Ultrasonic-assisted micro-electro-discharge machining(EDM)has the potential to enhance processing responses such as material removal rate(MRR)and surface finish.To understand the reasons for this enhancement,the physi...Ultrasonic-assisted micro-electro-discharge machining(EDM)has the potential to enhance processing responses such as material removal rate(MRR)and surface finish.To understand the reasons for this enhancement,the physical mechanisms responsible for the individual discharges and the craters that they form need to be explored.This work examines features of craters formed by single discharges at various parameter values in both conventional and ultrasonic-assistedEDM of Ti6Al4V.High-speed imaging of the plasma channel is performed,and data on the individual discharges are captured in real-time.A 2D axisymmetric model using finite element software is established to model crater formation.On the basis of simulation and experimental results,a comparative study is then carried out to examine the effects of ultrasonic vibrational assistance on crater geometry.For every set ofEDM parameters,the crater diameter and depth from a single discharge are found to be higher in ultrasonic-assistedEDM than in conventionalEDM.The improved crater geometry and the reduced bulge formation at the crater edges are attributed to the increased melt pool velocity and temperature predicted by the model.展开更多
The micro-ablation processes and morphological evolution of ablative craters on single-crystal magnesium under subpicosecond laser irradiation are investigated using molecular dynamics(MD) simulations and experiments....The micro-ablation processes and morphological evolution of ablative craters on single-crystal magnesium under subpicosecond laser irradiation are investigated using molecular dynamics(MD) simulations and experiments.The simulation results exhibit that the main failure mode of single-crystal Mg film irradiated by a low fluence and long pulse width laser is the ejection of surface atoms,which has laser-induced high stress.However,under high fluence and short pulse width laser irradiation,the main damage mechanism is nucleation fracture caused by stress wave reflection and superposition at the bottom of the film.In addition,Mg[0001] has higher pressure sensitivity and is more prone to ablation than Mg[0001].The evolution equation of crater depth is established using multi-pulse laser ablation simulation and verified by experiments.The results show that,under multiple pulsed laser irradiation,not only does the crater depth increase linearly with the pulse number,but also the quadratic term and constant term of the fitted crater profile curve increase linearly.展开更多
Chang’E-4(CE-4)successfully landed on the floor of the Von Kármán crater within the South Pole-Aitken basin(SPA).One of its scientific objectives is to determine the subsurface structure and the thickness o...Chang’E-4(CE-4)successfully landed on the floor of the Von Kármán crater within the South Pole-Aitken basin(SPA).One of its scientific objectives is to determine the subsurface structure and the thickness of lunar regolith at the landing site and along the traverse route of the Yutu-2 rover.Using orbital data,we employed small craters(diameters<1 km)on the floor of the Von Kármán crater as probes to investigate the subsurface structure and stratigraphy of the CE-4 landing site.In this study,40 dark-haloed craters that penetrate through the surface Finsen ejecta and excavate underlying mare deposits were identified,and 77 bright ray craters that expose only the underlying fresh materials but do not penetrate through the surface Finsen ejecta were found.The excavation depths of these craters and their distances from the Finsen crater center were calculated,and the thickness distribution of Finsen ejecta on the Von Kármán floor was systematically investigated.The boundary between Finsen ejecta and underlying mare basalt at the CE-4 landing site is constrained to a depth of 18 m.We have proposed the stratigraphy for the CE-4 site and interpreted the origins of different layers and the geological history of the Von Kármán crater.These results provide valuable geological background for interpreting data from the Lunar Penetrating Radar(LPR)and Visible and Near-infrared Imaging Spectrometer(VNIS)on the Yutu-2 rover.The CE-4 landing site could provide a reference point for crater ejecta distribution and mixing with local materials,to test and improve ejecta thickness models according to the in situ measurements of the CE-4 LPR.展开更多
In the present work,a state-based peridynamics with adaptive particle refinement is proposed to simulate water ice crater formation due to impact loads.A modified Drucker-Prager constitutive model was adopted to model...In the present work,a state-based peridynamics with adaptive particle refinement is proposed to simulate water ice crater formation due to impact loads.A modified Drucker-Prager constitutive model was adopted to model ice and was implemented in the state-based peridynamic equations to analyze the elastic-plastic deformation of ice.In simulations,we use the fracture toughness failure criterion in peridynamics to simulate the quasi-brittle failure of ice.An adaptive particle refinement method in peridynamics was proposed to improve computational efficiency.The results obtained using the peridynamic model were compared with the experiments in previous literatures.It was found that the peridynamic simulation results and the experiments matched well except for some minor differences discussed,and the state-based peridynamic model has shown the specific predictive capacity to capture the detailed crater features of the ice.展开更多
The six largest known impact craters of the last 250 Myr(≥70 km in diameter),which are capable of causing significant environmental damage,coincide with four times of recognized extinction events at 36(with 2 craters...The six largest known impact craters of the last 250 Myr(≥70 km in diameter),which are capable of causing significant environmental damage,coincide with four times of recognized extinction events at 36(with 2 craters),66,and 145 Myr ago,and possibly with two provisional extinction events at 168 and215 Myr ago.These impact cratering events are accompanied by layers in the geologic record interpreted as impact ejecta.Chance occurrences of impacts and extinctions can be rejected at confidence levels of99.96%(for 4 impact/extinctions)to 99.99%(for 6 impact/extinctions).These results argue that several extinction events over the last 250 Myr may be related to the effects of large-body impacts.展开更多
Recent attention has been put into recurring slope lineae (RSL), after the discovery that water is present in them. It is assumed that RSL are due to flowing water. However, even though that might be the case, the gen...Recent attention has been put into recurring slope lineae (RSL), after the discovery that water is present in them. It is assumed that RSL are due to flowing water. However, even though that might be the case, the general characteristics of RSL as well as their seasonal and spatial distribution in Mars, and their occurrence within craters, suggest that RSL correspond to the weathering of frozen aquifers, which coincides with slope stability processes occurring in impact craters and scree slopes from Earth. In this study, we associated RSL with similar weathering processes occurring on impact craters and hydrogeological processes occurring on Earth (including ice, water, and wind erosion and natural aquifer recharge processes). We were able to create a conceptual model on how RSL develop, why are they found mostly in mid latitudes around craters, why are they present in more frequency in one side of crates in high latitudes, and why are there more RSL in the Martian southern hemisphere. Considering the whole hydrogeological processes occurring in craters that experience RSL, we were able to predict where large quantities of liquid water are most likely to be present in the red planet.展开更多
The ever-increasing recovery rate of natural resources from terrestrial impact craters over the last fewdecades across the globe offers new avenues for further exploration of mineral and hydrocarbon resources in such ...The ever-increasing recovery rate of natural resources from terrestrial impact craters over the last fewdecades across the globe offers new avenues for further exploration of mineral and hydrocarbon resources in such settings.As of today,60 of the 208 terrestrial craters have been identified to host diverseresources such as hydrocarbons,metals and construction materials.The potential of craters as plausibleresource contributors to the energy sector is therefore,worthy of consideration,as 42(70%)of the 60craters host energy resources such as oil,gas,coal,uranium,mercury,critical and major minerals as wellas hydropower resources.Among others,19 craters are of well-developed hydrocarbon reserves.Mineraldeposits associated with craters are also classified similar to other mineral resources such as progenetic,syngenetic and epigenetic sources.Of these,the progenetic and syngenetic mineralization are confinedto the early and late excavation stage of impact crater evolution,respectively,whereas epigenetic deposits are formed during and after the modification stage of crater formation.Thus,progenetic andsyngenetic mineral deposits(like Fe,Ni,Pb,Zn and Cu)associated with craters are formed as a directresult of the impact event,whereas epigenetic deposits(e.g.hydrocarbon)are hosted by the impactstructure and result from post-impact processes.In the progenetic and syngenetic deposits,the shockwave induced fracturing and melting aid the formation of deposits,whereas in the epigenetic deposits,the highly fractured lithostratigraphic units of higher porosity and permeability,like the centralelevated area(CEA)or the rim,act as traps.In this review,we provide a holistic view of the mineral andenergy resources associated with impact craters,and use some of the remote sensing techniques toidentify the mineral deposits as supplemented by a schematic model of the types of deposits formedduring cratering process.展开更多
The plume-surface interaction(PSI)is a common phenomenon that describes the environment surrounding the landers resulting from the impingement of hot rocket exhaust on the regolith of planetary bodies.The PSI will cau...The plume-surface interaction(PSI)is a common phenomenon that describes the environment surrounding the landers resulting from the impingement of hot rocket exhaust on the regolith of planetary bodies.The PSI will cause obscuration,erosion of the planetary surface,and high-speed spreading of dust or high-energy ejecta streams,which will induce risks to a safe landing and cause damage to payloads on the landers or to nearby assets.Safe landings and the subsequent scientific goals of deep-space exploration in China call for a comprehensive understanding of the PSI process,including the plume flow mechanics,erosion mechanism,and ejecta dynamics.In addition,the landing crater caused by the plume provides a unique and insightful perspective on the understanding of PSI.In particular,the PSI can be used directly to constrain the composition,structure,and mechanical properties of the surface and subsurface soil.In this study,we conducted a systematic review of the phenomenology and terrestrial tests of PSI:we analyzed the critical factors in the PSI process and compared the differences in PSI phenomena between lunar and Martian conditions;we also reviewed the main erosion mechanisms and the evolution and development of terrestrial tests on PSI.We discuss the problems with PSI,challenges of terrestrial tests,and prospects of PSI,and we show the preliminary results obtained from the landing crater caused by the PSI of Tianwen-1.From analysis of the camera images and digital elevation model reconstructions,we concluded that the landing of Tianwen-1 caused the deepest crater(depth>40 cm)on a planetary surface reported to date and revealed stratigraphic layers in the subsurface of Martian soil.We further constrained the lower bounds of the mechanical properties of Martian soil by a slope stability analysis of the Tianwen-1 landing crater.The PSI may offer promising opportunities to obtain greater insights into planetary science,including the subsurface structure,mineral composition,and properties of soil.展开更多
小行星撞遇陆地是一个复杂的非线性动力学过程,难以通过模型试验的方法开展相关研究。数值计算为这一灾害动力学过程分析提供了重要的工具,基于自主研发的CoSim软件中离散元(Discrete Element Method,DEM)模块初步实现了小行星撞遇陆地...小行星撞遇陆地是一个复杂的非线性动力学过程,难以通过模型试验的方法开展相关研究。数值计算为这一灾害动力学过程分析提供了重要的工具,基于自主研发的CoSim软件中离散元(Discrete Element Method,DEM)模块初步实现了小行星撞遇陆地的大规模计算模拟。基于小行星撞遇陆地三维动力学全过程的数值仿真结果:实现了初始接触、撞遇挖掘、高速抛射和回落调整4个撞击阶段全过程仿真;小行星的碰撞入射角及撞遇过程中动力学行为将影响撞击坑的地形地貌特征。研究也表明大规模数值计算方法可较好地实现小行星撞遇地球这一动力学过程,为小行星防御提供支撑。展开更多
In the northern part of the Ordos Basin, there is a 325 km long arc-shaped Langshan uplift and a 15 km-deep Linhe Trench in front of Langshan, which are rare geological phenomena for which origins no one has explained...In the northern part of the Ordos Basin, there is a 325 km long arc-shaped Langshan uplift and a 15 km-deep Linhe Trench in front of Langshan, which are rare geological phenomena for which origins no one has explained. This article comprehensively analyzes the research achievements over the past 40 years of geology, geomorphology, seismic exploration, paleogeography, and oil and gas exploration in the Ordos Basin and Langshan. It recognizes that the northern part of the Ordos Basin experienced a meteorite impact in the Late Cretaceous period. The impact pushed the block northwest ward, subducting after colliding with igneous rocks in the north. This sudden event formed a clear arc-shaped mountain zone in the north and a wedge-shaped trench in front of the mountain. The chaotic layers, prolonged and continuous faults, and numerous thrust layers in the Langshan, a negative anomaly area in the center of the northern Ordos, abnormal orientation of crystalline basement structures in the north of Ordos, Moho uplift, and distribution of meteorite fragments in the northwest of Langshan, all of these geological phenomena support the occurrence of the meteorite impact event, forming the arc-shaped Langshan and the Trench.展开更多
基金support from the Department of Science and Technology (DST),Government of India (Grant No.ECR/DST/2017/000918)the Indian Institute of Technology Ropar for providing financial support under an ISIRD grant (F.No.9-282/2017IITRPR/705).
