Transferability of Adhesive Fracture Toughness Measurements between Peel and TDCB Test Methods for a Nano-Toughened Epoxy

Our previous work [1] on a nano rubber modified epoxy
adhesive suggested that the observed bond thickness effect
was due to the level of constraint (σhyd/σeq), a measure of
the stress triaxiality, in the adhesive layer. In that study
tapered double cantilever beam (TDCB) specimens were
tested under quasi-static conditions for a range of bond gap
thicknesses. The void diameters on the resulting fracture
surfaces were measured from which the fracture strain was
estimated in each case. The ratio of fracture strains corresponding
to different constraint levels was found to agree
with the predictions of the Rice and Tracey model.
The current work attempts to further investigate the
effects of constraint on adhesive joint fracture. Three experimental
test methods are employed (i) the standardised
LEFM tapered double cantilever beam (TDCB) test, in
which the substrates experiences small elastic deformations,
(ii) the fixed arm peel test where the substrate peel
arm undergoes extensive plastic deformation and (iii) a
recently developed circumferentially deep notched tensile
(CDNT) test. Finite Volume simulations of the TDCB and
CDNT tests were utilised to examine the role of constraint
on the adhesive joint fracture.