Micro-Mechanical Modelling of Void Growth, Damage and Fracture of Nano-Phase Structural Adhesives Using the Finite Volume Method

Significant toughening of structural adhesives is attainable
with the addition of nano and/or micro particles1,2,3. A deep understanding
of the effect of particle de-bonding and subsequent
void growth to coalescence is key to evaluating the strengthening
and failure mechanisms occurring in the damage and fracture
of these adhesives. Tapered Double Cantilever Beam (TDCB)
experiments, conducted at University College Dublin (UCD),
have observed a significant dependence of the fracture toughness
of these adhesives on bond gap thickness5. In conjunction
with this change in fracture toughness, scanning electronmicroscopy
(SEM) of the fracture surface has also revealed corresponding
changes in void evolution as the bond gap is varied.
Classical analysis suggests the change in toughness may be attributed
to a physical constraint of the size to which the plastic
zone around a crack tip may develop6. However, simulation of
these TDCB tests using finite volume stress analysis has found
that little plasticity develops in the bulk adhesive layer and is instead
concentrated in the fracture process zone. The change in
fracture toughness and void evolution present can be attributed
to the change in triaxiality at different bond gap thicknesses and
the results agree quite well with the void growth model of Rice
& Tracey4. The variance of void growth with triaxiality is investigated
here.
The initial work considered here concerned 3D modelling
of a void in an elastic perfectly plastic material with a view to
verifying exponential dependence of void growth on the macroscopic
stress triaxiality in the system in accordance with the
Rice & Tracey model. The model examines void growth rate
dependence on the stress triaxiality, for a given effective strain.