Modeling solidification cracking: A new perspective on solid bridge fracture

Solidification cracking is a longstanding and serious problem in metallurgical engineering that is encountered during casting, welding, and additive manufacturing. Extensive research has been conducted on the cracking susceptibility associated with solidification paths, microstructural effects, and thermal conditions, but it remains highly challenging to precisely predict and evaluate the solidification cracking, especially its solid bridging and grain size dependence. In this study, a new theoretical model based on solid bridge fracture is proposed for modeling solidification cracking. The occurrence of cracking depends on competition between thermal stress accumulation and solid-bridge strength development, which is fundamentally distinct from existing models in which the occurrence of cracking depends on liquid feeding. A crack-like structure is utilized to determine the thermal stress at a dendrite root, and demonstrates the absence of stress singularity in a solidifying crack. Grain features are incorporated to show that grain refinement effectively inhibits cracking by lowering the rate of accumulation of thermal stress. Hence, the cracking susceptibility is quantified based on grain size distributions. Numerical analyses of binary aluminum alloys validate the proposed model and provide a rational interpretation of reported experimental results in terms of cracking susceptibility, grain size effects, and cooling rate effects. This study presents and validates one of the first solid-bridge fracture-based solidification cracking models, and thus provides a new perspective to support investigation of solidification cracking.