Microcrack growth during progressive compressive failure in brittle rocks strongly influences the safety of deep underground engineering.The external shear stressτxy on brittle rocks greatly affects microcrack growth...Microcrack growth during progressive compressive failure in brittle rocks strongly influences the safety of deep underground engineering.The external shear stressτxy on brittle rocks greatly affects microcrack growth and progressive failure.However,the theoretical mechanism of the growth direction evolution of the newly generated wing crack during progressive failure has rarely been studied.A novel analytical method is proposed to evaluate the shear stress effect on the progressive compressive failure and microcrack growth direction in brittle rocks.This model consists of the wing crack growth model under the principal compressive stresses,the direction correlation of the general stress,the principal stress and the initial microcrack inclination,and the relationship between the wing crack length and strain.The shear stress effect on the relationship between y-direction stress and wing crack growth and the relationship between y-direction stress and y-direction strain are analyzed.The shear stress effect on the wing crack growth direction during the progressive compressive failure is determined.The initial crack angle effect on the y-direction peak stress and the wing crack growth direction during the progressive compressive failure considering shear stress is also discussed.A crucial conclusion is that the direction of wing crack growth has a U-shaped variation with the growth of the wing crack.The rationality of the analytical results is verified by an experiment and from numerical results.The study results provide theoretical support for the evaluation of the safety and stability of surrounding rocks in deep underground engineering.展开更多
This study leverages machine learning to perform high-throughput computational screening of n-hexane cracking initiators.Artificial neural networks are applied to predict the chemical performance of initiators,using s...This study leverages machine learning to perform high-throughput computational screening of n-hexane cracking initiators.Artificial neural networks are applied to predict the chemical performance of initiators,using simulated pyrolysis data as the training dataset.Various feature extraction methods are utilized,and five neural network architectures are developed to predict the co-cracking product distribution based on molecular structures.High-throughput screening of 12946 molecules outside the training dataset identifies the top 10 initiators for each target product—ethylene,propylene,and butadiene.The relative error between predicted and simulated values is less than 7%.Additionally,reaction pathway analysis elucidates the mechanisms by which initiators influence the distribution of cracking products.The proposed framework provides a practical and efficient approach for the rapid identification and evaluation of high-performance cracking initiators.展开更多
Crack initiation mechanism of dwell fatigue has always been a key problem in rationalizing the dwell effect,and it is not completely understood yet.This study conducted stress-controlled low-cycle fatigue and dwell fa...Crack initiation mechanism of dwell fatigue has always been a key problem in rationalizing the dwell effect,and it is not completely understood yet.This study conducted stress-controlled low-cycle fatigue and dwell fatigue tests on Ti-6Al-3Nb-2Zr-1Mo alloy with bimodal microstructure to reveal its microstructural characteristics and crack initiation mechanisms.The study demonstrated that the faceted primaryα nodules located near the specimen surface acted as crack initiation sites during both fatigue and dwell fatigue tests.Slip trace analysis revealed that faceted cracking occurred at(0001)basal plane with the maximum Schmid factor value through a special cracking mode referred to as(0001)twist boundary cracking.Innovative criteria of parameters C1 and C2 were proposed based on experimental observation and molecular dynamics simulations,which well identify candidates for(0001)twist boundary crack nucleation.It demonstrated that grain pairs combining a moderately high Schmid factor for basal slip and a well-orientated Burgers vector in the out-of-surface plane was the preferable location for surface(0001)twist-boundary crack initiation,and grain pairs combining a high Schmid factor for basal slip and a high normal stress on basal plane are perfect candidates for subsurface cracking.Based on this,phenomeno-logical models are proposed to explain the surface(0001)twist-boundary cracking mechanism from the perspective of surface extrusion-intrusion-induced micro-notches.展开更多
Mg-Li alloys hold significant potential for applications in aerospace,automotive manufacturing,military weaponry,and biomedical implants,due to their excellent recyclability,high specific strength,biocompatibility,and...Mg-Li alloys hold significant potential for applications in aerospace,automotive manufacturing,military weaponry,and biomedical implants,due to their excellent recyclability,high specific strength,biocompatibility,and superior electromagnetic shielding properties.However,their poor corrosion resistance and high susceptibility to environmentally assisted cracking(EAC)significantly limit broader application.In recent years,growing attention has been directed toward understanding the corrosion and EAC behavior of Mg-Li alloys,as localized corrosion areas and hydrogen generated during the corrosion process can serve as crack initiation points and promote crack propagation.A comprehensive understanding of these mechanisms is essential for enhancing the reliability and performance of Mg-Li alloys in practical environments.This paper presents a detailed review of corrosion and EAC in Mg-Li alloys,focusing on corrosion behavior,crack initiation and propagation mechanisms,and the key factors influencing these processes.It summarizes recent advances in alloying,heat treatment,mechanical processing,microstructural control,environmental influences,mechanical loading,and surface treatments.In addition,the paper explores future research directions,highlights emerging trends,and proposes strategies to improve the durability and service performance of Mg-Li alloys.展开更多
The dynamic mechanical response and deformation mechanism of magnesium-yttrium alloy at high strain rate were investigated using split-Hopkinson pressure bar(SHPB)impact,and the microstructure evolution and crack form...The dynamic mechanical response and deformation mechanism of magnesium-yttrium alloy at high strain rate were investigated using split-Hopkinson pressure bar(SHPB)impact,and the microstructure evolution and crack formation mechanism were revealed.The yield strength and work hardening rate increase significantly with increasing impact strain rate.Deformation twinning and non-basal dislocation slip are the primary deformation mechanisms during testing.Contrary to crack initiation mechanism facilitated by adiabatic shear bands,we find that high-density co-axial nanocrystalline grains form near cracks,which leads to local softening and promotes crack initiation and rapid propagation.Most grains have similar<1^(-)21^(-)0>orientations,with unique misorientation of 24°,32°,62°,78°and 90°between adjacent grains,suggesting that these grains are primarily formed by interface transformation,which exhibits distinct differences from recrystallized grains.Our results shed light upon the dynamic mechanical response and crack formation mechanism in magnesium alloys under impact deformation.展开更多
