Peridynamics(PD)is an effective method for simulating the spontaneous initiation and propagation of tensile cracks in materials.However,it faces great challenges in simulating compression-shear cracking of geomaterial...Peridynamics(PD)is an effective method for simulating the spontaneous initiation and propagation of tensile cracks in materials.However,it faces great challenges in simulating compression-shear cracking of geomaterials due to the lack of efficient contact-friction models.This paper introduces an original contact-friction model that leverages twin mesh and potential function principles within PD to model rock cracking under tensile and compressive stresses.The contact detection algorithm,based on space segmentation axis-aligned bounding box(AABB)tree data structure,is used to address the significant challenge of highly efficient contact detection in compression and shear problems.In this method,the twin mesh and potential function are utilized to quantify contact detection and contact degree,as well as friction behavior.This is in contrast to the distance and circular contact area model,which lacks physical significance in the classical PD method.As demonstrated by the tests on specimens containing cracks,the proposed model can capture 8 types of secondary fractures,reduce the contact detection error by about 29%e56%,and increase the contact retrieval efficiency by over 1600 times compared to the classic PD models.This significantly enhances the capability of PD to simulate the initiation,expansion,and coalescence of intricate compression-shear cracks.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
A comparative study of products of thermal and thermocatalytic cracking of polypropylene(PP) in the presence of potassium polytitanate(PPT) synthesized by treatment of TiO_(2)(rutile) powder with molten mixture of KOH...A comparative study of products of thermal and thermocatalytic cracking of polypropylene(PP) in the presence of potassium polytitanate(PPT) synthesized by treatment of TiO_(2)(rutile) powder with molten mixture of KOH and KNO_(3) taken in a weight ratio of 30∶30∶40 has been carried out.It was shown that the studied type of PPT powder exhibits catalytic properties in the reaction of thermal decomposition of PP,compared to the effect of commercial zeolite catalyst CBV-780 traditionally used for this purpose.Based on the analysis performed,the differences in the mechanism of catalytic action of PPT and the zeolite were considered.The reasons for the observed differences in the composition of PP cracking products and in the rate of coke formation on the surface of studied catalysts were analyzed.Considering the obtained results,it has been proposed that the CBV-780 catalyst promoted more intensive production of the gaseous hydrocarbons compared to PPT,due to higher specific surface area(internal surface) accessible for relatively light and small-sized hydrocarbon products of cracking.However,intensive coke formation on the outer surface of the microporous zeolite contributes to the blocking of transport channels and the rapid loss of catalytic action.At the same time,PPT,which initially has a smaller specific surface area,retains its catalytic activity significantly longer due to slit-shaped flat pores and higher transport accessibility of the inner surface.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
Fruit cracking is a persistent challenge for table grape growing.To investigate the mechanism of this disorder,a comprehensive two-year investigation was conducted to assess the fruit cracking percentage of 15 table g...Fruit cracking is a persistent challenge for table grape growing.To investigate the mechanism of this disorder,a comprehensive two-year investigation was conducted to assess the fruit cracking percentage of 15 table grape(Vitis vinifera L.)varieties.Based on the findings,the cracking-susceptible variety‘Xiangfei'and the cracking-resistant variety‘Zuijinxiang'were selected for further study.Fruit growth curves for‘Zuijinxiang'and‘Xiangfei'were plotted based on fruit diameter and total soluble solids content,revealing that both varieties exhibited typical double-sigmoidal patterns that were highly similar.The period between 48 and 53 days after full bloom(DAFB)was identified as the critical phase for fruit cracking incidence.Furthermore,during the fruit cracking period,‘Xiangfei'fruit exhibited significantly higher water content and mesocarp cell area compared with those of‘Zuijinxiang'.Applying aquaporin inhibitors(nano-silver)to‘Xiangfei'berries reduced fruit water uptake and cracking percentage,whereas applying aquaporin activators(forskolin)to‘Zuijinxiang'berries increased fruit water uptake and cracking percentage.Additionally,expression analysis of six genes associated with plasma membrane intrinsic proteins(PIPs)synthesis(VvPIP1;1,VvPIP1;2,VvPIP1;3,VvPIP2;1,VvPIP2;2,and VvPIP2;3)revealed that only the expression level of VvPIP1;1 was higher in‘Zuijinxiang'than in‘Xiangfei'during the fruit cracking period,whereas the expression levels of the other genes exhibited no significant difference between the two varieties.Transgenic overexpression of VvPIP1;1 in tomato resulted in increased fruit water content,enlarged mesocarp cell size,and enhanced fruit cracking percentage.These findings indicate that VvPIP1;1 plays a pivotal role in controlling grape berry cracking.展开更多
Cracking affected by wetting-drying cycles is a major cause of shallow failure of soft rock slopes.Knowledge of rock tensile properties and cracking behaviors helps better assess the stability of soft rock slopes.This...Cracking affected by wetting-drying cycles is a major cause of shallow failure of soft rock slopes.Knowledge of rock tensile properties and cracking behaviors helps better assess the stability of soft rock slopes.This study aims to examine the cracking behaviors and tensile strength of silty mudstone under wetting-drying cycles.The wetting-drying cycle and Brazilian splitting tests were performed on silty mudstone considering various cycle number and amplitude.The cracking behaviors of wetting-drying cycles were analyzed by digital image correlation,three-dimensional(3D)scanning technology,and scanning electron microscopy.The results reveal a spiral-like pattern of crack ratio escalation in silty mudstone,with a higher crack ratio observed during drying than wetting.Tensile strength and fracture energy correlate negatively with cycle number or amplitude,with cycle number exerting a more pronounced effect.The variance of the maximum principal strain reflects stages of initial deformation,linear deformation,strain localization,and stable deformation.The formation of strain localization zones reveals the physical process of crack propagation.Crack tip opening displacement progresses through stages of slow growth,exponential growth,and linear growth,delineating the process from crack initiation to stable extension.Failure modes of silty mudstone primarily involve tensile and tensile-shear failure,influenced by the geometric parameters of cracks induced by wetting-drying cycles.Fracture surface roughness and fractal dimension increase with cycle number due to mineral dissolution,physical erosion,and nondirectional crack propagation.Hydration-swelling and dehydration-shrinkage of clay minerals,along with absorption-drying cracking,initiate and merge cracks,leading to degradation of the rock mechanical properties.The findings could provide insights for mitigating shallow cracking of soft rock slopes under wetting-drying cycles.展开更多
