These RDCB test pieces were designed by MERL and form the basis of
a draft CEN Standard. Since the surface properties of metals (which
can
affect bond durability significantly) vary with thickness and forming
method, it is important that the test
bond
is made between metallic substrates identical to those used for
actual engineering applications. However, to avoid plastic deformation
of the typically thin gauge metals, thicker reinforcement beams
are bonded to the back of the substrates.
The rate of crack growth (da/dN) depends on the strain energy release
rate (G). The fatigue resistance of an adhesive system can be reduced
by environmental effects which cause loss of adhesion and interfacial
breakdown. Fatigue crack growth properties can be measured
under various service
related environmental conditions to assess these effects. MERL
has pioneered a method of obtaining these data using compliance calibration
approaches.
Special purpose test equipment has also been developed so that multiple
specimens can be tested and monitored simultaneously, as shown below. |
