Tensile cracking is a predominant mode of failure in rocks within underground resource excavation and engineering structures,where rocks are frequently subjected to dynamic disturbances while simultaneously experienci...Tensile cracking is a predominant mode of failure in rocks within underground resource excavation and engineering structures,where rocks are frequently subjected to dynamic disturbances while simultaneously experiencing in-situ stresses.This paper proposes a new dynamic split tension setup utilising a cubic specimen to investigate the dynamic behaviour of rocks across various tensile strain rates and confining pressures.The objective is to extend the applicability of the triaxial Hopkinson bar in studying dynamic behaviour of geomaterials.For comparison,the dynamic Brazilian disc(BD)tests were performed using three rock types(e.g.,sandstone,granite and marble)under different strain rates ranging from 10^(−3)∼10^(2) s^(−1).Besides,the Digital Image Correlation(DIC)technique was adopted to measure full-field real-time tensile strain of rocks and demonstrated that tensile crack initiated at the middle part and split the specimen into two similar halves.Effects of specimen size,geometry,loading rate as well as the confining pressure are investigated in detail.The dynamic fracture behaviours,including dynamic tensile strength,tensile strain,time to fracture and dynamic increase factor(DIF),were characterised for the rocks.It is found that dynamic tensile strength of rock minimal dependence on size and geometry but is significantly influenced by loading rate and confinement.It exhibited a linear increase with strain rate(10^(0)∼10^(2) s^(−1))and demonstrated a nonlinear growth with lateral confinement from 0 to 15 MPa.The nonlinear dependency on confinement can be attributed to the restriction imposed on the opening and propagation of tensile cracks due to the presence of confinement.These findings enhance our understanding of the safety aspects associated with underground rock excavations,particularly in situations where considering in-situ stress is crucial for evaluating the dynamic tensile failure of rocks.展开更多
The response of three-dimensional sample of Al, containing vacancy complex, under shear loading was simulated. The molecular dynamics method was used and interaction between atoms was described on the base of pseudopo...The response of three-dimensional sample of Al, containing vacancy complex, under shear loading was simulated. The molecular dynamics method was used and interaction between atoms was described on the base of pseudopotential theory Solitary waves were generated in the sample under mechanical loading. Their interaction with the vacancy complexes was shown to be able to initiate hot spot in that local region of the complexes. Some parameters of the hot spot as well as solitary waves were calculated. The initiation of the hot spot is accompanied with sufficient local structural relaxation.展开更多
Recent advances in additive manufacturing have enabled the construction of metallic lattice structures with tailored mechanical and functional properties.One potential application of metallic lattice struc-tures is in...Recent advances in additive manufacturing have enabled the construction of metallic lattice structures with tailored mechanical and functional properties.One potential application of metallic lattice struc-tures is in the impact load mitigation where an external kinetic energy is absorbed by the deformation/crushing of lattice cells.This has motivated a growing number of experimental and numerical studies,recently,on the crushing behavior of additively produced lattice structures.The present study overviews the dynamic and quasi-static crushing behavior of additively produced Ti64,316L,and AlSiMg alloy lattice structures.The first part of the study summarizes the main features of two most commonly used additive processing techniques for lattice structures,namely selective-laser-melt(SLM)and electro-beam-melt(EBM),along with a description of commonly observed process induced defects.In the second part,the deformation and strain rate sensitivities of the selected alloy lattices are outlined together with the most widely used dynamic test methods,followed by a part on the observed micro-structures of the SLM and EBM-processed Ti64,316L and AlSiMg alloys.Finally,the experimental and numerical studies on the quasi-static and dynamic compression behavior of the additively processed Ti64,316L,and AlSiMg alloy lattices are reviewed.The results of the experimental and numerical studies of the dynamic properties of various types of lattices,including graded,non-uniform strut size,hollow,non-uniform cell size,and bio-inspired,were tabulated together with the used dynamic testing methods.The dynamic tests have been noted to be mostly conducted in compression Split Hopkinson Pressure Bar(SHPB)or Taylor-and direct-impact tests using the SHPB set-up,in all of which relatively small-size test specimens were tested.The test specimen size effect on the compression behavior of the lattices was further emphasized.It has also been shown that the lattices of Ti64 and AlSiMg alloys are relatively brittle as compared with the lattices of 316L alloy.Finally,the challenges associated with modelling lattice structures were explained and the micro tension tests and multi-scale modeling techniques combining microstructural characteristics with macroscopic lattice dynamics were recommended to improve the accuracy of the numerical simulations of the dynamic compression deformations of metallic lattice structures.展开更多
