Modelling deformation and fracture in confectionery wafers

Idris K. Mohammeda, Maria N. Charalambides , J. Gordon Williams , John Rasburn - Mechanical Engineering Department, Imperial College London, South Kensington, London ; Nestec York Ltd., Nestlé Product Technology Centre York

The aim of this research is to model the deformation and fracture behaviour of brittle wafers often used in chocolate confectionery products.

Three point bending and compression experiments were performed on beam and circular disc samples respectively to determine the ‘apparent’ stress-strain curves in bending and compression. The deformation of the wafer for both these testing types was observed in-situ within an SEM. The wafer is modelled analytically and numerically as a composite material with a core which is more porous than the skins. X-ray tomography was used to generate a three dimensional volume of the wafer microstructure which was then meshed and used for quantitative analysis. A linear elastic material model, with a damage function and element deletion, was used and the XMT generated architecture was loaded in compression. The output from the FE simulations correlates closely to the load-displacement deformation observed experimentally.

How Amira-Avizo Software is used

A CT system was used to scan the wafer and produce a stack of image slices. They were then used to generate a 3D volume of the wafer microstructure using Avizo software. With this virtual wafer, it was possible to accurately determine the porous volume fraction of the overall wafer and the porosity distribution throughout the wafer. The reconstructed 3D volume was meshed with tetrahedral elements and then exported to the finite element software, Abaqus, to perform a quantitative analysis. A static in-situ XMT compression test was performed to characterise the three dimensional deformation of the wafer.