Coefficient of viscous traction

When a material is subjected to a tensile or compressive stress, Eqs. (5.63) through (5.74) should be developed with the shear modulus, G, replaced by the elastic modulus, E, the viscosity, rj, replaced by a quantity known as Trouton s coefficient of viscous traction, k, and shear stress, r, replaced by the tensile or compressive stress, a. It can be shown that for incompressible materials, k = 3r], because the flow under tensile or compressive stress occurs in the direction of stress as well as in the two other directions perpendicular to the axis of stress. Recall from Section 5.1.1.3 that for incompressible solids, E = 3G therefore the relaxation or retardation times are k/E. 

Trouton FT (1906) The coefficient of viscous traction and its relation to that of viscosity. Proc R Soc A77 426-440... 

In the last five columns we provide the values of the interfacial mobility parameter n (here n corresponds to power in t F R ), the predicted ratio of the surface viscosity coefficient ri and the critical collapse distance 6, the predicted individual values of ri and 6, and, where available, values of r] = K +e or obtained by direct methods. In the latter cases, the r data were obtained from a drop deformation method (17,18), and the e data from tests in a viscous traction instrument (20). 

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