The evolution of cracks in shale directly affects the efficient production of shale gas.However,there is a lack of research on the characteristics of crack initiation in deep dense shale under different stress conditi...The evolution of cracks in shale directly affects the efficient production of shale gas.However,there is a lack of research on the characteristics of crack initiation in deep dense shale under different stress conditions.In this work,considering the different combinations of confining pressure and bedding plane inclination angle(α),biaxial mechanical loading experiments were conducted on shale containing circular holes.The research results indicate that the confining pressure and inclination angle of the bedding planes significantly influence the failure patterns of shale containing circular holes.The instability of shale containing circular holes can be classified into five types:tensile failure along the bedding planes,tensile failure through the bedding planes,shear slip along the bedding planes,shear failure through the bedding planes,and block instability failure.Furthermore,the evolution of strain and stress fields around the circular holes was found to be the fundamental cause of variations in the initiation characteristics and locations of shale cracks.The crack initiation criterion for shale containing circular hole was established,providing a new method for evaluating the trajectory of shale hole wall fractures.This study holds significant importance for evaluating the evolution and stability of fracture networks within shale reservoirs.展开更多
Hydrogen has emerged as a promising clean energy source,leading to numerous recent efforts to integrate hydrogen into turbine engine applications[1].This integration has the potential to significantly enhance engine e...Hydrogen has emerged as a promising clean energy source,leading to numerous recent efforts to integrate hydrogen into turbine engine applications[1].This integration has the potential to significantly enhance engine efficiency while reducing carbon dioxide emissions[2].However,the degradation of nickel alloys induced by hydrogen has been well documented[3-7].Consequently,hydrogen-assisted failure of nickel alloys poses a critical concern for the design and safe operation of hydrogen-powered turbine engines.展开更多
This paper deals with the mechanism of the formation of initial cracks in the yttria partially stabilized zirconia thermal barrier coatings prepared by EB-PVD method.The microcracks were only recognized inside the cer...This paper deals with the mechanism of the formation of initial cracks in the yttria partially stabilized zirconia thermal barrier coatings prepared by EB-PVD method.The microcracks were only recognized inside the ceramic top coat of the thermalcycled TBCs. SEM/EDS observations indicated that some special oxides exist in the area just below the cracks.It seems that the formation of the initial cracks can result from the oxidation stress as well as the thermal stress.展开更多
The crack initiation stress threshold is widely used in excavation industries as rock spalling strength when designing deep underground structures to avoid unwanted brittle failures.While various strain-based methods ...The crack initiation stress threshold is widely used in excavation industries as rock spalling strength when designing deep underground structures to avoid unwanted brittle failures.While various strain-based methods have been developed for the estimation of this critical design parameter,such methods are destructive and often requires subjective interpretations of the stress–strain curves,particularly in rocks with pre-existing microcracks or high porosity.This study explore the applicability of non-destructive ultrasonic through-transmission methods for determining rock damage levels by assessing the changes in transmitted signal characteristics during loading.The change in velocity,amplitude,dominant frequency,and root-mean-square voltage are investigated with four different rock types including marble,sandstone,granite,and basalt under various stress levels.Results suggest the rate of signal variations can be reliably used to estimate crack closure and crack initiation stress levels across the tested rocks before failure.Comparison of the results between the conventional techniques and the new proposed methods based on ultrasonic monitoring are further discussed.展开更多
Low-cycle fatigue crack initiation behavior of nickel-based single crystal superalloy at 530℃ was investigated.Results show that the behavior of crack initiation is closely related to the maximum strain.When the maxi...Low-cycle fatigue crack initiation behavior of nickel-based single crystal superalloy at 530℃ was investigated.Results show that the behavior of crack initiation is closely related to the maximum strain.When the maximum strain is 2.0%,the fatigue crack is originated at the position of persistent slip bands on the surface of specimen,which is located on the{111}slip plane.No defects are observed at the crack initiation position.When the maximum strain is lower than 1.6%,the cracks are initiated at the casting defects on sub-surface or at interior of the specimen.The casting defects are located on the{100}slip plane vertical to the axial force.The crack is initiated along the{100}slip plane and then expanded along different{111}slip planes after a short stage of expansion.As the maximum strain decreases,the position of crack initiation gradually changes from the surface to the interior.Moreover,the secondary cracks extending inward along the fracture surface appear in the crack initiation area,and there is obvious stress concentration near the secondary cracks.The dislocation density is high near the fracture surface in the crack initiation zone,where a lot of dislocations cutting into the γ'phase exist.An oxide layer of 50‒100 nm is presented on the fracture surface,and Ni,Al,Cr and Co elements are mainly segregated into the oxide layer of the surface.展开更多
Fatigue failure can still occur beyond 107 cycles,i.e.very-high-cycle fatigue(VHCF),in many metallic materials,such as aluminium alloys and high-strength steels.For VHCF of high-strength steels,a fine granular area(FG...Fatigue failure can still occur beyond 107 cycles,i.e.very-high-cycle fatigue(VHCF),in many metallic materials,such as aluminium alloys and high-strength steels.For VHCF of high-strength steels,a fine granular area(FGA)surrounding an inclusion is commonly identified as the characteristic region of crack initiation on the fracture surface.However,no such FGA feature and related crack initiation behaviour were observed in VHCF of conventionally cast or wrought aluminium alloys.Here,we first reported the distinct mechanisms of crack initiation and early growth,namely the microstructure feature and the role of FGA in VHCF performance for an additively manufactured(AM)AlSi10Mg alloy.The AM pores play a key role in fatigue crack initiation similar to that of the inclusions in high-strength steels,resulting in almost identical FGA behaviour for different materials under a range of mean stress with a stress ratio at R<0 or R>0.The profile microstructure of FGA is identified as a nanograin layer with Si rearrangement and grain boundary transition.This process consumes a large amount of cyclic plastic energy making FGA undertake a vast majority of VHCF life.These results will deepen the understanding of VHCF nature and shed light on crack initiation mechanism of other aluminium and AM alloys.展开更多
