No abstract

No abstract

The study of oral processing and specifically cutting of the food piece during mastication can lead towards optimization of products for humans or animals. Food materials are complex biocomposites with a highly nonlinear constitutive response. Their fracture properties have not been largely investigated, while the need for models capable of predicting food breakdown increases. In this study, the blade cutting and the essential work of fracture (EWF) methodologies assessed the fracture behaviour of starch-based pet food. Tensile tests revealed rate-dependent stiffness and stress softening effects, attributed to viscoplasticity and micro-cracking, respectively. Cutting data were collected for 5, 10 and 30 mm s −1 sample feed rates, whereas the EWF tests were conducted at 1.7, 3.3 and 8.3 mm s −1 crosshead speeds corresponding to average crack speeds of 4, 7 and 15 mm s −1 , respectively. A reasonable agreement was achieved between cutting and EWF, reporting 1.26, 1.78, 1.76 kJ m −2 and 1.52, 1.37, 1.45 kJ m −2 values, respectively, for the corresponding crack speeds. These toughness data were used in a novel numerical model simulating the ‘first’ bite mastication process. A viscoplastic material model is adopted for the food piece, combined with a damage law that enabled predicting fracture patterns in the product.

Large deformation and fracture properties of two types of starch gels were investigated through uniaxial compression, single edge-notched bend (SENB) and wire cutting experiments. Tests were performed at various loading rates and for various starch/powder concentrations (%w/w). It was found that starch gels exhibit rate independent stress-strain behaviour but show rate-dependent fracture behaviour, i.e. stress-strain curves at three loading rates are similar but fracture stress and fracture strain increase with increasing strain rate. This is rather unusual and interesting behaviour. SENB and wire cutting experiments also revealed ratedependent fracture behaviour and that the true fracture toughness (G c ) values increase with loading/cutting speeds and starch powder concentration. In addition, the G c values from wire cutting and SENB tests were in reasonable agreement. The wire cutting process was also studied numerically using finite element techniques. A nonlinear elastic constitutive relationship based on Ogden was used to model the starch gels and a frictionless condition was assumed at the wire-starch gel contact interface.A fracture criterion based on maximum principal strain was assumed for the prediction of the steady state cutting force.

No abstract