Understanding microcracking near coalesced fracture generation is critically important for hydrocarbon and geothermal reservoir characterization as well as damage evaluation in civil engineering structures. Dense and ...Understanding microcracking near coalesced fracture generation is critically important for hydrocarbon and geothermal reservoir characterization as well as damage evaluation in civil engineering structures. Dense and sometimes random microcracking near coalesced fracture formation alters the mechanical properties of the nearby virgin material. Individual microcrack characterization is also significant in quantifying the material changes near the fracture faces （i.e. damage）. Acoustic emission （AE） monitoring and analysis provide unique information regarding the microcracking process temporally, and infor- mation concerning the source characterization of individual microcracks can be extracted. In this context, laboratory hydraulic fracture tests were carried out while monitoring the AEs from several piezoelectric transducers. In-depth post-processing of the AE event data was performed for the purpose of under- standing the individual source mechanisms. Several source characterization techniques including moment tensor inversion, event parametric analysis, and volumetric deformation analysis were adopted. Post-test fracture characterization through coring, slicing and micro-computed tomographic imaging was performed to determine the coalesced fracture location and structure. Distinct differences in fracture characteristics were found spatially in relation to the openhole injection interval. Individual microcrack AE analysis showed substantial energy reduction emanating spatially from the injection interval. It was quantitatively observed that the recorded AE signals provided sufficient information to generalize the damage radiating spatially away from the injection wellbore.展开更多
For decades,nacre has inspired researchers because of its sophisticated hierarchical structure and remarkable mechanical properties,especially its extreme fracture toughness compared with that of its predominant const...For decades,nacre has inspired researchers because of its sophisticated hierarchical structure and remarkable mechanical properties,especially its extreme fracture toughness compared with that of its predominant constituent,CaCO_(3),in the form of aragonite.Crack deflection has been extensively reported and regarded as the principal toughening mechanism for nacre.In this paper,our attention is focused on crack evolution in nacre under a quasi-static state.We use the notched three-point bending test of dehydrated nacre in situ in a scanning electron microscope(SEM)to monitor the evolution of damage mechanisms ahead of the crack tip.The observations show that the crack deflection actually occurs by constrained microcracking.On the basis of our findings,a crack propagation model is proposed,which will contribute to uncovering the underlying mechanisms of nacre’s fracture toughness and its damage evolution.These investigations would be of great value to the design and synthesis of novel biomimetic materials.展开更多
This paper addresses the conservation laws in finite brittle solids with microcracks. The discussion is limited to the 2-D cases. First, after considering the combination of the Pseudo-Traction Method and the indirect...This paper addresses the conservation laws in finite brittle solids with microcracks. The discussion is limited to the 2-D cases. First, after considering the combination of the Pseudo-Traction Method and the indirect Boundary Element Method, a versatile method for solving multi-crack interacting problems in finite plane solids is proposed, by which the fracture parameters （SIF and path-independent integrals） can be calculated with a desirable accuracy. Second, with the aid of the method proposed, the roles the conservation laws play in the fracture analysis for finite microcracking solids are studied. It is concluded that the conservation laws do play important roles in not only the fracture analysis but also the analysis of damage and stability for the finite microcracking system. Finally, the physical interpretation of the M-integral is discussed further. An explicit relation between the M-integral and the crack face area, i.e., M = GS, has been discovered using the analytical method, which can shed some light on the Damage Mechanics issues from a different perspective.展开更多
This study develops a mesoscopic framework and methodology for the modeling of microcracks in concrete. A new algorithm is first proposed for the generation of random concrete meso-structure including microcracks and ...This study develops a mesoscopic framework and methodology for the modeling of microcracks in concrete. A new algorithm is first proposed for the generation of random concrete meso-structure including microcracks and then coupled with the extended finite element method to simulate the heterogeneities and discontinuities present in the meso-structure of concrete. The proposed procedure is verified and exemplified by a series of numerical simulations. The simulation results show that microcracks can exert considerable impact on the fracture performance of concrete. More broadly, this work provides valuable insight into the initiation and propagation mechanism of microcracks in concrete and helps to foster a better understanding of the micro-mechanical behavior of cementitious materials.展开更多
The stress shielding effect of profuse microcracks at the tip of a macroscopic stationary mode Ⅰ crack is studied. The analysis method adopted combines the micromechanical approach with the effective elastic med...The stress shielding effect of profuse microcracks at the tip of a macroscopic stationary mode Ⅰ crack is studied. The analysis method adopted combines the micromechanical approach with the effective elastic medium approach. The anisotropic constitutive relation of the effective elastic medium is based on the DMG damage model developed by the authors for microcrack weakened brittle materials undergoing damage in form of elastic modulus degradation as a result of stable microcrack growth. The stress and strain fields at the crack tip and the condition of path independence of J integral in the damage zone are discussed under some reasonable approximations. A modified J integral method is thereby proposed to calculate the ratio of near tip to remote stress intensity factors and compared with the conventional method of J conservation.展开更多