Soil desiccation cracking is ubiquitous in nature and has significantpotential impacts on the engineering geological properties of soils.Previous studies have extensively examined various factors affecting soil cracki...Soil desiccation cracking is ubiquitous in nature and has significantpotential impacts on the engineering geological properties of soils.Previous studies have extensively examined various factors affecting soil cracking behavior through a numerous small-sample experiments.However,experimental studies alone cannot accurately describe soil cracking behavior.In this study,we firstly propose a modeling framework for predicting the surface crack ratio of soil desiccation cracking based on machine learning and interpretable analysis.The framework utilizes 1040 sets of soil cracking experimental data and employs random forest(RF),extreme gradient boosting(XGBoost),and artificialneural network(ANN)models to predict the surface crack ratio of soil desiccation cracking.To clarify the influenceof input features on soil cracking behavior,feature importance and Shapley additive explanations(SHAP)are applied for interpretability analysis.The results reveal that ensemble methods(RF and XGBoost)provide better predictive performance than the deep learning model(ANN).The feature importance analysis shows that soil desiccation cracking is primarily influencedby initial water content,plasticity index,finalwater content,liquid limit,sand content,clay content and thickness.Moreover,SHAP-based interpretability analysis further explores how soil cracking responds to various input variables.This study provides new insight into the evolution of soil cracking behavior,enhancing the understanding of its physical mechanisms and facilitating the assessment of potential regional development of soil desiccation cracking.展开更多
In subtropical regions,soil desiccation cracking often exerts a significant impact on the interactions between soil water and the atmosphere,making it a subject of great interest in the fields of geotechnical and geoe...In subtropical regions,soil desiccation cracking often exerts a significant impact on the interactions between soil water and the atmosphere,making it a subject of great interest in the fields of geotechnical and geoenvironmental engineering.Despite the growing utilization of biochar as a sustainable soil amendment,there remains a lack of in-depth understanding of biocharewateresoil interactions,as well as its impact on soil desiccation cracking behavior.To address this gap,this study investigated the influence and mechanism of woody biochar dosages and particle sizes on the cracking behavior of three typical clayey soils in subtropical regions in China,namely Pukou expansive soil(PKE),Xiashu soil(XS),and Zhongshan lateritic soil(ZSL).The quantitative analysis of crack images revealed that the use of biochar was not consistently effective in preventing soil cracking.The application of biochar reduced the crack ratio in PKE and XS by up to 24.03%and 53.89%,respectively.In contrast,ZSL exhibited a 74.57%increase in crack ratio with the addition of 10%biochar.This influence can be further enhanced by increasing the dosage and reducing the particle size of biochar.The microstructural analysis demonstrated that biochar exerts an inhibitory effect on PKE and XS primarily through direct replacement,direct barrier,and indirect physical mechanisms.Moreover,an indirect chemical effect between biochar and clay particles was proposed to explain the exacerbated cracking observed in biochar-amended ZSL.To effectively utilize biochar for soil cracking mitigation in subtropical regions,it is essential to evaluate the initial mineral composition and cation type of the soil.展开更多
Implants are inevitably subjected to stress corrosion,bringing serious challenges to the controlled degradation of biomedical Mg alloys.It is worth studying the stress corrosion cracking(SCC)behavior of Mg alloy and e...Implants are inevitably subjected to stress corrosion,bringing serious challenges to the controlled degradation of biomedical Mg alloys.It is worth studying the stress corrosion cracking(SCC)behavior of Mg alloy and exploring Mg alloy with good SCC resistance for wide biomedical applications.In this work,the as-cast and as-extruded Mg-3Gd-1Zn-0.4Zr(GZ31K)alloys with uniform corrosion were used to investigate SCC behavior.The as-extruded GZ31K alloy exhibited better corrosion resistance and mechanical properties than the as-cast one mainly owing to grain refinement and uniformly distributed fine precipitates,and possessed superior SCC resistance.To clarify the SCC mechanism,the slow strain rate tests were assisted with applied constant potentials via an electrochemical workstation.Accelerated anodic dissolution at anodic polarization deteriorated SCC resistance due to the initiation of corrosion pits and micro-cracks.However,cathodic polarization had no obvious effects on SCC resistance,along with both retarded corrosion and accelerated hydrogen evolution.Stacking faults in GZ31K alloy were hydrogen capture containers to reduce the effect of hydrogen on SCC resistance during cathodic polarization.These findings provide new insights into the evaluation of SCC mechanism,and offer more opportunities to explore Mg alloys with good SCC resistance by regulating anodic dissolution.展开更多
The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weld...The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weldability of components with thin walls after small punch sampling,such as ethylene cracking furnace tubes,requires further investigation.Therefore,the weldability of in-service ethylene cracking furnace tubes following small punch sampling was investigated through nondestructive testing,microstructural characterization,and mechanical testing.Additionally,the impact of small punch sampling size and residual stress on the creep performance of the specimens was studied using an improved ductility exhaustion model.The results indicate that both the surface and interior of the weld repair areas on new furnace tubes and service-exposed furnace tubes after small-punch sampling are defect-free,exhibiting good weld quality.The strength of the specimens after weld repair was higher than that before sampling,whereas toughness decreased.Weld repair following small punch sampling of furnace tubes is both feasible and necessary.Furthermore,a linear relationship was observed between specimen thickness,diameter,and creep fracture time.The residual stress of welding affects the creep performance of the specimen under different stresses.展开更多
In this work,a new process for achieving the recovery of elemental sulfur by utilizing a fluidized catalytic cracking(FCC) riser reactor for SOxtreatment(FCC-DeSOx) is proposed.The process leverages the high temperatu...In this work,a new process for achieving the recovery of elemental sulfur by utilizing a fluidized catalytic cracking(FCC) riser reactor for SOxtreatment(FCC-DeSOx) is proposed.The process leverages the high temperatures and hydrocarbon concentrations in the FCC riser reactor to convert SOxinto H_(2)S.Subsequently,H_(2)S,along with the cracked gas,is processed downstream to produce sulfur.Thermodynamic analysis of the key reduction reactions in the FCC-DeSOxprocess revealed that complete conversion of SOxto H_(2)S is feasible in the dry gas(hydrogen-rich) prelift zone,as well as the upper and lower zones of the riser,upon achieving thermodynamic equilibrium.Experimental studies were conducted to replicate the conditions of these reaction zones using a low concentration of hydrogen gas as the reducing agent.Through process optimization,investigation of the minimum reaction time,and kinetic studies,the potential of this method for the complete reduction of SOxwas further confirmed.展开更多
