Determination of large deformation and fracture behaviour of starch gels from conventional and wire cutting experiments

Abstract

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.

Fracture investigation in starch-based foods

“…Moreover, no literature is found on the comparison of the EWF with the orthogonal cutting as methods of measuring toughness. The use of toughness as an input material parameter in FE analyses has been discussed [9][10][11][12][13], but this has never been implemented in modelling chewing. In this work, the fracture toughness of starch-based products is evaluated via the EWF and cutting methods.…”

“…In addition, two relaxation tests were conducted via loading up to the strains of 0.06 and 0.08 (0.01 s 21 rate), which were then held constant, whereas the stress decay was recorded for 30 min. Stress relaxation experiments are widely used in time-dependent materials [9,[11][12][13], and here they served in increasing accuracy in modelling the time dependency.…”

On modeling the large strain fracture behaviour of soft viscous foods

“…Yet, these were limited to a linear elastic hard food response upon a simple bite geometry (Agrawal and Lucas 2003;Agrawal et al 1997). Recent developments include complex hyperviscoelastic food material models used to relate mechanical properties to sensory attributes and breakdown behaviour Charalambides et al 2002;Goh, Charalambides, and Williams 2005;Gamonpilas, Charalambides, and Williams 2009). These material constitutive laws were fed into Finite Element (FE) models of soft food separation, in the form of wire cutting and blade indentation (McCarthy, Annaidh, and Gilchrist 2010;Gamonpilas, Charalambides, and Williams 2009;Goh, Charalambides, and Williams 2005).…”

“…Recent developments include complex hyperviscoelastic food material models used to relate mechanical properties to sensory attributes and breakdown behaviour Charalambides et al 2002;Goh, Charalambides, and Williams 2005;Gamonpilas, Charalambides, and Williams 2009). These material constitutive laws were fed into Finite Element (FE) models of soft food separation, in the form of wire cutting and blade indentation (McCarthy, Annaidh, and Gilchrist 2010;Gamonpilas, Charalambides, and Williams 2009;Goh, Charalambides, and Williams 2005). However, these techniques postulate a predefined fracture path (Vandenberghe et al 2017), which is certainly not the case for oral (Skamniotis et al 2016) and gastrointestinal breakdown (Cleary et al 2015).…”

Fiber-reinforced tough hydrogels

“…These hybrid gels consist of a covalently cross-linked polyacrylamide (PAAm) network and an ionically cross-linked alginate network, and can attain fracture energies as large as 9000 Jm -2 . The need for a tough composite matrix is illustrated graphically in Figure 1, where we use a metal wire to cut through two different types of hydrogels, a standard technique for measuring the fracture toughness of foods and soft gels [20,21]. Two examples are shown: (1) a brittle alginate gel and (2) a tough alginate-polyacrylamide hybrid hydrogel.…”