Water is a critical factor affecting the mechanical properties of rocks, leading to their degradation. Understanding the creep mechanical behavior of deep roadway surrounding rock under the influence of underground wa...Water is a critical factor affecting the mechanical properties of rocks, leading to their degradation. Understanding the creep mechanical behavior of deep roadway surrounding rock under the influence of underground water is of great significance. Compression and creep experiments on sandstone with varying water contents were conducted using a deep soft rock five-linked rheological experiment system. The experimental conditions, including water content (0%, 0.8%, 1.6%, 2.4% and 3.3%) and confining pressure (0, 6, 9 and 12 MPa), were determined based on pressure-free water absorption tests and in-situ stress measurements. The experimental results show that the compressive strength, creep failure stress, and dilatancy stress of sandstone decrease exponentially with increasing water content, while they increase exponentially with confining pressure. The ratio of lateral to axial instantaneous strain increases nearly linearly with the increase of stress, and the lateral creep strain characteristics of the sample are more significant than the axial ones. The duration of the attenuation creep stage of sandstone decreases with increasing water content and increases with increasing confining pressure. The lateral strain enters the steady-state creep stage before the axial strain, and the onset time of the accelerated creep stage of lateral strain under the failure stress is earlier than that of axial strain. The long-term strength of sandstone was determined based on the lateral steady-state creep rate curve, showing a negative exponential relationship with water content and a positive exponential relationship with confining pressure. A method for determining the long-term strength of rocks based on the ratio of lateral strain to axial strain (μc) is proposed, which is independent of water content. The research results provide a reliable theoretical basis for the analysis of the long-term stability of roadways under the influence of groundwater and the early prediction of creep failure.展开更多
The study focuses on the creep characteristics of significant yellow sandstone for water conservancy, hydropower, and other waterrelated slope excavation unloading rock-graded loading creep characteristics. It conduct...The study focuses on the creep characteristics of significant yellow sandstone for water conservancy, hydropower, and other waterrelated slope excavation unloading rock-graded loading creep characteristics. It conducts a uniaxial graded loading creep test on yellow sandstone under different pre-peak unloading and wetting-drying cycles. The improved nonlinear Nishihara model was obtained by introducing a nonlinear viscous element with an accelerated creep threshold switch. The sensitivity characteristics of the parameters of the improved creep model were analyzed and a nonlinear creep constitutive model was established, considering the unloading-cyclic intrinsic damage induced by water intrusion. The research results show that:(1)With an increase in the unloading point, the porosity of the rock samples initially decreases and then increases. As the number of cyclic water intrusions rises, the porosity of the rock samples gradually increases, reaching a maximum of 9.58% at an unloading point of 70% uniaxial compression stress(0.7 Rc) after five cycles.(2) Total creep deformation increases with the number of cyclic water intrusions;however, with an increase in the unloading ratio, the original samples show an initial decrease, followed by an increase in creep deformation. With a higher unloading ratio and various instances of cyclic water intrusion, the total creep time of the rock samples,compared to the original samples, is reduced by 21.8%and 23.02%. The creep damage mode gradually changes from shear damage to tensile damage.(3) The sensitivity characteristics of the improved creep model parameters show that transient elasticity modulus E1 is affected by the coupling of unloading and cyclic water intrusion. The viscoelastic modulus E2 and viscous coefficient η1 are mainly affected by unloading and cyclic water intrusion.(4) Based on the strain equivalence principle of damage mechanics, the damage treatment of the parameters in the original model is improved to construct a nonlinear creep constitutive model that considers unloading-cyclic water intrusion damage. A parameter inversion and comparison to the traditional Nishihara model reveal an average relative standard deviation of 0.271%,significantly less than 1%, indicating a more accurate nonlinear creep constitutive model. The research results are crucial for analyzing the long-term stability of water-related steep rocky slopes post-excavation and unloading and for preventing and controlling creep-type landslide disasters.展开更多
Existing creep constitutive models rarely incorporate studies on the coupling mechanism between creep damage and rock strain softening/hardening.This study analyzed the strain softening and hardening behaviors of argi...Existing creep constitutive models rarely incorporate studies on the coupling mechanism between creep damage and rock strain softening/hardening.This study analyzed the strain softening and hardening behaviors of argillaceous sandstone and sandy mudstone during load-induced failure based on the plastic increment theory.These behaviors were then coupled with an improved Burgers creep model to establish a coupled creep-damage and plastic softening/hardening model.Finally,the validity and engineering applicability of the proposed model were verified through FLAC~(3D)numerical simulations.The numerical simulation results of standard cylindrical specimens show that the established coupling model can effectively reflect the unloading creep deformation law and failure characteristics of argillaceous sandstone and sandy mudstone.Taking the diversion tunnel of a hydropower station in Northwest China as an example for engineering application,the coupled creep-damage and plastic softening/hardening model is introduced into FLAC~(3D)to carry out numerical simulation calculation of the tunnel under excavation and unsupported creep conditions.The results show that the uncoordinated deformation of the upper and lower walls of the surrounding rock of the tunnel is more prominent.When the buried depth of the tunnel increases to 80 m,the monitoring point C in the sandy mudstone area of the upper wall shows nonlinear accelerated deformation under unsupported creep conditions,and the maximum displacement in the horizontal direction reaches 44.5 mm,and the maximum displacement in the vertical direction reaches 53.5 mm.The coupled creep-damage and plastic softening/hardening model established in the research results can well describe the whole process of uncoordinated deformation and failure in the unloading creep process of soft-hard interbedded rock mass.展开更多
The creep-slip behavior of creeping landslides is closely related to the creep characteristics of slope rock.This study analyzed the creep behavior of ultra-soft mudstone from the Gaomiao landslide in Haidong City,Qin...The creep-slip behavior of creeping landslides is closely related to the creep characteristics of slope rock.This study analyzed the creep behavior of ultra-soft mudstone from the Gaomiao landslide in Haidong City,Qinghai Province,China.Uniaxial creep tests were carried out on ultra-soft mudstone with various moisture contents.The test results indicated that the creep duration of the rock sample with a natural moisture content of 9%is 2400 times longer than that of the sample with a natural moisture content of 13%,while its accumulated strain is 70%of the latter.For the rock sample with a natural moisture content of 9.80%,the creep duration under 0.5 MPa load is 80%of that under 0.25 MPa load,yet the accumulated strain is 1.4 times greater.Additionally,porosity significantly influences the creep behavior of mudstone.Analysis of the cause of the Gaomiao landslide and field monitoring data indicates that the instability of the Gaomiao landslide is related to the moisture content of the landslip mass and external forces.The creep-slip curves of landslides and the creep deformation curves of rocks share a common trend.Precisely identifying the moment when the shift occurs from steady state creep to accelerated creep is critical for comprehending slope instability and rock failure.Moreover,this study delves deeper into the issue of the consistency between landslide creep and rock deformation.展开更多