The effect of aging precipitation on the stress corrosion cracking(SCC)mechanism of Ni(Fe,Al)-maraging steel was studied through the comparative characterization and analyses of the microstructures and fracture featur...The effect of aging precipitation on the stress corrosion cracking(SCC)mechanism of Ni(Fe,Al)-maraging steel was studied through the comparative characterization and analyses of the microstructures and fracture features of solid–solution and peak-aged steels.Aging precipitation exerts a chain of impacts on the deformative compatibility and electrochemical difference between the matrix and oth-er phases or interfaces.The strength of the martensite matrix is enhanced by abundant and evenly dispersed Ni(Fe,Al)precipitates,thereby reducing the possibility of splitting across martensite laths.Meanwhile,the Volta potential difference(VPD)between the matrix and primary NbC particles increases from 11.43 to 18.60 mV.Given that most of the primary NbC particles tend to be distributed along high-angle grain boundaries(HAGBs),anodic dissolution along HAGBs accelerates.Therefore,mechanical and electrochemical factors triggered by aging precipitation are involved in the variation in SCC behavior and mechanism.The SCC susceptibility of the steel in-creases along with the increasing tendency for intergranular cracking.展开更多
Coking at the fractionating tower bottom and the decant oil circulation system disrupts the heat balance,leading to unplanned shutdown and destroying the long period stable operation of the Fluid Catalytic Cracking Un...Coking at the fractionating tower bottom and the decant oil circulation system disrupts the heat balance,leading to unplanned shutdown and destroying the long period stable operation of the Fluid Catalytic Cracking Unit(FCCU).The FCCU operates through interconnected subsystems,generating high-dimensional,nonlinear,and non-stationary data characterized by spatiotemporally correlated.The decant oil solid content is the crucial indicator for monitoring catalyst loss from the reactor-regenerator system and coking risk tendency at the fractionating tower bottom that relies on sampling and laboratory testing,which is lagging responsiveness and labor-intensive.Developing the online decant oil solid content soft sensor using industrial data to support operators in conducting predictive maintenance is essential.Therefore,this paper proposes a hybrid deep learning framework for soft sensor development that combines spatiotemporal pattern extraction with interpretability,enabling accurate risk identification in dynamic operational conditions.This framework employs a Filter-Wrapper method for dimensionality reduction,followed by a 2D Convolutional Neural Network(2DCNN)for extracting spatial patterns,and a Bidirectional Gated Recurrent Unit(BiGRU)for capturing long-term temporal dependencies,with an Attention Mechanism(AM)to highlight critical features adaptively.The integration of SHapley Additive exPlanations(SHAP),Complementary Ensemble Empirical Mode Decomposition with Adaptive Noise(CEEMDAN),2DCNN,and expert knowledge precisely quantifies feature contributions and decomposes signals,significantly enhancing the practicality of risk identification.Applied to a China refinery with processing capacity of 2.80×10^(6) t/a,the soft sensor achieved the R^(2) value of 0.93 and five-level risk identification accuracy of 96.42%.These results demonstrate the framework's accuracy,robustness,and suitability for complex industrial scenarios,advancing risk visualization and management.展开更多
A series of Sn microalloying high-strength low-alloy(HSLA)steels were prepared through vacuum melting and hot rolling.Their stress corrosion cracking(SCC)behavior under high Cl^(−)environments was investigated using U...A series of Sn microalloying high-strength low-alloy(HSLA)steels were prepared through vacuum melting and hot rolling.Their stress corrosion cracking(SCC)behavior under high Cl^(−)environments was investigated using U-bend immersion,slow strain rate testing,electrochemical methods,and novel SCC sensor.Results revealed that HSLA steel microalloying with 0.1 wt.%Sn demonstrated superior SCC resistance,primarily attributed to the effective inhibition of the anodic dissolution mechanism.Fracture morphology revealed a transformation in fracture mode from brittle to a mixture of brittle-ductile characteristics,accompanied by the formation of a protective SnO_(2)oxide film on the steel surface.However,excessive Sn content exacerbated SCC susceptibility due to the increased hydrolysis of Sn^(2+),leading to localized pitting and crack initiation.The critical role of optimal Sn content was highlighted in balancing mechanical properties and corrosion resistance,suggesting potential applications in industries where materials face harsh chloride environments.展开更多
Additive manufacturing (AM) of high-strength metallic alloys frequently encounters detrimental distortion and cracking, attributed to the accumulation of thermal stresses. These issues significantly impede the practic...Additive manufacturing (AM) of high-strength metallic alloys frequently encounters detrimental distortion and cracking, attributed to the accumulation of thermal stresses. These issues significantly impede the practical application of as-printed components. This study examines the Mg-15Gd-1Zn-0.4Zr (GZ151K, wt.%) alloy, a prototypical high-strength casting Mg-RE alloy, fabricated through laser powder bed fusion (LPBF). Despite achieving ultra-high strength, the GZ151K alloy concurrently exhibits a pronounced cold-cracking susceptibility. The as-printed GZ151K alloy consists of almost fully fine equiaxed grains with an average grain size of merely 2.87 µm. Subsequent direct aging (T5) heat treatment induces the formation of dense prismatic β' precipitates. Consequently, the LPBF-T5 GZ151K alloy manifests an ultra-high yield strength of 405 MPa, surpassing all previously reported yield strengths for Mg alloys fabricated via LPBF and even exceeding that of its extrusion-T5 counterpart. Interestingly, as-printed GZ151K samples with a build height of 2 mm exhibit no cracking, whereas samples with build heights ranging from 4 to 18 mm demonstrate severe cold cracking. Thermal stress simulation also suggests that the cold cracking susceptibility increases significantly with increasing build height. The combination of high thermal stress and low ductility in the as-printed GZ151K alloy culminates in a high cold cracking susceptibility. This study offers novel insights into the intricate issue of cold cracking in the LPBF process of high-strength Mg alloys, highlighting the critical balance between achieving high strength and mitigating cold cracking susceptibility.展开更多