The mineralogy and texture of granite have been found to have a pronounced effect on its mechanical behavior.However,the precise manner in which the texture of granite affects the shear behavior of fractures remains e...The mineralogy and texture of granite have been found to have a pronounced effect on its mechanical behavior.However,the precise manner in which the texture of granite affects the shear behavior of fractures remains enigmatic.In this study,fine-grained granite(FG)and coarse-grained granite(CG)were used to create tensile fractures with surface roughness(i.e.joint roughness coefficient(JRC))within the range of 5.48-8.34 and 12.68-16.5,respectively.The pre-fractured specimens were then subjected to direct shear tests under normal stresses of 1-30 MPa.The results reveal that shear strengths are smaller and stick-slip behaviors are more intense for FG fractures than for CG fractures,which is attributed to the different conditions of the shear surface constrained by the grain size.The smaller grain size in FG contributes to the smoother fracture surface and lower shear strength.The negative friction rate parameter a-b for both CG and FG fractures and the larger shear stiffness for FG than for CG fractures can account for the more intense stick-slip behaviors in FG fractures.The relative crack density for the post-shear CG fractures is greater than that of the FG fractures under the same normal stress,both of which decrease with the distance away from the shear surface following the power law.Moreover,the damage of CG fracture extends to a larger extent beneath the surface compared with the FG fracture.Our findings demonstrate that the grain size of the host rock exerts a significant influence on the fracture roughness,and thus should be incorporated into the assessment of fault slip behavior to better understand the role of mineralogy and texture in seismic activities.展开更多
Silicon(Si)-based anodes,where Si serves as the active material,have garnered significant attention due to their potential to achieve high electric capacity in lithium-ion batteries(LIBs).A key challenge with Si-based...Silicon(Si)-based anodes,where Si serves as the active material,have garnered significant attention due to their potential to achieve high electric capacity in lithium-ion batteries(LIBs).A key challenge with Si-based anodes is their susceptibility to create in-plane cracks caused by stresses from the manufacturing process and cyclic charging,which ultimately shortens battery life and reduces the overall electrochemical capacity.To address this issue,a refined microstructural design of the active material layer is in pressing need to enhance both the performance and longevity of LIBs.We successfully applied the Oyane failure criterion,which models ductile failure under stress triaxiality,to simulate crack initiation and propagation in the binder matrix containing Si particles in the finite element modeling.Given the non-linear plastic deformation of the binder,this criterion was formulated based on cumulative strain increments.The computational results of microcrack formation within the active material layer under uniaxial tension were then validated by the experimental observations.Furthermore,we developed several models with varied particle arrangements,comparing each simulated crack path to actual microstructural images obtained via scanning electron microscopy.The findings confirm the accuracy of the model,underlying its promising application in optimizing the microstructure of Si-based anodes for enhanced LIB performance and durability.展开更多
Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was appli...Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was applied on a rare-earth addition bearing steel.And rolling contact fatigue behavior of treated samples was compared with that of as-received counterparts at different contacting stresses.The results demonstrated that a 700μm-thick gradient nanostructured surface layer is produced on samples by surface mechanical rolling treatment.The grain size decreases while the microhardness increases gradually with decreasing depth,reaching~23 nm and~10.2 GPa,respectively,at the top surface.Consequently,the rolling contact fatigue property is significantly enhanced.The characteristic life of treated samples is~3.2 times that of untreated counterparts according to Weibull curves at 5.6 GPa.Analyses of fatigue mechanisms demonstrated that the gradient nanostructured surface layer might not only retard material degradation and microcrack formation,but also prolong the steady-state elastic response stage under rolling contact fatigue.展开更多
Ultrahigh nickel oxides(Ni content>90%)hold great promise for high-performance cathodes for the future generation of lithium-ion batteries(LIBs).However,these cathode materials cause problems such as harmful parasi...Ultrahigh nickel oxides(Ni content>90%)hold great promise for high-performance cathodes for the future generation of lithium-ion batteries(LIBs).However,these cathode materials cause problems such as harmful parasitic reactions at the cathode/electrolyte interface,degradation of the layered structure,and the creation of microcracks.Herein,a microstructural refinement and intergranular coating strategy is proposed to engineer ultrahigh nickel cathode LiNi_(0.96)Co_(0.03)Mn_(0.01)O_(2)(NCM).The W-doping-induced fine-grained microstructure not only endows NCM with excellent mechanical properties but also promotes infiltration of the fluoride-containing coating along the grain boundaries inside the secondary particles,thereby forming intergranular coatings.This combined fine-grained microstructure and intergranular coating strategy reduces the formation of microcracks and suppresses the additional parasitic electrolyte reactions caused by them,thereby inhibiting the degradation of the layered phase.Consequently,the modified NCM cathode achieved exceptional electrochemical properties,especially delivering a high initial capacity of 230.8 mA h g^(-1)(0.1 C)and a capacity retention exceeding 96% after100 cycles at 0.5 C in half cells.After 500 cycles in full cells,the capacity retention increases by 21.2% compared with NCM.This strategy mitigates multiple degradation mechanisms in Ni-rich cathodes and provides a generalized strategy for developing advanced ultrahigh-nickel cathodes for industrial application.展开更多
LiNixCoyMn_(2)O_(2)(NCM,x≥0.8,x+y+z=1)cathodes have attracted much attention due to their high specific capacity and low cost.However,severe anisotropic volume changes and oxygen evolution induced capacity decay and ...LiNixCoyMn_(2)O_(2)(NCM,x≥0.8,x+y+z=1)cathodes have attracted much attention due to their high specific capacity and low cost.However,severe anisotropic volume changes and oxygen evolution induced capacity decay and insecurity have hindered their commercial application at scale.In order to overcome these challenges,a kind of tantalum(Ta)doped nickel-rich cathode with reduced size and significantly increased number of primary particles is prepared by combining mechanical fusion with high temperature co-calcination.The elaborately designed micro-morphology of small and uniform primary particles effectively eliminates the local strain accumulation caused by the random orientation of primary particles.Moreover,the uniform distribution of small primary particles stabilizes the spherical secondary particles,thus effectively inhibiting the formation and extension of microcracks.In addition,the formed strong Ta-O bonds restrain the release of lattice oxygen,which greatly increases the structural stability and safety of NCM materials.Therefore,the cathode material with the designed primary particle morphology shows superior electrochemical performance.The 1 mol%Ta-modified cathode(defined as1%Ta-NCM)shows a capacity retention of 97.5%after 200 cycles at 1 C and a rate performance of 137.3 mAh g^(-1)at 5 C.This work presents promising approach to improve the structural stability and safety of nickel-rich NCM.展开更多