The computer simulation of Al three-dimensional crystallite containing grain boundary of special type was carried out and its behaviour under high rate loading was investigated. The molecular dynamics method was used ...The computer simulation of Al three-dimensional crystallite containing grain boundary of special type was carried out and its behaviour under high rate loading was investigated. The molecular dynamics method was used and interaction betwen atoms was described based on pseudopotential method. Vortical character of the atom movements in the grain boundary region is realized under shear loading in certain directions. Back and forth movements of atoms in the direction which is perpendicular to the shear also arise. Amplitude of such movements is approximately equal to an interplanar distance in this direction.展开更多
To address the inherent trade-off between mechanical strength and repair efficiency in conventional microcapsule-based self-healing technologies,this study presents an eggshell-inspired approach for fabricating high-l...To address the inherent trade-off between mechanical strength and repair efficiency in conventional microcapsule-based self-healing technologies,this study presents an eggshell-inspired approach for fabricating high-load rigid porous microcapsules(HLRPMs)through subcritical water etching.By optimizing the subcritical water treatment parameters(OH−concentration:0.031 mol/L,tem-perature:240°C,duration:1.5 h),nanoscale through-holes were generated on hollow glass microspheres(shell thickness≈700 nm).The subsequent gradient pressure infiltration of flaxseed oil enabled a record-high core content of 88.2%.Systematic investigations demonstrated that incorporating 3 wt%HLRPMs into epoxy resin composites preserved excellent dielectric properties(breakdown strength≥30 kV/mm)and enhanced tensile strength by 7.52%.In addressing multimodal damage,the system achieved a 95.5%filling efficiency for mechanical scratches,a 97.0%reduction in frictional damage depth,and a 96.2%recovery of insulation following electrical treeing.This biomimetic microcapsule system concurrently improved self-healing capability and matrix performance,offering a promising strategy for the development of next-generation smart insulating materials.展开更多
By using split Hopkinson pressure bar, optical microscopy and electronic microscopy, we investigate the influence of initial microstructures on the adiabatic shear behavior of high-strength Ti-5Al-5V-5Mo-3Cr(Ti-5553) ...By using split Hopkinson pressure bar, optical microscopy and electronic microscopy, we investigate the influence of initial microstructures on the adiabatic shear behavior of high-strength Ti-5Al-5V-5Mo-3Cr(Ti-5553) alloy with lamellar microstructure and bimodal microstructure. Lamellar alloy tends to form adiabatic shearing band(ASB) at low compression strain, while bimodal alloy is considerably ASBresistant. Comparing with the initial microstructure of Ti-5553 alloy, we find that the microstructure of the ASB changes dramatically. Adiabatic shear of lamellar Ti-5553 alloy not only results in the formation of recrystallized β nano-grains within the ASB, but also leads to the chemical redistribution of the alloying elements such as Al, V, Cr and Mo. As a result, the alloying elements distribute evenly in the ASB.In contrast, the dramatic adiabatic shear of bimodal alloy might give rise to the complete lamination of the globular primary a grain and the equiaxial prior β grain, which is accompanied by the dynamic recrystallization of a lamellae and β lamellae. As a result, ASB of bimodal alloy is composed of a/β nanomultilayers. Chemical redistribution does not occur in ASB of bimodal alloy. Bimodal Ti-5553 alloy should be a promising candidate for high performance armors with high mass efficiency due to the processes high dynamic flow stress and excellent ASB-resistance.展开更多
In order to enhance the start-up of anaerobic digestion(AD),the propionate-degrading methanogenic cultures were introduced to AD of food waste at a high organic loading rate(OLR)of 3.0 g VS/L∙d in this study,and the e...In order to enhance the start-up of anaerobic digestion(AD),the propionate-degrading methanogenic cultures were introduced to AD of food waste at a high organic loading rate(OLR)of 3.0 g VS/L∙d in this study,and the efficiency of different bioaugmentation strategies were investigated.The results demonstrated that bioaugmentation significantly improved the start-up efficiency and enhanced the methane production.Specifically,higher dosage and frequency of bioaugmentation had a positive effect on the performance of the AD reactors.Among three bioaugmented reactors,the reactor with a bioaugmentation strategy of 0.675 g VS/L of bioaugmentation seed added every 5 d during the first hydraulic retention time(HRT)performed the best and remained relatively stable for the next three HRTs without bioaugmentation.The 16S rRNA gene sequencing analysis revealed that Methanothrix predominated in bioaugmented reactors.A large proportion of Methanothrix accompanied by a small proportion of Methanospirillum played a key role in volatile fatty acid degradation and contributed to the successful start-up and long-term stability of AD at a high OLR.These findings suggest that bioaugmentation with methangenic consortium is a promising strategy to boost the AD process at high OLRs and achieve higher treatment capacity of food waste.展开更多
