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

In the aerospace industry, compression panels are usually designed not to b uckle at ultimate load. To obtain design allowables, test boxes have been u sed which are more representative to the real structure but are complex and expensive. Therefore, a simpler and cheaper method has to be devised to mi mic the real structure and gives more realistic results for compression aft er impact (CAI). This paper analyses the results of experimental studies us ing the new BAE Systems CAI rig. Three different thicknesses, 4, 6 and 8 mm composites plate specimens have been impacted at different energy levels f ollowed 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 see n at the threshold energy for the 4 ram plate and two times the threshold e nergy for the 6 and 8 mm plates. The experimental results for the unimpacte d plates were compared with finite element results. The plates with its sup ports conditions were modeled using the FE77 code and a good correlation wa s apparent between the experimental and finite element values of the initia l buckling load, within 9%. (C) 2001 Published by Elsevier Science Ltd.