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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.

There was an error in data reduction, resulting in incorrect values for the normal stress differences N 1 and N 2 shown in Figs. 7-10, and the corrected figures are shown here. In particular, the algebraic sign of N 1 is changed, as are the relative magnitudes of N 1 and N 2 . The negative values of N 1 for these non-shear-thickening suspensions are larger in magnitude than those reported by other workers, but both N 1 and N 2 are in general agreement with the accelerated Stokesian Dynamics calculations of Sierou and Brady [1].FIG. 7. Normal stress differences N 1 and N 2 of monodisperse suspensions at volume fractions of 0.4 and 0.5 for both 10 and 52.6 µm particles as functions of (a) shear rate and (b) shear stress (Insets are the same data on a semilog scale). SYNOPSISWe have measured the viscometric functions of mono-and bimodal non-colloidal suspensions of PMMA spheres in a density-matched aqueous Newtonian suspending fluid using parallelplate and cone-and-plate rheometry for particle volume fractions in the range 0.20 to 0.50.Cone-and-plate normal stress measurements employed the method of Marsh and Pearson, in which there is a finite gap between the cone tip and the plate. The monodisperse suspensionsshowed an unexpected particle size dependence of the viscometric functions, with the viscosity increasing with decreasing particle size. Normal stresses were very small in magnitude and difficult to measure at volume fractions below 0.30. At higher concentrations, N 2 was negative and much larger in magnitude than N 1 , for which the algebraic sign was positive over most of the shear rate range for the monodisperse suspensions but indeterminate and possibly negative for the bimodal suspensions. The normal stresses were insensitive to bidispersity when plotted as functions of the shear stress at each volume fraction.

a b s t r a c tAnalytical solutions are derived for the compression of cylinders with bonded surfaces and with Coulomb friction conditions at the interfaces. The bonded solution assumes that the radial displacement is linearly dependent on radius which leads to simple forms. These are compared with FE data and the apparent modulus is found to be within about 8% for the whole range of aspect ratios (10 À2 -10 3 ), and thus degrees of constraint for the cylinders. The apparent moduli are shown to be strong functions of both m and l and the solutions thus provide schemes for finding both parameters experimentally using inverse methods. This is demonstrated by using the FE results as such data to explore how many tests, and what aspect ratios, are needed. Some preliminary experimental results are also given.

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