Nonlinear mechanical response of PZT95/5 ferroelectric ceramics under high strain rate loading
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摘要: 采用添加造孔剂的方法制备了4种不同孔隙率的未极化PZT95/5铁电陶瓷。采用基于超高速相机与数字图像相关性方法的试样全场应变测量技术以及分离式霍普金森压杆（SHPB）技术，对多孔未极化PZT95/5铁电陶瓷进行高应变率单轴压缩实验研究。全场应变测量结果显示：轴向应变仅在试样中部分布较均匀，将该区域的平均应变作为应力-应变关系中的试样应变测量值较为合理，而由SHPB原理计算的试样应变值明显偏大，需要摒弃或修正传统的SHPB数据处理方法。通过波形整形技术实现了恒应变率加载，弱化了径向惯性效应的影响，揭示出多孔未极化PZT95/5铁电陶瓷的压缩强度具有显著的应变率效应。通过分析试样轴向应变和径向应变随着加载应力的变化，阐明多孔未极化PZT95/5铁电陶瓷的非线性变形行为的物理机制是畴变和相变共同作用，并发现畴变临界应力和相变临界应力都随着应变率升高而增大。保持加载应变率不变，讨论了孔隙率对多孔未极化PZT95/5铁电陶瓷动态力学行为的影响，发现随着孔隙率的升高，动态压缩强度呈非线性衰减，而畴变临界应力和相变临界应力则基本呈线性衰减。Abstract: In this study we fabricated four kinds of unpoled PZT95/5 ferroelectric ceramics in a range of different porosity levels by systematic additions of pore formers and investigated the high strain rate response of the unpoled PZT95/5 using the ultra-high speed camera and digital image correlation (DIC) technique to measure the full-field strain in a split Hopkinson pressure bar (SHPB) test. Based on the results of the full-field strain, we found that the strain distribution is uniform in the middle of the specimen and its average value as the strain of the specimen is more reasonable than the strain calculated from the traditional theory of SHPB. By using the pulse shaping technique to obtain an early constant strain rate, the effect of the lateral inertia confinement can be eliminated. The apparent dynamic compressive strength enhancement of the unpoled PZT95/5 in a SHPB test was observed to be strain-rate sensitive. Based on the variation of the axial strain and radial strain with axial stress, we attributed the nonlinear deformation mechanism of the unpoled PZT95/5 to the domain switching and phase transformation. The critical stresses for the domain switching and phase transformation increased with the strain rate. In addition, we discussed the influence of porosity in the high strain-rate response, and the results indicated that the dynamic compressive strength and the critical stresses for the domain switching and phase transformation of the unpoled PZT95/5 decreased with the increase of porosity.
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Key words:
- ferroelectric ceramics /
- high strain rate /
- porosity /
- domain switching /
- phase transformation
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图 1 具有不同孔隙率的未极化PZT95/5铁电陶瓷的SEM形貌
Figure 1. SEM micrographs of unpoled PZT 95/5 ferroelectric ceramics with different porosities
图 2 多孔未极化PZT95/5铁电陶瓷内微孔洞SEM图像
Figure 2. SEM image of spherical pore in porous unpoled PZT95/5 ferroelectric ceramics
图 7 不同方法得到的试样应变时程比较
Figure 7. Comparison of specimen's strain profiles obtained using different methods
图 8 不同应变率下试样的应力-应变曲线
Figure 8. Stress-strain curves of specimen at different strain rates
图 9 高应变率加载下应变率和应力时程曲线
Figure 9. Profiles of strain rate and stress for specimen under high strain rate loading
图 11 不同应变率下径向应变和轴向应变随轴向应力变化曲线
Figure 11. Variations of radial and axial strain with axial stress at different strain rates
图 12 归一化畴变临界应力与相变临界应力随应变率变化曲线
Figure 12. Normalized critical domain switching stress and phase transformation stress vs. strain rate
图 13 高应变率下4种孔隙率的未极化PZT95/5的应力-应变曲线
Figure 13. Stress-strain curves of unpoled PZT95/5 with different porosities at high strain rate
图 14 准静态和动态压缩强度与孔隙率的关系
Figure 14. Quasi-static and dynamic compressive fracture stress vs. porosity
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