Hydrogen-induced cracking (HIC) is one of the most complex material problems that hydrogen can diffuse into and interact with microstructure, degrading their mechanical properties. Microstructural modification is an e...Hydrogen-induced cracking (HIC) is one of the most complex material problems that hydrogen can diffuse into and interact with microstructure, degrading their mechanical properties. Microstructural modification is an effective way to enhance the resistance to HIC. The present study focused on the relationship between the retained austenite (RA) and HIC behavior in NiCrMoV/Nb multi-alloying ultra-strength steel. Results demonstrated that the maximum volume fraction of RA of 9.31% was obtained for QL30T specimen. After the deep cryogenic pretreatment, the volume fraction of RA reduced to 8.8%. RA could reduce the effective diffusion coefficient, while deep cryogenic pretreatment increased the susceptibility of the steel to HIC by a maxim of 14.8%. This was mainly due to the transformation of retained austenite into martensite, degrading the mechanical properties under hydrogen-charged condition. In addition, the deep cryogenic pretreatment had a significant effect on the crack initiation and propagation, with the intergranular (IG) fracture becoming the dominant fracture mode where an increase in the number of secondary cracks in the section. The interfaces of RA and matrix, as well as the grain boundaries, were the preferred sites for cracks initiation.展开更多
Percussive drilling is gaining interest for both shallow and deep applications due to its potential for higher drilling rates in hard rocks.Therefore,for efficient rock breaking,the development of advanced percussive ...Percussive drilling is gaining interest for both shallow and deep applications due to its potential for higher drilling rates in hard rocks.Therefore,for efficient rock breaking,the development of advanced percussive drilling simulation tools has the potential to be transformative.Such tools must accurately capture the rock’s response to enable an effective analysis of the fragmentation process.Traditional continuum numerical methods,such as the finite element method(FEM),do not simulate discrete cracks or the contact interaction between rock fragments.The finite-discrete element method(FDEM)is a three-dimensional hybrid method that combines FEM with the discrete element method(DEM)that addresses these limitations.New FDEM simulation results of impacts on Kuru Grey granite show good agreement with published experimental data.The interpretation focuses on two significant processes in percussive drilling:crack propagation and chipping generation.FDEM successfully simulates the evolution of cracks,including radial,side,and inclined cracks,as well as crushed and cracked zones.The simulation also reproduces the coalescence of adjacent craters to generate more chippings.Additionally,the stress state,velocity field and discrete fractures simulated by FDEM provide detailed insights into the different fracture patterns for Kuru Grey granite,enhancing understanding of the fundamental underlying mechanisms.展开更多
Cracking of early-age concrete can occur in the track beds of high-speed railways due to changes in material properties,environmental effects,and construction processes.This is a multi-field,time-varying issue involvi...Cracking of early-age concrete can occur in the track beds of high-speed railways due to changes in material properties,environmental effects,and construction processes.This is a multi-field,time-varying issue involving hydro-thermo-chemo-mechanical coupling.However,to date,research has not adequately described the early-age cracking mechanisms in track beds,and few risk control measures have been proposed.To solve this problem,we incorporated the hydration degree of concrete into multi-field coupling equations for early-age concrete,and set boundary conditions that account for environmental influences and various stress factors that typically cause early creep of concrete.A four-field coupled risk prediction model was built based on hydro-thermo-chemo-mechanical properties,and was used to calculate and analyze various time-varying behavior(including the risk and form of cracking)in the hydro,thermo,chemo,and mechanical fields of early-age concrete.Finally,we focused on material-related factors(maximum heat of hydration and peak heat release time),environmental factors(temperature difference between day and night,average daily cooling rate,and intensity of solar radiation),and construction technique factors(molding temperature,pouring time,and thermal insulation coefficient).The influence of these factors on the early-age cracking risk of the track bed was analyzed,and risk control measures against early cracking were proposed accordingly.展开更多
High cracking susceptibility of Al-Li alloys with Ti/Ce B6addition is thoroughly suppressed in laser powder bed fusion(LPBF)processing of Ti/Ce co-modified 2195 alloys at relatively high scan speeds,while the cracking...High cracking susceptibility of Al-Li alloys with Ti/Ce B6addition is thoroughly suppressed in laser powder bed fusion(LPBF)processing of Ti/Ce co-modified 2195 alloys at relatively high scan speeds,while the cracking suppression mechanism and phase formation in these composites are not clarified.In this work,microstructure evolution and mechanical performance of the LPBF-fabricated Ti/Ce co-modified 2195 are investigated to reveal their cracking suppression and strengthening mechanisms.The results show that apparent grain refinement of the composites is ascribed to high supercooling from rapid formation of constitutional supercooling zone in front of solid–liquid interfaces by high-Q-value Ti solute,and heterogeneous nucleation of in situ formed Al3Ti and Al11Ce3precipitates.Their synergistic interactions promote formation of fine equiaxed grains and thus inhibit crack initiation.The composites exhibit high microhardness of 100±5HV0.2,nano-hardness of 1.6±0.1 GPa and elastic modulus of 97±3 GPa,where the elastic modulus increases by 27%and 31%compared to those of LPBF-processed and conventionally manufactured 2195 alloys,respectively.A tensile strength of 336 MPa and an elongation of 3%are obtained from in-situ synchrotron X-ray diffraction measurement.The improved properties are derived from grain refinement and Orowan strengthening.Based on the optimal processing parameter and composition,a bracket component filled with lattice structures is designed and manufactured with good manufacturing quality and processing accuracy.展开更多
In order to study the mechanical properties of damaged reinforced concrete(RC)beams reinforced with ultra-high-performance concrete(UHPC),a four-point bending test was conducted to systematically investigate the influ...In order to study the mechanical properties of damaged reinforced concrete(RC)beams reinforced with ultra-high-performance concrete(UHPC),a four-point bending test was conducted to systematically investigate the influence of factors such as the number of reinforcement surfaces and the degree of damage.The results indicate that single-sided repaired beams have certain advantages in crack resistance performance,but are more disadvantageous in ultimate bearing capacity,with obvious debonding phenomenon before the end of loading.Compared with single-sided reinforcement,the cracking load of the three-sided reinforced beam increased by an average of 1.85 times,the ultimate bearing capacity increased by an average of 177.5%,and a good UHPC-RC combination effect could be formed,which could work synergistically until the end of loading.The degree of pre damage has a significant impact on the crack resistance performance of reinforced beams,while its impact on the ultimate bearing capacity is relatively limited.When the pre splitting width of the RC beam increases from 0.2 mm to 0.4 mm,the ultimate bearing capacity decreases by 28.33%.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52278333)the China Scholarship Council(CSC)and the Science and Technology Department of Liaoning Province(Grant No.2024JH2/102500069).
