Atomic-scale strain mapping has become increasingly vital for investigating deformation mechanisms and the governing principles of solid materials.This is due to the significant impact of atomic-scale strain on the ph...Atomic-scale strain mapping has become increasingly vital for investigating deformation mechanisms and the governing principles of solid materials.This is due to the significant impact of atomic-scale strain on the physical,chemical,and mechanical properties of nanomaterials that comprise functional devices such as nanoelectronics,communication devices,electromechanical systems,and sensors.The advent of advanced electron microscopes has enabled the acquisition of high-magnification images with atomic resolution,providing an exceptional platform for measuring the atomic-scale strain of solid materials.However,accurate and unified strain mapping methods and standards for evaluating atomic-scale strain distribution remain scarce.Consequently,a unified strain mapping framework is proposed for atomic-scale strain measurement.Utilizing finite deformation analysis and the least-squares mathematical method,two types of atomic-scale strain field mapping methods have been developed,including the phase analysis-based methods(PAD and PAS)and the peak matching-based strain mapping method(PMS)for high-resolution scanning transmission electron microscope images.The prototypical 2D materials,graphene and molybdenum disulfide,serve as the subjects for the strain field mapping research,conducted through both simulation and experimentation.Upon comparing the theoretical strain mapping results of single-layer graphene and molybdenum disulfide with and without defects,it is demonstrated that the proposed strain mapping methods,particularly the PMS method,can accurately describe the large deformation surrounding a significant strain gradient.展开更多
Thermal self-compressing bonding(TSCB) is a new solid-state bonding method pioneered by the authors. With electron beam as the non-melted heat source, previous experimental study performed on titanium alloys has prove...Thermal self-compressing bonding(TSCB) is a new solid-state bonding method pioneered by the authors. With electron beam as the non-melted heat source, previous experimental study performed on titanium alloys has proved the feasibility of TSCB. However, the thermal stress–strain process during bonding, which is of very important significance in revealing the mechanism of TSCB, was not analysed. In this paper, finite element analysis method is adopted to numerically study the thermal elasto-plastic stress–strain cycle of thermal self-compressing bonding. It is found that due to the localized heating, a non-uniform temperature distribution is formed during bonding, with the highest temperature existed on the bond interface. The expansion of high temperature materials adjacent to the bond interface are restrained by surrounding cool materials and rigid restraints, and thus an internal elasto-plastic stress–strain field is developed by itself which makes the bond interface subjected to thermal compressive action. This thermal self-compressing action combined with the high temperature on the bond interface promotes the atom diffusion across the bond interface to produce solid-state joints. Due to the relatively large plastic deformation, rigid restraint TSCB obtains sound joints in relatively short time compared to diffusion bonding.展开更多
Dynamic strain aging (DSA) is an important phenomenon in solutehardened metals and seri- ously affects the mechanical properties ofmetals. DSA is generally induced by the interaction between themoving dislocations and...Dynamic strain aging (DSA) is an important phenomenon in solutehardened metals and seri- ously affects the mechanical properties ofmetals. DSA is generally induced by the interaction between themoving dislocations and the mobile solute atoms. In this paper, onlythe interaction between moving disloca- tions and mobile solute atomsin a dislocation core area (core atmosphere) will be taken intoaccount. To es- tablish the constitutive model which can describe theDSA phenomenon, we improved the Zerilli-Armstrongdislocation-mechanics-based thermal viscoplastic constitutiverelation, and added the effect of the interaction between the movingdislocations and core atmosphere.展开更多
Since rate effect of materials plays a key role in impact engineering, the microscopic mechanism of rate effect is investigated at molecular level in this paper. The results show that rate effect on the strength of at...Since rate effect of materials plays a key role in impact engineering, the microscopic mechanism of rate effect is investigated at molecular level in this paper. The results show that rate effect on the strength of atomic system is closely related to the coupled evolution of atomic motions and potential landscapes. Accordingly, it becomes possible to develop a new algorithm of molecular simulation, which could properly and efficiently demonstrate strain rate effect under a wide range of loading rates and unveil the mecha- nisms underlying the strain rate effects.展开更多