The as-deposited coating-substrate microstructure has been identified to substantially influence the high-cycle fatigue(HCF)behavior of Ni-based single-crystal(SX)superalloys at 900℃,but the impact of degraded micros...The as-deposited coating-substrate microstructure has been identified to substantially influence the high-cycle fatigue(HCF)behavior of Ni-based single-crystal(SX)superalloys at 900℃,but the impact of degraded microstructure on the HCF behavior remains unclear.In this work,a PtAl-coated third-generation SX superalloy with sheet specimen was thermal-exposed at 1100℃ with different durations and then subjected to HCF tests at 900℃.The influence of microstructural degradation on the HCF life and crack initiation were clarified by analyzing the development of microcracks and coating-substrate microstructure.Notably,the HCF life of the thermal-exposed coated alloy increased abnormally,which was attributed to the transformation of the fatigue crack initiation site from surface mi-crocracks to internal micropores compared to the as-deposited coated alloy.Although the nucleation and growth of surface microcracks occurred along the grain boundaries in the coating and the interdiffusion zone(IDZ)for both the as-deposited and the thermal-exposed coated alloys,remarkable differences of the microcrack growth into the substrate adjacent to the IDZ were observed,changing the crack initiation site.Specifically,the surface microcracks grew into the substrate through the cracking of the non-protective oxide layers in the as-deposited coated alloy.In comparison,the hinderance of the surface microcracks growth was found in the thermal-exposed coated al-loy,due to the formation of a protective Al_(2)O_(3) layer within the microcrack and theγ′rafting in the substrate close to the IDZ.This study will aid in improving the HCF life prediction model for the coated SX superalloys.展开更多
In this work,the effect of high angle grain boundaries(HAGBs),including prior austenite grain boundaries(PAGB),packet grain boundaries(PGB)and block grain boundaries(BGB),on the priority of pitting and microcrack init...In this work,the effect of high angle grain boundaries(HAGBs),including prior austenite grain boundaries(PAGB),packet grain boundaries(PGB)and block grain boundaries(BGB),on the priority of pitting and microcrack initiation for 10Cr13Co13Mo5Ni3W1VE ultra-high strength stainless steel(UHSS)has been clarified.PAGB had the highest carbide distribution coefficient and was the main location where pitting preferentially initiated for the UHSS in 3.5 wt.%NaCl solution without strain.It was shown that nanocarbides were the key factor of pitting initiation for the UHSS without strain.However,BGB was the key factor of pitting/microcrack initiation for the UHSS with strain,which was attributed to the high-density dislocations accumulated at BGB and then enhanced the local electrochemical activity of the UHSS surface.The change of the key factor for the pitting initiation in the UHSS was the result of the synergy between strain and corrosion environment.This study provides guidance for designing advanced UHSS with high service stability and safety.展开更多
Thermal shock,a phenomenon known to cause rock fracturing,has gained increasing significance with advancements in enhanced geothermal systems.In this comprehensive review,we delve into the intricacies of thermal shock...Thermal shock,a phenomenon known to cause rock fracturing,has gained increasing significance with advancements in enhanced geothermal systems.In this comprehensive review,we delve into the intricacies of thermal shock in rocks,exploring its mechanisms,mechanical interpretations,impacts,and applications.Despite generations of researchers'attempts to identify the conditions that trigger thermal shock and propose various thresholds for heating rates,temperatures,and durations,establishing a universal threshold remains elusive.Commonly adopted heating rate threshold of 2℃/min and critical temperature around 75℃still require further experimental data and theoretical model support.This study scrutinizes the typical thermal shock process in rocks during heating and cooling,employing both microscopic and macroscopic approaches.To examine the effects of thermal shock,we compile and analyze published experimental findings on rock physico-mechanical properties under rapid heating,cooling,and cyclic conditions.Our review reveals that both external and internal conditions significantly impact a rock's response to thermal shock.We assess several analytical equations related to rock thermal shock;nevertheless,a thorough and strong mechanical model is still required.Thermal shock can be harnessed to support underground rock engineering project design and construction,ranging from thermal spallation drilling to cryogenic fracturing.This review examines the evolution of thermal spallation drilling regarding mechanical models and experimental investigations,and discusses cryogenic fracturing in terms of mechanisms,advantages,application cases,and future developments.Serving as a crucial resource,this review paper consolidates the current understanding of thermal shock in rocks,enabling researchers and engineers to develop improved,sustainable solutions for underground engineering projects that cater to the growing demand for underground space and energy.展开更多
During the excavation of deep engineering,high in situ stress is one prominent feature that often causes instability in the vicinity of underground openings.The propagation and coalescence of cracks in the surrounding...During the excavation of deep engineering,high in situ stress is one prominent feature that often causes instability in the vicinity of underground openings.The propagation and coalescence of cracks in the surrounding rock are characterized by anisotropy under a true triaxial stress state and play a crucial role in the development of stress-induced engineering disasters.Thus,a three-dimensional anisotropic fracturing model of hard rock is proposed to interpret fracturing activities and evaluate the mechanical property deterioration under complex stress conditions.This anisotropic fracturing model is derived from the evolution of microcracks and attributes the inelastic deformation of hard rock to crack propagation and coalescence.Through analyzing the competitive process of crack propagation in different orientations,the stress-induced anisotropic fracturing characteristics and the post-peak brittle-ductile transition could be revealed.Finally,the accuracy and effectiveness of this model are validated.Results show that this proposed anisotropic fracturing model can elucidate the primary characteristics observed in triaxial compression tests,which offers a fresh perspective on comprehending the failure process of hard rock.展开更多
The commonly used method for estimating crack opening displacement(COD)is based on analytical models derived from strain transferring.However,when large background noise exists in distributed fiber optic sensing(DFOS)...The commonly used method for estimating crack opening displacement(COD)is based on analytical models derived from strain transferring.However,when large background noise exists in distributed fiber optic sensing(DFOS)data,estimating COD through an analytical model is very difficult even if the DFOS data have been denoised.To address this challenge,this study proposes a machine learning(ML)-based methodology to complete rock's COD estimation from establishment of a dataset with one-to-one correspondence between strain sequence and COD to the optimization of ML models.The Bayesian optimization is used via the Hyperopt Python library to determine the appropriate hyper-parameters of four ML models.To ensure that the best hyper-parameters will not be missing,the configuration space in Hyperopt is specified by probability distribution.The four models are trained using DFOS data with minimal noise while being examined on datasets with different noise levels to test their anti-noise robustness.The proposed models are compared each other in terms of goodness of fit and mean squared error.The results show that the Bayesian optimization-based random forest is promising to estimate the COD of rock using noisy DFOS data.展开更多
