Impact response of interleaved composite materials
The need for better impact resistant composites has resulted in the development of many toughened resin systems. A combination of a tougher resin system along with higher strength fibers increases the impact resistance of the composite. The use of an adhesive layer between two plies of the improved prepreg system has been found to considerably increase the impact resistance. This concept is known as "Interleafing."
This investigation studies the response of the interleaf materials to instrumented drop weight impact as compared with the response of non-interleaved materials. Two non-destructive quality evaluation techniques, namely, ultrasonics and eddy currents, are used to qualitatively evaluate the damage developed in the specimens. Several different energy levels of damage are studied.
The interleaved laminate had significantly better impact response than the non-interleaved laminate for the same impact energy. The onset of delamination was delayed by the use of the interleaf. Whereas damage could be detected at an impact energy as low as 1.75 ft-lb in the baseline laminate; the interleaved laminate did not show any ultrasonic C-scan indication up to an impact of 2.45 ft-lb. The increase of delamination with increasing impact energy was slower in the interleaved specimen.
The eddy current method is not effective in detecting damage in the interleaved laminate because of the shielding effect of the interleaf. Compression Strength After Impact (CSAI) could not be used for the test laminates in this project, but the Tensile Strength After Impact test provided useful results. The tensile strength after impact of the interleaved specimen was between 20%-80% more than the baseline laminate up to impact energy of 10 ft-lb. The advantage of the interleaved specimen reduced at higher energy levels of impact.