In rock engineering,natural cracks in rock masses subjected to external loads tend to initiate and propagate,leading to potential safety hazards.To investigate the effect of cracking behavior on the mechanical propert...In rock engineering,natural cracks in rock masses subjected to external loads tend to initiate and propagate,leading to potential safety hazards.To investigate the effect of cracking behavior on the mechanical properties of rocks,the cracking processes of pre-cracked rocks have been extensively studied using numerical modeling methods.The peridynamics(PD)exhibits advantages over other numerical methods due to the absence of the requirements for remeshing and external crack growth criterion.However,for modeling pre-cracked rock cracking processes under impact,current PD implementations lack generally applicable rock constitutive models and impact contact models,which leads to difficulties in determining rock material parameters and efficiently calculating impact loads.This paper proposes a non-ordinary state-based peridynamics(NOSBPD)modeling method integrating the Drucker-Prager(DP)plasticity model and an efficient contact model to address the above problems.In the proposed method,the Drucker-Prager plasticity model is integrated into the NOSBPD,thereby equipping NOSBPD with the capability to accurately characterize the nonlinear stress-strain relationship inherent in rocks.An efficient contact model between particles and meshes is designed to calculate the impact loads,which is essentially a coupling method of PD with the finite element method(FEM).The effectiveness of the proposed NOSBPD modeling method is verified by comparison with other numerical methods and experiments.Experimental results indicate that the proposed method can effectively and accurately predict the 3D cracking processes of pre-cracked cracks under impact loading,and the maximum principal stress is the key driver behind wing crack formation in pre-cracked rocks.展开更多
A simultaneous experimental and numerical study on crack propagation in the pre-cracked beams specimens(concrete-like materials)is carried out using three-point bending flexural test.The crack propagation and coalesce...A simultaneous experimental and numerical study on crack propagation in the pre-cracked beams specimens(concrete-like materials)is carried out using three-point bending flexural test.The crack propagation and coalescence paths of internal cracks in side beam specimens are experimentally studied by inserting double internal cracks.The effects of crack positions on the fracturing path in the bridge areas of the double cracked beam specimens are also studied.It has been observed that the breaking of concrete-like cracked beams specimens occurs mainly by the propagation of wing cracks emanating from the tips of the pre-existing cracks in the numerical and experimental analyses,respectively.The same specimens are numerically simulated by an indirect boundary element method(IBEM)known as displacement discontinuity method(DDM)using higher displacement discontinuity.These numerical results are compared with the existing experimental results.This comparison illustrates the higher accuracy of the results obtained by the indirect boundary element method by using only a small number of elements compared with the discrete element method(PFC2D code).展开更多
It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass.Based on digital speckle correlation(DSCM),acoustic emission(AE)and ...It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass.Based on digital speckle correlation(DSCM),acoustic emission(AE)and electromagnetic radiation(EMR),uniaxial hierarchical cyclic loading and unloading tests were carried out on sandstones with different fracture numbers under dry,natural and saturated water content,to explore the fracture propagation,failure precursor characteristics and damage response mechanism under the influence of water content effect.The results show that with the increase of water content,the peak stress and crack initiation stress decrease gradually,and the decreases are 15.28%-21.11%and 17.64%-23.04%,respectively.The peak strain and crack initiation strain increase gradually,and the increases are 19.85%-44.53%and 19.15%-41.94%,respectively.The precracked rock with different water content is mainly characterized by tensile failure at different loading stages.However,with the increase of water content,the proportion of shear cracks gradually increases,while acoustic emission events gradually decrease,the dissipative energy and energy storage limits of the rock under peak load gradually decrease,and the charge signal increases significantly,which is because the lubrication effect of water reduces the friction coefficient between crack surfaces.展开更多
