孔边裂纹塑性应变疲劳扩展试验研究

简介了循环J积分ΔJ*path体系,以16MnR钢单边椭圆孔边裂纹试件进行了6种循环应力比的恒幅应变疲劳裂纹扩展试验,采用材料应变疲劳循环加载条件下的应力-应变关系,通过弹塑性有限元素法计算ΔJ*path参量,研究了孔边高应变区裂纹塑性应变疲劳扩展规律。结果表明：ΔJ*path能够作为缺口高应变区裂纹塑性应变疲劳扩展的控制参量,与裂纹扩展速率da/dN之间的指数关系,可通过相同材料的标准试件应力疲劳裂纹扩展由Paris公式与ΔJ*path=ΔK2/E转换得到。     

Tunable Electromagnetic Cloaking by External Field

Electromagnetic cloaking based on the scattering cancellation method have been reviewed. The possibility of designing the tunable electromagnetic cloaking is analytically suggested with a single cloak composed of homoge- neous materials, including semiconductor, superconductor, ferrite and ferroelectrics by using Mie scattering theo- ry. The simulated results demonstrate that the cloaks with these homogeneous materials can drastically reduce the total scattering cross sections of the cloaked system by using the finite element method. These cloaking frequencies can be controlled by external field through tuning the permittivity or permeability of these materials by the applied field, such as temperature, magnetic field and electric field. These may provide some potential ways to design tunable cloaking with considerable flexibility.