基金support from the National Natural Science Foundation of China through Grants 12172190,11872035,11632010,and 12302236。
文摘Atomic-scale strain mapping has become increasingly vital for investigating deformation mechanisms and the governing principles of solid materials.This is due to the significant impact of atomic-scale strain on the physical,chemical,and mechanical properties of nanomaterials that comprise functional devices such as nanoelectronics,communication devices,electromechanical systems,and sensors.The advent of advanced electron microscopes has enabled the acquisition of high-magnification images with atomic resolution,providing an exceptional platform for measuring the atomic-scale strain of solid materials.However,accurate and unified strain mapping methods and standards for evaluating atomic-scale strain distribution remain scarce.Consequently,a unified strain mapping framework is proposed for atomic-scale strain measurement.Utilizing finite deformation analysis and the least-squares mathematical method,two types of atomic-scale strain field mapping methods have been developed,including the phase analysis-based methods(PAD and PAS)and the peak matching-based strain mapping method(PMS)for high-resolution scanning transmission electron microscope images.The prototypical 2D materials,graphene and molybdenum disulfide,serve as the subjects for the strain field mapping research,conducted through both simulation and experimentation.Upon comparing the theoretical strain mapping results of single-layer graphene and molybdenum disulfide with and without defects,it is demonstrated that the proposed strain mapping methods,particularly the PMS method,can accurately describe the large deformation surrounding a significant strain gradient.
基金Supported by National Natural Science Foundation of China(Grant No.51705491)
文摘Thermal self-compressing bonding(TSCB) is a new solid-state bonding method pioneered by the authors. With electron beam as the non-melted heat source, previous experimental study performed on titanium alloys has proved the feasibility of TSCB. However, the thermal stress–strain process during bonding, which is of very important significance in revealing the mechanism of TSCB, was not analysed. In this paper, finite element analysis method is adopted to numerically study the thermal elasto-plastic stress–strain cycle of thermal self-compressing bonding. It is found that due to the localized heating, a non-uniform temperature distribution is formed during bonding, with the highest temperature existed on the bond interface. The expansion of high temperature materials adjacent to the bond interface are restrained by surrounding cool materials and rigid restraints, and thus an internal elasto-plastic stress–strain field is developed by itself which makes the bond interface subjected to thermal compressive action. This thermal self-compressing action combined with the high temperature on the bond interface promotes the atom diffusion across the bond interface to produce solid-state joints. Due to the relatively large plastic deformation, rigid restraint TSCB obtains sound joints in relatively short time compared to diffusion bonding.
基金the Chinese Academy of Sciences and the High Technical Project.
文摘Dynamic strain aging (DSA) is an important phenomenon in solutehardened metals and seri- ously affects the mechanical properties ofmetals. DSA is generally induced by the interaction between themoving dislocations and the mobile solute atoms. In this paper, onlythe interaction between moving disloca- tions and mobile solute atomsin a dislocation core area (core atmosphere) will be taken intoaccount. To es- tablish the constitutive model which can describe theDSA phenomenon, we improved the Zerilli-Armstrongdislocation-mechanics-based thermal viscoplastic constitutiverelation, and added the effect of the interaction between the movingdislocations and core atmosphere.
基金supported by the National Basic Research Program of China (973 Program)(2012CB937500)the National Natural Science Foundation of China (11202212,10932011,11021262,11172024,11172305,and 11232013)
文摘Since rate effect of materials plays a key role in impact engineering, the microscopic mechanism of rate effect is investigated at molecular level in this paper. The results show that rate effect on the strength of atomic system is closely related to the coupled evolution of atomic motions and potential landscapes. Accordingly, it becomes possible to develop a new algorithm of molecular simulation, which could properly and efficiently demonstrate strain rate effect under a wide range of loading rates and unveil the mecha- nisms underlying the strain rate effects.
