Micromechanics models have been developed For the determination of the elastic moduli of microcracked solids based on different approaches and interpretations, including the dilute or non-interacting solution, the Mor...Micromechanics models have been developed For the determination of the elastic moduli of microcracked solids based on different approaches and interpretations, including the dilute or non-interacting solution, the Mori-Tanaka method, the self-consistent method, and the generalized self-consistent method. It is shown in the present study that all these micromechanics models can be unified within an energy-equivalence framework, and that they differ only in the way in which the microcrack opening and sliding displacements are evaluated. Relevance to the differential methods and the verification of these models are discussed.展开更多
P-and SV-wave dispersion and attenuation have been extensively investigated in saturated poroelastic media with aligned fractures.However,there are few existing models that incorporate the multiple wave attenuation me...P-and SV-wave dispersion and attenuation have been extensively investigated in saturated poroelastic media with aligned fractures.However,there are few existing models that incorporate the multiple wave attenuation mechanisms from the microscopic scale to the macroscopic scale.Hence,in this work,we developed a unified model to incorporate the wave attenuation mechanisms at different scales,which includes the microscopic squirt flow between the microcracks and pores,the mesoscopic wave-induced fluid flow between fractures and background(FB-WIFF),and the macroscopic Biot's global flow and elastic scattering(ES)from the fractures.Using Tang's modified Biot's theory and the mixed-boundary conditions,we derived the exact frequency-dependent solutions of the scattering problem for a single penny-shaped fracture with oblique incident P-and SV-waves.We then developed theoretical models for a set of aligned fractures and randomly oriented fractures using the Foldy approximation.The results indicated that microcrack squirt flow considerably influences the dispersion and attenuation of P-and SV-wave velocities.The coupling effects of microcrack squirt flow with the FB-WIFF and ES of fractures cause much higher velocity dispersion and attenuation for P waves than for SV waves.Randomly oriented fractures substantially reduce the attenuation caused by the FB-WIFF and ES,particularly for the ES attenuation of SV waves.Through a comparison with existing models in the limiting cases and previous experimental measurements,we validated our model.展开更多
With the rapid development of wearable intelligent devices,low-cost wearable strain sensors with high sensitivity and low detection limit are urgently demanded.Meanwhile,sensing stability of sensor in wet or corrosive...With the rapid development of wearable intelligent devices,low-cost wearable strain sensors with high sensitivity and low detection limit are urgently demanded.Meanwhile,sensing stability of sensor in wet or corrosive environments should also be considered in practical applications.Here,superhydrophobic microcracked conductive paper-based strain sensor was fabricated by coating conductive Ti_(3)C_(2)T_(x) MXene on printing paper via dip-coating process and followed by depositing superhydrophobic candle soot layer on its surface.Owing to the ultrasensitive microcrack structure in the conductive coating layer induced by the mismatch of elastic modulus and thermal expansion coefficient between conductive coating layer and paper substrate during the drying process,the prepared paper-based strain sensor exhibited a high sensitivity(gauge factor,GF=17.4)in the strain range of 0–0.6%,ultralow detection limit(0.1%strain)and good fatigue resistance over 1000 cycles towards bending deformation.Interestingly,it was also applicable for torsion deformation detection,showing excellent torsion angle dependent,repeatable and stable sensing performances.Meanwhile,it displayed brilliant waterproof,self-cleaning and corrosion-resistant properties due to the existence of micro/nano-structured and the low surface energy candle soot layer.As a result,the prepared paper-based strain sensor can effectively monitor a series of large-scale and small-scale human motions even under water environment,showing the great promising in practical harsh outdoor environments.Importantly,it also demonstrated good applicability for spatial strain distribution detection of skin upon body movement when assembled into electronic-skin(E-skin).This study will provide great guidance for the design of next generation wearable strain sensor.展开更多
A fast multipole boundary element method （FM-BEM） was applied for the analysis of microcracked solids. Both the computational complexity and memory requirement are reduced to O（N）, where N is the number of degrees...A fast multipole boundary element method （FM-BEM） was applied for the analysis of microcracked solids. Both the computational complexity and memory requirement are reduced to O（N）, where N is the number of degrees of freedom. The effective elastic moduli of a 2-D solid containing thousands of randomly distributed microcracks were evaluated using the FM-BEM. The results prove that both the differential method and the method proposed by Feng and Yu provide satisfactory estimates to such problems. The effect of a non-uniform distribution of microcracks has been studied using a novel model. The numerical results show that the non-uniform distribution induces a small increase in the global stiffness.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
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
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
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
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
Nonequilibrium statistical theory of fracture is a theory of fracture that macromechanical quantities can be derived from the microscopic atomic mechanism of microcrack(or microvoid)evolution kinetcs by means of noneq...Nonequilibrium statistical theory of fracture is a theory of fracture that macromechanical quantities can be derived from the microscopic atomic mechanism of microcrack(or microvoid)evolution kinetcs by means of nonequilibrium statistical physical concepts and methods. The microcrack evolution equation is the central equation in the theory.The coefficents of the equation, the microcrack growth rate and the microcrack nucleation rate,come from microscopic atomic mechanism.The solution of the equation connects with macromechanical quantities by the model of the weakest chain. All the other formulas and quantities, for instance, distribution function,fracture probability, reliability, failure rate and macromechanical quantities such as strength, toughness, life etc. and their statistical distribution function and statistical fluctuation are derived in a unified fashion and expressed by a few physical parameters. This theory can be widely applied to various kinds of fracture, such as the brittle, fatigue, delayed and environmental fracture of metals and structural ceramics. The theoretical framework of this theory is given in this paper.展开更多
The nominal Ti44Al6Nb1.0Cr2.0V alloy was newly designed and prepared by vacuum consumable melting technique with the ingot sizes of d225 mm×320 mm. The results show that the average lamella colony size is 780-18...The nominal Ti44Al6Nb1.0Cr2.0V alloy was newly designed and prepared by vacuum consumable melting technique with the ingot sizes of d225 mm×320 mm. The results show that the average lamella colony size is 780-1830 μm. This as-cast alloy has a modified near lamellar(M-NL) structure that is composed of mainly larger(α2+γ) lamella colonies and smaller(B2+equiaxed γ) blocky morphology. It exhibits the moderate tensile properties at room temperature, in which the Region(5) yields the ultimate tensile strength(UTS) about 499 MPa and the elongation about 0.53%. The obvious brittle fracture characteristics and trans-granular interlamellar fracture are the predominant modes. After room temperature tensile testing, there are some <101] and a few 1/2<112] superdislocations in the γ phase. The as-cast microcrack is the main factor to deteriorate the tensile property, which results in the premature fracture, poor ductility and few dislocations. The addition of Nb, Cr and V can decrease stacking fault energy(SFE) obviously, which is helpful to enhancing the ductility of the alloy.展开更多
In order to investigate the failure process of brittle rock under triaxial compression through both experimental and numerical approaches, the particle simulation method was used in numerical simulations and the simul...In order to investigate the failure process of brittle rock under triaxial compression through both experimental and numerical approaches, the particle simulation method was used in numerical simulations and the simulated results were compared with those of the experiment. The numerical simulation results, such as fracture propagation, microcrack distribution, stress-strain response, and damage patterns, were discussed in detail. The simulated results under various confining pressures （0-60 MPa） are in good agreement with the experimental results. The simulated results reveal that rock failure is caused by axial splitting under uniaxial compression. As the confining pressure increases, rock failure occurs in a few localized shear planes and the rock mechanical behavior is changed from brittle to ductile. Consequently, the peak failure strength, microcrack numbers, and the shear plane angle increase, but the ratio of tensile to shear microcracks decreases. The damage formation during the compression simulations indicates that the particle simulation method can produce similar behaviors as those observed through laboratory compression tests.展开更多