The mechanical characteristics and failure behavior of rocks containing flaws or discontinuities have received wide attention in the field of rock mechanics.When external loads are applied to rock materials,stress-ind...The mechanical characteristics and failure behavior of rocks containing flaws or discontinuities have received wide attention in the field of rock mechanics.When external loads are applied to rock materials,stress-induced cracks would initiate and propagate from the flaws,ultimately leading to the irreversible failure of rocks.To investigate the cracking behavior and the effect of flaw geometries on the mechanical properties of rock materials,a series of samples containing one,two and multiple flaws have been widely investigated in the laboratory.In this paper,the experimental results for pre-cracked rocks under quasistatic compression were systematically reviewed.The progressive failure process of intact rocks is briefly described to reveal the background for experiments on samples with flaws.Then,the nondestructive measurement techniques utilized in experiments,such as acoustic emission(AE),X-ray computed tomography(CT),and digital image correlation(DIC),are summarized.The mechanical characteristics of rocks with different flaw geometries and under different loading conditions,including the geometry of pre-existing flaws,flaw filling condition and confining pressure,are discussed.Furthermore,the cracking process is evaluated from the perspective of crack initiation,coalescence,and failure patterns.展开更多
To investigate the mechanical properties of concrete under the leakage condition for a liquefied natural gas storage tank,cryogenic freeze-thaw cycle tests were performed under liquid nitrogen refrigeration and water ...To investigate the mechanical properties of concrete under the leakage condition for a liquefied natural gas storage tank,cryogenic freeze-thaw cycle tests were performed under liquid nitrogen refrigeration and water immersion melting.The effects of the cryogenic temperature,freeze-thaw cycle,pre-crack,and addition of steel fiber on the compressive strength,flexural strength,and splitting tensile concrete strength were analyzed.The experimental results show that the width of pre-cracks tends to expand after freeze-thaw cycles.When the freezing temperature is -80℃,the relative width of the pre-cracks expands by 1 to 2 times.However,when the freezing temperature is -120℃,the relative width of the pre-cracks expands by 2 to 5 times.Compared with the specimens without steel fibers,the specimens with steel fibers can still maintain a relatively complete appearance structure after the mechanical property tests.The compressive strength,flexural strength,and splitting tensile concrete strength decrease with the drop in the freezing temperature.After adding steel fibers,all of the three strengths increased.展开更多
BACKGROUND Endoscopic submucosal dissection(ESD)is a standardized therapeutic approach for early carcinoma of the digestive tracts.In this regard,the process of histopathological diagnosis requires standardization.How...BACKGROUND Endoscopic submucosal dissection(ESD)is a standardized therapeutic approach for early carcinoma of the digestive tracts.In this regard,the process of histopathological diagnosis requires standardization.However,the uneven development of healthcare in China,especially in eastern and western China,creates challenges for sharing a standardized diagnostic process.AIM To optimize the process of ESD specimen sampling,embedding and slide production,and to provide complete and accurate pathological reports.METHODS We established a practical process of specimen sampling,created standardized reporting templates,and trained pathologists from neighboring hospitals and those in the western region.A training effectiveness survey was conducted,and the collected data were assessed by the corresponding percentages.RESULTS A total of 111 valid feedback forms have been received,among which 58%of the participants obtained photographs during specimen collection,whereas the percentage increased to 79%after training.Only 58%and 62%of the respondents ensured the mucosal tissue strips were flat and their order remained unchanged;after training,these two proportions increased to 95%and 92%,respectively.Approximately half the participants measured the depth of the submucosal infiltration,which significantly increased to 95%after training.The percentage of pathologists who did not evaluate lymphovascular invasion effectively reduced.Only 22%of the participants had fixed clinic-pathological meetings before training,which increased to 49%after training.The number of participants who had a thorough understanding of endoscopic diagnosis also significantly increased.CONCLUSION There have been significant improvements in the process of specimen collection,section quality,and pathology reporting in trained hospitals.Therefore,our study provides valuable insights for others facing similar challenges.展开更多
