With the aid of non-contact measurements of vibrating surfaces through laser scanning,operating deflection shapes(ODSs)with high spatial resolutions can be used to graphically characterize damage in plane structures.A...With the aid of non-contact measurements of vibrating surfaces through laser scanning,operating deflection shapes(ODSs)with high spatial resolutions can be used to graphically characterize damage in plane structures.Although numerous damage identification approaches relying on laser-measured ODSs have been developed for plate-type structures,they cannot be directly applied to circular cylinders due to the gap between equations of motions of plates and circular cylinders.To fill this gap,a novel approach is proposed in this study for damage identification of circular cylinders.Damage-induced discontinuities of the derivatives of ODSs can be used to gra-phically manifest the occurrence of the damage,and characterize the location and size of the damage.The approach is experimentally validated on a specimen of the circular cylinder component,whose out-of-plane ODSs in an inspection region are acquired through laser scanning using a scanning laser vibrometer.The results suggest that the occurrence,location,and size of the internal damage of the circular cylinder can be identified.展开更多
During the threshing process of rice,the grains fall off the head of the rice ear due to the impact of the threshing bar.At the same time,the impact force of the threshing element causes a certain degree of damage to ...During the threshing process of rice,the grains fall off the head of the rice ear due to the impact of the threshing bar.At the same time,the impact force of the threshing element causes a certain degree of damage to the grain.However,there are relatively few methods to analyze the internal damage of rice grains during the threshing process.In this study,the connection force between rice grains and stalks and the compressive bearing capacity of the grains were tested on a push-pull test machine,and then the critical impact force and velocity of rice grains during plastic deformation and brittle fracture were obtained by Hertz theory.On this basis,the quantitative evaluation model of grain internal damage was established through the extraction and calculation of the damaged area inside the grain,and the damage degrees inside the grain under different loading times and loading forces were analyzed.The results showed that the average threshing force required for rice grains is 1.57 N(variance is 0.0529),and the critical impact forces for plastic deformation and brittle fracture of the grains during threshing are 138.79 N and 145.77 N.Since the threshing force during the threshing process was 43.9-71.9 N,it could be known from the internal damage model that the grain is in the safe loading area.Under the same load,the vertical pressure causes the most damage,the lateral pressure takes second place,and the positive pressure was the least.The results of this study can provide a basis for the development of combine harvester and rice grains damage evaluation.展开更多
Carbon fiber reinforced silicon carbide matrix composites(C/SiC)have emerged as key materials for ther-mal protection systems owing to their high strength-to-weight ratio,high-temperature durability,resis-tance to oxi...Carbon fiber reinforced silicon carbide matrix composites(C/SiC)have emerged as key materials for ther-mal protection systems owing to their high strength-to-weight ratio,high-temperature durability,resis-tance to oxidation,and outstanding reliability.However,manufacturing defects deteriorate the mechani-cal response of these composites under extreme thermal-force coupling conditions,prompting significant research attention.This study demonstrates a customized in situ loading device compatible with syn-chrotron radiation facilities,enabling high spatial and temporal resolution recording of internal material damage evolution and failure behavior under thermal-force coupling conditions.Infrared thermal radia-tion units in a confocal configuration were used to create ultra-high-temperature environments,offering advantages of compactness,rapid heating,and versatility.In situ tensile tests were conducted on C/SiC samples in a nitrogen atmosphere at both room temperature and 1200℃.The high-resolution image data demonstrate various failure phenomena,such as matrix cracking and pore linkage.Image-based fi-nite element simulations indicate that the temperature-dependent variation of the failure mechanism is attributable to thermal residual stresses and defect-induced stress concentrations.This work seamlessly integrates extreme mechanical testing methods with in situ observation techniques,providing a compre-hensive solution for accurately quantifying crack initiation,pore connection,and failure behavior of C/SiC composites.展开更多
