Post-mortem through-thickness characterizing of impact fatigue damage in glass fiber/epoxy composite with embedded copper conductor

Multifunctional composite materials are highly used in high-tech industries; their unique properties make them a major economic asset. However, understanding their complex damage modes remains a challenge which affects the ability to predict the lifespan with accuracy. This work focuses on the low energy impact fatigue damage progression through-thickness of a glass fiber/copper/epoxy multifunctional composite material. Three levels of energy were chosen for the fatigue tests: E_i = 2 J, 3 J, and 4 J. A chemical process allowed the dissolution of the epoxy resin and the recovery and later inspection of the damaged copper and glass fiber woven fabric. Damage growth was quantified layer by layer, revealing a significant increase between the 4th and 5th plies corresponding to the location of the copper insert. This suggests that the insert initially delays damage propagation, but amplifies it after its own failure. Microscopic inspection of the recovered copper and the glass fiber allowed the observation of the ruptured surface of the copper and showed that the glass fibers are the origin of the initiation of the damage in the copper.