In this article,we explored the role of adipose tissue,especially mesenteric adipose tissue and creeping fat,and its association with the gut microbiota in the pathophysiology and progression of Crohn’s disease(CD).C...In this article,we explored the role of adipose tissue,especially mesenteric adipose tissue and creeping fat,and its association with the gut microbiota in the pathophysiology and progression of Crohn’s disease(CD).CD is a form of inflammatory bowel disease characterized by chronic inflammation of the gastrointestinal tract,influenced by genetic predisposition,gut microbiota dysbiosis,and environmental factors.Gut microbiota plays a crucial role in modulating immune response and intestinal inflammation and is associated with the onset and progression of CD.Further,visceral adipose tissue,particularly creeping fat,a mesenteric adipose tissue characterized by hypertrophy and fibrosis,has been implicated in CD pathogenesis,inflammation,and fibrosis.The bacteria from the gut microbiota may translocate into mesenteric adipose tissue,contributing to the formation of creeping fat and influencing CD progression.Although creeping fat may be a protective barrier against bacterial invasion,its expansion can damage adjacent tissues,leading to complications.Modulating gut microbiota through interventions such as fecal microbiota transplantation,probiotics,and prebiotics has shown potential in managing CD.However,more research is needed to clarify the mechanisms linking gut dysbiosis,creeping fat,and CD progression and develop targeted therapies for microbiota modulation and fat-related complications in patients with CD.展开更多
Understanding the anisotropic creep behaviors of shale under direct shearing is a challenging issue.In this context,we conducted shear-creep and steady-creep tests on shale with five bedding orientations (i.e.0°,...Understanding the anisotropic creep behaviors of shale under direct shearing is a challenging issue.In this context,we conducted shear-creep and steady-creep tests on shale with five bedding orientations (i.e.0°,30°,45°,60°,and 90°),under multiple levels of direct shearing for the first time.The results show that the anisotropic creep of shale exhibits a significant stress-dependent behavior.Under a low shear stress,the creep compliance of shale increases linearly with the logarithm of time at all bedding orientations,and the increase depends on the bedding orientation and creep time.Under high shear stress conditions,the creep compliance of shale is minimal when the bedding orientation is 0°,and the steady-creep rate of shale increases significantly with increasing bedding orientations of 30°,45°,60°,and 90°.The stress-strain values corresponding to the inception of the accelerated creep stage show an increasing and then decreasing trend with the bedding orientation.A semilogarithmic model that could reflect the stress dependence of the steady-creep rate while considering the hardening and damage process is proposed.The model minimizes the deviation of the calculated steady-state creep rate from the observed value and reveals the behavior of the bedding orientation's influence on the steady-creep rate.The applicability of the five classical empirical creep models is quantitatively evaluated.It shows that the logarithmic model can well explain the experimental creep strain and creep rate,and it can accurately predict long-term shear creep deformation.Based on an improved logarithmic model,the variations in creep parameters with shear stress and bedding orientations are discussed.With abovementioned findings,a mathematical method for constructing an anisotropic shear creep model of shale is proposed,which can characterize the nonlinear dependence of the anisotropic shear creep behavior of shale on the bedding orientation.展开更多
Backfill is often employed in mining operations for ground support,with its positive impact on ground stability acknowledged in many underground mines.However,existing studies have predominantly focused only on the st...Backfill is often employed in mining operations for ground support,with its positive impact on ground stability acknowledged in many underground mines.However,existing studies have predominantly focused only on the stress development within the backfill material,leaving the influence of stope backfilling on stress distribution in surrounding rock mass and ground stability largely unexplored.Therefore,this paper presents numerical models in FLAC3D to investigate,for the first time,the time-dependent stress redistribution around a vertical backfilled stope and its implications on ground stability,considering the creep of surrounding rock mass.Using the Soft Soil constitutive model,the compressibility of backfill under large pressure was captured.It is found that the creep deformation of rock mass exercises compression on backfill and results in a less void ratio and increased modulus for fill material.The compacted backfill conversely influenced the stress distribution and ground stability of rock mass which was a combined effect of wall creep and compressibility of backfill.With the increase of time or/and creep deformation,the minimum principal stress in the rocks surrounding the backfilled stope increased towards the pre-mining stress state,while the deviatoric stress reduces leading to an increased factor of safety and improved ground stability.This improvement effect of backfill on ground stability increased with the increase of mine depth and stope height,while it is also more pronounced for the narrow stope,the backfill with a smaller compression index,and the soft rocks with a smaller viscosity coefficient.Furthermore,the results emphasize the importance of minimizing empty time and backfilling extracted stope as soon as possible for ground control.Reduction of filling gap height enhances the local stability around the roof of stope.展开更多
Investigating the combined effects of mining damage and creep damage on slope stability is crucial,as it can comprehensively reveal the non-linear deformation characteristics of rock under their joint influence.This s...Investigating the combined effects of mining damage and creep damage on slope stability is crucial,as it can comprehensively reveal the non-linear deformation characteristics of rock under their joint influence.This study develops a fractional-order nonlinear creep constitutive model that incorporates the double damage effect and implements a non-linear creep subroutine for soft rock using the threedimensional finite difference method on the FLAC3D platform.Comparative analysis of the theoretical,numerical,and experimental results reveals that the fractional-order constitutive model,which incorporates the double damage effect,accurately reflects the distinct deformation stages of green mudstone during creep failure and effectively captures the non-linear deformation in the accelerated creep phase.The numerical results show a fitting accuracy exceeding 97%with the creep test curves,significantly outperforming the 61%accuracy of traditional creep models.展开更多
Energy is an important resource that supports the development of human society,and energy security is even more relevant to the strength of a country.In order to ensure energy security,countries around the world are t...Energy is an important resource that supports the development of human society,and energy security is even more relevant to the strength of a country.In order to ensure energy security,countries around the world are taking measures to carry out energy transformation and construct new energy systems.As an important part of the new energy system,energy storage technology is highly valued by all countries.Among many large-scale energy storage technologies,salt cavern compressed air energy storage(CAES)technology stands out for its safety and economy,which is recognized and valued by scholars from various countries.For the construction of salt cavern CAES power station,it is very important to ensure the stability of salt cavern.Therefore,scholars have investigated the mechanical properties of salt rocks and the stability of salt caverns for CAES.This paper synthesizes the findings of current research on the creep and fatigue properties of salt rock,highlighting three key points:The factors influencing the creep and fatigue characteristics of salt rock include its composition,stress levels,and temperature.Notably,impurities and surrounding pressure tend to inhibit the deformation of salt rock,whereas elevated temperature and differential stress facilitate its deformation;The mechanisms governing creep and fatigue damage in salt rock are primarily associated with dislocation movement and microcracking;Most existing constitutive models for creep and fatigue are based on viscoelastic-plasticity theory,with fewer models derived from micro-mechanical perspectives.Additionally,this paper reviews studies on the stability of salt cavern CAES reservoirs utilizing numerical simulation methods and offers insights into future research directions concerning the creep and fatigue properties of salt rocks.展开更多