We identify two interrelated but independent species of microcracks with different origins and different distributions. One species is the classic high-stress microcracks identified in laboratory stress-cells associat...We identify two interrelated but independent species of microcracks with different origins and different distributions. One species is the classic high-stress microcracks identified in laboratory stress-cells associated with acoustic emissions as microcracks open with increasing stress. The other species is the low-stress distributions of closely-spaced stress-aligned fluid-saturated microcracks that observations of shear-wave splitting(SWS) demonstrate pervade almost all in situ rocks in the upper crust, the lower crust, and the uppermost 400 km of the mantle. On some occasions these two sets of microcracks may be interrelated and similar(hence ‘species') but they typically have fundamentally-different properties, different distributions, and different implications. The importance for hydrocarbon exploration and recovery is that SWS in hydrocarbon reservoirs monitors crack alignments and preferred directions of fluid-flow. The importance for earthquake seismology is that SWS above small earthquakes monitors the effects of increasing stress on the pervasive low-stress microcrack distributions so that stress-accumulation before, possibly distant, earthquakes can be recognised and impending earthquakes stress-forecast.展开更多
The cracking patterns of a thin sheet with a pre-existing crack subjected to dynamic loading are numerically simulated to investigate the mechanism of crack branching by using the FEM method.Six numerical models were ...The cracking patterns of a thin sheet with a pre-existing crack subjected to dynamic loading are numerically simulated to investigate the mechanism of crack branching by using the FEM method.Six numerical models were set up to study the effects of load,tensile strength and heterogeneity on crack branching.The crack propagation is affected by the applied loads,tensile strength and heterogeneity.Before crack branching,the crack propagates by some distance along the direction of the pre-existing crack.For the materials with low heterogeneity,the higher the applied stress level is and the lower the tensile strength of the material is,the shorter the propagation distance is.Moreover,the branching angle becomes larger and the number of branching cracks increases.In the case of the materials with high heterogeneity,a lot of disordered voids and microcracks randomly occur along the main crack,so the former law is not obvious.The numerical results not only are in good agreement with the experimental observations in laboratory,but also can be extended to heterogeneity media.The work can provide a good approach to model the cracking and fracturing of heterogeneous quasi-brittle materials,such as rock,under dynamic loading.展开更多
文摘Micromechanics models have been developed For the determination of the elastic moduli of microcracked solids based on different approaches and interpretations, including the dilute or non-interacting solution, the Mori-Tanaka method, the self-consistent method, and the generalized self-consistent method. It is shown in the present study that all these micromechanics models can be unified within an energy-equivalence framework, and that they differ only in the way in which the microcrack opening and sliding displacements are evaluated. Relevance to the differential methods and the verification of these models are discussed.
基金This work was supported by the Laoshan National Laboratory Science and Technology Innovation Project(No.LSKJ202203407)the National Natural Science Foundation of China(Grant Nos.42174145,41821002,42274146)+1 种基金Guangdong Provincial Key Laboratory of Geophysical High-resolution Imaging Technology(2022B1212010002)Shenzhen Stable Support Plan Program for Higher Education Institutions(20220815110144003).
文摘P-and SV-wave dispersion and attenuation have been extensively investigated in saturated poroelastic media with aligned fractures.However,there are few existing models that incorporate the multiple wave attenuation mechanisms from the microscopic scale to the macroscopic scale.Hence,in this work,we developed a unified model to incorporate the wave attenuation mechanisms at different scales,which includes the microscopic squirt flow between the microcracks and pores,the mesoscopic wave-induced fluid flow between fractures and background(FB-WIFF),and the macroscopic Biot's global flow and elastic scattering(ES)from the fractures.Using Tang's modified Biot's theory and the mixed-boundary conditions,we derived the exact frequency-dependent solutions of the scattering problem for a single penny-shaped fracture with oblique incident P-and SV-waves.We then developed theoretical models for a set of aligned fractures and randomly oriented fractures using the Foldy approximation.The results indicated that microcrack squirt flow considerably influences the dispersion and attenuation of P-and SV-wave velocities.The coupling effects of microcrack squirt flow with the FB-WIFF and ES of fractures cause much higher velocity dispersion and attenuation for P waves than for SV waves.Randomly oriented fractures substantially reduce the attenuation caused by the FB-WIFF and ES,particularly for the ES attenuation of SV waves.Through a comparison with existing models in the limiting cases and previous experimental measurements,we validated our model.
