Bridging the Atomistic Deformation Mechanisms to the Microscopic Adhesive-to-Cohesive Fracture at Ice-Metal Interfaces

A fundamental study was conducted by combining multi-physics, multi-scale simulation and experimentation, i.e., coarse-grained modeling of water, novel concurrent atomistic-continuum modeling of metallic materials, and experiments in a unique Icing Research Tunnel facility, to elucidate the underlying physics pertinent to adhesive-to-cohesive interface fracture in ice-metal material systems.  More specifically, a comprehensive investigation was conducted to characterize grain size distribution together with an identification of the most possible grain boundaries (i.e., GBs) in polycrystalline ice and their dependences on cooling rates, chemical environments, and substrate roughness. A concurrent atomistic-continuum (CAC) model of crystalline solids was developed to analyze the stresses induced by the micrometer-level dislocation pileup at an atomically structured interface for the first time to address the challenge when using the classical continuum theory-based Eshelby model for estimating the internal stresses near a buried interface in materials. The material surface microstructure and the environmental chemistry were correlated with the ice nucleation/growth rate, and ice grain size/misorientation angle distribution to support the development of novel anti-icing coatings to be applied on many engineering infrastructures in cold regions. A processing-structure-property-mechanism relationship was established for the ice-substrate system to provide support in the search for promising anti-icing materials for the optimal designs of de-icing strategies.  In coordinating with theoretic modelling and numerical simulations, a series of experimental studies were performed to quantify the dynamic ice accretion and crystallization rate upon the impact of supercooled water droplets on test surfaces with different surface wettability. The measurement results were used to validate/verify the predictions of the theoretic models and the numerical simulations. By leveraging the unique icing research tunnel of Iowa State University (i.e., ISU-IRT), a comprehensive experimental campaign was also conducted to quantify the effects of the thermal conductivity of the substrate (i.e., metal vs. polymeric materials) on the dynamic ice accretion and associated unsteady heat transfer processes.

This research project advances the science of interfacial mechanics by identifying the fundamental mechanisms for the adhesive-to-cohesive fracture in an ice-metal material system; correlate an ice-metal interface structure with its ice adhesion strength; and support the search of more efficient de-icing strategies that consume far less power than existing approaches.  The new findings will also enable more rational designs of new materials/surfaces that either inhibit or enhance ice adhesion, with implications for a wide range of safety-critical infrastructures operating in arctic and cold weathers, supporting the NSF Big Idea on Navigating the New Arctic (NNA) through impact on the design and engineering of civil infrastructure for an increasing marine commerce in the Arctic.

As an important component of this program, a new “aircraft icing and demo experiments” module was developed and integrated into the existing undergraduate/graduate laboratory courses offered at Iowa State University to augment fundamental principles introduced in classes and to stimulate students’ interests in thermal-fluid sciences. 6 graduate students and 5 undergraduate students (including 3 URM students) were recruited to work on this research project. Outreach activities for local K-12 schools were also carried out to impart K-12 teachers and students, and by extension, the public at large, a greater awareness about the recent advances in aerospace engineering and technology and their importance to our daily lives.