A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method...A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method. The center-cracked tension specimen is connected between the bars with a specially designed fixture device. The fracture initiation time is measured by the strain gage method, and dynamic stress intensity factors （DSIF） are obtained with the aid of 3D finite element analysis （FEA）. In this approach, the dimensions of the specimen are not restricted by the connec- tion strength or the stress-state equilibrium conditions, and hence plane strain state can be attained conveniently at the crack tip. Through comparison between the obtained results and those in open publication, it is concluded that the ex- perimental data are valid, and the method proposed here is reliable. The validity of the obtained DFT is checked with the ASTM criteria, and fracture surfaces are examined at the end of paper.展开更多
In the field of disaster prevention mitigation and protection engineering,it is important to identify the mechanical behaviors of reinforced concrete(RC)under explosive load by simulation.A three dimensional beam-part...In the field of disaster prevention mitigation and protection engineering,it is important to identify the mechanical behaviors of reinforced concrete(RC)under explosive load by simulation.A three dimensional beam-particle model(BPM),which is suitable to simulate the fracture process of RC under explosive load,has been developed in the frame of discrete element method (DEM).In this model,only the elastic deformations of beams between concrete particles were considered.The matrix displacement method(MDM)was employed to describe the relationship between the deformation and forces of the beam.A fracture criterion expressed by stress was suggested to identify the state of the beam.A BPM for steel bar,which can simulate the deformation of steel bar under high loading rate,was also developed based on the Cowper-Symonds theory.A program has been coded using C++language.Experiments of RC slab under explosive load were carried out using the program.Good agreement was achieved between the experimental and simulated results.It is indicated that the proposed theoretical model can well simulate the fracture characteristics of RC slab under explosive load such as blasting pit formation,cracks extension, spallation formation,etc.展开更多
基金supported by the Australian Research Council(LE150100058)the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering(Z020002)State Key Laboratory of Coal Mine Disaster Dynamics and Control.The specimens were scanned at the Imaging and Medical beamline(IMBL)under the Australian Synchrotron projects(NO:M15862 and M14428).
文摘Tensile cracking is a predominant mode of failure in rocks within underground resource excavation and engineering structures,where rocks are frequently subjected to dynamic disturbances while simultaneously experiencing in-situ stresses.This paper proposes a new dynamic split tension setup utilising a cubic specimen to investigate the dynamic behaviour of rocks across various tensile strain rates and confining pressures.The objective is to extend the applicability of the triaxial Hopkinson bar in studying dynamic behaviour of geomaterials.For comparison,the dynamic Brazilian disc(BD)tests were performed using three rock types(e.g.,sandstone,granite and marble)under different strain rates ranging from 10^(−3)∼10^(2) s^(−1).Besides,the Digital Image Correlation(DIC)technique was adopted to measure full-field real-time tensile strain of rocks and demonstrated that tensile crack initiated at the middle part and split the specimen into two similar halves.Effects of specimen size,geometry,loading rate as well as the confining pressure are investigated in detail.The dynamic fracture behaviours,including dynamic tensile strength,tensile strain,time to fracture and dynamic increase factor(DIF),were characterised for the rocks.It is found that dynamic tensile strength of rock minimal dependence on size and geometry but is significantly influenced by loading rate and confinement.It exhibited a linear increase with strain rate(10^(0)∼10^(2) s^(−1))and demonstrated a nonlinear growth with lateral confinement from 0 to 15 MPa.The nonlinear dependency on confinement can be attributed to the restriction imposed on the opening and propagation of tensile cracks due to the presence of confinement.These findings enhance our understanding of the safety aspects associated with underground rock excavations,particularly in situations where considering in-situ stress is crucial for evaluating the dynamic tensile failure of rocks.
文摘The response of three-dimensional sample of Al, containing vacancy complex, under shear loading was simulated. The molecular dynamics method was used and interaction between atoms was described on the base of pseudopotential theory Solitary waves were generated in the sample under mechanical loading. Their interaction with the vacancy complexes was shown to be able to initiate hot spot in that local region of the complexes. Some parameters of the hot spot as well as solitary waves were calculated. The initiation of the hot spot is accompanied with sufficient local structural relaxation.
