Three-dimensional printing(3DP)offers valuable insight into the characterization of natural rocks and the verification of theoretical models due to its high reproducibility and accurate replication of complex defects ...Three-dimensional printing(3DP)offers valuable insight into the characterization of natural rocks and the verification of theoretical models due to its high reproducibility and accurate replication of complex defects such as cracks and pores.In this study,3DP gypsum samples with different printing directions were subjected to a series of uniaxial compression tests with in situ micro-computed tomography(micro-CT)scanning to quantitatively investigate their mechanical anisotropic properties and damage evolution characteristics.Based on the two-dimensional(2D)CT images obtained at different scanning steps,a novel void ratio variable was derived using the mean value and variance of CT intensity.Additionally,a constitutive model was formulated incorporating the proposed damage variable,utilizing the void ratio variable.The crack evolution and crack morphology of 3DP gypsum samples were obtained and analyzed using the 3D models reconstructed from the CT images.The results indicate that 3DP gypsum samples exhibit mechanical anisotropic characteristics similar to those found in naturally sedimentary rocks.The mechanical anisotropy is attributed to the bedding planes formed between adjacent layers and pillar-like structures along the printing direction formed by CaSO_(4)·2H_(2)O crystals of needle-like morphology.The mean gray intensity of the voids has a positive linear relationship with the threshold value,while the CT variance and void ratio have concave and convex relationships,respectively.The constitutive model can effectively match the stress–strain curves obtained from uniaxial compression experiments.This study provides comprehensive explanations of the failure modes and anisotropic mechanisms of 3DP gypsum samples,which is important for characterizing and understanding the failure mechanism and microstructural evolution of 3DP rocks when modeling natural rock behavior.展开更多
As a critical mechanical characteristic of rock,brittleness significantly influences fracture modes and damage evolution processes.Accurate quantitative evaluation of brittleness is essential for ensuring the stabilit...As a critical mechanical characteristic of rock,brittleness significantly influences fracture modes and damage evolution processes.Accurate quantitative evaluation of brittleness is essential for ensuring the stability of various engineering applications.Based on the pre-peak and post-peak stages of the rock stress-strain curve,this study constructed a brittleness index BI^(*).The index quantifies the ability of rock to resist plastic deformation during the pre-peak crack growth stage and evaluates the intensity of strength drop during the post-peak softening stage.Another index,BII,was established based on the degree of pre-peak elastic energy accumulation and the instability characteristics of post-peak dissipated energy.This index reflects the essential properties of rock failure by revealing the energy evolution mechanism.Furthermore,by defining a damage variable from the energy dissipation over the entire deformation process,an index B_(D)was introduced to evaluate brittleness from the perspective of internal damage development.Triaxial compression and cyclic loading tests were conducted on rocks of different lithologies to evaluate the new index.The influences of confining pressure and lithology on rock brittleness were analyzed,along with the sensitivity analysis of various brittleness index parameters.The results indicated that the proposed brittleness indices accurately distinguish the brittleness differences among various lithologies and show effective consistency with the failure modes of specimens under different confining pressures.Meanwhile,different brittleness indices were affected by confining pressure and lithology to different degrees.The post-peak softening stage of rock played a particularly significant role in brittleness analysis.A brittleness classification system under different confining pressures and lithologies was established.The research results contribute to the enhancement and refinement of the rock brittleness evaluation system.展开更多
This paper presents a nonlinear model for piezoelastic laminated plates with damage effect of the intra-layers and inter-laminar interfaces. Discontinuity of displacement and electric potential on the interfaces are d...This paper presents a nonlinear model for piezoelastic laminated plates with damage effect of the intra-layers and inter-laminar interfaces. Discontinuity of displacement and electric potential on the interfaces are depicted by three shape functions. By using the Hamilton variation principle, the three-dimensional nonlinear dynamic equations of piezoelastic laminated plates with damage effect are derived. Then, by using the Galerkin method, a mathematical solution is presented. In the numerical studies, effects of various factors on the natural frequencies and nonlinear amplitude-frequency response of the simply-supported peizoelastic laminated plates with interfacial imperfections are discussed. These factors include different damage models, thickness of the piezoelectric layer, side-to-thickness ratio, and length-to-width ratio.展开更多
