays a pivotal role in determining flow distribution.Configuration 3(Config-3),which features an enlarged manifold and reduced inlet velocity,achieves a 40%reduction in velocity fluctuations compared to Configuration 1(Config-1).This improvement leads to a more uniform mass flow distribution,with a relative standard deviation(RSD)of less than 0.15%.Furthermore,this design effectively mitigates localized hot spots near the nozzle-where temperature gradients are most severe-achieving a reduction of approximately 1135 K.展开更多
The liquid cooling system(LCS)of fuel cells is challenged by significant time delays,model uncertainties,pump and fan coupling,and frequent disturbances,leading to overshoot and control oscillations that degrade tempe...The liquid cooling system(LCS)of fuel cells is challenged by significant time delays,model uncertainties,pump and fan coupling,and frequent disturbances,leading to overshoot and control oscillations that degrade temperature regulation performance.To address these challenges,we propose a composite control scheme combining fuzzy logic and a variable-gain generalized supertwisting algorithm(VG-GSTA).Firstly,a one-dimensional(1D)fuzzy logic controler(FLC)for the pump ensures stable coolant flow,while a two-dimensional(2D)FLC for the fan regulates the stack temperature near the reference value.The VG-GSTA is then introduced to eliminate steady-state errors,offering resistance to disturbances and minimizing control oscillations.The equilibrium optimizer is used to fine-tune VG-GSTA parameters.Co-simulation verifies the effectiveness of our method,demonstrating its advantages in terms of disturbance immunity,overshoot suppression,tracking accuracy and response speed.展开更多
Helium sorption cooler technology is a key means to realize highly reliable low-vibration very lowtemperature environments,which have important applications in fields such as quantum computing and space exploration.Th...Helium sorption cooler technology is a key means to realize highly reliable low-vibration very lowtemperature environments,which have important applications in fields such as quantum computing and space exploration.The laboratory designed a superfluid suppression small hole and a multi-ribbed condenser,developed a reliable-performance helium sorption cooler(HSC),and conducted experimental studies.Experimental results show that the prototype can achieve the lowest cooling temperature of 873 mK without load by filling 6MPa helium at room temperature.The low-temperature hold time is 26 h,and the temperature fluctuation is within 0.8 mK.The cooling power of the helium sorption cooler is 1 mW@0.98 K@3.5 h.Experimental results indicate that when the charging pressure is reduced to 4MPa,theminimum temperature decreases to 836mK,and the hold time shortens to 16 h.When the pre-cooling temperature increases from 3.9 to 4.9 K,the hold time is reduced to 3 h.展开更多
Temperature-swing adsorption(TSA)is an effective technique for CO_(2) capture,but the temperature swing procedure is energy-intensive.Herein,we report a low-energy-consumption system by combining passive radiative coo...Temperature-swing adsorption(TSA)is an effective technique for CO_(2) capture,but the temperature swing procedure is energy-intensive.Herein,we report a low-energy-consumption system by combining passive radiative cooling and solar heating for the uptake of CO_(2) on commercial activated carbons(CACs).During adsorption,the adsorbents are coated with a layer of hierarchically porous poly(vinylidene fluoride-co-hexafluoropropene)[P(VdF-HFP)HP],which cools the adsorbents to a low temperature under sunlight through radiative cooling.For desorption,CACs with broad absorption of the solar spectrum are exposed to light irradiation for heating.The heating and cooling processes are completely driven by solar energy.Adsorption tests under mimicked sunlight using the CACs show that the performance of this system is comparable to that of the traditional ones.Furthermore,under real sunlight irradiation,the adsorption capacity of the CACs can be well maintained after multiple cycles.The present work may inspire the development of new temperature swing procedures with little energy consumption.展开更多
Gifford-McMahon-type pulse-tube cryocoolers(GM-PTCs)working at liquid helium temperatures are promising in quantum technology and cryogenic physics for their high reliability and minimal vibration.These features stem ...Gifford-McMahon-type pulse-tube cryocoolers(GM-PTCs)working at liquid helium temperatures are promising in quantum technology and cryogenic physics for their high reliability and minimal vibration.These features stem from the fact that there are no extra moving parts introduced into the system.The rotary valve is a key component in GM-PTCs that transfers the output exergy from the compressor to the cold head.Because a low Carnot efficiency of 1.58%is achieved at liquid helium temperatures,optimizing the rotary valve is crucial for improving the efficiency of GM-PTCs.In this regard,an exergy-loss analysis method is proposed in this paper to quantitatively obtain the leakage loss and viscosity loss of a rotary valve by experimental measurements.The results show that viscosity loss accounts for more than 97.5%of the total exergy loss in the rotary valve,and that it is possible to improve the structure of the rotary valve by expanding the flow area by 1.5 times.To verify the method,the cooling temperature and power of a remote two-stage GM-PTC were monitored,with original or optimized rotary valves installed.The experimental results show that compared to the original rotary valve,the optimized rotary valve can improve the cooling efficiency of a GM-PTC by 16.4%,with a cooling power of 0.78 W at 4.2 K.展开更多
Ambient temperature affects the occurrence and prevalence of plant disease.Most bacterial diseases are damaging at high temperatures.However,kiwifruit bacterial canker caused by Pseudomonas syringae pv.actinidiae(Psa)...Ambient temperature affects the occurrence and prevalence of plant disease.Most bacterial diseases are damaging at high temperatures.However,kiwifruit bacterial canker caused by Pseudomonas syringae pv.actinidiae(Psa)has been found to be prevalent at relatively cool temperatures,and it is unclear how ambient temperature affects the development of kiwifruit bacterial canker.In this study,basal resistance to Psa was suppressed in kiwifruit at cool growth temperature(16℃)compared with at normal temperature(24℃).In addition,RNA sequence analysis and ethylene content assessment indicated that ethylene modulated kiwifruit resistance to Psa at normal growth temperature and that cool temperature inhibited ethylene accumulation and Psa-induced activation of the ethylene signaling pathway in kiwifruit.Virusmediated silencing of the kiwifruit ethylene signaling gene AcEIN2 suppressed kiwifruit resistance to Psa at normal growth temperature.Exogenous application of ethylene inhibitor 1-methylcyclopropene eliminated the difference in kiwifruit resistance to Psa at 16 and 24℃.Exogenous application of ethylene analogues ethephon induced resistance to Psa in kiwifruit.In conclusion,cool temperatures impair basal resistance to Psa by reducing the activation of ethylene biosynthesis and signaling in kiwifruit.The results provide clues for new strategies to control plant diseases in a context of global environmental change.展开更多
Materials with both large magnetocaloric response and high thermoelectric performance are of vital importance for all-solid-state thermoelectromagnetic cooling.These two properties,however,hardly coexist in single pha...Materials with both large magnetocaloric response and high thermoelectric performance are of vital importance for all-solid-state thermoelectromagnetic cooling.These two properties,however,hardly coexist in single phase materials except previously reported hexagonal Cr_(1-x)Te half metal where a relatively high magnetic entropy change(-△S_(M))of~2.4 J·kg^(-1)·K^(-1)@5 T and a moderate thermoelectric figure of merit(ZT)of~1.2×10^(-2)@300 K are simultaneously recorded.Herein we aim to increase the thermoelectric performance of Cr_(1-x)Te by compositing with semiconducting Ag_(2)Te.It is discovered that the in-situ synthesis of Cr_(1-x)Te/Ag_(2)Te composites by reacting their constitute elements above melting temperatures is unsuccessful because of strong phase competition.Specifically,at elevated temperatures(T>800 K),Cr_(1-x)Te has a much lower deformation energy than Ag_(2)Te and tends to become more Cr-deficient by capturing Te from Ag_(2)Te.Therefore,Ag is insufficiently reacted and as a metal it deteriorates ZT.We then rationalize the synthesis of Cr_(1-x)Te/Ag_(2)Te composites by ex-situ mix of the pre-prepared Cr_(1-x)Te and Ag_(2)Te binary compounds followed by densification at a low sintering temperature of 573 K under a pressure of 3.5 GPa.We show that by compositing with 7 mol%Ag_(2)Te,the Seebeck coefficient of Cr_(1-x)Te is largely increased while the lattice thermal conductivity is considerably reduced,leading to 72%improvement of ZT.By comparison,-△S_(M)is only slightly reduced by 10%in the composite.Our work demonstrates the potential of Cr_(1-x)Te/Ag_(2)Te composites for thermoelectromagnetic cooling.展开更多
This study investigates the impact of the salinity barrier layer(BL)on the upper ocean response to Super Typhoon Mangkhut(2018)in the western North Pacific.After the passage of Mangkhut,a noticeable increase(~0.6 psu)...This study investigates the impact of the salinity barrier layer(BL)on the upper ocean response to Super Typhoon Mangkhut(2018)in the western North Pacific.After the passage of Mangkhut,a noticeable increase(~0.6 psu)in sea surface salinity and a weak decrease(<1℃)in sea surface temperature(SST)were observed on the right side of the typhoon track.Mangkhut-induced SST change can be divided into the three stages,corresponding to the variations in BL thickness and SST before,during,and after the passage of Mangkhut.During the pre-typhoon stage,SST slightly warmed due to the entrainment of BL warm water,which suppressed the cooling induced by surface heat fluxes and horizontal advection.During the forced stage,SST cooling was controlled by entrainment,and the preexisting BL reduced the total cooling by 0.89℃ d-1,thus significantly weakening the overall SST cooling induced by Mangkhut.During the relaxation stage,the SST cooling was primarily caused by the entrainment.Our results indicate that a preexisting BL can limit typhoon-induced SST cooling by suppressing the entrainment of cold thermocline water,which contributed to Mangkhut becoming the strongest typhoon in 2018.展开更多
Mathematical physics equations are often utilized to describe physical phenomena in various fields of science and engineering.One such equation is the Fourier equation,which is a commonly used and effective method for...Mathematical physics equations are often utilized to describe physical phenomena in various fields of science and engineering.One such equation is the Fourier equation,which is a commonly used and effective method for evaluating the effectiveness of temperature control measures for mass concrete.One important measure for temperature control in mass concrete is the use of cooling water pipes.However,the mismatch of grids between large-scale concrete models and small-scale cooling pipe models can result in a significant waste of calculation time when using the finite element method.Moreover,the temperature of the water in the cooling pipe needs to be iteratively calculated during the thermal transfer process.The substructure method can effectively solve this problem,and it has been validated by scholars.The Abaqus/Python secondary development technology provides engineers with enough flexibility to combine the substructure method with an iteration algorithm,which enables the creation of a parametric modeling calculation for cooling water pipes.This paper proposes such a method,which involves iterating the water pipe boundary and establishing the water pipe unit substructure to numerically simulate the concrete temperature field that contains a cooling water pipe.To verify the feasibility and accuracy of the proposed method,two classic numerical examples were analyzed.The results showed that this method has good applicability in cooling pipe calculations.When the value of the iteration parameterαis 0.4,the boundary temperature of the cooling water pipes can meet the accuracy requirements after 4∼5 iterations,effectively improving the computational efficiency.Overall,this approach provides a useful tool for engineers to analyze the temperature control measures accurately and efficiently for mass concrete,such as cooling water pipes,using Abaqus/Python secondary development.展开更多