Deep hole pre-cracking blasting(DHPB)technology is the preferred means of preventing and controlling rockburst induced by hard-thick rock layers in coal mines.When DHPB is applied to hard-thick rock layers,the insuffi...Deep hole pre-cracking blasting(DHPB)technology is the preferred means of preventing and controlling rockburst induced by hard-thick rock layers in coal mines.When DHPB is applied to hard-thick rock layers,the insufficient knowledge about the crack extension scale under different rock properties and blasting parameters may result in undesirable pressure relief.Therefore,LS-DYNA was adopted to analyse the crack extension characteristics under the combined effect of rock tensile strength,explosive density,blasthole spacing,and decoupled coefficient.The Holmquist–Johnson–Cook model(HJC),verified by the results of blasting experiment and numerical simulation in literature,was used to characterise coal-bearing rocks.Numerical analysis was conducted to study the blasting crack extension and fractal damage for rock tensile strength,explosive densities,blasthole spacing,and decoupled coefficients.The results show that the tensile strength of rock is the key factor for blasting design.The fractal damage caused by blasting increases when the tensile strength of rock decreases.For rocks with lower tensile strength,more blasting energy is consumed by the increasing damage area in the crushed zone.Higher explosive density can promote the development of blasting cracks and increase fractal damage,but the increasing range of the crushed zone also wastes a large amount of energy.As the blasthole spacing increases,the fractal damage decreases,and the crack extension scale in the fractured zone first increases and then decreases,and eventually remains almost unchanged.An optimum interval exists for the decoupled coefficient,and the full utilization of explosive energy within the interval leads to penetrating blast cracks and smaller crushed zones.Based on the simulation results,the optimal blasting parameters for coarse sandstone were validated in the field practice.Monitoring data show that the optimized blasting significantly reduces the risk of rockburst.展开更多
The objective of this study is to evaluate the efficacy of laparoscopic surgery combined with the rectal inversion and specimen extraction(RIES)technique for rectal cancer,focusing on both short-term and long-term out...The objective of this study is to evaluate the efficacy of laparoscopic surgery combined with the rectal inversion and specimen extraction(RIES)technique for rectal cancer,focusing on both short-term and long-term outcomes.A retrospective comparative analysis was performed on 120 patients who underwent laparoscopic radical excision for rectal cancer from June 2017 to June 2021.Patients were categorized into two groups:Group RIES(n=58),which received the novel RIES technique,and Group AIES(n=62),which underwent the conventional abdominal incision for specimen extraction.Short-term outcomes,such as postoperative pelvic sepsis,temporary ileus,anastomotic leakage,and anastomotic stricture,were meticulously recorded.Longterm efficacy was evaluated through the 3-year overall survival(OS),disease-free survival(DFS),and local recurrence rate(LRR).The RIES group demonstrated a 3-year OS,DFS,and LRR of 86.2%,77.6%,and 8.6%,respectively,with a low incidence of short-term complications.Comparatively,the AIES group showed a 3-year OS,DFS,and LRR of 83.9%,74.2%,and 19.4%,respectively,with slightly higher rates of postoperative complications.Statistical analysis using the Student's t-test,the chi-square(χ^(2))test revealed no significant differences in the primary outcomes between the two groups,and suggested the noninferiority of the RIES technique.The study suggests that the RIES technique is a safe,feasible,and potentially functional and oncological superior approach to rectal cancer treatment,without compromising clinical efficacy.Further research is warranted to validate thesefindings in a larger,multicenter,and randomized controlled trial.展开更多
The paper designs a novel material-level specimen and its dedicated fixture suitable for applying Combined high-and low-Cycle Fatigue(CCF)loads.Unlike full-scale or simulation specimens,the CCF specimen eliminates geo...The paper designs a novel material-level specimen and its dedicated fixture suitable for applying Combined high-and low-Cycle Fatigue(CCF)loads.Unlike full-scale or simulation specimens,the CCF specimen eliminates geometrically induced stress gradients in the test region.Experimental data on CCF life and strain responses of ZSGH4169 alloy are acquired under different CCF loads.The Maximum Strain within Each(MSE)CCF cycle is demonstrated to be independent of the Low-Cycle Fatigue(LCF)loads and High-Cycle Fatigue(HCF)stress amplitudes,but exhibits a correlation with the Cycle Ratio of HCF/LCF(Rf).The growth law of MSE changes from linear to logarithmic as Rfdecreases.Strain amplitudes in the dwell stage,observed unaffected by Rf,are quantified as a function of LCF nominal stresses and HCF stress amplitudes.However,under a defined CCF load,strain amplitudes in the dwell stage remain constant.Strain peaks in the dwell stage in a single CCF cycle decrease in a power function with increasing HCF cycles.展开更多
基金support from the National Natural Science Foundation of China(Grant Nos.42277161 and 42230709).
