Page 192 - MODELING OF ASPHALT CONCRETE

170 Cha pte r Se v e n

FIGURE 7-5 Constant crosshead rate test results in (a) Stress-strain space and (b) stress-
pseudostrain space. (Underwood et al. 2006b, with permission from Association of Asphalt
Paving Technologists.)

Fig. 7-5(a), nonlinearity appears in the initial stage of loading, which suggests that
damage commences from the outset. However, the nonlinearity in this zone is related
only to the time effects of the material. When these time effects are removed using
pseudostrain, seen in Fig. 7-5(b), damage does not commence at the outset of loading
and, in fact, does not begin until the stress level reaches approximately 500 kPa.
These two examples demonstrate the benefit of using pseudostrain; that is,
pseudostrain essentially accounts for the viscoelasticity of the material and reduces the
viscoelastic problem into a corresponding elastic problem, making the modeling of the