Residual stress measurement is of critical significance to in-service security and the reliability of engineering components, and has been an active area of scientific interest. This paper offers a review o[ several p...Residual stress measurement is of critical significance to in-service security and the reliability of engineering components, and has been an active area of scientific interest. This paper offers a review o[ several prominent mechanical release methods for residual stress measurement and recent developments, focusing on the hole-drilling method combined with advanced optical sensing. Some promising trends for mechanical release methods are also analyzed.展开更多
In the electron moiré method, a high-frequency grating is used to measure microscopic deformation, which promises significant potential applications for the method in the microscopic analysis of materials. Howeve...In the electron moiré method, a high-frequency grating is used to measure microscopic deformation, which promises significant potential applications for the method in the microscopic analysis of materials. However, a special beam scanning control device is required to produce a grating and generate a moiré fringe pattern for the scanning electron microscope （SEM）. Because only a few SEMs used in the material science studies are equipped with this device, the use of the electron moiré method is limited. In this study, an electron moiré method for a common SEM without the beam control device is presented. A grating based on a multi-scanning concept is fabricated in any observing mode. A real-time moiré pattern can also be generated in the SEM or an optical filtering system. Without the beam control device being a prerequisite, the electron moiré method can be more widely used. The experimental results from three different types of SEMs show that high quality gratings with uniform lines and less pitch error can be fabricated by this method, and moiré patterns can also be correctly generated.展开更多
This paper deals with the mode I crack problem of a cracked rubber sheet under plane stress condition using the delicate digital moiré technique. Through the four step phaseshifting method of automated fringe ana...This paper deals with the mode I crack problem of a cracked rubber sheet under plane stress condition using the delicate digital moiré technique. Through the four step phaseshifting method of automated fringe analysis, the displacement fields in the Cartesian coordinate system are given. By the coordinate-transform equation, the radial and circular displacement distributions in the polar coordinate system are obtained. The displacement isoline distributions and displacement vector distributions near the crack tip are discussed. The strain isoline distributions near the crack tip are also analyzed in this paper. Finally, the distribution rules for the mechanical fields near the crack tip are discussed with the sector division method.展开更多
In this paper,a new method combining focused ion beam(FIB)and scanning electron microscope(SEM)Moirétechnique for the measurement of residual stress at micro scale is proposed.The FIB is employed to introduce str...In this paper,a new method combining focused ion beam(FIB)and scanning electron microscope(SEM)Moirétechnique for the measurement of residual stress at micro scale is proposed.The FIB is employed to introduce stress relief like the macro ring-core method and fabricate gratings with a frequency of 5000 lines/mm on the measured area of the sample surface.Three groups of gratings in different radial directions are manufactured in order to form a micro-scale strain rosette.After milling ring-core by FIB,the deformation incurred by relief of the stress will be recorded with the strain rosette.The displacement/strain field can be measured using SEM scanning Moiréwith random phase-shifting algorithm.In this study,the Nickel alloy GH4169 sample(which was processed by laser shock peening)is selected as a study object to determine its residual stress.The results showed that the components of the in-plane principal stresses were-359 MPa and-207 MPa,respectively,which show good agreement with the results obtained from the available literature.展开更多
A hybrid method is established by combining photoelastic experiment and finite element analysis. The method is used to evaluate contact stress distribution on dry friction interfaces, such as the contact interfaces...A hybrid method is established by combining photoelastic experiment and finite element analysis. The method is used to evaluate contact stress distribution on dry friction interfaces, such as the contact interfaces between shrouds of fan blades and turbine blades. The photoelastic stress frozen experiment method is used to decide the displacement boundary conditions of numerical calculation. Higher accuracy and efficiency of solving problems are improved by the method. Technical difficulty and high cost of experiment are also avoided by the method. Good agreement of the stress distribution by using the hybrid method and experiment is obtained. \{展开更多
