地磁环境下结构变形引起的扰动磁场

基于磁弹性相互作用的线性化理论，针对地磁环境特点，忽略磁场对结构位移的影 响而仅考虑位移对磁场的耦合作用，通过将位移梯度引入变形后界面外法线矢量方 法，给出了变形引起的扰动磁场计算的定解场方程和界面衔接条件，并计算了符拉 芒问题的变形扰动磁场. 结果表明，变形扰动磁场完全取决于位移梯度在界面外法 向上的投影；扰动场强与外力成正比；空气中扰动磁场的法向强度和切向强度分布 特征明显不同，法向强度在力作用点对称分布，并且在 力作用点处存在奇点；切向强度则呈反对称分布，在力作用点处发生突变.

PERTURBED MAGNETIC FIELDS GENERATED BY DEFORMATION OF STRUCTURES IN EARTH MAGNETIC FIELD

Development of magnetism based non-destructive test (NDT) technologies requires quantitative relations between deformation,stress,damage or fracture of structures and their induced magnetic field which can be measured as indicators to assess integrity of the structures.Based on linearized magnetoelastic theory, the perturbed magnetic fields induced by mechanical stress and deformation in steel or other ferromagnetic structures working in the environment of the Earth magnetic field,are investigated theoretically in this paper. Governing equations and boundary conditions to determine the perturbed fields are derived.The effect of mechanical deformation on the magnetic fields is taken into account by coupling structural displacement into continity conditions of the perturbed magnetic field on the boundary of the structure.When the applied magnetic field is weak,such as the Earth's magnetic field,the effect of magnetic fields on structural deformation can be neglected.This greatly simplifies the coupling equations of magnetomechanical interactions.It shows that the normal projection of displacement gradient on the structure boundary plays a dominating role in the perturbed magnetic fields. As an example,the perturbed field of a half-plane magnetized structure caused by a point force is calculated by the Fourier transform method.The calculated magnetic intensity component normal to the boundary of the structure assumes a symmetric distribution about the point where the forces is acted and reaches its maximum at that point while the component tangent to the boundary is asymmetric and inverses its direction sharply at that point.The magnetic flux density of the perturbed fields is proportional to the magnitude of the applied force.These features provide a possible way for NDT technologies.