Discontinuously reinforced titanium matrix composites(DRTMCs)with a network structure have been extensively researched due to their superior combination of strength and ductility.However,their fatigue performance has ...Discontinuously reinforced titanium matrix composites(DRTMCs)with a network structure have been extensively researched due to their superior combination of strength and ductility.However,their fatigue performance has remained unknown.In order to elucidate the fatigue behavior of DRTMCs,a tension-tension fatigue test was performed on a TiB/nearα-Ti composite with network structure.The results showed that the variability of fatigue lifetime increased as the stress level decreased.Fractography analysis indicated that fatigue crack initiation was associated with facet formation,while the subsequent propagation was hindered by the network structure comprising TiB whiskers and silicides.Crystallographic characterization further revealed that facets formed due to a combination of shear and normal stress.The reduction in fatigue lifetime was attributed to an increase in the effective slip length,which was influenced by the orientation of grains near the crack-initiation sites toward basal slip in the life-limiting specimen.Quasi in situ observation suggested that the crack initiation was facilitated by both basal and prismatic slip ofα-Ti as well as fracture of TiBw.Crack propagation was found to be associated with basal and prismatic slip systems with high Schmid factors,regardless of whether the crack was intergranular or intragranular.展开更多
Although the seemingly negative effect of deformation-induced martensite(DIM)volume fraction on the impact toughness of austenitic steels has been well documented,it relies mostly on analyzing crack propagation withou...Although the seemingly negative effect of deformation-induced martensite(DIM)volume fraction on the impact toughness of austenitic steels has been well documented,it relies mostly on analyzing crack propagation without explicitly considering the crack initiation process which,however,plays a crucial role in these ductile alloys.The dependence of crack initiation energy(Ei)on martensitic transformation mechanisms is still ambiguous,inhibiting the precise design of damage-tolerant and ductile alloys.Here,we explore the temperature-dependent crack initiation energy of a SUS321 stainless steel at various temperatures(25,-50,and-196℃).Contrary to the crack propagation energy(Ep),the Ei has a weak correlation with the volume fraction ofα′-martensite but a strong correlation with the martensitic transformation rate.Also contrary to the traditional viewpoint of Ep consideringε-martensite as a detrimental phase,a high volume fraction ofε-martensite turns out to be beneficial to the increase of Ei,thereby enhancing impact toughness.As such,an optimal value(15 mJ/m^(2))for the stacking fault energy(SFE),which dictates theγ→ε→α′transformation sequence,is given as a new design guideline for enhancing the Ei and consequently the impact toughness of ductile steels.The generality of this guideline is further validated in multiple austenitic steels with different compositions and grain sizes.展开更多
The fatigue crack initiation and early propagation behavior of 2A97 Al-Li alloy was studied. The smooth specimens were fatigued at room temperature under constant maximum stress control when stress ratio （R） is 0.1 ...The fatigue crack initiation and early propagation behavior of 2A97 Al-Li alloy was studied. The smooth specimens were fatigued at room temperature under constant maximum stress control when stress ratio （R） is 0.1 and frequency （f） is 40 Hz. Microstructure observations were examined by optical microscopy, transmission electron microscopy, scanning electron microscopy and electron back scattered diffusion, in order to investigate the relationship between microstructure and fatigue crack initiation and early propagation behavior of 2A97 alloy. The results show that the fatigue cracks are predominantly initiated at inclusions and coarsen secondary phases on the surface of 2A97 alloy. The fatigue crack early propagation behavior of 2A97 alloy is predominantly influenced by the interactions between grain structure and dislocations or persistent slip bands （PSBs）. When the misorientation of two neighbouring grains is close to the orientations of the favorable slip plane within these two grains, high-angle grain boundary severely hinders the PSBs passing through, and thus leads to crack bifurcation and deflection.展开更多
The long-term stability of the roof is particularly important in designing underground rock structures.To estimate the durability of roof strata in underground excavation,a computation scheme of subcritical crack grow...The long-term stability of the roof is particularly important in designing underground rock structures.To estimate the durability of roof strata in underground excavation,a computation scheme of subcritical crack growth is proposed in this study.By adopting the proposed method,the potential collapse location of strata is derivable in accordance with a static model,the durability of roof strata can be estimated,a dynamic time step control strategy is achieved to balance the accuracy and speed of computing,and the initial crack size of rock can be estimated.In addition to the above,a mechanical model of underground excavation with non-uniformly distributed loads and partially yielded foundation is presented as the prototypical case.A set of case studies is carried out that showcase a power correlation between applied stress and roof durability.The allowable applied tensile stress for a 100-year life cycle is about 76%of the tensile strength.By using the proposed subcritical crack growth computation scheme,the roof stability in an underground excavation can be identified not only from the spatial view but also from the temporal perspective.展开更多
An analytical model for predicting the corrosion-induced cracking of concrete cover of reinforced concrete(RC) structures was developed.The effects of influence factors such as practical initial defects,corrosion rate...An analytical model for predicting the corrosion-induced cracking of concrete cover of reinforced concrete(RC) structures was developed.The effects of influence factors such as practical initial defects,corrosion rate,strength and elastic modulus of concrete on the corrosion-induced cracking of concrete cover were investigated.It was found that the size of practical initial defects was the most effective factor.Therefore,improving the compactness of concrete is an effective way to improve the durability of RC structures.It was also demonstrated that the accelerated corrosion tests may be unfavorable in the study of the relationship between cracking time and crack width.展开更多
The loaded rock experiences multiple stages of deformation.It starts with the formation of microcracks at low stresses(crack initiation,CI)and then transitions into unstable crack propagation(crack damage,CD)near the ...The loaded rock experiences multiple stages of deformation.It starts with the formation of microcracks at low stresses(crack initiation,CI)and then transitions into unstable crack propagation(crack damage,CD)near the ultimate strength.In this study,both the acoustic emission method(AEM)and the ultrasonic testing method(UTM)were used to examine the characteristics of AE parameters(b-value,peak frequency,frequency-band energy ratio,and fractal dimension)and ultrasonic(ULT)properties(velocity,amplitude,energy attenuation,and scattering attenuation)of bedded shale at CI,CD,and ultimate strength.The comparison involved analyzing the strain-based method(SBM),AEM,and UTM to determine the thresholds for damage stress.A fuzzy comprehensive evaluation model(FCEM)was created to describe the damage thresholds and hazard assessment.The results indicate that the optimal AE and ULT parameters for identifying CI and CD stress are ringing count,ultrasonic amplitude,energy attenuation,and scattering attenuation of the S-wave.Besides,damage thresholds were detected earlier by AE monitoring,ranging from 3 MPa to 10 MPa.CI and CD identified by UTM occurred later than SBM and AEM,and were in the range of 12 MPa.The b-value,peak frequency,energy ratio in the low-frequency band(0e62.5 kHz),correlation dimension,and sandbox dimension showed low values at the peak stress,while the energy ratio in a moderate-frequency band(187.5e281.25 kHz)and amplitude showed high values.The successful application of FCEM to laboratory testing of shales has demonstrated its ability to quantitatively identify AE/ULT precursors of seismic hazards associated with rock failure.展开更多
