On modes and criteria of ABS melt failure in extension

Melt failure of a commercial ABS polymer in uniaxial extension over ranges of elongation rate ((e)\dot] = 0.01 - 1.0 s ^{- 1}\dot \varepsilon = 0.01 - 1.0\,{\rm s}^{ - 1} ) and temperature (140-200 °C) was investigated. Four methods of experimental and numerical calculation for determination of modes and criteria of melt failure in uniaxial extension were investigated: 1) visual observation of necking; 2) visual observation of non-uniform flow during stress relaxation after cessation of steady elongation; 3) calculation of the Considère criterion from the measured elongational stress-strain curve; 4) numerical calculation of inflection point (‘C²/‘)²=0) from the tensile stress-strain curve. In addition, under higher Deborah number conditions the critical Hencky strains at Considère criterion were calculated using PSM model parameters (! and #) and were compared with those obtained from the measured elongational stress-strain curve. The relationship between these failure modes is discussed in terms of rheological properties of the polymer, putting emphasis on the relationship with the thermoforming process. The Considère criterion appears to be the most effective indicator of the non-uniform deformation of ABS melt in uniaxial extension under conditions where cohesive fracture does not occur. The rheological properties such as elongational viscosity, strain hardening and/or strain softening, and their temperature dependence play an important role in determining the growth and transition of melt failure of ABS polymer in uniaxial extension.