A new method for evaluating the residual compression strength of composites after impact

In the aerospace industry, compression panels are usually designed not to buckle at ultimate load. To obtain design allowables, test boxes have been used which are more representative to the real structure but are complex and expensive. Therefore, a simpler and cheaper method has to be devised to mimic the real structure and gives more realistic results for compression after impact (CAI). This paper analyses the results of experimental studies using the new BAE Systems CAI rig. Three different thicknesses, 4, 6 and 8 mm composites plate specimens have been impacted at different energy levels followed by CAI tests. The support conditions were identical for the impact and CAI tests but differed for the three plate thicknesses. The effects of impact damage on the initial buckling load and compression strength was seen at the threshold energy for the 4 mm plate and two times the threshold energy for the 6 and 8 mm plates. The experimental results for the unimpacted plates were compared with finite element results. The plates with its supports conditions were modeled using the FE77 code and a good correlation was apparent between the experimental and finite element values of the initial buckling load, within 9%.