文摘In rock engineering,natural cracks in rock masses subjected to external loads tend to initiate and propagate,leading to potential safety hazards.To investigate the effect of cracking behavior on the mechanical properties of rocks,the cracking processes of pre-cracked rocks have been extensively studied using numerical modeling methods.The peridynamics(PD)exhibits advantages over other numerical methods due to the absence of the requirements for remeshing and external crack growth criterion.However,for modeling pre-cracked rock cracking processes under impact,current PD implementations lack generally applicable rock constitutive models and impact contact models,which leads to difficulties in determining rock material parameters and efficiently calculating impact loads.This paper proposes a non-ordinary state-based peridynamics(NOSBPD)modeling method integrating the Drucker-Prager(DP)plasticity model and an efficient contact model to address the above problems.In the proposed method,the Drucker-Prager plasticity model is integrated into the NOSBPD,thereby equipping NOSBPD with the capability to accurately characterize the nonlinear stress-strain relationship inherent in rocks.An efficient contact model between particles and meshes is designed to calculate the impact loads,which is essentially a coupling method of PD with the finite element method(FEM).The effectiveness of the proposed NOSBPD modeling method is verified by comparison with other numerical methods and experiments.Experimental results indicate that the proposed method can effectively and accurately predict the 3D cracking processes of pre-cracked cracks under impact loading,and the maximum principal stress is the key driver behind wing crack formation in pre-cracked rocks.
文摘A simultaneous experimental and numerical study on crack propagation in the pre-cracked beams specimens(concrete-like materials)is carried out using three-point bending flexural test.The crack propagation and coalescence paths of internal cracks in side beam specimens are experimentally studied by inserting double internal cracks.The effects of crack positions on the fracturing path in the bridge areas of the double cracked beam specimens are also studied.It has been observed that the breaking of concrete-like cracked beams specimens occurs mainly by the propagation of wing cracks emanating from the tips of the pre-existing cracks in the numerical and experimental analyses,respectively.The same specimens are numerically simulated by an indirect boundary element method(IBEM)known as displacement discontinuity method(DDM)using higher displacement discontinuity.These numerical results are compared with the existing experimental results.This comparison illustrates the higher accuracy of the results obtained by the indirect boundary element method by using only a small number of elements compared with the discrete element method(PFC2D code).
基金financially supported by National Natural Science Foundation of China(No.52304136)Young Talent of Lifting Engineering for Science and Technology in Shandong,China(No.SDAST2024QTA060)Key Project of Research and Development in Liaocheng(No.2023YD02)。
文摘It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass.Based on digital speckle correlation(DSCM),acoustic emission(AE)and electromagnetic radiation(EMR),uniaxial hierarchical cyclic loading and unloading tests were carried out on sandstones with different fracture numbers under dry,natural and saturated water content,to explore the fracture propagation,failure precursor characteristics and damage response mechanism under the influence of water content effect.The results show that with the increase of water content,the peak stress and crack initiation stress decrease gradually,and the decreases are 15.28%-21.11%and 17.64%-23.04%,respectively.The peak strain and crack initiation strain increase gradually,and the increases are 19.85%-44.53%and 19.15%-41.94%,respectively.The precracked rock with different water content is mainly characterized by tensile failure at different loading stages.However,with the increase of water content,the proportion of shear cracks gradually increases,while acoustic emission events gradually decrease,the dissipative energy and energy storage limits of the rock under peak load gradually decrease,and the charge signal increases significantly,which is because the lubrication effect of water reduces the friction coefficient between crack surfaces.
基金financial support from the National Key R&D Program of China(Grant No.2020YFA0711802)。
文摘The mechanical characteristics and failure behavior of rocks containing flaws or discontinuities have received wide attention in the field of rock mechanics.When external loads are applied to rock materials,stress-induced cracks would initiate and propagate from the flaws,ultimately leading to the irreversible failure of rocks.To investigate the cracking behavior and the effect of flaw geometries on the mechanical properties of rock materials,a series of samples containing one,two and multiple flaws have been widely investigated in the laboratory.In this paper,the experimental results for pre-cracked rocks under quasistatic compression were systematically reviewed.The progressive failure process of intact rocks is briefly described to reveal the background for experiments on samples with flaws.Then,the nondestructive measurement techniques utilized in experiments,such as acoustic emission(AE),X-ray computed tomography(CT),and digital image correlation(DIC),are summarized.The mechanical characteristics of rocks with different flaw geometries and under different loading conditions,including the geometry of pre-existing flaws,flaw filling condition and confining pressure,are discussed.Furthermore,the cracking process is evaluated from the perspective of crack initiation,coalescence,and failure patterns.
文摘To investigate the mechanical properties of concrete under the leakage condition for a liquefied natural gas storage tank,cryogenic freeze-thaw cycle tests were performed under liquid nitrogen refrigeration and water immersion melting.The effects of the cryogenic temperature,freeze-thaw cycle,pre-crack,and addition of steel fiber on the compressive strength,flexural strength,and splitting tensile concrete strength were analyzed.The experimental results show that the width of pre-cracks tends to expand after freeze-thaw cycles.When the freezing temperature is -80℃,the relative width of the pre-cracks expands by 1 to 2 times.However,when the freezing temperature is -120℃,the relative width of the pre-cracks expands by 2 to 5 times.Compared with the specimens without steel fibers,the specimens with steel fibers can still maintain a relatively complete appearance structure after the mechanical property tests.The compressive strength,flexural strength,and splitting tensile concrete strength decrease with the drop in the freezing temperature.After adding steel fibers,all of the three strengths increased.
基金Supported by the Medical Education Research Project from Nanjing Drum Tower Hospital,No.2021-7the Clinical Trials Fund from Nanjing Drum Tower Hospital,No.2022-YXZX-XH-04National Natural Science Foundation of China,No.82203063.
文摘BACKGROUND Endoscopic submucosal dissection(ESD)is a standardized therapeutic approach for early carcinoma of the digestive tracts.In this regard,the process of histopathological diagnosis requires standardization.However,the uneven development of healthcare in China,especially in eastern and western China,creates challenges for sharing a standardized diagnostic process.AIM To optimize the process of ESD specimen sampling,embedding and slide production,and to provide complete and accurate pathological reports.METHODS We established a practical process of specimen sampling,created standardized reporting templates,and trained pathologists from neighboring hospitals and those in the western region.A training effectiveness survey was conducted,and the collected data were assessed by the corresponding percentages.RESULTS A total of 111 valid feedback forms have been received,among which 58%of the participants obtained photographs during specimen collection,whereas the percentage increased to 79%after training.Only 58%and 62%of the respondents ensured the mucosal tissue strips were flat and their order remained unchanged;after training,these two proportions increased to 95%and 92%,respectively.Approximately half the participants measured the depth of the submucosal infiltration,which significantly increased to 95%after training.The percentage of pathologists who did not evaluate lymphovascular invasion effectively reduced.Only 22%of the participants had fixed clinic-pathological meetings before training,which increased to 49%after training.The number of participants who had a thorough understanding of endoscopic diagnosis also significantly increased.CONCLUSION There have been significant improvements in the process of specimen collection,section quality,and pathology reporting in trained hospitals.Therefore,our study provides valuable insights for others facing similar challenges.
基金funded by the projects:National Natural Science Foundation of China(52274098,U21A20110)National key research and development program(2022YFC3004603)+1 种基金Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX23_2798)Graduate Innovation Program of China University of Mining and Technology(2023WLKXJ036).
