Comparison of the viscous and elastic components of two ABS materials with creep, stress relaxation and constant strain rate measurements using the universal viscoelastic model

In general, the universal viscoelastic model evaluated in this study was found to adequately predict constant strain rate, creep, and/or stress relaxation measurements from the constants determined from constant strain rate measurements. The elastic and viscous components for two acrylonitrile-butadiene-styrene (ABS) viscoelastic materials were also easily isolated using this new universal viscoelastic model. The creep measurements for ABS-A (25383-A) and ABS-N (LL-4102-N) at three different stresses allowed elucidation of the common creep intercept strain of the calculated creep slopes that was designated as the "projected elastic limit." Once the values for n and beta were evaluated from creep measurements, then the creep variation of the universal viscoelastic model yielded a reasonably good fit of the measured creep data for both ABS-A and ABS-N. The extensional viscosity constant lambda(E) was found to be 7.2% greater for ABS-A than for ABS-N. Consequently, ABS-N was found to have a lower extensional viscosity in secondary creep than that of ABS-A at any specific strain rate. The value of the efficiency of yield energy dissipation n for ABS-N as determined from creep measurements was also 37.6% larger than the value of n for ABS-A. In addition, the projected elastic limit epsilon(1) for ABS-A was 2% greater than the projected elastic limit for ABS-N. These observations indicated that ABS-A should be slightly more solidlike than ABS-N. However, both ABS-A and ABS-N were significantly more solidlike than liquidlike because both of their values for the efficiency of yield energy dissipation n were very close to zero. In general, values of n range from 0 < n < 1 with a material characterized as being essentially pure elastic having a value of n = 0. Using the yield strain as the failure condition for constant strain rate and stress relaxation measurements and the strain at critical creep, the failure condition for creep, it was found that the universal viscoelastic model allowed these failure criteria to yield remarkably good agreement on a projected time scale. This agreement resulted even though separate and independent data were used to evaluate these three different techniques for both ABS-A and ABS-N. (C) 2003 Wiley Periodicals, Inc.