Two-dimensional(2D)twisted moirématerials,a new class of van der Waals(vdW)layered heterostructures with different twist angles between neighboring layers,have attracted tremendous attention due to their rich eme...Two-dimensional(2D)twisted moirématerials,a new class of van der Waals(vdW)layered heterostructures with different twist angles between neighboring layers,have attracted tremendous attention due to their rich emerging properties.In this review,we systematically summarize the recent progress of 2D twisted moirématerials.Firstly,we introduce several representative fabrication methods and the fascinating topographies of the twisted moirématerials.Specifically,we discuss various remarkable physical properties related to twisted angles,including flat bands,unconventional superconductivity,ferromagnetism,and ferroelectricity.We also analyze the potential applications in various twisted moirésystems.Finally,the challenges and future perspectives of the twisted moirématerials are discussed.This work would spur edge-cutting ideas and related achievements in the scientific and technological frontiers of 2D twisted moirématerials.展开更多
A novel method for automatic ultra-precision alignment is presented.This method relies on the modified Moiré technique,and alignment marks are used in the form of gratings.The modified Moiré technique can ef...A novel method for automatic ultra-precision alignment is presented.This method relies on the modified Moiré technique,and alignment marks are used in the form of gratings.The modified Moiré technique can effectively improve detecting sensitivity of signals and simplify the control system by using only one pair of laser-Moiré sensors.We present the mathematical model and simulation results of diffracting two gratings.The effect of various parameters on Moiré signals is studied theoretically and experimentally,and the results are found to be consistent.A computer controlled alignment device using one pair of Moiré sensors is designed.The device can achieve a fully automatic precision alignment by the modified Moiré signal.The experimental result shows that the alignment device can obtain the resolution of 5 nm and the positioning accuracy of ±0 5 μm.展开更多
Recent studies in van der Waals coupled two-dimensional(2D) bilayer materials have demonstrated a new freedom for material engineering by the formation of moiré pattern. By tuning the twist angle between two laye...Recent studies in van der Waals coupled two-dimensional(2D) bilayer materials have demonstrated a new freedom for material engineering by the formation of moiré pattern. By tuning the twist angle between two layers, one can modulate their electronic band structures and therefore the associated electrical transport and optical properties, which are distinct from the original ones of each individual layer. These new properties excite great passion in the exploration of new quantum states and possible applications of 2D bilayers. In this article, we will mainly review the prevailing fabrication methods and emerging physical properties of twisted bilayer materials and lastly give out a perspective of this topic.展开更多
We report on emergence of an abnormal electronic polarization in twisted double bilayer WSe_(2) in antiparallel interface stacking geometry,where local centrosymmetry of atomic registries at the twist interface does n...We report on emergence of an abnormal electronic polarization in twisted double bilayer WSe_(2) in antiparallel interface stacking geometry,where local centrosymmetry of atomic registries at the twist interface does not favor the spontaneous electronic polarizations as recently observed in the parallel interface stacking geometry.The unconventional ferroelectric behaviors probed by electronic transport measurement occur at half filling insulating states at 1.5 K and gradually disappear at about 40 K.Single band Hubbard model based on the triangular moirélattice and the interlayer charge transfer controlled by insulating phase transition are proposed to interpret the formation of electronic polarization states near half filling in twisted WSe_(2) devices.Our work highlights the prominent role of many-body electronic interaction in fostering novel quantum states in moiré-structured systems.展开更多
Using experimental mechanics method of moiré analysis, strain field distributions of 2024 aluminum alloy welded joints under different conditions were investigated. The results show that moiré stripes of wel...Using experimental mechanics method of moiré analysis, strain field distributions of 2024 aluminum alloy welded joints under different conditions were investigated. The results show that moiré stripes of welded joint without trailing peening just before fracture are not only few and scattered but also uneven, and the stress mainly concentrates on the poor position welded toes during the tensioning process with the relatively poor mechanical properties of welded joints; When the method of welding with trailing peening is adopted, moiré stripes of welded joint just before fracture are relatively thick and even due to the strengthening welded toes during the welding process, and fracture position transfers from the welded toes to weld, at the same time the mechanical properties of welded joints are improved greatly than conventional welding which can show that the technology of trailing peening is effective to strengthen welded joints of aluminum alloy with high strength.展开更多
