DYNAMIC FRACTURE 
MODELING ON THE 
CM-200

It is important to study the dynamic 
properties of materials under the influ-
ence of various microstructural condi-
tions. Microstructure is known to have 
an important influence on the fracture 
properties of materials. A parallel com-
puter code has therefore been imple-
mented for the study of dynamic 
fracture problems on the CM-200. This 
code implements a "balls and spring" 
model which lives on a 2D triangular 
lattice. The balls are connected to near-
est neighbors by nonlinear springs and 
are allowed to move around their equi-
librium positions. Also being modeled 
are bond fractures by the following 
rule: if a bond is extended beyond a 
given length, it is designated as broken 
and only the repulsive part of the 
potential for that bond is retained for 
the rest of the simulation. The model 
has Langevin dynamics built in and 
thereby allows the study of the influ-
ence of temperature and other stochas-
tic effects. It is also possible to run it 
with zero noise. The massively parallel 
nature of the problem is established by 
assigning one ball (and three bonds) to 
each processor of the CM-200. Because 
each processor has its own memory it is 
easy to give the balls different proper-
ties, e.g. they can have different mate-
rial parameters. In this way it is 
possible to model grain boundaries and 
real microstructure. The goal of this 
investigation is to accurately describe 
how microstructure affects fracture 
and, in particular, to be able to follow 
the dynamics of fracture.

Some preliminary runs on shear-stress 
induces fracture in a block of materials 
with microstructure has been investi-
gated. To date the runs show that it is 
possible to dynamically observe several 
fracture scenarios. For example, it is 
possible by tuning the parameters in 
the inter-particle potential to observe 
trans-granular fracture and also frac-
ture along grain boundaries.

These figures show dynamic fracture 
in a 2D Lattice Model. A shear stress 
has been applied to the top part of the 
lattice. The colors show the distribu-
tion of kinetic energy: low values cor-
respond to gray, intermediate values 
to purple, and high values to yellow 
and red. Because of weaker bonding 
across grain boundaries as compared 
with the intragrain bond strength, the 
fracture is seen to occur predomi-
nantly along grain boundaries in this 
simulation. The way in which micro-
structure affects the strength of these 
material can be studied by adjusting 
these parameters.

Acknowledgement:  Peter Lomdahl, LANL, T-11