The aim of this study is to investigate the sea surface temperature(SST) cooling as typhoons pass the Kuroshio Current.A numerical circulation model,denoted as the Stony Brook Parallel Ocean Model(sbPOM),was used to s...The aim of this study is to investigate the sea surface temperature(SST) cooling as typhoons pass the Kuroshio Current.A numerical circulation model,denoted as the Stony Brook Parallel Ocean Model(sbPOM),was used to simulate the SST,which includes four wave-induced effect terms(i.e.,radiation stress,nonbreaking waves,Stokes drift,and breaking waves) simulated using the third-generation wave model,called WAVEWATCH-Ⅲ(WW3).The significant wave height(SWH) measurements from the Jason-2 altimeter were used to validate the WW3-simulated results,yielding a root mean square error(RMSE) of less than 0.50 m and a correlation coefficient(COR) of approximately 0.93.The water temperature measured from the Advanced Research and Global Observation Satellite was applied to validate the model simulation.Accordingly,the RMSE of the SST is 0.92℃ with a COR of approximately 0.99.As revealed in the sbPOM-simulated SST fields,a reduction in the SST at the Kuroshio Current region was observed as a typhoon passed,although the water temperature of the Kuroshio Current is relatively high.The variation of the SST is consistent with that of the current,whereas the maximum SST lagged behind the occurrence of the peak SWH.Moreover,the Stokes drift plays an important role in the SST cooling after analyzing four wave-induced terms in the background of the Kuroshio Current.The sensitivity experiment also showed that the accuracy of the water temperature was significantly reduced when including breaking waves,which play a negative role in the inside part of the ocean.The variation in the mean mixing layer depth(MLD) showed that a typhoon could enhance the mean MLD in the Kuroshio Current area in September and October,whereas a typhoon has little influence on the mean MLD in the Kuroshio Current area in May.Moreover,the mean MLD rapidly decreased with the weakening of the strong wind force and wave-induced effects when a typhoon crossed the Kuroshio Current.展开更多
Understanding the differences in mechanical properties and damage characteristics of granitoid under high temperatures is crucial for exploring deep geothermal resources.This study analyzes the evolution of the acoust...Understanding the differences in mechanical properties and damage characteristics of granitoid under high temperatures is crucial for exploring deep geothermal resources.This study analyzes the evolution of the acoustic emission(AE)characteristics and mechanical parameters of granodiorite and granite after heating and water cooling by uniaxial compression and variable-angle shear tests under different temperature gradients.We identify their changes in mesostructure and mineral composition with electron probe microanalysis and scanning electron microscopy.Results show that these two hot dry rocks have similar diagenetic minerals and microstructure,but show significantly different mechanical and acoustic characteristics,and even opposing evolution trends in a certain temperature range.At the temperatures ranging from 100℃to 500℃,the compressive and shear mechanical properties of granodiorite switch repeatedly between weakening and strengthening,and those of granite show a continuous weakening trend.At 600℃,both rocks exhibit a deterioration of mechanical properties.The damage mode of granite is characterized by initiating at low stress,exponential evolutionary activity,and intensified energy release.In contrast,granodiorite exhibits the characteristics of initiating at high stress,volatile evolutionary activity,and intermittent energy release,due to its more stable microstructure and fewer thermal defects compared to granite.As the temperature increases,the initiation and propagation of secondary cracks in granodiorite are suppressed to a certain extent,and the seismicity and brittleness are enhanced.The subtle differences in grain size,microscopic heterogeneity,and mineral composition of the two hot dry rocks determine the different acoustic-mechanical characteristics under heating and cooling,and the evolution trends with temperature.These findings are of great significance for the scientific and efficient construction of rock mass engineering by rationally utilizing different rock strata properties.展开更多
Microstructure, precipitate and magnetic characteristic of fmal products with different normalizing cooling processes for Fe-3.2%Si low-temperature hot-rolled grain-oriented silicon steel were analyzed and compared wi...Microstructure, precipitate and magnetic characteristic of fmal products with different normalizing cooling processes for Fe-3.2%Si low-temperature hot-rolled grain-oriented silicon steel were analyzed and compared with the hot-rolled plate by optical microscopy （OM）, transmission electron microscopy （TEM）, and energy dispersive spectrometry （EDS）. The results show that, the surface microstructure is uniform, the proportion of recrystallization in matrix increases, and the banding textures are narrowed; the precipitates, whose quantity in normalized plate is more than that in hot-rolled plate greatly, are mainly A1N, MnS, composite precipitates （Cu,Mn）S and so on. Normalizing technology with a temperature of 1120 ℃, holding for 3 min, and a two-stage cooling is a most advantaged method to obtain oriented silicon steel with sharper Goss texture and higher magnetic properties, owing to the uniform surface microstructures and the obvious inhomogeneity of microstructures along the thickness. The normalizing technology with the two-stage cooling is the optimum process, which can generate more fine precipitates dispersed over the matrix, and be beneficial for finished products to get higher magnetic properties.展开更多
The mathematical model of the grinding temperature is established. The grinding temperature and the cooling rate are measured in the grind-hardening process of 40Cr steel under different conditions. Moreover, the grin...The mathematical model of the grinding temperature is established. The grinding temperature and the cooling rate are measured in the grind-hardening process of 40Cr steel under different conditions. Moreover, the grind-hardening effects are investigated. Experimental results show that the calculated temperatures are comparatively close to the measured ones, and the required temperature and cooling rate can be achieved. Furthermore, the microstructure of the hardened zone is similar to that obtained through the high-frequency induction technique. The average hardness of the entirely hardened zone is HV670 and the thickness of the hardened layer is adjacent to 1.3 mm. It indicates that the hardening mechanism induced by the grinding heat and high-frequency heating is identical. Finally, the fine needlelike martensite is obtained.展开更多