文摘Peridynamics(PD)is an effective method for simulating the spontaneous initiation and propagation of tensile cracks in materials.However,it faces great challenges in simulating compression-shear cracking of geomaterials due to the lack of efficient contact-friction models.This paper introduces an original contact-friction model that leverages twin mesh and potential function principles within PD to model rock cracking under tensile and compressive stresses.The contact detection algorithm,based on space segmentation axis-aligned bounding box(AABB)tree data structure,is used to address the significant challenge of highly efficient contact detection in compression and shear problems.In this method,the twin mesh and potential function are utilized to quantify contact detection and contact degree,as well as friction behavior.This is in contrast to the distance and circular contact area model,which lacks physical significance in the classical PD method.As demonstrated by the tests on specimens containing cracks,the proposed model can capture 8 types of secondary fractures,reduce the contact detection error by about 29%e56%,and increase the contact retrieval efficiency by over 1600 times compared to the classic PD models.This significantly enhances the capability of PD to simulate the initiation,expansion,and coalescence of intricate compression-shear cracks.
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.
文摘A comparative study of products of thermal and thermocatalytic cracking of polypropylene(PP) in the presence of potassium polytitanate(PPT) synthesized by treatment of TiO_(2)(rutile) powder with molten mixture of KOH and KNO_(3) taken in a weight ratio of 30∶30∶40 has been carried out.It was shown that the studied type of PPT powder exhibits catalytic properties in the reaction of thermal decomposition of PP,compared to the effect of commercial zeolite catalyst CBV-780 traditionally used for this purpose.Based on the analysis performed,the differences in the mechanism of catalytic action of PPT and the zeolite were considered.The reasons for the observed differences in the composition of PP cracking products and in the rate of coke formation on the surface of studied catalysts were analyzed.Considering the obtained results,it has been proposed that the CBV-780 catalyst promoted more intensive production of the gaseous hydrocarbons compared to PPT,due to higher specific surface area(internal surface) accessible for relatively light and small-sized hydrocarbon products of cracking.However,intensive coke formation on the outer surface of the microporous zeolite contributes to the blocking of transport channels and the rapid loss of catalytic action.At the same time,PPT,which initially has a smaller specific surface area,retains its catalytic activity significantly longer due to slit-shaped flat pores and higher transport accessibility of the inner surface.
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 Hunan Provincial Natural Science Foundation of China(Grant No.2022JJ40194)National Natural Science Foundation of China(Grant No.32102322)National Technology System for Grape Industry(Grant No.CARS-29-ZP-9)。
文摘Fruit cracking is a persistent challenge for table grape growing.To investigate the mechanism of this disorder,a comprehensive two-year investigation was conducted to assess the fruit cracking percentage of 15 table grape(Vitis vinifera L.)varieties.Based on the findings,the cracking-susceptible variety‘Xiangfei'and the cracking-resistant variety‘Zuijinxiang'were selected for further study.Fruit growth curves for‘Zuijinxiang'and‘Xiangfei'were plotted based on fruit diameter and total soluble solids content,revealing that both varieties exhibited typical double-sigmoidal patterns that were highly similar.The period between 48 and 53 days after full bloom(DAFB)was identified as the critical phase for fruit cracking incidence.Furthermore,during the fruit cracking period,‘Xiangfei'fruit exhibited significantly higher water content and mesocarp cell area compared with those of‘Zuijinxiang'.Applying aquaporin inhibitors(nano-silver)to‘Xiangfei'berries reduced fruit water uptake and cracking percentage,whereas applying aquaporin activators(forskolin)to‘Zuijinxiang'berries increased fruit water uptake and cracking percentage.Additionally,expression analysis of six genes associated with plasma membrane intrinsic proteins(PIPs)synthesis(VvPIP1;1,VvPIP1;2,VvPIP1;3,VvPIP2;1,VvPIP2;2,and VvPIP2;3)revealed that only the expression level of VvPIP1;1 was higher in‘Zuijinxiang'than in‘Xiangfei'during the fruit cracking period,whereas the expression levels of the other genes exhibited no significant difference between the two varieties.Transgenic overexpression of VvPIP1;1 in tomato resulted in increased fruit water content,enlarged mesocarp cell size,and enhanced fruit cracking percentage.These findings indicate that VvPIP1;1 plays a pivotal role in controlling grape berry cracking.
基金the financial support by the National Natural Science Foundation of China(Grant No.52108397)“Xiaohe”Science and Technology Talent Special Project(Grant No.2024 TJ-X06)Water Resources Science and Technology Project of Hunan Province(Grant No.XSKJ2023059-41).
文摘Cracking affected by wetting-drying cycles is a major cause of shallow failure of soft rock slopes.Knowledge of rock tensile properties and cracking behaviors helps better assess the stability of soft rock slopes.This study aims to examine the cracking behaviors and tensile strength of silty mudstone under wetting-drying cycles.The wetting-drying cycle and Brazilian splitting tests were performed on silty mudstone considering various cycle number and amplitude.The cracking behaviors of wetting-drying cycles were analyzed by digital image correlation,three-dimensional(3D)scanning technology,and scanning electron microscopy.The results reveal a spiral-like pattern of crack ratio escalation in silty mudstone,with a higher crack ratio observed during drying than wetting.Tensile strength and fracture energy correlate negatively with cycle number or amplitude,with cycle number exerting a more pronounced effect.The variance of the maximum principal strain reflects stages of initial deformation,linear deformation,strain localization,and stable deformation.The formation of strain localization zones reveals the physical process of crack propagation.Crack tip opening displacement progresses through stages of slow growth,exponential growth,and linear growth,delineating the process from crack initiation to stable extension.Failure modes of silty mudstone primarily involve tensile and tensile-shear failure,influenced by the geometric parameters of cracks induced by wetting-drying cycles.Fracture surface roughness and fractal dimension increase with cycle number due to mineral dissolution,physical erosion,and nondirectional crack propagation.Hydration-swelling and dehydration-shrinkage of clay minerals,along with absorption-drying cracking,initiate and merge cracks,leading to degradation of the rock mechanical properties.The findings could provide insights for mitigating shallow cracking of soft rock slopes under wetting-drying cycles.
基金supported by the National Key Research and Development Program of China(Grant Nos.2023YFC3707900 and 2024YFC3012700)the National Natural Science Foundation of China(Grant No.42230710).