A new unified constitutive model was developed to predict the two-stage creep-aging(TSCA)behavior of Al-Zn-Mg-Cu alloys.The particular bimodal precipitation feature was analyzed and modeled by considering the primary ...A new unified constitutive model was developed to predict the two-stage creep-aging(TSCA)behavior of Al-Zn-Mg-Cu alloys.The particular bimodal precipitation feature was analyzed and modeled by considering the primary micro-variables evolution at different temperatures and their interaction.The dislocation density was incorporated into the model to capture the effect of creep deformation on precipitation.Quantitative transmission electron microscopy and experimental data obtained from a previous study were used to calibrate the model.Subsequently,the developed constitutive model was implemented in the finite element(FE)software ABAQUS via the user subroutines for TSCA process simulation and the springback prediction of an integral panel.A TSCA test was performed.The result shows that the maximum radius deviation between the formed plate and the simulation results is less than 0.4 mm,thus validating the effectiveness of the developed constitutive model and FE model.展开更多
Inflammatory bowel disease,particularly Crohn's disease(CD),has been linked to modifications in mesenteric adipose tissue(MAT)and the phenomenon known as"creeping fat"(CrF).The presence of CrF is believe...Inflammatory bowel disease,particularly Crohn's disease(CD),has been linked to modifications in mesenteric adipose tissue(MAT)and the phenomenon known as"creeping fat"(CrF).The presence of CrF is believed to serve as a predictor for early clinical recurrence following surgical intervention in patients with CD.Notably,the incorporation of the mesentery during ileocolic resection for CD has been correlated with a decrease in surgical recurrence,indicating the significant role of MAT in the pathogenesis of CD.While numerous studies have indicated that dysbiosis of the gut microbiota is a critical factor in the development of CD,the functional implications of translocated microbiota within the MAT of CD patients remain ambiguous.This manuscript commentary discusses a recent basic research conducted by Wu et al.In their study,intestinal bacteria from individuals were transplanted into CD model mice,revealing that fecal microbiota trans-plantation(FMT)from healthy donors alleviated CD symptoms,whereas FMT from CD patients exacerbated these symptoms.Importantly,FMT was found to affect intestinal permeability,barrier function,and the levels of proinflammatory factors and adipokines.Collectively,these findings suggest that targeting MAT and CrF may hold therapeutic potential for patients with CD.However,the study did not evaluate the composition of the intestinal microbiota of the donors or the subsequent alterations in the gut microbiota.Overall,the gut microbiota plays a crucial role in the histopathology of CD,and thus,targeting MAT and CrF may represent a promising avenue for treatment in this patient population.展开更多
The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the init...The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the initial stage of high-temperature creep,two sets of dislocations with different Burgers vectors move and meet inγmatrix channels,and react to form a quadrilateral dislocation network.Andγ′phases with raft-like microstructure are generated after the formation of dislocation networks.As creep progresses,the quadrilateral dislocation network is gradually transformed into hexagonal and quadrilateral dislocation networks.During steady stage of creep,the superalloy undergoes deformation with the mechanism that a great number of dislocations slip and climb in the matrix across the raft-likeγ′phases.At the later stage of creep,the raft-likeγ′phases are sheared by dislocations at the breakage of dislocation networks,and then alternate slip occurs,which distorts and breaks the raft-likeγ′/γphases,resulting in the accumulation of micropores at the raft-likeγ′/γinterfaces and the formation of microcracks.As creep continues,the microcracks continue to expand until creep fracture occurs,which is the damage and fracture mechanism of the alloy at the later stage of creep at high temperature.展开更多
Four powder metallurgy(PM)Ni-based superalloys with different Hf and Ta contents were creep-tested at 650℃ and 970 MPa,700℃ and 770 MPa,and 750℃ and 580 MPa,respectively.The effect of Hf and Ta on creep deformation...Four powder metallurgy(PM)Ni-based superalloys with different Hf and Ta contents were creep-tested at 650℃ and 970 MPa,700℃ and 770 MPa,and 750℃ and 580 MPa,respectively.The effect of Hf and Ta on creep deformation behaviors of the superalloys was studied from multiple scales by SEM,electron backscatter diffraction(EBSD),and aberration-corrected scanning transmission electron microscope(AC-STEM).The results showed that Hf and Ta suppressed the intergranular fracture and initiation of cracks during the acceleration creep stage,which prolonged the creep rupture time.Hf and Ta inhibited the stacking faults extending and the dislocation climbing and promoted the Suzuki segregation of W during the steady-state creep stage,which reduced the minimum creep rate and delayed the start time of the acceleration creep stage.The Suzuki segregation of Co,Cr,Mo,Ti,Nb,W,and Ta along stacking faults was observed after Hf and Ta addition,leading to the localized phase transformation in the γ′phase,and the stacking fault phase was chemically disordered.This study provided ideas for the composition design of novel PM Ni-based superalloys and theoretical foundations for the combined addition of Hf and Ta.展开更多
The tensile creep anisotropy of a dilute-alloyed Mg-0.3wt%Ca sheet is investigated along the rolling direction(RD)and normal direction(ND).Strong creep anisotropy is shown between the RD and ND,owing to the easy twinn...The tensile creep anisotropy of a dilute-alloyed Mg-0.3wt%Ca sheet is investigated along the rolling direction(RD)and normal direction(ND).Strong creep anisotropy is shown between the RD and ND,owing to the easy twinning and the Ca-segregation along twin boundaries during creep loading along the ND.To weaken the creep anisotropy,hot-compression parallel to the RD-ND plane is performed and the continuous dynamic recrystallization mechanism induces a bimodal microstructure with the coexistence of unrecrystallized and recrystallized grains.The creep anisotropy is successfully weakened after hot-compression,and the creep resistance is also significantly enhanced along both loading directions.With the assistance of microstructural characterization,the weakened creep anisotropy is ascribed to the dislocation arrays in the interiors of recrystallized grains and the Ca-segregation along the boundaries of recrystallized grains.Compared to commercial Mg alloys with poor creep property and rare-earth alloyed Mg with high price,good creep performance and low production cost can be synchronously realized in the hot-compressed Mg-0.3wt%Ca alloy.Thus,this work proposes a new perspective for producing creep-resistant Mg alloys.展开更多
Creep is one of the most typical failure modes for the turbine blades of an aero-engine.The microstructure of the turbine blades after long-term service can be adjusted by rejuvenation heat treatment(RHT)to restore it...Creep is one of the most typical failure modes for the turbine blades of an aero-engine.The microstructure of the turbine blades after long-term service can be adjusted by rejuvenation heat treatment(RHT)to restore its creep properties.In this work,a series of RHT experiments were carried out on a directionally solidified(DS)nickel-based superalloy under different solution temperatures and primary aging temperatures based on the standard heat treatment(SHT)process parameters to investigate the mechanism of temperature influence on DS's microstructure after RHT.It is indicated that a more uniform microstructure can be obtained under higher solution temperatures and lower primary aging temperatures compared to the SHT process.Furthermore,by employing the image processing methods to quantify microstructural parameters,a comprehensive indicator parameter for the RHT effect(marked as Prej)was proposed to characterize the effects of RHT on DS superalloy's microstructure and creep property combined with the entropy weight method.Based on this,a regression model to describe the relationship between RHT process parameters and Prej was constructed by using the response surface methodology(RSM).It is revealed that the optimal solution temperature and primary aging temperature for this DS superalloy are 1283°C and 1095°C,respectively.Then the conclusion was validated through complete creep experiments on the DS superalloy,which showed the creep life after RHT reaches 95.5%of the SHT specimen,and the total life has increased by 20.6%.展开更多
