The commercial ZK 60 magnesium alloy with extruded state experienced aging heat treatment(T 6)was dynamically loaded at strain rate of 3000 s−1 by means of the split Hopkinson pressure bar(SHPB)in this paper.Transmiss...The commercial ZK 60 magnesium alloy with extruded state experienced aging heat treatment(T 6)was dynamically loaded at strain rate of 3000 s−1 by means of the split Hopkinson pressure bar(SHPB)in this paper.Transmission electron microscopy(TEM)observations showed that the precipitatedβ′_(1) phases partially dissolved(spheroidized)with blurred interfaces within 160μs at 3000 s^(−1).The average length and diameter of the rod-shapedβ′_(1) phase particles were 48.5 and 9.8 nm after the T 6 heat treatment;while the average diameter of the sphericalβ′_(1) phases changed to 8.8 nm after loading.The deformedβ′_(1) phase generated larger lattice distortion energy than Mg matrix under high strain rate loading.Therefore,the difference of free energy(the driving force of dissolution)between theβ′_(1) phase and the matrix increased,making the instantaneous dissolution of theβ′_(1) phase thermodynamically feasible.The dissolution(spheroidization)of theβ′_(1) phase particles was kinetically promoted because the diffusion rate of the solute Zn atoms was accelerated by combined actions of adiabatic temperature rise,high density of dislocations(vacancies)and high deviatoric stresses during high strain rate loading.The increase in hardness of ZK 60-T 6 alloy could be attributed to solid solution strengthening,dislocation strengthening and second phase particle strengthening.展开更多
An annealed 50 Cr V4 steel was subjected to cyclic heat treatment process that consists of repeated short-duration(200 s)held at 840 °C(above Ac3 temperature of 790 °C) and short-duration(100 s) held at 700 ...An annealed 50 Cr V4 steel was subjected to cyclic heat treatment process that consists of repeated short-duration(200 s)held at 840 °C(above Ac3 temperature of 790 °C) and short-duration(100 s) held at 700 °C(below Ac1 temperature of 710 °C). The spheroidization ratio of cementite and the average size of particles increase with increasing the cyclic number of heat treatment. After5-cycle heat treatment, the spheroidization ratio of cementite is 100%, and the average size of the cementite particles is about0.53 μm. After cyclic heat treatment, the hardness, ultimate tensile strength and yield strength of the experimental steel gradually decrease with increasing cyclic number of heat treatment. The elongation of the as-received specimens is about 7.4%, the elongation of the 1-cycle specimen is 14.3%, and the elongation of 5-cycle specimen reaches a peak value of 22.5%, thereafter marginally decreases to 18.3% after 6-cycle heat treatment. Accordingly, the fractured surface initially exhibits the regions of wavy lamellar fracture. By increasing the cyclic number of heat treatment cycles, the regions of dimples consume the entire fractured surface gradually. Some large dimples can be found in the fracture surface of the specimen subjected to six heat treatment cycles.展开更多
For the direction of arrival（DOA） estimation,traditional sparse reconstruction methods for wideband signals usually need many iteration times.For this problem,a new method for two-dimensional wideband signals based ...For the direction of arrival（DOA） estimation,traditional sparse reconstruction methods for wideband signals usually need many iteration times.For this problem,a new method for two-dimensional wideband signals based on block sparse reconstruction is proposed.First,a prolate spheroidal wave function（PSWF） is used to fit the wideband signals,then the block sparse reconstruction technology is employed for DOA estimation.The proposed method uses orthogonalization to choose the matching atoms,ensuring that the residual components correspond to the minimum absolute value.Meanwhile,the vectors obtained by iteration are back-disposed according to the corresponding atomic matching rules,so the extra atoms are abandoned in the course of iteration,and the residual components of current iteration are reduced.Thus the original sparse signals are reconstructed.The proposed method reduces iteration times comparing with the traditional reconstruction methods,and the estimation precision is better than the classical two-sided correlation transformation（TCT）algorithm when the snapshot is small or the signal-to-noise ratio（SNR） is low.展开更多