文摘Soil desiccation cracking is ubiquitous in nature and has significantpotential impacts on the engineering geological properties of soils.Previous studies have extensively examined various factors affecting soil cracking behavior through a numerous small-sample experiments.However,experimental studies alone cannot accurately describe soil cracking behavior.In this study,we firstly propose a modeling framework for predicting the surface crack ratio of soil desiccation cracking based on machine learning and interpretable analysis.The framework utilizes 1040 sets of soil cracking experimental data and employs random forest(RF),extreme gradient boosting(XGBoost),and artificialneural network(ANN)models to predict the surface crack ratio of soil desiccation cracking.To clarify the influenceof input features on soil cracking behavior,feature importance and Shapley additive explanations(SHAP)are applied for interpretability analysis.The results reveal that ensemble methods(RF and XGBoost)provide better predictive performance than the deep learning model(ANN).The feature importance analysis shows that soil desiccation cracking is primarily influencedby initial water content,plasticity index,finalwater content,liquid limit,sand content,clay content and thickness.Moreover,SHAP-based interpretability analysis further explores how soil cracking responds to various input variables.This study provides new insight into the evolution of soil cracking behavior,enhancing the understanding of its physical mechanisms and facilitating the assessment of potential regional development of soil desiccation cracking.
基金supported by the National Natural Science Foundation of China(Grant No.42277124)the National Key Research&Development Program of China(Grant No.2020YFC1808004)the Jiangsu Province 333 Talents Youth Talent Support Project.
文摘In subtropical regions,soil desiccation cracking often exerts a significant impact on the interactions between soil water and the atmosphere,making it a subject of great interest in the fields of geotechnical and geoenvironmental engineering.Despite the growing utilization of biochar as a sustainable soil amendment,there remains a lack of in-depth understanding of biocharewateresoil interactions,as well as its impact on soil desiccation cracking behavior.To address this gap,this study investigated the influence and mechanism of woody biochar dosages and particle sizes on the cracking behavior of three typical clayey soils in subtropical regions in China,namely Pukou expansive soil(PKE),Xiashu soil(XS),and Zhongshan lateritic soil(ZSL).The quantitative analysis of crack images revealed that the use of biochar was not consistently effective in preventing soil cracking.The application of biochar reduced the crack ratio in PKE and XS by up to 24.03%and 53.89%,respectively.In contrast,ZSL exhibited a 74.57%increase in crack ratio with the addition of 10%biochar.This influence can be further enhanced by increasing the dosage and reducing the particle size of biochar.The microstructural analysis demonstrated that biochar exerts an inhibitory effect on PKE and XS primarily through direct replacement,direct barrier,and indirect physical mechanisms.Moreover,an indirect chemical effect between biochar and clay particles was proposed to explain the exacerbated cracking observed in biochar-amended ZSL.To effectively utilize biochar for soil cracking mitigation in subtropical regions,it is essential to evaluate the initial mineral composition and cation type of the soil.
基金supported by the National Natural Science Foundation of China(52071175,52301304)the Natural Science Foundation of Jiangsu Province(BK20230704)+3 种基金the China Postdoctoral Science Foundation Funded Project(2023M731742)the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province(23KJB430019)the Research Fund of Nanjing Institute of Technology(YKJ202402)the Open Research Fund of Jiangsu Key Laboratory for Light Metal Alloys(LMA202401).
文摘Implants are inevitably subjected to stress corrosion,bringing serious challenges to the controlled degradation of biomedical Mg alloys.It is worth studying the stress corrosion cracking(SCC)behavior of Mg alloy and exploring Mg alloy with good SCC resistance for wide biomedical applications.In this work,the as-cast and as-extruded Mg-3Gd-1Zn-0.4Zr(GZ31K)alloys with uniform corrosion were used to investigate SCC behavior.The as-extruded GZ31K alloy exhibited better corrosion resistance and mechanical properties than the as-cast one mainly owing to grain refinement and uniformly distributed fine precipitates,and possessed superior SCC resistance.To clarify the SCC mechanism,the slow strain rate tests were assisted with applied constant potentials via an electrochemical workstation.Accelerated anodic dissolution at anodic polarization deteriorated SCC resistance due to the initiation of corrosion pits and micro-cracks.However,cathodic polarization had no obvious effects on SCC resistance,along with both retarded corrosion and accelerated hydrogen evolution.Stacking faults in GZ31K alloy were hydrogen capture containers to reduce the effect of hydrogen on SCC resistance during cathodic polarization.These findings provide new insights into the evaluation of SCC mechanism,and offer more opportunities to explore Mg alloys with good SCC resistance by regulating anodic dissolution.
基金supports provided by the National Natural Science Foundation of China(No.52372330).
文摘The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weldability of components with thin walls after small punch sampling,such as ethylene cracking furnace tubes,requires further investigation.Therefore,the weldability of in-service ethylene cracking furnace tubes following small punch sampling was investigated through nondestructive testing,microstructural characterization,and mechanical testing.Additionally,the impact of small punch sampling size and residual stress on the creep performance of the specimens was studied using an improved ductility exhaustion model.The results indicate that both the surface and interior of the weld repair areas on new furnace tubes and service-exposed furnace tubes after small-punch sampling are defect-free,exhibiting good weld quality.The strength of the specimens after weld repair was higher than that before sampling,whereas toughness decreased.Weld repair following small punch sampling of furnace tubes is both feasible and necessary.Furthermore,a linear relationship was observed between specimen thickness,diameter,and creep fracture time.The residual stress of welding affects the creep performance of the specimen under different stresses.
基金supported by General Program of National Natural Science Foundation of China (22178385)。
文摘In this work,a new process for achieving the recovery of elemental sulfur by utilizing a fluidized catalytic cracking(FCC) riser reactor for SOxtreatment(FCC-DeSOx) is proposed.The process leverages the high temperatures and hydrocarbon concentrations in the FCC riser reactor to convert SOxinto H_(2)S.Subsequently,H_(2)S,along with the cracked gas,is processed downstream to produce sulfur.Thermodynamic analysis of the key reduction reactions in the FCC-DeSOxprocess revealed that complete conversion of SOxto H_(2)S is feasible in the dry gas(hydrogen-rich) prelift zone,as well as the upper and lower zones of the riser,upon achieving thermodynamic equilibrium.Experimental studies were conducted to replicate the conditions of these reaction zones using a low concentration of hydrogen gas as the reducing agent.Through process optimization,investigation of the minimum reaction time,and kinetic studies,the potential of this method for the complete reduction of SOxwas further confirmed.