Aiming at mitigating the high risks associated with conventional explosive blasting,this study developed a safe directional fracturing technique,i.e.instantaneous expansion with a single fracture(IESF),using a coal-ba...Aiming at mitigating the high risks associated with conventional explosive blasting,this study developed a safe directional fracturing technique,i.e.instantaneous expansion with a single fracture(IESF),using a coal-based solid waste expanding agent.First,the mechanism of directional fracturing blasting by the IESF was analyzed,and the criterion of directional crack initiation was established.On this basis,laboratory experiments and numerical simulations were conducted to systematically evaluate the directional fracturing blasting performance of the IESF.The results indicate that the IESF presents an excellent directional fracturing effect,with average surface undulation differences ranging from 8.1 mm to 22.7 mm on the fracture surfaces.Moreover,during concrete fracturing tests,the stresses and strains in the fracturing direction are measured to be 2.16-3.71 times and 8 times larger than those in the nonfracturing direction,respectively.Finally,the IESF technique was implemented for no-pillar mining with gob-side entry retaining through roof cutting and pressure relief in an underground coal mine.The IESF technique effectively created directional cracks in the roof without causing severe roadway deformation,achieving an average cutting rate and maximum roadway deformation of 94%and 197 mm,respectively.These on-site test results verified its excellent directional rock fracturing performance.The IESF technique,which is safe,efficient,and green,has considerable application prospects in the field of rock mechanics and engineering.展开更多
A laboratory study was undertaken to investigate drying shrinkage and cracking sensitivity subjected to restrained shrinkage of mortar containing fly ash (FA), granulated blast-furnace slag (GBFS) and silica fume (SF)...A laboratory study was undertaken to investigate drying shrinkage and cracking sensitivity subjected to restrained shrinkage of mortar containing fly ash (FA), granulated blast-furnace slag (GBFS) and silica fume (SF). Six mortar mixtures including control Portland cement (PC) and FA, GBFS and SF mortar mixtures were prepared. FA replaced the cement on mass basis at the replacement ratios of 20% and 35%, GBFS replaced the cement at the replacement ratios of 40%, SF replaced the cement at the replacement ratios of 8% and the blended mixtures with 20% FA, 20% GBFS and 8% SF. Water-cementitious materials ratio and sand-cementitious materials ratio were 0.4 and 2.0 for all mixtures, respectively. The mixtures were cured at 65% relative humidity and 20℃. The drying shrinkage value, initial cracking time and cracking width of the mortar samples were measured. The results show that all the mortar mixture containing FA exhibited the decrease of drying shrinkage. Moreover, initial cracking time was markedly delayed, and the crack width of the initial crack was reduced. However, the incorporations of various ratios of GBFS and SF led to an increase of drying shrinkage, initial cracking time and cracking width as compared to control mixture.展开更多
The critical wear rate,surface damage,deformation layer,crack initiation and propagation of U76CrRE heavy rail steel samples of two different cooling conditions(rolled rail,and heat-treated rail)under intermittent loa...The critical wear rate,surface damage,deformation layer,crack initiation and propagation of U76CrRE heavy rail steel samples of two different cooling conditions(rolled rail,and heat-treated rail)under intermittent load were measured and observed by friction and wear tester,laser confocal microscope,scanning electron microscope and EBSD.The experimental results show that when the same kind of rail is matched with wheel steel with low hardness and high hardness successively,the critical wear rate of rail moves to the right.Moreover,when the rolled rail is matched with wheel steel with low hardness,the deformation layer and wear amount are larger than those of heat-treated rail are,while when it is matched with wheel steel with high hardness,the deformation layer and wear amount are smaller than those of heat-treated rail.When the rolled rail and heat-treated rail are matched with the same kind of wheel steel successively,the critical wear rate moves down,and the wear deformation layer of heat-treated rail is smaller than that of rolled rail.The failure life of the heat-treated rail is better than that of the rolled rail,which is due to the increase of the hardness of the heat-treated rail and the refinement of pearlite lamellae.With the increase of the distance from the surface layer,the proportion of large-angle grain boundaries of ferrite grains gradually increases of rolled rail and heat-treated rail,but the rolled rail presents the characteristics of large crack angle,deep depth and small length,mainly due to wear failure.While the heat-treated rail has the characteristics of small crack angle,shallow depth and long length,the crack propagation trend is obvious,and the failure form of the heat-treated rail is mainly fatigue failure.Moving the critical wear rate to the right and down is beneficial to inhibit the formation and propagation of fatigue cracks.展开更多
基金National Natural Science Foundation of China,Grant/Award Numbers:51708016,12172036R&D Program of Beijing Municipal Education Commission,Grant/Award Number:KM202110016014+1 种基金Government of Perm Krai,Research Project,Grant/Award Numbers:СED-26-08-08-28,С-26/628Graduate Innovation Program of Beijing University of Civil Engineering and Architecture,Grant/Award Number:PG2024035。
文摘Microcrack growth during progressive compressive failure in brittle rocks strongly influences the safety of deep underground engineering.The external shear stressτxy on brittle rocks greatly affects microcrack growth and progressive failure.However,the theoretical mechanism of the growth direction evolution of the newly generated wing crack during progressive failure has rarely been studied.A novel analytical method is proposed to evaluate the shear stress effect on the progressive compressive failure and microcrack growth direction in brittle rocks.This model consists of the wing crack growth model under the principal compressive stresses,the direction correlation of the general stress,the principal stress and the initial microcrack inclination,and the relationship between the wing crack length and strain.The shear stress effect on the relationship between y-direction stress and wing crack growth and the relationship between y-direction stress and y-direction strain are analyzed.The shear stress effect on the wing crack growth direction during the progressive compressive failure is determined.The initial crack angle effect on the y-direction peak stress and the wing crack growth direction during the progressive compressive failure considering shear stress is also discussed.A crucial conclusion is that the direction of wing crack growth has a U-shaped variation with the growth of the wing crack.The rationality of the analytical results is verified by an experiment and from numerical results.The study results provide theoretical support for the evaluation of the safety and stability of surrounding rocks in deep underground engineering.