In the present paper,a hierarchical multi-scale method is developed for the nonlinear analysis of composite materials undergoing heterogeneity and damage.Starting from the homogenization theory,the energy equivalence ...In the present paper,a hierarchical multi-scale method is developed for the nonlinear analysis of composite materials undergoing heterogeneity and damage.Starting from the homogenization theory,the energy equivalence between scales is developed.Then accompanied with the energy based damage model,the multi-scale damage evolutions are resolved by homogenizing the energy scalar over the meso-cell.The macroscopic behaviors described by the multi-scale damage evolutions represent the mesoscopic heterogeneity and damage of the composites.A rather simple structure made from particle reinforced composite materials is developed as a numerical example.The agreement between the fullscale simulating results and the multi-scale simulating results demonstrates the capacity of the proposed model to simulate nonlinear behaviors of quasi-brittle composite materials within the multi-scale framework.展开更多
Arching and cracking of joints between slabs have become a problem in China Railway Track System(CRTS)II slab track.The slab track is susceptible to complex temperature variations as a longitudinal continuous structur...Arching and cracking of joints between slabs have become a problem in China Railway Track System(CRTS)II slab track.The slab track is susceptible to complex temperature variations as a longitudinal continuous structure.Based on measured data,a thermal-mechanical coupling model of the track was established.The deformation characteristics and interfacial damage behavior of joints under typical temperature fields were studied.The findings indicate that the annual extreme temperature range of the slab track,fluctuates from−1.4 to 49.8℃.The annual temperature gradient within the vertical depth range of 0 to 0.2 m of the track varies between−16.19℃/m and 30.15℃/m.The vertical deformation of joints is significantly influenced by high temperatures,with a maximum measured deformation of 0.828 mm.The joint seams are primarily affected by low temperatures,which lead to a separation of 0.9 to 1.0 mm.Conversely,interlayer damage of joints is predominantly influenced by elevated temperatures.In summer,the maximum ratio of interface damage area in the joint can reach up to 95%,with the maximum debonding area ratio can be as high as 84%.The research results can provide help for joint damage regularity and deformation control of CRTS II slab track.展开更多
Recently developed multi-scale fiber(i.e.,CaCO3 whisker,polyvinyl alcohol(PVA)fiber,and steel fiber)reinforced rubberized concrete exhibits excellent mechanical properties and spalling resistance at high temperatures....Recently developed multi-scale fiber(i.e.,CaCO3 whisker,polyvinyl alcohol(PVA)fiber,and steel fiber)reinforced rubberized concrete exhibits excellent mechanical properties and spalling resistance at high temperatures.Measurement of macro properties such as strength and Young’s modulus cannot reveal and characterize damage mechanisms,particularly those relating to the multi-scale fiber strengthening effect.In this study,acoustic emission(AE)technology is applied to investigate the impact of multi-scale fiber on the damage evolution of rubberized concrete exposed to high temperatures,under the uniaxial compression and tension loading processes.The mechanical properties,AE event location,peak frequency,b-value,the ratio of rise time to amplitude(RA),average frequency(AF)values,and AE energy of specimens are investigated.The results show that the number of events observed using AE gradually increases as the loading progresses.The crumb rubber and fibers inhibit the generation and development of the cracks.It is concluded that both the peak frequency and b-value reflect the extension process of cracks.As the cracks develop from the micro scale to the macro scale,the peak frequency tends to be distributed in a lower frequency range,and the b-value decreases gradually.At the peak stress point,the AE energy increases rapidly and the b-value decreases.The specimens without multi-scale fibers exhibit brittle failure,while the specimens with fibers exhibit ductile failure.In addition,adding multi-scale fibers and crumb rubber increases the peak frequency in the medium and high frequency ranges,indicating a positive effect on inhibiting crack development.After being subjected to high temperatures,the maximum and minimum b-values decrease,reflecting an increase in the number of initial cracks due to thermal damage.Meanwhile,the RA and AF values are used to classify tensile and shear cracks.The specimens fracture with more shear cracks under compression,and there are more tensile cracks in specimens with multi-scale fibers under tension.展开更多
