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Title: Mechanical characterisation of confectionery wafers
Author: Mohammed, Idris Kevin
ISNI:       0000 0004 2702 8361
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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The aim of this research is to model the deformation and fracture behaviour of wafers used in chocolate confectionery products. Compression and bending tests showed that the mechanical behaviour of the wafer was characteristic of a brittle foam. The wafer sheet was examined with a Scanning Electron Microscope (SEM) to determine the wafer dimensions and to observe the internal microstructure. These images showed that the core of the wafer sheet was more porous than the dense skins of the wafer. An analytical model was developed to calculate the modulus of the wafer core and skin sections. A finite element (FE) model using a simple repetitive geometry of the wafer was implemented. The ‘crushable foam’ material model was the closest fit to the wafer deformation under compression and was applied to the core of the wafer. An alternative FE model was proposed, which used the actual complex architecture of the wafer. To attain the wafer architecture, X-ray Microtomography (XMT) was used on a sample to produce a stack of image slices which were reconstructed as a 3D volume. The microstructure of the 3D volume was characterised and then meshed with tetrahedral elements for finite element analysis. The cell walls of the model were given a linear elastic material model and a damage criterion to simulate the fracture of the cell walls. In-situ SEM and XMT experiments were conducted which allowed the deformation and fracture of the wafer sheet to be observed simultaneously as the global mechanical response was recorded. The FE model of the complex architecture was able to predict the deformation behaviour of the wafer in compression. In the future, the model can be used to simulate the cutting process of the wafer, allowing the effect of parameters such as cutting speed and blade dimensions to be determined efficiently.
Supervisor: Charalambides, Maria ; Williams, Gordon Sponsor: Nestlé
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral