电场、残余应力和介质对PZT-5H铁电陶瓷压痕裂纹扩展的耦合作用

COUPLING EFFECT OF ELECTRIC FIELD, RESIDUAL STRESS AND MEDIUM ON PROPAGATION OF INDENTATION CRACKS IN A PZT-5H CERAMIC

通过在硅油中加恒电场实验,研究了PZT-5H铁电陶瓷Vickers压痕裂纹的扩展行为,探讨了电场、残余应力以及介质间的耦合作用.结果表明,残余应力不足以使压痕裂纹在硅油中发生滞后扩展,只有外加恒电场E>0.2 kV/cm,电场、残余应力和介质的耦合才能使压痕裂纹在经过一个孕育期tp后发生滞后扩展.由于有效应力强度因子随裂纹扩展而下降,故压痕裂纹扩展10-30 μm后就将止裂.压痕裂纹在硅油中滞后扩展的门槛电场强度EDp=0.2 kV/cm.如外加电场大于临界电场Ep=5.25 kV/cm,电场和残余应力的耦合可使压痕裂纹瞬时扩展;保持恒电场,裂纹能继续扩展,然后止裂.如外加电场大于12.6 kV/cm,不需要残余应力协助,电致裂纹也能在光滑试样上形核、长大、连接,导致试样断裂.试样发生电致滞后断裂的门槛电场EDF=12.6 kV/cm,发生瞬时断裂的临界电场EF=19.1 kV/cm.

The experiment of a coupling effect on propagation of unloaded indentation cracks in a PZT-5H ceramic shows that residual stress itself is too small to induce delayed propagation of the indentation crack in silicon oil. If applied constant electric field is larger than 0.2 kV/cm, the coupling of electric field, residual stress and silicon oil can cause delayed propagation of the crack after incubation time, but the crack will arrest after propagating for 10-30 mum because of decrease of the stress intensity factor with increasing the crack length. The threshold electric field of delayed propagation of the crack in silicon oil is E-DP = 0.2 kV/cm. If the field is larger than the critical field of 5.25 kV/cm, coupling of the electric field and residual stress is enough to cause instant propagation of the crack and propagates continuously, then arrests if under the constant electric field. If the applied field is larger than 12.6 kV/cm, even if no residual stress, the electric field itself can make many cracks initiate, grow and connect in a smooth specimen, resulting in delayed failure. The threshold electric field of delayed failure of a smooth specimen in silicon oil is E-DF = 12.6 kV/cm and the critical electric field for instant failure is E-F=19.1 kV/cm.