Epoxy asphalt is widely used in steel bridge deck pavements,airport pavements,and high-grade roadways due to its superior performance,yet its fatigue damage evolution mechanisms remain insufficiently studied.This stud...Epoxy asphalt is widely used in steel bridge deck pavements,airport pavements,and high-grade roadways due to its superior performance,yet its fatigue damage evolution mechanisms remain insufficiently studied.This study investigated the fatigue performance of epoxy asphalt binder(EAB)and epoxy asphalt mixture(EAM)through linear amplitude sweep tests and four-point bending beam fatigue experiments.By analyzing fatigue parameters across varying epoxy contents and strain levels,predictive correlation models were developed between EAB and EAM fatigue performance.Furthermore,the finite element method(FEM)was employed to compare the fatigue behavior of conventional asphalt and epoxy asphalt pavements.Results demonstrate that the EAM enters a stable fatigue damage accumulation phase when the stiffness modulus decays to 75%of its initial value.Both EAB and EAM exhibit extended fatigue life with increased epoxy content or reduced strain levels,accompanied by enhanced cumulative dissipated energy(CDE)and reduced energy dissipation rates in EAM.Notably,CDE and plateau values exhibit robust logarithmic-linear correlations with EAM fatigue life(R^(2)=0.99 and R^(2)=0.97,respectively),independent of variations in strain or epoxy content.Sensitivity analysis reveals CDE as the most epoxy-content-sensitive parameter,suggesting its potential as a key control factor in fatigue design.The proposed EAB-EAM correlation model further enables accurate prediction of mixture fatigue life based on binder properties.FEM simulations demonstrate that EAM pavement structures have significantly lower tensile strain and better fatigue resistance compared to conventional asphalt mixtures,translating to reduced maintenance frequency and lower lifecycle carbon emissions.The findings of this research enhance the understanding of epoxy asphalt fatigue mechanisms while offering practical guidance for optimizing pavement design.展开更多
基金supported by grants from the Human Resources Development program(Grant No.20204010600250)the Training Program of CCUS for the Green Growth(Grant No.20214000000500)by the Korea Institute of Energy Technology Evaluation and Planning(KETEP)funded by the Ministry of Trade,Industry,and Energy of the Korean Government(MOTIE).
文摘Three-dimensional printing(3DP)offers valuable insight into the characterization of natural rocks and the verification of theoretical models due to its high reproducibility and accurate replication of complex defects such as cracks and pores.In this study,3DP gypsum samples with different printing directions were subjected to a series of uniaxial compression tests with in situ micro-computed tomography(micro-CT)scanning to quantitatively investigate their mechanical anisotropic properties and damage evolution characteristics.Based on the two-dimensional(2D)CT images obtained at different scanning steps,a novel void ratio variable was derived using the mean value and variance of CT intensity.Additionally,a constitutive model was formulated incorporating the proposed damage variable,utilizing the void ratio variable.The crack evolution and crack morphology of 3DP gypsum samples were obtained and analyzed using the 3D models reconstructed from the CT images.The results indicate that 3DP gypsum samples exhibit mechanical anisotropic characteristics similar to those found in naturally sedimentary rocks.The mechanical anisotropy is attributed to the bedding planes formed between adjacent layers and pillar-like structures along the printing direction formed by CaSO_(4)·2H_(2)O crystals of needle-like morphology.The mean gray intensity of the voids has a positive linear relationship with the threshold value,while the CT variance and void ratio have concave and convex relationships,respectively.The constitutive model can effectively match the stress–strain curves obtained from uniaxial compression experiments.This study provides comprehensive explanations of the failure modes and anisotropic mechanisms of 3DP gypsum samples,which is important for characterizing and understanding the failure mechanism and microstructural evolution of 3DP rocks when modeling natural rock behavior.
基金support from the National Natural Science Foundation of China(Grant Nos.12072102 and 12102129).
