Cooking crystalline candies and the ductile to brittle transition in concentrated suspensions

TL;DR

This paper investigates the ductile to brittle transition in concentrated suspensions, exemplified by candies, revealing how increasing solid fraction causes a transition from fluid to ductile and then brittle states, supported by experiments and simulations.

Contribution

It demonstrates the ductile to brittle transition in candies and suspensions, linking it to solid fraction and boundary conditions, with experimental and simulation insights.

Findings

Transition from fluid to ductile and brittle states with increasing solid fraction

Similar behavior observed in both candies and calcite suspensions

Boundary conditions significantly influence the observed phenomena

Abstract

The existence and origin of the ductile to brittle transition in non-Brownian suspensions and pastes is underexplored despite the ubiquity of such materials in practical applications. We demonstrate the phenomenon in candies of sugar crystals in a water-protein-fat matrix prepared by boiling a sugar-cream-butter mixture (known as 'fudge' in some countries). As cooking time or final cooking temperature increases, we observe a transition from a fluid to a ductile solid, then to a brittle solid that abruptly fractures in compression. We propose that this is driven by rising solid sugar crystal volume fraction, and indeed find the same sequence of behaviour in a suspension of non-Brownian calcite particles as the solid fraction moves from frictional jamming to random close packing. Particle-based simulations reveal the sensitivity of the observed phenomenon to boundary conditions.