Viscoelasticity stress birefringence

Another method to calculate viscoelastic quantities uses measurements of flow birefringence (see Chap. 10). In these measurements, two quantities are determined as functions of the shear rate y the birefringence An and the extinction angle y. The following relationships exist with the stress tensor components ... 

Humbert C, Decruppe IP (1998a) Flow birefringence and stress optical law of viscoelastic solutions of cationic surfactants and sodium salicylate. Eur Phys J B 6(4) 511-518... 

Figure 13.15 shows the birefringence behavior of SPS against the applied stress during the melt extrusion. From the slope, the stress-optical coefficient is calculated to be -9.6 x l(F Pa. Tlie study of the dynamic viscoelasticity and the dynamic birefringence measurements demonstrated that a similar value (-9.5 x KUPa ) is obtained for the stress-optical coefficient of SPS, and this value is almost twice as much of that of APS (-4.7 x l(F Pa ) obtained by the same measurements [13]. 

The classical viscoelastic properties are the dynamic shear moduli, written in the frequency domain as the storage modulus G ( y) and the loss modulus G a>), the shear stress relaxation function G t), and the shear-dependent viscosity j (k). Optical flow birefringence and analogous methods determine related solution properties. Nonlinear viscoelastic phenomena are treated briefly in Chapter 14. 

The present study attempted to numerically predict residual stress and birefringence in injection molded PC specimens with different thickness, 2.0mm and 6.5mm. Numerical simulations have been done based on a viscoelastic fluid model and commercial software MOLDFLOW by three dimensional finite element methods. The former is used to compute flow-induced residual stress, while the latter for combined residual stresses, including thermal-induced and flow-induced stresses. Effects of processing conditions on the residual are considered by the numerical simulations. As for 2.0mm PC injection molded parts, the predicted residual stresses of viscoelastic model show quite precise in accordance with experimental results. But for 6.5mm PC specimen, Moldflow simulated results have less error. 

In the present work, viscoelastic numerical simulation of birefringence and gas/polymer interface distribution for GAIM is presented and compared with experimental data obtained on polystyrene moldings. A nonlinear constitutive equation proposed by Leonov [7] was employed to describe the development of shear and normal stresses. Afterward, the birefringence was calculated from stresses using the stress-optical rule [8]. 

The thermal birefringence was calculated based on a linear viscoelastic and a photoviscoelastic constitutive equation as given in [7] along with a measured stress- and strain-optical coefficient functions [8]. For a onedimensional quenching problem... 

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