Microstructure,texture,and mechanical properties of the extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy were investigated at different extrusion temperatures(260 and 320℃),extrusion ratios(10:1,15:1,and 30:1),and extrusi...Microstructure,texture,and mechanical properties of the extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy were investigated at different extrusion temperatures(260 and 320℃),extrusion ratios(10:1,15:1,and 30:1),and extrusion speeds(3 and 6 mm/s).The experimental results exhibited that the grain sizes after extrusion were much finer than that of the homogenized alloy,and the second phase showed streamline distribution along the extrusion direction(ED).With extrusion temperature increased from 260 to 320℃,the microstructure,texture,and mechanical properties of alloys changed slightly.The dynamic recrystallization(DRX)degree and grain sizes enhanced as the extrusion ratio increased from 10:1 to 30:1,and the strength gradually decreased but elongation(EL)increased.With the extrusion speed increased from 3 to 6 mm/s,the grain sizes and DRX degree increased significantly,and the samples presented the typical<2111>-<1123>rare-earth(RE)textures.The alloy extruded at 260℃ with extrusion ratio of 10:1 and extrusion speed of 3 mm/s showed the tensile yield strength(TYS)of 213 MPa and EL of 30.6%.After quantitatively analyzing the contribution of strengthening mechanisms,it was found that the grain boundary strengthening and dislocation strengthening played major roles among strengthening contributions.These results provide some guidelines for enlarging the industrial application of extruded Mg-RE alloy.展开更多
文摘The stress-strain behavior of confined concrete under heating and residual conditions has been preliminarily addressed in previous research;however,its behavior at subsequent cooling temperatures after being heated to peak temperature has yet to be thoroughly investigated.It is crucial for determining confined concrete structures’post-fire performance and burnout resistance.The paper presents the fundamental behavior of the confined concrete constitutive parameters and stress-strain curve at subsequent cooling temperatures after being heated to peak temperature.The study includes the stress-stress relationship of a 200 mm diameter cylinder with two distinct confinement spacings of 60 mm and 120 mm.The constitutive parameters for confined concrete were initially determined for a peak heating temperature of 750℃ and then modified to establish the stress-strain relationship for successive cooling temperatures of 500℃,250℃,and ambient temperature.The study results show that confinement has a considerable impact on compressive strength,stiffness,and ductility at ambient and fire conditions.After being heated to peak temperature,the confined concrete compressive strength recovers during successive cooling temperatures,with the recovery dependent on confinement spacing.The established stress-strain relationship can assist in better comprehending structural performance and capacity degradation for different tie spacings,and is useful for the analysis and design of confined RC(reinforced concrete)elements during and after a fire.
基金Project(2018XK2301) supported by the Change-Zhu-Tan National Independent Innavation Demonstration Zone Special Program,China。
文摘The ductile-to-brittle transition temperature(DBTT)of high strength steels can be optimized by tailoring microstructure and crystallographic orientation characteristics,where the start cooling temperature plays a key role.In this work,X70 steels with different start cooling temperatures were prepared through thermo-mechanical control process.The quasi-polygonal ferrite(QF),granular bainite(GB),bainitic ferrite(BF)and martensite-austenite constituents were formed at the start cooling temperatures of 780℃(C1),740℃(C2)and 700℃(C3).As start cooling temperature decreased,the amount of GB decreased,the microstructure of QF and BF increased.Microstructure characteristics of the three samples,such as high-angle grain boundaries(HAGBs),MA constituents and crystallographic orientation,also varied with the start cooling temperatures.C2 sample had the lowest DBTT value(−86℃)for its highest fraction of HAGBs,highest content of<110>oriented grains and lowest content of<001>oriented grains parallel to TD.The high density of{332}<113>and low density of rotated cube{001}<110>textures also contributed to the best impact toughness of C2 sample.In addition,a modified model was used in this paper to quantitatively predict the approximate DBTT value of steels.
基金supported by the National Key R&D Program of China(No.2022YFE0123300)the National Natural Science Foundation of China(Nos.U20A20277 and 52474351)Major Project of Liaoning Province Innovation Consortium(No.2023JH1/11200012).
文摘For P91 steel weldment,performing post-weld heat treatment immediately after welding can enhance welding efficiency and reduce the risk of hydrogen-induced cracking.However,determining the post-weld cooling temperature(PWCT)is challenging due to potential impact on the mechanical properties of weldment after subsequent heat treatment.A systematic investigation is conducted to explore the effect of PWCT on the impact toughness of P91 steel welded joints.It has been demonstrated that the impact energy of the weld metal gradually increases from 40.2 to 49.5 J as the PWCT decreases from 300 to 100℃.Microstructural analysis reveals that PWCTs above 100℃ led to an increased dislocation density in the weld metal.Furthermore,in situ observations using a high-temperature confocal laser scanning microscope confirm that excessively high PWCTs result in the formation of untempered martensite after post-weld heat treatment.Such untempered martensites are identified as the primary cause of the reduced impact toughness in the weld metal.These findings underscore the importance of carefully controlling PWCT in welding procedures for P91 steel and similar grades.
基金supported by the National Natural Science Foundation of China(52372279,52103071,52203322,52473289,52303220)the Interdisciplinary Research Project for Young Teachers of USTB(Fundamental Research Funds for the Central Universities in China,FRF-IDRY-GD22-001)。
文摘The advancement of sophisticated smart windows exhibiting superior thermoregulation capabilities in both solar spectrum and long-wave infrared range maintains a prominent objective for researchers in this field.In this study,a Janus window is proposed and prepared based on polymer-stabilized liquid-crystal films/thermochromic materials.It can achieve switchable front long-wave infrared emissivity(ε_(Front))and solar modulation ability(ΔT_(sol))through dynamic flipping,making it suitable for different seasonal energy-saving requirements.Outdoor experiments show that under daytime illumination,the indoor temperature decreases by 8℃,and the nighttime temperature drops by 5℃.MATLAB simulation calculations indicate that the daytime cooling power is 93 W m^(-2),while the nighttime cooling power reaches 142 W m^(-2).Interestingly,by modifying the conductive layer,it can effectively shield electromagnetic radiation(within the X-band frequency range(8.2-12.4)GHz).Energy simulation reveals the substantial superiority of this device in energy savings compared with single-layer polymer-stabilized liquid crystal,poly(N-isopropyl acrylamide),and normal glass when applied in different climate zones.This research presents a compelling opportunity for the development of sophisticated smart windows characterized by exceptional thermoregulation capabilities.