文摘Ultrasonic-assisted micro-electro-discharge machining(EDM)has the potential to enhance processing responses such as material removal rate(MRR)and surface finish.To understand the reasons for this enhancement,the physical mechanisms responsible for the individual discharges and the craters that they form need to be explored.This work examines features of craters formed by single discharges at various parameter values in both conventional and ultrasonic-assistedEDM of Ti6Al4V.High-speed imaging of the plasma channel is performed,and data on the individual discharges are captured in real-time.A 2D axisymmetric model using finite element software is established to model crater formation.On the basis of simulation and experimental results,a comparative study is then carried out to examine the effects of ultrasonic vibrational assistance on crater geometry.For every set ofEDM parameters,the crater diameter and depth from a single discharge are found to be higher in ultrasonic-assistedEDM than in conventionalEDM.The improved crater geometry and the reduced bulge formation at the crater edges are attributed to the increased melt pool velocity and temperature predicted by the model.
文摘The micro-ablation processes and morphological evolution of ablative craters on single-crystal magnesium under subpicosecond laser irradiation are investigated using molecular dynamics(MD) simulations and experiments.The simulation results exhibit that the main failure mode of single-crystal Mg film irradiated by a low fluence and long pulse width laser is the ejection of surface atoms,which has laser-induced high stress.However,under high fluence and short pulse width laser irradiation,the main damage mechanism is nucleation fracture caused by stress wave reflection and superposition at the bottom of the film.In addition,Mg[0001] has higher pressure sensitivity and is more prone to ablation than Mg[0001].The evolution equation of crater depth is established using multi-pulse laser ablation simulation and verified by experiments.The results show that,under multiple pulsed laser irradiation,not only does the crater depth increase linearly with the pulse number,but also the quadratic term and constant term of the fitted crater profile curve increase linearly.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41490633 and 41590851)the open fund of the State Key Laboratory of Lunar and Planetary Sciences (Macao University of Science and Technology) (Macao FDCT Grant No. 119/2017/A3)+6 种基金the open fund of the Key Laboratory of Lunar and Deep Space Exploration, Chinese Academy of Sciencessupported by the National Natural Science Foundation of China (U1931211, 41972322 and 11941001)the Natural Science Foundation of Shandong Province (ZR2019MD008)Qilu (Tang) Young Scholars Program of Shandong University, Weihai (2015WHWLJH14)supported by the Program for JLU Science and Technology Innovative Research Team (JLUSTIRT, 2017TD-26)the Focus on Research and Development Plan in Shandong Province (2018GGX101028)the Shandong Provincial Natural Science Foundation (ZR2019MD015)
文摘Chang’E-4(CE-4)successfully landed on the floor of the Von Kármán crater within the South Pole-Aitken basin(SPA).One of its scientific objectives is to determine the subsurface structure and the thickness of lunar regolith at the landing site and along the traverse route of the Yutu-2 rover.Using orbital data,we employed small craters(diameters<1 km)on the floor of the Von Kármán crater as probes to investigate the subsurface structure and stratigraphy of the CE-4 landing site.In this study,40 dark-haloed craters that penetrate through the surface Finsen ejecta and excavate underlying mare deposits were identified,and 77 bright ray craters that expose only the underlying fresh materials but do not penetrate through the surface Finsen ejecta were found.The excavation depths of these craters and their distances from the Finsen crater center were calculated,and the thickness distribution of Finsen ejecta on the Von Kármán floor was systematically investigated.The boundary between Finsen ejecta and underlying mare basalt at the CE-4 landing site is constrained to a depth of 18 m.We have proposed the stratigraphy for the CE-4 site and interpreted the origins of different layers and the geological history of the Von Kármán crater.These results provide valuable geological background for interpreting data from the Lunar Penetrating Radar(LPR)and Visible and Near-infrared Imaging Spectrometer(VNIS)on the Yutu-2 rover.The CE-4 landing site could provide a reference point for crater ejecta distribution and mixing with local materials,to test and improve ejecta thickness models according to the in situ measurements of the CE-4 LPR.