Post-disaster very high resolution（VHR） satellite data are potential sources to provide detailed information on damage and geological changes for a large area in a short time.In this paper,we studied landslides trig...Post-disaster very high resolution（VHR） satellite data are potential sources to provide detailed information on damage and geological changes for a large area in a short time.In this paper,we studied landslides triggered by the M_w 6.9 earthquake in Sikkim,India which occurred on 18 September 2011 using VHR data from Cartosat-1,GeoEye-1,QuickBird-2 and WorldView-2 satellites.Since the earthquake-affected area is located in mostly inaccessible Himalayan terrain,VHR data from these satellites provided a unique opportunity for quick and synoptic assessment of the damage.Using visual change analysis technique through comparison of pre- and post-earthquake images,we assessed the damage caused by the event.A total of 123 images acquired from eight satellites,covering an area of4105 km2 were analysed and 1196 new landslides triggered by the earthquake were mapped.Road blockages and severely affected villages were also identified.Geological assessment of the terrain highlighted linear disposition of landslides along existing fault scarps,suggesting a reactivation of fault.The landslide inventory map prepared from VHR images also showed a good correlation with the earthquake shake map.Results showed that several parts of north Sikkim,particularly Mangan and Chungthang,which are close to the epicentre,were severely affected by the earthquake,and that the event-based landslide inventory map can be used in future earthquake-triggered landslide susceptibility assessment studies.展开更多
Many researches on drilling force and temperature have been done with the aim to reduce the labour intensiveness of surgery, avoid unnecessary damage and improve drilling quality. However, there has not been a systema...Many researches on drilling force and temperature have been done with the aim to reduce the labour intensiveness of surgery, avoid unnecessary damage and improve drilling quality. However, there has not been a systematic study of mid- and high-speed drilling under dry and physiological conditions（injection of saline）. Furthermore, there is no consensus on optimal drilling parameters. To study these parameters under dry and physiological drilling conditions, pig humerus bones are drilled with medical twist drills operated using a wide range of drilling speeds and feed rates. Drilling force and temperature are measured using a YDZ-II01W dynamometer and a NEC TVS-500EX thermal infrared imager, respectively, to evaluate internal bone damage. To evaluate drilling quality, bone debris and hole morphology are observed by SEM（scanning electron microscopy）. Changes in drilling force and temperature give similar results during drilling such that the value of each parameter peaks just before the drill penetrates through the osteon of the compact bone into the trabeculae of the spongy bone. Drilling temperatures under physiological conditions are much lower than those observed under dry conditions, while a larger drilling force occurs under physiological conditions than dry conditions. Drilling speed and feed rate have a significant influence on drilling force, temperature, bone debris and hole morphology. The investigation of the effect of drilling force and temperature on internal bone damage reveals that a drilling speed of 4500 r/min and a feed rate of 50 mm/min are recommended for bone drilling under physiological conditions. Drilling quality peaks under these optimal parameter conditions. This paper proposes the optimal drilling parameters under mid- and high-speed surgical drilling, considering internal bone damage and drilling quality, which can be looked as a reference for surgeons performing orthopedic operations.展开更多
This paper presents an investigation of brittle rock failure by the quaternion-based bonded-particle model in discrete element method(DEM).Unlike traditional approaches that utilize Euler angles or rotation matrices,t...This paper presents an investigation of brittle rock failure by the quaternion-based bonded-particle model in discrete element method(DEM).Unlike traditional approaches that utilize Euler angles or rotation matrices,this model employs unit quaternions to represent the spatial rotations of particles.This method simplifies the rep-resentation of 3D rotations,providing a more intuitive framework for modelling complex interactions in granular materials.The numerical model was validated by the uniaxial compression tests on rock,with good agreement with well-documented experimental data in terms of the rock uniaxial compression strength(UCS)and failure mode.During loading,the rock sample demonstrated a linear-elastic response at an axial strain of smaller than 0.45%.However,as internal bond breakage accumulated,this linear relationship weakened,and the stress-strain curve began to deviate from its initial linear trajectory.The bond breakage and the overall deformation of the rock were primarily controlled by the shear bonding force.The UCS was achieved at an axial strain of 0.625%,at which point the internal shear bonding force chains were predominantly aligned vertically.The brittle failure occurred when the internal damage of solids nucleated to form an interconnected failure plane,accompanied by a sharp rise in the internal damage ratio.The area of failure plane increased with the loading strain rate,gradually transforming the failure pattern from the local damage to a complete fragmentation.展开更多
基金The authors are grateful for the supports from the Changzhou Policy Guidance Plan-International Science and Technology Cooperation(No.CZ20200003)the Anhui International Joint Research Center of Data Diagnosis and Smart Maintenance on Bridge Structures(No.2021AHGHYB01)+1 种基金the Nantong Science and Technology Opening Cooperation Project in 2021(No.BW2021001)the Key R&D Project of Anhui Science and Technology Department(202004b11020026).