基金support from the National Key Research and Development Program of China(No.2023YFB3710300)National Natural Science Foundation of China(Nos.12174296 and 52101088)+1 种基金Major Program(JD)of Hubei Province,China(No.2023BAA019-5)Numerical calculation is supported by the High-Performance Computing Center of Wuhan University of Science and Technology,China.
文摘The effect of aging precipitation on the stress corrosion cracking(SCC)mechanism of Ni(Fe,Al)-maraging steel was studied through the comparative characterization and analyses of the microstructures and fracture features of solid–solution and peak-aged steels.Aging precipitation exerts a chain of impacts on the deformative compatibility and electrochemical difference between the matrix and oth-er phases or interfaces.The strength of the martensite matrix is enhanced by abundant and evenly dispersed Ni(Fe,Al)precipitates,thereby reducing the possibility of splitting across martensite laths.Meanwhile,the Volta potential difference(VPD)between the matrix and primary NbC particles increases from 11.43 to 18.60 mV.Given that most of the primary NbC particles tend to be distributed along high-angle grain boundaries(HAGBs),anodic dissolution along HAGBs accelerates.Therefore,mechanical and electrochemical factors triggered by aging precipitation are involved in the variation in SCC behavior and mechanism.The SCC susceptibility of the steel in-creases along with the increasing tendency for intergranular cracking.
基金supported by the Innovative Research Group Project of the National Natural Science Foundation of China(22021004)Sinopec Major Science and Technology Projects(321123-1)。
文摘Coking at the fractionating tower bottom and the decant oil circulation system disrupts the heat balance,leading to unplanned shutdown and destroying the long period stable operation of the Fluid Catalytic Cracking Unit(FCCU).The FCCU operates through interconnected subsystems,generating high-dimensional,nonlinear,and non-stationary data characterized by spatiotemporally correlated.The decant oil solid content is the crucial indicator for monitoring catalyst loss from the reactor-regenerator system and coking risk tendency at the fractionating tower bottom that relies on sampling and laboratory testing,which is lagging responsiveness and labor-intensive.Developing the online decant oil solid content soft sensor using industrial data to support operators in conducting predictive maintenance is essential.Therefore,this paper proposes a hybrid deep learning framework for soft sensor development that combines spatiotemporal pattern extraction with interpretability,enabling accurate risk identification in dynamic operational conditions.This framework employs a Filter-Wrapper method for dimensionality reduction,followed by a 2D Convolutional Neural Network(2DCNN)for extracting spatial patterns,and a Bidirectional Gated Recurrent Unit(BiGRU)for capturing long-term temporal dependencies,with an Attention Mechanism(AM)to highlight critical features adaptively.The integration of SHapley Additive exPlanations(SHAP),Complementary Ensemble Empirical Mode Decomposition with Adaptive Noise(CEEMDAN),2DCNN,and expert knowledge precisely quantifies feature contributions and decomposes signals,significantly enhancing the practicality of risk identification.Applied to a China refinery with processing capacity of 2.80×10^(6) t/a,the soft sensor achieved the R^(2) value of 0.93 and five-level risk identification accuracy of 96.42%.These results demonstrate the framework's accuracy,robustness,and suitability for complex industrial scenarios,advancing risk visualization and management.
基金support of the National Natural Science Foundation of China(No.52171063).
文摘A series of Sn microalloying high-strength low-alloy(HSLA)steels were prepared through vacuum melting and hot rolling.Their stress corrosion cracking(SCC)behavior under high Cl^(−)environments was investigated using U-bend immersion,slow strain rate testing,electrochemical methods,and novel SCC sensor.Results revealed that HSLA steel microalloying with 0.1 wt.%Sn demonstrated superior SCC resistance,primarily attributed to the effective inhibition of the anodic dissolution mechanism.Fracture morphology revealed a transformation in fracture mode from brittle to a mixture of brittle-ductile characteristics,accompanied by the formation of a protective SnO_(2)oxide film on the steel surface.However,excessive Sn content exacerbated SCC susceptibility due to the increased hydrolysis of Sn^(2+),leading to localized pitting and crack initiation.The critical role of optimal Sn content was highlighted in balancing mechanical properties and corrosion resistance,suggesting potential applications in industries where materials face harsh chloride environments.
基金supported by the National Key Research and Development Program of China(No.2021YFB3701000)the National Natural Science Foundation of China(Nos.51971130,52201129,U21A2047,51821001,U2037601)+2 种基金support by the China Postdoctoral Science Foun-dation(2023M742219)the Postdoctoral Fellowship Program of CPSF under Grant Number GZB20240419support by the Ministry of Education,Singapore,under its Academic Research Fund Tier 2(MOE-T2EP50221-0013).
文摘Additive manufacturing (AM) of high-strength metallic alloys frequently encounters detrimental distortion and cracking, attributed to the accumulation of thermal stresses. These issues significantly impede the practical application of as-printed components. This study examines the Mg-15Gd-1Zn-0.4Zr (GZ151K, wt.%) alloy, a prototypical high-strength casting Mg-RE alloy, fabricated through laser powder bed fusion (LPBF). Despite achieving ultra-high strength, the GZ151K alloy concurrently exhibits a pronounced cold-cracking susceptibility. The as-printed GZ151K alloy consists of almost fully fine equiaxed grains with an average grain size of merely 2.87 µm. Subsequent direct aging (T5) heat treatment induces the formation of dense prismatic β' precipitates. Consequently, the LPBF-T5 GZ151K alloy manifests an ultra-high yield strength of 405 MPa, surpassing all previously reported yield strengths for Mg alloys fabricated via LPBF and even exceeding that of its extrusion-T5 counterpart. Interestingly, as-printed GZ151K samples with a build height of 2 mm exhibit no cracking, whereas samples with build heights ranging from 4 to 18 mm demonstrate severe cold cracking. Thermal stress simulation also suggests that the cold cracking susceptibility increases significantly with increasing build height. The combination of high thermal stress and low ductility in the as-printed GZ151K alloy culminates in a high cold cracking susceptibility. This study offers novel insights into the intricate issue of cold cracking in the LPBF process of high-strength Mg alloys, highlighting the critical balance between achieving high strength and mitigating cold cracking susceptibility.