文摘In the present work,a state-based peridynamics with adaptive particle refinement is proposed to simulate water ice crater formation due to impact loads.A modified Drucker-Prager constitutive model was adopted to model ice and was implemented in the state-based peridynamic equations to analyze the elastic-plastic deformation of ice.In simulations,we use the fracture toughness failure criterion in peridynamics to simulate the quasi-brittle failure of ice.An adaptive particle refinement method in peridynamics was proposed to improve computational efficiency.The results obtained using the peridynamic model were compared with the experiments in previous literatures.It was found that the peridynamic simulation results and the experiments matched well except for some minor differences discussed,and the state-based peridynamic model has shown the specific predictive capacity to capture the detailed crater features of the ice.
基金Support for Rampino came from an NYU Research Challenge grant
文摘The six largest known impact craters of the last 250 Myr(≥70 km in diameter),which are capable of causing significant environmental damage,coincide with four times of recognized extinction events at 36(with 2 craters),66,and 145 Myr ago,and possibly with two provisional extinction events at 168 and215 Myr ago.These impact cratering events are accompanied by layers in the geologic record interpreted as impact ejecta.Chance occurrences of impacts and extinctions can be rejected at confidence levels of99.96%(for 4 impact/extinctions)to 99.99%(for 6 impact/extinctions).These results argue that several extinction events over the last 250 Myr may be related to the effects of large-body impacts.
文摘Recent attention has been put into recurring slope lineae (RSL), after the discovery that water is present in them. It is assumed that RSL are due to flowing water. However, even though that might be the case, the general characteristics of RSL as well as their seasonal and spatial distribution in Mars, and their occurrence within craters, suggest that RSL correspond to the weathering of frozen aquifers, which coincides with slope stability processes occurring in impact craters and scree slopes from Earth. In this study, we associated RSL with similar weathering processes occurring on impact craters and hydrogeological processes occurring on Earth (including ice, water, and wind erosion and natural aquifer recharge processes). We were able to create a conceptual model on how RSL develop, why are they found mostly in mid latitudes around craters, why are they present in more frequency in one side of crates in high latitudes, and why are there more RSL in the Martian southern hemisphere. Considering the whole hydrogeological processes occurring in craters that experience RSL, we were able to predict where large quantities of liquid water are most likely to be present in the red planet.
文摘The ever-increasing recovery rate of natural resources from terrestrial impact craters over the last fewdecades across the globe offers new avenues for further exploration of mineral and hydrocarbon resources in such settings.As of today,60 of the 208 terrestrial craters have been identified to host diverseresources such as hydrocarbons,metals and construction materials.The potential of craters as plausibleresource contributors to the energy sector is therefore,worthy of consideration,as 42(70%)of the 60craters host energy resources such as oil,gas,coal,uranium,mercury,critical and major minerals as wellas hydropower resources.Among others,19 craters are of well-developed hydrocarbon reserves.Mineraldeposits associated with craters are also classified similar to other mineral resources such as progenetic,syngenetic and epigenetic sources.Of these,the progenetic and syngenetic mineralization are confinedto the early and late excavation stage of impact crater evolution,respectively,whereas epigenetic deposits are formed during and after the modification stage of crater formation.Thus,progenetic andsyngenetic mineral deposits(like Fe,Ni,Pb,Zn and Cu)associated with craters are formed as a directresult of the impact event,whereas epigenetic deposits(e.g.hydrocarbon)are hosted by the impactstructure and result from post-impact processes.In the progenetic and syngenetic deposits,the shockwave induced fracturing and melting aid the formation of deposits,whereas in the epigenetic deposits,the highly fractured lithostratigraphic units of higher porosity and permeability,like the centralelevated area(CEA)or the rim,act as traps.In this review,we provide a holistic view of the mineral andenergy resources associated with impact craters,and use some of the remote sensing techniques toidentify the mineral deposits as supplemented by a schematic model of the types of deposits formedduring cratering process.