基金supported by the National Natural Science Foundation of China(51803191,12072325)the National Key R&D Program of China(2019YFA0706802)+2 种基金the 111 project(D18023)Key Scientific and Technological Project of Henan Province(202102210038)Major projects of Ningbo。
文摘With the rapid development of wearable intelligent devices,low-cost wearable strain sensors with high sensitivity and low detection limit are urgently demanded.Meanwhile,sensing stability of sensor in wet or corrosive environments should also be considered in practical applications.Here,superhydrophobic microcracked conductive paper-based strain sensor was fabricated by coating conductive Ti_(3)C_(2)T_(x) MXene on printing paper via dip-coating process and followed by depositing superhydrophobic candle soot layer on its surface.Owing to the ultrasensitive microcrack structure in the conductive coating layer induced by the mismatch of elastic modulus and thermal expansion coefficient between conductive coating layer and paper substrate during the drying process,the prepared paper-based strain sensor exhibited a high sensitivity(gauge factor,GF=17.4)in the strain range of 0–0.6%,ultralow detection limit(0.1%strain)and good fatigue resistance over 1000 cycles towards bending deformation.Interestingly,it was also applicable for torsion deformation detection,showing excellent torsion angle dependent,repeatable and stable sensing performances.Meanwhile,it displayed brilliant waterproof,self-cleaning and corrosion-resistant properties due to the existence of micro/nano-structured and the low surface energy candle soot layer.As a result,the prepared paper-based strain sensor can effectively monitor a series of large-scale and small-scale human motions even under water environment,showing the great promising in practical harsh outdoor environments.Importantly,it also demonstrated good applicability for spatial strain distribution detection of skin upon body movement when assembled into electronic-skin(E-skin).This study will provide great guidance for the design of next generation wearable strain sensor.
基金the National Natural Science Foundation of China (No. 10472051)
文摘A fast multipole boundary element method （FM-BEM） was applied for the analysis of microcracked solids. Both the computational complexity and memory requirement are reduced to O（N）, where N is the number of degrees of freedom. The effective elastic moduli of a 2-D solid containing thousands of randomly distributed microcracks were evaluated using the FM-BEM. The results prove that both the differential method and the method proposed by Feng and Yu provide satisfactory estimates to such problems. The effect of a non-uniform distribution of microcracks has been studied using a novel model. The numerical results show that the non-uniform distribution induces a small increase in the global stiffness.
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.
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.
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 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.
文摘Nonequilibrium statistical theory of fracture is a theory of fracture that macromechanical quantities can be derived from the microscopic atomic mechanism of microcrack(or microvoid)evolution kinetcs by means of nonequilibrium statistical physical concepts and methods. The microcrack evolution equation is the central equation in the theory.The coefficents of the equation, the microcrack growth rate and the microcrack nucleation rate,come from microscopic atomic mechanism.The solution of the equation connects with macromechanical quantities by the model of the weakest chain. All the other formulas and quantities, for instance, distribution function,fracture probability, reliability, failure rate and macromechanical quantities such as strength, toughness, life etc. and their statistical distribution function and statistical fluctuation are derived in a unified fashion and expressed by a few physical parameters. This theory can be widely applied to various kinds of fracture, such as the brittle, fatigue, delayed and environmental fracture of metals and structural ceramics. The theoretical framework of this theory is given in this paper.
