Some Exact and Variational Methods 
                       for Analysis of Fracture in
                    Composites with Residual Stresses, 
            Traction Loaded Cracks, and Imperfect Interfaces

                              John A. Nairn

         Material Science & Engineering Department, University of Utah


                  INSCC 110, 3:30pm  Monday, 9 November 1998

                                Abstract

Using thermodynamics, the problem of predicting crack growth can
be reduced to finding the change in free energy due to a small amount of
crack growth --- the energy release rate. In homogeneous materials with
traction-free surfaces, this problem can be solved using stress intensity
factors. Such an approach is not useful (or at least very cumbersome) for
analysis of heterogeneous materials (i.e. composites) or for inclusion of
residual stresses, traction loaded cracks, and interface effects. This
talk will outline some exact results that can serve as new starting points
for analysis of composite fracture. Some uses of these exact results are:

1. To analyze the effect of residual stresses without any
thermoelasticity analysis

2. To derive variational bounds on the energy release rate for
the first formation of damage

3. To suggest useful bounds to the energy release rate for
propagation of damage

4. To point out an error in finite element crack closure methods
when applied to materials with imperfect interfaces or traction loaded
cracks


Requests for preprints and reprints send to: John A. Nairn at 
John.Nairn@m.cc.utah.edu