Development of a Microstructure-Based Finite Element Model of Thermomechanical Response of a Fully Metallic Composite Phase Change Material

Form-stable composite Phase Change Materials (C-PCMs), among which Al-Sn alloys, store/release heat during the transformation of one of the phases they are made of, without significant dimensional and shape changes. A microstructural based model of the thermomechanical behaviour of these materials can help to check their form-stability under various potential service conditions. The volume changes induced by melting/solidification of the low-melting Sn phase and different thermal expansion of solid Al and Sn can actually induce strains and stress fields during thermal cycles. A numerical simulation of a modelled Al-Sn C-PCM dilatometric test, a technique generally addressed toward the estimation of material thermal expansion, has been run and validated. The model describes the complex evolution of stress-strain fields and local plastic strains during the thermal cycle. The most critical conditions arise during cooling, after the completion of Sn solidification, at the highly stressed interface between Sn and Al phase. While at the end of a thermal cycle the overall shrinkage is minimal, the microscopic plastic strain remain locally. The phases properties and the representative microstructure are thus critical features for the development of a reliable model. The model could be used to consider repeated cycles and thermomechanical behaviour of C-PCMs.