基金Project(2011CB605504)supported by the National Basic Research Program of ChinaProject(NCET-12-0153)supported by the Program of New Century Excellent Talents in UniversityProject(51274076)supported by the National Natural Science Foundation of China
文摘The nominal Ti44Al6Nb1.0Cr2.0V alloy was newly designed and prepared by vacuum consumable melting technique with the ingot sizes of d225 mm×320 mm. The results show that the average lamella colony size is 780-1830 μm. This as-cast alloy has a modified near lamellar(M-NL) structure that is composed of mainly larger(α2+γ) lamella colonies and smaller(B2+equiaxed γ) blocky morphology. It exhibits the moderate tensile properties at room temperature, in which the Region(5) yields the ultimate tensile strength(UTS) about 499 MPa and the elongation about 0.53%. The obvious brittle fracture characteristics and trans-granular interlamellar fracture are the predominant modes. After room temperature tensile testing, there are some <101] and a few 1/2<112] superdislocations in the γ phase. The as-cast microcrack is the main factor to deteriorate the tensile property, which results in the premature fracture, poor ductility and few dislocations. The addition of Nb, Cr and V can decrease stacking fault energy(SFE) obviously, which is helpful to enhancing the ductility of the alloy.
基金supported by the Graduate Degree Thesis Innovation Foundation of Central South University (No.2009ssxt226)
文摘In order to investigate the failure process of brittle rock under triaxial compression through both experimental and numerical approaches, the particle simulation method was used in numerical simulations and the simulated results were compared with those of the experiment. The numerical simulation results, such as fracture propagation, microcrack distribution, stress-strain response, and damage patterns, were discussed in detail. The simulated results under various confining pressures （0-60 MPa） are in good agreement with the experimental results. The simulated results reveal that rock failure is caused by axial splitting under uniaxial compression. As the confining pressure increases, rock failure occurs in a few localized shear planes and the rock mechanical behavior is changed from brittle to ductile. Consequently, the peak failure strength, microcrack numbers, and the shear plane angle increase, but the ratio of tensile to shear microcracks decreases. The damage formation during the compression simulations indicates that the particle simulation method can produce similar behaviors as those observed through laboratory compression tests.
基金This study was partially supported by the National Natural Science Foundation of China （No. 41174042）.
文摘We identify two interrelated but independent species of microcracks with different origins and different distributions. One species is the classic high-stress microcracks identified in laboratory stress-cells associated with acoustic emissions as microcracks open with increasing stress. The other species is the low-stress distributions of closely-spaced stress-aligned fluid-saturated microcracks that observations of shear-wave splitting(SWS) demonstrate pervade almost all in situ rocks in the upper crust, the lower crust, and the uppermost 400 km of the mantle. On some occasions these two sets of microcracks may be interrelated and similar(hence ‘species') but they typically have fundamentally-different properties, different distributions, and different implications. The importance for hydrocarbon exploration and recovery is that SWS in hydrocarbon reservoirs monitors crack alignments and preferred directions of fluid-flow. The importance for earthquake seismology is that SWS above small earthquakes monitors the effects of increasing stress on the pervasive low-stress microcrack distributions so that stress-accumulation before, possibly distant, earthquakes can be recognised and impending earthquakes stress-forecast.
基金Project(50820125405)supported by the National Natural Science Foundation of ChinaProject(51121005)supported by the National Natural Science Foundation of China
文摘The cracking patterns of a thin sheet with a pre-existing crack subjected to dynamic loading are numerically simulated to investigate the mechanism of crack branching by using the FEM method.Six numerical models were set up to study the effects of load,tensile strength and heterogeneity on crack branching.The crack propagation is affected by the applied loads,tensile strength and heterogeneity.Before crack branching,the crack propagates by some distance along the direction of the pre-existing crack.For the materials with low heterogeneity,the higher the applied stress level is and the lower the tensile strength of the material is,the shorter the propagation distance is.Moreover,the branching angle becomes larger and the number of branching cracks increases.In the case of the materials with high heterogeneity,a lot of disordered voids and microcracks randomly occur along the main crack,so the former law is not obvious.The numerical results not only are in good agreement with the experimental observations in laboratory,but also can be extended to heterogeneity media.The work can provide a good approach to model the cracking and fracturing of heterogeneous quasi-brittle materials,such as rock,under dynamic loading.