文摘With the aid of non-contact measurements of vibrating surfaces through laser scanning,operating deflection shapes(ODSs)with high spatial resolutions can be used to graphically characterize damage in plane structures.Although numerous damage identification approaches relying on laser-measured ODSs have been developed for plate-type structures,they cannot be directly applied to circular cylinders due to the gap between equations of motions of plates and circular cylinders.To fill this gap,a novel approach is proposed in this study for damage identification of circular cylinders.Damage-induced discontinuities of the derivatives of ODSs can be used to gra-phically manifest the occurrence of the damage,and characterize the location and size of the damage.The approach is experimentally validated on a specimen of the circular cylinder component,whose out-of-plane ODSs in an inspection region are acquired through laser scanning using a scanning laser vibrometer.The results suggest that the occurrence,location,and size of the internal damage of the circular cylinder can be identified.
基金This work was supported by the National Natural Science Foundation of China(Grant No.51705212)Jiangsu Province“Six Talents Peak”High-level Talent Project(GDZB-085)+2 种基金Natural Science Foundation of Jiangsu Province(BK20170553)Open Fund of Jiangsu Key Laboratory of Agricultural Equipment and Intelligent High Technology(JNZ201912)and Jiangsu Province Postgraduate Research and Innovation Project(KYCX20_3086).
文摘During the threshing process of rice,the grains fall off the head of the rice ear due to the impact of the threshing bar.At the same time,the impact force of the threshing element causes a certain degree of damage to the grain.However,there are relatively few methods to analyze the internal damage of rice grains during the threshing process.In this study,the connection force between rice grains and stalks and the compressive bearing capacity of the grains were tested on a push-pull test machine,and then the critical impact force and velocity of rice grains during plastic deformation and brittle fracture were obtained by Hertz theory.On this basis,the quantitative evaluation model of grain internal damage was established through the extraction and calculation of the damaged area inside the grain,and the damage degrees inside the grain under different loading times and loading forces were analyzed.The results showed that the average threshing force required for rice grains is 1.57 N(variance is 0.0529),and the critical impact forces for plastic deformation and brittle fracture of the grains during threshing are 138.79 N and 145.77 N.Since the threshing force during the threshing process was 43.9-71.9 N,it could be known from the internal damage model that the grain is in the safe loading area.Under the same load,the vertical pressure causes the most damage,the lateral pressure takes second place,and the positive pressure was the least.The results of this study can provide a basis for the development of combine harvester and rice grains damage evaluation.
基金supported by the National Natural Science Foundation of China(No.52325407)Science and Technology Innovation Plan of Shanghai Science and Technology Commission(No.21511104800).
文摘Carbon fiber reinforced silicon carbide matrix composites(C/SiC)have emerged as key materials for ther-mal protection systems owing to their high strength-to-weight ratio,high-temperature durability,resis-tance to oxidation,and outstanding reliability.However,manufacturing defects deteriorate the mechani-cal response of these composites under extreme thermal-force coupling conditions,prompting significant research attention.This study demonstrates a customized in situ loading device compatible with syn-chrotron radiation facilities,enabling high spatial and temporal resolution recording of internal material damage evolution and failure behavior under thermal-force coupling conditions.Infrared thermal radia-tion units in a confocal configuration were used to create ultra-high-temperature environments,offering advantages of compactness,rapid heating,and versatility.In situ tensile tests were conducted on C/SiC samples in a nitrogen atmosphere at both room temperature and 1200℃.The high-resolution image data demonstrate various failure phenomena,such as matrix cracking and pore linkage.Image-based fi-nite element simulations indicate that the temperature-dependent variation of the failure mechanism is attributable to thermal residual stresses and defect-induced stress concentrations.This work seamlessly integrates extreme mechanical testing methods with in situ observation techniques,providing a compre-hensive solution for accurately quantifying crack initiation,pore connection,and failure behavior of C/SiC composites.