Purpose–Severe scarcity of natural river sand(RS),exacerbated by environmental protection policies and extraction constraints,has significantly impacted aggregate supply for railway concrete.While manufactured sand(M...Purpose–Severe scarcity of natural river sand(RS),exacerbated by environmental protection policies and extraction constraints,has significantly impacted aggregate supply for railway concrete.While manufactured sand(MS)offers a substitute for RS in railway applications,its widespread adoption in high-strength railway prestressed structures is challenged by lack of drying shrinkage and creep research data on concrete.Design/methodology/approach–High-strength manufactured sand concrete(MSC)was prepared using MS with varying lithologies and stone powder contents.Its drying shrinkage and creep behaviors were evaluated in accordance with the Chinese standard GB/T 50082.The deformation mechanism was analyzed by combining nano-scratch testing.Findings–Compared to RS concrete,MSC from all tested lithologies showed higher drying shrinkage but lower creep deformation.The drying shrinkage rose steadily with increased stone powder content,while the creep strain displayed a distinct non-linear trend,decreasing first before rising.To prepare low-deformation MSC,select high-strength MS and limit stone powder content not greater 10%.Nano-scratch tests indicated that harder MS particles suppress microcracking at the interfacial transition zone(ITZ),improving the creep resistance.The predictive models for drying shrinkage and creep were also developed by incorporating coefficients for stone powder and lithology effects.Originality/value–These findings serve as a foundation for the application of MSC in railway prestressed structures,offering both theoretical and practical guidance.展开更多
The creep behavior of two PM superalloys,U720Li and RR1000,each alloyed with trace amount of Sc,was systematically investigated.Findings reveal that RR1000 alloy with 0.064 wt.%Sc(R-0.064)demonstrates superior creep r...The creep behavior of two PM superalloys,U720Li and RR1000,each alloyed with trace amount of Sc,was systematically investigated.Findings reveal that RR1000 alloy with 0.064 wt.%Sc(R-0.064)demonstrates superior creep resistance compared to U720Li alloy with 0.043 wt.%Sc(U-0.043),at 650℃ and 1000 MPa,and the primary creep mechanisms in both alloys are identified as dislocation shearing and precipitate bypassing.When tested at 700℃ and 700 MPa,the U-0.043 alloy predominantly exhibits micro-twinning and dislocation bypassing,while the R-0.064 alloy engages in extended stacking fault shearing ofγ'precipitate,dislocation bypassing and climb.At 750℃ and 460 MPa,dislocation bypassing and climb emerge as the main creep mechanisms for both alloys.展开更多
The limited creep resistance of wrought Mg-Al alloys restricts their lightweight applications at intermediate temperatures due to the softening effect of discontinuous precipitation(DP)on the dislocation-controlled cr...The limited creep resistance of wrought Mg-Al alloys restricts their lightweight applications at intermediate temperatures due to the softening effect of discontinuous precipitation(DP)on the dislocation-controlled creep.Here,we developed a creep-resistant wrought Mg-Al alloy through microalloying of Y and Ca.The resulting alloy exhibited an order of magnitude enhancement in the creep resistance at 125℃/50±100 MPa.In contrast to the grain boundary instabilities by DP in the previously reported wrought Mg-Al alloys,we show that the addition of 0.21Y+0.15Ca wt%produces a(Zn+Ca)co-segregation at the grain boundaries as a result of their segregation energy and the activation energy of grain boundary migration,thereby stabilizing the grain boundaries.The(Zn+Ca)co-segregation inhibits the dynamic DP and promotes the formation of intragranular Al-enriched clusters,which favorthe formation of Al_(2)Y,Mg_(17)Al_(12)nano precipitates,thereby impeding intragranular dislocation motion during creep.Furthermore,the addition of 0.21Y+0.15Ca wt%facilitates the formation of a fine and uniform recrystallization structure in the microalloyed alloys compared to AZ80 due to the high activation energy of mobility for the(Zn+Ca)segregated grain boundary.Therefore,the microalloyed alloys exhibit good tensile properties with 380 MPa tensile strength and 18%elongation.Our constitutive analysis revealed that the(Y+Ca)microalloying decreased the creep stress exponent by 29%and increased the creep resistance in the medium to high-stress range.Microalloying provides a promising way to develop low-cost creep-resistant wrought Mg-Al alloys.展开更多
The creep phenomenon of inelastic deformation of surrounding rock may occur under the action of deepgeological stress for a long period of time,potentially resulting in large-scale deformations or eveninstability fail...The creep phenomenon of inelastic deformation of surrounding rock may occur under the action of deepgeological stress for a long period of time,potentially resulting in large-scale deformations or eveninstability failure of the underground engineering.Accurate characterization of the creep behavior of thesurrounding rock is essential for evaluating the long-term stability and safety of high-level radioactivewaste(HLW)disposal repositories.Although the laboratory creep tests of brittle undamaged rocks,suchas granite,have been extensively performed,the creep characteristics of fractured surrounding rockunder the multi-field coupling environment still require attention.In this study,a series of creep experimentswas conducted on Beishan granite,which was identified as the optimal candidate surroundingrock for the disposal repository in China.The effects of various factors,including inclination angle offractures,stress conditions,temperatures,and water content,were investigated.The experimental resultsshow that the axial total strain increases linearly with increasing stress level,while the lateral totalstrain,axial and lateral creep strain rates increase exponentially.The failure time of saturated specimensfractured at 45°and 60°is approximately 1.05‰and 0.84‰of that of dry specimens,respectively.Theeffect of temperature,ranging from room temperature to 120℃,is minimal,compared to the substantialvariations in strain and creep rates caused by stress and water content.The creep failure of specimensfractured at 30°is dominated by rock material failure,whereas the creep failure of specimens fractured at60°is dominated by pre-existing fracture slip.At a 45°fracture angle,a composite failure mechanism isobserved that includes both rock material failure and pre-existing fracture slip.展开更多
γʹvolume fraction(fv)plays a critical role in the mechanical properties of Ni-based single-crystal superalloys.A creep phase-field model is utilized to simulate the microstructure evolution and creep performance duri...γʹvolume fraction(fv)plays a critical role in the mechanical properties of Ni-based single-crystal superalloys.A creep phase-field model is utilized to simulate the microstructure evolution and creep performance during creep under different fv conditions.The influence mechanism of fv on creep properties is investigated based on the analysis of evolutions of internal stress and strain fields.As fv increases,the morphology ofγʹrafts changes from discontinuous to continuous,while the morphological change ofγchannels is opposite,the inclination ofγchannels from the[010]direction to(011)directions during tertiary creep first decreases and then increases,the creep life first increases and then decreases,and the main distribution of creep damage shifts fromγʹtoγʹ/γinterfaces andγchannels.The longest creep life under fv of 0.65 can be attributed to the stableγʹraft structure,the lowest stress and strain inγchannels,and the slowest damage accumulation.展开更多
基金Projects(52174096, 52304110) supported by the National Natural Science Foundation of China。
文摘Water is a critical factor affecting the mechanical properties of rocks, leading to their degradation. Understanding the creep mechanical behavior of deep roadway surrounding rock under the influence of underground water is of great significance. Compression and creep experiments on sandstone with varying water contents were conducted using a deep soft rock five-linked rheological experiment system. The experimental conditions, including water content (0%, 0.8%, 1.6%, 2.4% and 3.3%) and confining pressure (0, 6, 9 and 12 MPa), were determined based on pressure-free water absorption tests and in-situ stress measurements. The experimental results show that the compressive strength, creep failure stress, and dilatancy stress of sandstone decrease exponentially with increasing water content, while they increase exponentially with confining pressure. The ratio of lateral to axial instantaneous strain increases nearly linearly with the increase of stress, and the lateral creep strain characteristics of the sample are more significant than the axial ones. The duration of the attenuation creep stage of sandstone decreases with increasing water content and increases with increasing confining pressure. The lateral strain enters the steady-state creep stage before the axial strain, and the onset time of the accelerated creep stage of lateral strain under the failure stress is earlier than that of axial strain. The long-term strength of sandstone was determined based on the lateral steady-state creep rate curve, showing a negative exponential relationship with water content and a positive exponential relationship with confining pressure. A method for determining the long-term strength of rocks based on the ratio of lateral strain to axial strain (μc) is proposed, which is independent of water content. The research results provide a reliable theoretical basis for the analysis of the long-term stability of roadways under the influence of groundwater and the early prediction of creep failure.