文摘Hydrogen-induced cracking (HIC) is one of the most complex material problems that hydrogen can diffuse into and interact with microstructure, degrading their mechanical properties. Microstructural modification is an effective way to enhance the resistance to HIC. The present study focused on the relationship between the retained austenite (RA) and HIC behavior in NiCrMoV/Nb multi-alloying ultra-strength steel. Results demonstrated that the maximum volume fraction of RA of 9.31% was obtained for QL30T specimen. After the deep cryogenic pretreatment, the volume fraction of RA reduced to 8.8%. RA could reduce the effective diffusion coefficient, while deep cryogenic pretreatment increased the susceptibility of the steel to HIC by a maxim of 14.8%. This was mainly due to the transformation of retained austenite into martensite, degrading the mechanical properties under hydrogen-charged condition. In addition, the deep cryogenic pretreatment had a significant effect on the crack initiation and propagation, with the intergranular (IG) fracture becoming the dominant fracture mode where an increase in the number of secondary cracks in the section. The interfaces of RA and matrix, as well as the grain boundaries, were the preferred sites for cracks initiation.
文摘Percussive drilling is gaining interest for both shallow and deep applications due to its potential for higher drilling rates in hard rocks.Therefore,for efficient rock breaking,the development of advanced percussive drilling simulation tools has the potential to be transformative.Such tools must accurately capture the rock’s response to enable an effective analysis of the fragmentation process.Traditional continuum numerical methods,such as the finite element method(FEM),do not simulate discrete cracks or the contact interaction between rock fragments.The finite-discrete element method(FDEM)is a three-dimensional hybrid method that combines FEM with the discrete element method(DEM)that addresses these limitations.New FDEM simulation results of impacts on Kuru Grey granite show good agreement with published experimental data.The interpretation focuses on two significant processes in percussive drilling:crack propagation and chipping generation.FDEM successfully simulates the evolution of cracks,including radial,side,and inclined cracks,as well as crushed and cracked zones.The simulation also reproduces the coalescence of adjacent craters to generate more chippings.Additionally,the stress state,velocity field and discrete fractures simulated by FDEM provide detailed insights into the different fracture patterns for Kuru Grey granite,enhancing understanding of the fundamental underlying mechanisms.
基金supported by the National Key R&D Program of China(No.2021YFF0502100)the National Natural Science Foundation of China(Nos.52278461 and 52308467).
文摘Cracking of early-age concrete can occur in the track beds of high-speed railways due to changes in material properties,environmental effects,and construction processes.This is a multi-field,time-varying issue involving hydro-thermo-chemo-mechanical coupling.However,to date,research has not adequately described the early-age cracking mechanisms in track beds,and few risk control measures have been proposed.To solve this problem,we incorporated the hydration degree of concrete into multi-field coupling equations for early-age concrete,and set boundary conditions that account for environmental influences and various stress factors that typically cause early creep of concrete.A four-field coupled risk prediction model was built based on hydro-thermo-chemo-mechanical properties,and was used to calculate and analyze various time-varying behavior(including the risk and form of cracking)in the hydro,thermo,chemo,and mechanical fields of early-age concrete.Finally,we focused on material-related factors(maximum heat of hydration and peak heat release time),environmental factors(temperature difference between day and night,average daily cooling rate,and intensity of solar radiation),and construction technique factors(molding temperature,pouring time,and thermal insulation coefficient).The influence of these factors on the early-age cracking risk of the track bed was analyzed,and risk control measures against early cracking were proposed accordingly.
基金supported by the National Natural Science Foundation of China(Nos.52205382,52225503)National Key Research and Development Program(No.2023YFB4603300)+3 种基金Key Research and Development Program of Jiangsu Province(Nos.BE2022069,BZ2024019)National Natural Science Foundation of China for Creative Research Groups(No.51921003)International Joint Laboratory of Sustainable Manufacturing,Ministry of Education and the Fundamental Research Funds for the Central Universities(NG2024014)Postgraduate Research&Practice Innovation Program of NUAA(xcxjh20230616)。
文摘High cracking susceptibility of Al-Li alloys with Ti/Ce B6addition is thoroughly suppressed in laser powder bed fusion(LPBF)processing of Ti/Ce co-modified 2195 alloys at relatively high scan speeds,while the cracking suppression mechanism and phase formation in these composites are not clarified.In this work,microstructure evolution and mechanical performance of the LPBF-fabricated Ti/Ce co-modified 2195 are investigated to reveal their cracking suppression and strengthening mechanisms.The results show that apparent grain refinement of the composites is ascribed to high supercooling from rapid formation of constitutional supercooling zone in front of solid–liquid interfaces by high-Q-value Ti solute,and heterogeneous nucleation of in situ formed Al3Ti and Al11Ce3precipitates.Their synergistic interactions promote formation of fine equiaxed grains and thus inhibit crack initiation.The composites exhibit high microhardness of 100±5HV0.2,nano-hardness of 1.6±0.1 GPa and elastic modulus of 97±3 GPa,where the elastic modulus increases by 27%and 31%compared to those of LPBF-processed and conventionally manufactured 2195 alloys,respectively.A tensile strength of 336 MPa and an elongation of 3%are obtained from in-situ synchrotron X-ray diffraction measurement.The improved properties are derived from grain refinement and Orowan strengthening.Based on the optimal processing parameter and composition,a bracket component filled with lattice structures is designed and manufactured with good manufacturing quality and processing accuracy.
文摘In order to study the mechanical properties of damaged reinforced concrete(RC)beams reinforced with ultra-high-performance concrete(UHPC),a four-point bending test was conducted to systematically investigate the influence of factors such as the number of reinforcement surfaces and the degree of damage.The results indicate that single-sided repaired beams have certain advantages in crack resistance performance,but are more disadvantageous in ultimate bearing capacity,with obvious debonding phenomenon before the end of loading.Compared with single-sided reinforcement,the cracking load of the three-sided reinforced beam increased by an average of 1.85 times,the ultimate bearing capacity increased by an average of 177.5%,and a good UHPC-RC combination effect could be formed,which could work synergistically until the end of loading.The degree of pre damage has a significant impact on the crack resistance performance of reinforced beams,while its impact on the ultimate bearing capacity is relatively limited.When the pre splitting width of the RC beam increases from 0.2 mm to 0.4 mm,the ultimate bearing capacity decreases by 28.33%.
