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 .