Experimental investigation on the adhesively bonded repair of composite structures

In this paper, an experimental study is undertaken to investigate the influence of repaired parameters on the strength of repaired structure. The repaired parameters investigated in this paper are the patch diameter, patch thickness and patch ply-sequence. The repaired structures including penetrated specimen and semi-penetrated specimen are study in this paper. The penetrated specimen is a plate with a penetrated hole in the central region symmetrically repaired with two circular composite patches. The semi-penetrated specimen is a plate with a semi-penetrated hole in the central region repaired with a circular composite patch. The composite parent plate is made from unidirectional T300/QY8911 carbon fiber/epoxy preimpregnated tape. The ply sequence of the parent plate is [(0/90/7+/-45/90/0)2]s, The dimension of the parent plate is 250x100x2.88 mm. The ply material of patch is unidirectional DHS217.325.30 preimpregnated tape. The thickness of the tape is 0.175 mm. The strain gauges are stuck on parent plate and patches to measure the strain of them. All repaired structures are tested in uniaxial tension using an 'MTS' testing machine at room temperature. According to the results of the experiment, it is found that the repair will have good effect when the patch diameter is 2 to 3 times of the hole and the patch thickness is 40%-60% of the parent plate. The ply sequence of the patch has influence upon the strength recovery of repaired structure. The ply sequence of the patch can be designed according to the style of load. The different strain variations correspond to different failure modes.