Compression behaviour of bread crumb up to densification investigated using X-ray tomography and finite element computation

• X-ray tomography reveals residual porosity of 24% after severe crumb compression.
• Major structural changes appear at two load levels 6% and 60%.
• Poisson's expansion does not follow exclusively porosity reduction kinetics.
• Minor mechanical anisotropy is associated with air content reduction.

We propose to shed more light on deformation and structural changes of bread crumb submitted to severe compression. The analysis of such behaviour refers to an adequate approximation of human mastication of airy and spongy products. X-ray microtomography is coupled to mechanical testing of soft bread characterised by a fine cellular architecture. Structural attributes, namely, relative density, cell size and cell wall thickness distributions are determined using image analysis and related to the load level. Kinetics of pore shrinkage is also studied depending on its shape and size. Finite element model is developed to assess mechanical anisotropy induced by deformed airy structure. Results show that the pore content decreases from 72% to 24% after more than 89% of reduction in height. An irregular trend of pore shrinkage is also revealed which depends on deformation stages. Finite element results show a heterogeneous stress distribution but only a minor mechanical anisotropy is revealed as a result of the deformed airy structure.