The expansion and micro-cracks of the mortar with composite mineral admixtures （fly ash, zeolite and slag） due to the alkali-silica reaction （ASR） are studied. Results show that composite mineral admixtures cannot...The expansion and micro-cracks of the mortar with composite mineral admixtures （fly ash, zeolite and slag） due to the alkali-silica reaction （ASR） are studied. Results show that composite mineral admixtures cannot absolutely diminish the ASR of mortar bars with the low-alkali cement and a highly reactive aggregate. But the expansion rate and the deleterious expansion of the mortar bar are mostly reduced with increasing composite mineral admixture. The influence of mineral admixtures on the fluidity of the paste and the strength of the mortar is also studied.展开更多
The commercialization of nickel-rich LiNi_(0.8)Mn_(0.1)Co_(0.1)O_(2)(NMC811) has been hindered by its continuous loss of practical capacity and reduction in average working voltage.To address these issues,surface modi...The commercialization of nickel-rich LiNi_(0.8)Mn_(0.1)Co_(0.1)O_(2)(NMC811) has been hindered by its continuous loss of practical capacity and reduction in average working voltage.To address these issues,surface modification has been well-recognized as an effective strategy.Different from the coatings reported in literature to date,in this work,we for the first time report a sulfide coating,amorphous Li_(2)S via atomic layer deposition (ALD).Our study revealed that the conformal nano-Li_(2)S coating shows exceptional protection over the NMC811 cathodes,accounting for the dramatically boosted capacity retention from~11.6%to~71%and the evidently mitigated voltage reduction from 0.39 to 0.18 V after 500 charge–discharge cycles.In addition,the Li_(2)S coating remarkably improved the rate capability of the NMC811 cathode.Our investigation further revealed that all these beneficial effects of the ALD-deposited nano-Li_(2)S coating lie in the following aspects:(i) maintain the mechanical integrity of the NMC811 electrode:(ii) stabilize the NMC electrode/electrolyte interface:and (iii) suppress the irreversible phase transition of NMC structure.Particularly,this study also has revealed that the nano-Li_(2)S coating has played some unique role not associated with traditional non-sulfide coatings such as oxides.In this regard,we disclosed that the Li_(2)S layer has reacted with the released O_(2) from the NMC lattices,and thereby has dramatically mitigated electrolyte oxidation and electrode corrosion.Thus,this study is significant and has demonstrated that sulfides may be an important class of coating materials to tackle the issues of NMCs and other layered cathodes in lithium batteries.展开更多
This paper presents a theoretical study on time-dependent dilatancy behaviors for brittle rocks. The theory employs a well-accepted postulation that macroscopically observed dilatancy originates from the expansion of ...This paper presents a theoretical study on time-dependent dilatancy behaviors for brittle rocks. The theory employs a well-accepted postulation that macroscopically observed dilatancy originates from the expansion of microcracks. The mechanism and dynamic process that microcracks initiate from local stress concentration and grow due to localized tensile stress are analyzed. Then, by generalizing the results from the analysis of single cracks, a parameter and associated equations for its evolution are developed to describe the behaviors of the microcracks. In this circumstance, the relationship between microcracking and dilatancy can be established, and the theoretical equations for characterizing the process of rock dilatancy behaviors are derived. Triaxial compression and creep tests are conducted to validate the developed theory. With properly chosen model parameters, the theory yields a satisfactory accuracy in comparison with the experimental results.展开更多
The recent development of high-performance-modified spray arc processes in gas metal arc welding due to modern digital control technology and inverter power sources enables a focused spray arc, which results in higher...The recent development of high-performance-modified spray arc processes in gas metal arc welding due to modern digital control technology and inverter power sources enables a focused spray arc, which results in higher penetration depths and welding speed. However, rnicrocracks occurred in the weld metal while approaching the process limits of the modified spray arc, represented by a 20-mm double layer DV-groove butt-weld, These cracks were detected in structural steel exhibiting a yield strength level of up to 960 MPa and are neither dependent on the used weld power source nor a consequence of the modified spray arc process itself. The metallographic and fractographic investigations of the rather exceptional fracture surface lead to the classification of the microcracks as hot cracks, The effects of certain welding parameters on the crack probability are clarified using a statistical design of experiment. However, these microcracks do not impact the design specification for toughness in the Charpy V-notch test （absorbed energy at -40 ℃ for the present material is 30 J）.展开更多
基金financial support for much of the early development of the AE analysis methods was provided by the U.S. Department of Energy (DOE) (Grant No. DE-FE0002760)
文摘Understanding microcracking near coalesced fracture generation is critically important for hydrocarbon and geothermal reservoir characterization as well as damage evaluation in civil engineering structures. Dense and sometimes random microcracking near coalesced fracture formation alters the mechanical properties of the nearby virgin material. Individual microcrack characterization is also significant in quantifying the material changes near the fracture faces （i.e. damage）. Acoustic emission （AE） monitoring and analysis provide unique information regarding the microcracking process temporally, and infor- mation concerning the source characterization of individual microcracks can be extracted. In this context, laboratory hydraulic fracture tests were carried out while monitoring the AEs from several piezoelectric transducers. In-depth post-processing of the AE event data was performed for the purpose of under- standing the individual source mechanisms. Several source characterization techniques including moment tensor inversion, event parametric analysis, and volumetric deformation analysis were adopted. Post-test fracture characterization through coring, slicing and micro-computed tomographic imaging was performed to determine the coalesced fracture location and structure. Distinct differences in fracture characteristics were found spatially in relation to the openhole injection interval. Individual microcrack AE analysis showed substantial energy reduction emanating spatially from the injection interval. It was quantitatively observed that the recorded AE signals provided sufficient information to generalize the damage radiating spatially away from the injection wellbore.
