Mechanical Properties And Failure Behavior Of Porous Pb(Zr_0.95Ti_0.05)O₃ Ferroelectric Ceramics

Ferroelectric ceramics have been widely used in sensors,intelligent materials and smart structures,storage and memory devices because of their superior electromechanical characterization.Ferroelectric ceramics are rich in species numbers,where PZT-based of perovskite structure is the more application value and is the research hotspot at home and abroad.In this paper,the PZT95/5 ferroelectric ceramics which stabilized near the boundary of ferroelectric(FE)and antiferroelectric(AFE)phases was concerned.Shock wave compression of PZT95/5 ferroelectric ceramics results in FE-AFE phase transition and release of bound charge to generate the megawatt pulse power supply has extensive application prospects in industry processes and national defence areas.However,for dense PZT95/5,many of observed dielectric breakdowns are preceded by mechanical failure during the shock wave loading.But for porous PZT95/5,it has higher dielectric breakdown field and lower transition pressure than dense PZT95/5 under the shock compression,is beneficial to reliability and miniaturization design of the explosive-ferroelectric power supply.In this paper,based on quasi static and dynamic uniaxial compression experiment?three point bending experiment and plate impact experiments,main contributions to transformation kinetics?constitute response and microcrack damage evolution etc,and also discussed the influences of polarization state,polarization direction and porosity.Major original works in the research are listed in details as follows:(1)Four kinds of PZT95/5 ferroelectric ceramics with different porosities were prepared.The quasi-static uniaxial compression experiments were carried out on PZT95/5 ferroelectric ceramics.The experimental results show that porous PZT95/5 ferroelectric ceramics exhibit obvious nonlinear deformation characteristics,which are mainly attributed to the interaction of domain switching and phase transformation.The mechanical properties of porous PZT95/5 decrease with the increase of porosity,and the micropores do not improve the toughness of PZT95/5 ferroelectric ceramics;(2)Based on the variation of the axial strain and transverse strain with axial stress,the effects of poling state and poling direction of PZT95/5 ferroelectric ceramics on the domain switching and phase transformation behaviors were explored.Domain switching occurs in both unpoled and Z-axis poled PZT95/5 ferroelectric ceramics,while domain switching in the Y-axis poled PZT95/5 ferroelectric ceramic are not observed.By means of strain decomposition analysis,it was proved that the domain switching and the phase transition process can be decoupled,and domain switching strain and phase transformation strain can be distinguished successfully.Compared with the Z-axis poled PZT95/5 ferroelectric ceramic,the unpoled PZT95/5 ferroelectric ceramic has a smaller critical stress of phase transformation,while the critical stress of the Y-axis poled PZT95/5 ferroelectric ceramics is bigger,which may be concluded that the domain switching behavior has a favor to the phase transformation process.(3)By using the ultra-high speed camera and digital image correlation(DIC)technique to measure the full-field strain in split Hopkinson pressure bar(SHPB)test,the high strain rate response of porous PZT95/5 was investigated.The apparent dynamic compressive strength enhancement of unpoled PZT95/5 in a SHPB test is caused by the strain-rate sensitivity.The critical stresses for domain switching and phase transformation increase with strain rate.(4)Based on the Instron universal mechanical and DIC technique,the effect porosity and position of prefabricated cavities on the crack propagation of PZT95/5 were investigated in three point bending experiments.The experimental results show the fracture strain of porous samples increases with the increase of porosity,whereas the fracture strength decreases with the porosity;The crack propagation has been obviously influence by prefabricated cavities which prefabricated by femto-second laser technique in different position in dense samples.(5)The experimental study of the shock response for porous PZT95/5 ferroelectric ceramics were performed under one-dimensional strain shock wave loading and by using one-stage light-gas gun and laser interference particle velocity measurement technique.The effects of shock loading rate and porosity on the free surface velocity profile response of porous PZT95/5 ferroelectric ceramics were obtained,and the relationship between the typical feature of free surface velocity and loading rate? porosity was revealed.(6)Based on the measured free surface velocity profile,by using of discrete element simulation,the damage evolution mechanism of porous PZT95/5 ferroelectric ceramics under plate impact loading was studied.The mechanism of free surface velocity profile was explored,and divided four stages: Elastic deformation,Failure ramp,Shock deformation and Hugoniot state.