基金We gratefully acknowledge the financial support from the Key Laboratory of Geological Safety of Coastal Urban Underground Space,Ministry of Natural Resources(BHKF2022Y03)Shandong Provincial Colleges and Universities Youth Innovation Technology Support Program,Education Department of Shandong Province(grant number 2023KJ092).
文摘The study focuses on the creep characteristics of significant yellow sandstone for water conservancy, hydropower, and other waterrelated slope excavation unloading rock-graded loading creep characteristics. It conducts a uniaxial graded loading creep test on yellow sandstone under different pre-peak unloading and wetting-drying cycles. The improved nonlinear Nishihara model was obtained by introducing a nonlinear viscous element with an accelerated creep threshold switch. The sensitivity characteristics of the parameters of the improved creep model were analyzed and a nonlinear creep constitutive model was established, considering the unloading-cyclic intrinsic damage induced by water intrusion. The research results show that:(1)With an increase in the unloading point, the porosity of the rock samples initially decreases and then increases. As the number of cyclic water intrusions rises, the porosity of the rock samples gradually increases, reaching a maximum of 9.58% at an unloading point of 70% uniaxial compression stress(0.7 Rc) after five cycles.(2) Total creep deformation increases with the number of cyclic water intrusions;however, with an increase in the unloading ratio, the original samples show an initial decrease, followed by an increase in creep deformation. With a higher unloading ratio and various instances of cyclic water intrusion, the total creep time of the rock samples,compared to the original samples, is reduced by 21.8%and 23.02%. The creep damage mode gradually changes from shear damage to tensile damage.(3) The sensitivity characteristics of the improved creep model parameters show that transient elasticity modulus E1 is affected by the coupling of unloading and cyclic water intrusion. The viscoelastic modulus E2 and viscous coefficient η1 are mainly affected by unloading and cyclic water intrusion.(4) Based on the strain equivalence principle of damage mechanics, the damage treatment of the parameters in the original model is improved to construct a nonlinear creep constitutive model that considers unloading-cyclic water intrusion damage. A parameter inversion and comparison to the traditional Nishihara model reveal an average relative standard deviation of 0.271%,significantly less than 1%, indicating a more accurate nonlinear creep constitutive model. The research results are crucial for analyzing the long-term stability of water-related steep rocky slopes post-excavation and unloading and for preventing and controlling creep-type landslide disasters.
基金funded by the Natural Science Foundation of China(Grant No.U22A20600)。
文摘Existing creep constitutive models rarely incorporate studies on the coupling mechanism between creep damage and rock strain softening/hardening.This study analyzed the strain softening and hardening behaviors of argillaceous sandstone and sandy mudstone during load-induced failure based on the plastic increment theory.These behaviors were then coupled with an improved Burgers creep model to establish a coupled creep-damage and plastic softening/hardening model.Finally,the validity and engineering applicability of the proposed model were verified through FLAC~(3D)numerical simulations.The numerical simulation results of standard cylindrical specimens show that the established coupling model can effectively reflect the unloading creep deformation law and failure characteristics of argillaceous sandstone and sandy mudstone.Taking the diversion tunnel of a hydropower station in Northwest China as an example for engineering application,the coupled creep-damage and plastic softening/hardening model is introduced into FLAC~(3D)to carry out numerical simulation calculation of the tunnel under excavation and unsupported creep conditions.The results show that the uncoordinated deformation of the upper and lower walls of the surrounding rock of the tunnel is more prominent.When the buried depth of the tunnel increases to 80 m,the monitoring point C in the sandy mudstone area of the upper wall shows nonlinear accelerated deformation under unsupported creep conditions,and the maximum displacement in the horizontal direction reaches 44.5 mm,and the maximum displacement in the vertical direction reaches 53.5 mm.The coupled creep-damage and plastic softening/hardening model established in the research results can well describe the whole process of uncoordinated deformation and failure in the unloading creep process of soft-hard interbedded rock mass.
基金The work described in this paper is partially supported by the Second Tibetan Plateau Scientific Expedition and Research Grant(2019QZKK0708)ARC Discovery Project grants(DP210100437,DP230100126),for which the authors are very grateful.
文摘The creep-slip behavior of creeping landslides is closely related to the creep characteristics of slope rock.This study analyzed the creep behavior of ultra-soft mudstone from the Gaomiao landslide in Haidong City,Qinghai Province,China.Uniaxial creep tests were carried out on ultra-soft mudstone with various moisture contents.The test results indicated that the creep duration of the rock sample with a natural moisture content of 9%is 2400 times longer than that of the sample with a natural moisture content of 13%,while its accumulated strain is 70%of the latter.For the rock sample with a natural moisture content of 9.80%,the creep duration under 0.5 MPa load is 80%of that under 0.25 MPa load,yet the accumulated strain is 1.4 times greater.Additionally,porosity significantly influences the creep behavior of mudstone.Analysis of the cause of the Gaomiao landslide and field monitoring data indicates that the instability of the Gaomiao landslide is related to the moisture content of the landslip mass and external forces.The creep-slip curves of landslides and the creep deformation curves of rocks share a common trend.Precisely identifying the moment when the shift occurs from steady state creep to accelerated creep is critical for comprehending slope instability and rock failure.Moreover,this study delves deeper into the issue of the consistency between landslide creep and rock deformation.
基金Supported by the Postdoctoral Scholarship Grant,No.5552/2024 PROPG/PROPE N°06/2024.
文摘In this article,we explored the role of adipose tissue,especially mesenteric adipose tissue and creeping fat,and its association with the gut microbiota in the pathophysiology and progression of Crohn’s disease(CD).CD is a form of inflammatory bowel disease characterized by chronic inflammation of the gastrointestinal tract,influenced by genetic predisposition,gut microbiota dysbiosis,and environmental factors.Gut microbiota plays a crucial role in modulating immune response and intestinal inflammation and is associated with the onset and progression of CD.Further,visceral adipose tissue,particularly creeping fat,a mesenteric adipose tissue characterized by hypertrophy and fibrosis,has been implicated in CD pathogenesis,inflammation,and fibrosis.The bacteria from the gut microbiota may translocate into mesenteric adipose tissue,contributing to the formation of creeping fat and influencing CD progression.Although creeping fat may be a protective barrier against bacterial invasion,its expansion can damage adjacent tissues,leading to complications.Modulating gut microbiota through interventions such as fecal microbiota transplantation,probiotics,and prebiotics has shown potential in managing CD.However,more research is needed to clarify the mechanisms linking gut dysbiosis,creeping fat,and CD progression and develop targeted therapies for microbiota modulation and fat-related complications in patients with CD.