基金supported by the National Natural Science Foundation of China(Grants 91216108,11432014,11672301,11372318,and 11502273)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant XDB22040501)
文摘For decades,nacre has inspired researchers because of its sophisticated hierarchical structure and remarkable mechanical properties,especially its extreme fracture toughness compared with that of its predominant constituent,CaCO_(3),in the form of aragonite.Crack deflection has been extensively reported and regarded as the principal toughening mechanism for nacre.In this paper,our attention is focused on crack evolution in nacre under a quasi-static state.We use the notched three-point bending test of dehydrated nacre in situ in a scanning electron microscope(SEM)to monitor the evolution of damage mechanisms ahead of the crack tip.The observations show that the crack deflection actually occurs by constrained microcracking.On the basis of our findings,a crack propagation model is proposed,which will contribute to uncovering the underlying mechanisms of nacre’s fracture toughness and its damage evolution.These investigations would be of great value to the design and synthesis of novel biomimetic materials.
基金Project supported by the National Natural Science Foundation of China (No. 19472053).
文摘This paper addresses the conservation laws in finite brittle solids with microcracks. The discussion is limited to the 2-D cases. First, after considering the combination of the Pseudo-Traction Method and the indirect Boundary Element Method, a versatile method for solving multi-crack interacting problems in finite plane solids is proposed, by which the fracture parameters （SIF and path-independent integrals） can be calculated with a desirable accuracy. Second, with the aid of the method proposed, the roles the conservation laws play in the fracture analysis for finite microcracking solids are studied. It is concluded that the conservation laws do play important roles in not only the fracture analysis but also the analysis of damage and stability for the finite microcracking system. Finally, the physical interpretation of the M-integral is discussed further. An explicit relation between the M-integral and the crack face area, i.e., M = GS, has been discovered using the analytical method, which can shed some light on the Damage Mechanics issues from a different perspective.
基金supported by the National Basic Research Program of China(2014CB046904)the Hubei Provincial Key Laboratory of Safety for Geotechnical and Structural Engineering at Wuhan University(HBKLCIV201207)the China Postdoctoral Science Foundation(2013M540604)
文摘This study develops a mesoscopic framework and methodology for the modeling of microcracks in concrete. A new algorithm is first proposed for the generation of random concrete meso-structure including microcracks and then coupled with the extended finite element method to simulate the heterogeneities and discontinuities present in the meso-structure of concrete. The proposed procedure is verified and exemplified by a series of numerical simulations. The simulation results show that microcracks can exert considerable impact on the fracture performance of concrete. More broadly, this work provides valuable insight into the initiation and propagation mechanism of microcracks in concrete and helps to foster a better understanding of the micro-mechanical behavior of cementitious materials.
文摘The stress shielding effect of profuse microcracks at the tip of a macroscopic stationary mode Ⅰ crack is studied. The analysis method adopted combines the micromechanical approach with the effective elastic medium approach. The anisotropic constitutive relation of the effective elastic medium is based on the DMG damage model developed by the authors for microcrack weakened brittle materials undergoing damage in form of elastic modulus degradation as a result of stable microcrack growth. The stress and strain fields at the crack tip and the condition of path independence of J integral in the damage zone are discussed under some reasonable approximations. A modified J integral method is thereby proposed to calculate the ratio of near tip to remote stress intensity factors and compared with the conventional method of J conservation.
基金the National Natural Science Foundation of China(Grant No.52309130)the Natural Science Foundation of Shandong Province(Grant No.ZR2022QD004).
文摘The mineralogy and texture of granite have been found to have a pronounced effect on its mechanical behavior.However,the precise manner in which the texture of granite affects the shear behavior of fractures remains enigmatic.In this study,fine-grained granite(FG)and coarse-grained granite(CG)were used to create tensile fractures with surface roughness(i.e.joint roughness coefficient(JRC))within the range of 5.48-8.34 and 12.68-16.5,respectively.The pre-fractured specimens were then subjected to direct shear tests under normal stresses of 1-30 MPa.The results reveal that shear strengths are smaller and stick-slip behaviors are more intense for FG fractures than for CG fractures,which is attributed to the different conditions of the shear surface constrained by the grain size.The smaller grain size in FG contributes to the smoother fracture surface and lower shear strength.The negative friction rate parameter a-b for both CG and FG fractures and the larger shear stiffness for FG than for CG fractures can account for the more intense stick-slip behaviors in FG fractures.The relative crack density for the post-shear CG fractures is greater than that of the FG fractures under the same normal stress,both of which decrease with the distance away from the shear surface following the power law.Moreover,the damage of CG fracture extends to a larger extent beneath the surface compared with the FG fracture.Our findings demonstrate that the grain size of the host rock exerts a significant influence on the fracture roughness,and thus should be incorporated into the assessment of fault slip behavior to better understand the role of mineralogy and texture in seismic activities.