基金supported by National Natural Science Foundation of China(Nos.51806092,52201410)Non-Carbon Energy Conversion and Utilization Institute under the Shanghai Class IV Peak Disciplinary Development Program,High-End Foreign Experts Recruitment Plan of China(G2022013028L).
文摘Phase Change Material(PCM)-based cold energy storage system(CESS)can effectively utilize the peak and valley power resources to reduce the excessive dependence on the power grid.In this study,a PCM-based CESS was designed for cold storage applications.The optimal number of PCM plates was determined through numerical simulations to meet the required cold storage temperature and control time.Additionally,the air temperature field,flow field,and melting characteristics of the PCMplates during the cooling release process were analyzed.The effects of plate positioning and thickness on the cooling release performance were further investigated.The results indicated that when 64PCMplateswere used,the duration formaintaining temperatures below−18℃increased from0.6 h to approximately 16.94 h.During the cooling release process,the temperature field in the cold storage exhibited stratification,and the melting of the PCM plates was non-uniform.Placing the PCM plates at the top or within the interlayers without cargo above proved more effective,with their cooling release power being approximately twice that of the PCM plates placed in the interlayers with cargo above.Furthermore,reducing the thickness of the PCMplates from15 to 7.5mmresulted in a 3.6-h increase in the time below−18℃and a 4.5-h reduction in the time required to reach 80%liquid phase fraction.
基金Project supported by the National Natural Science Foundation of China (Grant No. 52406102)Shandong Provincial Natural Science Foundation (Grant No. ZR2023QE258)。
文摘In order to meet the growing global energy demand and fulfill energy conservation and emission reduction goals, the efficient utilization of solar energy is becoming increasingly critical. However, the effects of high temperatures on solar absorption are rarely considered in practical research. Therefore, this study presents a porous zinc and silver sulfide solar absorber with high-temperature radiative cooling capabilities. The solar absorption rate and radiative cooling efficiency in the high-temperature range(636 K–1060 K) are computed using the finite-difference time-domain method. Furthermore, the impact of parameters such as characteristic length, porosity, incident angle, and pore shape factor on both the absorption rate and efficiency of the solar absorber is analyzed. The mechanism is further examined from the perspective of microscopic thermal radiation. The results show that, in the high-temperature range, the solar absorption rate increases with higher porosity and incident angles, reaching its peak when the characteristic length is 1 μm. These findings highlight the significant potential of the solar absorber for efficient solar energy harvesting in photo-thermal conversion applications within a specific high-temperature range.
基金supported by the Key project of Hunan Provincial Education Department(Grant Number:22A0485)The Natural Science Foundation of Hunan(Grant Number:2024JJ5293)The Key project of Hunan University of Arts and Science(Grant Number:23ZZ08).
文摘In liquid rocket engines,regenerative cooling technology is essential for preserving structural integrity under extreme thermal loads.However,non-uniform coolant flow distribution within the cooling channels often leads to localized overheating,posing serious risks to engine reliability and operational lifespan.This study employs a three-dimensional fluid–thermal coupled numerical model to systematically investigate the influence of geometric parameters-specifically the number of inlets,the number of channels,and inlet manifold configurations-on flow uniformity and thermal distribution in non-pyrolysis zones.Key findings reveal that increasing the number of inlets from one to three significantly enhances flow uniformity,reducing mass flow rate deviation from 1.2%to below 0.3%.However,further increasing the inlets to five yields only marginal improvements indicating diminishing(<0.1%),returns beyond three inlets.Additionally,temperature non-uniformity at the combustion chamber throat decreases by 37%-from 3050 K with 18 channels to 1915 K with 30 channels-highlighting the critical role of channel density in effective thermal regulation.Notably,while higher channel counts improve cooling efficiency,they also result in increased pressure losses of approximately 18%–22%,emphasizing the need to balance thermal performance against hydraulic resistance.An optimal configuration comprising 24 channels and three inlets was identified,providing minimal temperature gradients while maintaining acceptable pressure losses.The inlet manifold structure also plays a pivotal role in determining flow distribution.Configuration 3(Config-3),which features an enlarged manifold and reduced inlet velocity,achieves a 40%reduction in velocity fluctuations compared to Configuration 1(Config-1).This improvement leads to a more uniform mass flow distribution,with a relative standard deviation(RSD)of less than 0.15%.Furthermore,this design effectively mitigates localized hot spots near the nozzle-where temperature gradients are most severe-achieving a reduction of approximately 1135 K.
基金Supported by the Major Science and Technology Project of Jilin Province(20220301010GX)the International Scientific and Technological Cooperation(20240402071GH).
文摘The liquid cooling system(LCS)of fuel cells is challenged by significant time delays,model uncertainties,pump and fan coupling,and frequent disturbances,leading to overshoot and control oscillations that degrade temperature regulation performance.To address these challenges,we propose a composite control scheme combining fuzzy logic and a variable-gain generalized supertwisting algorithm(VG-GSTA).Firstly,a one-dimensional(1D)fuzzy logic controler(FLC)for the pump ensures stable coolant flow,while a two-dimensional(2D)FLC for the fan regulates the stack temperature near the reference value.The VG-GSTA is then introduced to eliminate steady-state errors,offering resistance to disturbances and minimizing control oscillations.The equilibrium optimizer is used to fine-tune VG-GSTA parameters.Co-simulation verifies the effectiveness of our method,demonstrating its advantages in terms of disturbance immunity,overshoot suppression,tracking accuracy and response speed.