基金The financial support provided by the Project of the National Natural Science Foundation of China (22308314,U22A20415)the Natural Science Foundation of Zhejiang Province (LQ24B060001)+1 种基金the "Pioneer" and "Leading Goose" Research & Development Program of Zhejiang (2022C01SA442617)the SINOPEC Technology Development Project (224244)
文摘This study leverages machine learning to perform high-throughput computational screening of n-hexane cracking initiators.Artificial neural networks are applied to predict the chemical performance of initiators,using simulated pyrolysis data as the training dataset.Various feature extraction methods are utilized,and five neural network architectures are developed to predict the co-cracking product distribution based on molecular structures.High-throughput screening of 12946 molecules outside the training dataset identifies the top 10 initiators for each target product—ethylene,propylene,and butadiene.The relative error between predicted and simulated values is less than 7%.Additionally,reaction pathway analysis elucidates the mechanisms by which initiators influence the distribution of cracking products.The proposed framework provides a practical and efficient approach for the rapid identification and evaluation of high-performance cracking initiators.
基金supported by the National Natural Science Foundation of China(Nos.52074231,52274396 and 52001258)the Chongqing Natural Science Foundation(No.cstc2020jcyj-msxmX1056).
文摘Crack initiation mechanism of dwell fatigue has always been a key problem in rationalizing the dwell effect,and it is not completely understood yet.This study conducted stress-controlled low-cycle fatigue and dwell fatigue tests on Ti-6Al-3Nb-2Zr-1Mo alloy with bimodal microstructure to reveal its microstructural characteristics and crack initiation mechanisms.The study demonstrated that the faceted primaryα nodules located near the specimen surface acted as crack initiation sites during both fatigue and dwell fatigue tests.Slip trace analysis revealed that faceted cracking occurred at(0001)basal plane with the maximum Schmid factor value through a special cracking mode referred to as(0001)twist boundary cracking.Innovative criteria of parameters C1 and C2 were proposed based on experimental observation and molecular dynamics simulations,which well identify candidates for(0001)twist boundary crack nucleation.It demonstrated that grain pairs combining a moderately high Schmid factor for basal slip and a well-orientated Burgers vector in the out-of-surface plane was the preferable location for surface(0001)twist-boundary crack initiation,and grain pairs combining a high Schmid factor for basal slip and a high normal stress on basal plane are perfect candidates for subsurface cracking.Based on this,phenomeno-logical models are proposed to explain the surface(0001)twist-boundary cracking mechanism from the perspective of surface extrusion-intrusion-induced micro-notches.
基金supported by the National Natural Science Foundation of China Projects under Grant(nos.52301112,52331004,U21A2049,and 51871211)Guangdong Basic and Applied Basic Research Foundation(Grant no.2024A1515030065)+4 种基金Basic and Applied Basic Research Project of Guangzhou(Grant no.2024A04J6299)LiaoNing Revitalization Talents Program(XLYC1907062,and XLYC2403026)Shenyang Young and Middle-aged Science and Technology Innovation Talent Support Program(RC231178)the Fundamental Research Funds for the Central Universities(N25GFY002)the Innovation Fund of Institute of Metal Research(IMR),Chinese Academy of Sciences(CAS).
文摘Mg-Li alloys hold significant potential for applications in aerospace,automotive manufacturing,military weaponry,and biomedical implants,due to their excellent recyclability,high specific strength,biocompatibility,and superior electromagnetic shielding properties.However,their poor corrosion resistance and high susceptibility to environmentally assisted cracking(EAC)significantly limit broader application.In recent years,growing attention has been directed toward understanding the corrosion and EAC behavior of Mg-Li alloys,as localized corrosion areas and hydrogen generated during the corrosion process can serve as crack initiation points and promote crack propagation.A comprehensive understanding of these mechanisms is essential for enhancing the reliability and performance of Mg-Li alloys in practical environments.This paper presents a detailed review of corrosion and EAC in Mg-Li alloys,focusing on corrosion behavior,crack initiation and propagation mechanisms,and the key factors influencing these processes.It summarizes recent advances in alloying,heat treatment,mechanical processing,microstructural control,environmental influences,mechanical loading,and surface treatments.In addition,the paper explores future research directions,highlights emerging trends,and proposes strategies to improve the durability and service performance of Mg-Li alloys.
基金support from the National Natural Science Foundation of China(Grant Nos.52301137,51974097,52364050)the Natural Science Special Foundation of Guizhou University(No.(2023)20)+1 种基金Guizhou Province Science and Technology Project(Grant Nos.[2023]001,[2019]2163)Guiyang city Science and Technology Project(Grant No.[2023]48-16).
