Specimens with patch
Specimens with patch show a very similar load/displacement behaviour as
the unpatched ones. Differences in elasticity between metal sheet and
the rather stiff patch combined with the increasing strain lead to a
patch detachment right after exceeding the linear-elastic region so that
the stiffening effect of the patch cannot be monitored. In most test
cases the patch detaches below the hole and sticks partly to the sheet
above the hole. For the test evaluation this means that the patch still
covers the hole but does not longer stiffen the specimen.
Analyses of the patched specimens monitored from the metallic side
therefore do not give any considerable additional information compared
to the specimens without patch. A comparison of the load/displacement
curves and the thermal images shows that the damage behaviour including
the characteristic events of specimen failure are comparable. The patch
detaches in a one- or two-stage process resulting in one or two
additional characteristic event(s) in the load/displacement curve, as
shown in Fig. 10, denoted with the symbols and .