| In the research field of shock wave physics and high-pressure physics mechanics,the study of high-pressure physics mechanical properties and dynamic response characteristics of window materials is very critical.On the one hand,in the experimental research on the physical and mechanical properties of other materials,most of them need to use a transparent window as an anvil to maintain a high pressure state,and opaque materials need to transmit optical signals through the window for real-time continuous time resolution or thermal radiation temperature diagnosis,so suitable window materials have always been the goals and research topics that scientists are trying to find;on the other hand,for optically transparent window materials,conventional optical observation methods can be used to determine the internal dynamic response and optical properties.The research methods and understandings established there out can provide important references for the research of non-transparent materials.With high-pressure optical transparency,Gd3GasO12 single crystal(GGG)is an important high-impedance window material in shock wave experiment.At present,some studies have been carried out on the high-pressure physical properties and dynamic response behavior of GGG single crystals,including elastoplastic transition,Hugoniot equation of state,high-voltage conductivity,optical absorption,shock-induced phase transition,shock temperature and melting,and high-pressure refractive index.In the experimental pressure range of 0 GPa?300 GPa,GGG single crystal has a series of transitions including elastic response? incipient plasticity? complete plastic response? structure phase transition?melting.From the velocity wave profile,elastoplastic double-wave structures and elastic,plastic,and phase-transition three-wave structures can be observed.Corresponding to this,the changes in the optical refractive index of each phase show different changes.Although there have been some sporadic reports before,the complete image is not clear.In addition,the GGG Hugoniot elastic limit(HEL)value reported in the literature also has not reached a common understanding.Why is there such a big difference and how to determine the true HEL value are scientific problems that need to be solved.In response to the above problems,we performed the plate impact experiments on the first-stage light-gas gun(14 mm inner diameter).The plane impact method and laser interferometry(Doppler Pin System-DPS)were used to accurately measure the interface velocity profile of the Gd3Ga5O12 single crystal in pure elastic region and elastic-plastic region.Combined with the original DPS data accumulated by Zhou Xianming Group,the characteristics of the interference fringes and velocity wave profiles near the critical region of elastoplastic transition and their relationship with birefringence,incipient plasticity,Hugoniot elastic limit,and the change of refractive index in the range of 0 GPa-300 GPa were comprehensively analyzed.The new knowledge gained is as follows:1.When the final pressure is loaded slightly above the Hugoniot elastic limit of GGG,by the DPS data combined with the short-term Fourier transformation(STFT),the interference fringes of DPS show three different states:amplitude stable state,dumbbell-like modulation state and fast irregular modulation state.Since the birefringence phenomenon was not observed in the pure elastic response experiment of the GGG,it was determined that the lattice rotation occurred in the shock compression of the GGG,at which point the sample was compressed to the incipient plasticity.These three states correspond to three states:the elastic region,the incipient plastic region(causing birefringence),and the plastic region.2.When[111]GGG sample was compressed to the state of incipient plasticity,the Hugoniot elastic limit(HEL)in[111]GGG samples can be determined by the incubation time of the incipient plasticity(?).This value(HEL=8.78 GPa)is much lower than the previously reported HEL of GGG single crystals.From this,it is concluded that the true HEL is not related to the decay of elastic precursor wave,and this long-confused concept is clarified.3.In the range of 0 GPa?300 GPa,the optical refractive index of the GGG single crystal changes with the sample density,and there are different changes law in different phase regions:in the low-pressure phase region,the refractive index increases slowly with the increase in solid density;the change in the solid-solid phase boundary is continuous;in the high-pressure phase,the refractive index increases greatly with the solid density;in the solid-liquid boundary,the refractive index suddenly decreases;The refractive index of GGG single crystal in the liquid phase region increases with the increase of density,which is contrary to the change of the refractive index of sapphire in the liquid phase region.Based on the interference fringe data from DPS,we got the changes of refractive index in elastic region,elastic-plastic region,plastic region and shock-induce phase transition region for GGG single crystal.The true HEL value of GGG was determined.The results and understanding of this paper can provide a new inspiration for the research of the incipient plasticity of the solid material under impact loading and the study of the real Hugoniot elastic limit. |
PDF Full Text Request