基金supported by the Hundred Talents Programof the Chinese Academy of Sciences,the Pre-Research Project JZX7Y20220414101801the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB35000000)the National Natural Science Foundation Projects(No.51806231).
文摘Helium sorption cooler technology is a key means to realize highly reliable low-vibration very lowtemperature environments,which have important applications in fields such as quantum computing and space exploration.The laboratory designed a superfluid suppression small hole and a multi-ribbed condenser,developed a reliable-performance helium sorption cooler(HSC),and conducted experimental studies.Experimental results show that the prototype can achieve the lowest cooling temperature of 873 mK without load by filling 6MPa helium at room temperature.The low-temperature hold time is 26 h,and the temperature fluctuation is within 0.8 mK.The cooling power of the helium sorption cooler is 1 mW@0.98 K@3.5 h.Experimental results indicate that when the charging pressure is reduced to 4MPa,theminimum temperature decreases to 836mK,and the hold time shortens to 16 h.When the pre-cooling temperature increases from 3.9 to 4.9 K,the hold time is reduced to 3 h.
基金supported by the National Science Fund for Distinguished Young Scholars(22125804)the National Natural Science Foundation of China(21808110,22078155,and 21878149).
文摘Temperature-swing adsorption(TSA)is an effective technique for CO_(2) capture,but the temperature swing procedure is energy-intensive.Herein,we report a low-energy-consumption system by combining passive radiative cooling and solar heating for the uptake of CO_(2) on commercial activated carbons(CACs).During adsorption,the adsorbents are coated with a layer of hierarchically porous poly(vinylidene fluoride-co-hexafluoropropene)[P(VdF-HFP)HP],which cools the adsorbents to a low temperature under sunlight through radiative cooling.For desorption,CACs with broad absorption of the solar spectrum are exposed to light irradiation for heating.The heating and cooling processes are completely driven by solar energy.Adsorption tests under mimicked sunlight using the CACs show that the performance of this system is comparable to that of the traditional ones.Furthermore,under real sunlight irradiation,the adsorption capacity of the CACs can be well maintained after multiple cycles.The present work may inspire the development of new temperature swing procedures with little energy consumption.
基金supported by the National Key Research&Development Program of China(No.2023YFF0721304)the Key Research&Development Program of Jiangsu Province(No.2021015-4),China。
文摘Gifford-McMahon-type pulse-tube cryocoolers(GM-PTCs)working at liquid helium temperatures are promising in quantum technology and cryogenic physics for their high reliability and minimal vibration.These features stem from the fact that there are no extra moving parts introduced into the system.The rotary valve is a key component in GM-PTCs that transfers the output exergy from the compressor to the cold head.Because a low Carnot efficiency of 1.58%is achieved at liquid helium temperatures,optimizing the rotary valve is crucial for improving the efficiency of GM-PTCs.In this regard,an exergy-loss analysis method is proposed in this paper to quantitatively obtain the leakage loss and viscosity loss of a rotary valve by experimental measurements.The results show that viscosity loss accounts for more than 97.5%of the total exergy loss in the rotary valve,and that it is possible to improve the structure of the rotary valve by expanding the flow area by 1.5 times.To verify the method,the cooling temperature and power of a remote two-stage GM-PTC were monitored,with original or optimized rotary valves installed.The experimental results show that compared to the original rotary valve,the optimized rotary valve can improve the cooling efficiency of a GM-PTC by 16.4%,with a cooling power of 0.78 W at 4.2 K.
基金supported by grants from the National Key Research and Development Program of China(Grant No.2022YFD1400200)the Special Support Plan for High-Level Talent of Shaanxi Province。
文摘Ambient temperature affects the occurrence and prevalence of plant disease.Most bacterial diseases are damaging at high temperatures.However,kiwifruit bacterial canker caused by Pseudomonas syringae pv.actinidiae(Psa)has been found to be prevalent at relatively cool temperatures,and it is unclear how ambient temperature affects the development of kiwifruit bacterial canker.In this study,basal resistance to Psa was suppressed in kiwifruit at cool growth temperature(16℃)compared with at normal temperature(24℃).In addition,RNA sequence analysis and ethylene content assessment indicated that ethylene modulated kiwifruit resistance to Psa at normal growth temperature and that cool temperature inhibited ethylene accumulation and Psa-induced activation of the ethylene signaling pathway in kiwifruit.Virusmediated silencing of the kiwifruit ethylene signaling gene AcEIN2 suppressed kiwifruit resistance to Psa at normal growth temperature.Exogenous application of ethylene inhibitor 1-methylcyclopropene eliminated the difference in kiwifruit resistance to Psa at 16 and 24℃.Exogenous application of ethylene analogues ethephon induced resistance to Psa in kiwifruit.In conclusion,cool temperatures impair basal resistance to Psa by reducing the activation of ethylene biosynthesis and signaling in kiwifruit.The results provide clues for new strategies to control plant diseases in a context of global environmental change.