基金support of JSPS KAKENHI(Grant No.21H01217)from the Japan Society for the Promotion of Science.
文摘Silicon(Si)-based anodes,where Si serves as the active material,have garnered significant attention due to their potential to achieve high electric capacity in lithium-ion batteries(LIBs).A key challenge with Si-based anodes is their susceptibility to create in-plane cracks caused by stresses from the manufacturing process and cyclic charging,which ultimately shortens battery life and reduces the overall electrochemical capacity.To address this issue,a refined microstructural design of the active material layer is in pressing need to enhance both the performance and longevity of LIBs.We successfully applied the Oyane failure criterion,which models ductile failure under stress triaxiality,to simulate crack initiation and propagation in the binder matrix containing Si particles in the finite element modeling.Given the non-linear plastic deformation of the binder,this criterion was formulated based on cumulative strain increments.The computational results of microcrack formation within the active material layer under uniaxial tension were then validated by the experimental observations.Furthermore,we developed several models with varied particle arrangements,comparing each simulated crack path to actual microstructural images obtained via scanning electron microscopy.The findings confirm the accuracy of the model,underlying its promising application in optimizing the microstructure of Si-based anodes for enhanced LIB performance and durability.
基金The financial supports by the Chinese Academy of Sciences(Nos.XDC04030300 and XDB0510303)CAS-HK Joint Laboratory of Nanomaterials and MechanicsShenyang National Laboratory for Materials Science are acknowledged.
文摘Rolling contact fatigue performance is among the most important issues for applications of bearing steels.In this work,a recently developed surface modification technique,surface mechanical rolling treatment,was applied on a rare-earth addition bearing steel.And rolling contact fatigue behavior of treated samples was compared with that of as-received counterparts at different contacting stresses.The results demonstrated that a 700μm-thick gradient nanostructured surface layer is produced on samples by surface mechanical rolling treatment.The grain size decreases while the microhardness increases gradually with decreasing depth,reaching~23 nm and~10.2 GPa,respectively,at the top surface.Consequently,the rolling contact fatigue property is significantly enhanced.The characteristic life of treated samples is~3.2 times that of untreated counterparts according to Weibull curves at 5.6 GPa.Analyses of fatigue mechanisms demonstrated that the gradient nanostructured surface layer might not only retard material degradation and microcrack formation,but also prolong the steady-state elastic response stage under rolling contact fatigue.
基金financially supported by the National Natural Science Foundation of China(52071073)the Fundamental Research Funds for the Central Universities(2024GFZD002)+3 种基金the Natural Science Foundation of Hebei Province(E2024501015)the Liaoning Applied Basic Research Program(2023JH2/101300011)the Basic Scientific Research Project of Liaoning Province Department of Education(LJKZZ20220024)the Shenyang Science and Technology Project(23-407-3-13)。
文摘Ultrahigh nickel oxides(Ni content>90%)hold great promise for high-performance cathodes for the future generation of lithium-ion batteries(LIBs).However,these cathode materials cause problems such as harmful parasitic reactions at the cathode/electrolyte interface,degradation of the layered structure,and the creation of microcracks.Herein,a microstructural refinement and intergranular coating strategy is proposed to engineer ultrahigh nickel cathode LiNi_(0.96)Co_(0.03)Mn_(0.01)O_(2)(NCM).The W-doping-induced fine-grained microstructure not only endows NCM with excellent mechanical properties but also promotes infiltration of the fluoride-containing coating along the grain boundaries inside the secondary particles,thereby forming intergranular coatings.This combined fine-grained microstructure and intergranular coating strategy reduces the formation of microcracks and suppresses the additional parasitic electrolyte reactions caused by them,thereby inhibiting the degradation of the layered phase.Consequently,the modified NCM cathode achieved exceptional electrochemical properties,especially delivering a high initial capacity of 230.8 mA h g^(-1)(0.1 C)and a capacity retention exceeding 96% after100 cycles at 0.5 C in half cells.After 500 cycles in full cells,the capacity retention increases by 21.2% compared with NCM.This strategy mitigates multiple degradation mechanisms in Ni-rich cathodes and provides a generalized strategy for developing advanced ultrahigh-nickel cathodes for industrial application.
基金financial support provided by the National Natural Science Foundation of China(52271201)the Science and Technology Department of Sichuan Province(2025NSFTD0005,2022YFG0100,2022ZYD0045)。
文摘LiNixCoyMn_(2)O_(2)(NCM,x≥0.8,x+y+z=1)cathodes have attracted much attention due to their high specific capacity and low cost.However,severe anisotropic volume changes and oxygen evolution induced capacity decay and insecurity have hindered their commercial application at scale.In order to overcome these challenges,a kind of tantalum(Ta)doped nickel-rich cathode with reduced size and significantly increased number of primary particles is prepared by combining mechanical fusion with high temperature co-calcination.The elaborately designed micro-morphology of small and uniform primary particles effectively eliminates the local strain accumulation caused by the random orientation of primary particles.Moreover,the uniform distribution of small primary particles stabilizes the spherical secondary particles,thus effectively inhibiting the formation and extension of microcracks.In addition,the formed strong Ta-O bonds restrain the release of lattice oxygen,which greatly increases the structural stability and safety of NCM materials.Therefore,the cathode material with the designed primary particle morphology shows superior electrochemical performance.The 1 mol%Ta-modified cathode(defined as1%Ta-NCM)shows a capacity retention of 97.5%after 200 cycles at 1 C and a rate performance of 137.3 mAh g^(-1)at 5 C.This work presents promising approach to improve the structural stability and safety of nickel-rich NCM.
