Dependence of repair strength on the size of FRP patch bonded to a cracked aluminum alloy panel

A polymer composite patched specimen, made of a thin skin of aluminum alloy 6061-T6 and a patch consisting of a main load bearing ply of CFRP and a thin ply of GFRP, was tested for its strength under quasi-static tensile loading. The crack in the skin with a very sharp crack tip was not observed to grow during the testing. The failure was caused by the separation of the patch from the skin. For small sized patches, the separation initiated at the crack edges, grew with the increasing applied load and caused the complete separation. However, when the size of the patch was increased in length-wise direction or width-wise, the growth of the separation, initiated at the crack edge, was suppressed substantially. A stage was reached when separation was also initiated at the leading edges of the patch that grew at much faster rate to cause the complete separation with further increase in the applied load. The results of this study suggest that the patch size should be large enough to cause the separation-initiation at the leading edges also.