Analytical solution for the stress field of hierarchical defects: multiscale framework and applications

Hierarchical defects are defined as adjacent defects at different length scales. Involved are the two scales where the stress field distribution is interrelated. Based on the complex variable method and conformal mapping, a multiscale framework for solving the problems of hierarchical defects is formulated. The separated representations of mapping function, the governing equations of potentials, and the stress field are subsequently obtained. The proposed multiscale framework can be used to solve a variety of simplified engineering problems. The case in point is the analytical solution of a macroscopic elliptic hole with a microscopic circular edge defect. The results indicate that the microscopic defect aggregates the stress concentration on the macroscopic defect and likely leads to global propagation and rupture. Multiple micro-defects have interactive effects on the distribution of the stress field. The level of stress concentration may be reduced by the coalescence of micro-defects. This work provides a unified method to analytically investigate the influence of edge micro-defects within the scope of multiscale hierarchy. The formulated multiscale approach can also be potentially applied to materials with hierarchical defects, such as additive manufacturing and bio-inspired materials.

Microstructure and Properties of Cast Iron Using Chromizing Process

Cast iron was chromized by solid powder method at 1000°C. Micro-morphology and microstructure of chromized alloy layer and cast iron matrix were analyzed, their hardness, elements distribution and corrosion resistance were studied in depth. The analysis results revealed that the chromized carbide-chromium layer grew well on cast iron surface, which was smooth and free from macroscopic defect. Campared with the hardness of original cast iron matrix, the hardness of the chromized alloy layer has been improved by 3.5 times, which was as high as 918.8 HV. And the corrosion resistance of the chromized alloy layer has been greatly improved. The relative corrosion rate of the original cast iron matrix was 2.2 times that of the chromized alloy layer according to their polarization curves.