基金Projects(51871243,51574290)supported by the National Natural Science Foundation of ChinaProject(ASSIKFJJ202304001)supported by the Open Fund of the National Key Laboratory of Strength and Structural Integrity,China+3 种基金Project(HT-CSNS-DG-CD-0092/2021)supported by the Guangdong-Hong Kong-Macao Joint Laboratory for Neutron Scattering Science and Technology,ChinaProject(2022KF-08)supported by the Hubei Longzhong Laboratory,ChinaProject(22kfgk06)supported by the Shock and Vibration of Engineering Materials and Structures Key Laboratory of Sichuan Province,ChinaProject(PBSKL2022C01)supported by the State Key Laboratory of Precision Blasting and Hubei Key Laboratory of Blasting Engineering,China。
文摘The commercial ZK 60 magnesium alloy with extruded state experienced aging heat treatment(T 6)was dynamically loaded at strain rate of 3000 s−1 by means of the split Hopkinson pressure bar(SHPB)in this paper.Transmission electron microscopy(TEM)observations showed that the precipitatedβ′_(1) phases partially dissolved(spheroidized)with blurred interfaces within 160μs at 3000 s^(−1).The average length and diameter of the rod-shapedβ′_(1) phase particles were 48.5 and 9.8 nm after the T 6 heat treatment;while the average diameter of the sphericalβ′_(1) phases changed to 8.8 nm after loading.The deformedβ′_(1) phase generated larger lattice distortion energy than Mg matrix under high strain rate loading.Therefore,the difference of free energy(the driving force of dissolution)between theβ′_(1) phase and the matrix increased,making the instantaneous dissolution of theβ′_(1) phase thermodynamically feasible.The dissolution(spheroidization)of theβ′_(1) phase particles was kinetically promoted because the diffusion rate of the solute Zn atoms was accelerated by combined actions of adiabatic temperature rise,high density of dislocations(vacancies)and high deviatoric stresses during high strain rate loading.The increase in hardness of ZK 60-T 6 alloy could be attributed to solid solution strengthening,dislocation strengthening and second phase particle strengthening.
文摘An annealed 50 Cr V4 steel was subjected to cyclic heat treatment process that consists of repeated short-duration(200 s)held at 840 °C(above Ac3 temperature of 790 °C) and short-duration(100 s) held at 700 °C(below Ac1 temperature of 710 °C). The spheroidization ratio of cementite and the average size of particles increase with increasing the cyclic number of heat treatment. After5-cycle heat treatment, the spheroidization ratio of cementite is 100%, and the average size of the cementite particles is about0.53 μm. After cyclic heat treatment, the hardness, ultimate tensile strength and yield strength of the experimental steel gradually decrease with increasing cyclic number of heat treatment. The elongation of the as-received specimens is about 7.4%, the elongation of the 1-cycle specimen is 14.3%, and the elongation of 5-cycle specimen reaches a peak value of 22.5%, thereafter marginally decreases to 18.3% after 6-cycle heat treatment. Accordingly, the fractured surface initially exhibits the regions of wavy lamellar fracture. By increasing the cyclic number of heat treatment cycles, the regions of dimples consume the entire fractured surface gradually. Some large dimples can be found in the fracture surface of the specimen subjected to six heat treatment cycles.
基金supported by the National Natural Science Foundation of China(6150117661201399)+1 种基金the Education Department of Heilongjiang Province Science and Technology Research Projects(12541638)the Developing Key Laboratory of Sensing Technology and Systems in Cold Region of Heilongjiang Province and Ministry of Education,(Heilongjiang University),P.R.China(P201408)
文摘For the direction of arrival（DOA） estimation,traditional sparse reconstruction methods for wideband signals usually need many iteration times.For this problem,a new method for two-dimensional wideband signals based on block sparse reconstruction is proposed.First,a prolate spheroidal wave function（PSWF） is used to fit the wideband signals,then the block sparse reconstruction technology is employed for DOA estimation.The proposed method uses orthogonalization to choose the matching atoms,ensuring that the residual components correspond to the minimum absolute value.Meanwhile,the vectors obtained by iteration are back-disposed according to the corresponding atomic matching rules,so the extra atoms are abandoned in the course of iteration,and the residual components of current iteration are reduced.Thus the original sparse signals are reconstructed.The proposed method reduces iteration times comparing with the traditional reconstruction methods,and the estimation precision is better than the classical two-sided correlation transformation（TCT）algorithm when the snapshot is small or the signal-to-noise ratio（SNR） is low.