Sintered permanent magnetic strontium ferrites were studied using transmission electron microscopy to investigate the microstructure morphology and its correlation with the magnetic properties. The present study shows...Sintered permanent magnetic strontium ferrites were studied using transmission electron microscopy to investigate the microstructure morphology and its correlation with the magnetic properties. The present study shows that the microstructure of sintered permanent magnetic strontium ferrites is an important parameter in determining their magnetic properties. The microstructure morphology in low-performance ferrite magnet is obviously different from high-performance one. The magnetic properties of sintered permanent strontium ferrite depend strongly on the orientation degree of strong magnetic crystals. The presence of ferric oxide phase in ferrite magnet can deteriorate the magnetic properties. Moreover, proper quantities of crystal defects are beneficial to high coercive force due to the fixing of magnetic domain.展开更多
A novel method to separate and simultaneously record the Moiréinterferometry fringe patterns of three deformation fields with only one CCD camera is developed;details of its operation principle,key points and err...A novel method to separate and simultaneously record the Moiréinterferometry fringe patterns of three deformation fields with only one CCD camera is developed;details of its operation principle,key points and error analysis are presented.With this technique,the deformation in U,V and W fields can be measured simultaneously,so dynamic test with comprehensive information can be performed.The advantage of this technique over other similar techniques lies in its simplicity,easy implementation and low cost.An application of this technique is given to show its feasibility.Technical problems that may be caused with this technique are also analyzed.展开更多
We deposited Ge films on Si substrates by molecular beam epitaxy (MBE) method. The specimens were annealed at around 750 C using microwave- plasma heating technique which we had reported before. After these pro- cesse...We deposited Ge films on Si substrates by molecular beam epitaxy (MBE) method. The specimens were annealed at around 750 C using microwave- plasma heating technique which we had reported before. After these pro- cesses, we carried out special scanning transmission electron microscopic (STEM) observation. The moiré between the crystal lattices and the scanning lines controlled by STEM was utilized to show lattice-spacing distribution. The results exhibited that we were succeeded in forming lattice-relaxed Ge thin films. It was also recognized that this STEM moiré technique is very useful to observe lattice-spacing distribution for large area with high resolution.展开更多
A moiré between crystal lattice planes and scanning electron beam-lines formed in a scanning transmission electron microscope includes the information of the lattice spacing. We apply these phenomena to a composi...A moiré between crystal lattice planes and scanning electron beam-lines formed in a scanning transmission electron microscope includes the information of the lattice spacing. We apply these phenomena to a compositionally graded SiGe thin film deposited onto a Si substrate by molecular beam epitaxy method. The results of the experiments and image analysis show the potential of this technique to analyze a slight change of the lattice spacing according to a compositional change.展开更多
基金the financial support from the National Basic Research Program of China(Project‘973’)(Nos.2010CB631005 and 2011CB606105)the National Natural Science Foundation of China(Nos.91216301,11172151,11232008,11072033 and 11372037)+1 种基金Tsinghua University Initiative Scientific Research Program,Program for New Century Excellent Talents in University(grant No.NCET-12-0036)Natural Science Foundation of Beijing,China(grant No.3122027)
文摘Residual stress measurement is of critical significance to in-service security and the reliability of engineering components, and has been an active area of scientific interest. This paper offers a review o[ several prominent mechanical release methods for residual stress measurement and recent developments, focusing on the hole-drilling method combined with advanced optical sensing. Some promising trends for mechanical release methods are also analyzed.
基金The project supported by the National Natural Science Foundation of China (10662005)JSPS fellowship in Japan.
文摘In the electron moiré method, a high-frequency grating is used to measure microscopic deformation, which promises significant potential applications for the method in the microscopic analysis of materials. However, a special beam scanning control device is required to produce a grating and generate a moiré fringe pattern for the scanning electron microscope （SEM）. Because only a few SEMs used in the material science studies are equipped with this device, the use of the electron moiré method is limited. In this study, an electron moiré method for a common SEM without the beam control device is presented. A grating based on a multi-scanning concept is fabricated in any observing mode. A real-time moiré pattern can also be generated in the SEM or an optical filtering system. Without the beam control device being a prerequisite, the electron moiré method can be more widely used. The experimental results from three different types of SEMs show that high quality gratings with uniform lines and less pitch error can be fabricated by this method, and moiré patterns can also be correctly generated.
基金Project supported by the National Natural Sciences Foundation of China (No. 10572102).