文摘The dynamic mechanical response and deformation mechanism of magnesium-yttrium alloy at high strain rate were investigated using split-Hopkinson pressure bar(SHPB)impact,and the microstructure evolution and crack formation mechanism were revealed.The yield strength and work hardening rate increase significantly with increasing impact strain rate.Deformation twinning and non-basal dislocation slip are the primary deformation mechanisms during testing.Contrary to crack initiation mechanism facilitated by adiabatic shear bands,we find that high-density co-axial nanocrystalline grains form near cracks,which leads to local softening and promotes crack initiation and rapid propagation.Most grains have similar<1^(-)21^(-)0>orientations,with unique misorientation of 24°,32°,62°,78°and 90°between adjacent grains,suggesting that these grains are primarily formed by interface transformation,which exhibits distinct differences from recrystallized grains.Our results shed light upon the dynamic mechanical response and crack formation mechanism in magnesium alloys under impact deformation.
基金Projects(52104143,52109135,52374099)supported by the National Natural Science Foundation of ChinaProject(2025YFHZ0323)supported by the Natural Science Foundation of Sichuan Province,China。
文摘The evolution of cracks in shale directly affects the efficient production of shale gas.However,there is a lack of research on the characteristics of crack initiation in deep dense shale under different stress conditions.In this work,considering the different combinations of confining pressure and bedding plane inclination angle(α),biaxial mechanical loading experiments were conducted on shale containing circular holes.The research results indicate that the confining pressure and inclination angle of the bedding planes significantly influence the failure patterns of shale containing circular holes.The instability of shale containing circular holes can be classified into five types:tensile failure along the bedding planes,tensile failure through the bedding planes,shear slip along the bedding planes,shear failure through the bedding planes,and block instability failure.Furthermore,the evolution of strain and stress fields around the circular holes was found to be the fundamental cause of variations in the initiation characteristics and locations of shale cracks.The crack initiation criterion for shale containing circular hole was established,providing a new method for evaluating the trajectory of shale hole wall fractures.This study holds significant importance for evaluating the evolution and stability of fracture networks within shale reservoirs.
基金supported by the Science Center for Gas Turbine Project(No.P2022-B-IV-009-002).
文摘Hydrogen has emerged as a promising clean energy source,leading to numerous recent efforts to integrate hydrogen into turbine engine applications[1].This integration has the potential to significantly enhance engine efficiency while reducing carbon dioxide emissions[2].However,the degradation of nickel alloys induced by hydrogen has been well documented[3-7].Consequently,hydrogen-assisted failure of nickel alloys poses a critical concern for the design and safe operation of hydrogen-powered turbine engines.
文摘This paper deals with the mechanism of the formation of initial cracks in the yttria partially stabilized zirconia thermal barrier coatings prepared by EB-PVD method.The microcracks were only recognized inside the ceramic top coat of the thermalcycled TBCs. SEM/EDS observations indicated that some special oxides exist in the area just below the cracks.It seems that the formation of the initial cracks can result from the oxidation stress as well as the thermal stress.
基金support from the Australian Research Council(ARC)through Discovery Project DP210102224.
文摘The crack initiation stress threshold is widely used in excavation industries as rock spalling strength when designing deep underground structures to avoid unwanted brittle failures.While various strain-based methods have been developed for the estimation of this critical design parameter,such methods are destructive and often requires subjective interpretations of the stress–strain curves,particularly in rocks with pre-existing microcracks or high porosity.This study explore the applicability of non-destructive ultrasonic through-transmission methods for determining rock damage levels by assessing the changes in transmitted signal characteristics during loading.The change in velocity,amplitude,dominant frequency,and root-mean-square voltage are investigated with four different rock types including marble,sandstone,granite,and basalt under various stress levels.Results suggest the rate of signal variations can be reliably used to estimate crack closure and crack initiation stress levels across the tested rocks before failure.Comparison of the results between the conventional techniques and the new proposed methods based on ultrasonic monitoring are further discussed.
基金National Science and Technology Major Project(J2019-VI-0022-0138)。
文摘Low-cycle fatigue crack initiation behavior of nickel-based single crystal superalloy at 530℃ was investigated.Results show that the behavior of crack initiation is closely related to the maximum strain.When the maximum strain is 2.0%,the fatigue crack is originated at the position of persistent slip bands on the surface of specimen,which is located on the{111}slip plane.No defects are observed at the crack initiation position.When the maximum strain is lower than 1.6%,the cracks are initiated at the casting defects on sub-surface or at interior of the specimen.The casting defects are located on the{100}slip plane vertical to the axial force.The crack is initiated along the{100}slip plane and then expanded along different{111}slip planes after a short stage of expansion.As the maximum strain decreases,the position of crack initiation gradually changes from the surface to the interior.Moreover,the secondary cracks extending inward along the fracture surface appear in the crack initiation area,and there is obvious stress concentration near the secondary cracks.The dislocation density is high near the fracture surface in the crack initiation zone,where a lot of dislocations cutting into the γ'phase exist.An oxide layer of 50‒100 nm is presented on the fracture surface,and Ni,Al,Cr and Co elements are mainly segregated into the oxide layer of the surface.
基金financially supported by the National Natural Science Foundation of China(No.11932020).
文摘Fatigue failure can still occur beyond 107 cycles,i.e.very-high-cycle fatigue(VHCF),in many metallic materials,such as aluminium alloys and high-strength steels.For VHCF of high-strength steels,a fine granular area(FGA)surrounding an inclusion is commonly identified as the characteristic region of crack initiation on the fracture surface.However,no such FGA feature and related crack initiation behaviour were observed in VHCF of conventionally cast or wrought aluminium alloys.Here,we first reported the distinct mechanisms of crack initiation and early growth,namely the microstructure feature and the role of FGA in VHCF performance for an additively manufactured(AM)AlSi10Mg alloy.The AM pores play a key role in fatigue crack initiation similar to that of the inclusions in high-strength steels,resulting in almost identical FGA behaviour for different materials under a range of mean stress with a stress ratio at R<0 or R>0.The profile microstructure of FGA is identified as a nanograin layer with Si rearrangement and grain boundary transition.This process consumes a large amount of cyclic plastic energy making FGA undertake a vast majority of VHCF life.These results will deepen the understanding of VHCF nature and shed light on crack initiation mechanism of other aluminium and AM alloys.