基金funded by the National Natural Science Foundation of China(Grant Nos.U22A20166 and 12172230)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2023A1515012654)+1 种基金funded by the National Natural Science Foundation of China(Grant Nos.U22A20166 and 12172230)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2023A1515012654)。
文摘Understanding the anisotropic creep behaviors of shale under direct shearing is a challenging issue.In this context,we conducted shear-creep and steady-creep tests on shale with five bedding orientations (i.e.0°,30°,45°,60°,and 90°),under multiple levels of direct shearing for the first time.The results show that the anisotropic creep of shale exhibits a significant stress-dependent behavior.Under a low shear stress,the creep compliance of shale increases linearly with the logarithm of time at all bedding orientations,and the increase depends on the bedding orientation and creep time.Under high shear stress conditions,the creep compliance of shale is minimal when the bedding orientation is 0°,and the steady-creep rate of shale increases significantly with increasing bedding orientations of 30°,45°,60°,and 90°.The stress-strain values corresponding to the inception of the accelerated creep stage show an increasing and then decreasing trend with the bedding orientation.A semilogarithmic model that could reflect the stress dependence of the steady-creep rate while considering the hardening and damage process is proposed.The model minimizes the deviation of the calculated steady-state creep rate from the observed value and reveals the behavior of the bedding orientation's influence on the steady-creep rate.The applicability of the five classical empirical creep models is quantitatively evaluated.It shows that the logarithmic model can well explain the experimental creep strain and creep rate,and it can accurately predict long-term shear creep deformation.Based on an improved logarithmic model,the variations in creep parameters with shear stress and bedding orientations are discussed.With abovementioned findings,a mathematical method for constructing an anisotropic shear creep model of shale is proposed,which can characterize the nonlinear dependence of the anisotropic shear creep behavior of shale on the bedding orientation.
基金the funding support from the National Natural Science Foundation of China(Grant Nos.52304101 and 52004206)the China Postdoctoral Science Foundation(Grant No.2023MD734215)。
文摘Backfill is often employed in mining operations for ground support,with its positive impact on ground stability acknowledged in many underground mines.However,existing studies have predominantly focused only on the stress development within the backfill material,leaving the influence of stope backfilling on stress distribution in surrounding rock mass and ground stability largely unexplored.Therefore,this paper presents numerical models in FLAC3D to investigate,for the first time,the time-dependent stress redistribution around a vertical backfilled stope and its implications on ground stability,considering the creep of surrounding rock mass.Using the Soft Soil constitutive model,the compressibility of backfill under large pressure was captured.It is found that the creep deformation of rock mass exercises compression on backfill and results in a less void ratio and increased modulus for fill material.The compacted backfill conversely influenced the stress distribution and ground stability of rock mass which was a combined effect of wall creep and compressibility of backfill.With the increase of time or/and creep deformation,the minimum principal stress in the rocks surrounding the backfilled stope increased towards the pre-mining stress state,while the deviatoric stress reduces leading to an increased factor of safety and improved ground stability.This improvement effect of backfill on ground stability increased with the increase of mine depth and stope height,while it is also more pronounced for the narrow stope,the backfill with a smaller compression index,and the soft rocks with a smaller viscosity coefficient.Furthermore,the results emphasize the importance of minimizing empty time and backfilling extracted stope as soon as possible for ground control.Reduction of filling gap height enhances the local stability around the roof of stope.
基金support from the National Natural Science Foundation of China(No.52308316)the Scientific Research Foundation of Weifang University(Grant No.2024BS42)+2 种基金China Postdoctoral Science Foundation(No.2022M721885)the Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province(No.ZJRMG-2022-01)supported by Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences(NO.SKLGME023017).
文摘Investigating the combined effects of mining damage and creep damage on slope stability is crucial,as it can comprehensively reveal the non-linear deformation characteristics of rock under their joint influence.This study develops a fractional-order nonlinear creep constitutive model that incorporates the double damage effect and implements a non-linear creep subroutine for soft rock using the threedimensional finite difference method on the FLAC3D platform.Comparative analysis of the theoretical,numerical,and experimental results reveals that the fractional-order constitutive model,which incorporates the double damage effect,accurately reflects the distinct deformation stages of green mudstone during creep failure and effectively captures the non-linear deformation in the accelerated creep phase.The numerical results show a fitting accuracy exceeding 97%with the creep test curves,significantly outperforming the 61%accuracy of traditional creep models.
基金supported by the Natural Science Fund of China(No.51834003,52274073,52022014).
文摘Energy is an important resource that supports the development of human society,and energy security is even more relevant to the strength of a country.In order to ensure energy security,countries around the world are taking measures to carry out energy transformation and construct new energy systems.As an important part of the new energy system,energy storage technology is highly valued by all countries.Among many large-scale energy storage technologies,salt cavern compressed air energy storage(CAES)technology stands out for its safety and economy,which is recognized and valued by scholars from various countries.For the construction of salt cavern CAES power station,it is very important to ensure the stability of salt cavern.Therefore,scholars have investigated the mechanical properties of salt rocks and the stability of salt caverns for CAES.This paper synthesizes the findings of current research on the creep and fatigue properties of salt rock,highlighting three key points:The factors influencing the creep and fatigue characteristics of salt rock include its composition,stress levels,and temperature.Notably,impurities and surrounding pressure tend to inhibit the deformation of salt rock,whereas elevated temperature and differential stress facilitate its deformation;The mechanisms governing creep and fatigue damage in salt rock are primarily associated with dislocation movement and microcracking;Most existing constitutive models for creep and fatigue are based on viscoelastic-plasticity theory,with fewer models derived from micro-mechanical perspectives.Additionally,this paper reviews studies on the stability of salt cavern CAES reservoirs utilizing numerical simulation methods and offers insights into future research directions concerning the creep and fatigue properties of salt rocks.
基金supported by the National Key R&D Program of China(No.2021YFB3400900)the National Natural Science Foundation of China(Nos.52175373,52205435)+1 种基金Natural Science Foundation of Hunan Province,China(No.2022JJ40621)the Innovation Fund of National Commercial Aircraft Manufacturing Engineering Technology Center,China(No.COMACSFGS-2022-1875)。
文摘A new unified constitutive model was developed to predict the two-stage creep-aging(TSCA)behavior of Al-Zn-Mg-Cu alloys.The particular bimodal precipitation feature was analyzed and modeled by considering the primary micro-variables evolution at different temperatures and their interaction.The dislocation density was incorporated into the model to capture the effect of creep deformation on precipitation.Quantitative transmission electron microscopy and experimental data obtained from a previous study were used to calibrate the model.Subsequently,the developed constitutive model was implemented in the finite element(FE)software ABAQUS via the user subroutines for TSCA process simulation and the springback prediction of an integral panel.A TSCA test was performed.The result shows that the maximum radius deviation between the formed plate and the simulation results is less than 0.4 mm,thus validating the effectiveness of the developed constitutive model and FE model.