基金the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 101034425 for the project titled A2M2TECHThe Scientific and Technological Research Council of Türkiye (TUBITAK) with grant No 120C158 for the same A2M2TECH project under the TUBITAK's 2236/B program
文摘Recent advances in additive manufacturing have enabled the construction of metallic lattice structures with tailored mechanical and functional properties.One potential application of metallic lattice struc-tures is in the impact load mitigation where an external kinetic energy is absorbed by the deformation/crushing of lattice cells.This has motivated a growing number of experimental and numerical studies,recently,on the crushing behavior of additively produced lattice structures.The present study overviews the dynamic and quasi-static crushing behavior of additively produced Ti64,316L,and AlSiMg alloy lattice structures.The first part of the study summarizes the main features of two most commonly used additive processing techniques for lattice structures,namely selective-laser-melt(SLM)and electro-beam-melt(EBM),along with a description of commonly observed process induced defects.In the second part,the deformation and strain rate sensitivities of the selected alloy lattices are outlined together with the most widely used dynamic test methods,followed by a part on the observed micro-structures of the SLM and EBM-processed Ti64,316L and AlSiMg alloys.Finally,the experimental and numerical studies on the quasi-static and dynamic compression behavior of the additively processed Ti64,316L,and AlSiMg alloy lattices are reviewed.The results of the experimental and numerical studies of the dynamic properties of various types of lattices,including graded,non-uniform strut size,hollow,non-uniform cell size,and bio-inspired,were tabulated together with the used dynamic testing methods.The dynamic tests have been noted to be mostly conducted in compression Split Hopkinson Pressure Bar(SHPB)or Taylor-and direct-impact tests using the SHPB set-up,in all of which relatively small-size test specimens were tested.The test specimen size effect on the compression behavior of the lattices was further emphasized.It has also been shown that the lattices of Ti64 and AlSiMg alloys are relatively brittle as compared with the lattices of 316L alloy.Finally,the challenges associated with modelling lattice structures were explained and the micro tension tests and multi-scale modeling techniques combining microstructural characteristics with macroscopic lattice dynamics were recommended to improve the accuracy of the numerical simulations of the dynamic compression deformations of metallic lattice structures.
文摘The computer simulation of Al three-dimensional crystallite containing grain boundary of special type was carried out and its behaviour under high rate loading was investigated. The molecular dynamics method was used and interaction betwen atoms was described based on pseudopotential method. Vortical character of the atom movements in the grain boundary region is realized under shear loading in certain directions. Back and forth movements of atoms in the direction which is perpendicular to the shear also arise. Amplitude of such movements is approximately equal to an interplanar distance in this direction.
基金supported by the National Natural Science Foundation of China(Nos.52377133 and 52077014)the Youth Talent Support Program of Chongqing(CQYC2021058945)the General Program of the Natural Science Foundation of Chongqing Municipality(CSTB2022NSCQ-MSX0444).
文摘To address the inherent trade-off between mechanical strength and repair efficiency in conventional microcapsule-based self-healing technologies,this study presents an eggshell-inspired approach for fabricating high-load rigid porous microcapsules(HLRPMs)through subcritical water etching.By optimizing the subcritical water treatment parameters(OH−concentration:0.031 mol/L,tem-perature:240°C,duration:1.5 h),nanoscale through-holes were generated on hollow glass microspheres(shell thickness≈700 nm).The subsequent gradient pressure infiltration of flaxseed oil enabled a record-high core content of 88.2%.Systematic investigations demonstrated that incorporating 3 wt%HLRPMs into epoxy resin composites preserved excellent dielectric properties(breakdown strength≥30 kV/mm)and enhanced tensile strength by 7.52%.In addressing multimodal damage,the system achieved a 95.5%filling efficiency for mechanical scratches,a 97.0%reduction in frictional damage depth,and a 96.2%recovery of insulation following electrical treeing.This biomimetic microcapsule system concurrently improved self-healing capability and matrix performance,offering a promising strategy for the development of next-generation smart insulating materials.
基金the National Natural Science Foundation of China(Grant No.11872317)Science Challenge Project(Grant No.TZ2018001)the Fundamental Research Funds for the Central Universities(Grant No.3102019ZX001).
