Physical Chemistry of Foods

17 Soft Solids Many foods can be considered soft solids: bread, cheese, margarine, peanut butter, meat, several fruits, jam, pud ...

flexible polymer chains that are cross-linked and (b) aggregated particles. Closely packed systems, in which deformable particle ...

where thePoisson ratiomis given by m¼ 1 2 ð 1
dlnv de Þð 17 : 2 Þ The second term between parentheses is a measure of the chan ...

cross section perpendicular tox, andDxis the deformation of the bond between two structural elements; dFinis the change in the i ...

Figure 17.2), but it makes more sense to determine the full deformation curve. Most solid foods eventually fracture upon increas ...

Thespecific work of fractureof the materialWfr(in J?m
^3 ) can be called ‘‘toughness.’’ It is given by Wfr¼ Zefr 0 sde ð 17 : 5 ...

affected. Just plotting force against linear deformation can readily lead to wrong conclusions. For very small strains, as appli ...

It is often (implicitly) assumed that the modulus of a material is a measure of its strength. Figure 17.4 shows that this can be ...

deformation is permanent, and a second deformation (broken line) leads to significantly smaller stresses. Frame (d) is a rather ...

stress in the material can relax before a considerable strain is attained; this means thatscan not attain a high value. If defor ...

Inhomogeneity. For large deformation, most rheological relations, including time scale dependence, can be quite different from w ...

the half cone angleyand of the cone massmaffect the value ofLpfor a givensy value? What are the advantages of the test? Answer A ...

fracture is generally visible. In soft solids the situation is more complicated, since fracture is generally preceded by local s ...

sharper tip of the notch. Supposing that the notch is 100mm deep and thatR ¼10 nm,sloc/sovwill equal about 200. A well-known exa ...

must be taken into account. Fracture means an increase in surface area and hence an increase in surface free energy, and this en ...

blunted[i.e., a larger value ofRin Eq. (17.7)], which means that the stress concentration becomes smaller and a higher overall s ...

Time-Dependent Fracture. (This is not an established term.) In this regime, which is frequently observed in soft-solid foods, th ...

Several soft solids showyieldingat low and fracture at high strain rates, although the critical strain rate for fracture may var ...

in tension. The two samples of cheese discussed give good examples, illustrated in Figure 17.8c. The ‘‘short’’ sample (1) fractu ...

It follows that the curve will decrease more steeply with increasingLfor a smaller value ofL^0 cr. The fracture propagation stre ...