基金support work carried out under the Decision Support Centre(DSC) activities of NRSC
文摘Post-disaster very high resolution（VHR） satellite data are potential sources to provide detailed information on damage and geological changes for a large area in a short time.In this paper,we studied landslides triggered by the M_w 6.9 earthquake in Sikkim,India which occurred on 18 September 2011 using VHR data from Cartosat-1,GeoEye-1,QuickBird-2 and WorldView-2 satellites.Since the earthquake-affected area is located in mostly inaccessible Himalayan terrain,VHR data from these satellites provided a unique opportunity for quick and synoptic assessment of the damage.Using visual change analysis technique through comparison of pre- and post-earthquake images,we assessed the damage caused by the event.A total of 123 images acquired from eight satellites,covering an area of4105 km2 were analysed and 1196 new landslides triggered by the earthquake were mapped.Road blockages and severely affected villages were also identified.Geological assessment of the terrain highlighted linear disposition of landslides along existing fault scarps,suggesting a reactivation of fault.The landslide inventory map prepared from VHR images also showed a good correlation with the earthquake shake map.Results showed that several parts of north Sikkim,particularly Mangan and Chungthang,which are close to the epicentre,were severely affected by the earthquake,and that the event-based landslide inventory map can be used in future earthquake-triggered landslide susceptibility assessment studies.
基金Supported by Foundation for High-level Talents in Higher Education of Guangdong,China (Grant No.501111018)Panyu District Science and Technology Program of China (Grant No.2009-Z-53-1)
文摘Many researches on drilling force and temperature have been done with the aim to reduce the labour intensiveness of surgery, avoid unnecessary damage and improve drilling quality. However, there has not been a systematic study of mid- and high-speed drilling under dry and physiological conditions（injection of saline）. Furthermore, there is no consensus on optimal drilling parameters. To study these parameters under dry and physiological drilling conditions, pig humerus bones are drilled with medical twist drills operated using a wide range of drilling speeds and feed rates. Drilling force and temperature are measured using a YDZ-II01W dynamometer and a NEC TVS-500EX thermal infrared imager, respectively, to evaluate internal bone damage. To evaluate drilling quality, bone debris and hole morphology are observed by SEM（scanning electron microscopy）. Changes in drilling force and temperature give similar results during drilling such that the value of each parameter peaks just before the drill penetrates through the osteon of the compact bone into the trabeculae of the spongy bone. Drilling temperatures under physiological conditions are much lower than those observed under dry conditions, while a larger drilling force occurs under physiological conditions than dry conditions. Drilling speed and feed rate have a significant influence on drilling force, temperature, bone debris and hole morphology. The investigation of the effect of drilling force and temperature on internal bone damage reveals that a drilling speed of 4500 r/min and a feed rate of 50 mm/min are recommended for bone drilling under physiological conditions. Drilling quality peaks under these optimal parameter conditions. This paper proposes the optimal drilling parameters under mid- and high-speed surgical drilling, considering internal bone damage and drilling quality, which can be looked as a reference for surgeons performing orthopedic operations.
基金supported by the UK Engineering and Physical Sciences Research Council(EPSRC)New Investigator Award(Grant No.EP/V028723/1)the Royal Society,Sino-British Fellowship Trust International Exchanges Award(No.IES\R2\202023)。
文摘This paper presents an investigation of brittle rock failure by the quaternion-based bonded-particle model in discrete element method(DEM).Unlike traditional approaches that utilize Euler angles or rotation matrices,this model employs unit quaternions to represent the spatial rotations of particles.This method simplifies the rep-resentation of 3D rotations,providing a more intuitive framework for modelling complex interactions in granular materials.The numerical model was validated by the uniaxial compression tests on rock,with good agreement with well-documented experimental data in terms of the rock uniaxial compression strength(UCS)and failure mode.During loading,the rock sample demonstrated a linear-elastic response at an axial strain of smaller than 0.45%.However,as internal bond breakage accumulated,this linear relationship weakened,and the stress-strain curve began to deviate from its initial linear trajectory.The bond breakage and the overall deformation of the rock were primarily controlled by the shear bonding force.The UCS was achieved at an axial strain of 0.625%,at which point the internal shear bonding force chains were predominantly aligned vertically.The brittle failure occurred when the internal damage of solids nucleated to form an interconnected failure plane,accompanied by a sharp rise in the internal damage ratio.The area of failure plane increased with the loading strain rate,gradually transforming the failure pattern from the local damage to a complete fragmentation.
