Page 368 - Mechanics of Asphalt Microstructure and Micromechanics

T
360 Ch a p t e r e n

Case 1 Case 2 Case 3
Dimension 2D 2D 2D 2D 3D 3D
Total 10000 10000 10000 10000 5000 5000
element
number
Rigid 0 80 0 80 0 Defined
element by image,
number elements
representing
aggregate of
mixture
Element 4-node 4-node 4-node 4-node 8-node 8-node
type bilinear, bilinear, bilinear, bilinear, linear brick linear brick
reduced reduced reduced reduced
integration integration integration integration
Constitutive Elastic Elastic Damage Damage Elastic Elastic
model concrete concrete (different (different
plasticity plasticity for each for each
component component
of the of the
mixture) mixture)
Loading Top Top Top Top Top Top
application pressure pressure pressure pressure pressure pressure
Calculation 4s 3s 8s 4s 8s 3s
time (s)
TABLE 10.7 Computational efficiency using rigid element.

10.4.2 Rigid Element Method
Considering the significant difference in stiffness between aggregates and asphalt bind-
er at relatively high temperatures, the aggregates may be treated as rigid. The major
advantage of representing aggregates as rigid bodies rather than deformable finite ele-
ments is computational efficiency. Element-level calculations are not performed for ele-
ments that are part of a rigid body. Although some computational effort is required to
update the motion of the nodes of the rigid body and to assemble concentrated and
distributed loads, the motion of the rigid body is determined completely by a maxi-
mum of six degrees of freedom at the reference node. Table 10.7 (Wang, 2010) presents
a preliminary estimation of the computation efficiency when ABAQUS is run on the
System X platform at Virginia Tech.

10.5 Extension to Other Materials
These techniques can be extended to various other materials including composite met-
als, soils, cement concrete, wood composite (Figure 10.46), and other composite materi-
als at different length scales. The digital specimens can also be used to study other
phenomena including transport, conductivity, and stress-strain relation. They are fun-
damental tools for many other materials.