文摘As a critical mechanical characteristic of rock,brittleness significantly influences fracture modes and damage evolution processes.Accurate quantitative evaluation of brittleness is essential for ensuring the stability of various engineering applications.Based on the pre-peak and post-peak stages of the rock stress-strain curve,this study constructed a brittleness index BI^(*).The index quantifies the ability of rock to resist plastic deformation during the pre-peak crack growth stage and evaluates the intensity of strength drop during the post-peak softening stage.Another index,BII,was established based on the degree of pre-peak elastic energy accumulation and the instability characteristics of post-peak dissipated energy.This index reflects the essential properties of rock failure by revealing the energy evolution mechanism.Furthermore,by defining a damage variable from the energy dissipation over the entire deformation process,an index B_(D)was introduced to evaluate brittleness from the perspective of internal damage development.Triaxial compression and cyclic loading tests were conducted on rocks of different lithologies to evaluate the new index.The influences of confining pressure and lithology on rock brittleness were analyzed,along with the sensitivity analysis of various brittleness index parameters.The results indicated that the proposed brittleness indices accurately distinguish the brittleness differences among various lithologies and show effective consistency with the failure modes of specimens under different confining pressures.Meanwhile,different brittleness indices were affected by confining pressure and lithology to different degrees.The post-peak softening stage of rock played a particularly significant role in brittleness analysis.A brittleness classification system under different confining pressures and lithologies was established.The research results contribute to the enhancement and refinement of the rock brittleness evaluation system.
基金supported by the National Natural Science Foundation of China (No. 10572049)
文摘This paper presents a nonlinear model for piezoelastic laminated plates with damage effect of the intra-layers and inter-laminar interfaces. Discontinuity of displacement and electric potential on the interfaces are depicted by three shape functions. By using the Hamilton variation principle, the three-dimensional nonlinear dynamic equations of piezoelastic laminated plates with damage effect are derived. Then, by using the Galerkin method, a mathematical solution is presented. In the numerical studies, effects of various factors on the natural frequencies and nonlinear amplitude-frequency response of the simply-supported peizoelastic laminated plates with interfacial imperfections are discussed. These factors include different damage models, thickness of the piezoelectric layer, side-to-thickness ratio, and length-to-width ratio.
基金the Natural Science Foundation of Jiangsu Province(Grant No.BK20170680)the National Natural Science Foundation of China(Grant No.51708106)are gratefully appreciated.
文摘In the present paper,a hierarchical multi-scale method is developed for the nonlinear analysis of composite materials undergoing heterogeneity and damage.Starting from the homogenization theory,the energy equivalence between scales is developed.Then accompanied with the energy based damage model,the multi-scale damage evolutions are resolved by homogenizing the energy scalar over the meso-cell.The macroscopic behaviors described by the multi-scale damage evolutions represent the mesoscopic heterogeneity and damage of the composites.A rather simple structure made from particle reinforced composite materials is developed as a numerical example.The agreement between the fullscale simulating results and the multi-scale simulating results demonstrates the capacity of the proposed model to simulate nonlinear behaviors of quasi-brittle composite materials within the multi-scale framework.
基金Projects(U23A20666,52178405)supported by the National Natural Science Foundation of ChinaProject(K2022G038)supported by the Science and Technology Research and Development Program of China State Railway Group Co.,Ltd.Project(2021B03)supported by the Science and Technology Plan of Shandong Provincial Department of Transportation,China。
文摘Arching and cracking of joints between slabs have become a problem in China Railway Track System(CRTS)II slab track.The slab track is susceptible to complex temperature variations as a longitudinal continuous structure.Based on measured data,a thermal-mechanical coupling model of the track was established.The deformation characteristics and interfacial damage behavior of joints under typical temperature fields were studied.The findings indicate that the annual extreme temperature range of the slab track,fluctuates from−1.4 to 49.8℃.The annual temperature gradient within the vertical depth range of 0 to 0.2 m of the track varies between−16.19℃/m and 30.15℃/m.The vertical deformation of joints is significantly influenced by high temperatures,with a maximum measured deformation of 0.828 mm.The joint seams are primarily affected by low temperatures,which lead to a separation of 0.9 to 1.0 mm.Conversely,interlayer damage of joints is predominantly influenced by elevated temperatures.In summer,the maximum ratio of interface damage area in the joint can reach up to 95%,with the maximum debonding area ratio can be as high as 84%.The research results can provide help for joint damage regularity and deformation control of CRTS II slab track.
