Page 300 - Handbook of Materials Failure Analysis

296 CHAPTER 12 A nonlocal damage-mechanics-based approach

1,000,000

800,000

1T CT (expt.)
600,000 1T CT (simul.)
Load (N) 2T CT (expt.)
2T CT (simul.)
400,000 4T CT (simul.)

200,000

0
0 1 2 3 4 5 6
CMOD (mm)
FIGURE 12.9
Load-CMOD response of a 1T, 2T, and 4T CT specimen (experiment and FE simulation).

dimensionsofthe1TCTspecimens,thatis,thespecimenswerejustscaledbyafactorof
twoandfour,respectively.Theaim ofthisexerciseis to demonstratethatthe sameset of
micro-mechanical parameters should be able to satisfactorily predict the load-CMOD
responsesofallthesedifferentsizesofCTspecimens.TheresultsofFEanalysiswiththe
nonlocal model are plotted in Figure 12.9 along with the experimental data and a very
good agreement between the two sets can be observed.

6.4 EFFECT OF SYMMETRY BOUNDARY CONDITIONS ON CRACK
GROWTH SIMULATION
Often, laboratory specimens and noncomplex components are built up and loaded
symmetrically. For example, in the case of a CT specimen, it is sufficient to model
and simulate half of the specimen if the symmetric nature of the boundary conditions
is exploited. If the full model is analyzed instead of the half or the symmetric model,
the results of analysis should not change. However, it was observed that the results of
the local version of the Rousselier’s damage model are not only mesh-dependent, but
also dependent upon the choice of the boundary condition. Figure 12.10 shows the
load-CMOD response of the 1T CT specimen as obtained from FE analysis when
local model was used for the half and the full model, respectively. It can be observed
that the two results are different. However, the nonlocal model predicts exactly the
same result for both the cases. It is because of the localization of crack growth in one
side of the symmetry line in case of the simulation with local model as can be seen
from Figure 12.11. In case of FE simulation with the nonlocal damage model, mate-
rial damage occurs in a symmetric fashion on both sides of the line of symmetry dem-
onstrating that the crack grows along the center line when all the conditions for