He Hongliang

DISCHARGE OF PZT95/5 FERROELECTRIC CERAMICS UNDER TILTED SHOCK WAVE COMPRESSION

The current waveform of Ferroelectric ceramics PZT 95/5 depoling under tilted shock wave compression has been studied. An analytic model was established to analyze the effects of incident angle on the rising time, duration and peak amplitude of the depoling current. Experiments were conducted as well to confirm these effects. Results indicated that with the increasing of incident angle, the depoling current rises more slowly, the pulse duration becomes broader and the peak amplitude remains constant until the waveform decays into a triangular form.

Mechanism of the Pyroelectric Response under Direct-Current Bias in La-Modified Lead Zirconate Titanate Stannate Ceramics

Dielectric and pyroelectric properties of Pb0.97La0.02(Zr0.42Sn0.40Ti0.18)O3 ceramics are investigated as functions of temperature and dc bias field. Induced and intrinsic pyroelectric coefficients pind and p0 are calculated and analyzed. It is found that the sign, value and variation of the net pyroelectric coefficient p with increasing dc bias all are dominated by p0 under applied biases. Polarization and depolarization processes under dc biases are analyzed. Besides the contribution of pind, the diffuse and decreased pyroelectric response under dc bias compared with that of an identical field poled sample without dc bias is mainly attributed to the depolarization process under dc bias.

Damage evolution on dynamic tensile fracture of ductile metals

Dynamic tensile failure, e.g. spallation, of ductile metals is a complex phenomenon, due to its multiple tempo-spatial scales and structural levels involved on one hand, and due to its irreversible and nonlinear features as a non-equilibrium process on the other. Activated/Stimulated by tensile stress, non-uniform mesoscopic structures of materials evolve, leading to internal damage nucleation, growth, coalescence and final fracture, which consist the basic physical processes of dynamic tensile failure of ductile metals. Damage evolution on dynamic tensile fracture of ductile metals has been reported elsewhere, however, our ability to understand the mechanism of damage evolution in micro-scale and to accurately predict fracture in macro-scale is still limited. In this paper, we present investigations on macroscopic response, microscopic mechanism and physical models of dynamic tensile failure, based on our previous works. Current difficulties and challenges encountered when studying such a complex, multi-scale phenomenon are also discussed.