文摘This paper deals with the mode I crack problem of a cracked rubber sheet under plane stress condition using the delicate digital moiré technique. Through the four step phaseshifting method of automated fringe analysis, the displacement fields in the Cartesian coordinate system are given. By the coordinate-transform equation, the radial and circular displacement distributions in the polar coordinate system are obtained. The displacement isoline distributions and displacement vector distributions near the crack tip are discussed. The strain isoline distributions near the crack tip are also analyzed in this paper. Finally, the distribution rules for the mechanical fields near the crack tip are discussed with the sector division method.
基金supported by the National Basic Research Program of China(Grant Nos.2010CB631005 and 2011CB606105)the National Natural Science Foundation of China(Grant Nos.90916010,11172151 and 11232008)+1 种基金Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20090002110048)Tsinghua University Initiative Scientific Research Program
文摘In this paper,a new method combining focused ion beam(FIB)and scanning electron microscope(SEM)Moirétechnique for the measurement of residual stress at micro scale is proposed.The FIB is employed to introduce stress relief like the macro ring-core method and fabricate gratings with a frequency of 5000 lines/mm on the measured area of the sample surface.Three groups of gratings in different radial directions are manufactured in order to form a micro-scale strain rosette.After milling ring-core by FIB,the deformation incurred by relief of the stress will be recorded with the strain rosette.The displacement/strain field can be measured using SEM scanning Moiréwith random phase-shifting algorithm.In this study,the Nickel alloy GH4169 sample(which was processed by laser shock peening)is selected as a study object to determine its residual stress.The results showed that the components of the in-plane principal stresses were-359 MPa and-207 MPa,respectively,which show good agreement with the results obtained from the available literature.
基金Youth Foundation of Beijing Polytechnic Universit
文摘A hybrid method is established by combining photoelastic experiment and finite element analysis. The method is used to evaluate contact stress distribution on dry friction interfaces, such as the contact interfaces between shrouds of fan blades and turbine blades. The photoelastic stress frozen experiment method is used to decide the displacement boundary conditions of numerical calculation. Higher accuracy and efficiency of solving problems are improved by the method. Technical difficulty and high cost of experiment are also avoided by the method. Good agreement of the stress distribution by using the hybrid method and experiment is obtained. \{
文摘Two-dimensional(2D)twisted moirématerials,a new class of van der Waals(vdW)layered heterostructures with different twist angles between neighboring layers,have attracted tremendous attention due to their rich emerging properties.In this review,we systematically summarize the recent progress of 2D twisted moirématerials.Firstly,we introduce several representative fabrication methods and the fascinating topographies of the twisted moirématerials.Specifically,we discuss various remarkable physical properties related to twisted angles,including flat bands,unconventional superconductivity,ferromagnetism,and ferroelectricity.We also analyze the potential applications in various twisted moirésystems.Finally,the challenges and future perspectives of the twisted moirématerials are discussed.This work would spur edge-cutting ideas and related achievements in the scientific and technological frontiers of 2D twisted moirématerials.
文摘A novel method for automatic ultra-precision alignment is presented.This method relies on the modified Moiré technique,and alignment marks are used in the form of gratings.The modified Moiré technique can effectively improve detecting sensitivity of signals and simplify the control system by using only one pair of laser-Moiré sensors.We present the mathematical model and simulation results of diffracting two gratings.The effect of various parameters on Moiré signals is studied theoretically and experimentally,and the results are found to be consistent.A computer controlled alignment device using one pair of Moiré sensors is designed.The device can achieve a fully automatic precision alignment by the modified Moiré signal.The experimental result shows that the alignment device can obtain the resolution of 5 nm and the positioning accuracy of ±0 5 μm.
基金Project supported by the National Key R&D Program of China(Grant Nos.2016YFA0300903 and 2016YFA0300804)National Equipment Program of China(Grant No.ZDYZ2015-1)+3 种基金Beijing Graphene Innovation Program,China(Grant No.Z181100004818003)Beijing Municipal Science&Technology Commission,China(Grant No.Z181100004218006)Bureau of Industry and Information Technology of Shenzhen,China(Graphene platform contract No.201901161512)the Key R&D Program of Guangdong Province,China(Grant No.2019B010931001)
文摘Recent studies in van der Waals coupled two-dimensional(2D) bilayer materials have demonstrated a new freedom for material engineering by the formation of moiré pattern. By tuning the twist angle between two layers, one can modulate their electronic band structures and therefore the associated electrical transport and optical properties, which are distinct from the original ones of each individual layer. These new properties excite great passion in the exploration of new quantum states and possible applications of 2D bilayers. In this article, we will mainly review the prevailing fabrication methods and emerging physical properties of twisted bilayer materials and lastly give out a perspective of this topic.