基金supported by the National Natural Science Foundation of China(Grant 42230111)the Key Research Program of the Institute of Geology and Geophysics,CAS(Mars Mission,Grant IGGCAS-202102)+1 种基金the Key Research Program of the Institute of Geology and Geophysics,CAS(Grant IGGCAS-201904)the CAS Key Technology Talent Program.
文摘The plume-surface interaction(PSI)is a common phenomenon that describes the environment surrounding the landers resulting from the impingement of hot rocket exhaust on the regolith of planetary bodies.The PSI will cause obscuration,erosion of the planetary surface,and high-speed spreading of dust or high-energy ejecta streams,which will induce risks to a safe landing and cause damage to payloads on the landers or to nearby assets.Safe landings and the subsequent scientific goals of deep-space exploration in China call for a comprehensive understanding of the PSI process,including the plume flow mechanics,erosion mechanism,and ejecta dynamics.In addition,the landing crater caused by the plume provides a unique and insightful perspective on the understanding of PSI.In particular,the PSI can be used directly to constrain the composition,structure,and mechanical properties of the surface and subsurface soil.In this study,we conducted a systematic review of the phenomenology and terrestrial tests of PSI:we analyzed the critical factors in the PSI process and compared the differences in PSI phenomena between lunar and Martian conditions;we also reviewed the main erosion mechanisms and the evolution and development of terrestrial tests on PSI.We discuss the problems with PSI,challenges of terrestrial tests,and prospects of PSI,and we show the preliminary results obtained from the landing crater caused by the PSI of Tianwen-1.From analysis of the camera images and digital elevation model reconstructions,we concluded that the landing of Tianwen-1 caused the deepest crater(depth>40 cm)on a planetary surface reported to date and revealed stratigraphic layers in the subsurface of Martian soil.We further constrained the lower bounds of the mechanical properties of Martian soil by a slope stability analysis of the Tianwen-1 landing crater.The PSI may offer promising opportunities to obtain greater insights into planetary science,including the subsurface structure,mineral composition,and properties of soil.
文摘小行星撞遇陆地是一个复杂的非线性动力学过程,难以通过模型试验的方法开展相关研究。数值计算为这一灾害动力学过程分析提供了重要的工具,基于自主研发的CoSim软件中离散元(Discrete Element Method,DEM)模块初步实现了小行星撞遇陆地的大规模计算模拟。基于小行星撞遇陆地三维动力学全过程的数值仿真结果:实现了初始接触、撞遇挖掘、高速抛射和回落调整4个撞击阶段全过程仿真;小行星的碰撞入射角及撞遇过程中动力学行为将影响撞击坑的地形地貌特征。研究也表明大规模数值计算方法可较好地实现小行星撞遇地球这一动力学过程,为小行星防御提供支撑。
文摘In the northern part of the Ordos Basin, there is a 325 km long arc-shaped Langshan uplift and a 15 km-deep Linhe Trench in front of Langshan, which are rare geological phenomena for which origins no one has explained. This article comprehensively analyzes the research achievements over the past 40 years of geology, geomorphology, seismic exploration, paleogeography, and oil and gas exploration in the Ordos Basin and Langshan. It recognizes that the northern part of the Ordos Basin experienced a meteorite impact in the Late Cretaceous period. The impact pushed the block northwest ward, subducting after colliding with igneous rocks in the north. This sudden event formed a clear arc-shaped mountain zone in the north and a wedge-shaped trench in front of the mountain. The chaotic layers, prolonged and continuous faults, and numerous thrust layers in the Langshan, a negative anomaly area in the center of the northern Ordos, abnormal orientation of crystalline basement structures in the north of Ordos, Moho uplift, and distribution of meteorite fragments in the northwest of Langshan, all of these geological phenomena support the occurrence of the meteorite impact event, forming the arc-shaped Langshan and the Trench.