flexible polymer chains that are cross-linked and (b) aggregated
particles.
Closely packed systems, in which deformable particles make up by far
the largest volume fraction, whereby they deform each other. The
interstitial material can be a liquid or a weak gel.
Cellular materials. Most vegetable tissues are in this category. They are
characterized by connected, fairly rigid, cell walls, enclosing a
liquidlike material. Several man-made cellular materials contain
gas-filled cells.Not all soft solids fit in this classification, e.g., meat and some types of
cheese, and intermediate types occur.
Mechanical and other properties of some fairly simple soft solid
materials will be discussed.
17.1 RHEOLOGY AND FRACTURE
Mechanical properties are essential attributes of soft solids, and this
concerns primarily consistency during handling or eating. Moreover,
physical stability often depends on these properties. Basic aspects of
rheology are discussed in Section 5.1.3. This section is primarily about large
deformation, including the phenomena of yielding and fracture.
17.1.1 Rheology of Solids
Elastic Moduli. A modulus is defined as the ratio of stress over
strain (relative deformation); see Figure 5.8. There are various modes of
deformation, as illustrated in Figure 17.1, corresponding to various types of
modulus. Important types are
G¼shearmodulus;g¼shear strain.
Eu¼Young’s modulus oruniaxial elongationalmodulus;eu¼uniaxial
elongational strain.
Eb¼biaxial elongationalmodulus;eb¼biaxial elongational strain.Figure 17.1c illustrates that uniaxial compression (vertical in this case) leads
to biaxial extension in the directions perpendicular to the compression.
The various moduli are related to each other. For instance,
Eu¼ 2 Gð 1 þmÞ
Eb¼ 4 Gð 1 þmÞð 17 : 1 Þ