基金Project supported by the National Key Research and Development Program of China(Grant No.2019YFA0704900)the National Natural Science Foundation of China(Grant No.52171221)。
文摘Materials with both large magnetocaloric response and high thermoelectric performance are of vital importance for all-solid-state thermoelectromagnetic cooling.These two properties,however,hardly coexist in single phase materials except previously reported hexagonal Cr_(1-x)Te half metal where a relatively high magnetic entropy change(-△S_(M))of~2.4 J·kg^(-1)·K^(-1)@5 T and a moderate thermoelectric figure of merit(ZT)of~1.2×10^(-2)@300 K are simultaneously recorded.Herein we aim to increase the thermoelectric performance of Cr_(1-x)Te by compositing with semiconducting Ag_(2)Te.It is discovered that the in-situ synthesis of Cr_(1-x)Te/Ag_(2)Te composites by reacting their constitute elements above melting temperatures is unsuccessful because of strong phase competition.Specifically,at elevated temperatures(T>800 K),Cr_(1-x)Te has a much lower deformation energy than Ag_(2)Te and tends to become more Cr-deficient by capturing Te from Ag_(2)Te.Therefore,Ag is insufficiently reacted and as a metal it deteriorates ZT.We then rationalize the synthesis of Cr_(1-x)Te/Ag_(2)Te composites by ex-situ mix of the pre-prepared Cr_(1-x)Te and Ag_(2)Te binary compounds followed by densification at a low sintering temperature of 573 K under a pressure of 3.5 GPa.We show that by compositing with 7 mol%Ag_(2)Te,the Seebeck coefficient of Cr_(1-x)Te is largely increased while the lattice thermal conductivity is considerably reduced,leading to 72%improvement of ZT.By comparison,-△S_(M)is only slightly reduced by 10%in the composite.Our work demonstrates the potential of Cr_(1-x)Te/Ag_(2)Te composites for thermoelectromagnetic cooling.
基金supported by the National Natural Science Foundation of China(Grant No.42176015)the National Natural Science Foundation of China(Grant No.41605070)+3 种基金the National Key Research and Development Program(Grant No.2021YFC3101500)the Hunan Provincial Natural Science Outstanding Youth Fund(Grant No.2023JJ10053)the Innovation Group Project of the Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(Grant No.311022001)a project of the Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(Grant No.SML2021SP207)。
文摘This study investigates the impact of the salinity barrier layer(BL)on the upper ocean response to Super Typhoon Mangkhut(2018)in the western North Pacific.After the passage of Mangkhut,a noticeable increase(~0.6 psu)in sea surface salinity and a weak decrease(<1℃)in sea surface temperature(SST)were observed on the right side of the typhoon track.Mangkhut-induced SST change can be divided into the three stages,corresponding to the variations in BL thickness and SST before,during,and after the passage of Mangkhut.During the pre-typhoon stage,SST slightly warmed due to the entrainment of BL warm water,which suppressed the cooling induced by surface heat fluxes and horizontal advection.During the forced stage,SST cooling was controlled by entrainment,and the preexisting BL reduced the total cooling by 0.89℃ d-1,thus significantly weakening the overall SST cooling induced by Mangkhut.During the relaxation stage,the SST cooling was primarily caused by the entrainment.Our results indicate that a preexisting BL can limit typhoon-induced SST cooling by suppressing the entrainment of cold thermocline water,which contributed to Mangkhut becoming the strongest typhoon in 2018.
文摘Mathematical physics equations are often utilized to describe physical phenomena in various fields of science and engineering.One such equation is the Fourier equation,which is a commonly used and effective method for evaluating the effectiveness of temperature control measures for mass concrete.One important measure for temperature control in mass concrete is the use of cooling water pipes.However,the mismatch of grids between large-scale concrete models and small-scale cooling pipe models can result in a significant waste of calculation time when using the finite element method.Moreover,the temperature of the water in the cooling pipe needs to be iteratively calculated during the thermal transfer process.The substructure method can effectively solve this problem,and it has been validated by scholars.The Abaqus/Python secondary development technology provides engineers with enough flexibility to combine the substructure method with an iteration algorithm,which enables the creation of a parametric modeling calculation for cooling water pipes.This paper proposes such a method,which involves iterating the water pipe boundary and establishing the water pipe unit substructure to numerically simulate the concrete temperature field that contains a cooling water pipe.To verify the feasibility and accuracy of the proposed method,two classic numerical examples were analyzed.The results showed that this method has good applicability in cooling pipe calculations.When the value of the iteration parameterαis 0.4,the boundary temperature of the cooling water pipes can meet the accuracy requirements after 4∼5 iterations,effectively improving the computational efficiency.Overall,this approach provides a useful tool for engineers to analyze the temperature control measures accurately and efficiently for mass concrete,such as cooling water pipes,using Abaqus/Python secondary development.
基金supported by the National Natural Science Foundation of China(Nos.42076238,42176012,and 42130402)the National Key Research and Development Program of China(No.2021YFC3101702)the Shanghai Frontiers Research Center of the Hadal Biosphere.
文摘The aim of this study is to investigate the sea surface temperature(SST) cooling as typhoons pass the Kuroshio Current.A numerical circulation model,denoted as the Stony Brook Parallel Ocean Model(sbPOM),was used to simulate the SST,which includes four wave-induced effect terms(i.e.,radiation stress,nonbreaking waves,Stokes drift,and breaking waves) simulated using the third-generation wave model,called WAVEWATCH-Ⅲ(WW3).The significant wave height(SWH) measurements from the Jason-2 altimeter were used to validate the WW3-simulated results,yielding a root mean square error(RMSE) of less than 0.50 m and a correlation coefficient(COR) of approximately 0.93.The water temperature measured from the Advanced Research and Global Observation Satellite was applied to validate the model simulation.Accordingly,the RMSE of the SST is 0.92℃ with a COR of approximately 0.99.As revealed in the sbPOM-simulated SST fields,a reduction in the SST at the Kuroshio Current region was observed as a typhoon passed,although the water temperature of the Kuroshio Current is relatively high.The variation of the SST is consistent with that of the current,whereas the maximum SST lagged behind the occurrence of the peak SWH.Moreover,the Stokes drift plays an important role in the SST cooling after analyzing four wave-induced terms in the background of the Kuroshio Current.The sensitivity experiment also showed that the accuracy of the water temperature was significantly reduced when including breaking waves,which play a negative role in the inside part of the ocean.The variation in the mean mixing layer depth(MLD) showed that a typhoon could enhance the mean MLD in the Kuroshio Current area in September and October,whereas a typhoon has little influence on the mean MLD in the Kuroshio Current area in May.Moreover,the mean MLD rapidly decreased with the weakening of the strong wind force and wave-induced effects when a typhoon crossed the Kuroshio Current.