文摘Deep hole pre-cracking blasting(DHPB)technology is the preferred means of preventing and controlling rockburst induced by hard-thick rock layers in coal mines.When DHPB is applied to hard-thick rock layers,the insufficient knowledge about the crack extension scale under different rock properties and blasting parameters may result in undesirable pressure relief.Therefore,LS-DYNA was adopted to analyse the crack extension characteristics under the combined effect of rock tensile strength,explosive density,blasthole spacing,and decoupled coefficient.The Holmquist–Johnson–Cook model(HJC),verified by the results of blasting experiment and numerical simulation in literature,was used to characterise coal-bearing rocks.Numerical analysis was conducted to study the blasting crack extension and fractal damage for rock tensile strength,explosive densities,blasthole spacing,and decoupled coefficients.The results show that the tensile strength of rock is the key factor for blasting design.The fractal damage caused by blasting increases when the tensile strength of rock decreases.For rocks with lower tensile strength,more blasting energy is consumed by the increasing damage area in the crushed zone.Higher explosive density can promote the development of blasting cracks and increase fractal damage,but the increasing range of the crushed zone also wastes a large amount of energy.As the blasthole spacing increases,the fractal damage decreases,and the crack extension scale in the fractured zone first increases and then decreases,and eventually remains almost unchanged.An optimum interval exists for the decoupled coefficient,and the full utilization of explosive energy within the interval leads to penetrating blast cracks and smaller crushed zones.Based on the simulation results,the optimal blasting parameters for coarse sandstone were validated in the field practice.Monitoring data show that the optimized blasting significantly reduces the risk of rockburst.
文摘The objective of this study is to evaluate the efficacy of laparoscopic surgery combined with the rectal inversion and specimen extraction(RIES)technique for rectal cancer,focusing on both short-term and long-term outcomes.A retrospective comparative analysis was performed on 120 patients who underwent laparoscopic radical excision for rectal cancer from June 2017 to June 2021.Patients were categorized into two groups:Group RIES(n=58),which received the novel RIES technique,and Group AIES(n=62),which underwent the conventional abdominal incision for specimen extraction.Short-term outcomes,such as postoperative pelvic sepsis,temporary ileus,anastomotic leakage,and anastomotic stricture,were meticulously recorded.Longterm efficacy was evaluated through the 3-year overall survival(OS),disease-free survival(DFS),and local recurrence rate(LRR).The RIES group demonstrated a 3-year OS,DFS,and LRR of 86.2%,77.6%,and 8.6%,respectively,with a low incidence of short-term complications.Comparatively,the AIES group showed a 3-year OS,DFS,and LRR of 83.9%,74.2%,and 19.4%,respectively,with slightly higher rates of postoperative complications.Statistical analysis using the Student's t-test,the chi-square(χ^(2))test revealed no significant differences in the primary outcomes between the two groups,and suggested the noninferiority of the RIES technique.The study suggests that the RIES technique is a safe,feasible,and potentially functional and oncological superior approach to rectal cancer treatment,without compromising clinical efficacy.Further research is warranted to validate thesefindings in a larger,multicenter,and randomized controlled trial.
基金co-supported by the National Natural Science Foundation of China(51805017)National Science and Technology Project(J2017-IV-0012-0049)+1 种基金National Science and Technology Project,China(J2019-IV-0007-0075)the Fundamental Research Funds for the Central Universities,China(JKF-20240036).
文摘The paper designs a novel material-level specimen and its dedicated fixture suitable for applying Combined high-and low-Cycle Fatigue(CCF)loads.Unlike full-scale or simulation specimens,the CCF specimen eliminates geometrically induced stress gradients in the test region.Experimental data on CCF life and strain responses of ZSGH4169 alloy are acquired under different CCF loads.The Maximum Strain within Each(MSE)CCF cycle is demonstrated to be independent of the Low-Cycle Fatigue(LCF)loads and High-Cycle Fatigue(HCF)stress amplitudes,but exhibits a correlation with the Cycle Ratio of HCF/LCF(Rf).The growth law of MSE changes from linear to logarithmic as Rfdecreases.Strain amplitudes in the dwell stage,observed unaffected by Rf,are quantified as a function of LCF nominal stresses and HCF stress amplitudes.However,under a defined CCF load,strain amplitudes in the dwell stage remain constant.Strain peaks in the dwell stage in a single CCF cycle decrease in a power function with increasing HCF cycles.
