Interlaminar properties of polymer laminates containing internal sensor cavities

This research paper presents an experimental investigation into the sensitivity of the interlaminar properties of polymer laminates to long, narrow interlaminar galleries used in comparative vacuum monitoring (CVM). CVM is a structural health monitoring technique for the non-destructive detection of cracks in engineering materials. The paper examines the effect of CVM galleries on the mode I delamination toughness, interlaminar shear strength, and impact damage resistance of a carbon/epoxy laminate. It was found that the galleries improve the mode I delamination toughness by blunting and/or deflecting the crack tip; with the maximum improvement being double the toughness of the laminate free of galleries. The toughness increased with the diameter of the gallery up to a critical size, above which no further improvement was achieved. However, the composite is more prone to unstable delamination cracking in the presence of the galleries. The apparent interlaminar shear strength (ILSS) decreased at a linear rate with an increase in the diameter and volume fraction of galleries. The loss in ILSS is due to the reduction in the effective interlaminar load-bearing area caused by the galleries. Low-energy impact testing revealed that the galleries do not affect the impact damage resistance when below a critical diameter; however, above a threshold gallery size the impact resistance is degraded. This study shows that the incorporation of CVM galleries into laminates can have the added benefit of increased mode I delamination toughness, although the ILSS is degraded and the impact resistance is reduced by large galleries.