基金supported by the National Key R&D Program of China(2020YFA 0309600)the Hong Kong Research Grants Council(AoE/P-701/20,C6025-19G,16305919 ECS26302118,16303720,16305019,16306220 and N_HKUST626/18)+1 种基金the National Natural Science Foundation of China(NSFC20SC07)the William Mong Institute of Nano Science and Technology.
文摘We report on emergence of an abnormal electronic polarization in twisted double bilayer WSe_(2) in antiparallel interface stacking geometry,where local centrosymmetry of atomic registries at the twist interface does not favor the spontaneous electronic polarizations as recently observed in the parallel interface stacking geometry.The unconventional ferroelectric behaviors probed by electronic transport measurement occur at half filling insulating states at 1.5 K and gradually disappear at about 40 K.Single band Hubbard model based on the triangular moirélattice and the interlayer charge transfer controlled by insulating phase transition are proposed to interpret the formation of electronic polarization states near half filling in twisted WSe_(2) devices.Our work highlights the prominent role of many-body electronic interaction in fostering novel quantum states in moiré-structured systems.
文摘Using experimental mechanics method of moiré analysis, strain field distributions of 2024 aluminum alloy welded joints under different conditions were investigated. The results show that moiré stripes of welded joint without trailing peening just before fracture are not only few and scattered but also uneven, and the stress mainly concentrates on the poor position welded toes during the tensioning process with the relatively poor mechanical properties of welded joints; When the method of welding with trailing peening is adopted, moiré stripes of welded joint just before fracture are relatively thick and even due to the strengthening welded toes during the welding process, and fracture position transfers from the welded toes to weld, at the same time the mechanical properties of welded joints are improved greatly than conventional welding which can show that the technology of trailing peening is effective to strengthen welded joints of aluminum alloy with high strength.
基金This work was financially supported by the Key Technologies R&D Program of Guangdong Province, China (No. 2004B10301009).
文摘Sintered permanent magnetic strontium ferrites were studied using transmission electron microscopy to investigate the microstructure morphology and its correlation with the magnetic properties. The present study shows that the microstructure of sintered permanent magnetic strontium ferrites is an important parameter in determining their magnetic properties. The microstructure morphology in low-performance ferrite magnet is obviously different from high-performance one. The magnetic properties of sintered permanent strontium ferrite depend strongly on the orientation degree of strong magnetic crystals. The presence of ferric oxide phase in ferrite magnet can deteriorate the magnetic properties. Moreover, proper quantities of crystal defects are beneficial to high coercive force due to the fixing of magnetic domain.
文摘A novel method to separate and simultaneously record the Moiréinterferometry fringe patterns of three deformation fields with only one CCD camera is developed;details of its operation principle,key points and error analysis are presented.With this technique,the deformation in U,V and W fields can be measured simultaneously,so dynamic test with comprehensive information can be performed.The advantage of this technique over other similar techniques lies in its simplicity,easy implementation and low cost.An application of this technique is given to show its feasibility.Technical problems that may be caused with this technique are also analyzed.
文摘We deposited Ge films on Si substrates by molecular beam epitaxy (MBE) method. The specimens were annealed at around 750 C using microwave- plasma heating technique which we had reported before. After these pro- cesses, we carried out special scanning transmission electron microscopic (STEM) observation. The moiré between the crystal lattices and the scanning lines controlled by STEM was utilized to show lattice-spacing distribution. The results exhibited that we were succeeded in forming lattice-relaxed Ge thin films. It was also recognized that this STEM moiré technique is very useful to observe lattice-spacing distribution for large area with high resolution.
文摘A moiré between crystal lattice planes and scanning electron beam-lines formed in a scanning transmission electron microscope includes the information of the lattice spacing. We apply these phenomena to a compositionally graded SiGe thin film deposited onto a Si substrate by molecular beam epitaxy method. The results of the experiments and image analysis show the potential of this technique to analyze a slight change of the lattice spacing according to a compositional change.