文摘Inflammatory bowel disease,particularly Crohn's disease(CD),has been linked to modifications in mesenteric adipose tissue(MAT)and the phenomenon known as"creeping fat"(CrF).The presence of CrF is believed to serve as a predictor for early clinical recurrence following surgical intervention in patients with CD.Notably,the incorporation of the mesentery during ileocolic resection for CD has been correlated with a decrease in surgical recurrence,indicating the significant role of MAT in the pathogenesis of CD.While numerous studies have indicated that dysbiosis of the gut microbiota is a critical factor in the development of CD,the functional implications of translocated microbiota within the MAT of CD patients remain ambiguous.This manuscript commentary discusses a recent basic research conducted by Wu et al.In their study,intestinal bacteria from individuals were transplanted into CD model mice,revealing that fecal microbiota trans-plantation(FMT)from healthy donors alleviated CD symptoms,whereas FMT from CD patients exacerbated these symptoms.Importantly,FMT was found to affect intestinal permeability,barrier function,and the levels of proinflammatory factors and adipokines.Collectively,these findings suggest that targeting MAT and CrF may hold therapeutic potential for patients with CD.However,the study did not evaluate the composition of the intestinal microbiota of the donors or the subsequent alterations in the gut microbiota.Overall,the gut microbiota plays a crucial role in the histopathology of CD,and thus,targeting MAT and CrF may represent a promising avenue for treatment in this patient population.
基金Guizhou Province Science and Technology Plan Project(QKHJC-ZK[2024]yiban604)Guizhou Province Science and Technology Plan Project(CXTD[2021]008)+4 种基金Bijie City Science and Technology Project(BKLH[2023]9)Technology Project of Bijie City(BKLH[2023]36)Natural Science Research Project of Guizhou Higher Education Institutions of China(QJJ[2023]047)Science and Technology Project of Guizhou Department of Transportation(2022-121-011)Sanmenxia City Science and Technology Bureau Science and Technology Research Project(2022002005)。
文摘The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the initial stage of high-temperature creep,two sets of dislocations with different Burgers vectors move and meet inγmatrix channels,and react to form a quadrilateral dislocation network.Andγ′phases with raft-like microstructure are generated after the formation of dislocation networks.As creep progresses,the quadrilateral dislocation network is gradually transformed into hexagonal and quadrilateral dislocation networks.During steady stage of creep,the superalloy undergoes deformation with the mechanism that a great number of dislocations slip and climb in the matrix across the raft-likeγ′phases.At the later stage of creep,the raft-likeγ′phases are sheared by dislocations at the breakage of dislocation networks,and then alternate slip occurs,which distorts and breaks the raft-likeγ′/γphases,resulting in the accumulation of micropores at the raft-likeγ′/γinterfaces and the formation of microcracks.As creep continues,the microcracks continue to expand until creep fracture occurs,which is the damage and fracture mechanism of the alloy at the later stage of creep at high temperature.
基金financially supported by the National Science and Technology Major Project of China(No.2017-Ⅵ-0008-0078)。
文摘Four powder metallurgy(PM)Ni-based superalloys with different Hf and Ta contents were creep-tested at 650℃ and 970 MPa,700℃ and 770 MPa,and 750℃ and 580 MPa,respectively.The effect of Hf and Ta on creep deformation behaviors of the superalloys was studied from multiple scales by SEM,electron backscatter diffraction(EBSD),and aberration-corrected scanning transmission electron microscope(AC-STEM).The results showed that Hf and Ta suppressed the intergranular fracture and initiation of cracks during the acceleration creep stage,which prolonged the creep rupture time.Hf and Ta inhibited the stacking faults extending and the dislocation climbing and promoted the Suzuki segregation of W during the steady-state creep stage,which reduced the minimum creep rate and delayed the start time of the acceleration creep stage.The Suzuki segregation of Co,Cr,Mo,Ti,Nb,W,and Ta along stacking faults was observed after Hf and Ta addition,leading to the localized phase transformation in the γ′phase,and the stacking fault phase was chemically disordered.This study provided ideas for the composition design of novel PM Ni-based superalloys and theoretical foundations for the combined addition of Hf and Ta.
基金financial supports received from the National Key Research and Development Program of China(No.2022YFE0109600)the Science and Technology Innovation Program of Hunan Province(No.2024RC3010)the National Natural Science Foundation of China(No.51974376).
文摘The tensile creep anisotropy of a dilute-alloyed Mg-0.3wt%Ca sheet is investigated along the rolling direction(RD)and normal direction(ND).Strong creep anisotropy is shown between the RD and ND,owing to the easy twinning and the Ca-segregation along twin boundaries during creep loading along the ND.To weaken the creep anisotropy,hot-compression parallel to the RD-ND plane is performed and the continuous dynamic recrystallization mechanism induces a bimodal microstructure with the coexistence of unrecrystallized and recrystallized grains.The creep anisotropy is successfully weakened after hot-compression,and the creep resistance is also significantly enhanced along both loading directions.With the assistance of microstructural characterization,the weakened creep anisotropy is ascribed to the dislocation arrays in the interiors of recrystallized grains and the Ca-segregation along the boundaries of recrystallized grains.Compared to commercial Mg alloys with poor creep property and rare-earth alloyed Mg with high price,good creep performance and low production cost can be synchronously realized in the hot-compressed Mg-0.3wt%Ca alloy.Thus,this work proposes a new perspective for producing creep-resistant Mg alloys.
基金Supported by National Natural Science Foundation of China(Grant No.52275142)Science Center for Gas Turbine Project(Grant Nos.P2022-AIII-003-001,P2022-B-III-005-001)+1 种基金National Science and Technology Major Project(Grant Nos.J2019-IV-0009-0077,Y2022-IV-0002-0019,J2019-IV-0008-0076)National Basic Scientific Research Project(Grant No.JCKY2021601B204)。
文摘Creep is one of the most typical failure modes for the turbine blades of an aero-engine.The microstructure of the turbine blades after long-term service can be adjusted by rejuvenation heat treatment(RHT)to restore its creep properties.In this work,a series of RHT experiments were carried out on a directionally solidified(DS)nickel-based superalloy under different solution temperatures and primary aging temperatures based on the standard heat treatment(SHT)process parameters to investigate the mechanism of temperature influence on DS's microstructure after RHT.It is indicated that a more uniform microstructure can be obtained under higher solution temperatures and lower primary aging temperatures compared to the SHT process.Furthermore,by employing the image processing methods to quantify microstructural parameters,a comprehensive indicator parameter for the RHT effect(marked as Prej)was proposed to characterize the effects of RHT on DS superalloy's microstructure and creep property combined with the entropy weight method.Based on this,a regression model to describe the relationship between RHT process parameters and Prej was constructed by using the response surface methodology(RSM).It is revealed that the optimal solution temperature and primary aging temperature for this DS superalloy are 1283°C and 1095°C,respectively.Then the conclusion was validated through complete creep experiments on the DS superalloy,which showed the creep life after RHT reaches 95.5%of the SHT specimen,and the total life has increased by 20.6%.
基金supported by National Natural Science Foundation of China(award no.52408309)National Natural Science Foundation of China(award no.52438002).
