Analytical and Integrative Aspects of the Stress-Strain-Time Problem

The foremost problem of Rheology concerns the relation between stress, strain and time in complex materials. There are two ways in which the behaviour of a complex body may be expressed in terms of the Hookean and Newtonian prototypes: the analytical approach regards the material as a physical mixture of ideal Hookean and Newtonian components whereas the integrative view considers the behaviour as intermediate, molecular conditions being regarded as too complex to justify the useful construction of idealised models. Psycho-physical experiments have shown the advantages of the latter approach in studying those industrially important rheological concepts, such as `firmness', which cannot be expressed in dimensionally simple terms. It is unjustifiable to insist on the exclusive use of either method of approach: indeed it is probable that further experimentation will lead to their effective synthesis.