基金supported by the National Natural Science Foundation of China(Grant No.52108379)the Natural Science Foundation of Hebei Province(No.E2021210002)+3 种基金the Youth Top Talent Program,Education Department of Hebei Province(No.BJK2022047)Innovation Research Group Program of Natural Science,the Hebei Province(No.E2021210099)the Technology Development Project of Shuohuang Railway Development Co.,Ltd.(No.GJNY-20-230)the Innovation Research for the Postgraduates of Shijiazhuang Tiedao University(No.YC2023009).
文摘Recently developed multi-scale fiber(i.e.,CaCO3 whisker,polyvinyl alcohol(PVA)fiber,and steel fiber)reinforced rubberized concrete exhibits excellent mechanical properties and spalling resistance at high temperatures.Measurement of macro properties such as strength and Young’s modulus cannot reveal and characterize damage mechanisms,particularly those relating to the multi-scale fiber strengthening effect.In this study,acoustic emission(AE)technology is applied to investigate the impact of multi-scale fiber on the damage evolution of rubberized concrete exposed to high temperatures,under the uniaxial compression and tension loading processes.The mechanical properties,AE event location,peak frequency,b-value,the ratio of rise time to amplitude(RA),average frequency(AF)values,and AE energy of specimens are investigated.The results show that the number of events observed using AE gradually increases as the loading progresses.The crumb rubber and fibers inhibit the generation and development of the cracks.It is concluded that both the peak frequency and b-value reflect the extension process of cracks.As the cracks develop from the micro scale to the macro scale,the peak frequency tends to be distributed in a lower frequency range,and the b-value decreases gradually.At the peak stress point,the AE energy increases rapidly and the b-value decreases.The specimens without multi-scale fibers exhibit brittle failure,while the specimens with fibers exhibit ductile failure.In addition,adding multi-scale fibers and crumb rubber increases the peak frequency in the medium and high frequency ranges,indicating a positive effect on inhibiting crack development.After being subjected to high temperatures,the maximum and minimum b-values decrease,reflecting an increase in the number of initial cracks due to thermal damage.Meanwhile,the RA and AF values are used to classify tensile and shear cracks.The specimens fracture with more shear cracks under compression,and there are more tensile cracks in specimens with multi-scale fibers under tension.
基金supported by the Southeast University(SEU)Innovation Capability Enhancement Plan for Doctoral Students(Grant No.CXJH_SEU 24)the Major Science and Technology Project of Nanjing(Grant No.202209012)the Carbon Peak and Carbon Neutrality Science and Technology Innovation Special Funds of Jiangsu Province(Grant No.BE2022615).
文摘Epoxy asphalt is widely used in steel bridge deck pavements,airport pavements,and high-grade roadways due to its superior performance,yet its fatigue damage evolution mechanisms remain insufficiently studied.This study investigated the fatigue performance of epoxy asphalt binder(EAB)and epoxy asphalt mixture(EAM)through linear amplitude sweep tests and four-point bending beam fatigue experiments.By analyzing fatigue parameters across varying epoxy contents and strain levels,predictive correlation models were developed between EAB and EAM fatigue performance.Furthermore,the finite element method(FEM)was employed to compare the fatigue behavior of conventional asphalt and epoxy asphalt pavements.Results demonstrate that the EAM enters a stable fatigue damage accumulation phase when the stiffness modulus decays to 75%of its initial value.Both EAB and EAM exhibit extended fatigue life with increased epoxy content or reduced strain levels,accompanied by enhanced cumulative dissipated energy(CDE)and reduced energy dissipation rates in EAM.Notably,CDE and plateau values exhibit robust logarithmic-linear correlations with EAM fatigue life(R^(2)=0.99 and R^(2)=0.97,respectively),independent of variations in strain or epoxy content.Sensitivity analysis reveals CDE as the most epoxy-content-sensitive parameter,suggesting its potential as a key control factor in fatigue design.The proposed EAB-EAM correlation model further enables accurate prediction of mixture fatigue life based on binder properties.FEM simulations demonstrate that EAM pavement structures have significantly lower tensile strain and better fatigue resistance compared to conventional asphalt mixtures,translating to reduced maintenance frequency and lower lifecycle carbon emissions.The findings of this research enhance the understanding of epoxy asphalt fatigue mechanisms while offering practical guidance for optimizing pavement design.