基金financially supported by the National Key R&D Program of China(No.2021YFB3701203)the National Natural Science Foundation of China(NSFC,Grant Nos.52171137,52261135543 and U22A20113)the Heilongjiang Provincial Natural Science Foundation of China(Grant No.TD2020E001).
文摘Discontinuously reinforced titanium matrix composites(DRTMCs)with a network structure have been extensively researched due to their superior combination of strength and ductility.However,their fatigue performance has remained unknown.In order to elucidate the fatigue behavior of DRTMCs,a tension-tension fatigue test was performed on a TiB/nearα-Ti composite with network structure.The results showed that the variability of fatigue lifetime increased as the stress level decreased.Fractography analysis indicated that fatigue crack initiation was associated with facet formation,while the subsequent propagation was hindered by the network structure comprising TiB whiskers and silicides.Crystallographic characterization further revealed that facets formed due to a combination of shear and normal stress.The reduction in fatigue lifetime was attributed to an increase in the effective slip length,which was influenced by the orientation of grains near the crack-initiation sites toward basal slip in the life-limiting specimen.Quasi in situ observation suggested that the crack initiation was facilitated by both basal and prismatic slip ofα-Ti as well as fracture of TiBw.Crack propagation was found to be associated with basal and prismatic slip systems with high Schmid factors,regardless of whether the crack was intergranular or intragranular.
基金supported by the National Natural Science Foundation of China(No.52201112,U22A20106,and 52071066)the China Postdoctoral Science Foundation(2022M710627)+1 种基金the support from the Innovation and Technology Fund(MHP-064-20)the support from the National Natural Science Foundation of China(No.52101133).
文摘Although the seemingly negative effect of deformation-induced martensite(DIM)volume fraction on the impact toughness of austenitic steels has been well documented,it relies mostly on analyzing crack propagation without explicitly considering the crack initiation process which,however,plays a crucial role in these ductile alloys.The dependence of crack initiation energy(Ei)on martensitic transformation mechanisms is still ambiguous,inhibiting the precise design of damage-tolerant and ductile alloys.Here,we explore the temperature-dependent crack initiation energy of a SUS321 stainless steel at various temperatures(25,-50,and-196℃).Contrary to the crack propagation energy(Ep),the Ei has a weak correlation with the volume fraction ofα′-martensite but a strong correlation with the martensitic transformation rate.Also contrary to the traditional viewpoint of Ep consideringε-martensite as a detrimental phase,a high volume fraction ofε-martensite turns out to be beneficial to the increase of Ei,thereby enhancing impact toughness.As such,an optimal value(15 mJ/m^(2))for the stacking fault energy(SFE),which dictates theγ→ε→α′transformation sequence,is given as a new design guideline for enhancing the Ei and consequently the impact toughness of ductile steels.The generality of this guideline is further validated in multiple austenitic steels with different compositions and grain sizes.
文摘The fatigue crack initiation and early propagation behavior of 2A97 Al-Li alloy was studied. The smooth specimens were fatigued at room temperature under constant maximum stress control when stress ratio （R） is 0.1 and frequency （f） is 40 Hz. Microstructure observations were examined by optical microscopy, transmission electron microscopy, scanning electron microscopy and electron back scattered diffusion, in order to investigate the relationship between microstructure and fatigue crack initiation and early propagation behavior of 2A97 alloy. The results show that the fatigue cracks are predominantly initiated at inclusions and coarsen secondary phases on the surface of 2A97 alloy. The fatigue crack early propagation behavior of 2A97 alloy is predominantly influenced by the interactions between grain structure and dislocations or persistent slip bands （PSBs）. When the misorientation of two neighbouring grains is close to the orientations of the favorable slip plane within these two grains, high-angle grain boundary severely hinders the PSBs passing through, and thus leads to crack bifurcation and deflection.
基金China Scholarship Council(CSC)The University of Queensland for a Ph D fellowship。
文摘The long-term stability of the roof is particularly important in designing underground rock structures.To estimate the durability of roof strata in underground excavation,a computation scheme of subcritical crack growth is proposed in this study.By adopting the proposed method,the potential collapse location of strata is derivable in accordance with a static model,the durability of roof strata can be estimated,a dynamic time step control strategy is achieved to balance the accuracy and speed of computing,and the initial crack size of rock can be estimated.In addition to the above,a mechanical model of underground excavation with non-uniformly distributed loads and partially yielded foundation is presented as the prototypical case.A set of case studies is carried out that showcase a power correlation between applied stress and roof durability.The allowable applied tensile stress for a 100-year life cycle is about 76%of the tensile strength.By using the proposed subcritical crack growth computation scheme,the roof stability in an underground excavation can be identified not only from the spatial view but also from the temporal perspective.
基金Supported by National Natural Science Foundation of China (No. 50908148)Natural Science Foundation for Team Project of Guangdong Province(No. 9351806001000001)+1 种基金Scientific Research Foundation for Returned Overseas Chinese Scholars,Ministry of Education(41 Batch)Open Fund of State Key Laboratory of Coastal and Of fshore Engineering of Dalian University of Technology (No. LP1111)
文摘An analytical model for predicting the corrosion-induced cracking of concrete cover of reinforced concrete(RC) structures was developed.The effects of influence factors such as practical initial defects,corrosion rate,strength and elastic modulus of concrete on the corrosion-induced cracking of concrete cover were investigated.It was found that the size of practical initial defects was the most effective factor.Therefore,improving the compactness of concrete is an effective way to improve the durability of RC structures.It was also demonstrated that the accelerated corrosion tests may be unfavorable in the study of the relationship between cracking time and crack width.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.U20A20266 and 12302503)Scientific and technological research projects in Sichuan province(Grant No.2024NSFSC0973).
