Oldroyd B, and not A?

We examine Oldroyd’s 1950 paper On the Formulation of Rheological Equations State (Oldroyd, 1950) in which he introduced upper and lower convected time-derivatives, along with Oldroyd-A Oldroyd-B model fluids. Those developments are placed context prior ideas his own subsequent papers on constitutive equations. The choice between A B models is addressed by looking at micro-structural studies, finding that something appropriate. Finally some refinements discussed terms elastic-dumbbell model.