基金The authors would like to acknowledge the financial support from the National Natural Science Foundation of China(Grant No.52104112)the Research Foundation of the Department of Natural Resources of Hunan Province,China(Grant No.20230101DZ)the Natural Science Foundation of Hunan Province,China(Grant No.2023JJ20062).
文摘Understanding the differences in mechanical properties and damage characteristics of granitoid under high temperatures is crucial for exploring deep geothermal resources.This study analyzes the evolution of the acoustic emission(AE)characteristics and mechanical parameters of granodiorite and granite after heating and water cooling by uniaxial compression and variable-angle shear tests under different temperature gradients.We identify their changes in mesostructure and mineral composition with electron probe microanalysis and scanning electron microscopy.Results show that these two hot dry rocks have similar diagenetic minerals and microstructure,but show significantly different mechanical and acoustic characteristics,and even opposing evolution trends in a certain temperature range.At the temperatures ranging from 100℃to 500℃,the compressive and shear mechanical properties of granodiorite switch repeatedly between weakening and strengthening,and those of granite show a continuous weakening trend.At 600℃,both rocks exhibit a deterioration of mechanical properties.The damage mode of granite is characterized by initiating at low stress,exponential evolutionary activity,and intensified energy release.In contrast,granodiorite exhibits the characteristics of initiating at high stress,volatile evolutionary activity,and intermittent energy release,due to its more stable microstructure and fewer thermal defects compared to granite.As the temperature increases,the initiation and propagation of secondary cracks in granodiorite are suppressed to a certain extent,and the seismicity and brittleness are enhanced.The subtle differences in grain size,microscopic heterogeneity,and mineral composition of the two hot dry rocks determine the different acoustic-mechanical characteristics under heating and cooling,and the evolution trends with temperature.These findings are of great significance for the scientific and efficient construction of rock mass engineering by rationally utilizing different rock strata properties.
基金Projects(51274083,51074062)supported by the National Natural Science Foundation of China
文摘Microstructure, precipitate and magnetic characteristic of fmal products with different normalizing cooling processes for Fe-3.2%Si low-temperature hot-rolled grain-oriented silicon steel were analyzed and compared with the hot-rolled plate by optical microscopy （OM）, transmission electron microscopy （TEM）, and energy dispersive spectrometry （EDS）. The results show that, the surface microstructure is uniform, the proportion of recrystallization in matrix increases, and the banding textures are narrowed; the precipitates, whose quantity in normalized plate is more than that in hot-rolled plate greatly, are mainly A1N, MnS, composite precipitates （Cu,Mn）S and so on. Normalizing technology with a temperature of 1120 ℃, holding for 3 min, and a two-stage cooling is a most advantaged method to obtain oriented silicon steel with sharper Goss texture and higher magnetic properties, owing to the uniform surface microstructures and the obvious inhomogeneity of microstructures along the thickness. The normalizing technology with the two-stage cooling is the optimum process, which can generate more fine precipitates dispersed over the matrix, and be beneficial for finished products to get higher magnetic properties.
文摘The mathematical model of the grinding temperature is established. The grinding temperature and the cooling rate are measured in the grind-hardening process of 40Cr steel under different conditions. Moreover, the grind-hardening effects are investigated. Experimental results show that the calculated temperatures are comparatively close to the measured ones, and the required temperature and cooling rate can be achieved. Furthermore, the microstructure of the hardened zone is similar to that obtained through the high-frequency induction technique. The average hardness of the entirely hardened zone is HV670 and the thickness of the hardened layer is adjacent to 1.3 mm. It indicates that the hardening mechanism induced by the grinding heat and high-frequency heating is identical. Finally, the fine needlelike martensite is obtained.
基金supported by the National Science and Technology Major Project,China(No.2019-VI-0004-0118)the National Natural Science Foundation of China(No.51771152)the National Key R&D Program of China(No.2018YFB1106800)。
文摘Microstructure,texture,and mechanical properties of the extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy were investigated at different extrusion temperatures(260 and 320℃),extrusion ratios(10:1,15:1,and 30:1),and extrusion speeds(3 and 6 mm/s).The experimental results exhibited that the grain sizes after extrusion were much finer than that of the homogenized alloy,and the second phase showed streamline distribution along the extrusion direction(ED).With extrusion temperature increased from 260 to 320℃,the microstructure,texture,and mechanical properties of alloys changed slightly.The dynamic recrystallization(DRX)degree and grain sizes enhanced as the extrusion ratio increased from 10:1 to 30:1,and the strength gradually decreased but elongation(EL)increased.With the extrusion speed increased from 3 to 6 mm/s,the grain sizes and DRX degree increased significantly,and the samples presented the typical<2111>-<1123>rare-earth(RE)textures.The alloy extruded at 260℃ with extrusion ratio of 10:1 and extrusion speed of 3 mm/s showed the tensile yield strength(TYS)of 213 MPa and EL of 30.6%.After quantitatively analyzing the contribution of strengthening mechanisms,it was found that the grain boundary strengthening and dislocation strengthening played major roles among strengthening contributions.These results provide some guidelines for enlarging the industrial application of extruded Mg-RE alloy.