文摘The loaded rock experiences multiple stages of deformation.It starts with the formation of microcracks at low stresses(crack initiation,CI)and then transitions into unstable crack propagation(crack damage,CD)near the ultimate strength.In this study,both the acoustic emission method(AEM)and the ultrasonic testing method(UTM)were used to examine the characteristics of AE parameters(b-value,peak frequency,frequency-band energy ratio,and fractal dimension)and ultrasonic(ULT)properties(velocity,amplitude,energy attenuation,and scattering attenuation)of bedded shale at CI,CD,and ultimate strength.The comparison involved analyzing the strain-based method(SBM),AEM,and UTM to determine the thresholds for damage stress.A fuzzy comprehensive evaluation model(FCEM)was created to describe the damage thresholds and hazard assessment.The results indicate that the optimal AE and ULT parameters for identifying CI and CD stress are ringing count,ultrasonic amplitude,energy attenuation,and scattering attenuation of the S-wave.Besides,damage thresholds were detected earlier by AE monitoring,ranging from 3 MPa to 10 MPa.CI and CD identified by UTM occurred later than SBM and AEM,and were in the range of 12 MPa.The b-value,peak frequency,energy ratio in the low-frequency band(0e62.5 kHz),correlation dimension,and sandbox dimension showed low values at the peak stress,while the energy ratio in a moderate-frequency band(187.5e281.25 kHz)and amplitude showed high values.The successful application of FCEM to laboratory testing of shales has demonstrated its ability to quantitatively identify AE/ULT precursors of seismic hazards associated with rock failure.
基金supported by the National Natural Science Foundation of China(Grant No.52404155)State Key Laboratory of Mining Disaster Prevention and Control(Shandong University of Science and Technology)+1 种基金Ministry of Education(Grant No.JMDPC202402)supported by the opening project of State Key Laboratory of Explosion Science and Safety Protection(Beijing Institute of Technology).The opening project number is KFJJ24-20M.
文摘Aiming at mitigating the high risks associated with conventional explosive blasting,this study developed a safe directional fracturing technique,i.e.instantaneous expansion with a single fracture(IESF),using a coal-based solid waste expanding agent.First,the mechanism of directional fracturing blasting by the IESF was analyzed,and the criterion of directional crack initiation was established.On this basis,laboratory experiments and numerical simulations were conducted to systematically evaluate the directional fracturing blasting performance of the IESF.The results indicate that the IESF presents an excellent directional fracturing effect,with average surface undulation differences ranging from 8.1 mm to 22.7 mm on the fracture surfaces.Moreover,during concrete fracturing tests,the stresses and strains in the fracturing direction are measured to be 2.16-3.71 times and 8 times larger than those in the nonfracturing direction,respectively.Finally,the IESF technique was implemented for no-pillar mining with gob-side entry retaining through roof cutting and pressure relief in an underground coal mine.The IESF technique effectively created directional cracks in the roof without causing severe roadway deformation,achieving an average cutting rate and maximum roadway deformation of 94%and 197 mm,respectively.These on-site test results verified its excellent directional rock fracturing performance.The IESF technique,which is safe,efficient,and green,has considerable application prospects in the field of rock mechanics and engineering.
基金Funded by the 863 Program from Ministry of Science and Technology of China(2005AA332010) the Key Technologies R&D Program from Department of Science and Technology. Hubei Province (200410G0121)
文摘A laboratory study was undertaken to investigate drying shrinkage and cracking sensitivity subjected to restrained shrinkage of mortar containing fly ash (FA), granulated blast-furnace slag (GBFS) and silica fume (SF). Six mortar mixtures including control Portland cement (PC) and FA, GBFS and SF mortar mixtures were prepared. FA replaced the cement on mass basis at the replacement ratios of 20% and 35%, GBFS replaced the cement at the replacement ratios of 40%, SF replaced the cement at the replacement ratios of 8% and the blended mixtures with 20% FA, 20% GBFS and 8% SF. Water-cementitious materials ratio and sand-cementitious materials ratio were 0.4 and 2.0 for all mixtures, respectively. The mixtures were cured at 65% relative humidity and 20℃. The drying shrinkage value, initial cracking time and cracking width of the mortar samples were measured. The results show that all the mortar mixture containing FA exhibited the decrease of drying shrinkage. Moreover, initial cracking time was markedly delayed, and the crack width of the initial crack was reduced. However, the incorporations of various ratios of GBFS and SF led to an increase of drying shrinkage, initial cracking time and cracking width as compared to control mixture.
基金Funded by the Inner Mongolia Autonomous Region Science and Technology Program(No.2023YFHH0036)the Natural Science Foundation of Inner Mongolia(No.2024LHMS05033)the Basic Scientific Research Fees for Colleges and Universities Directly under the Inner Mongolia(Nos.2023QNJS002,2023YXXS007,and 2024YXXS039)。
文摘The critical wear rate,surface damage,deformation layer,crack initiation and propagation of U76CrRE heavy rail steel samples of two different cooling conditions(rolled rail,and heat-treated rail)under intermittent load were measured and observed by friction and wear tester,laser confocal microscope,scanning electron microscope and EBSD.The experimental results show that when the same kind of rail is matched with wheel steel with low hardness and high hardness successively,the critical wear rate of rail moves to the right.Moreover,when the rolled rail is matched with wheel steel with low hardness,the deformation layer and wear amount are larger than those of heat-treated rail are,while when it is matched with wheel steel with high hardness,the deformation layer and wear amount are smaller than those of heat-treated rail.When the rolled rail and heat-treated rail are matched with the same kind of wheel steel successively,the critical wear rate moves down,and the wear deformation layer of heat-treated rail is smaller than that of rolled rail.The failure life of the heat-treated rail is better than that of the rolled rail,which is due to the increase of the hardness of the heat-treated rail and the refinement of pearlite lamellae.With the increase of the distance from the surface layer,the proportion of large-angle grain boundaries of ferrite grains gradually increases of rolled rail and heat-treated rail,but the rolled rail presents the characteristics of large crack angle,deep depth and small length,mainly due to wear failure.While the heat-treated rail has the characteristics of small crack angle,shallow depth and long length,the crack propagation trend is obvious,and the failure form of the heat-treated rail is mainly fatigue failure.Moving the critical wear rate to the right and down is beneficial to inhibit the formation and propagation of fatigue cracks.