基金financially supported by National Key Research and Development Program of China(No.2022YFB 3708100)the Science Center for Gas Turbine Project,China(No.P2021-A-IV-002-001)+1 种基金the National Natural Science Foundation of China(Nos.52331005 and 52201100)the State Key Laboratory for Advanced Metals and Materials,China(No.2024-Z02).
文摘The as-deposited coating-substrate microstructure has been identified to substantially influence the high-cycle fatigue(HCF)behavior of Ni-based single-crystal(SX)superalloys at 900℃,but the impact of degraded microstructure on the HCF behavior remains unclear.In this work,a PtAl-coated third-generation SX superalloy with sheet specimen was thermal-exposed at 1100℃ with different durations and then subjected to HCF tests at 900℃.The influence of microstructural degradation on the HCF life and crack initiation were clarified by analyzing the development of microcracks and coating-substrate microstructure.Notably,the HCF life of the thermal-exposed coated alloy increased abnormally,which was attributed to the transformation of the fatigue crack initiation site from surface mi-crocracks to internal micropores compared to the as-deposited coated alloy.Although the nucleation and growth of surface microcracks occurred along the grain boundaries in the coating and the interdiffusion zone(IDZ)for both the as-deposited and the thermal-exposed coated alloys,remarkable differences of the microcrack growth into the substrate adjacent to the IDZ were observed,changing the crack initiation site.Specifically,the surface microcracks grew into the substrate through the cracking of the non-protective oxide layers in the as-deposited coated alloy.In comparison,the hinderance of the surface microcracks growth was found in the thermal-exposed coated al-loy,due to the formation of a protective Al_(2)O_(3) layer within the microcrack and theγ′rafting in the substrate close to the IDZ.This study will aid in improving the HCF life prediction model for the coated SX superalloys.
文摘In this work,the effect of high angle grain boundaries(HAGBs),including prior austenite grain boundaries(PAGB),packet grain boundaries(PGB)and block grain boundaries(BGB),on the priority of pitting and microcrack initiation for 10Cr13Co13Mo5Ni3W1VE ultra-high strength stainless steel(UHSS)has been clarified.PAGB had the highest carbide distribution coefficient and was the main location where pitting preferentially initiated for the UHSS in 3.5 wt.%NaCl solution without strain.It was shown that nanocarbides were the key factor of pitting initiation for the UHSS without strain.However,BGB was the key factor of pitting/microcrack initiation for the UHSS with strain,which was attributed to the high-density dislocations accumulated at BGB and then enhanced the local electrochemical activity of the UHSS surface.The change of the key factor for the pitting initiation in the UHSS was the result of the synergy between strain and corrosion environment.This study provides guidance for designing advanced UHSS with high service stability and safety.
基金supported by the National Natural Science Foundation of China(Grant No.42377149)the Research Grants Council of Hong Kong,China(General Research Fund Project Nos.17200721 and 17202423)。
文摘Thermal shock,a phenomenon known to cause rock fracturing,has gained increasing significance with advancements in enhanced geothermal systems.In this comprehensive review,we delve into the intricacies of thermal shock in rocks,exploring its mechanisms,mechanical interpretations,impacts,and applications.Despite generations of researchers'attempts to identify the conditions that trigger thermal shock and propose various thresholds for heating rates,temperatures,and durations,establishing a universal threshold remains elusive.Commonly adopted heating rate threshold of 2℃/min and critical temperature around 75℃still require further experimental data and theoretical model support.This study scrutinizes the typical thermal shock process in rocks during heating and cooling,employing both microscopic and macroscopic approaches.To examine the effects of thermal shock,we compile and analyze published experimental findings on rock physico-mechanical properties under rapid heating,cooling,and cyclic conditions.Our review reveals that both external and internal conditions significantly impact a rock's response to thermal shock.We assess several analytical equations related to rock thermal shock;nevertheless,a thorough and strong mechanical model is still required.Thermal shock can be harnessed to support underground rock engineering project design and construction,ranging from thermal spallation drilling to cryogenic fracturing.This review examines the evolution of thermal spallation drilling regarding mechanical models and experimental investigations,and discusses cryogenic fracturing in terms of mechanisms,advantages,application cases,and future developments.Serving as a crucial resource,this review paper consolidates the current understanding of thermal shock in rocks,enabling researchers and engineers to develop improved,sustainable solutions for underground engineering projects that cater to the growing demand for underground space and energy.
基金support from the National Natural Science Foundation of China(Grant No.52209125).
文摘During the excavation of deep engineering,high in situ stress is one prominent feature that often causes instability in the vicinity of underground openings.The propagation and coalescence of cracks in the surrounding rock are characterized by anisotropy under a true triaxial stress state and play a crucial role in the development of stress-induced engineering disasters.Thus,a three-dimensional anisotropic fracturing model of hard rock is proposed to interpret fracturing activities and evaluate the mechanical property deterioration under complex stress conditions.This anisotropic fracturing model is derived from the evolution of microcracks and attributes the inelastic deformation of hard rock to crack propagation and coalescence.Through analyzing the competitive process of crack propagation in different orientations,the stress-induced anisotropic fracturing characteristics and the post-peak brittle-ductile transition could be revealed.Finally,the accuracy and effectiveness of this model are validated.Results show that this proposed anisotropic fracturing model can elucidate the primary characteristics observed in triaxial compression tests,which offers a fresh perspective on comprehending the failure process of hard rock.
