Page 191 - MODELING OF ASPHALT CONCRETE

VEPCD Modeling of Asphalt Concr ete with Gr owing Damage 169

FIGURE 7-4 (a) Stress-strain behavior for mixture under LVE cyclic loading and (b) Stress-
pseudostrain behavior for same data. (Daniel and Kim 2002, with permission from Association
of Asphalt Paving Technologists.)

and pseudostrain (instead of physical strain) would make the hysteretic behavior
appear to be the same as linear elastic behavior. This observation is illustrated using the
experimental data in Fig. 7-4. Figure 7-4(a) shows the stress-strain behavior for
controlled-stress cyclic loading within the material’s LVE range (such as for a complex
modulus test). Because the material is being tested in its LVE range, no damage is
induced and the hysteretic behavior and accumulating strain are due to viscoelasticity
only. Figure 7-4(b) shows the same stress data plotted against the pseudostrains
calculated from Eq. (7-6) with E = 1. As can be seen from Fig. 7-4(b), hysteretic behavior
R
due to both loading-unloading and repetitive loading has disappeared using the
pseudostrains. It is also noted that the stress-pseudostrain behavior in Fig. 7-4(b) is
linear with a slope of one (i.e., following the line of equality).
Another illustration is given in Fig. 7-5 using the stress-strain data from constant
crosshead rate monotonic tests at two different rates of loading. The behavior during
initial loading is shown as an inset in these figures. In stress-strain space, as seen in