文摘Purpose–Severe scarcity of natural river sand(RS),exacerbated by environmental protection policies and extraction constraints,has significantly impacted aggregate supply for railway concrete.While manufactured sand(MS)offers a substitute for RS in railway applications,its widespread adoption in high-strength railway prestressed structures is challenged by lack of drying shrinkage and creep research data on concrete.Design/methodology/approach–High-strength manufactured sand concrete(MSC)was prepared using MS with varying lithologies and stone powder contents.Its drying shrinkage and creep behaviors were evaluated in accordance with the Chinese standard GB/T 50082.The deformation mechanism was analyzed by combining nano-scratch testing.Findings–Compared to RS concrete,MSC from all tested lithologies showed higher drying shrinkage but lower creep deformation.The drying shrinkage rose steadily with increased stone powder content,while the creep strain displayed a distinct non-linear trend,decreasing first before rising.To prepare low-deformation MSC,select high-strength MS and limit stone powder content not greater 10%.Nano-scratch tests indicated that harder MS particles suppress microcracking at the interfacial transition zone(ITZ),improving the creep resistance.The predictive models for drying shrinkage and creep were also developed by incorporating coefficients for stone powder and lithology effects.Originality/value–These findings serve as a foundation for the application of MSC in railway prestressed structures,offering both theoretical and practical guidance.
基金supported by the Natural Science Foundation of China(No.52074366)the Top Ten Science and Technology Projects in Hunan Province,China(No.2024GK1080)+4 种基金the Aero Engine Corporation of China(No.HFZL2022CXY029)the Young Elite Scientists Sponsorship Program by CAST,China(No.2022QNRC001)the Natural Science Foundation of Hunan Province,China(No.2021JJ40757)the Science and Technology Innovation Program of Hunan Province,China(No.2021RC3131)the High Performance Computing Center of Central South University,and the Project supported by State Key Laboratory of Powder Metallurgy,Central South University,China.
文摘The creep behavior of two PM superalloys,U720Li and RR1000,each alloyed with trace amount of Sc,was systematically investigated.Findings reveal that RR1000 alloy with 0.064 wt.%Sc(R-0.064)demonstrates superior creep resistance compared to U720Li alloy with 0.043 wt.%Sc(U-0.043),at 650℃ and 1000 MPa,and the primary creep mechanisms in both alloys are identified as dislocation shearing and precipitate bypassing.When tested at 700℃ and 700 MPa,the U-0.043 alloy predominantly exhibits micro-twinning and dislocation bypassing,while the R-0.064 alloy engages in extended stacking fault shearing ofγ'precipitate,dislocation bypassing and climb.At 750℃ and 460 MPa,dislocation bypassing and climb emerge as the main creep mechanisms for both alloys.
基金financial support from the National Natural Science Foundation of China(No:52061040,No:52371121,No:52031011)China Postdoctoral Science Foundation(No:2021M692512)the 2020 open projects(No:KLATM202003)of Key Laboratory of Advanced Technologies of Materials,Ministry of Education China,Southwest Jiaotong University。
文摘The limited creep resistance of wrought Mg-Al alloys restricts their lightweight applications at intermediate temperatures due to the softening effect of discontinuous precipitation(DP)on the dislocation-controlled creep.Here,we developed a creep-resistant wrought Mg-Al alloy through microalloying of Y and Ca.The resulting alloy exhibited an order of magnitude enhancement in the creep resistance at 125℃/50±100 MPa.In contrast to the grain boundary instabilities by DP in the previously reported wrought Mg-Al alloys,we show that the addition of 0.21Y+0.15Ca wt%produces a(Zn+Ca)co-segregation at the grain boundaries as a result of their segregation energy and the activation energy of grain boundary migration,thereby stabilizing the grain boundaries.The(Zn+Ca)co-segregation inhibits the dynamic DP and promotes the formation of intragranular Al-enriched clusters,which favorthe formation of Al_(2)Y,Mg_(17)Al_(12)nano precipitates,thereby impeding intragranular dislocation motion during creep.Furthermore,the addition of 0.21Y+0.15Ca wt%facilitates the formation of a fine and uniform recrystallization structure in the microalloyed alloys compared to AZ80 due to the high activation energy of mobility for the(Zn+Ca)segregated grain boundary.Therefore,the microalloyed alloys exhibit good tensile properties with 380 MPa tensile strength and 18%elongation.Our constitutive analysis revealed that the(Y+Ca)microalloying decreased the creep stress exponent by 29%and increased the creep resistance in the medium to high-stress range.Microalloying provides a promising way to develop low-cost creep-resistant wrought Mg-Al alloys.
基金supported by the National Natural Science Foundation of China(Grant No.42307258)the China Atomic Energy Authority(CAEA)through the Geological Disposal Program,and the Science and Technology Department of Sichuan Province Project,China(Grant No.2023ZYD0154).
文摘The creep phenomenon of inelastic deformation of surrounding rock may occur under the action of deepgeological stress for a long period of time,potentially resulting in large-scale deformations or eveninstability failure of the underground engineering.Accurate characterization of the creep behavior of thesurrounding rock is essential for evaluating the long-term stability and safety of high-level radioactivewaste(HLW)disposal repositories.Although the laboratory creep tests of brittle undamaged rocks,suchas granite,have been extensively performed,the creep characteristics of fractured surrounding rockunder the multi-field coupling environment still require attention.In this study,a series of creep experimentswas conducted on Beishan granite,which was identified as the optimal candidate surroundingrock for the disposal repository in China.The effects of various factors,including inclination angle offractures,stress conditions,temperatures,and water content,were investigated.The experimental resultsshow that the axial total strain increases linearly with increasing stress level,while the lateral totalstrain,axial and lateral creep strain rates increase exponentially.The failure time of saturated specimensfractured at 45°and 60°is approximately 1.05‰and 0.84‰of that of dry specimens,respectively.Theeffect of temperature,ranging from room temperature to 120℃,is minimal,compared to the substantialvariations in strain and creep rates caused by stress and water content.The creep failure of specimensfractured at 30°is dominated by rock material failure,whereas the creep failure of specimens fractured at60°is dominated by pre-existing fracture slip.At a 45°fracture angle,a composite failure mechanism isobserved that includes both rock material failure and pre-existing fracture slip.
基金the supports provided by the National Natural Science Foundation of China(Nos.52301171,52031012,51971174)the National Science and Technology Major Project,China(Nos.2019-VI-0020-0135)+1 种基金the Key Research and Development Program of Shaanxi Province,China(No.2020ZDLGY13-02)the Research Fund of the State Key Laboratory of Solidification Processing(NPU),China(No.2022-TZ-01)。
文摘γʹvolume fraction(fv)plays a critical role in the mechanical properties of Ni-based single-crystal superalloys.A creep phase-field model is utilized to simulate the microstructure evolution and creep performance during creep under different fv conditions.The influence mechanism of fv on creep properties is investigated based on the analysis of evolutions of internal stress and strain fields.As fv increases,the morphology ofγʹrafts changes from discontinuous to continuous,while the morphological change ofγchannels is opposite,the inclination ofγchannels from the[010]direction to(011)directions during tertiary creep first decreases and then increases,the creep life first increases and then decreases,and the main distribution of creep damage shifts fromγʹtoγʹ/γinterfaces andγchannels.The longest creep life under fv of 0.65 can be attributed to the stableγʹraft structure,the lowest stress and strain inγchannels,and the slowest damage accumulation.