文摘By using split Hopkinson pressure bar, optical microscopy and electronic microscopy, we investigate the influence of initial microstructures on the adiabatic shear behavior of high-strength Ti-5Al-5V-5Mo-3Cr(Ti-5553) alloy with lamellar microstructure and bimodal microstructure. Lamellar alloy tends to form adiabatic shearing band(ASB) at low compression strain, while bimodal alloy is considerably ASBresistant. Comparing with the initial microstructure of Ti-5553 alloy, we find that the microstructure of the ASB changes dramatically. Adiabatic shear of lamellar Ti-5553 alloy not only results in the formation of recrystallized β nano-grains within the ASB, but also leads to the chemical redistribution of the alloying elements such as Al, V, Cr and Mo. As a result, the alloying elements distribute evenly in the ASB.In contrast, the dramatic adiabatic shear of bimodal alloy might give rise to the complete lamination of the globular primary a grain and the equiaxial prior β grain, which is accompanied by the dynamic recrystallization of a lamellae and β lamellae. As a result, ASB of bimodal alloy is composed of a/β nanomultilayers. Chemical redistribution does not occur in ASB of bimodal alloy. Bimodal Ti-5553 alloy should be a promising candidate for high performance armors with high mass efficiency due to the processes high dynamic flow stress and excellent ASB-resistance.
基金financially supported by the Fundamental and Applied Basic Research Fund Project of Guangdong Province(Grant No.2022A1515111019)the National Natural Science Foundation of China(Grant No.52170143,Grant No.52300180)+1 种基金the National Key Research and Development Program of China(Grant No.2023YFC3905800)the Technological Project of Yantai(Grant No.2023ZDCX026)。
文摘In order to enhance the start-up of anaerobic digestion(AD),the propionate-degrading methanogenic cultures were introduced to AD of food waste at a high organic loading rate(OLR)of 3.0 g VS/L∙d in this study,and the efficiency of different bioaugmentation strategies were investigated.The results demonstrated that bioaugmentation significantly improved the start-up efficiency and enhanced the methane production.Specifically,higher dosage and frequency of bioaugmentation had a positive effect on the performance of the AD reactors.Among three bioaugmented reactors,the reactor with a bioaugmentation strategy of 0.675 g VS/L of bioaugmentation seed added every 5 d during the first hydraulic retention time(HRT)performed the best and remained relatively stable for the next three HRTs without bioaugmentation.The 16S rRNA gene sequencing analysis revealed that Methanothrix predominated in bioaugmented reactors.A large proportion of Methanothrix accompanied by a small proportion of Methanospirillum played a key role in volatile fatty acid degradation and contributed to the successful start-up and long-term stability of AD at a high OLR.These findings suggest that bioaugmentation with methangenic consortium is a promising strategy to boost the AD process at high OLRs and achieve higher treatment capacity of food waste.
基金supported by the 111 Project (B07050)the National Natural Science Foundation of China (10932008)
文摘A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method. The center-cracked tension specimen is connected between the bars with a specially designed fixture device. The fracture initiation time is measured by the strain gage method, and dynamic stress intensity factors （DSIF） are obtained with the aid of 3D finite element analysis （FEA）. In this approach, the dimensions of the specimen are not restricted by the connec- tion strength or the stress-state equilibrium conditions, and hence plane strain state can be attained conveniently at the crack tip. Through comparison between the obtained results and those in open publication, it is concluded that the ex- perimental data are valid, and the method proposed here is reliable. The validity of the obtained DFT is checked with the ASTM criteria, and fracture surfaces are examined at the end of paper.
基金supported by the National Natural Science Foundation of China(Grant No.51044003)the National Basic Research Program of China("973"Project)(Grant No.2007CB714104)
文摘In the field of disaster prevention mitigation and protection engineering,it is important to identify the mechanical behaviors of reinforced concrete(RC)under explosive load by simulation.A three dimensional beam-particle model(BPM),which is suitable to simulate the fracture process of RC under explosive load,has been developed in the frame of discrete element method (DEM).In this model,only the elastic deformations of beams between concrete particles were considered.The matrix displacement method(MDM)was employed to describe the relationship between the deformation and forces of the beam.A fracture criterion expressed by stress was suggested to identify the state of the beam.A BPM for steel bar,which can simulate the deformation of steel bar under high loading rate,was also developed based on the Cowper-Symonds theory.A program has been coded using C++language.Experiments of RC slab under explosive load were carried out using the program.Good agreement was achieved between the experimental and simulated results.It is indicated that the proposed theoretical model can well simulate the fracture characteristics of RC slab under explosive load such as blasting pit formation,cracks extension, spallation formation,etc.
