The Mixed-Mode Fatigue Crack Propagation Model of Piezoelectric Materials Under Electric Fatigue Loading by the J_(k)-Integral

The electric fatigue load has a significant effect on the crack propagation behavior and failure life of piezoelectric materials and devices. In this paper, an electrical mixed-mode fatigue crack propagation model for piezoelectric materials is proposed based on the piezoelectric J_(k)-integral theory. The crack initiation, propagation, and life prediction criteria of piezoelectric materials under electric fatigue loading are given by this model, and the finite element simulation model is established to study the electrical mixed-mode crack propagation behavior of piezoelectric structures. Meanwhile, the electrical mixed-mode fatigue crack propagation model is applied to the fatigue crack propagation behavior of a piezoelectric typical defective structure, the crack–hole interference model. The mixed-mode crack propagation, fatigue life, and the interference behavior between the crack and hole at various hole locations of the crack–hole interference model are well recognized by this model. The crack propagation behavior under different electrical load intensities is also considered. The results show that the hole in front of the crack tip inhibits crack propagation to a certain extent, and the strength of electrical load affects the fatigue life of piezoelectric materials and structures. Therefore, the proposed electrical mixed-mode fatigue crack propagation model provides a reference for predicting the mixed-mode fatigue crack propagation behavior and fatigue life of piezoelectric structures under electric fatigue loading.

FURTHER INVESTIGATION OF THE J_2-INTEGRAL IN BIMATERIAL SOLIDS

The J_2-integral induced from the interface of bimaterial solids(J_2^(interface))is stud- ied by numerical method.First,the effect on the J_2-integral induced from the interface is very significant in bimaterial solids,which is inherently related to that induced from the subinterface cracks.Moreover,it can be concluded that either the first or the second component of the J_k- vector is always equal to zero when the contour encloses both the cracks and the whole interface in bimaterial solids.Secondly,it can also be concluded that the interface does produce significant effect on the J_2-integral induced from the subinterface cracks(J_2^(sub))in bimaterial solids.This effect depends on the geometry of the crack arrangement,which is corresponding to the different interaction effect among the cracks and the interface.Moreover,the interface effect on the J_2^(sub) can be neglected when the distance from the crack center to the interface is large enough,which reveals that the bimaterial solids can be regarded as homogenous solids in fracture analysis when the subinterface crack is far enough from the interface.Three examples are given in this paper.

沙利度胺下调JNK信号通路抑制肺纤维化大鼠Ⅰ型胶原蛋白的过度表达

目的探讨沙利度胺抑制肺纤维化大鼠I型胶原蛋白的过度表达，从而减轻博莱霉素诱导的大鼠肺间质纤维化的机制。方法将90只健康雄性W[star大鼠随机分为对照组（N组）、模型组（M组）、沙利度胺组（T组）、SP600125组（SP组）和沙利度胺＋SP600125组（T＋SP组）。气管内滴注博莱霉素（BLM）5mg／kg生理盐水诱导肺纤维模型，于造模当日起，各组给予相应药物，第7、14、28天处死大鼠，取肺组织行苏木素一伊红（HE）染色和Masson染色，光镜下观察肺泡炎和肺纤维化程度；碱水解法检测肺组织羟脯氨酸（Hyp）含量；免疫印迹法（Westernblot法）、实时荧光定量PCR法检测肺组织中c—jun氨基末端激酶（JNK）及I型胶原蛋白表达水平。结果M组第7天肺泡炎性程度最严重，第28天形成显著肺纤维化，Hyp含量于第28天达高峰，其p—JNK、I型胶原蛋白含量与对照组比较均明显升高（F=277．87、472．51，均P〈0．01）；T组、SP组和T＋SP组各时间点肺泡炎和纤维化程度均低于M组，p-JNK、I型胶原蛋白含量亦低于M组（F=14．77、61．59、101．73，均P〈0．01；F=10．33、79．12、57．48，均P〈0．01）；SP组P—JNK含量与T＋SP组比较差异无统计学意义。结论沙利度胺可能通过下调JNK信号通路抑制肺纤维化大鼠I型胶原蛋白的过度表达，从而减轻大鼠肺间质纤维化。