基金The Young Scientists Fund of the National Natural Science Foundation of China(Grant No.42407250)the Fund from Research Centre for Resources Engineering towards Carbon Neutrality(RCRE)of The Hong Kong Polytechnic University(Grant No.No.1-BBEM)the Fund from Natural Science Foundation of Jiangsu Province(Grant No.BK20241211)。
文摘The commonly used method for estimating crack opening displacement(COD)is based on analytical models derived from strain transferring.However,when large background noise exists in distributed fiber optic sensing(DFOS)data,estimating COD through an analytical model is very difficult even if the DFOS data have been denoised.To address this challenge,this study proposes a machine learning(ML)-based methodology to complete rock's COD estimation from establishment of a dataset with one-to-one correspondence between strain sequence and COD to the optimization of ML models.The Bayesian optimization is used via the Hyperopt Python library to determine the appropriate hyper-parameters of four ML models.To ensure that the best hyper-parameters will not be missing,the configuration space in Hyperopt is specified by probability distribution.The four models are trained using DFOS data with minimal noise while being examined on datasets with different noise levels to test their anti-noise robustness.The proposed models are compared each other in terms of goodness of fit and mean squared error.The results show that the Bayesian optimization-based random forest is promising to estimate the COD of rock using noisy DFOS data.
文摘The expansion and micro-cracks of the mortar with composite mineral admixtures （fly ash, zeolite and slag） due to the alkali-silica reaction （ASR） are studied. Results show that composite mineral admixtures cannot absolutely diminish the ASR of mortar bars with the low-alkali cement and a highly reactive aggregate. But the expansion rate and the deleterious expansion of the mortar bar are mostly reduced with increasing composite mineral admixture. The influence of mineral admixtures on the fluidity of the paste and the strength of the mortar is also studied.
基金support from the Center for Advanced Surface Engineering, under the National Science Foundation Grant No. OIA-1457888the Arkansas EPSCoR Program, ASSET Ⅲ. X. M+1 种基金the financial support from the University of Arkansas, Fayetteville, AR, USAfunded by the U.S. Department of Energy (DOE), Vehicle Technologies Office。
文摘The commercialization of nickel-rich LiNi_(0.8)Mn_(0.1)Co_(0.1)O_(2)(NMC811) has been hindered by its continuous loss of practical capacity and reduction in average working voltage.To address these issues,surface modification has been well-recognized as an effective strategy.Different from the coatings reported in literature to date,in this work,we for the first time report a sulfide coating,amorphous Li_(2)S via atomic layer deposition (ALD).Our study revealed that the conformal nano-Li_(2)S coating shows exceptional protection over the NMC811 cathodes,accounting for the dramatically boosted capacity retention from~11.6%to~71%and the evidently mitigated voltage reduction from 0.39 to 0.18 V after 500 charge–discharge cycles.In addition,the Li_(2)S coating remarkably improved the rate capability of the NMC811 cathode.Our investigation further revealed that all these beneficial effects of the ALD-deposited nano-Li_(2)S coating lie in the following aspects:(i) maintain the mechanical integrity of the NMC811 electrode:(ii) stabilize the NMC electrode/electrolyte interface:and (iii) suppress the irreversible phase transition of NMC structure.Particularly,this study also has revealed that the nano-Li_(2)S coating has played some unique role not associated with traditional non-sulfide coatings such as oxides.In this regard,we disclosed that the Li_(2)S layer has reacted with the released O_(2) from the NMC lattices,and thereby has dramatically mitigated electrolyte oxidation and electrode corrosion.Thus,this study is significant and has demonstrated that sulfides may be an important class of coating materials to tackle the issues of NMCs and other layered cathodes in lithium batteries.
基金the financial support from the National Natural Science Foundation of China(Grant Nos.51679249 and 51527810)
文摘This paper presents a theoretical study on time-dependent dilatancy behaviors for brittle rocks. The theory employs a well-accepted postulation that macroscopically observed dilatancy originates from the expansion of microcracks. The mechanism and dynamic process that microcracks initiate from local stress concentration and grow due to localized tensile stress are analyzed. Then, by generalizing the results from the analysis of single cracks, a parameter and associated equations for its evolution are developed to describe the behaviors of the microcracks. In this circumstance, the relationship between microcracking and dilatancy can be established, and the theoretical equations for characterizing the process of rock dilatancy behaviors are derived. Triaxial compression and creep tests are conducted to validate the developed theory. With properly chosen model parameters, the theory yields a satisfactory accuracy in comparison with the experimental results.
基金the financial support for this research from the Federal Ministry of Economics and Technology(BMWi) through the "Arbeitsgemeinschaft industrieller Forschungsvereinigungen e.V."
文摘The recent development of high-performance-modified spray arc processes in gas metal arc welding due to modern digital control technology and inverter power sources enables a focused spray arc, which results in higher penetration depths and welding speed. However, rnicrocracks occurred in the weld metal while approaching the process limits of the modified spray arc, represented by a 20-mm double layer DV-groove butt-weld, These cracks were detected in structural steel exhibiting a yield strength level of up to 960 MPa and are neither dependent on the used weld power source nor a consequence of the modified spray arc process itself. The metallographic and fractographic investigations of the rather exceptional fracture surface lead to the classification of the microcracks as hot cracks, The effects of certain welding parameters on the crack probability are clarified using a statistical design of experiment. However, these microcracks do not impact the design specification for toughness in the Charpy V-notch test （absorbed energy at -40 ℃ for the present material is 30 J）.
